JP2004014652A - Method of forming fine pattern - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a fine pattern in an Å order of a correctly controllable "thickness of an oxide film" as a parameter, regardless of the exposure light radiation method, by forming a fine pattern line from a material having a different oxidation rate. <P>SOLUTION: A silicon nitride film is formed on a substrate, and a polysilicon film is formed thereon, and then a silicon nitride layer is formed thereon. Exposure and development are carried out to pattern the silicon nitride layer on a surface layer. Then, with the patterned silicon nitride layer on the surface layer as a mask, the polysilicon layer is plasma-etched. Furthermore, the substrate is subject to an oxidation treatment in a diffusion furnace to form an oxide film on the polysilicon layer. The nitride layer on a front surface is plasma-etched, and at the same time, the polysilicon layer between the oxide films is removed, leaving the fine pattern of the oxide layer. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
[Industrial applications]
The present invention relates to a method for forming a fine pattern by a line having a width smaller than 0.3 μm, and is used for manufacturing an optical disk stamper, a video disk stamper, a DRAW disk, an EDRAW disk, an optical element, a grating, and a photonic element. In addition, the present invention can be applied to the manufacturing technology of semiconductors, transistors, and memories.
[0002]
[Prior art]
In a method of forming a fine pattern in an IC manufacturing technique or the like, a photoresist film is formed on a substrate having a thin film for element formation, and an exposure pattern is formed on the photoresist film by an optical projection method through a glass mask plate. A resist pattern is formed by developing the resist pattern. Then, the thin film for element formation is etched by RIE (Reactive Ion Edging) using the resist pattern as a mask, and then the resist pattern is removed. In general, a fine pattern is formed by a thin film for element formation. In this manner, when a fine pattern is formed by exposing and etching a photoresist film, miniaturization of the exposed pattern requires resolution. This resolution is limited because it depends on the wavelength of the exposure light and the lens numerical aperture (NA).
As one of techniques for forming a finer fine pattern beyond the limit due to the above-described resolution, there is one described in Japanese Patent Application Laid-Open No. Hei 5-3191, the outline of which is as follows.
[0003]
A fine wiring is formed by using the polysilicon film 1 laminated on the substrate 2 (FIG. 5). In this device, the first SiN film 3 on the polysilicon film 1 of the substrate 2 is exposed and developed to form a fine groove, and then a second SiN film 4 is laminated on the first SiN film 3 (for example, with a thickness of 0. 1 μm) to further narrow the fine groove (FIG. 5B), and then etch by anisotropic RIE to remove the second SiN film 4 leaving only the 0.1 μm side wall 4a (FIG. 5). (C)). Next, this is heated at 800 to 900 ° C. to form a thin silicon oxide film (SiO ₂ film, thickness 1000 °, width 0.3 μm) 6 on the surface of the polysilicon film 1 exposed at the bottom of the fine groove. (FIG. 6A) Next, the side wall 4a of the second SiN film on the first SiN film 3 is removed by using H ₃ PO ₄ (FIG. 6B). At this time, the remaining silicon oxide film 6 functions as an etching stopper (mask) in the etching process using the H ₃ PO _4, and the polysilicon wiring of a fine line having a width of 0.3 μm (the same width as the SiO ₂ film 6) is formed on the substrate 1. It is formed on top (FIG. 6C).
[0004]
In addition to the method of shortening the wavelength of an exposure light source to form a fine pattern (for example, KrF, ArF, VUV (vacuum ultraviolet light)) and forming a high NA of an optical system as in the above conventional technique, EUV In addition to using (soft X-rays), a method for forming a finer pattern by silylating the outermost surface of the resist has also been devised.
[0005]
[Problem to be solved]
Since there is a limit in simply shortening the wavelength of the exposure light, the wavelength is shortened by using VUV (vacuum ultraviolet light) as described above, and the NA of the optical system is increased. In addition, methods using EUV (soft X-ray) and EB have been devised. However, these methods require a high degree of care for incidental equipment for exposure in a vacuum or the like. Yes, the equipment cost increases.
Further, the prior art described in the above-mentioned Japanese Patent Application Laid-Open No. Hei 5-3191 utilizes the fact that the polysilicon is patterned and the silicon nitride (Si ₃ N ₄ ) deposit wall surface becomes thicker. Thus, although a fine pattern is formed by this, it is necessary to form a thick silicon nitride layer, and to precisely control the thickness of the silicon nitride layer and to reduce the width of the silicon oxide film 6. It is difficult to control accurately and stably, which impairs the precision of the fine pattern. Therefore, it is difficult to stably form a pattern of the order of Å.
Further, the pattern profile according to the above-mentioned conventional technique is simple and not multi-step, so that its use range is limited.
[0006]
[Problem 1] (corresponding to claim 1)
The first object of the present invention is to form a fine pattern processing line width with a material having a different oxidation rate, and to use an “oxide film thickness” which is easy to control accurately as a parameter regardless of the exposure light source method. It is to devise a method for forming a fine pattern so that a fine pattern can be formed.
[Problem 2] (corresponding to claim 2)
A second object of the present invention is to make it possible to optimize a pattern profile.
[Problem 3] (corresponding to Claims 3 and 4)
A third object of the present invention is to make it possible to provide three steps in a pattern profile.
[Problem 4] (corresponding to claim 5)
A fourth object of the present invention is to provide an optical element and a medium which are inexpensive and widely used.
[Measures taken to solve the problem]
[0007]
[Solution 1]
Means taken to solve the above problem 1 is a method of forming a fine pattern according to the following (a) to (f).
(A) forming a silicon nitride layer on a substrate, forming a polysilicon layer thereon, further forming a silicon nitride layer,
(B) Exposure and development to pattern the surface silicon nitride layer,
(C) The polysilicon layer is plasma-etched using the surface silicon nitride layer as a mask,
(D) oxidation treatment in a diffusion furnace to form a silicon oxide film on the polysilicon layer,
(E) Plasma etching the nitride layer on the surface,
(F) removing the polysilicon layer between the silicon oxide films to leave the silicon oxide film.
[0008]
[Action]
A groove having a predetermined width is formed in the polysilicon layer by patterning the surface silicon nitride layer by exposure and development by a normal method, and plasma-etching the polysilicon layer using the surface silicon nitride layer as a mask. . By oxidizing in this state in a diffusion furnace, a silicon oxide film (SiO ₂ film) is formed on the exposed surface of the polysilicon layer, that is, on the side surface of the groove. Since the thickness of the silicon oxide film can be controlled by the temperature and the oxidation time of the oxidation treatment, the silicon oxide film thickness can be easily and accurately controlled by controlling the oxidation temperature and the oxidation time. Therefore, it is easy to control the thickness of the silicon oxide film to stably form a fine pattern having a thickness of, for example, 0.1 μm.
Next, when the polysilicon layer between the silicon oxide films is removed, the oxide film remains, and an extremely fine pattern of a thin silicon oxide film is accurately and stably formed on the silicon nitride layer.
Therefore, by adjusting the thickness of the silicon oxide film, it is possible to freely form a fine pattern with a line having an appropriate thickness regardless of the exposure light source method.
[0009]
[Solution 2]
The solution 2 is based on the solution (1) and is further based on the following (g). (G) selectively removing the silicon nitride layer using the silicon oxide film as a mask, and finally removing the silicon oxide film;
[0010]
[Action]
When the silicon nitride layer is plasma-etched using the silicon oxide layer as a mask, a fine pattern of silicon nitride having the same thickness as the silicon oxide film is formed. As described above, since the silicon oxide film thickness is accurately and stably controlled by the temperature and time of the oxidation treatment, an extremely fine pattern of silicon nitride is accurately and stably formed. You.
[0011]
[Solution 3]
The solution 3 is based on the following (h) on the premise of the solution 1.
(H) Three layers having different heights are formed by simultaneously etching the silicon nitride layer and the base substrate using the silicon oxide film as a mask and finally removing the silicon oxide film.
[0012]
[Action]
In the first aspect, at a stage where the polysilicon layer between the oxide films is removed to leave the oxide layer, the surface of the substrate includes a portion covered with a silicon nitride layer between the oxide films, There are portions where the silicon nitride layer is removed by plasma etching and is exposed. When the silicon nitride layer and the base substrate are simultaneously etched using the silicon oxide film as a mask, the silicon nitride layer and the exposed surface are etched. Therefore, only the exposed surface of the substrate surface is etched, so that a step is formed. When the etching is further advanced, the etching does not proceed in a portion masked by the silicon oxide film, but the etching proceeds on the substrate surface in the same manner. Thereafter, when the silicon oxide film is removed, a total of three steps of a portion masked by the oxide film and the above-mentioned two step portions are formed on the upper surface of the substrate.
[0013]
Embodiment
Next, embodiments will be described with reference to the drawings.
Embodiment 1
In Example 1 shown in FIG. 1, a first silicon nitride layer (Si ₃ N ₄ layer, thickness 200 °) 12, a polysilicon layer (thickness 400 °) 13, a second With respect to the laminated silicon nitride layer (thickness: 80 °) 14 (FIG. 1A), the second silicon nitride layer 14 was formed into a fine pattern having a width of 0.3 μm. (It is related to the pitch of the typical fine pattern but not related to the width of the line), and is developed (FIG. 1B). When the polysilicon layer 13 is etched using the second silicon nitride layer 14 as a mask, a pattern of the groove 15 (exposed portion) having a width of 0.3 μm is formed (FIG. 1C). When this is heated and oxidized, the upper surface of the remaining polysilicon layer 16 is covered with the second silicon nitride layer 14 and is not oxidized, and the side surface of the groove 15 is oxidized to form a silicon oxide film 17. (FIG. 1D). The thickness of the silicon oxide film 17 increases in proportion to the heating temperature and the oxidation time. In this example, the oxidation temperature is set to 1100 ° C., the oxidation time is adjusted, and an oxide film 17 having a thickness of 500 ° is formed.
[0014]
Then, the substrate is immersed in a phosphoric acid solution to remove the remaining second silicon nitride layer 14 (FIG. 1E), and the polysilicon layer 18 is removed by “nitric acid + hydrofluoric acid” to thereby form the first silicon nitride layer 14. The pillars 19 of the silicon oxide film remain on the silicon nitride layer 12 (FIG. 1F). It is possible to use the fine pattern formed by the pillars 19 of the silicon oxide film as the final pattern. However, the first silicon nitride 12 is plasma-etched using the oxide film as a mask to form a fine pattern ( (Thickness of 500 °).
[0015]
Embodiment 2
The second embodiment shown in FIG. 2 is the same up to the step (e) in FIG. 1 of the first embodiment, and the first silicon nitride layer (thickness: 100 °) 26 and the oxide film 28 on the silicon substrate 25 remain. In the state (FIG. 2A, corresponding to step (f) of Example 1), plasma etching is performed using the silicon oxide film 28 as a mask (FIG. 2B), and the silicon oxide film 28 is further plasma-etched. , The first silicon nitride (width 500 °) 26a is left (FIG. 2C).
[0016]
Embodiment 3
Example 3 shown in FIG. 3 is an example in which a silicon wafer is used as the substrate 30, the first and second silicon nitride layers 31 and 33 are both 200 mm thick, and the polysilicon layer 32 is 400 mm thick. It is.
From the state of FIG. 3A (corresponding to FIG. 1D), the second silicon nitride layer 33 and the first silicon nitride 31 at the bottom of the groove 35 are removed (FIG. 3B). Then, the polysilicon layer 32 between the silicon oxide films 34, 34 is removed (FIG. 3C), and the first silicon nitride layer 31 in the gap 37 between the silicon oxide films 34, 34 is plasma-etched. (FIG. 3 (d)). At this time, the etching also proceeds on the exposed surface layer of the silicon wafer substrate 30 at the same time, and a concave portion 39 (for example, a depth of 300 °) is formed (the concave portion 39 in FIG. 3D). Then, even if the silicon nitride layer 31 disappears, the step due to the concave portion 39 is maintained.
[0017]
Further, when plasma etching is performed using the silicon oxide film 34 as a mask from the state of FIG. 3D, etching proceeds on other portions of the upper surface of the substrate 30 except for the portion masked by the silicon oxide film 34. As a result, a profile having three steps of A, B, and C due to the projection 40 and the depressions 41 and 42 is obtained (FIG. 3E).
By changing the type of plasma etching gas for the silicon nitride layer, the step between steps A and B can be appropriately adjusted in the range of 100 to 1000 °.
[0018]
Further, by combining this method of forming a fine pattern with highly anisotropic plasma etching, a grating as shown in FIG. 4A and other optical elements can be formed.
That is, by the method for forming a fine pattern of the present invention, an oxide layer having a very small width is formed at a fine pitch, and using this as a mask, plasma etching with high anisotropy is performed, so that a thickness of 3 to A 5 μm grating (which constitutes an appropriate optical element) may be formed at a depth of 3 to 5 μm.
Further, as shown in FIG. 4B, silicon oxide film layers having a height of 5 μm (thickness: 500 °) are arranged at a pitch of 1000 °, and a polysilicon layer 55 is sandwiched between a pair of silicon oxide film layers 53. It is also possible to easily form a pattern in which a large number of elements having an elliptical shape are arranged via the gap 54.
[0019]
【The invention's effect】
The effects of the present invention are summarized as follows for each of the claimed inventions.
1. According to the first aspect of the present invention, the thickness of the silicon oxide film is converted to the line width of the fine pattern. Since the silicon oxide film thickness is accurately controlled, the line width of the fine pattern can be controlled. Can be formed accurately and stably on the order of Å. Also, regardless of the exposure method, the line width of the formed silicon nitride can be divided into three by the interposition of the silicon oxide film, so that the density of the recording medium can be improved by that much, and Multifunctionalization can be achieved.
2. According to the second aspect of the invention, since the fine pattern profile is finally formed using the silicon nitride shape, the profile shape can be formed stably.
3. According to the third and fourth aspects of the present invention, it is possible to form a stamper having three steps by a silicon oxide film portion, a silicon nitride portion, and (silicon nitride + polysilicon + silicon nitride portion). Therefore, three-dimensional fine pattern position control is possible.
4. According to the fifth aspect of the invention, fine pattern processing with a line width of a wavelength level can be easily performed, so that a more inexpensive and high-performance optical element can be produced.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a procedure of a first embodiment.
FIG. 2 is a diagram schematically illustrating a procedure of a second embodiment.
FIG. 3 is a diagram schematically showing a procedure of a third embodiment.
FIG. 4 is a diagram schematically showing an application example of the present invention.
FIG. 5 is a diagram schematically showing a procedure of a conventional technique.
FIG. 6 is a diagram schematically showing a procedure of the prior art of FIG. 5;
[Explanation of symbols]
11: silicon substrate 12: silicon nitride 13: polysilicon 14: silicon nitride 15: groove 16: polysilicon 17: silicon oxide film 18: polysilicon 19: pillar of silicon oxide film 20: groove 21: silicon nitride

Claims (5)

Forming a silicon nitride layer on the substrate, forming a polysilicon layer thereon, further forming a silicon nitride layer,
Exposure and development to pattern the surface silicon nitride layer,
Etching the polysilicon layer using the surface silicon nitride layer as a mask,
Oxidation treatment in a diffusion furnace to form a silicon oxide film on the polysilicon layer,
Etch the nitride layer on the surface,
A method for forming a fine pattern, comprising removing a polysilicon layer between the silicon oxide films to leave the silicon oxide film. The method for forming a fine pattern according to claim 1,
A method for forming a fine pattern, characterized by selectively removing a silicon nitride layer using a remaining silicon oxide film as a mask and finally removing the silicon oxide film. The method for forming a fine pattern according to claim 1,
A method for forming a fine pattern, characterized by simultaneously etching a silicon nitride layer and a base substrate using a remaining silicon oxide film as a mask. The method for forming a fine pattern according to claim 1,
A fine pattern characterized by forming three layers having different heights by simultaneously etching the silicon nitride layer and the base substrate using the remaining silicon oxide film as a mask and finally removing the oxide film. Formation method. An optical element and an optical disk formed by using the method according to claim 1.

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