JPH05315217A - Aligner for semiconductor photoprocess use - Google Patents

Abstract

(57) [Abstract] [Objective] When a photoresist film applied to a wafer in a semiconductor photo process is exposed with a pattern of a photomask, the reflectance of the wafer surface varies from wafer to wafer or within the wafer surface. Also, the accuracy of the photosensitive pattern of the photoresist film should not be degraded. [Structure] Before exposing a pattern of a photomask 3 onto a photoresist film 2 spin-coated on the surface of a wafer 1, weak illumination light Li from a light projecting means 70 is passed through an exposure range ER and a different path from an exposure light beam Le. And the reflected light Lr from the surface of the wafer 1 is measured by the photometric means 80, for example, the processor 90
The reflectance of the wafer 1 is calculated by the method, and the exposure amount given to the photoresist film 2 is calculated according to the result, for example, the shutter 60
Adjust by the exposure time to open.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus for a photo process for exposing a photoresist film coated on a wafer surface to a pattern designated by a photo mask in a wafer process for manufacturing various semiconductor devices.

[0002]

2. Description of the Related Art As is well known, when manufacturing a semiconductor device such as an integrated circuit device, a photoresist film is formed on the surface of the wafer for patterning a semiconductor layer, an insulating film, a wiring film, etc. to be formed in the wafer. It is applied, exposed in a pattern designated by a photomask in a photoprocess, developed, and used as a mask for a diffusion process or an etching process. The present invention relates to an exposure device used when exposing this photoresist film to light. In a recent exposure apparatus, it is possible to increase the pattern accuracy to about 0.5 μm by using, for example, ultraviolet rays with a wavelength of 365 nm by an ultra-high pressure mercury lamp. Usually, a so-called reticle is used as a photomask to store several to ten or more semiconductor devices. It is possible to complete exposure of the photoresist film in about 1 minute while projecting the pattern on the exposure area of about 20 mm square with a bright lens and moving the wafer at an exposure interval of about 1 second.

In the wafer process of a semiconductor device, the film type and film quality of the wafer surface are different for each process. Therefore, the type of photoresist film is selected and the coating film thickness is adjusted accordingly. However, since the photoresist film coated on the wafer is transparent and is exposed to not only the projected light but also the reflected light from the wafer surface, its effective photosensitivity is usually 10 to 95%, which can vary in a wide range. It depends greatly on the reflectance. Therefore, the exposure amount given to the photoresist film has been conventionally set according to the type and film thickness as well as the type of film such as an insulating film or a wiring film covering the wafer surface, and the exposure intensity is measured while the exposure is performed. It is customary to control the exposure time so that the amount is at this set value.

[0004]

In the conventional exposure apparatus,
By setting the exposure dose according to the type of film covering the wafer surface as described above, it is possible to compensate for the change in the surface reflectance and expose the photoresist film in a pattern that is theoretically accurate. However, in reality, even with the same type of film, the film quality and film thickness differ slightly depending on the process conditions when depositing it, and the surface reflectance tends to vary from wafer to wafer or within the wafer surface. Therefore, there is a problem that the pattern accuracy is affected and fluctuates.

For example, when a wafer is covered with a silicon oxide film, the surface reflectivity is changed due to variations in film quality and film thickness.
It may fluctuate within the range of 10 to 30%, and even within the range of 80 to 95% when the wiring film of aluminum is used. In the case of 0.8 μm rule integrated circuit device, the patterning accuracy by the photoresist film is affected by the influence. However, there is a problem that the maximum range is about ± 0.15 μm for each wafer and about ± 0.05 μm within the wafer surface. The present invention solves this problem,
An object of the present invention is to provide an exposure apparatus capable of compensating for variations in surface reflectance on a wafer-by-wafer basis or within a wafer surface and reducing variations in effective photosensitivity of a photoresist film.

[0006]

According to the exposure apparatus of the present invention, there is provided a projecting means for providing illumination light weak only in the exposure range of the photoresist film through a path different from the light passing through the photomask. A photometric means for measuring the intensity of the reflected light from the exposure range of the illumination light is provided, and the illumination light is applied to the wafer from the light projecting means prior to the actual exposure, and the intensity of the reflected light is measured by the photometric means, and the photoresist is used. This is achieved by controlling the exposure amount when the film is exposed to the pattern of the photomask according to the measurement result.

The intensity of the illumination light given from the light projecting means to the exposure range is actually measured, and the exposure amount to the photoresist film is controlled according to the ratio of the reflected light intensity measured by the photometric means to the illumination light intensity. This is advantageous for improving pattern accuracy. The intensity of the illumination light by the light projecting means is preferably set so that the photoresist film is not exposed to light, and it is desirable to select the wavelength in a range where the photoresist film has no sensitivity, if necessary. In addition, since the surface of the wafer is not always smooth and the reflected light is often scattered, it is more accurate to measure the intensity of the reflected light by the photometric means including most of the scattered light from the exposure range. It is advantageous in improving. Further, the exposure amount is preferably controlled by the exposure time while keeping the emission intensity of the exposure light source substantially constant. Especially, the time integration is measured according to the measurement result of the reflected light intensity by the photometric means while actually measuring the exposure intensity. It is desirable to control by the time until the exposure amount is reached.

[0008]

According to the present invention, as described in the preceding paragraph, prior to the actual exposure of the photoresist film, the illumination light is first applied to the surface of the wafer coated with the photoresist film from the light projecting means.
By measuring the intensity of the reflected light with a photometric means, the reflectance of the wafer surface, or more accurately, the reflectance including the transmittance of the photoresist film is evaluated, and the photoresist film is changed to the mask of the photomask according to this result. By controlling the exposure amount when the pattern is exposed, the accuracy of patterning is improved by compensating for the effective fluctuation of the photosensitivity of the photoresist film caused by the variation of the reflectance for each wafer or within the wafer surface. It is a thing. In the present invention, when the reflectance of the wafer surface is evaluated in advance, illumination light is generated by the light projecting means with an intensity that does not cause the photoresist film to be exposed to light, and the exposure amount for the photoresist film is reflected in the wafer surface. This illumination light is given only in the exposure range so that it can be controlled according to the variation in the rate.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a main part of an exposure apparatus according to the present invention, and measuring means for alignment or the like usually incorporated in the exposure apparatus is omitted because it is complicated.
A photoresist film 2 suitable for the surface film of the wafer 1 is applied in a predetermined film thickness, and the wafer 1 is loaded on a moving stage 10 of the exposure apparatus. The photomask 3 for designating the pattern for exposing the photoresist film 2 by exposure is, for example, as described above, a reticle for a plurality of semiconductor devices, which is attached to the mask holder 20.

For example, 365 nm to be given to the photomask 3
The exposure light flux Le, which is an ultraviolet ray with a wavelength of, is generated by a powerful ultra-high pressure mercury lamp of, for example, 1 kW in the exposure light source 30, which is simply shown in the upper left part of the figure, and becomes a substantially parallel light flux by means of its built-in lens system. Then, while increasing the parallelism by the collimators 31 and 32, the photomask 3 on the mask holder 20 is in a state of almost perfect parallel light flux through the optical paths bent by the total reflection mirrors 33 to 36 as shown in the figure. Given to.

The exposure light flux Le that has passed through the photomask 3
Is given to the projection lens system 40, whose numerical aperture is, for example, 0.4
The pattern specified by the photomask 3 is reduced by a fraction of a few to a 20 mm square exposure range ER of the photoresist film 2 at the focal position by the bright projection lens system 40 of .about.0.5 and is accurately imaged. .. In order to sequentially switch the in-plane position of the wafer 1 in the exposure range ER, the moving stage 10 moves or rotates the wafer 1 in the left and right x directions, the front and rear y directions, and the θ direction in the xy plane. It is constructed by stacking individual stage parts 11 to 13.

A control computer 50 shown in the lower left portion of the figure automatically controls the movement and positioning of the wafer 1 by the moving stage 10, the focusing of the projection lens system 40 to the exposure range ER, etc. Such control is performed based on the alignment signals received from the measuring devices and the detection signals for automatic focusing. Another important role of the control computer 50 is the control of the exposure amount, which controls the shutter 60 inserted in the optical path of the exposure light flux Le via the operation device 61. This exposure amount is specified by inputting the type of the insulating film, the wiring film, etc. on the surface of the wafer 1 to the keyboard 51, and the control computer 50 sets the exposure amount set for each film type in the storage area to the specified film. The exposure amount is read out, the intensity detection value of the exposure light flux Le is received from a means (not shown), and the exposure command Se is sent to the operation unit 61 only during the time when the time integrated value reaches the specified exposure amount to open the shutter 60.

In the present invention, the light projecting means 70 and the photometric means 80 are incorporated in the exposure apparatus as described above, and in the illustrated example, a simple processor 90 is provided exclusively for them. The light projecting means 70 provides the weak illumination light Li to the extent that the photoresist film 2 is not exposed to the exposure range ER through a route different from the exposure light flux Le. In the illustrated example, the illumination light Li from the small light source 71 is optically emitted. The system 72 forms a parallel light flux having a rectangular cross section, and then makes it enter the exposure range ER from the oblique direction via the mirror 73. Further, in this embodiment, the angle of the mirror 73 can be switched by the operation device 74, and the mirror 73 is oriented in the vertical direction except when the photometry command Sm is given to the operation device 74, and the illumination light is applied to the detector 75. It is designed to give Li and measure its strength.

The photometric means 80 thus measures the intensity of the reflected light Lr from the surface of the wafer 1 of the illumination light Li given from the light projecting means 70 only in the exposure range ER. The reflected light Lr is usually shown in the figure. As described above, since the light sensor 81 has a slight scattering property, the light sensor 81 for that purpose has a condenser lens or the like to widen the light receiving area and dispose the light receiving area near the exposure range ER to include most of the scattered light. It is better to measure the intensity of the reflected light Lr. The measurement signal Si of the intensity of the illumination light Si by the detector 75 of the light projecting means 70 and the measurement signal of the intensity of the reflected light Lr by the optical sensor 81 of the photometry means 80.
In this embodiment, Sr is converted into a digital value by means of an AD converter 91 or the like and then given to the processor 90.

In the exposure apparatus configured as described above, the exposure light ER is first exposed to the illumination light Si from the light projecting means 70 before exposing each exposure area ER of the photoresist film 2 to the pattern formed by the photomask 3 which is a reticle. Then, the intensity of the reflected light Sr from the surface of the wafer 1 is measured by the photometric means 80. Therefore, the processor 90 uses the detector 75 in the light projecting means 70.
First, the value of the measurement signal Si of the intensity of the illumination light Si is read, and then the photometric command Sm is given to the operation unit 74 of the light projecting means 70 to make the illumination light Si incident on the exposure range ER. The value of the measurement signal Sr of the intensity of the reflected light Lr is read from the optical sensor 81. This measurement operation can be completed within a short time within 0.5 seconds.

The ratio of the value of the measurement signal Sr of the intensity of the reflected light Lr to the value of the measurement signal Si of the intensity of the illumination light Si obtained in this manner is the reflectance of the wafer 1, more specifically, the transmission of the photoresist film 2. Since it is the effective reflectance including the reflectance, the processor 90 reduces the exposure amount when the actually measured reflectance is higher than the expected reflectance corresponding to the type of the surface film of the wafer 1, and conversely when it is low. Control to increase. At this time, the degree of increase or decrease of the exposure amount is of course adjusted according to the type and thickness of the photoresist film 2. Since the exposure amount is controlled by the control computer 50 by the exposure time for opening the shutter 60 according to the designated exposure amount as described above, in this embodiment, the processor 90 instructs the control computer 50 to specify the control operation standard. By giving the exposure correction amount Ce to the exposure amount, the actual exposure amount to the photoresist film 2 is controlled.

As described above, while the processor 90 side is actually measuring the reflectance of the wafer 1 and calculating the exposure correction amount Ce, the control computer 50 side is in parallel with this while the pattern of the photomask 3 and the exposure range ER are being calculated. We are proceeding with preparatory operations such as alignment for aligning and
Is sent from the processor 90, the exposure operation is started immediately after the preparation is completed, and the exposure can be normally completed in about 0.2 seconds. After completion of such one exposure, the same operation is repeated while operating the moving stage 10 to switch the position of the in-plane exposure range ER of the wafer 1.

The reflectance of the wafer 1 or the intensity of the reflected light Sr, which is the basis for controlling the exposure amount according to the present invention, strictly includes the transmittance of the photoresist film 2. When the film thickness of the resist film 2 is thin and the photosensitivity thereof is high, the reflectance is increased and control is performed so as to reduce the exposure amount. Conversely, when the film thickness is thick and the sensitivity is low, the reflectance is decreased and the exposure is performed. Since the control works to increase the amount, the present invention can also compensate for the variation in the film thickness of the photoresist film 2 from wafer to wafer.

[0019]

As described above, in the exposure apparatus for semiconductor photoprocess of the present invention, the light projecting means for giving the weak illumination light only to the exposure range in the wafer through a different route from the light passing through the photomask, and the illumination light. Providing a photometric means for measuring the intensity of the reflected light from the exposure range, measuring the intensity of the reflected light from the wafer by applying illumination light to the exposure range from the light projecting means prior to the exposure, and depending on this measurement result. By controlling the exposure amount for exposing the photoresist film coated on the wafer surface to the pattern of the photomask, it is possible to automatically compensate the influence of the variation in the surface reflectance that may occur for each wafer or within the wafer surface. Furthermore, since the effect of wafer-to-wafer variation in the coating thickness of the photoresist film can be almost compensated for,
It is possible to improve the photo process accuracy remarkably by exposing the photoresist film exactly according to the pattern of the photo mask. The present invention is particularly advantageous for a photo process of a submicron rule integrated circuit device, and can improve patterning accuracy and improve the manufacturing yield of the integrated circuit device.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a main part of an exposure apparatus for a semiconductor photo process according to the present invention.

[Explanation of symbols]

 1 wafer 2 photoresist film 3 photomask or reticle 10 moving stage 20 mask holder 30 exposure light source 40 projection lens system 50 control computer 60 exposure shutter 70 light projecting means 80 photometric means 90 processor Ce exposure correction amount Le exposure light flux Li illumination light Lr Reflected light Si Illuminated light intensity measurement signal Sm Photometric command Sr Reflected light intensity measurement signal

Claims (4)

[Claims] 1. A device for applying light passing through a photomask to a wafer in which a semiconductor device is formed to expose a photoresist film on the wafer to a pattern designated by the photomask, which is weak only in an exposure range within the wafer. An illumination light is provided on the wafer from the light emission means prior to the exposure by providing a light projection means for giving the illumination light through a path different from the light passing through the photomask and a photometric means for measuring the intensity of the reflected light from the exposure range of the illumination light. Is applied to measure the intensity of the reflected light by the photometric means, and the exposure amount for exposing the photoresist film to the pattern of the photomask is controlled according to the measurement result. Exposure equipment. 2. The apparatus according to claim 1, wherein the intensity of the illumination light given to the wafer from the light projecting means is measured, and the photo based on the ratio of the intensity of the reflected light measured by the photometric means to the intensity of the illumination light. An exposure apparatus for a semiconductor photoprocess, characterized in that an exposure amount for exposing a resist film to a pattern of a photomask is controlled. 3. The apparatus according to claim 1, wherein the photometric means measures the intensity of the reflected light from the exposure range of the illumination light, including most of the scattered light from the exposure range. Exposure apparatus for semiconductor photo process. 4. The apparatus according to claim 1, wherein the exposure amount for exposing the photoresist film to the pattern of the photomask is controlled by the exposure time while keeping the emission intensity of the exposure light source substantially constant. An exposure apparatus for semiconductor photo processes, which is characterized in that