JPH03211719A - Method of applying resist - Google Patents

Abstract

PURPOSE:To form a resist film which can be exposed to obtain high-accurate uniform pattern width by applying light to which the resist is insensitive to the periphery, on which no semiconductor chip is formed, to measure film thickness when resist of the desired thickness is applied to the surface of a semiconductor wafer. CONSTITUTION:A light projector-receiver 8 to measure the reflection factor, refractive index, and thickness of a multilayer thin film 7 laminated on a wafer 1 is installed. The light projector-receiver 8 applies light as a beam b1 from a light source to the specified section 10 through the tip of an optical fiber 8, enters the reflected light b2 of the beam b1 through the tip of the optical fiber 9, converts it into an electric signal with a light receiving element, and measures the thickness of the thin film 7 by the light interference method. Since an excess region 17 is formed in the periphery 16 of the wafer 1, a detection part 10 is made there. Resist which is the pollution source of the wafer 1 and applied to the periphery 16 is removed from the flat detection part 10 on which no pattern is formed, therefore, the reflected light can be measured, while that on a semiconductor chip 15 having an uneven surface on which a pattern is formed cannot be measured because of irregular reflection.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a resist coating method.

[Prior art and problems to be solved by the invention] Generally, in the semiconductor manufacturing process, a resist is applied on a thin film of SiC2, polysilicon, etc. formed on a wafer by CVD or sputtering, and then exposed to light through a mask to form a resist. A circuit pattern is formed on a thin film by causing a photoreaction and developing to remove the exposed (or unexposed) areas of the reacted resist, or by etching the parts other than the remaining resist according to the pattern of the mask after a photoreaction process or a lithography process. A semiconductor chip is formed by stacking a large number of patterned thin films on a wafer, without repeating the process of forming a pattern on the thin film through an etching process in which the resist is removed after transfer.

Here, the resist coating device that coats the resist onto the thin film formed on the wafer uses a rotating mechanism to rotate a chuck that supports the wafer by suction or the like at several tens of microseconds per minute, so that the resist dropped onto the wafer is coated over the entire surface of the wafer. A spin coater is used to apply the coating uniformly. The resist film thickness applied with a spin coater depends on the wafer rotation speed, rotation acceleration,
Uniformity is maintained while controlling resist temperature, environmental temperature and humidity, etc. In addition, as a means for photoelectrically measuring film thickness, Japanese Patent Application Laid-Open No. 59-11287
No. 3, JP-A No. 63-198329.

Furthermore, in the exposure process of exposing the resist film, a stepper is used to perform successive baking in a step-and-repeat method by projecting a circuit pattern at the same size or reduction through a mask on which a circuit pattern is formed on an exposure area of, for example, 20 mm square on an aligned wafer. is used. Since the projection lens optical system of a stepper is a combination of many lenses, monochromatic light is used for exposure, and when the resist is irradiated with these monochromatic lights, light is mainly emitted at the interface between the resist and the thin film, where there is a large difference in refractive index. A portion of the light travels into the multilayer thin film and is reflected by the wafer substrate. This incident light and reflected light interfere with each other, and a standing wave is generated in the resist film. Even if the material is the same and the same monochromatic light is used, the reflectance changes depending on the thickness of the resist and the thickness of the multilayer thin film. As a result, the phase of the standing wave is displaced. These base reflectance, refractive index, film thickness, and resist film thickness determine the pattern width to be formed, so in order to obtain a uniform pattern width with high precision, the minute difference between the resist film thickness and the multilayer thin film thickness is necessary. This has a very large effect due to the phase shift of the standing wave. The resist film formed by a resist coating device has an error of approximately ±0°3%, and the thin film formed by a thin film deposition device has large lot-to-lot variations (error about ±3%). Since the film is laminated in many layers, the film thickness varies greatly depending on the loft, and it is extremely difficult to form a uniform pattern width with high precision.

The present invention has been made in order to eliminate the above-mentioned drawbacks, and is a resist coating that can form a resist film that can be exposed to light with a uniform pattern width with high precision even for multilayer thin films with lot-to-lot variations. The purpose is to provide a method.

[Means for Solving the Problems] In order to achieve the above object, the resist coating method of the present invention coats a resist on the surface of a semiconductor wafer, measures the coating thickness, and coats a resist with a desired thickness. On this occasion,
The film thickness is measured by irradiating insensitive wavelength light onto the peripheral portion of the semiconductor wafer where no semiconductor chips are formed.

[Function] According to the present invention, when monochromatic light is applied to a resist coated on a thin film laminated on a wafer, it is not 100% reflected at the boundary between the resist and the multilayer thin film, but a portion of the light travels through the multilayer thin film and reaches the wafer substrate. reflected. Therefore, various standing waves occur,
Even if the material is the same, the phase of the standing wave differs depending on the thickness of the resist and the thickness of the multilayer thin film, so the line width (pattern width) of the exposed resist differs. In order to keep this line width constant and form a uniform pattern with high precision, we use the reflectance and approximate film thickness to form a uniform line width for multilayer thin films formed on wafers, which have large variations in film thickness between lots. A calculation device calculates the optimal resist film thickness, and controls the rotation speed of the chuck that supports the wafer so that the resist is applied to the optimal film thickness, automatically eliminating large differences between lots in the film thickness of multilayer thin films. This is to offset the

At this time, the thickness of the multilayer thin film is measured by setting a detection area on the periphery of the wafer where no semiconductor chips are formed, and when removing the resist around the wafer by exposure and development using a peripheral exposure device. At the same time, this area is exposed and developed, and the applied resist is removed from the areas where thin films and resist films are alternately layered because they would normally not be exposed, resulting in a multilayer thin film with the same thickness as the semiconductor chip formed on the wafer. form a part. This area is irradiated with light by a light emitting/receiving device, and the reflectance and refractive index in the multilayer film are measured to determine the approximate film thickness. Although it is difficult to measure the film thickness of a semiconductor chip with uneven surfaces, it is possible to measure the reflectance and refractive index equal to the film thickness of the semiconductor chip at the flat periphery where no pattern is formed on the semiconductor chip. , it is possible to manufacture a semiconductor circuit element in which the line width of the exposure pattern is uniform with high precision.

[Embodiment] An embodiment to which the resist coating method of the present invention is applied will be described with reference to the drawings.

The resist coating apparatus shown in FIG. 1 mounts and fixes a wafer 1 by vacuum suction or the like, and installs a nozzle above the center of the disc of an upper disc-shaped chuck 3 that is fixed to the rotating shaft of a motor 2, which is a rotating mechanism. 4 is provided.

The nozzle 4 is connected to a scanner (not shown) and is movable from above the chuck 3 when performing dummy dispensing. Nozzle 4 is connected to resist supply system 5 . The resist supply system 5 includes a resist container that stores resist, a bellows pump that supplies a desired constant amount of resist, a filter, a valve that opens and closes in conjunction with the bellows pump, a suckback valve that prevents resist from dripping, etc. . Further, a cup 6 is provided surrounding the chuck 3 to prevent the resist from scattering during resist application, and the cup 6 is lowered when the wafer 1 is loaded at 8 to facilitate loading and unloading of the wafer 1.

Furthermore, the reflectance of the multilayer thin film 7 stacked on the wafer 1,
A light emitting/receiving device 8 is provided for measuring the refractive index and film thickness. The light emitting/receiving device 8 transmits light from a light source used for exposure, such as a xenon mercury lamp, from the tip of the optical fiber 8 to a predetermined portion 1o with a diameter of 2II1, such as 500-800 nm.
A beam b1 of about m is irradiated, and the reflected light b2 of this beam b1 enters from the tip of an optical fiber 9, and is converted into an electric signal by a light receiving element to measure the thickness of the thin film 7 using optical interferometry. be. Furthermore, the phase of the standing wave in the thin film is predicted by using the ■ line and G line used for exposure with a stepper. In addition, when measuring the film thickness of a resist coated on a thin film using this light emitting/receiving device 8, a filter is used to set the wavelength of the light from the light source to, for example, 560 mm or more so that the resist is not exposed to the light from the light source. Just set it up.

A position detection device 11 is provided near the light emitting/receiving device 8 to inspect the position of the wafer having the light emitting element and the light receiving element. 8.

The detection value detected by the light emitting/receiving device 8 is input to the calculation device 12 which calculates the optimum resist film thickness based on the detection value.
Further, the rotation speed of the motor 2 for forming the optimum resist film thickness is determined here, and a control device 13 is provided which controls the rotation of the motor 2 based on a signal from the arithmetic device 12.

As shown in FIG. 2, a half-manufactured wafer 1 processed by a resist coating apparatus having such a configuration is formed into a circular shape, and a part of its periphery is cut off to provide an orientation flat 14, and an orientation flat 14 is provided in the center of the circular shape. A large number of layered semiconductor chips 15 are formed with patterned film thicknesses.

Since these semiconductor chips 15 are rectangular, the wafer 1
Since a surplus area 17 is formed in the peripheral edge part 16 of , the detection part 10 is provided in this part. The detection area 10 is equipped with a peripheral exposure device in order to remove the resist applied to the peripheral area 16 which is a source of contamination of the wafer 1! ! By 18 the peripheral part 1
When exposing the semiconductor chips 15 and 6 formed on the wafer 1, for example, the periphery is exposed with a normal width of 2no++, and a certain angle is exposed with a program of 4m+n, for example, and the semiconductor chips 15 formed on the wafer 1 are exposed and developed at the same time. Similarly, the resist is removed and the film is formed to have the same thickness as the semiconductor chip 15. Moreover, since this detection part 1o is not patterned, it is possible to measure reflected light that is flat and cannot be measured because it is diffusely reflected by the semiconductor chip 15, which has a patterned surface and an uneven surface. There is.

A method of applying a resist onto a thin film on a wafer using the resist applying method configured as above will be described.

First, in order to measure the reflectance, refractive index, and film thickness of the thin film formed on the wafer 1 mounted and fixed on the chuck 3 by the transport mechanism, the motor 2 is slowly rotated, and the position detection device 11 moves the orientation flat 14 When the detection site 10 is located below the optical fiber 9, the motor 2 is stopped and the light emitting/receiving device 8 is activated.

The light emitting/receiving device 8 causes the detection region 10 to be irradiated with monochromatic light, for example, the g-line having a wavelength of 436 nm, which is used in the exposure device from the optical fiber 9 . The g-line beam b1 is reflected by the detection part 10, and the reflected light b2 is incident from the optical fiber 9 into the light projecting/receiving device 8 equipped with a light receiving element, where the reflectance and refractive index of the thin film 7 formed on the wafer 1 are determined. Detected. When this detected value is input to the calculation device 12, the optimum resist film thickness is calculated.

When a resist film is irradiated with monochromatic light using an exposure device such as a stepper, the baking speed of the resist film is slow at the nodal portions and slow at the abdominal portions due to the difference in the amount of energy in the nodal and abdominal portions of the monochromatic light. Because the process progresses quickly, the line width (critical dimension) formed by exposure of the resist film is
n) depends on the resist film thickness as shown in FIG. If the line width is set to an extreme value where the amount of change Δa is smaller than the amount of change Δd in the resist film thickness, a constant line width can be maintained even if the resist film thickness changes somewhat. In order to obtain the line width determined in this way, the refractive index and reflectance of the thin film 7 are detected to calculate the optimum resist film thickness, and the motor 2, which has been determined in advance, is When the rotation speed is set and inputted to the control device 13, the control device 1
3 drives the motor 2, supplies an appropriate amount of resist from the resist supply system 5, and drops it onto the wafer 1 from the nozzle 4 to coat the resist with a desired thickness. It goes without saying that at this time, the resist temperature, environmental temperature, humidity, etc., which affect the resist film thickness, may be controlled.

After applying the resist, the position detection device 11 detects the thickness of the formed resist film at the detection site 1o, and then a light emitting/receiving device 8 is provided at the detection site 10 with a filter so that the resist is not sensitive to light (non-sensitivity wavelength). The resist film thickness is measured and checked.

In this way, by measuring the refractive index and reflectance of the thin film 7 formed on the wafer 1 for each lot and setting the resist film thickness to be applied, a pattern with a constant line width can be automatically formed. .

[Effects of the Invention] As is clear from the above explanation, according to the resist coating method of the present invention, it is possible to detect that the resist is removed and a thin film is stacked on the peripheral edge of the wafer, similar to the semiconductor chips formed on the wafer. Because of the location, it is possible to easily measure the reflectance, refractive index, and film thickness of a thin film on a wafer, which was difficult to measure with patterned semiconductor chips due to diffuse reflection. Since the thickness of the applied resist film can be automatically and slightly changed, the resist film can be applied in accordance with the thickness of the thin film that differs from lot to lot. A highly uniform pattern can be automatically formed.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment to which the resist coating method of the present invention is applied, Fig. 2 is a front view of a wafer applied to the embodiment shown in Fig. 1@, and Fig. 3 is shown in Fig. 1. It is a figure explaining one example. 1 - 1 Wafer 2 Motor (rotating mechanism) 3 Chuck 5 Resist supply system 7 Thin film 8 ...Light emitting and receiving device 9 ... Optical fiber 10 ... Detection part 12 ... Arithmetic device 13 ... Control device 15 ... Semiconductor chip 16... Peripheral section 18... Peripheral exposure device

Claims (1)

[Claims] A resist is applied to the surface of a semiconductor wafer, the thickness of the applied film is measured, and when applying the resist to a desired thickness, the peripheral edge of the semiconductor wafer where no semiconductor chips are formed is irradiated with insensitive wavelength light to form a film. A resist coating method characterized by measuring thickness.