JP3258853B2 - Method of forming fine pattern and fine periodic pattern - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a fine pattern and a fine periodic pattern.

[0002]

2. Description of the Related Art A technique for forming a fine pattern is important as a technique for improving the performance of a semiconductor device. For example, it has been proposed to form a quantum wire or quantum box in order to improve the characteristics of a transistor.

FIG. 5 is a process chart showing a first example of a conventional method for forming a fine pattern. The method of forming this fine pattern is described in Jpn. J. Appl. Phys. Vol. 33 (1994) pp. 919 -924 Pa
rt 1, No. 1B, January 1994.

First, as shown in FIG. 5A, a positive resist is applied by spin coating on an InP substrate 21 having a crystal growth plane of (100) plane orientation, and a wavelength of 488 is applied.
The positive resist is periodically exposed by an interference exposure method using an Ar ion laser of nm as a light source. Thereby, a pattern of the stripe-shaped positive resist 22 parallel to the <01-1> direction is formed. The period of the pattern of the positive resist 22 is set to 1 μm.

[0005] As shown in FIG. 5 (b), the InP substrate 21 is etched using a mixture of hydrochloric acid, acetic acid and hydrogen peroxide (15 ° C.) at a ratio of 1: 2: 1 to form a V-shaped groove 2 having a triangular cross section.
Form 3 The inner surface of the V-groove 23 is formed into two types, a (111) plane and a (211) plane, by a surface treatment method. Thereafter, as shown in FIG. 5C, an InGaAs quantum wire is formed in the V groove 23 by a selective MBE growth method (molecular beam epitaxial growth method).

FIG. 6 is a process sectional view showing a second example of the conventional fine pattern forming method. The method of forming this fine pattern is described in Jpn.J.Appl.Phys.Vol.32 (1993) pp.6224-62.
27 Part 1, No. 12B, December 1993.

First, as shown in FIG. 6A, a GaAs substrate 31 is formed by electron beam exposure and wet chemical etching.
A V-shaped groove 32 is formed on the substrate. Each of the width and the depth of the V-shaped groove 32 is 40 to 60 nm. Thereafter, as shown in FIG. 6B, an AlAs layer 33 is grown in the V-shaped groove 32 by MOCVD (metal organic chemical vapor deposition). At this time, the (001) plane, the (110) plane, and the (1) plane
11) Due to the difference in growth rate from the surface, the groove 34 having a rectangular section
Is formed. The width of the groove 34 is 20 nm.

[0008] Thereafter, as shown in FIG.
A GaAs line 35 is formed in the inside, and an AlA layer is formed on the AlAs layer 33 and the GaAs line 35 as shown in FIG.
An s or AlGaAs cover layer 36 is formed. In this way, a GaAs / AlAs trench buried quantum wire having a width of about 20 nm is formed.

On the other hand, a distributed feedback semiconductor laser device having a diffraction grating provided near an active layer for the purpose of oscillating at a single wavelength has been developed. In this distributed feedback semiconductor laser device, the monochromaticity of the oscillating light is improved by utilizing the Bragg reflection on the diffraction grating.

In such a diffraction grating, the following relationship is required between the oscillation wavelength λ and the period の of the diffraction grating to cause Bragg reflection. Λ = m · λ / (2 · _ne ) (1) where m is a positive integer, and _ne is an equivalent refractive index inside the semiconductor laser device. In the above equation (1), the case where m = 1 is called a first-order diffraction grating, and the case where m = 2 is called a second-order diffraction grating, and the period of the second-order diffraction grating is 2 times that of the first-order diffraction grating.
Double. As described above, there are first to higher order diffraction gratings, but the Bragg reflectance increases as the order of the diffraction grating decreases. Therefore, it is most desirable to form a first-order diffraction grating.

FIG. 7 is a process sectional view showing a conventional method of forming a diffraction grating in a distributed feedback semiconductor laser device.
The method of forming this diffraction grating is ELECTRONICS LETTERS 7th
July1988 Vol.24, No.14, pp.842-843.

As shown in FIG. 7A, a GaAs substrate 4
A photoresist film is applied on the substrate 1 by a spin coating method, and the photoresist film is periodically exposed by an interference exposure method using a 325 nm wavelength He-Cd laser. Thus, a diffraction grating made of the photoresist 42 is formed. The period of the diffraction grating is 240 nm, which is the period of the secondary diffraction grating in the distributed feedback semiconductor laser device.

Next, as shown in FIG.
CVD (Electron Cyclotron Resonance Chemical Vapor Deposition)
To form a silicon nitride film (SiN) on the GaAs substrate 41
_X film) 43 is formed.

Thereafter, as shown in FIG. 7C, the silicon nitride film 43 on and near the photoresist 42 is selectively etched using buffered hydrofluoric acid. Thus, a periodic mask including the photoresist 42 and the silicon nitride film 43 is formed. The period of the mask is the same as that of the photoresist 42 formed in the process of FIG.
周期 of the period of the diffraction grating composed of

Finally, as shown in FIG. 7D, after the GaAs substrate 41 is etched using the photoresist 42 and the silicon nitride film 43 as a mask to form a groove 44, the photoresist 42 and the silicon nitride film 43 are removed. Remove. As a result, the period 120 on the GaAs substrate 41 is obtained.
A first order diffraction grating of nm is produced.

[0016]

In the conventional method for forming a fine pattern shown in FIG. 5, an InP is formed by using an interference exposure method.
A V groove 23 having a period of 1 μm is formed on a substrate 21. When the interference exposure method is used, there is a limit to the minimum pattern size.

For example, a cycle using a two-beam interference exposure method
When forming a typical groove, the groove period Λ ₀Satisfies the relationship
Add. Λ₀= Λ₀/ 2n · sin θ (2) where λ₀Is the wavelength of the laser light source, θ is the intersection of the two light beams
Angle, n is the refractive index of the space medium above the sample surface (resist film)
It is.

From the above equation (2), the groove period Λ ₀ is limited to が of the wavelength λ ₀ of the laser light source. Therefore, when an Ar laser having a wavelength of 488 nm is used as the laser light source, the groove period Λ ₀ is limited to 244 nm. Therefore, it is difficult to form the V-groove 23 to a width of about several tens nm or less used for a quantum wire or the like by a normal edging method.

In the conventional method for forming a fine pattern shown in FIG. 6, a groove 34 having a rectangular cross section with a width of 20 nm is formed by MOCVD utilizing the difference in growth rate depending on the plane orientation. Therefore, in this method, complicated crystal growth control is required for forming the groove 34.

As described above, it is difficult to form a fine pattern of about several tens of nm or less with high accuracy by the conventional photolithography technique. Further, in the conventional method of forming a diffraction grating shown in FIG. 7, by selectively etching the silicon nitride film 43 above and near the photoresist 42 in the step of FIG. A mask having a half period of the diffraction grating of the photoresist 42 formed in the step is formed. However, the difference between the composition of the silicon nitride film 43 deposited on the photoresist 42 and the silicon nitride film 43 deposited on the GaAs substrate 11 and the difference in the etching rate using buffered hydrofluoric acid are not clear.

Therefore, GaAs is used in the step of FIG.
Photoresist 42 on substrate 41 and silicon nitride film 43
It is difficult to keep the distance between them constant. As a result, G
It is not easy to uniformly form a diffraction grating having a half period on the aAs substrate 41.

Therefore, in the semiconductor laser device, the period 2
It is relatively easy to form a secondary diffraction grating of about 40 nm, but it is difficult to form a primary diffraction grating of about 120 nm period.

An object of the present invention is to provide a method for forming a fine pattern accurately and easily. Another object of the present invention is to provide a method for forming a fine periodic pattern uniformly and easily.

[0024]

According to a method of forming a fine pattern according to the present invention, a step having an upper surface, a lower surface and an inclined side surface is formed in an underlayer, and a mask material is formed on at least the lower surface of the step except for the upper surface of the step. after forming the, is formed in the underlying layer
The upper surface of the step is etched to form a pattern along the edge of the mask material on the underlying layer.

The etching is preferably performed such that the upper surface of the step and the lower surface of the step are flush. After the mask material is formed on the lower surface of the step, the upper surface of the step
A groove may be formed along the edge of the mask material in the underlayer by etching the surface and the side surface .

Alternatively, after a mask material is formed on the lower surface and the inclined side surface of the step, the step formed on the underlayer is formed.
May be formed on the underlayer by etching the upper surface of the mask material.

The underlayer may be a substrate or a mask film formed on the substrate. The method for forming a fine periodic pattern according to the present invention includes forming a concave / convex pattern in which a plurality of convex portions having a trapezoidal cross section are periodically arranged on an underlayer, and forming at least the convex portions except for the upper surfaces of the plurality of convex portions. After a mask material is formed on the bottom surface of the intervening concave portion, a plurality of convex portions are etched to form a periodic pattern along the edge portion of the mask material on the underlying layer.

The etching is preferably performed such that the upper surfaces of the plurality of convex portions are flush with the bottom surfaces of the concave portions.

[0029]

In the method for forming a fine pattern according to the present invention, after forming a mask material on at least the lower surface of the step except for the upper surface of the step, the underlying layer is etched from the upper surface.
At this time, when the mask material is not formed on the inclined side surface, the inclined side surface is simultaneously etched. Thereby, a groove having an inner surface inclined at substantially the same angle as the side surface is formed between the lower surface region and the upper surface region of the step of the underlayer.

When a mask material is formed on the lower surface of the step and on the inclined side surface, a region below the inclined side surface remains without being etched. As a result, a protrusion having an outer surface inclined at substantially the same angle as the side surface is formed between the lower surface region and the upper surface region of the step of the underlayer.

In the method of forming a fine periodic pattern according to the present invention, after forming a mask material on at least the bottom surface of the concave portion between the convex portions except for the upper surface of the plural convex portions, the plural convex portions are etched. Thus, a periodic pattern is formed on the underlayer along the edge of the mask material. Since this periodic pattern is formed between the projections and the depressions, the period of the periodic pattern is half the period of the uneven pattern.

When the mask material is not formed on the inclined side surface between the concave portion and the convex portion, a periodic pattern including a plurality of grooves is formed. When the mask material is formed on the inclined side surface between the concave portion and the convex portion, a periodic pattern having a plurality of protrusions is formed.

[0033]

FIG. 1 is a process sectional view showing a method of forming a fine periodic pattern according to a first embodiment of the present invention.

First, as shown in FIG. 1A, a photoresist film is applied and baked on a GaAs substrate 1 having a crystal growth surface of (100) plane orientation, and then the photoresist film is formed by a two-beam interference exposure method. Is periodically exposed. As a result, a stripe-shaped periodic pattern of the photoresist 2 along the <01-1> direction is formed. The period L of this periodic pattern is 300 nm.

Next, as shown in FIG. 1B, the GaAs substrate 1 is etched using an etchant having a plane orientation dependency.
Etch to a depth of 0 nm. Thereby, GaA
A plurality of concave portions 3 having an inverted trapezoidal cross section are periodically formed in the s substrate 1. When a mixed solution of phosphoric acid, hydrogen peroxide and water is used as an etching solution, the mixing ratio of phosphoric acid and hydrogen peroxide is set in the range of 2: 1 to 1: 8, and the mixing ratio of hydrogen peroxide and water is set. Is set to about 1: 100. Note that a mixed solution of ammonium hydroxide, hydrogen peroxide, and water or a mixed solution of bromo and methanol may be used as the etching solution.

Thereafter, as shown in FIG.
A 10 nm-thick silicon nitride film (SiN _x film) 4 is deposited as a mask material on the entire surface of the GaAs substrate 1 and the photoresist 2 by the CVD method. Here, the coverage of the silicon nitride film 4 on the inclined side surface at the step portion is controlled by adjusting the substrate temperature during deposition.

For example, the substrate temperature was set to 25 ° C.
In this case, as shown in FIG.
Is not deposited on the inclined side surface of the step. Deposition conditions
The high frequency output is 400 W and the degree of vacuum is 10^-3
Torr and SiH_FourAnd N _TwoIs assumed to be 1.

Next, as shown in FIG.
The substrate 1 is immersed in acetone and a resist stripper, and the photoresist 2 and the silicon nitride film 4 thereon are removed by a lift-off process. Thereby, the upper surface of the convex portion 1a of the GaAs substrate 1 is exposed.

Finally, as shown in FIG.
The exposed convex portion 1a of the s-substrate 1 is etched to a thickness of 30 nm to form a V-shaped groove 5 along the edge of the photoresist 2 in a lower region on both side surfaces of the convex portion 1a. As the etchant, a mixture of phosphoric acid, hydrogen peroxide and water having the same mixing ratio as described above is used. After the etching, the silicon nitride film 4 is removed using buffered hydrofluoric acid.

In this case, as shown in FIG. 2, since the silicon nitride film 4 is not formed on the inclined side surfaces on both sides of the convex portion 1a, the upper surface and the inclined side surface of the convex portion 1a move in the direction of arrow A. Etched. The upper surface of the convex portion 1a is the concave portion 3
When the etching proceeds by the thickness t until it becomes flush with the bottom surface of the silicon nitride film 4, a V-shaped groove 5 is formed below the edge of the silicon nitride film 4. At the time of this etching, the convex portion 1a
Has a large exposed portion, so that the influence of the stagnation of the etching solution or etching gas is small. Therefore, the groove 5 is formed uniformly.

Thus, a plurality of fine grooves 5 are periodically formed on the same plane of the GaAs substrate 1. The width W of the groove 5 is 20 nm, and the depth h is 15 nm. The period L2 of the groove 5 is 1/2 of the period L of the periodic pattern of the photoresist 2 formed in the step of FIG.

The periodic pattern of the grooves 5 can be used as a primary diffraction grating. Thus, a first-order diffraction grating is formed from a second-order diffraction grating. When the substrate temperature is set to 100 ° C. in the step of FIG. 1C, as shown in FIG. 3, the silicon nitride film 4 is also formed on the inclined side surfaces on both sides of the projection 1a. In this case, FIG.
When the etching is performed in the step (e), the upper surface of the projection 1a is etched in the direction of arrow B as shown in FIG. At this time, since the inclined side surface of the convex portion 1a is not etched, the etching proceeds by the thickness t until the upper surface of the convex portion 1a becomes flush with the bottom surface of the concave portion. Inverted V-shaped projection 7
Is formed.

In this way, fine projections 7 are periodically formed on the same plane of the GaAs substrate 1. The period of the protrusion 7 is the same as that of the photoresist 2 formed in the process of FIG.
Becomes 1/2 of the period L of the pattern, and becomes 150 nm.

FIG. 4 is a process sectional view showing a method of forming a fine periodic pattern according to the second embodiment of the present invention. First, as shown in FIG. 4A, a SiO ₂ film 12 having a thickness of 40 nm is formed on a GaAs substrate 11 having a crystal growth surface of a plane orientation (100) by an electron beam evaporation method. Then, after coating and baking a photoresist film on the SiO ₂ film 12, the photoresist film is periodically exposed in a stripe shape by an interference exposure method. Thereby, <01-
1> A periodic pattern of the photoresist 13 along the direction is formed. The thickness of the photoresist 13 after development is 7
It is about 0 nm. The period L of the periodic pattern of the photoresist 13 is 300 nm.

Next, as shown in FIG. 4B, the SiO ₂ film 12 is formed to a depth of 30 by RIE (reactive ion etching) using an etching gas mainly composed of CF _4.
Etch to nm. Thereby, the SiO ₂ film 12
A plurality of concave portions 14 having an inverted trapezoidal cross section are formed periodically.
The etching conditions were a pressure of 5 × 10 ¹² torr, a high frequency output of 80 W, and an etching rate of 35 n.
m / min.

Next, as shown in FIG.
By a CVD method, a 10-nm-thick silicon nitride film (SiN _{x) is formed on} the entire surface of the SiO ₂ film 12 and the photoresist 13.
A film 15 is deposited. The deposition conditions are the same as the deposition conditions in the step of FIG. 1C in the first embodiment.

Thereafter, as shown in FIG.
The substrate 11 is immersed in acetone and a resist stripper, and the photoresist 13 and the silicon nitride film 15 thereon are removed by a lift-off process. Thereby, SiO ₂
The upper surface of the projection 12a of the film 12 is exposed.

Next, as shown in FIG. 4 (e), SiO ₂ by using an etching gas mainly composed of CF ₄ and O ₂
The entire surface of the film 12 and the silicon nitride film 15 are etched. In this case, the SiO ₂ film 12 and the silicon nitride film 1
Etching is performed under the condition that the ratio of the etching rates of No. 5 is about 3: 1. Thereby, the protrusions 12 of the SiO ₂ film 12 are formed.
A groove 16 is formed in a lower region of the side surface of FIG.

Next, as shown in FIG. 4 (f), SiO ₂
The GaAs substrate 11 is etched through the grooves 16 formed in the film 12. Thus, a V-shaped groove 17 is formed in the GaAs substrate 11. It is formed. As the etchant, phosphoric acid having the same mixing ratio as in the first embodiment,
30 nm is etched using a mixed solution of hydrogen peroxide and water. After the etching, the SiO ₂ film 12 and the silicon nitride film 15 are removed using buffered hydrofluoric acid.

Thus, fine grooves 17 are periodically formed on the same plane of the GaAs substrate 11. The width W of the groove 17 is 20 nm, and the depth h is 15 nm. The period L2 of the groove 17 is 1/1/3 of the period L of the periodic pattern of the photoresist 13 formed in the step of FIG.
2, which is 150 nm.

The periodic pattern of the grooves 17 can be used as a first-order diffraction grating. Thus, a first-order diffraction grating is formed from a second-order diffraction grating. According to the method of forming a fine periodic pattern according to the first and second embodiments, it is possible to form a fine pattern having a size equal to or smaller than a limit of a minimum pattern size of the photolithography technique. Therefore, several tens n required for quantum wires and quantum boxes
A fine pattern of about m or less can be accurately and easily formed.

Further, according to the method for forming a fine periodic pattern of the first and second embodiments, the primary diffraction grating can be formed uniformly and easily based on the secondary diffraction grating. Therefore, by applying this method of forming a fine periodic pattern to a distributed feedback semiconductor laser device or a distributed reflection semiconductor laser device, characteristics such as threshold current and external differential efficiency can be improved.

According to the first and second embodiments, GaAs
Since a fine pattern with a width of about 20 nm can be obtained on both sides of each convex portion on the s substrate, it is possible to form a primary diffraction grating with a period of about 100 nm.

In the first and second embodiments, GaAs is used.
s substrate is used, but instead of the GaAs substrate, Al
A substrate made of another semiconductor crystal such as GaAs, InP, Si, Ge or a substrate made of a dielectric crystal such as LiNbO ₃ can also be used.

In the first embodiment, the underlayer is made of GaAs.
In the second embodiment, the underlayer is made of GaAs.
Although the case where the SiO ₂ film 12 is formed on the substrate 11 has been described, the underlying layer may be a semiconductor layer.

[0056]

As described above, according to the present invention, a fine pattern can be formed accurately and easily.
In particular, when the mask material is not formed on the inclined side surface, a fine groove can be formed. When a mask material is formed on the inclined side surface, a fine projection can be formed.

Further, according to the present invention, a periodic pattern having a half period of the periodic uneven pattern can be uniformly and easily formed.

[Brief description of the drawings]

FIG. 1 is a process sectional view showing a method for forming a fine periodic pattern according to a first embodiment of the present invention.

FIG. 2 is a view showing a process of forming a V-shaped groove.

FIG. 3 is a view showing a process of forming an inverted V-shaped protrusion;

FIG. 4 is a process sectional view showing a method for forming a fine periodic pattern in a second embodiment of the present invention.

FIG. 5 is a process cross-sectional view showing a first example of a conventional method for forming a fine pattern.

FIG. 6 is a process cross-sectional view showing a second example of a conventional method for forming a fine pattern.

FIG. 7 is a process sectional view showing a conventional diffraction grating forming method.

[Explanation of symbols]

1,11 GaAs substrate 1a, 12a convex part 2,13 photoresist 3,14 concave part 4,15 silicon nitride film 5,16,17 groove 7 protruding 12 SiO ₂ film

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-3-268357 (JP, A) JP-A-60-206138 (JP, A) JP-A-2-295122 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01L 21/3065

Claims (4)

(57) [Claims] 1. A step having an upper surface, a lower surface, and an inclined side surface is formed in an underlayer, and a mask material is formed on at least the lower surface of the step except for the upper surface of the step, and then the mask formed on the underlayer is formed. A method of forming a fine pattern, comprising: forming a pattern along an edge of the mask material on the underlayer by etching an upper surface of a step . 2. After forming a mask material on the lower surface of the step, the upper surface and the side surface of the step formed on the base layer are etched to form a groove along the edge of the mask material in the base layer. The method for forming a fine pattern according to claim 1, wherein Forming a mask material on the lower surface of the step and on the inclined side surface, and then forming the mask material on the underlayer ;
2. The method for forming a fine pattern according to claim 1, wherein an upper surface of the step is etched to form a protrusion on the underlayer along an edge of the mask material. 4. An uneven pattern in which a plurality of convex portions having a trapezoidal cross section are periodically arranged on an underlayer, and at least on the bottom surface of the concave portion between the convex portions except for the upper surface of the plurality of convex portions. A method for forming a fine periodic pattern, comprising: forming a periodic pattern along an edge of the mask material on the underlayer by etching the plurality of protrusions after forming the mask material.