JPH05326367A - Exposure method, aligner and photomask used therefor - Google Patents

Abstract

PURPOSE:To restrain that the image formation face of a projection lens becomes out of focus due to its curved deformation which is caused in an exposure treatment as one process in the manufacturing process of a semiconductor integrated circuit device. CONSTITUTION:In an exposure treatment, a photoresist film on a semiconductor wafer 3 is irradiated, via a reticle 12 and a reduction-projection lens 13, with light which has been radiated from an exposure light source 2, and a prescribed pattern on the reticle 12 is transferred to the photoresist film on the semiconductor wafer 3. The exposure treatment is executed in a state that the reticle 12 has been deformed so as to correct the image-face deformation of the image of a semiconductor integrated circuit pattern on the reticle 12 which is projected onto the main face of the semiconductor wafer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure method, an exposure apparatus and a photomask technique used therefor, and more particularly to an exposure method, an exposure apparatus and a photomask (hereinafter referred to as a mask) used in a manufacturing process of a semiconductor integrated circuit device. It relates to technology that is effective when applied.

[0002]

2. Description of the Related Art As an exposure apparatus used in an exposure process of a semiconductor integrated circuit device, there is, for example, a reduction projection exposure apparatus.

A reduction projection exposure apparatus irradiates a semiconductor wafer with light emitted from a light emitting portion through a reticle and a reduction projection lens, and reduces a pattern formed on the reticle by the reduction projection lens to reduce the semiconductor wafer. It is a device to transfer to.

In the reduction projection exposure apparatus, since the area of the region exposed in one exposure process is small, each region is sequentially exposed while the semiconductor wafer is moved stepwise during the exposure process, and the entire surface of the semiconductor wafer is exposed. It is processing.

The reticle used in the reduction projection exposure apparatus is formed by forming a metal pattern made of chromium (Cr) or the like on a flat transparent glass substrate having, for example, a flat rectangular shape. The part with the metal pattern forms a light-shielding region, and the part without the metal pattern forms a light-transmitting region. However,
The pattern on the reticle is larger than the actual pattern of elements and wirings of the semiconductor integrated circuit device.

Regarding the exposure technique of the semiconductor integrated circuit device, for example, Ohmsha Co., Ltd., November 3, 1984.
Published on 0th, "LSI Handbook" P253-P260
And the projection exposure method and the like are described.

[0007]

By the way, it is known that the image forming surface of the projection lens of the projection exposure apparatus is not flat but is deformed in a curved shape. This curvature is called image plane distortion.

However, since the semiconductor wafer to which the pattern is transferred is held so that its upper surface is substantially flat, a part of the exposure area is caused by the image plane distortion distortion.
In particular, there is a problem that the focus is blurred around the periphery and the transfer accuracy is lowered.

This problem becomes more noticeable as the resolution of the projection exposure apparatus is improved with the miniaturization of elements and wirings of the semiconductor integrated circuit device. This is because a projection lens with a high numerical aperture (hereinafter, abbreviated as NA) is usually used in order to obtain high resolution. However, if NA is increased, the curvature of field is increased and the depth of focus is significantly increased. Becoming shallower,
This is because the range that can cover the image surface distortion becomes narrower.

In order to avoid such a problem, conventionally, for example, in a reduction projection exposure apparatus, the focus is not blurred around the exposure area, that is, the optical path length of light passing through the projection lens is at the center of the exposure area. The lens and the shape of the projection lens itself have been set so that multiple lenses are overlapped so that the projection lens and the periphery are the same, but the projection optical system mechanism becomes complicated. There was a problem such as an increase in restrictions.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of suppressing defocusing due to image plane distortion.

Another object of the present invention is to provide a technique capable of simplifying the mechanism of the projection optical system of the exposure apparatus.

Another object of the present invention is to provide a technique capable of relaxing the restriction of the projection lens of the exposure apparatus.

The above and other objects and novel features of the present invention will be apparent from the description of the specification and the accompanying drawings.

[0015]

Among the inventions disclosed in the present application, a brief description will be given to the outline of typical ones.
It is as follows.

That is, according to the first aspect of the invention, the pattern formed on the photomask is transferred to the sample by irradiating the sample with the transmitted light of the light applied to the photomask through the projection optical system. So that the image plane distortion of the image of the pattern projected on the sample is corrected,
An exposure method is used in which the photomask is exposed in a distorted state.

According to a second aspect of the present invention, light emitted from the light emitting unit is applied to the sample placed on the sample stage through the photomask and the projection optical system so that the photomask is exposed to the photomask. An exposure apparatus for transferring a formed predetermined pattern to the sample, wherein a photomask distorted so as to correct the image plane distortion of the image of the predetermined pattern projected on the sample is set on a mask holding table. The exposure apparatus has a structure.

[0018]

According to the above-mentioned means, by exposing in a state where the image plane curvature distortion is corrected by the distortion of the photomask,
It is possible to suppress the defocusing around the exposure area due to the image plane distortion.

[0019]

Embodiment 1 FIG. 1 is an explanatory view of an exposure apparatus which is an embodiment of the present invention, and FIG. 2 is a sectional view of a mask used in the exposure apparatus of FIG.

The exposure apparatus of the first embodiment is, as shown in FIG. 1, a reduction projection exposure apparatus 1 used in the exposure process of manufacturing a semiconductor integrated circuit device.

Exposure light source (light emitting section) of the reduction projection exposure apparatus 1
A first plane mirror 4, a shutter 5, a condenser lens 6, an aperture 7, a shortcut filter 8, a second plane mirror 9, a mask blind 10 and a condenser lens 11 are provided on an optical path connecting the semiconductor wafer (sample) 3 and the semiconductor wafer 2. , A reticle (photomask) 12 and a reduction projection lens (projection optical system) 13 are arranged.

The exposure light source 2 includes, for example, i-line (wavelength 365).
High pressure mercury lamps that emit light such as (nm) are used. An ellipsoidal mirror 14 is installed around the exposure light source 2. The reduction projection lens 13 has, for example, a maximum exposure area of 20 × 20 mm and an NA of 1/5 of 0.5.
A reduction projection lens is used.

The semiconductor wafer 3 is made of, for example, silicon (S
i) It is made of a single crystal and is placed on the sample table 15 with its main surface facing upward. A photoresist (not shown) has already been applied to the main surface of the semiconductor wafer 3 by a spin coating method or the like. The sample table 15 is configured by stacking a Y-axis moving table 15y, an X-axis moving table 15x, a Z-axis moving table 15z, and a wafer suction table 15a in order from the bottom.

The reticle 12 is a mask for forming a predetermined semiconductor integrated circuit pattern on the semiconductor wafer 3, and is held on a reticle holding base (mask holding base) 16 in a detachable state. On the reticle 12, for example, an original image of a semiconductor integrated circuit pattern that is five times the actual size is formed.

By the way, in the first embodiment, the light path length when the light transmitted through the center of the reticle 12 reaches the semiconductor wafer 3 via the reduction projection lens 13 and the light transmitted around the reticle 12 are: The reticle 12 is formed in a curved shape along the spherical surface so that the optical path length when reaching the semiconductor wafer 3 via the reduction projection lens 13 is substantially equal.

Therefore, in the reduction projection exposure apparatus 1 of the first embodiment, the image plane of the semiconductor integrated circuit pattern on the reticle 12 projected on the semiconductor wafer 3 is corrected so that it is substantially flat due to the distortion of the reticle 12. The structure is such that exposure processing can be performed in this state. However, if the image plane in the exposure region is within the depth of focus, it is not necessary to completely remove the image plane distortion of the entire exposure region.

A cross-sectional view of the reticle 12 is shown in FIG. Reticle substrate that constitutes the reticle 12 (photomask substrate)
12a is made of, for example, transparent synthetic quartz glass, and a metal pattern 12b made of, for example, Cr or the like is formed on its main surface.
Are formed. The part where the metal pattern 12b is provided forms a light-shielding region, and the part where the metal pattern 12b is not provided forms a light-transmitting region.

The spherical radius of the reticle 12 cannot be generally stated because it varies depending on the characteristics of the reduction projection lens 13 and the like, but is set to a radius of about 50 m, for example. This spherical radius is approximated by, for example, a value obtained by measuring the image plane distortion of the reduction projection lens 13 when using a normal flat mask and then multiplying the measured value by the reciprocal of the reduction ratio of the reduction projection lens 13. To be done.

For example, in the case of the reduction projection lens 13 of the first embodiment, if an ordinary flat plate mask is used, the image plane distortion around the exposure area is about 0.4 μm. In this case, the image plane curvature distortion on the sample surface side can be approximated by a spherical surface having a radius of about 250 m, for example. Therefore, the image plane curvature distortion on the mask surface side can be approximated by a spherical surface having a radius of about 50 m.

To manufacture such a reticle 12,
For example: First, a transparent synthetic quartz glass substrate or the like is prepared, and the reticle substrate 12a is formed by polishing the surface of the substrate in a curved shape along a spherical surface.

Subsequently, after depositing a metal film (not shown) made of Cr or the like on the concave side of the reticle substrate 12a by, for example, a sputtering method or the like, a resist film for electron beam (see FIG. (Not shown) is deposited.

After that, a semiconductor integrated circuit pattern is transferred to the resist film by using, for example, an electron beam drawing method,
Using the pattern transferred to the resist film as a mask, the metal film is patterned to form a metal pattern 12b,
The reticle 12 is manufactured.

The reason for using the electron beam drawing method in forming the pattern of the metal pattern 12b is that the electron beam drawing method has a large depth of focus. Therefore, as in the reticle substrate 12a of the first embodiment, the electron beam drawing method is used at the center and the periphery. This is because it is possible to form a highly accurate pattern even on a substrate having a height difference of about 5 μm.

Next, an exposure method of the reduction projection exposure apparatus 1 of the first embodiment will be described. First, the exposure light source 2 irradiates the first plane mirror 4 with light.

In the first plane mirror 4, the path of the light incident from the exposure light source 2 is changed to a direction substantially perpendicular to the incident direction, and the light is emitted by the shutter 5, the condenser lens 6, and the aperture 7.
And the second plane mirror 9 via the shortcut filter 8.
To irradiate.

In the second plane mirror 9, the path of the light incident from the first plane mirror 4 is changed to a direction substantially perpendicular to the incident direction, and the light is masked blind 10 and the condenser lens 1.
Irradiate the reticle 12 via 1.

Then, the light transmitted through the transmission area of the reticle 12 is irradiated onto the semiconductor wafer 3 through the reduction projection lens 13 to form the semiconductor integrated circuit pattern on the reticle 12.
For example, it is reduced to ⅕ and transferred to the photoresist on the semiconductor wafer 3.

At this time, in the first embodiment, the exposure process is performed in a state where the image plane distortion of the image transferred to the photoresist on the semiconductor wafer 3 is corrected by the distortion of the reticle 12. This makes it possible to suppress defocusing around the exposure area due to the image plane distortion.

As described above, according to the first embodiment, the following effects can be obtained.

(1). By exposing the image surface of the semiconductor integrated circuit pattern on the reticle 12 transferred to the photoresist on the semiconductor wafer 3 to be substantially flat by the distortion of the reticle 12, the image surface is exposed. It is possible to suppress defocusing around the exposure area due to the curvature distortion.
That is, it becomes possible to perform the exposure processing in the optimal focusing state over the entire exposure area. Therefore, it is possible to significantly improve the pattern transfer accuracy in the exposure process.

(2) By the above (1), the constraint for correcting the image plane distortion in the projection optical system mechanism, such as the case where lenses must be laminated in order to correct the image plane distortion, is relaxed. It becomes possible to do.

(3). By the above (1), it is possible to relax the restriction of the reduction projection lens 13 itself for correcting the image plane distortion.

(4) Due to the above (2) and (3), the mechanism of the projection optical system of the reduction projection exposure apparatus 1 can be simplified and the reduction projection lens 13 can be easily designed. Therefore, the reduction projection exposure apparatus 1 can be easily manufactured.

[0044]

[Embodiment 2] FIG. 3 is an explanatory view of an exposure apparatus according to another embodiment of the present invention, FIG. 4 is a sectional view of a mask and a mask holding portion used in the exposure apparatus of FIG. 3, and FIG. 5 is an exposure apparatus of FIG. FIG. 3 is a cross-sectional view of the mask before being installed on the mask holding table of FIG.

In the second embodiment, the center of the reticle holding table 16 of the reduction projection exposure apparatus 1 is formed in a curved shape along the spherical surface. A cross-sectional view of the reticle 12 and the reticle holding table 16 is shown in FIG.

Holding table body 16a of reticle holding table 16
Is made of a transparent material such as synthetic quartz glass and has a suction surface 16s that is curved along a spherical surface.

The reticle 1 is attached to the outer periphery of the holding table body 16a.
A suction nozzle 16b for vacuum-sucking 2 is installed. The reticle substrate (photomask substrate) 12a ₁ of the reticle 12 is vacuum-sucked by the suction nozzle 16b, and is held on the reticle holding table 16 in a curved state along the curved suction surface 16s of the holding table body 16a. There is. The amount of curvature of the reticle 12 is the same as that in the first embodiment.

In the second embodiment, the reticle substrate 12a ₁ of the reticle 12 is made of a flexible transparent material such as polyimide resin, and the reticle holding table 1 is used.
Before being installed in No. 6, it has a flat plate shape as shown in FIG.

That is, in the second embodiment, when the reticle 12 is installed on the reticle holding table 16, the shape of the reticle 12 is set to be curved as shown in FIG.

Thus, also in the second embodiment, as in the first embodiment, the image plane of the semiconductor integrated circuit pattern on the reticle 12 projected onto the semiconductor wafer 3 is the reticle 1.
The exposure processing can be performed in a state where the distortion is corrected to be substantially flat by the distortion of 2.

In the case of the second embodiment, the reticle substrate 1
Since 2a ₁ is made of a flexible resin, the cost of the reticle 12 can be reduced as compared with the first embodiment.

Although the invention made by the present inventor has been concretely explained based on the embodiments, the present invention is not limited to the above-mentioned Embodiments 1 and 2, and various modifications can be made without departing from the scope of the invention. It goes without saying that it is possible.

For example, in Example 2, the constituent material of the reticle is a polyimide resin, but the constituent material is not limited to this, and various modifications are possible. For example, a polyester resin may be used.

In the above description, the case where the invention made by the present inventor is mainly applied to the exposure method and apparatus used in the manufacturing process of the semiconductor integrated circuit device which is the background field of application has been described, but the invention is not limited to this. However, the present invention can be applied to various methods, such as an exposure method and an exposure apparatus that are used when forming a predetermined pattern on a liquid crystal substrate, and an exposure method and an exposure apparatus that are used in the manufacturing process of products that require large-area exposure. It is also possible.

[0055]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.
It is as follows.

That is, according to the above-mentioned means, by exposing in the state where the image plane distortion is corrected by the distortion of the photomask, it is possible to suppress the defocusing around the exposure area due to the image plane distortion. It will be possible. That is, it becomes possible to perform the exposure processing in the optimal focusing state over the entire exposure area. Therefore, it is possible to significantly improve the pattern transfer accuracy in the exposure process.

As a result, it is possible to relax the constraint for correcting the image plane distortion in the mechanism of the projection optical system, such as the case where the lenses must be laminated to correct the image plane distortion. In addition, the constraint of the projection lens itself for correcting the image plane distortion can be relaxed. Therefore, since the mechanism of the projection optical system of the exposure apparatus can be simplified and the design of the projection lens can be facilitated, the manufacture of the exposure apparatus can be facilitated.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an exposure apparatus that is an embodiment of the present invention.

FIG. 2 is a sectional view of a mask used in the exposure apparatus of FIG.

FIG. 3 is an explanatory diagram of an exposure apparatus that is another embodiment of the present invention.

FIG. 4 is a cross-sectional view of a mask and a mask holder used in the exposure apparatus of FIG.

5 is a cross-sectional view of the mask before being placed on the mask holder of the exposure apparatus of FIG.

[Explanation of symbols]

1 Reduction Projection Exposure Device 2 Exposure Light Source (Light Emitting Unit) 3 Semiconductor Wafer (Sample) 4 First Plane Mirror 5 Shutter 6 Condenser Lens 7 Aperture 8 Shortcut Filter 9 Second Plane Mirror 10 Mask Blind 11 Condenser Lens 12 Reticle (Photomask) 12a reticle substrate (photomask substrate) 12a ₁ reticle substrate (photomask substrate) 12b metal pattern 13 reduction projection lens (projection optical system) 14 ellipsoidal mirror 15 sample stage 15a wafer suction stage 15x x-axis movement stage 15y y-axis movement stage 15z z-axis moving table 16 reticle holding table (mask holding table) 16a holding table body 16b suction nozzle 16s suction surface

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location 7352-4M H01L 21/30 311 N

Claims (5)

[Claims] 1. When a predetermined pattern formed on the photomask is transferred to the sample by irradiating the sample with transmitted light of the light applied to the photomask through a projection optical system, the sample An exposure method comprising exposing the photomask in a distorted state so that the image plane distortion of the image of the predetermined pattern projected on the substrate is corrected. 2. A predetermined pattern formed on the photomask is formed by irradiating a sample placed on a sample table with light emitted from a light emitting section through a photomask and a projection optical system. An exposure apparatus for transferring onto a sample, characterized in that a photomask distorted so as to correct the image plane distortion of the image of the predetermined pattern projected onto the sample is installed on a mask holder. apparatus. 3. The mask holder has a suction surface formed in a spherical shape so that the image plane distortion of an image of a predetermined pattern projected on the sample is corrected. The exposure apparatus described. 4. A photomask in which a predetermined pattern is formed on a photomask substrate, wherein the photomask substrate is projected onto the sample when the transmitted light of the light irradiating the photomask substrate is irradiated through a projection optical system. A photomask, wherein the photomask substrate is distorted so that the image plane distortion of an image of a predetermined pattern is corrected. 5. The photomask according to claim 4, wherein the photomask substrate is made of a flexible material.