JPH0982596A - Formation of pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the formation of an edge at the bottom of resist and obtain a favorable resist profile by adjusting the thickness and optical constants of a thin film so that the phase of second light that returns from the interface to the photoresist side will have a specified value relative to the phase of first light incident on the interface. SOLUTION: A thin film 2 is formed between a photoresist layer 1 and a substrate 3 to be processed in order to adjust the intensity or phase of the component of exposure light returning from the interface between the photoresist layer 1 and a layer direct thereunder according to exposure wavelength. The direction of the propagation of light 4 incident on the photoresist layer 1 is taken as reference. Then the thickness and optical constants of the thin film 2 are adjusted so that, when second light returns from the interface between the photoresist layer 1 and the thin film 2 thereunder, the phase 6 of the second light is at an angle of 240-300 deg. to the phase 5 of first light incident on the interface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resist pattern forming method, and more particularly to a large-scale semiconductor integrated circuit (LS).
The present invention relates to a pattern forming method used for fine processing of electronic components such as I).

[0002]

2. Description of the Related Art A microfabrication technique by photolithography is used in a manufacturing process of various electronic components such as a semiconductor integrated circuit. In this technique, for example, a photoresist layer is formed on a silicon wafer and an insulator / conductor / semiconductor thin film formed thereon by a spin coating method or the like, and the photoresist layer is pattern-exposed and then subjected to a development step to form a resist. Form a pattern. Then, using this resist pattern as an etching mask, the insulator, conductor, and semiconductor thin film formed on the substrate are etched to form fine wiring, openings, and the like.

In the photolithography technique, it is important to control the dimension of the resist pattern with high accuracy. However, in the pattern formation process on a substrate that has a high reflectance for exposure light, such as a metal or silicon thin film for forming a wiring pattern, the local resist size is affected by the action of the reflected light from the substrate step. Fluctuation and deterioration of profile may occur. Further, when there is a silicon oxide or silicon nitride film which is relatively transparent to ultraviolet rays immediately below the resist, the exposure light is multiply reflected in these films. Therefore, if these film thicknesses change, the behavior of the multiple reflection is affected.

As a result, the amount of light energy applied to the resist layer substantially fluctuates, which seriously hinders the controllability of the resist size. Furthermore, since multiple reflection occurs even in the resist layer, when the resist film thickness varies, the dimensional variation is also greatly affected.

Therefore, recently, in order to solve the above problems, a method of forming an antireflection film 2 between a photoresist 1 and a film to be processed (film substrate to be processed) 3 as shown in FIG. 9 has been proposed. Has been taken. In this method, the light passing through the resist 1 is absorbed by the antireflection film 2 under the resist, so that the intensity of the light reflected by the resist 1 again can be significantly reduced. Moreover, the influence of multiple reflection in the lower layer of the antireflection film 2 can be eliminated, and further, the dimensional fluctuation and profile deterioration due to the above-mentioned fluctuation of the resist film thickness can be reduced.

Various types of antireflection films have been proposed. For example, in JP-A-59-93448, a resin having a property of absorbing exposure light, or a dye having a property of absorbing exposure light, for example, curcumin or coumarin dispersed in a resin is spin-coated. There is proposed a method of forming an antireflection film on a substrate by the method. Further, in JP-A-5-308049, an antireflection film made of a carbon compound is disclosed in JP-A-5-3080.
In JP-A-299338 and JP-A-6-196400, a method using an antireflection film made of a silicon compound is proposed.

However, even when such an antireflection film is used, if the values of the refractive index and the extinction coefficient and the film thickness are not properly selected, the resist profile has a bottomed shape as shown in FIG. May be indicated. When the resist has such a shape, if the resist is used as a mask for etching, the hem of the bottom of the resist causes a large difference in etching size conversion, which significantly reduces the controllability of the processing size.

[0008]

As described above, conventionally, a method of forming an antireflection film between a resist layer and an underlying layer has been adopted for forming a resist pattern, but an antireflection film is used. Even in this case, if the film thickness and the optical constant are not properly selected, the resist profile may show a bottoming shape as shown in FIG. When the resist has such a shape, if the resist is used as a mask for etching, the hem of the bottom of the resist causes a large difference in etching size conversion, which significantly reduces the controllability of the processing size.

The present invention has been made in consideration of the above circumstances, and it is an object of the present invention that, of course, it is possible to reduce fluctuations in the resist dimension due to reflection from the resist base, and the bottom of the resist. It is an object of the present invention to provide a pattern forming method capable of suppressing the occurrence of defects and forming a good resist profile and improving the dimensional accuracy of a resist pattern.

[0010]

[Means for Solving the Problems] (Outline) In order to solve the above problems, the present invention employs the following configurations. That is, the present invention is a pattern forming method for forming a resist pattern by exposing a desired pattern to a photoresist layer formed on a substrate to be processed, wherein a photoresist layer is formed between the photoresist layer and the substrate to be processed. A thin film for adjusting the intensity or phase of the component of the exposure light returning to the photoresist layer from the interface with the layer immediately below is provided, and the traveling direction of the light incident on the photoresist layer is used as a reference. Therefore, the phase of the second light returning from the interface to the photoresist side is 240 to 300 ° with respect to the phase of the first light incident on the interface between the photoresist layer and the underlying thin film from the photoresist side. It is characterized in that the film thickness and the optical constant of the thin film are adjusted so that the film has a value within the range. Further, the advance of the phase of the second light with respect to the first light is set to around 270 °. (Function) According to the present invention, by providing a thin film such as an antireflection film between the photoresist layer and the substrate to be processed, it is possible to reduce variation in the resist dimension due to reflection from the resist base. In addition to this, the phase of the second light returning from the interface to the photoresist side with respect to the phase of the first light entering from the photoresist side to the interface between the photoresist layer and the underlying thin film is 240- By adjusting the film thickness and the optical constant of the thin film so as to proceed with a value in the range of 300 °, it is possible to suppress the formation of the bottom of the resist bottom and form a good resist profile. As a result, the dimensional accuracy of the resist pattern can be improved.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Before describing the embodiments of the present invention, the basic principle of the present invention will be described first. As a result of various experiments and earnest studies conducted by the present inventors regarding the shape of the resist bottom portion described above, it has been clarified that the phenomenon that the resist bottom portion has a bottoming shape is caused by the following causes. This will be described with reference to FIG.

The exposure light 5 entering the resist 1 from the resist-air interface by the irradiation of the exposure light 4 reaches the resist-base interface while changing its intensity and phase. The complex amplitude intensity of the exposure light 5 at the resist-underlying interface can be expressed as A = A ₀ cos (qx−ωt + φ ₁ ) (1) with the direction of the incident light as the reference of the traveling direction of the light wave. Here, q is the wave number of the exposure light in the resist, and is shown as q = 2πη ₁ / λ (2) by the wavelength λ in vacuum and the complex refractive index η ₁ = n ₁ −jk _{1 of} the resist. Be done.

Next, the exposure light 5 reaching the resist-underlying interface is reflected to the resist side according to the complex reflectance γ uniquely determined by the layer structure of the underlying layer and the complex refractive index of the material forming the under layer. The complex amplitude can be expressed as R = γA = R ₀ cos (qx + ωt + φ ₂ ) ... (3).

The intensity of light absorbed by the resist 1, and hence the effective amplitude of the light which influences the photosensitive reaction of the resist 1, is
It is proportional to A + R. On the other hand, depending on the structure of the layer below the resist 1 and the complex refractive index, the phase relationship between the incident light 5 and the reflected light 6 may be a constructive relationship or a destructive relationship between the two.

FIGS. 2 (a) to 2 (d) show this state by the light intensity distribution in the resist. From this figure, the phase difference (φ ₂ -φ ₁₎ is the case of 0 ° (φ ₂ -φ
It can be seen that when ₁ ) is 180 °, the light intensity at the resist-underlayer interface becomes maximum and minimum, respectively.

However, this optical latent image is not completely faithfully reproduced at the time of patterning the photoresist. This is because, in a normal resist process, an additional process such as post-exposure baking is performed to reduce the standing wave effect. Therefore, the concentration distribution of the photosensitizer in the resist becomes a profile in which the optical latent image profile is smoothed under the influence of diffusion of the photosensitizer in the resist.

In order to investigate this situation, the latent image profile in the resist after the post exposure bake was obtained by numerical calculation in FIGS. 3 (a) to 3 (d). In the figure, 7 indicates an unexposed portion and 8 indicates an exposed portion. In the positive resist, the unexposed portion 7 remains as a pattern.

As can be seen from these results, the tailing appears remarkably in the actual resist profile when the above-mentioned phase difference (φ ₂ −φ ₁ ) is about 90 °. Therefore, in order to eliminate this phenomenon, the phase difference (φ
The phase difference (φ ₂ −φ ₁ ) is 240 to 300 ° while avoiding the combination of the underlying structure and the optical constants and film thicknesses of the materials forming the underlying so that ₂ −φ ₁ ) becomes a value of about 90 °. The range may be set so that it is more preferably 270 °.

Further, the present inventors have proposed the above phase difference (φ ₂ −φ
₁ ) to find the desired range of ARC (Anti-R
The relationship between the phase difference of the reflected light with respect to the incident light and the amount of resist skirting was investigated when a thin film was used. The horizontal axis of FIG. 4 is the phase difference corresponding to the ARC film thickness, and the vertical axis is the trailing amount. The trailing amount is 0 when the phase difference is 270 °, and the trailing amount is maximum when the phase difference is 90 °. Then, it is understood that the phase difference may be set to 270 ° ± 30 ° in order to suppress the trailing amount to be smaller than 0.05 μm.

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) In this embodiment, a polymer organic thin film having a refractive index of 1.7 and an extinction coefficient of 0.3 is formed on a substrate (high-reflecting substrate) having a surface coated with an aluminum film as a substrate to be processed. Is formed as an antireflection film, and a photoresist layer, for example, a layer made of a novolac-based positive resist is further formed thereon. First, in order to calculate the reflectance and phase of incident light and reflected light at the resist-antireflection film interface, the optical constants of the photoresist and aluminum film were measured by a spectroscopic ellipsometer. As a result, the following (Table 1) was obtained at a wavelength of 248 nm. Using this result, the reflectance at the resist-substrate interface and the phase difference between the incident light and the reflected light were calculated, and the appropriate film thickness of this layer was determined by the following procedure.

FIG. 5 shows a resist in the case where a photoresist having a refractive index of 1.7 at the light wavelength and an extinction coefficient of 0.03 is applied to the lower surface of the above-mentioned structure and exposure is performed. The phase difference defined above at the antireflection film interface,
And the ratio of the intensity of the light A incident on this interface to the intensity of the reflected light R returning from this interface to the resist side, that is, the intensity reflectance | R / A
² is the result of calculation for various film thicknesses of the antireflection film.

Such calculation can be performed, for example, in the literature (PHBern
ing: Physics of Thin Films, Vol.1, pp69-121 (1963),
AEBe ll & FWSpong: IEEE Jounal of Quantum Ele
ctronics, Vol.QE-14, pp487-495 (1978), K.Ohta & HI
shida: Applied Optics, Vol.29, pp1952-1958 (1990))
This can be done using the calculation method detailed in.

From FIG. 5, the antireflection film thickness is 47 nm, 11
It can be seen that the reflectance becomes minimum when the thicknesses are 3 nm, 184 nm, and 256 nm, but when the film thickness is selected from such values without considering the phase difference, for example, the film thickness is 47
nm or 113 nm, the phase difference (φ ₂
−φ ₁ ) is 132 ° and 97 °, respectively, and the shape of the resist bottom portion becomes a truncated shape due to the reason described above.

Therefore, it was decided to select a film thickness of 184 nm, which corresponds to the third minimum value from the smallest antireflection film thickness. At this film thickness, the reflectance is 0.1% and the phase difference is 272 °, which is a film thickness condition where good characteristics can be expected from the viewpoint of antireflection and the resist profile.

Here, in order to maximize the antireflection effect, of the conditions where the reflectance at the resist-underlying interface is minimized, the condition in which the phase difference is closer to 270 ° is adopted, but the reflectance is not necessarily required. Does not have to take a minimum value, and from the condition that the reflectance value is suppressed to a value that is small enough to achieve the dimensional accuracy required for the resist pattern, the condition that the phase difference becomes closer to 270 ° is You just have to choose.

Based on the above calculation results, the antireflection film was formed to a thickness of 184 nm on the aluminum film formed to a thickness of 400 nm by the sputtering method. Then, a photoresist having the optical constant shown in Table 1 was formed to a film thickness of 1 μm. Then, pattern exposure is performed by using a KrF excimer laser stepper, and thereafter, development is performed using an organic alkaline aqueous solution such as an aqueous solution of tetramethylammonium hydroxide as a developing solution to form a resist pattern of 0.3 μm line and space. .

As a result of observing the resist pattern thus obtained with a scanning electron microscope, it is possible to obtain a good resist pattern having a profile without tailing and having no pattern dimension disturbance due to irregular reflection, that is, halation. It was confirmed. (Embodiment 2) A coating type antireflection film is formed on a substrate in which a silicon nitride film is formed with a thickness of 140 nm on a WSi substrate, and a photoresist layer, for example, a novolac-based positive type resist is formed thereon. A case in which a layer is formed and an i-line having an exposure wavelength of 365 nm is used will be described.

As in the case of the first embodiment, in order to calculate the optimum film thickness of the antireflection film, the refractive index and the extinction coefficient of the photoresist, the nitride film, and the WSi film at a wavelength of 365 nm are measured by a spectroscopic ellipsometer. It was measured. As a result, the following values (Table 2) were obtained. (Table 2) Material Refractive index Extinction coefficient Photoresist 1.707 0.003 SiN 2.074 0.000 WSi 3.526 2.833 Next, on the nitride film of the substrate, the refractive index at the exposure wavelength is An organic film having an extinction coefficient of 1.7 and 0.2 was formed.
The proper film thickness of this layer was determined by the following procedure.

FIG. 6 shows a case where a photoresist having a refractive index at the light wavelength of 1.707 and an extinction coefficient of 0.003 is applied to the lower surface of the above structure and exposure is performed.
The phase difference defined above at the resist-antireflection film interface, and the ratio of the intensity of the light A incident on this interface to the reflected light R returning from this interface to the resist side, that is, the intensity reflectance |
R / A | ² is the result of calculation similar to that of the first embodiment for various film thicknesses of the antireflection film.

From this calculation result, the value of the phase difference (φ ₂ −φ ₁ ) is about 8 when the antireflection film is not used.
It is 3 °, which is a region where the resist profile has a skirted shape. On the other hand, the antireflection film thickness is 57 nm, 16
If the thickness is selected to be 5 nm, 215 nm, or 274 nm or more, the phase difference can be set to about 270 °, and a good shape without skirting of the resist can be obtained.

In particular, if an antireflection film thickness of 274 nm or more is selected, the reflectance and phase difference at this time are
It is a constant value determined by reflection at the interface of the antireflection film. At this time, the reflectance is suppressed to a very low value of 1.5% or less, and the phase difference is also in the range of 250 to 285 °, so that it is affected by the fluctuation of the antireflection film and the underlying film thickness. It is possible to form a resist pattern having a good profile with high dimensional controllability and no skirting.

Therefore, based on the above calculation result, 150
on the substrate in which the silicon nitride film is formed by the CVD method so as to have a thickness of 140 nm on the WSi film having a thickness of 1 nm.
7. A coating type antireflection film having an extinction coefficient of 0.2 was applied so as to have a film thickness of 280 nm, and then a photoresist layer having a film thickness of 1 μm was formed. Then, a line and space pattern of 0.4 μm was exposed by an i-line stepper, baked after the exposure, and then developed with an aqueous TMAH solution.

In order to examine the result of the above patterning, a cross section was observed with a scanning electron microscope. As a result, a photoresist pattern having a good cross-sectional shape without skirting as shown in FIG. 7 could be obtained. However, in the figure, 9 is a resist pattern, 10 is an antireflection film, 11 is a SiN film, 1
Reference numeral 2 indicates a WSi film.

For comparison, the result of similar patterning without forming the antireflection film 10 on the substrate is shown as follows.
As shown in FIG. The cross-sectional shape of the resist had a large skirt shape, and the sidewall was markedly rough due to the standing wave effect.

The present invention is not limited to the above embodiments. For example, although the i-line and the KrF excimer laser are used as the exposure light in the embodiment, the present invention is not limited to these, and the exposure light having any wavelength and band width such as the g-line or the ArF excimer light is used. It is also applicable in cases.

As the film for adjusting the intensity or phase of the reflected light in the resist, a polymer type antireflection film having a refractive index of 1.7 and an extinction coefficient of 0.3 or 0.2 is used here. However, various modifications can be made to this, for example, an antireflection film made of a carbon compound as disclosed in JP-A-5-308049, and a silicon compound as disclosed in JP-A-5-299338. The above method can be applied to the case where the following antireflection film is used.
In addition, various modifications can be made without departing from the scope of the present invention.

[0037]

As described in detail above, according to the present invention, with respect to the phase of the first light incident on the interface between the photoresist layer and the thin film thereunder from the photoresist side, the photoresist is introduced from the interface. The phase of the second light returning to the side is 240 to 3
By adjusting the film thickness and the optical constants of the thin film so as to proceed with a value in the range of 00 °, a good resist pattern is formed, and there is no dimensional variation due to halation, variation of underlying film thickness, etc. It is possible to form an accurate resist pattern.

[Brief description of drawings]

FIG. 1 is a diagram showing the behavior of exposure light incident on a resist.

FIG. 2 is a view showing a light intensity distribution in a resist in contour lines.

FIG. 3 is a view showing a line image profile of a resist after post exposure baking.

FIG. 4 is a diagram showing a relationship between a phase difference of reflected light and a resist trailing amount.

FIG. 5 is a diagram used to determine an optimum film thickness of an antireflection film in the first embodiment.

FIG. 6 is a diagram used to determine an optimum film thickness of an antireflection film in the second embodiment.

FIG. 7 is a view showing a resist pattern obtained according to the second embodiment.

FIG. 8 is a diagram showing a resist pattern obtained in a comparative example.

FIG. 9 is a diagram showing the shape of a positive resist pattern formed by a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Resist pattern 2 ... Antireflection film 3 ... Substrate to be processed 4 ... Exposure light 5 ... Incident light to resist-substrate interface 6 ... Reflected light from resist-substrate interface 7 ... Exposed portion of resist 8 ... Unexposed resist Part 9 ... Resist pattern 10 ... Antireflection film 11 ... SiN film 12 ... WSi film

Claims (2)

[Claims] 1. A pattern forming method for forming a resist pattern by exposing a desired pattern on a photoresist layer formed on a substrate to be processed, wherein the photoresist layer is provided between the photoresist layer and the substrate to be processed. A thin film for adjusting the intensity or phase of the component of the exposure light returning to the photoresist layer from the interface between the layer immediately below and the layer, and the traveling direction of the light incident on the photoresist layer. The phase of the first light incident from the photoresist side to the interface between the photoresist layer and the underlying thin film, with respect to the phase of the second light returning from the interface to the photoresist side. , The pattern forming method is characterized in that the film thickness and the optical constant of the thin film are adjusted so as to proceed with a value in the range of 240 to 300 °. 2. The phase lead of the second light with respect to the first light is set in the vicinity of 270 °.
The pattern forming method described in the above.