JP2005150222A - Method of forming pattern - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming a pattern in which a substrate to be processed is processed to a fine pattern having predetermined size and shape by using a heat shrinking method. <P>SOLUTION: The method of forming the pattern includes steps of: sequentially forming a first resist film and a second resist film on the film 2 to be processed on the substrate 1; forming a second resist pattern 6 by developing after the predetermined region of the first resist film is exposed; then forming the first resist pattern 7 having an opening 9 to the film 2 to be processed by etching the first resist film with the second resist pattern 6 as a mask; and thereafter contracting the size L of the opening 9 by heat treating at the temperature of the glass transition point or higher of the first resist film. The heat treatment is preferable to be performed after an SiO<SB>2</SB>film 8 is formed on the upper surface of the second resist pattern 6 and the side walls of the second resist pattern 6 and the first resist pattern 7. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pattern forming method, and more particularly, to a method for forming a pattern using a resist pattern that is miniaturized by utilizing the thermal flow of the resist.

  In recent years, with the increase in the degree of integration of semiconductor devices, the dimensions of individual elements have been reduced, and the widths of wirings and gates constituting each element have also been reduced.

  The photolithography technology that supports this miniaturization includes a step of applying a resist composition to the surface of a substrate to be processed to form a resist film, and exposing a predetermined resist pattern by irradiating light with a resist pattern latent. A step of forming an image, a step of performing a heat treatment if necessary, a step of developing the image to form a desired resist pattern, and a step of performing processing such as etching on the substrate to be processed using the resist pattern as a mask Is included.

  Typical shapes of the resist pattern are a line pattern and a hole pattern. Here, the hole pattern has a lower exposure resolution than the line pattern, and it is difficult to miniaturize the pattern by photolithography.

  Therefore, as a technique for miniaturizing a hole pattern, a technique based on a thermal shrink method is conventionally known. This is a method in which after forming a resist pattern, heat treatment is performed at a temperature equal to or higher than the glass transition point (Tg) of the resist to cause the resist to flow and shrink the pattern dimensions.

  However, the resist pattern formed by the conventional thermal shrink method has the following problems.

  FIG. 7 is a cross-sectional view showing resist patterns before and after shrinking. As shown in FIG. 7A, a resist pattern 13 is formed on a film to be processed 12 provided on a semiconductor substrate 11. When heat having a temperature equal to or higher than the glass transition point of the resist is applied to the resist, thermal flow of the resist occurs, and the resist around the opening (hole) 14 flows into the opening 14. By doing in this way, the internal diameter of the opening part 14 can be shrunk. FIG. 7B shows the resist pattern 13 after shrinking. As the resist flows into the opening 14, the cross-sectional shape of the resist pattern 13 is changed to a rounded shape near the upper portion due to a decrease in linearity of the side wall. When the processed film 12 is etched using the resist pattern 13 having such a shape as a mask, it is difficult to process the processed film 12 into a pattern having a desired size and shape.

By the way, in the manufacturing process of a semiconductor device, the wavelength of exposure light used when forming the resist pattern latent image is being shortened as one of means for reducing the pattern. Then, F 2 _(fluorine) laser light (wavelength: 157 nm) in order to ensure the transmittance for exposure light of short wavelength, such as and the resist pattern is made to be thin. This is because the aspect ratio (resist pattern film thickness / resist pattern line width) is set to a value equal to or smaller than a predetermined value in order to prevent the resist pattern from being tilted or tilted due to the reduction in line width due to miniaturization. It is necessary from the point to do.

  Specifically, the thickness of the resist pattern is required to be reduced to about 100 nm to 200 nm. However, when such a thin resist pattern is heat-shrinked, there is a problem that the shape of the resist pattern after shrinking becomes more deteriorated than the shape shown in FIG.

  FIG. 8 is a cross-sectional view of the thin film resist pattern after shrinking. As in FIG. 7, the resist pattern 17 is formed on the film 16 to be processed provided on the semiconductor substrate 15. When the resist flows by the heat treatment, the resist flows into the opening (hole) 18. However, in this case, since the resist pattern 17 is thin, the linearity of the side wall portion of the resist pattern 17 is further lowered, and not only the upper portion but also the entire side wall portion is rounded. When etching the film to be processed 12 using the resist pattern 17 having such a shape as a mask, it becomes very difficult to process the film to be processed 12 into a pattern having a desired size and shape.

  Further, the resist pattern 17 having a reduced thickness has a problem that the inner diameter of the opening 18 cannot be shrunk to a desired dimension because the amount of resist flowing into the opening 18 is reduced.

  The present invention has been made in view of such problems. That is, an object of the present invention is to provide a pattern forming method capable of processing a substrate to be processed into a fine pattern having a predetermined size and shape using a thermal shrink method.

  Other objects and advantages of the present invention will become apparent from the following description.

  The pattern forming method of the present invention includes a step of forming a first resist film on a film to be processed, a step of forming a second resist film on the first resist film, and the second resist A step of exposing a predetermined region of the film, a step of developing the second resist film after the exposure to form a second resist pattern, and dry etching the first resist film using the second resist pattern as a mask A step of forming a first resist pattern having an opening reaching the film to be processed, a step of performing a heat treatment at a temperature equal to or higher than the glass transition point of the first resist film, and reducing the size of the opening; And a step of dry-etching the film to be processed using the second resist pattern and the first resist pattern as a mask after the heat treatment, and forming a pattern on the film to be processed.

  In the above pattern formation method, the second resist film is preferably thinner than the first resist film and has a thickness of 100 nm to 200 nm. The second resist film is preferably a chemically amplified resist film. Further, the second resist film contains silicon, and dry etching of the first resist film is performed using an etching gas containing oxygen, whereby the first resist pattern is formed and the upper surface of the second resist pattern is formed. It is preferable to form a silicon oxide film on the second resist pattern and the side walls of the first resist pattern. In this case, the second resist film can be a siloxane ladder polymer.

  The pattern forming method of the present invention includes a step of forming a resist film on a film to be processed, a step of exposing a predetermined region of the resist film, and developing the resist film after exposure to reach the film to be processed. A step of forming a resist pattern having an opening, a step of forming a thin film made of a material having a glass transition point higher than that of the resist film on the upper surface and side wall of the resist pattern, and a temperature lower than the glass transition point of the thin film. A process of flowing the resist film by heat treatment to reduce the size of the opening, and a process of dry etching the film to be processed using the resist pattern after the heat treatment as a mask to form a pattern on the film to be processed. It is characterized by having. Here, the substance having a high glass transition point can be silicon oxide.

  As described above, according to the present invention, the second resist pattern is formed on the first resist film, and the first resist pattern is formed by dry etching of the first resist film using the second resist pattern as a mask. Form. Thereafter, heat treatment is performed to flow the first resist film, and the size of the opening of the resist pattern is reduced (hereinafter referred to as shrink). That is, since the resist pattern formed by the photolithography method and the resist pattern to be flowed by the heat treatment are separated, the former resist pattern can be formed sufficiently thin, while the latter resist pattern is formed by photolithography. It can be formed thick regardless of the method. Therefore, since the amount of resist flowing into the opening can be increased, the pattern can be shrunk to a desired dimension.

  Further, the present invention provides a resist film by forming a thin film made of a substance having a glass transition point higher than that of the resist film on the upper surface and side wall of the resist pattern, and then performing a heat treatment at a temperature lower than the glass transition point of the thin film. The size of the opening of the resist pattern is shrunk. The presence of the thin film makes it possible to suppress the flow of the resist pattern to some extent. Therefore, it is possible to prevent the side wall portion of the resist pattern after shrinking from being rounded.

  1 to 6 show an example of a pattern forming method according to the present invention. In these drawings, the same reference numerals indicate the same parts.

  First, as shown in FIG. 1, a film to be processed 2 is formed on a substrate 1. For example, a TEOS (tetraethoxysilane) film having a thickness of about 400 nm can be formed on a semiconductor substrate such as a silicon substrate by a plasma CVD method. Here, a conductive layer such as a copper wiring layer or an impurity doping region may be formed on the semiconductor substrate.

In the present embodiment, the substrate 1 is not limited to a semiconductor substrate, and other substrates such as a glass substrate or a plastic substrate may be used. Further, the film to be processed 2 is not limited to the TEOS film, and is Si _x N such as SiO ₂ (silicon oxide) film, SiC (silicon carbide) film, Si ₃ N ₄ film, Si ₂ N ₃ film, or SiN film. _Y (silicon nitride) film, SiCN (silicon carbonitride) film, SiOC (silicon oxycarbide) film, or a film made of a polymer of an aromatic compound such as polyimide derivative, polyallyl ether derivative, polyquinoline derivative, and polyparaxylene derivative Can be used. These films can be formed by a CVD (Chemical Vapor Deposition, hereinafter referred to as CVD) method, a sputtering method, a spin coating method, or the like.

  Next, a first resist film 3 is formed on the work film 2 (FIG. 1). The first resist film 3 is patterned in a subsequent step and then heated at a temperature equal to or higher than the glass transition point to cause flow and shrink the formed pattern. Therefore, any material that can fulfill this role can be used as the first resist film 3. Specifically, a resist film having an organic polymer skeleton is preferably used as the first resist film 3. The film thickness of the first resist film 3 is set so that a sufficient amount of resist can flow to obtain a fine pattern with a desired dimension.

  For example, a novolac resist resin composition is spin-coated on the TEOS film and subjected to a heat treatment at 130 ° C. for about 60 seconds. In this way, a novolac resist film having a thickness of about 300 nm can be formed as the first resist film 3.

  After forming the first resist film 3, a second resist film 4 is formed thereon (FIG. 1). The second resist film 4 serves as a mask for patterning the first resist film 3, and is processed into a fine resist pattern by a photolithography method. For this reason, the second resist film 4 is preferably thinner than the first resist film 3 and has a thickness of about 100 nm to 200 nm. The material of the second resist film 4 preferably has a higher glass transition point than the material of the first resist film 3. Accordingly, when the first resist pattern is caused to flow by heat treatment in a later process, the second resist pattern can be prevented from flowing together with the first resist pattern to some extent. It becomes possible to prevent the upper part of the pattern from being rounded.

The second resist film 4 is a resist containing silicon in a polymer skeleton, and is a resist (hereinafter referred to as F ₂ resist) corresponding to an exposure machine using an F ₂ excimer laser (wavelength: 157 nm) as a light source. be able to. The second resist film 4 is made of a light source other than the F ₂ excimer laser, such as a KrF (krypton fluoride) excimer laser (wavelength: 248 nm) or an ArF (argon fluoride) excimer laser (wavelength: 193 nm). It is also possible to use a resist corresponding to the above.

For example, a ladder polymer (siloxane ladder polymer) having a polysiloxane structure represented by the formula (1) can be used as the second resist film 4. In the formula (1), the substituents R ₁ , R ₂ , R ₃ can be appropriately changed according to the type of the exposure light source.

For example, a positive F ₂ resist resin composition to be the second resist film 4 is spin-coated on a novolak resist film as the first resist film 3. Here, F ₂ resist resin composition, it is preferable that the resist resin composition of the chemical amplification type. Specifically, the F ₂ resist resin composition comprises an alkali-insoluble polymer in which an acid labile group is introduced into at least a part of functional groups of a base polymer containing silicon and soluble in an alkaline aqueous solution, and an acid generator. It can be set as the chemically amplified resist resin composition containing. In addition, as an acid generator, the photo-acid generator which generate | occur | produces an acid by light, such as a triphenylsulfonium triflate, can be used. Hereinafter, the case where the second resist film 4 is formed using this chemically amplified resist resin composition will be described as an example.

After the F ₂ resist resin composition is applied on the first resist film 3, a heat treatment is performed at 140 ° C. for about 90 seconds to form a second resist film 4 having a thickness of about 120 nm.

Next, a predetermined region of the second resist film 4 is exposed (FIG. 2). For example, the second resist film 4 is irradiated with F ₂ excimer laser light through the mask 5. Thereby, as shown in FIG. 2, a resist pattern latent image composed of the exposed portion 4 a and the unexposed portion 4 b is formed in the second resist film 4. At this time, in the exposed portion 4a, acid is generated from the acid generator contained in the second resist film 4, but no acid is generated in the unexposed portion 4b because the acid generator is not exposed.

  Next, heat treatment is performed on the exposed second resist film 4. The conditions for the heat treatment can be, for example, about 110 ° C. for about 60 seconds. When heat treatment is performed, the alkali-insoluble polymer in the second resist film 4 in the exposed portion 4a becomes an alkali-soluble polymer. Specifically, an acid labile group blocking an alkali-soluble functional group is thermally decomposed and eliminated by the catalytic action of an acid. As a result, an alkali-soluble polymer structure is formed in the exposed portion 4a.

  After finishing the heat treatment, the second resist film 4 is developed.

  An alkaline aqueous solution can be used as the developer. As the alkaline aqueous solution, for example, an aqueous solution of tetramethylammonium hydroxide having a concentration of 2.38% can be used. In addition, as long as it is aqueous alkali solution which can be used as a developing solution, substances other than tetramethylammonium hydroxide may be contained.

  Through the above steps, the second resist pattern 6 can be formed on the first resist film 3 as shown in FIG.

  Next, the first resist film 3 is dry-etched using the second resist pattern 6 as a mask. Thereby, as shown in FIG. 4, the 1st resist pattern 7 is formed. In FIG. 4, the first resist pattern 7 has an opening 9 that reaches the film 2 to be processed. Here, the opening 9 can be a hole pattern, for example.

In this embodiment mode, it is preferable to perform the dry etching using an etching gas containing oxygen. For example, a mixed gas of O ₂ (oxygen) gas and N ₂ (nitrogen) gas can be used as the etching gas. When a gas containing oxygen is used as an etching gas, a reaction occurs between the oxygen active species generated by the plasma and the silicon in the second resist pattern 6 together with the dry etching of the first resist film 3, and in the atmosphere. SiO ₂ (silicon oxide) is generated. The generated SiO ₂ adheres to the upper surface of the second resist pattern 6 and the side walls of the second resist pattern 6 and the first resist pattern 7. As a result, as shown in FIG. 4, a thin SiO ₂ film 8 is formed thereon. Here, the SiO ₂ film 8 has a thickness that does not completely hinder the flow of the first resist pattern 7 described later.

When the SiO ₂ film 8 is also formed on the film to be processed 2 during the dry etching, the film to be processed 2 is dry after shrinking the first resist pattern 7 described later. It is preferable to remove the SiO ₂ film 8 by wet etching or the like before etching.

  After the first resist pattern 7 is formed, the first resist pattern 7 is caused to flow by performing a heat treatment at a temperature equal to or higher than the glass transition point of the resist. When the first resist pattern 7 is formed using a novolac resist film, the resist can be flowed by performing a heat treatment at 120 ° C. for about 60 seconds.

  In the present embodiment, since the thick first resist pattern 7 is flowed instead of the thin second resist pattern 6, the dimension of the pattern can be shrunk to a desired fine pattern (FIG. 5).

  That is, conventionally, in order to form a fine resist pattern by a photolithography method, the resist film is formed with a thin film thickness. In order to make the resist pattern finer than the exposure resolution, the resist is flowed by heating to shrink the pattern. However, in the case of a thin resist pattern, the amount of resist flowing into the opening is reduced, and the pattern cannot be shrunk to a desired dimension.

  On the other hand, in the present invention, the resist pattern formed by the photolithography method and the resist pattern made to flow by the heat treatment are made different. Thereby, the former resist pattern can be formed sufficiently thin, while the latter resist pattern can be formed thick regardless of the photolithography method. Therefore, since the amount of resist flowing into the opening can be increased, the pattern can be shrunk to a desired dimension.

In addition, when the SiO ₂ film 8 is formed during the dry etching of the first resist film, the cross-sectional shape of the side wall portion of the first resist pattern 7 can be prevented from being deteriorated by the resist flow. it can. This will be described in detail below.

SiO ₂ is harder than the resist material and has a high glass transition point. Therefore, even when heat treatment is performed at a temperature at which the resist flows (for example, a temperature of about a few hundred degrees), as long as this temperature is lower than the glass transition point of the SiO ₂ film, SiO _{2 The two} membranes do not flow by themselves. Therefore, by forming the SiO ₂ film 8 with a thin film thickness on the side wall portion of the first resist pattern 7, the flow of the first resist pattern 7 can be suppressed to some extent by the SiO ₂ film 8. Become. Therefore, the resist can be made to flow while the linearity of the side wall portion is maintained. That is, it is possible to prevent the side wall portion of the first resist pattern 7 from being rounded and bent. Further, since the SiO ₂ film 8 is also formed on the upper surface and the side wall portion of the second resist pattern 6, even when the second resist pattern 6 flows together with the first resist pattern 7, Similar effects can be obtained.

  In FIG. 5, the first resist pattern 7 and the second resist pattern 6 have good cross-sectional shapes, and the dimension L ′ of the opening 9 is larger than the dimension L of the opening 9 in FIG. 4. It is shrinking.

After shrinking the resist pattern, dry etching of the film to be processed 2 is performed using the second resist pattern 6 and the first resist pattern 7 as a mask. When a TEOS film is used as the film 2 to be processed, the above dry etching can be performed using a mixed gas of C ₄ F ₈ (octafluorobutene), Ar (argon) and O ₂ (oxygen) as an etching gas. it can.

  According to the present embodiment, since the cross-sectional shapes of the first resist pattern 7 and the second resist pattern 6 have good linearity, the processed film 2 is processed into a desired size and shape. Can do.

After the dry etching of the film to be processed 2 is finished, the unnecessary second resist pattern 6 and first resist pattern 7 are removed. Specifically, these resist patterns can be removed by ashing using oxygen plasma. If the SiO ₂ film 8 is formed, the SiO ₂ film 8 is also removed together. The film pattern 10 to be processed shown in FIG. 6 is obtained through the above steps.

In this embodiment, the SiO ₂ film 8 is formed by using oxygen gas when the first resist film 3 is dry-etched. However, the present invention is not limited to this. After forming the first resist pattern 7, a SiO ₂ film may be deposited by sputtering or CVD. Further, after the first resist pattern 7 is formed, a reaction layer is formed on the surfaces of the first resist pattern 7 and the second resist pattern 6 by, for example, irradiating with a lamp annealing method or an electron beam or a short wavelength ultraviolet ray. Once formed, this reaction layer may be used in place of the SiO ₂ film. The SiO ₂ film and the reaction layer have a thickness that does not completely hinder the flow of the first resist pattern.

In the present embodiment, the second resist film is formed on the first resist film, but the present invention is not limited to this. For example, when the thickness of the resist pattern can be increased to some extent, a resist pattern consisting of only one layer is formed, an SiO ₂ film is formed on the upper surface and side wall portions of the resist pattern, and then the resist is formed by heat treatment. May be allowed to flow. Also in this case, by providing the SiO ₂ film, it is possible to suppress the upper part of the resist pattern from being rounded, so that the film to be processed can be processed into a desired size and shape. .

When a resist pattern is formed on a film to be processed using only one resist, the SiO ₂ film can be formed using a sputtering method or a CVD method after the formation of the resist pattern. However, the thin film provided on the upper surface and the side wall of the resist pattern may be a thin film made of a substance having a glass transition point higher than that of the resist film, and is not limited to the SiO ₂ film. The thin film is formed with a film thickness that does not completely hinder the flow of the resist pattern. After the thin film is formed, the resist film is caused to flow by performing a heat treatment at a temperature lower than the glass transition point of the thin film. Thereby, the dimension of an opening part can be shrunk in the state which maintained the linearity of the resist pattern cross section.

It is sectional drawing which shows the pattern formation method concerning this Embodiment. It is sectional drawing which shows the pattern formation method concerning this Embodiment. It is sectional drawing which shows the pattern formation method concerning this Embodiment. It is sectional drawing which shows the pattern formation method concerning this Embodiment. It is sectional drawing which shows the pattern formation method concerning this Embodiment. It is sectional drawing which shows the pattern formation method concerning this Embodiment. It is a figure which shows the conventional pattern formation method, (a) is sectional drawing of the resist pattern before shrinking, (b) is sectional drawing of the resist pattern after shrinking. It is sectional drawing of the thin film resist pattern after the conventional shrink.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2,12,16 Processed film 3 First resist film 4 Second resist film 5 Mask 6 Second resist pattern 7 First resist pattern 8 SiO ₂ film 9, 14, 18 Opening 10 Processed Film pattern 11, 15 Semiconductor substrate 13, 17 Resist pattern

Claims (7)

Forming a first resist film on the film to be processed;
Forming a second resist film on the first resist film;
Exposing a predetermined region of the second resist film;
Developing the second resist film after the exposure to form a second resist pattern;
Dry etching the first resist film using the second resist pattern as a mask to form a first resist pattern having an opening reaching the film to be processed;
Performing a heat treatment at a temperature equal to or higher than the glass transition point of the first resist film to reduce the size of the opening;
And a step of dry-etching the film to be processed using the second resist pattern and the first resist pattern as a mask after the heat treatment, and forming a pattern on the film to be processed. .   The pattern forming method according to claim 1, wherein the second resist film is thinner than the first resist film and is formed with a film thickness of 100 nm to 200 nm.   The pattern forming method according to claim 1, wherein the second resist film is a chemically amplified resist film. The second resist film includes silicon;
By performing dry etching of the first resist film using an etching gas containing oxygen, together with the formation of the first resist pattern, the upper surface of the second resist pattern, the second resist pattern, and the The pattern formation method according to claim 1, wherein a silicon oxide film is formed on a side wall portion of the first resist pattern.   The pattern forming method according to claim 4, wherein the second resist film is a siloxane ladder polymer. Forming a resist film on the film to be processed;
Exposing a predetermined region of the resist film;
Developing the exposed resist film and forming a resist pattern having an opening reaching the film to be processed;
Forming a thin film made of a material having a glass transition point higher than that of the resist film on the upper surface and side wall of the resist pattern;
Reducing the size of the opening by flowing the resist film by performing a heat treatment at a temperature lower than the glass transition point of the thin film;
And a step of dry etching the film to be processed using the resist pattern after the heat treatment as a mask to form a pattern on the film to be processed.   The pattern forming method according to claim 6, wherein the substance having a high glass transition point is silicon oxide.

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