JPH1126347A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the line width variation of a transfered pattern due to the thickness nonuniformity of a resist film at stepped parts by applying a resist on a wafer and obliquely incident illumination of a light quantity over a certain level on and near the optical source center. SOLUTION: A resist is applied on a wafer by the spin coating, and the obliquely incident illumination having a light quantity over a certain level is applied to and near the optical source center, using a filter or prism such that a laser beam from an optical source 11 is slit by a beam splitter 12, reduced by a prism unit 13 at adequate angles, transmitted through a fly-eye lens 14, illumination lens system 15 and mask pattern of a reticle 16, and collected by an imaging lens system 17 to illuminate the resist. This reduces the line width variation of a transfer pattern due to the thickness nonuniformity of the resist film at stepped parts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device in which a resist is coated on a wafer by a spin coating method and then exposed.

[0002]

2. Description of the Related Art Conventionally, memory elements, logical operation elements, CCs
Illumination is usually used in a pattern transfer step in the manufacture of various semiconductor devices such as a D element and an LCD drive element, that is, in a so-called photolithography step. here,
The normal illumination is a method of irradiating the optical axis of the light source perpendicular to the transfer surface.

When a resist is actually exposed to form a device, there are steps on the substrate due to an element isolation step or an element formation step up to that time. This step appears, for example, at a cell end in a memory cell array. Normally, when a resist is applied on a memory cell array by a spin coating method in a state where there is a step, the thickness of the resist becomes uneven. When exposure is performed by ordinary illumination in this state, the pattern transferred to the resist (hereinafter, referred to as “resist”) is affected by unevenness in film thickness.
(Referred to as a transfer pattern) fluctuates, making it difficult to obtain desired electrical characteristics of the device.

For this reason, conventionally, it was necessary to arrange a pattern called a dummy cell. A dummy cell is a pattern formed outside a cell edge to fill a step, and does not function as a device.

[0005]

However, when the dummy cells are arranged, there is a problem that the area of the cell array increases and it becomes impossible to reduce the chip area. In addition, since the influence of the line width variation of the transfer pattern extends to a range of 50 μm or more at the cell edge, it is difficult to suppress the variation in device characteristics even if dummy cells are arranged.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and has been made in consideration of the above-described problems. It is intended to provide a manufacturing method.

[0007]

According to the present invention, in order to solve the above-mentioned problems, in a method of manufacturing a semiconductor device, a first step of applying a resist on a wafer by a spin coating method, a light source center and the light source center are provided. And a second step of performing oblique incidence illumination having a light amount of a certain level or more near the semiconductor device.

In such a method of manufacturing a semiconductor device, in the first step, when the resist is applied on the wafer by the spin coating method, even if the film thickness of the resist becomes uneven due to the step, the second step does not. By performing oblique incidence illumination having a light amount of a certain degree or more at the center of the light source and near the center of the light source, the line width variation of the transfer pattern is experimentally reduced.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart showing a schematic procedure of a method for manufacturing a semiconductor device of the present embodiment. [S1] A resist is applied on the wafer by a spin coating method. [S2] By using a filter or a prism, oblique incidence illumination having a light intensity of a certain level or more is performed at the light source center and near the light source center.

Next, a more specific example of the above manufacturing method will be described. FIG. 2 is a diagram showing a schematic configuration of an exposure apparatus for performing a photolithography step in the method for manufacturing a semiconductor device of the present embodiment. The exposure apparatus 10
It is a line stepper, and a mercury lamp is used as the light source 11. The laser light output from the light source 11 is split by the beam splitter 12, narrowed down at an appropriate angle by the prism unit 13, and further passes through a fly-eye lens 14 to form a modified illumination or a halftone annular illumination described later. Becomes The light passes through the mask pattern of the reticle 16 via the illumination lens system 15, is condensed by the imaging lens system 17, and is obliquely illuminated on the resist applied on the wafer 18.

Note that the modified illumination or the halftone annular illumination is formed by using a filter having a shape that transmits a certain amount or more of light at the center of the light source and near the center of the light source instead of using the beam splitter 12 and the prism unit 13. Is also good.

FIG. 2 shows an example of an exposure apparatus for an i-line stepper. However, the present invention is not limited to this, and other types of exposure apparatuses such as a g-line stepper, a KrF excimer laser stepper, and an ArF excimer laser stepper can be used. It may be a device.

Next, the specific shape of the oblique incidence illumination used in the exposure apparatus 10 of the present embodiment will be described. However, here, it is assumed that the oblique incidence illumination is formed by a filter, and the shape of the filter is shown for easy understanding in a plane. Of course, even when the prism unit 13 or the like is used, almost the same illumination can be obtained as a result.

FIG. 3 is a view showing an example of a filter shape for oblique incidence illumination used in the exposure apparatus 10 of the present embodiment, and FIG.
FIG. 7 is a diagram illustrating an example of a filter shape for deformed illumination, and FIG. 7B is a diagram illustrating an example of a filter shape for annular illumination. First, in the modified illumination filter 21 of FIG. 7A, regions 21a having a light transmittance of 1.0 are formed at four outer corners. Also, four regions 21b connecting between the regions 21a are:
The transmittance is the second highest after the region 21a (for example, the transmittance is 0.6).
It is set to be. Further, inside the region 21b, the regions 21c, 21d, 2
1e is formed. These areas 21c, 21d, 2
1e is, for example, 0.5 for the region 21c, 0.4 for the region 21d, and
e is set to 0.3.

By using such a filter 21, it is possible to obtain a deformed illumination in which the amount of light gradually decreases from the outside, but has a certain amount of light even at the center. Of course, even when the prism unit 13 or the like is used, deformed illumination having substantially the same shape can be formed as a result depending on the control method.

On the other hand, a filter 2 for annular illumination shown in FIG.
In No. 2, the transmittance is substantially 1.0 in the orbicular zone 22a. And the center part 22b is halftone, that is,
Only a predetermined amount of light is transmitted. The transmittance of the central portion 22b is set to, for example, 0.35 as shown in an actual measurement example described later.

By using such a filter 22, it is possible to obtain annular illumination having a light quantity of a certain level or more even at the center. Of course, even when the prism unit 13 or the like is used, annular illumination having substantially the same shape can be formed as a result depending on the control method.

Next, regarding the effect of the manufacturing method of the present embodiment,
A description will be given based on actually measured values. In this experiment, the exposure apparatus 1
An i-line stepper was used as 0. The optical conditions are: resist numerical aperture NA = 0.57, partial coherency σ =
It was set to 0.67. In addition, a substrate used for processing a gate pattern for a memory element is used for the substrate. In order to prevent reflection of light from the substrate into the resist, a SiO ₂ film and a SiON film are formed at 270 nm and 30 nm, respectively, before applying the resist.
m. Further, the step at the end of the gate array is 0.4 μm.

Then, a resist was applied on the wafer by spin coating on the substrate. At this time, the thickness of the resist was set to be 0.77 μm in the non-step portion.
The evaluation pattern used was a 0.34 μm gate pattern.

First, an experiment was performed on the substrate after the application of the resist by using conventional ordinary illumination to form a transfer pattern of a gate pattern. And
The line width of the pattern at that position was actually measured according to the distance from the end of the cell array.

FIG. 4 is a diagram showing an experimental result when this conventional ordinary illumination is used. Here, the horizontal axis represents the distance from the end of the cell array, and the vertical axis represents the measured line width of the transferred gate. As can be seen from the figure, the line width of the transfer pattern is reduced within a range of 50 μm from the end of the cell array.
The difference between the maximum value and the minimum value of the line width of the transfer pattern is 0.02
It was 1 μm.

FIG. 5 is a diagram showing a first experimental result when oblique incidence illumination of the present embodiment is performed. Here, the horizontal axis represents the distance from the end of the cell array, and the vertical axis represents the measured line width of the transferred gate. In this experiment, the modified illumination filter 21 shown in FIG. 3A was used. As can be seen from the figure, in the first experiment, the line width of the transfer pattern was constant up to 75 μm from the end of the cell array, that is, constant over a wider range than when a conventional filter for ordinary illumination was used. The difference between the maximum value and the minimum value of the line width of the transfer pattern was 0.014 μm. This is almost equal to the measured value variation of a length measuring SEM (Scanning Electron Microscope) used for the length measurement.

FIG. 6 is a diagram showing the results of a second experiment when oblique illumination is performed according to the present embodiment. Here, the horizontal axis represents the distance from the end of the cell array, and the vertical axis represents the measured line width of the transferred gate. In this experiment, the filter 22 for annular illumination of FIG. 3B was used. The transmittance of the central portion 22b of the filter 22 was 0.35. As can be seen from the figure, in the second experiment, as in the first experiment, the line width of the transfer pattern was constant from the cell array end to 75 μm. The difference between the maximum value and the minimum value of the line width of the transfer pattern was 0.014 μm. This is substantially equal to the measured value variation of the length measuring SEM used for the length measurement.

FIG. 7 is a diagram showing the results of a second experiment in the case where oblique incidence illumination of the present embodiment is performed. Here, the horizontal axis represents the distance from the end of the cell array, and the vertical axis represents the measured line width of the transferred gate. In this experiment, the filter 22 for annular illumination of FIG. 3B was used. The transmittance of the central portion 22b of the filter 22 was set to 0.20. As can be seen from the figure, in this third experiment, the line width of the transfer pattern was 75 μm from the end of the cell array, as in the first and second experiments.
m. The difference between the maximum value and the minimum value of the line width of the transfer pattern was 0.015 μm. This is substantially equal to the measured value variation of the length measuring SEM used for the length measurement.

As described above, in the present embodiment, the filter 21,
22 and the like, oblique incidence illumination having a light intensity of a certain degree or more is performed at the center of the light source and in the vicinity of the center of the light source. Even if the thickness is uneven, the line width of the transfer pattern can be made substantially constant. Therefore, device characteristics can be improved without using a conventionally required dummy cell.

[0026]

As described above, according to the present invention, oblique incidence illumination having a light intensity of a certain degree or more is performed at the center of the light source and in the vicinity of the center of the light source. Even if the thickness of the resist becomes uneven due to the step, the line width of the transfer pattern can be made substantially constant. Therefore, device characteristics can be improved without using a conventionally required dummy cell.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a schematic procedure of a method for manufacturing a semiconductor device of the present embodiment.

FIG. 2 is a diagram showing a schematic configuration of an exposure apparatus for performing a photolithography step in a method for manufacturing a semiconductor device of the present embodiment.

3A and 3B are diagrams illustrating an example of a filter shape for oblique incidence illumination used in the exposure apparatus of the present embodiment, in which FIG. 3A illustrates an example of a filter shape for deformed illumination, and FIG. FIG. 3 is a diagram showing an example of a filter shape for use.

FIG. 4 is a diagram showing an experimental result when a conventional filter for normal illumination is used.

FIG. 5 is a diagram illustrating a first experimental result when oblique illumination according to the present embodiment is performed.

FIG. 6 is a diagram illustrating a second experimental result when oblique incidence illumination of the present embodiment is performed.

FIG. 7 is a diagram showing a third experimental result when oblique incidence illumination of the present embodiment is performed.

[Explanation of symbols]

10 exposure apparatus, 11 light source, 12 beam splitter, 13 prism unit, 14 fly-eye lens, 15 illumination lens system, 16 reticle,
17: imaging lens system, 18: wafer, 21: filter, 22: filter

Claims (3)

[Claims] 1. A method of manufacturing a semiconductor device, comprising: applying a resist on a wafer by a spin coating method;
And a second step of performing oblique incidence illumination having a light amount of a certain level or more in the center of the light source and in the vicinity of the center of the light source. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the oblique incidence illumination is formed so that the transmittance increases stepwise from a central portion. 3. The method of manufacturing a semiconductor device according to claim 1, wherein said oblique incidence illumination is formed in an annular illumination shape having a central portion having a predetermined transmittance.