JPH10270329A - Method for determining condition of antireflective film and formation of resist pattern using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize the condition of an antireflective film by finding the reflectance of the film in the worst case by taking the variation of the optical constant and film thickness of the film into consideration and selecting the optical constant and film thickness at which the reflectance becomes the minimum. SOLUTION: A lower-layer structure inputting section 1 inputs the optical constant, film thickness, and film thickness variation of each layer including a film to be worked and an antireflective film variation inputting section 2 inputs the variation of the optical constant, film thickness, etc., in an antireflective film forming process. A reflectance calculating section 3 finds the reflectance of an antireflective film by changing the film thickness of a lower-layer structure and the film thickness and optical constant of the antireflective film within the inputted variation. Of the found reflectance, the maximum reflectance is determined as the worst-case reflectance at the optical constant and film thickness assumed by a worst-case reflectance calculating section 4 and an optimum condition determining section 5 determining the optical constant and film thickness at which the worst-case reflectance becomes the minimum by finding the worst-case reflectance for various antireflective film optical constants and film thicknesses.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical lithography technique for manufacturing a semiconductor integrated circuit and the like, and more particularly to an antireflection film for preventing light reflected from a lower layer on a resist.

[0002]

2. Description of the Related Art In an optical lithography process used for forming a pattern of a semiconductor integrated circuit or the like, a pattern having a size close to a resolution limit is formed, and accordingly, requirements for dimensional accuracy are becoming stricter.

In order to improve the dimensional accuracy, it is necessary to increase the allowance for the focus allowance, the dose allowance, and the variation of the resist film thickness / base film thickness. Among them, the tolerance for the variation of the resist film thickness / base film thickness is realized by suppressing the intensity of the reflected light to the resist. Exposure light is reflected from the lower layer after entering from the resist surface and enters the resist again. Therefore, the irradiation dose to the resist effectively increases. When the thickness of the underlayer varies, the degree of the multiple interference in the underlayer changes, so that the intensity of the reflected light to the resist varies. Further, even when the intensity of the reflected light with respect to the variation in the base film thickness is constant, the dimensional variation due to the variation in the resist film thickness occurs due to the standing wave effect. A standing wave is caused by interference between reflected light and incident light. The resist applied on the stepped substrate has a film thickness distribution, and the degree of interference varies depending on the resist film thickness, so that the latent image distribution (= development speed distribution) differs. This causes a variation in resist dimensions.

As one of the techniques for reducing the reflection from the underlayer, there is a technique for providing an antireflection film below the resist layer to reduce the intensity of light reflected on the resist.
As the anti-reflection film, an absorption-type anti-reflection film that absorbs incident light that passes through the resist layer and travels toward the substrate, and an interference-type anti-reflection film that interferes and cancels light reflected at each of the upper and lower interfaces of the anti-reflection film. However, in any case, in order to obtain the effect of reducing the reflectance, it is essential to optimize the optical constant (= complex refractive index) of the antireflection film and its film thickness.

[0005] The method of determining the conditions of the antireflection film is disclosed in
-299338 and JP-A-6-196400. In the method described in JP-A-5-299338, an antireflection film having generality is selected from a range in which the reflection at the interface between the resist and the antireflection film is suppressed and a range in which the reflection of the lower layer of the antireflection film is suppressed under the strictest conditions. The optical constant range is determined. Further, according to the method described in JP-A-6-196400, an antireflection optical constant at which the light absorption amounts of a plurality of resist film thicknesses are substantially equal is obtained, and this is repeated for various antireflection film thicknesses, whereby the conditions of the antireflection film condition are obtained. Finding the optimal value.

Further, Japanese Patent Application Laid-Open No. 7-273010 describes a structure in which an antireflection film is provided under a transparent oxide film in a multilayer film to be processed to improve the antireflection effect. That is, by providing an anti-reflection film under a transparent layer to be processed (reflectance variation factor layer) in which the amount of change in the reflectance to the resist increases due to the film thickness variation, the amount of reflected light entering the reflectance variation factor layer is reduced. In addition, the variation of the entire reflectance is suppressed to increase the anti-reflection effect.

[0007]

Problems to be Solved by the Invention Japanese Patent Laid-Open No. 5-2 of the prior art
In 99338, the antireflection film condition under the condition that the reflection from the lower layer is maximized is obtained, and thus the antireflection film obtained here is of the absorption type. For this reason, there is a possibility that a film condition for performing excessive antireflection, such as an antireflection film having an unnecessarily thick film, may be set. Further, the structure is limited to the case where an antireflection film is placed immediately below the resist.

On the other hand, JP-A-6-196400 does not describe a case where there is a change in the structure of a base substrate requiring an antireflection film. In an actual device, there is a step on the substrate, and the thickness of a film deposited thereon fluctuates. Further, even on a flat substrate, there is a variation in film thickness due to the process. For this reason, even if the optimum condition of the antireflection film is set only for the film structure of a certain specification, there is a case where the antireflection function does not play a role where the film configuration is different from the specification due to the step / process. .

Further, none of the techniques disclosed in the above two conventional examples takes into account the process variation of the antireflection film itself. That is, the antireflection film is not optimized in consideration of the film thickness variation and the optical constant variation at the time of forming the antireflection film.

The anti-reflection film disclosed in Japanese Patent Application Laid-Open No. 7-273010 remains in the device, and the anti-reflection film may adversely affect the film immediately below the anti-reflection film. Not been.

A first object of the present invention is to provide an anti-reflection film condition determining method for selecting an optimum anti-reflection film condition including a change in a film structure of a lower layer and a process fluctuation of an anti-reflection film. .

A second object of the present invention is to provide a method of forming a resist pattern which eliminates the influence of an antireflection film on a layer to be processed.

[0013]

The above first object is solved by optimizing the optical constant and the film thickness of the antireflection film according to the following procedure. (1) Input the optical constant, film thickness and film thickness variation of the film / substrate to be processed. (2) Input the optical constant fluctuation amount and the film thickness fluctuation amount of the antireflection film. (3) The set optical constant and the set film thickness of the antireflection film are arbitrarily determined.
(4) The thickness of the lower layer is changed within the variation input in (1), and the optical constant and the thickness of the antireflection film are set within the variation input in (2) from the set values determined in (3). , The reflectance to the resist is calculated, and the maximum reflectance within these variations, that is, the worst case reflectance in consideration of the process variation is obtained. (5) The above (3) and (4) are repeated to select the optical constant and the film thickness of the antireflection film that minimize the worst-case reflectance.

[0014] The second problem can be solved by forming a thin film under the antireflection film. When a new film is provided under the anti-reflection film, a change in the thickness of the film may cause a change in the reflectance of the resist. However, if the film is a thin film, the amount of change in the film thickness can be suppressed to a very small value, and the change in the reflectivity to the resist hardly occurs.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) This embodiment is applied to determination of antireflection film conditions when a resist pattern for processing a poly-Si gate is formed by an i-line exposure apparatus. FIG. 1 shows a flowchart of the antireflection condition determination method.

First, an optical constant, a film thickness, and a film thickness variation amount of each layer including a film to be processed are inputted in a lower layer structure input section 1.
Further, an antireflection film variation input unit 2 inputs a variation in the antireflection film forming process, such as an optical constant variation and a film thickness variation. Each variation is a variation within a wafer or between wafers due to a film forming process.

Next, the following calculation is repeated for an arbitrary optical constant and an arbitrary film thickness of the antireflection film (antireflection film condition loop 7). That is, the film thickness of the lower layer structure and the film thickness / optical constant of the antireflection film are changed within the input fluctuation amount (variation amount loop 8), and the reflectance is obtained (reflectance calculation unit 3).
Among them, the maximum reflectance is defined as the worst-case reflectance at the optical constant and the film thickness of the antireflection film assumed here (worst-case reflectance calculator 4). The worst-case reflectance is determined for various antireflection film optical constants and film thicknesses, and conditions under which the worst-case reflectance is reduced are determined as the optimum optical constant and film thickness of the antireflection film (optimum condition selection 5).

The above method is applied to the determination of the optimum conditions in the SiON-based antireflection film for processing the poly-Si gate shown in FIG. 2, and the condition of the thinnest antireflection film capable of reducing the worst case reflectance to 0.1 or less is set. I asked.

The layer structure including the film to be processed has a 200 nm poly-Si film 21 and 2 to be processed on the gate oxide film 22.
A gate protection oxide film 20 of 00 nm is deposited. The thickness of the gate oxide film 22 is 10 nm, but is 400 nm in the LOCOS portion. Further, the poly Si 21 and the gate protection oxide film 20 thereon are ± 10% of each specification.
The variation in film thickness occurs in the process.

Therefore, in the lower layer structure input section 1, the Si substrate 2
3, 6.5-2.61i and 1.1.6 as the optical constants of the gate oxide film 22, the poly-Si 21 and the gate protection oxide film 20, respectively.
51-0.0i, 3.9-2.66i, 1.51-0.0i
Was entered. Further, the gate oxide film 22, poly-Si 21,
The thickness of the gate protection oxide film 20 and the thickness variation amount are 10 nm + 390 nm, 200 nm ± 20 nm, 200 nm, respectively.
nm ± 20 nm. Since the uniformity of the optical constant of the anti-reflection film in the wafer is very good, the value input in the anti-reflection film variation input unit 2 is 0, and the optical constant variation is 0, and the film thickness variation is ± 10%.

Next, a combination of various optical constants and film thicknesses of the antireflection film 24 provided on the gate protection oxide film 20 as shown in FIG. The maximum reflectance was determined. here,
The range of the optical constant of the antireflection film is 1.8 to 3.8 and k is 0.0 to -1.
9

FIG. 3 shows a contour line of the worst case reflectance with respect to the optical constant of the antireflection film for each set film thickness of the antireflection film of 10 nm. The reflectance determined for each optical constant represents the maximum reflectance when the gate oxide film thickness, the poly-Si film thickness, the gate protection oxide film thickness, and the antireflection film thickness vary within the respective ranges. In the optimum condition selection 5, among the conditions where the worst case reflectivity is 0.1 or less from FIG. 3, the optical constant of 2.5 to 0.6i, which is the thinnest film, and a film thickness of 70 nm was set as the optimum antireflection film condition. .

A film satisfying this condition is formed as a gate protection oxide film 2
And a positive resist ip3
300 (manufactured by Tokyo Ohka) was applied. 365 nm wavelength, N
Exposure was performed using a 0.4 μm line and space (L / S) mask with a reduction projection exposure apparatus of A0.6, σ0.6, and
FIG. 4 shows the dimension (swing curve) with respect to the resist film thickness when developed for 0 second. FIG. 4 (a) shows the case where the antireflection film is not provided, and FIG. 4 (b) shows the case where the antireflection film is provided. . While the swing width without the anti-reflection film was 87 nm, when the anti-reflection film was provided, the swing width could be reduced to 34 nm, and a good device could be obtained because of little gate dimensional variation.

(Embodiment 2) Here, a method for optimizing an antireflection film by specifying a reflectance variation factor layer in the same structure as in Embodiment 1 will be described.

FIG. 5 shows the flow. First, as in the first embodiment, the optical constant, the film thickness, and the film thickness variation of each layer including the film to be processed are input in the lower layer structure input unit 1. Next, the reflectance variation factor layer specifying unit 6 determines which film thickness variation causes the reflectance variation to the resist without the antireflection film. The layer structure is determined so that an anti-reflection film is provided below the reflectivity variation factor layer (layer structure determining unit 9). Thereafter, the processes of the reflectance calculator 3 and the worst-case reflectance calculator 4 are repeated in the same manner as in the flow of the first embodiment, and the optimum optical constant and the film thickness of the antireflection film are obtained by the optimum condition selection 5.

The above method was applied to the same structure as in Example 1, and the antireflection film conditions for a thin film capable of making the worst-case reflectance 0.1 or less were obtained.

First, the lower layer structure input unit 1 uses the lower layer structure optical constant, film thickness, and film thickness variation (as the optical constants of the Si substrate, gate oxide film, poly-Si, and gate protection oxide film as 6.5-2. 61i, 1.51-0.0i, 3.9-2.6
6i, 1.51-0.0i, each film thickness and its variation amount were 1
0 nm + 390 nm, 200 nm ± 20 nm, 200 n
m ± 20 nm). Next, in the structure of FIG. 14 having no antireflection film, the reflectivity to the resist 25 is calculated by changing the film thickness within the input fluctuation, and it is determined which film thickness fluctuation is a factor of the reflectivity fluctuation. (Reflectance variation factor layer specifying unit 6). FIG. 6 shows the result. 20 poly-Si film
The reflectivity to the resist is constant at 0.39 even if the gate oxide film changes from 10 nm below the gate to 400 nm in the LOCOS part, at 0 nm ± 10%. On the other hand, when the gate protection oxide film changes from 180 nm to 220 nm, the reflectance changes from 0.41 to 0.34. Therefore, the structure shown in FIG. 15 in which the antireflection film 24 is provided under the gate protection oxide film 20 is determined by the layer structure determination unit 9.

Next, in the antireflection film variation input section 2, the optical constant variation of the antireflection film is input as 0, and the thickness variation as ± 10% with respect to the set film thickness. The reflectance calculation 3 was performed in consideration of the thickness variation of the gate protective oxide film 20 and the antireflection film 24, and the worst case reflectance was obtained. FIG. 7 shows a contour map of the worst case reflectance with respect to the optical constant of the antireflection film for every 10 nm of the antireflection film thickness.
The reflectance of each optical constant is 200 nm for the gate protective oxide film.
It shows the maximum reflectance when the anti-reflection film thickness changes by ± 10% with respect to the set film thickness. From FIG. 7, as the optimum anti-reflection film conditions, an optical constant of 2.6-0.3i and a film thickness of 3 were obtained.
0 nm was selected by the optimum condition selection unit 5.

An SiON-based antireflection film 24 satisfying the above conditions is deposited on the poly-Si 21 by plasma CVD, a gate protection oxide film 20 is deposited thereon to a thickness of 200 nm, and a positive resist ip3300 (Tokyo Ohka) is applied. did. Exposure was performed using a 0.4 μmL / S mask with a reduction projection exposure apparatus having a wavelength of 365 nm, NA of 0.6 and σ of 0.6, and
FIG. 8 shows the dimension (swing curve) with respect to the resist film thickness when developed for 0 second. FIG. 8A shows the case without the anti-reflection film, and FIG. 8B shows the case with the anti-reflection film.
While the swing width without an anti-reflection film is 87 nm,
In the case where an anti-reflection film was provided, the thickness could be reduced to 20 nm, and a good device could be obtained because of small variations in gate dimensions.

(Embodiment 3) In Embodiment 3, as in Embodiment 2, a reflectance variation factor layer is specified, an anti-reflection film is provided thereunder, and further under the anti-reflection film for protecting a gate material. The case of forming a thin film will be described.

As shown in FIG. 9, the target gate structure is a poly-Si 21 having a thickness of 50 nm and a WSi 26 having a thickness of 120 nm.
In this structure, a 200 nm SiN 27 is mounted on the two-layer gate, and a 248 nm wavelength KrF excimer laser is used for exposure.

First, in the lower layer structure input unit 1, the Si substrate 2
3, gate oxide film 22, poly Si21, WSi26, Si
The optical constants of each film of N27 are 1.57-3.57i, 1.
51-0.0i, 1.68-2.76i, 2.25-2.8
3i, 2.28-0.01i. The film thickness and the amount of change in film thickness are determined as follows.
From 10 nm to 400 nm, and the others have a variation of ± 10% with respect to the specified film thickness.

Next, the film thickness is changed within the fluctuation input without the anti-reflection film shown in FIG. 16, and the reflectance to the resist 25 is calculated. (Reflectance variation factor layer specifying unit 6). The result is shown in FIG. Since only the SiN27 film caused the change in the reflectance of the resist 25, an antireflection film was provided under this film. However, in this structure, an antireflection film remains in the device, and W
The antireflection film 2 may be adversely affected on the Si26 film.
A structure as shown in FIG. 11 in which a 10 nm oxide film 28 was provided as an insulating thin film underneath 4 was set by the layer structure setting section 9.

With this structure, the antireflection film was optimized as in the second embodiment. In determining the worst case reflectivity, the thickness variation of 10 nm ± 10% of the oxide film 28 inserted under the antireflection film was also considered. FIG. 1 showing the result
From 2, it can be seen that the optical constant is 2.35-
0.9i and a film thickness of 20 nm were selected.

On the gate oxide film 22, a 50 nm poly-S
i21, 120 nm WSi is sequentially deposited, and
An oxide film 28 having a thickness of 0 nm and a SiON-based antireflection film 24 having an optical constant satisfying the conditions obtained above were formed to have a thickness of 30 nm, and a SiN 27 was formed thereon to have a thickness of 200 nm. Device was obtained. Further, the antireflection film left in the device did not affect the device characteristics.

(Embodiment 4) In Embodiment 4, the same target structure and the same antireflection film condition optimization method as those of Embodiment 1 are used.
A case where an optical constant variation and a film thickness variation are input as the variation of the antireflection film will be described.

In the antireflection film forming apparatus used here, the uniformity of the optical constants within the wafer and between the wafers is ±±.
0.1 and k were ± 0.15, and the variation in film thickness was ± 10% with respect to the set film thickness. Therefore, FIG.
In the antireflection film fluctuation amount input section 2 of the antireflection film condition optimization flow of FIG.
k was input as ± 0.15, and the film thickness variation was input as ± 10%. The worst-case reflectance was determined for various thicknesses and optical constants of the antireflection film in the same manner as in Example 1, and the results in FIG. 17 were obtained. In the optimum condition selection 5, the worst case reflectivity of 0.1 or less in FIG. 17 is set as the optimum anti-reflection film condition with the optical constant of 2.2-0.7i and the film thickness of 80 nm being the thinnest. did.

Under these conditions, an anti-reflection film was deposited, resist was applied, exposed, and developed. As a result, the optimum conditions obtained on the assumption that there was no change in the optical constant of the anti-reflection film were used. Also, the dimensional variation could be reduced.

[0039]

According to the present invention, it is possible to optimize the conditions of the antireflection film in consideration of the process variation of the target layer structure and the process variation of the antireflection film itself.

Further, by providing an anti-reflection film under a transparent film to be processed and a thin film thereunder, the anti-reflection effect is large and the anti-reflection film remaining in the device does not affect the device characteristics. can do.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a flow of an antireflection film optimizing method according to a first embodiment.

FIG. 2 is a cross-sectional view of a device stack structure according to the first and second embodiments.

FIG. 3 is a contour diagram of the reflectivity to a resist calculated for obtaining an optimum antireflection film condition in Example 1.

FIG. 4 is a diagram comparing resist dimensional controllability depending on the presence or absence of an antireflection film in Example 1.

FIG. 5 is a flowchart showing the flow of an antireflection film optimization method according to a second embodiment.

FIG. 6 is a diagram illustrating a change in reflectance with respect to a change in film thickness of a lower layer.

FIG. 7 is a contour diagram of the reflectivity to a resist calculated for obtaining the optimum anti-reflection film conditions in Example 2.

FIG. 8 is a diagram comparing resist dimensional controllability depending on the presence or absence of an antireflection film in Example 2.

FIG. 9 is a cross-sectional view of a device stack structure targeted in Example 3.

FIG. 10 is a diagram illustrating a change in reflectance with respect to a change in thickness of a lower layer.

FIG. 11 is a sectional view illustrating a laminated structure set in a third embodiment.

FIG. 12 is a contour diagram of the reflectivity to a resist calculated for obtaining the optimum antireflection film conditions in Example 3.

FIG. 13 is a cross-sectional view of a laminated structure used for worst-case reflectance calculation in the first embodiment.

FIG. 14 is a cross-sectional view of a laminated structure used when specifying a reflectance variation factor layer in the second embodiment.

FIG. 15 is a sectional view of a layered structure determined by the layer structure determination in the second embodiment.

FIG. 16 is a cross-sectional view of a laminated structure used when specifying a reflectance variation factor layer in the third embodiment.

FIG. 17 is a contour diagram of the reflectivity to the resist calculated in order to determine the optimum antireflection film conditions in Example 4.

[Explanation of symbols]

Reference numeral 1 denotes a lower layer structure input unit; 2 denotes an antireflection film change amount input unit;
... Reflectance calculator, 4 ... Worst case reflectivity calculator, 5
... Optimum condition selection unit, 6 ... Reflectance variation factor layer identification unit, 7 ...
Antireflection film condition loop, 8: variation loop, 9: layer structure setting unit, 20: gate protection oxide film, 21: poly Si, 2
2: gate oxide film, 23: Si substrate, 24: antireflection film, 25: resist, 26: WSi, 27: SiN, 2
8 ... oxide film.

Claims (10)

[Claims] 1. A fine processing for forming a latent image in a photosensitive film by partially irradiating an energy beam to a photosensitive film on a film to be processed laminated on a substrate, and at least a part below the film to be processed. A lower layer structure input step of setting an optical constant, a film thickness, and a film thickness variation of a single-layer substrate; and an antireflection film for inputting at least one of an optical constant variation, a film thickness variation in an antireflection film forming process. Antireflection by calculating the reflectance to the photosensitive film in consideration of the film thickness fluctuation amount and the optical constant fluctuation amount obtained in the fluctuation amount input step, the lower layer structure input step, and the antireflection film fluctuation amount input step. An anti-reflection film condition determining method including an anti-reflection film condition optimization step of optimizing an optical constant and a film thickness of the film. 2. A method according to claim 1, further comprising the step of specifying a layer in which the reflectance to the photosensitive film changes due to a change in the thickness of the lower layer. 3. The method according to claim 2, wherein the antireflection film is provided below the layer that changes the reflectance. 4. A method for determining anti-reflection film conditions, comprising optimizing an anti-reflection film by providing a thin film under the anti-reflection film according to claim 3. 5. A method according to claim 1, wherein an anti-reflection film is provided on the layer to be processed. 6. The film thickness variation of the film to be processed and the layer under the film according to claim 1 includes at least one of a variation due to a step difference of an underlying substrate and a variation due to a process variation during film deposition. A method for determining conditions of an antireflection film, characterized by the following. 7. A resist pattern forming method for forming a latent image in a photosensitive film by partially irradiating a photosensitive film on a layer to be processed laminated on a substrate with an energy beam. A method of forming a resist pattern, comprising: providing an antireflection film; and further providing a thin film under the antireflection film. 8. The antireflection film according to claim 7, wherein the antireflection film is provided below a lowermost layer of the layers whose reflectivity to the photosensitive film changes due to a change in film thickness when the layers to be processed are laminated. Characteristic method of forming a resist pattern. 9. A method for forming a resist pattern, wherein the antireflection film according to claim 7 is provided on the uppermost layer of the layer to be processed. 10. A microfabrication apparatus for forming a latent image in a photosensitive film by partially irradiating an energy beam on a photosensitive film on a layer to be processed laminated on a substrate. Lower layer structure input means for setting the optical constant, film thickness and film thickness variation of at least one substrate, and antireflection inputting at least one of the optical constant variation and film thickness variation in the antireflection film forming process Optimal antireflection film conditions for optimizing the optical constant and film thickness of the antireflection film by calculating the reflectance to the photosensitive film in consideration of the film fluctuation amount input means, the lower layer structure input means, and the antireflection film fluctuation amount means step. An antireflection film condition determining apparatus, comprising: