JPH03187211A - Exposure device - Google Patents

Abstract

PURPOSE:To improve exposure accuracy by detecting AF set error from an ideal position of an exposure surface in advance and to correct AA detection value by AA detection error corresponding to the AF detection value. CONSTITUTION:A device is provided with an AA detection means to detect relative position relation between an exposure substrate 1 and an original plate 8 by position relation between an AA mark 201 on a substrate formed on the exposure substrate 1 and an AA mark 203 on the original plate 8 formed on the original plate; an AF detection means to detect position deviation from an ideal exposure plane of exposure object surface before AA detection; and a correction means to correct the AA detection value based on the AF detection value. Thereby, it is possible to correct the AA detection value in accordance with the AF detection value (AA detection gap) and to carry out AA more accurately, thereby improving exposure accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exposure apparatus that prints and transfers an image of an original, such as a mask, onto a substrate to be exposed, such as a semiconductor substrate, with high precision.

[Prior Art] Semiconductor integrated circuits have become increasingly highly integrated in recent years, and the exposure equipment (aligners) used to manufacture them are also required to have higher transfer precision.
In 56 megabit DRAM class integrated circuits, the line width is 0.
．． An exposure device that can print patterns of about 25 microns is required.

As an exposure apparatus for printing such ultrafine patterns, an apparatus that performs so-called proximity exposure using orbital synchrotron radiation (SOR-X-rays) has been proposed.

This orbital synchrotron radiation is in the form of a sheet beam that is uniform in the horizontal direction, so in order to expose the surface, ■ the mask and the square are moved in the vertical direction and the surface is scanned with horizontal sheet beam X-rays. scan exposure method; ■scan mirror exposure method in which sheet beam XLA is reflected by a swinging mirror and scanned over the mask and wafer in the vertical direction; A batch exposure method has been proposed in which sheet beam-shaped X-rays are diverged in the vertical direction and the entire exposure area is irradiated simultaneously.

The inventors of the present invention proposed an X-ray exposure apparatus based on this blanket exposure method and previously filed an application as Japanese Patent Application No. 71040/1983.

However, this X-ray proximity exposure apparatus has the disadvantage that the expected exposure accuracy cannot always be obtained. This is due to the following reasons. That is, in this type of exposure apparatus, positional information (AF information) in the optical axis direction of each shot surface can only be obtained on four sides;
All wafers are not perfectly flat and have some undulations. However, with conventional exposure equipment, because the surface shape inside the shot is not known, it is not always possible to align the entire shot with the optimal exposure surface (or focus position or imaging surface), which is a factor in deterioration of exposure accuracy. It had become.

Therefore, the present inventors first detected (AF detection) the position (focus) of the surface of the exposed substrate in the optical axis direction in multiple shots prior to exposure, and used this AF detection value to detect the entire surface of the exposed substrate. Calculate the surface shape (undulations) of the surface and find the optimal plane for exposure in each shot (optimum exposure plane) based on this surface shape. During step-and-repeat exposure, use the optimal exposure plane for each shot. In the so-called global AF method, the substrate to be exposed is exposed after being driven to match the ideal exposure plane of the exposure device, and AF detection is performed in multiple shots prior to exposure, and the detected value is used to determine the surface of the substrate to be exposed. In addition to calculating the overall surface shape, AF detection is also performed for each shot during step-and-repeat exposure, and the AF detection value for each shot is corrected based on the surface shape, a so-called modified die-by-die AF method. Ta.

By the way, in these global AF methods and modified die-by-die AF, the AF detection position is not necessarily on the optimum exposure plane C. Then, by applying these methods,
In line proximity exposure equipment, the setting of the gap between the mask and the wafer (the error in the AF stage setting affects the error in the detected value of the positional deviation (AA detected value) in the plane direction between the mask and the wafer). There was this inconvenience.

This is due to the following reason. That is, in the above-mentioned X-ray exposure apparatus, the positional relationship between the mask and the wafer is detected by the center of gravity of a spot that is diffracted by a diffraction grating formed on the mask and the wafer and imaged on the sensor. This spot has two different optical paths (110 diffraction and 01
This is the sum of the light passing through the 111 diffraction, and if the gap between the mask and the wafer changes, the amount of light passing through the two optical paths will change differently. Therefore, an error occurs in the center of gravity of the spot, that is, in the AA information.

In addition, the fact that the position setting error in the direction perpendicular to the wafer surface (AF stage setting error affects the position detection in the direction parallel to the wafer surface (AA detection) means that, for example, if the AA light is perpendicular to the wafer surface This problem occurs not only in the AA detection method using the above-mentioned diffraction grating, but also in cases where the AA detection method uses a diffraction grating.

[Problems to be Solved by the Invention] The present invention has been made in view of the problems in the conventional type described above, and an object of the present invention is to provide an exposure apparatus with a higher degree of AAM and, therefore, higher exposure accuracy.

[Means for solving the yJN point] In order to solve the above problems, the present invention solves the problem based on the positional relationship between the AA mark on the substrate formed on the exposed substrate and the AA mark on the original plate formed on the original plate. AA detection means for detecting the relative positional relationship between the exposed substrate and the original; AF detection means for detecting a positional deviation of the surface of the exposed object from the ideal exposure plane prior to AA detection; and AA detection by the AA detection means. It is characterized by comprising a correction means for correcting the value based on the AF detection value of the AF detection means.

The present invention preferably provides a plurality of pairs of the AA mark and the AF mark for detecting the AF nucleus in close proximity to each other for each shot on the substrate to be exposed.
Applicable to step-and-repeat type exposure equipment.

In this case, the correction means corrects the AA detection value of each AA mark based on the AF detection value of the AF mark paired with that AA mark.

[Function] According to the above configuration, when performing AA detection, the AF setting error from the ideal position of the surface to be exposed is detected in advance (AF core is detected, and the AA detection error corresponding to the AF setting error is used to detect the AF setting error from the ideal position of the surface to be exposed).
Correct the detected value. The AA detection error corresponding to the AF setting error may be set as an actual measurement value, a designed value, or the like using a manual key or the like.

To explain in more detail using a specific example, (1) Data on the wafer-mask gap versus AA detection error is obtained in advance.

(2) During AF detection and correction, store the gap deviation of each AA detection position from the determined optimum exposure plane.

(2) After the optimum exposure plane is aligned with the ideal exposure plane, that is, after the interval between the optimum exposure plane and the mask is aligned with the AA detection gap (reference gap), AA detection of a plurality of AA marks is performed simultaneously.

(2) Calculate the correction amount for each AA detection value from the stored gap deviation and gear pair AA detection error data, and correct the AA detection value.

[Effect] As described above, according to the present invention, since the AA detection value is corrected according to the AF detection value (AA detection gap), AA can be performed more accurately, and exposure accuracy is improved. do.

[Embodiment] FIGS. 1A and 1B are a sectional view and a plan view showing the structure of a mask wafer alignment and exposure stage portion of a step-and-repeat exposure apparatus (stepper) according to an embodiment of the present invention. In the same figure, 8 is pattern 4
1B, and 16 is an exposure light, for example SO
This is XM radiated from R. Further, 1 is a wafer to which the pattern 418 of the mask 8 is transferred, 2 is a wafer 1 that is moved in Z (moved in the optical axis direction of the exposure light 16) when the wafer 1 is opposed to the mask 8 through a predetermined proximity gap, ω
2 tilt stages for driving X (rotation around the X axis) and ωy (rotation around the y axis), 3 is a piezo element that is the drive source of the 2 tilt stages 2, and 17 is the displacement of the Z tilt stage 2 (z).

ω8. ωy), an electrostatic sensor which is a displacement sensor for measuring ωy), 4 a stage for rotating the wafer 1 within its plane, 5 a wafer X stage for driving the wafer 1 in the X direction, and 6 7 is a wafer X stage for driving the wafer 1 in the Y direction, 7 is assembled with a wafer stage 24 consisting of a Z tilt stage 2, a wafer X stage 4, a wafer X stage 5, a wafer X stage 6, etc. It is based on a wafer stage.

Further, 9 is a mask chuck that holds the mask 8 in a detachable manner, 10 is a mask θ stage for rotating the mask 8 within its plane, and 11 is a mask composed of the mask chuck 9 and the mask θ stage 10, etc. This is a mask stage base to which the stage is assembled.

A pickup 12 irradiates light onto alignment marks formed on the mask 8 and the wafer 1 and detects scattered light from these marks. In this embodiment, the alignment marks are as shown in FIG. 2A.
A total of four scribe lines, XU, XD, YL, and YR, are formed on the scribe line of each shot on the wafer 1 close to the edges of each side of the shot. As shown in FIG. 2B, one alignment mark consists of a diffraction grating and a mask 8, which become AA marks 201 for detecting mask-sea urchin fly alignment errors in the direction parallel to the side on which the mark is arranged. AF mark 202 for detecting the interval between wafers 1
A blank area is formed together with the semiconductor circuit pattern in a previous process. Also on the mask 8, four alignment marks 203 and 204 that are paired with the alignment marks on the wafer 1 are formed of gold or the like together with the semiconductor circuit pattern to be transferred.

In FIG. 2B, 205 is a semiconductor laser which is a light emitting element, 206 is a collimator lens that converts the light beam output from the semiconductor laser 205 into parallel light, and 207 is a projection that is output from the semiconductor laser 205 and is converted into parallel light by the collimator lens 206. Light beam, 20B is AA mark 201 on wafer
The AA light receiving beam 209 is given positional deviation information (AA information) by an optical system composed of the AF mark 202 on the wafer and the AF mark 204 on the mask. AF receiving beam given (AF information), 2
10 is an AA sensor, which is a line sensor such as a CCD, which converts the position of the AA light receiving spot 211 formed by the AA light receiving beam 20B into an electrical signal as AA information;
An AF sensor 212 is a line sensor such as a CCD, which converts the position of the AF light receiving spot 213 formed by the AF light receiving beam 209 into an electrical signal as AF information.

Figure 3 shows the configuration of the electrical control system of the exposure apparatus shown in the zi diagram. The main body unit includes a mirror unit that aligns the mask and the square, an alignment unit that aligns the mask and the square, and an exposure unit that exposes the aligned mask and the square with the planar X-rays, the mirror unit, and the main body unit. It is equipped with an attitude control unit, a chamber for controlling the atmosphere of the mirror unit and the main unit, an air conditioning unit, etc.

′! In figure J3, 301 is a main processor unit for controlling the operation of the entire device, 302 is a communication line connecting the main processor unit 301 and the main unit, 303 is a main unit side communication interface, 3
04 is a main body control unit, 305 is a pickup stage control unit, 307 and 306.3-08 are fine AA/AF for measuring mark position deviation between the main body control unit 304 and mask alignment and mask-wafer alignment in the main unit. Control units 309a, 309b, 309c.

309d, and 311, 310, and 312 are communication lines and communication interfaces that connect the main body control unit 304 and the stage control section 313 for controlling correction drive and step movement during alignment in the main unit. It is a communication interface.

FIG. 4 is a diagram showing a step-and-repeat exposure method. In order to simplify the explanation, the mask θ stage 10 . The wafer stage 24, which is a driving means for the wafer 1, is not shown.

In the figure, 12 (12a to 12d) is a mask 8
and a pickup for alignment of the wafer 1, 418 is a transferred i<turn drawn on the mask, 419 is a transferred pattern formed on the wafer by the preceding process, and 420 is the mask position on the wafer stage 24. 421 is a transfer pattern 418, which is a mask alignment mark for alignment with an alignment reference mark (not shown);
422 is an alignment mark on the wafer for the same purpose, 423 is a light beam projected from the big-up 12 for the same purpose, 401 is a scribe line between shots, An on-wafer alignment mark 422 is drawn on this scribe line. Further, a total of four on-mask alignment marks 420 are provided, one on each side of the transfer pattern 418 on the mask 8 corresponding to the scribe line 401 between shots on the wafer, at the substantially central portion on the outside of each side.

In the apparatus shown in FIG. 1, AF is alignment in the Z-axis direction and axis rotation (ω8, ωY) to set the gap between the mask and wafer to a predetermined exposure gap, and AF is alignment in the plane direction (x, ωY) of the mask and wafer. y.

Two types of alignment are performed with AA, which is alignment of θ). Here, AF measures the distance from the mask at multiple locations on the wafer in advance to detect waviness of the entire wafer, and AF is detected for each and repeat exposure special shot, and an optimal exposure plane, which is the optimal plane for exposure of each shot, is determined based on this AF detection value and the waviness information, and this optimal exposure plane matches the ideal exposure plane. A method also called modified die-by-die alignment is adopted in which the gap information of so-called die-by-die AF, which performs AF correction to align the gap between the wafer and mask, is corrected using global waviness information. In addition, in the so-called die-by-die alignment method in which positional deviation is measured and aligned for each shot, the AA measurement value is calculated based on the wafer-mask gap error at the AA measurement position obtained from the waviness information. A correction method is adopted based on the

Next, the operation of the apparatus shown in FIG. 1 will be explained with reference to the flowcharts shown in FIGS. 5 and 6.

When a wafer is supplied to the wafer stage 24, this device chucks the wafer, performs pre-alignment of the entire wafer, detects waviness of the entire wafer, and then performs the steps starting from step 501 in FIG. Start processing.

Waviness detection for the entire wafer approximates the surface shape of the entire wafer using a polynomial. For example, a bicubic equation (where A is a 4-by-4 determinant) is used as the polynomial, and AF measurement (mask-to-wafer gap measurement) is performed with several shots (sufficient number to determine parameter A). , to determine the unknown parameter A1, that is, the approximate curved surface of the entire wafer surface. FIG. 7A shows the surface shape of an ideal wafer, and FIG. 7B shows the surface shape of a typical wafer.

In the flowchart of FIG. 5, first, step 50
In step 1, it is determined whether or not the mask needs to be replaced. Step 504 when exposing with the currently chucked mask
If the mask is to be replaced and exposed, the process proceeds to step 502. In step 502, the currently chucked mask is removed from the mask stage using a mask traverser (not shown) and stored in a mask cassette (not shown). Then, the mask used for exposure is taken out from the mask cassette using a mask traverser and chucked onto the mask stage 10. Then, in step 503, the pickup 12 is used to align the mask alignment mark 420 drawn on the mask 8 with a reference mark (not shown) provided on the wafer stage.

Next, in step 504, the wafer stage 24 is driven to a position on the wafer (shot position,
That is, the transferred pattern 419) and the transferred pattern 418 on the mask are made to face each other. And step 505
Then, the gap between the mask and the wafer is measured using the on-mask alignment mark 421 and the on-wafer alignment mark 422, and the gap between the mask and the wafer is adjusted to a predetermined AA based on both the measured value and the approximate curved surface.
2 and tilt correction (A
AF correction drive), and during this AF correction drive,
AF setting value (gap alignment error) ΔG for each AF measurement point
yfi, ΔGyr (-see FIG. 8A), ΔGxu, and ΔGxd (not shown) are stored.

This Z and tilt correction does not use the AF detection value itself immediately before shot exposure, but uses the attitude (2
, ω×, ωY), which is the optimal posture (Z.

ω8. It is preferable to adjust the exposure plane 81 in the current shot as shown in FIG. ideal exposure plane 82 of
The maximum amount of deviation from the position can be made much smaller than the amount of deviation in the conventional example in which the wafer surface 83 obtained only from the AF measurement values around the seat coincides with the ideal exposure plane 82. That is, it is possible to improve exposure accuracy from the AF aspect. In Fig. 8A, the mask-queue gap at each AF measurement point after AF correction driving is the AA detection gap G.
As AA, GAA-ΔGyQ, GAA-
ΔG yr,...

When the AF correction drive is completed, in step 506, the deviation in the X and Y directions between the mask and the square is measured using the on-mask alignment mark 421 and the wafer alignment mark 422, and AA correction drive is performed to perform AA. . The detailed processing content of AA (step 506) will be described later.

When AA is completed, one shot exposure is performed in step 507, and the presence or absence of the next exposure shot is determined in step 508. If there is, the process returns to step 504; otherwise, the process ends.

FIG. 6 is a flowchart showing the contents of the AA process in step 506 in FIG. AA for one job
It represents measurement, calculation of X, Y, and θ deviation amounts, and correction driving.

First, in step 601, AA measurements are performed at these four points using the four alignment marks 422 and 421 provided on the four sides of the shot to be exposed (current shot), and in step 602, AF settings for these four points are performed. Calculate <AA correction amount based on the error. In this embodiment, as shown in FIGS. 2A and B and FIGS. 8A and B, the AF measurement mark and the AA measurement mark are provided very close to each other. AF setting value (gap error) ΔG yQ of the AF measurement point stored in step 505,
ΔG yr, ΔGxu, and ΔGxd are used as they are as AF setting values at the AA measurement point.

FIG. 9 shows the relationship between the gap error ΔG and the AA error ΔAA. The AA correction amount is a value obtained by inverting the sign of this AA error.

In step 603, the AA measurement values of these four points and the AA
Based on the amount of correction, the amount of deviation ΔX, ΔY between the mask and the square,
Calculate Δθ. In step 804, these deviation amounts Δ
It is determined whether or not X, ΔY, and Δθ are within a predetermined tolerance. If not, proceed to step 605 and perform X, Y.

After performing the deviation correction drive of θ, the process returns to step 601 and repeats the processing of steps 601 to 604 described above.Meanwhile, in the judgment of step 604, the deviation amount ΔX
, ΔY, and Δθ are within the predetermined tolerance, the AA processing is completed and the process returns to step 507 in FIG.

[Scope of Application of the Invention] In the above, an example in which the present invention is applied to a 5OR-X-ray proximity stepper using a batch exposure method has been mainly described, but the present invention can be applied not only to the above-mentioned example. is clear.

For example, the exposure method may be a scan exposure method or a scan mirror exposure method other than the block exposure method.
Further, the exposure light source may be X-rays other than 5OR-X-rays, furthermore, far ultraviolet rays such as excimer laser light or near ultraviolet rays such as g-line of mercury. The present invention can also be applied to a projection exposure apparatus in which a reticle (reticle) and a wafer face each other via an optical system.

Furthermore, the AF method may be the global AF method.

[Brief explanation of drawings]

FIG. 1 is a block diagram of main parts of a step-and-repeat exposure apparatus according to an embodiment of the present invention, FIGS. 2A and 2B are explanatory diagrams of alignment marks on a wafer and alignment marks on a mask, and FIG. , FIG. 4 is an explanatory diagram of the step-and-repeat exposure method, FIG. 5 is a flowchart showing step-and-repeat processing, and FIG. FIG. 7A and B are explanatory diagrams showing an example of the surface shape of an ideal wafer and a general wafer surface shape, respectively. FIGS. 8A and B are An explanatory diagram showing the positional relationship between the mask and the wafer after AF correction, and FIG. 9 are graphs showing the relationship between the gap error ΔG and the AA error ΔAA in the apparatus of FIG. 1. 1: Wafer (substrate to be exposed) 2: Z tilt stage 8: Mask (original plate) 12 (12a to 12d): Pickup 16: X
Line (exposure light) 24: Wafer stage 81: Queue surface (exposure surface) approximate curved surface 82: Ideal exposure plane (and optimal exposure plane) 304: Main body control unit 422 (XU, XD, YR, YL): On-wafer alignment Mark 421 (XU, XD, YR, YL): 7-screen alignment mark 423: Projection beam

Claims (2)

[Claims] (1) AA detection means for detecting the relative positional relationship between the exposed substrate and the original based on the positional relationship between the on-substrate AA mark formed on the exposed substrate and the original AA mark formed on the original; AF detection means for detecting a positional deviation of the exposed surface from an ideal exposure plane prior to detection; and correction means for correcting the AA detection value of the AA detection means based on the AF detection value of the AF detection means. An exposure apparatus comprising: (2) A step-and-repeat type exposure apparatus, in which the AA mark and the AF mark for AF detection form very close pairs, and a plurality of pairs are provided for each shot on the exposed substrate. The correction means converts the AA detection value of each AA mark into the A
The exposure apparatus according to claim 1, wherein the exposure apparatus performs correction based on the AF detection value of the F mark.