JP2003332201A - Exposure method and exposure system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To materialize accurate exposure by controlling the angle of incidence of EUV light impinging on a reflection type mask in an exposure method and an exposure system of using light reflected from the reflection type mask while the reflection type mask is irradiated with the EUV light. <P>SOLUTION: In the exposure method and the exposure system of irradiating a wafer 9 with the EUV light reflected from the reflection-type mask 4 while the reflection type mask 4 is irradiated at a prescribed angle with the EUV light emitted from an EUV light source 1, a change in an angle of incidence of the EUV light impinging on the reflection-type mask 4 is detected, an angle of incidence of the EUV light impinging on the reflection-type mask 4 is corrected on the basis of the detected change of the angle of incidence to carry out an exposure operation. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to EUV (Extreme
Ultra Violet) The present invention relates to an exposure method and an exposure apparatus for irradiating a reflective mask with light and transferring a circuit pattern on the reflective mask onto a substrate.

[0002]

2. Description of the Related Art In a lithographic process for manufacturing semiconductor devices, the wavelength of a light source of an exposure apparatus is shortened along with the miniaturization of patterns, i-line (wavelength 365 nm) → KrF excimer (wavelength 248 nm) → ArF excimer (wavelength 193 nm ) → F2 (wavelength
153 nm). In principle, the resolution can be increased by increasing the numerical aperture (NA) of the projection optical system and shortening the exposure wavelength. Generally, the resolution of the exposure apparatus that represents the minimum line width is given by the following equation (1).

Resolution = K1 · λ / NA (1) Here, K1 is determined by the process such as resist used.
The following positive constants.

Further, for further miniaturization, light in the soft X-ray region having a wavelength of 5 to 15 nm, EUV (Extreme
An exposure apparatus using Ultra Violet light as exposure light has been developed (see, for example, Japanese Patent Laid-Open No. 2000-91216).

In the exposure apparatus, when K1 = 0.8, 13.5 nm
When EUV light is used as the exposure wavelength, assuming that NA = 0.25, a resolution of 43 nm can be obtained from equation (1) above, and a minimum line width of 50
Allows processing of nm design rules. Because of this EU
V-exposure technology has been cited as a promising candidate for the next-generation exposure apparatus.

By the way, in EUV light, most existing substances are not transmitted but absorbed, and it is impossible to construct a refraction projection optical system like a conventional optical exposure device. For this reason, development is proceeding with a configuration using a catoptric projection optical system. In this case, the mask as the original plate is of a reflection type, and the illumination on the mask is oblique incidence illumination.

The angle of incidence on the mask is determined by the illumination NA (hereinafter referred to as NAill) on the mask incident surface, which is determined by the wafer surface NA and the projection magnification of the catoptric projection optical system determined by the desired resolution. The projection magnification is being developed as a 4x system or a 5x system following the existing optical exposure machine, and at the level of NA = 0.2 to 0.3 determined by the desired resolution when applying EUV exposure, The angle of incidence on the mask surface is about 4 °.

[0008]

Here, in the case of oblique incidence illumination as described above, the azimuth of the pattern with respect to the projection vector of the incident ray (assuming that the LSI pattern is divided into parallel or perpendicular to the scanning direction). Since the pattern line width transferred on the wafer varies depending on the orientation, the pattern width on the wafer is corrected to the mask pattern line width at the layout stage so that the transfer pattern line width on the wafer becomes uniform. Applying (VH line width correction) is under consideration.

However, since the EUV light source requires a very large-scale equipment, it is mechanically divided into several systems. That is, the EUV light source and the illumination system that reflects the light to the mask are separate devices, and the incident angle of the EUV light emitted from the EUV light source to the mask is likely to shift. Due to this deviation of the incident angle, even if the VH line width correction is performed on the mask, the difference in the pattern line width due to the azimuth changes, and it becomes impossible to maintain the correct transfer pattern size.

[0010]

The present invention has been made to solve the above problems. That is, the present invention is an exposure method in which EUV light is incident on a reflective mask at a predetermined angle and the pattern on the mask is transferred onto a substrate. The change in the incident angle of the EUV light on the reflective mask is detected, EU based on the change in the detected incident angle
In this method, the incident angle of V light with respect to the reflection type mask is corrected to perform exposure.

Further, an EUV light source for emitting EUV light,
The reflection type illumination means for making the EUV light emitted from the EUV light source enter the reflection type mask at a predetermined angle, the angle detection means for detecting a change in the incident angle of the EUV light with respect to the reflection type mask, and the angle detection means. The exposure apparatus also includes an angle correction unit that corrects the incident angle of the EUV light with respect to the reflective mask based on the change of the incident angle.

According to the present invention as described above, when the reflective mask is irradiated with the EUV light and the reflected light is exposed, a change in the incident angle of the EUV light with respect to the reflective mask is detected, and the initial setting value of the incident angle is detected. Since the exposure is performed by correcting the amount of change from, the EUV light can be incident on the reflective mask at an accurate incident angle, and the transfer pattern line width does not vary depending on the pattern orientation on the mask It becomes possible to perform various exposures.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram illustrating an exposure apparatus according to this embodiment. The exposure apparatus is roughly divided into a light source system, an illumination system, and a projection system. Here, the alignment system and the like are omitted.

In the exposure apparatus using EUV light, illumination light is obliquely incident on the reflective mask 4, and the reflected light from the mask surface is projected through the projection optical system 6 onto the wafer 9 coated with the photosensitive material (reflection). Type projection system). As a result, the pattern in the illumination area on the reflective mask 4 is transferred onto the wafer 9.

In the exposure apparatus of this embodiment, the reflective mask 4 is used.
The upper illumination area is designed to have an arc shape,
It is assumed that a scanning exposure method is adopted in which the pattern on the reflective mask 4 is sequentially transferred onto the wafer 9 by relatively scanning the reflective mask 4 and the wafer 9 with respect to the projection optical system 6.

The definition in this embodiment will be described below with reference to FIG. The reflective mask 4 is scanned in the Y direction in the figure, and the pattern is transferred onto the wafer. The vertical line and horizontal line azimuth in the present embodiment are defined by the vertical line (V line) indicating the direction parallel to the scanning direction and the horizontal line (H line) indicating the direction perpendicular to the scanning direction.
And The oblique incidence angle is defined as the angle around the X axis in FIG.

The structure of the reflective mask using EUV light is shown in the schematic perspective view of FIG. Low-expansion glass is used as the substrate, and the reflection surface is a multilayer film in which two kinds of substances are alternately laminated. Here, as an example, molybdenum (M
It is assumed that a reflective film having a reflectance of about 70% for EUV light with a wavelength of 13 nm is formed by using a multilayer film of o) and silicon (Si).

A substance that absorbs EUV light is applied to one surface of the reflective film and patterned. While patterning a reflective material such as a multilayer film on the absorbing film blanks makes it impossible to repair it when it fails, the method of providing an absorbing film for patterning makes it possible to start over, so that pattern repairing is possible. It will be possible.

When the vertical and horizontal differences in the pattern line width due to the oblique incidence illumination are to be strictly simulated, an electromagnetic field simulation that takes into account the three-dimensional structure of the steps of the absorption film as shown in FIG. 3 is required. Therefore, as a simulation, it is assumed to be approximated when obliquely incident on a two-dimensional binary mask assuming that the thickness of the absorption layer is zero.

FIG. 4 shows the simulation result of the VH (vertical line / horizontal line) difference of the transfer line width by the oblique incident illumination. This simulation result shows that the exposure wavelength = 13.5 nm, NA = 0.25, σ
= 0.70, incident angle on mask = 4 ° (around X-axis), projection magnification 4 times, pattern on wafer = 50 nm Line and space vertical and horizontal lines are the transfer line widths on the wafer for each vertical and horizontal lines. .

As shown in FIG. 4, there is a line width difference of about 5 nm in the best focus, and in order to correct this, the mask pattern line width is corrected in advance at the layout stage to pattern the mask pattern. This prevents vertical and horizontal differences in the line width of the transferred pattern.

Next, FIG. 5 shows the case where the incident angle is changed under the same calculation conditions as above. When the incident angle on the mask changes, the VH difference generated in the transfer pattern on the wafer also changes. Since the pattern line width correction amount for each direction of the mask is established based on a predetermined incident angle, as a result, the line width of the wafer transfer pattern varies depending on the direction except for an incident angle outside the predetermined range. In this embodiment,
The feature is that this VH line width variation is zero.

Assuming that the variation in CD difference between VHs at the best focus is ± 1 nm as an allowable error from FIG. 5, it is 4 ° ± 0.5.
It is estimated that it must be maintained at about °. In the prior art, such a tolerance including a variation in the illumination light incident angle has not been particularly discussed.

Furthermore, the line width of the transfer pattern also changes depending on the repeating periodicity (pitch) of the pattern on the mask, that is, the density (hereinafter referred to as OPE characteristic: Optical Proximity).
Effect), this sparse-dense characteristic also changes when the illumination light incident angle changes.

Since the line width correction for each pattern density of the mask is established under a predetermined incident angle, as a result, the line width of the wafer transfer pattern varies depending on the density of the pattern. The simulation results are shown in FIG. 6 (H line OPE characteristic), FIG. 7 (V line OPE characteristic), and FIG. 8 (OPE characteristic VH difference). The calculation conditions are as described above.

From this result, at an incident angle outside the range of 4 ° ± 0.5 °, not only the VH difference OPE characteristic may shift in parallel, but also the curve shape variation (that is, characteristic variation) may occur. If the system fluctuates with the incident angle of
When a mask whose sparse / dense characteristics are corrected in advance under the condition of an incident angle of 4 ° is transferred, the line width difference between VHs varies not only by the offset but also by the sparse / dense. The present embodiment is characterized in that this line width variation is set to zero.

Next, the EUV light source will be described. EU
One example of the V light source is a laser plasma system. This is, for example, a high-power laser beam such as an excimer laser is jetted from a nozzle in a jet shape to generate an EUV gas such as a rare gas.
The generated substance is condensed and irradiated to excite the substance into a plasma state, and EUV light is generated when the substance is transited to a low potential state.

As shown in the schematic view of FIG. 9, EUV light is
It is generated by the laser light focused on the EUV generation source 13 from the high-power laser 11. And it is radiated in all directions,
It is converted into parallel light by the parabolic reflector 12 on the back surface. After that, the reflection type intensity equalizing element 21 and the reflection type condenser mirror 23 are used to set the intensity, NA
It is emitted as a uniform elongated bow-shaped slit beam of ill.

FIG. 10 is a schematic diagram in which the conjugate relationship in the optical system of the exposure apparatus is extracted. In order to make the EUV light obliquely incident on the reflection type mask 4, the angle of the plane mirror 5 is specifically swung, or the pupil plane of the illumination system, specifically, the reflection type intensity equalizing element 21 (see FIG. 9). The exit surface (usually a diaphragm for determining the shape of the light source is installed here) is integrated with the diaphragm and the homogenizing element in one plane or two-dimensionally in the plane perpendicular to the optical axis traveling direction. It is realized by shift driving to.

FIG. 11 is a schematic diagram for explaining the change in irradiation angle due to the shift of the pupil plane of the illumination system. Controlling the incident angle to the mask by shifting the pupil plane of the illumination system as described above is easier to control than the mirror tilt, and good control accuracy can be obtained. Therefore, in this embodiment, this method is used to correct the incident angle. It is adopted as a means. Also, since the amount of change in the angle of incidence on the mask due to this illumination system pupil plane shift is uniquely determined in optical design, there is no problem with open control.

Next, detection of change in the incident angle of EUV light on the mask will be described with reference to the schematic diagram of FIG. Figure 1
In 2, the plane mirror 5 (reflection prism) that enters the mask is mechanically fixed to the projection optical system. A visible light reflection mirror 51 is installed on the back surface of the plane mirror 5. On the other hand, the measurement light source 52 and the position measurement sensor 53 are installed in the light source system. As a result, the measurement light emitted from the measurement light source 52 is reflected by the visible light reflection mirror 5
The emission angle deviation θ of the EUV light is detected by reflecting the light at 1 and receiving the reflected light at the position measurement sensor 53.

The emission direction of the measurement light (for example, He-Ne laser) installed in the light source light source system is adjusted in advance so as to coincide with the EUV light emission direction. The position measuring sensor 53 may be a simple two-dimensional sensor or a four-division sensor.

For example, taking the case where the angle of the entire light source system with respect to the projection optical system varies by θ with respect to the initial setting,
Measuring light source ~ Reflecting mirror ~ 2L if the span of the measuring surface is 2L
It is detected as a position shift of θ. In this way, the relative angle information between the light source system and the projection system is measured constantly or at regular time intervals.

If the angle of incidence on the mask deviates from the initial setting (4 ° in this embodiment), the line width difference between VH and the OPE sparse / dense characteristics fluctuate as described above, and the desired uniform dimension control is achieved. It cannot be achieved. Therefore, when the incident angle on the mask is out of the standard, the displaced angle amount is calculated, and the displaced angle is corrected by the position shift of the illumination system pupil plane as described above.

As an example of the flow of the exposure method, the mask incident angle is measured by the angle measuring system described above before the wafer exposure, and it is obtained in advance from the allowable variation amount of the line width difference between VH and the allowable variation amount of the OPE sparse / dense characteristic. The judgment is made for each wafer or for each shot whether the incident angle exceeds the allowable amount.

When the allowable amount is exceeded, the pupil plane of the illumination system is two-dimensionally driven in parallel in the plane perpendicular to the optical axis traveling direction so as to correct the angular deviation. After confirming that the angle correction is completed, the exposure operation is performed.

As a result, the incident angle of the EUV light on the reflective mask can be accurately controlled, and accurate exposure can be performed without causing a difference in the wafer transfer pattern line width depending on the pattern orientation.

Since these angular displacement measurements can always be measured, they may be dynamically corrected during one-shot scanning exposure. That is, based on the measured incident angle information on the mask surface, when the angle deviation exceeds a predetermined amount, it is controlled for each wafer, each shot, or arbitrarily when necessary in the exposure sequence to control the position of the illumination pupil. Correct by

In the present embodiment, the angle deviation is limited to the rotation angle around the X axis (reference angle is 4 ° in this example), but the rotation angle around the Y axis (reference angle is 0 °) is described. Similarly, the allowable angle deviation amount is obtained from the VH line width difference and the VH difference of the OPE sparse / dense characteristics. Regarding this, another system for measuring the relative angle deviation between the systems may be added and operated in the same manner. For correction, the illumination system pupil may be two-dimensionally parallel-shift driven in a plane perpendicular to the light ray traveling direction.

[0040]

As described above, the present invention has the following effects. That is, when irradiating the reflective mask with EUV light to perform exposure, the EUV to the reflective mask
Since the incident angle of UV light is accurately managed and controlled, the line width difference (between vertical and horizontal) of the transfer pattern and the OPE
It is possible to keep the characteristic fluctuation within the allowable fluctuation amount, and it is possible to perform highly accurate exposure with EUV light.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram illustrating an exposure apparatus according to this embodiment.

FIG. 2 is a schematic diagram illustrating a definition in this embodiment.

FIG. 3 is a schematic perspective view illustrating the structure of a reflective mask that uses EUV light.

FIG. 4 is a diagram illustrating a VH difference between pattern line widths.

FIG. 5 is a diagram showing a simulation result of VH difference of a transfer line width by oblique incidence illumination.

FIG. 6 is a diagram showing simulation results when the incident angle is changed.

FIG. 7 is a diagram showing a simulation result (VPE OPE characteristic of a line) of variation due to pattern density.

FIG. 8 is a diagram showing a simulation result (OPE characteristic VH difference) of variation due to sparse and dense patterns.

FIG. 9 is a schematic diagram illustrating a light source system and an illumination system.

FIG. 10 is a schematic diagram in which a conjugate relationship in an optical system of an exposure apparatus is extracted.

FIG. 11 is a schematic diagram illustrating a change in irradiation angle due to a shift of the illumination system pupil plane.

FIG. 12 is a schematic diagram illustrating detection of a change in an incident angle of EUV light on a mask.

[Explanation of symbols]

1 ... EUV light source, 2 ... Stage, 3 ... Mask holder, 4
... Reflective mask, 5 ... Planar mirror, 6 ... Projection optical system, 7
... Wafer stage, 8 ... Wafer holder, 9 ... Wafer

Claims (9)

[Claims] 1. An exposure method for semiconductor manufacturing, wherein EUV (Extreme Ultra Violet) light is incident on a reflective mask at a predetermined angle and the pattern on the reflective mask is transferred onto a wafer. An exposure method comprising: detecting a change in an incident angle with respect to a reflective mask, correcting the incident angle of the EUV light with respect to the reflective mask based on the detected amount of change in the incident angle, and performing exposure. 2. The exposure method according to claim 1, wherein visible light matching the incident direction of the EUV light to the reflective mask is used in detecting the change in the incident angle. 3. The exposure method according to claim 1, wherein a change in the incident angle is detected at any time to correct the incident angle. 4. The exposure method according to claim 1, wherein a change in the incident angle is periodically detected to correct the incident angle. 5. An EUV light source that emits EUV (Extreme Ultra Violet) light, a reflective illumination unit that irradiates a reflective mask with the EUV light emitted from the EUV light source at a predetermined angle, and the reflection of the EUV light. An angle detecting means for detecting a change in the incident angle with respect to the mask, and an angle correcting means for correcting the incident angle of the EUV light with respect to the reflective mask based on the change in the incident angle detected by the angle detecting means. An exposure apparatus. 6. The angle correcting means corrects the incident angle by translating a position of an illumination system pupil of the reflection illuminating means in a plane perpendicular to an optical axis traveling direction. The exposure apparatus according to claim 5. 7. The angle detecting means uses visible light that is aligned with the irradiation direction of the EUV light to the reflective mask when detecting the change in the incident angle. The exposure apparatus described. 8. The exposure apparatus according to claim 5, wherein the angle detection means detects a change in the incident angle at any time. 9. The exposure apparatus according to claim 5, wherein the angle detecting means detects a change in the incident angle periodically.