JP4497988B2 - Exposure apparatus and method, and wavelength selection method - Google Patents

Description

  The present invention generally relates to an exposure apparatus and method, and more particularly to an exposure apparatus and method for projecting and exposing an object to be processed such as a single crystal substrate for a semiconductor wafer and a glass substrate for a liquid crystal display (LCD). The present invention is suitable for, for example, an exposure apparatus and method for performing exposure by a step-and-scan method.

  When manufacturing fine semiconductor elements such as semiconductor memories and logic circuits or liquid crystal display elements using photolithography technology, a circuit pattern drawn on a reticle (mask) is projected onto a wafer or the like by a projection optical system. A projection exposure apparatus that transfers a circuit pattern is used.

In the projection exposure apparatus, as the integration of semiconductor elements increases, it is required to project and expose a reticle circuit pattern onto a wafer with higher resolution. The minimum dimension (resolution) that can be transferred by the projection exposure apparatus is proportional to the wavelength of light used for exposure and inversely proportional to the numerical aperture (NA) of the projection optical system. Therefore, the shorter the wavelength, the better the resolution. Therefore, recent light sources include ultra-high pressure mercury lamps (g-line (wavelength: about 436 nm), i-line (wavelength: about 365 nm)) to KrF excimer laser (wavelength: about 248 nm) and ArF excimer laser (wavelength: about 193 nm). Therefore, practical application of F ₂ laser (wavelength of about 157 nm) is also progressing. Furthermore, further expansion of the exposure area is also required.

  In order to achieve these requirements, the exposure area is formed into a rectangular slit shape from a step-and-repeat type exposure apparatus (also called a “stepper”) that reduces the exposure area of a substantially square shape to a wafer and performs batch exposure. For example, a step-and-scan type exposure apparatus (also referred to as a “scanner”) that scans a reticle and a wafer relatively quickly and exposes a large screen with high accuracy is becoming mainstream.

  In the scanner, before the predetermined position of the wafer reaches the exposure slit region during exposure, the surface position at the predetermined position of the wafer is measured by the surface position detecting means of the oblique incidence system, and the predetermined position is determined. Correction is performed to align the wafer surface with the optimum exposure image formation position during exposure.

In particular, in the longitudinal direction of the exposure slit (that is, the direction perpendicular to the scanning direction), in order to measure not only the height (focus) of the surface position of the wafer but also the tilt (tilt) of the surface, a plurality of exposure slit regions are provided. Has measuring points. Many methods for measuring the focus and tilt have been proposed (for example, see Patent Document 1).
JP-A-6-260391

  In recent years, however, the exposure light has become shorter in wavelength and the projection optical system has a higher NA. The depth of focus has become extremely small, and the accuracy of aligning the wafer surface to be exposed to the best imaging plane, the so-called focus accuracy, has increased. It is getting stricter. In particular, the measurement error of the surface position detecting means due to the influence of the pattern on the wafer and the uneven thickness of the resist applied to the wafer cannot be ignored.

  For example, due to uneven thickness of the resist, a large step is generated in the vicinity of the peripheral circuit pattern and the scribe line, although it is smaller than the focal depth, for focus measurement. For this reason, the inclination angle of the resist surface becomes large, and the reflected light detected by the surface position detecting means deviates from the regular reflection angle due to reflection and refraction. Further, due to the difference in density of the pattern on the wafer, a difference in reflectance occurs between the dense pattern area and the rough area. As described above, since the reflection angle and reflection intensity of the reflected light detected by the surface position detecting means change, asymmetry occurs in the detected waveform in which such reflected light is detected, resulting in a measurement error, or the contrast of the detected waveform is reduced. If it significantly decreases, the surface position of the wafer cannot be detected.

  In general, the wafer process causes non-uniformity in the pattern step in the wafer surface and uneven resist thickness, so that reproducibility within the wafer or between wafers is poor, and offset processing is difficult. Accordingly, the surface position of the wafer cannot be measured during exposure, and exposure stops or large defocusing occurs, resulting in chip failure, thereby reducing yield.

  Accordingly, an object of the present invention is to provide an exposure apparatus and method that achieves high focus accuracy with respect to a small depth of focus and achieves improvement in yield.

An exposure apparatus according to one aspect of the present invention is an exposure apparatus that exposes a pattern formed on a reticle to a plurality of shots on a target object via a projection optical system, and the exposure apparatus has the same position in each of the plurality of shots. And irradiating each of the first measurement points with light having a plurality of wavelengths, and each of the plurality of shots being at the same position and different from the first measurement point with respect to each of the second measurement points. Irradiation means for irradiating light of a plurality of wavelengths, detection means for detecting reflected light from the first and second measurement points , and a plurality of first wavelengths from the plurality of wavelengths based on the detection results of the detection means . the optimum wavelength is common to first measurement point, selection means for selecting optimum wavelength is common to a plurality of second measuring points, respectively, using light optimum wavelength selected by the selecting unit of each measurement point Measure the position in the optical axis direction And having a measuring means.

  Further objects and other features of the present invention will become apparent from the preferred embodiments described below with reference to the accompanying drawings.

  According to the present invention, it is possible to provide an exposure apparatus and method that achieves high focus accuracy with respect to a small depth of focus and improves yield.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. In addition, in each figure, the same reference number is attached | subjected about the same member and the overlapping description is abbreviate | omitted. FIG. 1 is a schematic block diagram showing a configuration of an exposure apparatus 1 as one aspect of the present invention.

  The exposure apparatus 1 is a projection exposure apparatus that exposes a circuit pattern formed on a reticle 20 onto a wafer 40 by a step-and-scan method. Such an exposure apparatus is suitable for a lithography process of submicron or quarter micron or less. As shown in FIG. 1, the exposure apparatus 1 includes an illumination apparatus 10, a reticle stage 25 on which the reticle 20 is placed, a projection optical system 30, a wafer stage 45 on which a wafer 40 is placed, and a focus tilt detection system 50. And a control unit 60. The control unit 60 includes a CPU and a memory, and is electrically connected to the illumination device 10, the reticle stage 25, the wafer stage 45, and the focus tilt detection system 50, and controls the operation of the exposure apparatus 1. In this embodiment, the control unit 60 also performs calculation and control for optimally setting the wavelength of light used when the focus tilt detection system 50 described later detects the surface position of the wafer 40.

  The illumination device 10 illuminates a reticle 20 on which a transfer circuit pattern is formed, and includes a light source unit 12 and an illumination optical system 14.

The light source unit 12 uses, for example, a laser. Laser, ArF excimer laser having a wavelength of about 193 nm, may be used, such as KrF excimer laser with a wavelength of approximately 248 nm, the kind of light source is not limited to excimer laser, for example, a wavelength of about 157 nm _{F 2} laser or a wavelength 20nm The following EUV (Extreme Ultraviolet) light may be used.

  The illumination optical system 14 is an optical system that illuminates a surface to be illuminated using a light beam emitted from the light source unit 12, and in this embodiment, the light beam is formed into an exposure slit having a predetermined shape optimum for exposure, and the reticle 20 is formed. Illuminate. The illumination optical system 14 includes a lens, a mirror, an optical integrator, a diaphragm, and the like. For example, a condenser lens, a fly-eye lens, an aperture diaphragm, a condenser lens, a slit, and an imaging optical system are arranged in this order. The illumination optical system 14 can be used regardless of on-axis light or off-axis light. The optical integrator includes an integrator configured by stacking a fly-eye lens and two sets of cylindrical lens array (or lenticular lens) plates, but may be replaced by an optical rod or a diffractive element.

  The reticle 20 is made of, for example, quartz, on which a circuit pattern to be transferred is formed, and is supported and driven by the reticle stage 25. Diffracted light emitted from the reticle 20 passes through the projection optical system 30 and is projected onto the wafer 40. The reticle 20 and the wafer 40 are arranged in an optically conjugate relationship. The pattern of the reticle 20 is transferred onto the wafer 40 by scanning the reticle 20 and the wafer 40 at the speed ratio of the reduction magnification ratio. The exposure apparatus 1 is provided with a light oblique incidence type reticle detection means 70, and the position of the reticle 20 is detected by the reticle detection means 70 and is arranged at a predetermined position.

  The reticle stage 25 supports the reticle 20 via a reticle chuck (not shown) and is connected to a moving mechanism (not shown). A moving mechanism (not shown) is configured by a linear motor or the like, and can move the reticle 20 by driving the reticle stage 25 in the X-axis direction, the Y-axis direction, the Z-axis direction, and the rotation direction of each axis.

  The projection optical system 30 has a function of forming an image of a light beam from the object plane on the image plane. In this embodiment, the projection optical system 30 forms an image on the wafer 40 of diffracted light that has passed through the pattern formed on the reticle 20. The projection optical system 30 includes an optical system including only a plurality of lens elements, an optical system (catadioptric optical system) having a plurality of lens elements and at least one concave mirror, a plurality of lens elements, and at least one kinoform. An optical system having a diffractive optical element such as can be used. When correction of chromatic aberration is required, a plurality of lens elements made of glass materials having different dispersion values (Abbe values) can be used, or the diffractive optical element can be configured to generate dispersion in the opposite direction to the lens element. To do.

  The wafer 40 is an object to be processed, and a photoresist is applied on the substrate. In the present embodiment, the wafer 40 is also a detected object whose position is detected by the focus tilt detection system 50. In another embodiment, the wafer 40 is replaced with a liquid crystal substrate or other object to be processed.

  The wafer stage 45 supports the wafer 40 by a wafer chuck (not shown). Similar to reticle stage 25, wafer stage 45 uses a linear motor to move wafer 40 in the X-axis direction, Y-axis direction, Z-axis direction, and the rotational direction of each axis. Further, the position of the reticle stage 25 and the position of the wafer stage 45 are monitored by, for example, a laser interferometer or the like, and both are driven at a constant speed ratio. The wafer stage 45 is provided on a stage surface plate supported on a floor or the like via a damper, for example, and the reticle stage 25 and the projection optical system 30 are, for example, on a base frame placed on the floor or the like. It is provided on a lens barrel surface plate (not shown) that is supported via a damper.

  In this embodiment, the focus tilt detection system 50 detects position information of the surface position (Z-axis direction) of the wafer 40 during exposure using an optical measurement system. The focus tilt detection system 50 makes a light beam incident on a plurality of measurement points to be measured on the wafer 40, guides each light beam to an individual sensor, and calculates the tilt of the surface to be exposed from position information (measurement results) at different positions. To detect.

  As shown in FIG. 2, the focus tilt detection system 50 detects an image shift of reflected light reflected from the surface of the wafer 40 and an illumination unit 52 that makes a light beam incident on the surface of the wafer 40 at a high incident angle. A unit 54 and a calculation unit 56. The illumination unit 52 includes a light source 521, a light combining unit 522, a pattern plate 523, an imaging lens 524, and a mirror 525. The detection unit 54 includes a mirror 541, a lens 542, an optical demultiplexing unit 543, and a light receiver 544. Here, FIG. 2 is an enlarged block diagram showing a configuration of the focus tilt detection system 50. In FIG. 2, illustrations of lenses necessary for illuminating the pattern plate 523 with a uniform illuminance distribution in the illumination unit 52 and lenses for correcting chromatic aberration in the detection unit 54 are omitted.

  Referring to FIG. 2, light having wavelengths λ1, λ2, and λ3 emitted from light sources 521a, 521b, and 521c such as LEDs and halogen lamps passes through a light combining unit 522 including a mirror 522a and dichroic mirrors 522b and 522c. Then, the pattern plate 523 on which a pattern such as a slit is formed is illuminated. The light that has passed through the pattern plate 15 is projected and imaged onto the wafer 40 via the imaging lens 524 and the mirror 525.

  Further, the light reflected by the wafer 40 is received by a light receiver 544 including light receiving elements 544 a, 544 b and 544 c such as a CCD element and a line sensor via a mirror 541 and a lens 542. In addition, an optical demultiplexing unit 543 including a mirror 543a and dichroic mirrors 543b and 543c is disposed in front of the light receiver 544. The light demultiplexing means 543 receives light of different wavelengths so that the light from the light source 521a is received by the light receiving element 544a, the light from the light source 521b is received by the light receiving element 544b, and the light from the light source 521c is received by the light receiving element 544c. Has the function of dividing. The pattern image on the wafer 40 surface of the pattern plate 523 is re-imaged on the light receiving elements 544 a to 544 c by the lens 542.

  When the wafer 40 moves in the vertical direction (that is, the Z-axis direction) via the wafer stage 45, the pattern image of the pattern plate 523 moves in the left-right direction (that is, the X-axis direction) on the light receiver 544. Therefore, the focus tilt detection system 50 detects the position of the surface of the wafer 40 for each measurement point by calculating the position of the pattern image with the calculation unit 56.

  Here, a pattern on the pattern plate 523 and a signal waveform detected by the detection unit 54 will be described. FIG. 3 is a plan view showing an example of the pattern plate 523. Referring to FIG. 3, the pattern plate 523 has a lattice pattern 523b in which four rectangular light-shielding patterns 523c are arranged at equal intervals in the transmission region 523a. FIG. 4 shows signal waveforms detected by the detection unit 54 when the pattern plate 523 (the lattice pattern 523b) is used. When a two-dimensional sensor is used as the light receiving elements 544a to 544c, the signal waveform is obtained by integrating (or averaging) the light amount in a direction perpendicular to the arrangement direction of the light shielding pattern 523c. Further, when a one-dimensional line sensor is used as the light receiving elements 544a to 544c, it is preferable to obtain a signal waveform by optically integrating using a cylindrical lens having power in a direction perpendicular to the arrangement direction of the light shielding pattern 523c. This is advantageous for improving the S / N (signal to noise ratio) of the signal waveform.

  Referring to FIG. 4, FIG. 4 (a) shows an example of a signal waveform obtained from light of wavelength λ1, and FIG. 4 (b) shows an example of a signal waveform obtained from light of wavelength λ3. The waveform signal shown in FIG. 4A has good symmetry of the image of the lattice pattern 523b, whereas the waveform signal shown in FIG. 4B has some asymmetry, and the same measurement point. It can be seen that the waveform signal in FIG.

  With reference to FIG. 5 thru | or FIG. 7, the dependence of the waveform signal detected by the detection part 54 with respect to the wavelength of the light to illuminate is demonstrated. FIG. 5 is a diagram for explaining the difference in reflectance caused by the film thickness non-uniformity of the resist 42 due to the pattern step 41 on the wafer 40. The reflectance of the wafer 40 coated with the resist 42 is determined by the interference between the reflected light of the resist surface 42a and the reflected light of the resist back surface (that is, the interface between the wafer 40 and the resist 42) 42b. Since the film thickness Rt ′ of the resist 42 in the region E2 with the pattern step 41 is thicker than the film thickness Rt of the resist 42 in the region E1 without the pattern step 41 on the wafer 40, the light irradiated to the region E1 The optical path length difference dA between the reflected light ka1 of the resist surface 42a and the reflected light ka2 of the resist back surface 42b, and the optical path length difference between the reflected light kb1 of the resist surface 42a and the reflected light kb2 of the resist back surface 42b of the light irradiated to the region E2 dB is different. As a result, a difference occurs in the reflectance between the region E1 and the region E2. When light is applied to a region having such a difference in reflectance, an asymmetric signal waveform is generated as shown in FIG.

The difference in reflectance generated on the wafer 40 is not limited to the simple non-uniform film thickness of the resist 42 as shown in FIG. Figure 6 is a diagram for explaining the difference in reflectance between the region E4 density large pattern area density of the step 41 is smaller (or no region) E3 and pattern step 41 on the wafer 40.

Referring to FIG. 6, the thickness of the resist 42 in the region E3 and the region E4 is equal, and the reflectances of the reflected lights kc1 and kd1 on the resist surface 42a are substantially equal. However, in the region E3 and the region E4, the density of the pattern level difference 41 on the wafer 40 are different, the resist back surface (i.e., the wafer 40 and the resist 42 and the interface) reflectance of the reflected light kc2 and kd2 at 42b are different . Furthermore, when the pattern level difference 41 on the wafer 40 falls below the wavelength of light illuminating the phenomenon of phase skip occurs in reflection called structural birefringence, the phase difference between the reflected light kc2 and kd2 of the resist back surface 42b This causes a difference in reflectivity.

Thus, although a difference in reflectivity caused by pattern step 41 on the wafer 40 (the thickness of the resist 42), a difference in reflectance due to the difference of the wavelength of the illumination light is generated.
FIG. 7 is a graph showing the wavelength dependence of the reflectance of the wafer 40 with respect to the film thickness of the resist 42. Considering the case where the film thickness of the resist 42 changes from Rt1 by ± dR, when the wavelength of the illuminating light is λ1, the reflectance changes only d1, but when the wavelength of the illuminating light is λ3, the reflectance is It changes by d3. That is, even when the film thickness of the resist 42 changes equally, the change in the reflectance at the wavelength λ1 is smaller than the change in the reflectance at the wavelength λ3. Measurement accuracy is improved. In other words, a difference occurs in the measurement accuracy of the focus tilt detection system 50 depending on the wavelength of the illuminating light.

  Measurement points for the surface position (focus) of the wafer 40 will be described. In the present embodiment, as shown in FIG. 8, a total of 21 measurement points KP of 7 points in the scan direction and 3 points in the direction perpendicular to the scan direction (slit longitudinal direction) with respect to one exposure area EE1. have. Two focus tilt detection systems 50 shown in FIG. 2 are arranged in the slit longitudinal direction (X-axis direction) to measure three measurement points KP in the slit longitudinal direction, and the wafer stage 45 is scanned in the Y-axis direction. It is configured to be able to measure 7 measurement points in the scan direction (Y-axis direction). Here, FIG. 8 is a plan view showing an example of the arrangement of the measurement points KP on the wafer 40.

  Further, as shown in FIG. 9, in order to expose a plurality of shots on the wafer 40, the wafer stage 45 is stepped or scanned for each shot, and measurement is performed on the 21 measurement points KP shown in FIG. As shown in FIG. 10, the measurement point KP in the slit longitudinal direction is required to obtain the tilt amount ωy of the wafer 40 in the slit longitudinal direction at the minimum, so that two or more measurement points KP are necessary. Furthermore, when it is necessary to measure the tilt amount ωx of the wafer 40 in the scan direction within the slit, as shown in FIG. 11, the measurement point KP at a different position in the scan direction within the slit and the corresponding focus tilt detection system 50 must be provided. Here, FIG. 9 is a plan view showing a shot layout on the wafer 40. 10 and 11 are plan views showing an example of the arrangement of the measurement points KP in the slits on the wafer 40. FIG.

  Hereinafter, a method for selecting the optimum wavelength of the light that illuminates the measurement point KP by the focus tilt detection system 50 will be described. FIG. 12 is a flowchart for explaining a method of selecting an optimum wavelength of light irradiated by the focus tilt detection system 50.

  Referring to FIG. 12, first, in the shot layout on the wafer 40 shown in FIG. 9, the surface positions of 14 shot sample shots are measured for light of all wavelengths of the focus tilt detection system 50 ( Step S602). Next, based on the signal waveform measured by the focus tilt detection system 50, the positions x1, x2, x3, and x4 (see FIG. 4A) of the images of the four light shielding patterns 523c on the pattern plate 523 are obtained (see FIG. 4A). In step S604), lattice intervals L1, L2, and L3 (see FIG. 4A) of the light shielding pattern 523c are obtained (step S606). Note that the lattice interval Lseij (λ) is calculated for all wavelengths of light and all measurement points KP. Here, the subscript s is the sample shot number, s = 1 to 14, e is the interval number of the light shielding pattern 523c, e = 1 to 3, i is the measurement position number in the shot in the slit longitudinal direction, and i = 1 to 3. , J is the in-shot measurement position number in the scanning direction, j = 1 to 7, and λ is the wavelength of the illuminating light, and λ = λ1 to λ3.

  Next, based on the lattice interval Lseij (λ), the standard deviation σLij (λ) of the lattice interval at the measurement position (i, j) in the shot is calculated (step S608). The wavelength λ having the smallest calculated standard deviation σLij (λ) is obtained, and this wavelength λ is set as the optimum wavelength λopt (i, j) of each measurement position (i, j) in the shot (step S610).

The wavelength λ that minimizes the standard deviation σLij (λ) of the lattice spacing Lseij (λ) at the measurement position (i, j) in the shot is the optimum wavelength λopt (i, j) between shots of the wafer 40. , the uneven coating of the pattern step 41 and the resist 42, because the change in the film thickness of the resist 42 occurs, because "likelihood" of the measurement, the better the reproducibility of the lattice spacing Lseij (λ) is excellent in between shots It is.

  After selecting the optimum wavelength λopt (i, j), the average value Xa (4) of the image positions x1 to x4 of the four light shielding patterns 523c is determined from the signal waveform of the pattern plate 523 illuminated with the optimum wavelength λopt (i, j). i, j) is obtained, and the surface position of the wafer 40 is measured.

  The number of sample shots used for selecting the optimum wavelength is not limited to 14 shots, and for example, all shots on the wafer may be measured. Furthermore, the number of wafers to be measured is not limited to one, and it is possible to improve the accuracy of wavelength optimization by measuring several wafers and increasing the denominator of the lattice spacing Lseij (λ). In the present embodiment, the pattern plate 523 is configured such that light does not pass through the lattice pattern 523b. However, the entire surface of the pattern plate 523 may be a light-shielding portion and light may be transmitted only through the lattice pattern 523b. .

Next, an outline of the surface position correction of the wafer 40 by measuring the focus and tilt at the time of scan exposure will be described. As shown in FIG. 13, measurement points KP (measurement positions FP) arranged at a plurality of points so as to form a plane in front of the exposure slit before the wafer 40 having an uneven shape in the scanning direction reaches the exposure position EP. The focus of the surface position of the wafer 40 and the tilt (hereinafter referred to as “tilt X”) in the longitudinal direction of the exposure slit region (that is, the direction perpendicular to the scanning direction) are measured. Then, based on the position information detected by the focus tilt detection system 50, the wafer stage 45 is driven to perform correction driving to the exposure position EP. For example, in FIG. 2, the surface position of j = 7 is measured during exposure of the position of j = 6 on the wafer 40. Then, after the exposure at the position of j = 6 is completed, the exposure at the position of j = 7 is performed while correcting and driving the focus and tilt X based on the measurement result of the surface position of the position of j = 7. Here, FIG. 13 is a schematic perspective view showing the exposure position EP and the focus and tilt measurement positions FP on the wafer 40.

  FIG. 14 is a flowchart for explaining an exposure method using the exposure apparatus 1. Referring to FIG. 14, first, the wafer 40 is loaded into the exposure apparatus 1 (step S1002), and it is determined whether or not the focus tilt detection system 50 optimizes the wavelength of light that illuminates the measurement point KP (step S1002). S1004). Whether or not to optimize the wavelength is registered in the exposure apparatus 1 in advance.

  When the wavelength needs to be optimized, the surface position is measured for all the wavelengths of light that can be used by the focus tilt detection system 50 with the sample shot as shown in FIG. 9 (step S1006). The surface position information is stored (step S1008). Then, it is determined whether there is an unmeasured sample shot (unmeasured sample shot) (step S1010). If there is an unmeasured sample shot, the measurement of the surface position of the unmeasured shot and the surface position information The storage is repeated until there are no unmeasured sample shots.

  When the measurement of the surface position of the sample shot and the storage of the surface position information are completed (that is, when there is no unmeasured sample shot), the measurement point KP in the shot is based on the surface position information of each sample shot stored in step S1008. The optimum wavelength λopt (i, j) is calculated for each step (step S1012).

  On the other hand, if it is not necessary to optimize the wavelength, it is determined whether or not the optimum wavelength of the light that illuminates the measurement point KP is calculated by the focus tilt detection system 50 (step S). Here, for example, the determination is made based on whether or not the optimum wavelength λopt (i, j) is calculated by the preceding wafer. If the optimum wavelength λopt (i, j) has been calculated, the process proceeds to step S1018. If the optimum wavelength λopt (i, j) has not been calculated, the same default wavelength (for example, λ1) is selected for all measurement points KP (step S1016), and the process proceeds to step S1018.

In step S1018, the focus tilt detection system 50 sets the wavelength of light that illuminates the measurement point KP to the optimum wavelength λopt (i, j) or the default wavelength. Then, set the exposure shot in the exposure position by driving the wafer stage 45 (step S1020), the exposure shots, the optimum wavelength λopt (i, j) or focus tilt detection system with light default wavelength 50 The surface position is measured by (Step S1022).

  Next, based on the surface position measured in step S1022, the wafer 40 is driven to correct focus and tilt (step S1024), and the pattern on the reticle 20 is exposed to the wafer 40 (step S1026). Then, it is determined whether or not there is a shot to be exposed (that is, an unexposed shot) (step S1028), and step S1020 and subsequent steps are repeated until there is no unexposed shot. When exposure of all exposure shots is completed, the wafer 40 is collected (step S1030), and the process ends.

  According to the exposure apparatus 1 and the exposure method using the exposure apparatus 1, high focus correction accuracy can be achieved with respect to the reduced depth of focus, and excellent resolution and yield can be realized.

  Note that, regarding the optimization of the wavelength of the light that illuminates the measurement point KP by the focus tilt detection system 50, there may be an effect even if the wavelength having good symmetry of the signal waveform detected by the focus tilt detection system 50 is set as the optimal wavelength. For example, when a device pattern in which a pattern similar to the lattice pattern 523b of the pattern plate 523 shown in FIG. 3 is repeatedly present on the wafer 40 is irradiated, the signal waveforms of all the lattice patterns 523b are similarly distorted. Therefore, the grating intervals L1, L2, and L3 do not vary with respect to any wavelength. In such a case, the effect of the present invention can be obtained by selecting a wavelength having good symmetry of the signal waveform as the optimum wavelength.

  Further, as shown in FIG. 15, the light source 521 can be replaced with a broadband light source 521A such as a halogen lamp. When the broadband light source 521A is used, the dichroic mirrors 543b and 543c of the detection unit 54 cause the light receiving elements 544a, 544b, and 544c to receive the light having the center wavelengths λ1, λ2, and λ3, thereby generating waveform signals of the respective wavelengths. Can be detected. Here, FIG. 15 is a block diagram showing a configuration of a modified example of the focus tilt detection system 50.

  Next, a method for selecting an optimum wavelength of light for illuminating the measurement point KP when using a pattern plate 523A as shown in FIG. 16 instead of the pattern plate 523 of the focus tilt detection system 50 will be described. FIG. 16 is a plan view showing a pattern plate 523A which is a modification of the pattern plate 523. FIG.

  Referring to FIG. 16, the pattern plate 523A has one rectangular pattern 523Ab that is a light non-transparent portion in a transmission region 523Aa as a light transmission portion. The pattern plate 523A can measure the surface position of the wafer 40 at a finer pitch because the area of the projected image on the wafer 40 is smaller than the pattern plate 523. On the other hand, since the lattice interval of the rectangular pattern 523Ab cannot be obtained, a method different from the above-described method is required as a method for selecting the optimum wavelength of light for illuminating the measurement point KP.

  FIG. 17 is a flowchart for explaining a method of selecting an optimum wavelength of light emitted from the focus tilt detection system 50 when the pattern plate 523A is used. First, in the shot layout on the wafer 40 shown in FIG. 9, the surface position of the sample shot of 14 shots is measured with respect to all wavelengths of light included in the focus tilt detection system 50 to obtain a signal waveform (step S702). ). FIG. 18 shows an example of a signal waveform detected by the detection unit 54 when the pattern plate 523A (the rectangular pattern 523Ab) is used.

  Next, based on the signal waveform measured by the focus tilt detection system 50, the signal contrast C = (It−Ie) / (It + Ie) from the light intensity It of the transmission region 523Aa of the pattern plate 523A and the signal intensity of the rectangular pattern 523Ab. Is obtained (step S704). The signal contrast Csij (λ) is calculated for all light wavelengths and all measurement points KP. Here, the subscript s is the sample shot number, s = 1 to 14, i is the in-shot measurement position number in the slit longitudinal direction, i = 1 to 3, and j is the in-shot measurement position number in the scanning direction, j = 1. 7 to λ are wavelengths of light to illuminate, and λ = λ1 to λ3.

  Next, based on the signal contrast Csij (λ), the average of the signal contrasts of all the sample shots is obtained, and the wavelength λ that maximizes the signal contrast at the measurement position (i, j) in the shot is determined in the shot. The optimum wavelength λopt (i, j) of each measurement position (i, j) is set (step S706). Since the light intensity It corresponding to the transmission region 523Aa of the pattern plate 523A depends on the reflectance on the surface of the wafer 40, the signal contrast C increases as the reflectance increases. As shown in FIG. 7, the signal waveform having a higher reflectivity at the wafer 40 has less variation in the reflectivity with respect to the film thickness change of the resist 42, and the influence of the distortion of the signal waveform is reduced, so that the measurement reproducibility is good. I can judge.

  After selecting the optimum wavelength λopt (i, j), the position X1 of the image of the rectangular pattern 523Ab is obtained from the signal waveform of the pattern plate 523A illuminated with the optimum wavelength λopt (i, j), and the surface of the wafer 40 Measure the position.

Instead of setting the maximum value of the signal contrast ratio as the optimum wavelength, the wavelength at which the reflectance of light that has passed through the transmission region 523Aa of the pattern plate 523A is maximized may be set as the optimum wavelength. In such a case, in order to obtain the reflectance, the incident intensity at the wavelength of the illumination light is required. Accordingly, a reference mark base having a known spectral reflectance Rref (λ) with respect to the wavelength of the illuminating light is placed on the wafer stage, and an area without a pattern on the reference mark base is measured by the focus tilt detection system 50, and the pattern plate The signal intensity Iref (λ) of the transmission region 523Aa of 523A is measured in advance.

  The reflectivity R (λ) at each measurement point KP is R (λ) = Isin (λ) × Rref (λ) where Isig (λ) is the signal intensity of the transmission region 523Aa when measuring the surface position of the wafer 40. / Iref (λ).

  Then, the reflectance Rsij (λ) is calculated for all wavelengths of light and all measurement points KP. Here, the subscript s is the sample shot number, s = 1 to 14, i is the in-shot measurement position number in the slit longitudinal direction, i = 1 to 3, and j is the in-shot measurement position number in the scanning direction, j = 1. 7 to λ are wavelengths of light to illuminate, and λ = λ1 to λ3.

  Based on the reflectance Rsij (λ), an average of all sample shots may be obtained, and the optimum wavelength λopt (i, j) at the measurement position (i, j) in the shot may be calculated.

  Alternatively, the pattern plate 523A may be a pattern plate 523B having a circular opening 523Bb in a light shielding region 523Ba for shielding light as shown in FIG. FIG. 20 shows signal waveforms detected by the detection unit 54 of the focus tilt detection system 50 when the pattern plate 523B (the opening 523Bb thereof) is used. 20A shows an example of a signal waveform with good symmetry, and FIG. 20B shows an example of a signal waveform with asymmetry. Here, FIG. 19 is a plan view showing a pattern plate 523B which is a modification of the pattern plate 523A.

  Further, instead of using the pattern plate 523A or 523B, an LED emitting portion is arranged at a position conjugate with the wafer 40, and the light emitted from the LED emitting portion is projected onto the wafer 40, and the projected image is detected by a sensor. It may be configured to receive light.

  Next, a selection method different from the optimal wavelength selection method shown in FIG. 12 will be described with reference to FIG. FIG. 21 is a flowchart for explaining a method for selecting an optimum wavelength of light irradiated by the focus tilt detection system 50.

  First, in the shot layout on the wafer 40 shown in FIG. 9, the surface positions of the 14 shot sample shots are measured for all wavelengths of light of the focus tilt detection system 50 (step S802), and each sample shot is measured. Then, a surface position measurement value Zsij (λ) is obtained for each measurement position in the shot and each wavelength of light used for the measurement (step S804). Here, the subscript s is the sample shot number, s = 1 to 14, i is the in-shot measurement position number in the slit longitudinal direction, i = 1 to 3, and j is the in-shot measurement position number in the scanning direction, j = 1. 7 to λ are wavelengths of light to illuminate, and λ = λ1 to λ3.

  Next, an average value Zasij between the wavelengths of the surface position measurement value Zsij (λ) is obtained (step S806). Then, using the average value Zasij, the surface shape of the wafer 40 (that is, the approximate curved surface of the surface shape) is obtained by curved surface fitting (step S808). FIG. 22 shows an approximate curve of the surface shape of the A-A ′ plane of the wafer 40 shown in FIG. 9 and a graph plotting the surface position measurement values of the respective wavelengths with respect to the sample shots L, D, and R.

  Next, a deviation amount dzsij (λ) of the surface position measurement value Zsij (λ) from the approximate curved surface of the wafer 40 obtained in step S808 is calculated (step S810), and each measurement point KP in the shot is measured between sample shots. A variation amount (standard deviation value) σdZij (λ) is calculated (step S812). Then, the wavelength λ having the smallest variation amount σdZij (λ) is set as the optimum wavelength λopt (i, j) at each measurement position (i, j) in the shot (step S814). That is, it is possible to select an optimum wavelength not using the characteristics of the signal waveform but using the measured value of the surface position of the wafer 40 at each wavelength.

  As described above, since the exposure apparatus 1 can adjust the surface of the wafer 40 to be exposed to the best imaging plane by the focus tilt detection system 50 or the like in exposure, the exposure apparatus 1 is a device with high throughput and good economic efficiency. (Semiconductor element, LCD element, imaging element (CCD, etc.), thin film magnetic head, etc.) can be provided.

  Hereinafter, an embodiment of a device manufacturing method using the above-described exposure apparatus 1 will be described with reference to FIGS. FIG. 23 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, and the like). Here, the manufacture of a semiconductor chip will be described as an example. In step 1 (circuit design), a device circuit is designed. In step 2 (mask production), a mask on which the designed circuit pattern is formed is produced. In step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the mask and the wafer. Step 5 (assembly) is called a post-process, and is a process of forming a semiconductor chip using the wafer created in step 4, and includes processes such as an assembly process (dicing and bonding) and a packaging process (chip encapsulation). Including. In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device created in step 5 are performed. Through these steps, the semiconductor device is completed and shipped (step 7).

  FIG. 24 is a detailed flowchart of the wafer process in Step 4. In step 11 (oxidation), the surface of the wafer is oxidized. In step 12 (CVD), an insulating film is formed on the surface of the wafer. In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition or the like. Step 14 (ion implantation) implants ions into the wafer. In step 15 (resist process), a photosensitive agent is applied to the wafer. Step 16 (exposure) uses the exposure apparatus 1 to expose a circuit pattern on the mask onto the wafer. In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist image are removed. In step 19 (resist stripping), the resist that has become unnecessary after the etching is removed. By repeatedly performing these steps, multiple circuit patterns are formed on the wafer. According to the device manufacturing method of the present embodiment, it is possible to manufacture a higher quality device than before. Thus, the device manufacturing method using the exposure apparatus 1 and the resulting device also constitute one aspect of the present invention.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist. For example, the present invention can also be applied to reticle detection means for detecting the position of the reticle.

It is a schematic block diagram which shows the structure of the exposure apparatus as 1 side surface of this invention. FIG. 2 is an enlarged block diagram illustrating a configuration of a focus tilt detection system illustrated in FIG. 1. It is a top view which shows an example of the pattern board shown in FIG. It is a figure which shows the signal waveform detected by the detection part shown in FIG. 2 when the pattern board shown in FIG. 3 is used. It is a figure for demonstrating the difference of the reflectance resulting from the film thickness nonuniformity of the resist by the pattern level | step difference on a wafer. It is a figure for demonstrating the difference in the reflectance of the area | region where the density of the level | step difference pattern on a wafer is small, and the area | region where the density of pattern level | step difference is large. It is a graph which shows the wavelength dependence of the reflectance of a wafer with respect to the film thickness of a resist. It is a top view which shows an example of arrangement | positioning of the measurement point on a wafer. It is a top view which shows the shot layout on a wafer. It is a top view which shows an example of arrangement | positioning of the measurement point in the slit on a wafer. It is a top view which shows an example of arrangement | positioning of the measurement point in the slit on a wafer. It is a flowchart for demonstrating the selection method of the optimal wavelength of the light which a focus tilt detection system irradiates. It is a schematic perspective view which shows the exposure area | region and the measurement position of the focus and tilt on a wafer. It is a flowchart for demonstrating the exposure method using the exposure apparatus shown in FIG. FIG. 4 is a block diagram showing a configuration of a modification of the focus tilt detection system shown in FIG. 2. It is a top view which shows the pattern board which is a modification of the pattern board shown in FIG. FIG. 17 is a flowchart for explaining a method of selecting an optimum wavelength of light emitted from the focus tilt detection system when the pattern plate shown in FIG. 16 is used. It is a figure which shows the signal waveform detected by the detection part shown in FIG. 2 when the pattern board shown in FIG. 16 is used. It is a top view which shows the pattern board which is a modification of the pattern board shown in FIG. It is a figure which shows the signal waveform detected by the detection part shown in FIG. 2 when the pattern board shown in FIG. 19 is used. It is a flowchart for demonstrating the selection method of the optimal wavelength of the light which a focus tilt detection system irradiates. It is a figure which shows the graph which plotted the approximate curve of the surface shape of the A-A 'surface of the wafer shown in FIG. 9, and the surface position measurement value of each wavelength with respect to a sample shot. It is a flowchart for demonstrating manufacture of devices (semiconductor chips, such as IC and LSI, LCD, CCD, etc.). FIG. 24 is a detailed flowchart of the wafer process in Step 4 shown in FIG. 23.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exposure apparatus 10 Illumination apparatus 20 Reticle 30 Projection optical system 40 Wafer 50 Focus tilt detection system 52 Illumination part 521 Light source 522 Photosynthesis means 522a Mirror 522b and 522c Dichroic mirror 523 Pattern plate 523a Transmission area 523b Grid pattern 523c Light-shielding pattern 524 Imaging lens 525 Mirror 54 Detection unit 541 Mirror 542 Lens 543 Light demultiplexing means 543a Mirrors 543b and 543c Dichroic mirror 544 Light receivers 544a to 544c Light receiving element 56 Operation unit 60 Control unit 70 Reticle detection means

Claims (10)

An exposure apparatus that exposes a pattern formed on a reticle to a plurality of shots on an object to be processed via a projection optical system,
Irradiating each of the first measurement points at the same position in each of the plurality of shots with light of a plurality of wavelengths, and at each of the plurality of shots, being at the same position and different from the first measurement point. Irradiating means for irradiating light of the plurality of wavelengths to each of two measurement points ;
Detecting means for detecting reflected light from the first and second measurement points;
Based on the detection result of said detecting means, from said plurality of wavelengths, a plurality of the optimum wavelength is common to the first measurement point, selection means for selecting optimum wavelength is common to a plurality of second measuring point, respectively When,
An exposure apparatus comprising: a measuring unit that measures the position of each measurement point in the optical axis direction using light of the optimum wavelength selected by the selecting unit. The irradiation means includes a pattern plate having a lattice pattern composed of a plurality of elements;
Projecting means for projecting an image of the lattice pattern onto each measurement point ;
The selection means includes a wavelength at which a standard deviation of an interval between the plurality of elements of the image of the lattice pattern at the plurality of first measurement points is minimum from the plurality of wavelengths, and the plurality of second measurement points. The exposure apparatus according to claim 1, wherein a wavelength that minimizes a standard deviation of an interval between the plurality of elements of the image of the lattice pattern is selected as the optimum wavelength . The irradiation unit includes a projection unit that projects an image of a predetermined pattern onto each measurement point .
Said selection means from said plurality of wavelengths, and the wavelength of the average of the signal contrast of the image of the predetermined pattern in the plurality of first measurement point becomes maximum, the predetermined pattern in the plurality of second measurement point 2. An exposure apparatus according to claim 1, wherein a wavelength at which an average of signal contrast of the image of said image is maximized is selected as said optimum wavelength . The irradiation means includes a pattern plate having a lattice pattern composed of a transmission part that transmits light and a light-shielding part that shields the light;
Projecting means for projecting an image of the lattice pattern onto each measurement point ;
Said selection means from said plurality of wavelengths, and the wavelength of the average of the light reflectance of which has passed through the transmissive portion of the grating pattern in the plurality of first measurement point becomes maximum, the plurality of second measurement point The exposure apparatus according to claim 1, wherein a wavelength at which an average reflectance of light that has passed through the transmission part of the grating pattern is maximized is selected as the optimum wavelength . The measurement means measures the position in the optical axis direction of each measurement point for each of the plurality of wavelengths, and measures the position in the optical axis direction measured with the light of the plurality of wavelengths at each of the plurality of first measurement points. Average the values, average the measured values of the position in the optical axis direction measured with the light of the plurality of wavelengths at each of the plurality of second measurement points, and use the average value to calculate the surface of the object to be processed Obtain an approximate curve of the shape, calculate the amount of deviation of the measured value from the approximate curve,
The selection means includes a wavelength at which a standard deviation of a deviation amount of the measurement value from the approximate curve at the plurality of first measurement points from the plurality of wavelengths is minimum, and the approximation at the plurality of second measurement points. 2. An exposure apparatus according to claim 1, wherein a wavelength at which a standard deviation of a deviation amount of the measured value from a curve is minimized is selected as the optimum wavelength . An exposure method for exposing a pattern formed on a reticle to a plurality of shots on an object to be processed via a projection optical system,
Irradiating each of the first measurement points at the same position in each of the plurality of shots with light of a plurality of wavelengths, and at each of the plurality of shots, being at the same position and different from the first measurement point. An irradiation step of irradiating each of the two measurement points with light of the plurality of wavelengths;
A detection step of detecting reflected light from the first and second measurement points;
A selection step for selecting, from the plurality of wavelengths, an optimum wavelength that is common to the plurality of first measurement points and an optimum wavelength that is common to the plurality of second measurement points, based on the detection result of the detection step. When,
A measurement step of measuring the position in the optical axis direction of each measurement point using light of the optimum wavelength selected in the selection step;
An exposure method comprising: scanning the object to be processed in synchronization with the reticle based on the position in the optical axis direction of each measurement point measured in the measurement step. In the irradiation step, a pattern image composed of a plurality of elements is projected onto each measurement point using light of the plurality of wavelengths,
It said detecting step detects a signal waveform from respective measurement points,
Based on the signal waveform detected in the detection step, obtaining intervals of the plurality of elements for each of the plurality of wavelengths;
Based on the spacing of the plurality of elements, calculating a standard deviation of intervals of the plurality of elements in said plurality of first measurement point, the standard deviation of the intervals of said plurality of elements in the plurality of second measurement point and, further comprising a,
The selection step, calculated from the plurality of wavelengths, and the wavelength in which the standard deviation calculated in the calculation step in the plurality of first measurement point is minimum, in the calculation step in the plurality of second measurement point length of the exposure method according to claim 6, wherein the standard deviation is characterized and Turkey to each selected as the optimum wavelength and wavelength, a the minimum. In the irradiation step, an image of a pattern composed of one element is projected onto each measurement point using light of the plurality of wavelengths,
It said detecting step detects a signal waveform from respective measurement points,
Based on the signal waveform detected in the detection step, further comprising obtaining a signal contrast of the signal waveform for each of the plurality of wavelengths,
The selecting step includes, from the plurality of wavelengths, a wavelength at which the average of the signal contrast at the plurality of first measurement points is maximum, and a wavelength at which the average of the signal contrast at the plurality of second measurement points is maximum. the exposure method according to claim 6, wherein the benzalkonium select each as the optimum wavelength. In the irradiation step, an image of a pattern composed of one element is projected onto each measurement point using light of the plurality of wavelengths,
It said detecting step detects a signal waveform from respective measurement points,
Based on the signal waveform detected in the detection step, further comprising calculating a reflectance at each measurement point of the light that has passed through the element for each of the plurality of wavelengths ,
In the selection step, from the plurality of wavelengths, a wavelength at which the average reflectance at the plurality of first measurement points is maximum and a wavelength at which the average reflectance at the second measurement point is maximum. the exposure method according to claim 6, wherein the benzalkonium select each as the optimum wavelength. In the detection step, the position in the optical axis direction of each measurement point is measured for each of the plurality of wavelengths irradiated in the irradiation step ,
The measured value of the position in the optical axis direction measured in the detection step at each of the plurality of first measurement points is averaged, and the position in the optical axis direction measured in the detection step at each of the plurality of second measurement points. Averaging the measured values, and using those average values to obtain an approximate curve of the surface shape of the object to be processed;
Calculating the amount of deviation of the measured value from the approximate curve , and
The selection step includes a wavelength at which a standard deviation of a deviation amount of the measurement value from the approximate curve at the plurality of first measurement points is minimum from the plurality of wavelengths, and the approximation at the plurality of second measurement points. the exposure method according to claim 6, wherein the benzalkonium be respectively selected wavelength standard deviation of the amount of deviation of the measured value from the curve is minimum, as the optimum wavelength.