JPH07140341A - Method of forming Y-shaped pattern - Google Patents

Abstract

(57) [Summary] [Object] To provide a technique for forming a mask pattern including a Y-shaped branch branched at an acute angle. A resist pattern 102 including a first branch made of a first resist film 101 is formed on a semiconductor substrate 100 by using a normal lithography technique. After curing the resist pattern 102 including the first branch, a resist pattern 104 including the second branch made of the second resist film 103 is formed by using a normal lithography technique. As a result, a Y-shaped resist mask having a first branch and a second branch branched at an acute angle can be formed. As a Y-shaped resist mask having a first branch and a second branch branched at an acute angle can be formed on the semiconductor 100 substrate, an acute branch is formed on the semiconductor substrate 100 by etching using the mask. It is possible to form an optical waveguide having a Y-shaped branch portion having the first branch and the second branch. Thereby, the optical loss caused by the branch portion can be significantly reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a Y-shaped pattern, and particularly to a Y-shaped pattern which is extremely useful as a technique for forming a dry etching mask when an optical waveguide branched at an acute angle is formed on a substrate. And a method of forming the same.

[0002]

2. Description of the Related Art When an optical waveguide having a Y-shaped branch having a first branch and a second branch is formed on a semiconductor substrate, the resist film has a first branch and a second branch. After forming the Y-shaped pattern, the semiconductor layer to be the waveguide is etched using the resist mask to form a Y-shaped optical waveguide having a first branch and a second branch.
For example, IEE Photonics Technology Letters Vol. 2 (1990) pages 32 to 34.
As described on the page, a Y-shaped branched resist pattern having a half angle of 4.2 ° is formed on a semiconductor substrate by using a normal photolithography technique, and then the compound semiconductor layer is etched using the resist pattern as a mask. The Y-shaped branched optical waveguide is formed. Further, it is known that in the above-mentioned Y-shaped branched optical waveguide, the radiation loss can be significantly reduced by making the branch angle acute.

[0003]

According to the above-mentioned ordinary optical lithography technique, Y having the first branch and the second branch is formed.
When forming a resist pattern having a V-shaped branch, a photomask having a Y-shaped branch pattern having a first branch and a second branch was used to form a resist pattern on the substrate by a contact exposure method or a reduced projection exposure method. A latent image is formed on the resist film. Then, a desired resist pattern is formed by performing development, washing with water and drying. However, when a resist pattern having a Y-shaped branch having the first branch and the second branch described above is formed by a normal optical lithography technique, as shown in FIG. 8, the first branch and the second branch are separated. The resist pattern between them is not sufficiently resolved, and a Y-shaped branch pattern that branches at an acute angle cannot be formed. Therefore, in the Y-shaped optical waveguide formed by using the resist mask, there is a problem that the radiation loss increases due to the Y-shaped branched portion which is distorted at an obtuse angle and branched.

An object of the present invention is to provide a technique for forming an etching mask pattern for forming a Y-shaped branch path having a first branch and a second branch which are acutely branched.

[0005]

The above-described object is achieved by using a normal lithography technique having a good alignment accuracy with respect to a pattern including a first branch formed on a substrate using the usual lithography technique. This can be achieved by forming a pattern including two branches.

[0006]

When forming the Y-shaped branch pattern having the first branch and the second branch which are branched at an acute angle, the pattern including the first branch and the pattern including the second branch are separately formed. Therefore, as shown in FIG. 8, the resolution between the first branch pattern and the second branch pattern is not limited by the pattern resolution limit (0.5 to 1 μm) of the usual optical lithography technique. Therefore, the first
It becomes possible to form a pattern having a Y-shaped branch having a second branch and a second branch.

[0007]

【Example】

(Embodiment 1) An embodiment of the present invention will be described with reference to the process top view shown in FIG. A first resist film 101 (for example, a negative resist TH manufactured by Tokyo Ohka Co., Ltd.) is formed on a semiconductor substrate 100.
MR-iN2000) was spin-coated (FIG. 1 (a)).
Next, by a normal photolithography technique using a photomask having a pattern including a first branch which is a part of a Y-shaped branch pattern having a first branch and a second branch,
A resist pattern 102 including the first branch was formed (FIG. 1B). Next, the resist pattern 102 including the first branch was baked (110 ° C., 10 minutes). After that, the second resist film 103 was spin-coated (FIG. 1C). At this time, since the resist pattern 102 including the first branch made of the first resist film 101 has been hardened by the baking treatment (110 ° C., 10 minutes), the pattern is not deformed or deteriorated. Then a second part that is part of a Y-shaped branch pattern having a first branch and a second branch.
A resist pattern 104 including the second branch was formed by a normal photolithography technique using a photomask having a pattern including the second branch (FIG. 1D). As a result, a Y-shaped resist mask having a first branch and a second branch branched at an acute angle could be formed. In this embodiment, the resist pattern 102 including the first branch and the resist pattern 104 including the second branch are combined by using a lithography alignment technique. The alignment accuracy at that time is ± 0.1 μm (3σ) when the normal reduction projection exposure method is used, which is sufficiently smaller than the resolution limit of optical lithography. In order to prevent a fatal pattern defect even when misalignment occurs between the two layers, for example, as shown in FIG. 8, a resist pattern 102 including a first branch and a resist pattern 104 including a second branch are formed. It is effective to design the photomask so that a part thereof overlaps in advance. Further, in consideration of the misalignment of the resist pattern 104 including the second branch with respect to the resist pattern 102 including the first branch, a plurality of offsets are provided within a range of ± 0.1 μm in the x-axis and y-axis directions. By using the photomask having the pattern including the second branch, the Y-shaped resist pattern having the first branch and the second branch formed with almost perfect alignment accuracy can be formed with a certain yield. .

In the present invention, the resist pattern 10 including the first branch when the second resist film 103 is spin coated.
Bake treatment (110 ℃, 1
However, by changing the solvent of the first resist film 101 and the solvent of the second resist film 103, it is possible to prevent the deformation and deterioration of the resist pattern 102 including the first branch. .

Further, although the reduction projection exposure method using a photomask is adopted as the lithography technique in this embodiment, a direct drawing method using a charged particle beam such as an electron beam or an ion beam can be adopted. Needless to say.

Although the above-described embodiment has been described with respect to the Y-shaped pattern having one branch as shown in FIG. 1, it is needless to say that the same can be applied to a pattern having a plurality of branches.

(Embodiment 2) An embodiment of the present invention will be described with reference to the process top view shown in FIG. A first resist film 201 (for example, a negative resist THMR-iN2000 manufactured by Tokyo Ohka Co., Ltd.) was spin-coated on the semiconductor substrate 200 (FIG. 2A). Then Y with a first branch and a second branch
The resist pattern 202 including the first branch is formed by a normal photolithography technique using a photomask having a pattern including the first branch which is a part of the letter-shaped branch pattern.
Was formed (FIG. 2 (b)). Next, an ultraviolet irradiation device (for example, Chemitronics model 380H) is applied to the sample.
Was subjected to ultraviolet irradiation treatment. Thereby, the first
In particular, the vicinity of the surface of the resist pattern 202 including the branches is cured. After that, the second resist film 203 was spin-coated (FIG. 2C). At this time, the first resist film 20
Since the resist pattern 202 including the first branch consisting of 1 has been hardened by the ultraviolet irradiation treatment, the pattern does not deform or deteriorate. Then, a resist pattern including the second branch is formed by a normal photolithography technique using a photomask having a pattern including the second branch which is a part of the Y-shaped branch pattern having the first branch and the second branch. Two
04 was formed (FIG. 2 (d)). As a result, a Y-shaped resist mask having a first branch and a second branch branched at an acute angle could be formed. In this embodiment, the resist pattern 202 including the first branch and the resist pattern 204 including the second branch are combined by using a lithography alignment technique. The alignment accuracy at that time is ± 0.1 μm (3σ) when the normal reduction projection exposure method is used, which is sufficiently smaller than the resolution limit of optical lithography. Also in this embodiment, as in the first embodiment, as shown in FIG. 9, the photomask is designed such that the resist pattern 202 including the first branch and the resist pattern 204 including the second branch partially overlap each other in advance. It goes without saying that is effective.

(Embodiment 3) An embodiment of the present invention will be described with reference to the process top view shown in FIG. A first resist film 301 (for example, a negative resist THMR-iN2000 manufactured by Tokyo Ohka Kabushiki Kaisha) was spin-coated on the semiconductor substrate 300 (FIG. 3A). Then Y with a first branch and a second branch
The resist pattern 302 including the first branch is formed by a normal photolithography technique using a photomask having a pattern including the first branch which is a part of the letter-shaped branch pattern.
Was formed (FIG. 3 (b)).

Next, the surface of the sample was irradiated with Ga ions using an ion implanter. Ion implantation conditions are a dose amount of 10 ¹⁰ to 10 ¹² ions / cm ₂ , and an acceleration energy of 20 to
It is 50 keV. As a result, the resist pattern 302 including the first branch, particularly near the surface, is cured. After that, the second resist film 303 was spin-coated (see FIG. 3).
(C)). At this time, the pattern is not deformed or deteriorated.
Then, a resist pattern including the second branch is formed by a normal photolithography technique using a photomask having a pattern including the second branch which is a part of the Y-shaped branch pattern having the first branch and the second branch. 304 was formed (FIG.3 (d)). As a result, a Y-shaped resist mask having a first branch and a second branch branched at an acute angle could be formed.
In this embodiment, the resist pattern 302 including the first branch
And the resist pattern 304 including the second branch are combined by using a lithography alignment technique. The alignment accuracy at that time is ± ± when using the normal reduction projection exposure method.
It is 0.1 μm (3σ), which is sufficiently smaller than the resolution limit of optical lithography. Also in this embodiment, as described in the first embodiment, as shown in FIG. 8, a photomask is used so that a part of the resist pattern 302 including the first branch and the resist pattern 304 including the second branch are overlapped in advance. It goes without saying that designing is effective.

(Embodiment 4) An embodiment of the present invention will be described with reference to the process top view shown in FIG. A SiO ₂ film (thickness of 500 nm) is formed on the semiconductor substrate 400 by the usual CVD method.
401 was deposited (FIG. 4A). Next, by a normal lithography and metal deposition method using a photomask having a pattern including the first branch which is a part of the Y-shaped branch pattern having the first branch and the second branch, the first An Al film pattern (50 nm thick) 402 including branches was formed by lift-off (FIG. 4B). Then, the second part that is part of the Y-shaped branch pattern having the first branch and the second branch.
The Al film pattern (50 nm thick) 403 including the second branch was formed by the lift-off method by the ordinary photolithography and the metal deposition method using the photomask having the pattern including the branch (FIG. 4C). ). As a result, a Y-shaped Al film pattern having a first branch and a second branch branched at an acute angle could be formed. Then, the first branch and the second
Using a Y-shaped Al film pattern having a branch of
The SiO ₂ film (500 nm thick) 401 was dry-etched (FIG. 4D). At this time, by using a fluorine-based gas such as C ₂ F ₆ and CHF ₃ as an etching gas, the SiO ₂ film (500 nm thick) 401 can be etched with almost no etching of the Al film. Further, here, the pattern including the first and second branches is formed using the Al film, but it goes without saying that a metal film having etching resistance can be applied instead of the Al film.

The first branch and the second branch which are branched at an acute angle as described above.
As for the resist pattern used for forming the Y-shaped Al film pattern having the branch of FIG.
A including the first branch as in the resist pattern shown in
It goes without saying that it is effective to design the photomask so that the l film pattern 402 and the Al film pattern 403 including the second branch partially overlap in advance. .

Further, in the present embodiment, the reduction projection exposure method using a photomask is adopted as the lithography technique, but a direct drawing method using a charged particle beam such as an electron beam or an ion beam can be adopted. Needless to say.

(Embodiment 5) One embodiment of the present invention is a top view of the optical waveguide shown in FIG. 5 and a process diagram of the element cross section at the broken line AA 'in FIG. 5 shown in FIGS. Will be explained. On the n-type InP substrate 600, the n-type InAlAs layer 601, InGaAs and InA are formed by MO-MBE method.
1A multiple quantum well layer 602, p-type InAlA
The s layer 603 and the p-type InGaAs layer 604 were sequentially stacked (FIG. 6A). Then, using the conventional CVD method, S
An iO ₂ film (700 nm thick) 605 was formed (FIG. 6).
(B)). Next, using a photolithography method using a photomask having a pattern including the first branch which is a part of the Y-shaped branch pattern having the first branch and the second branch, the first lithography is performed using a metal deposition method. Al film pattern including branches (50
(nm thickness) 606 was formed by lift-off (FIG. 6).
(C)). Then, the second branch is formed by ordinary photolithography and metal deposition using a photomask having a pattern including the second branch which is a part of the Y-shaped branch pattern having the first branch and the second branch. Al film pattern containing
607 (thickness of 50 nm) 607 was formed using the lift-off method (FIG. 6D). As a result, the Al film pattern for forming the optical waveguide having the Y-shaped branch portion having the first branch and the second branch branched at the acute angle shown in FIG. 5 was formed. Next, RIE (Reac) using C ₂ F ₆ and CHF ₃ gas
The SiO ₂ film 605 was etched by tive ion etching using the Al film patterns 606 and 607 as masks (FIG. 7E). Then RIBE using Cl ₂ gas (R
The SiO ₂ film 6 is formed by using the eactive ion beam etching method.
05 as a mask, p-type InGaAs layer 604, p-type I
The nAlAs layer 603 and the multiple quantum well layer 602 made of InGaAs and InAlAs were sequentially etched (FIG. 7F). As a result, the optical waveguide having the Y-shaped branch portion having the first branch and the second branch branched at the acute angle shown in FIG. 5 could be formed. Next, a p-type ohmic electrode 608 was formed on the p-type InGaAs layer 604 in a predetermined region of the optical waveguide shown in FIG. 5, and an n-type ohmic electrode 609 was formed on the back surface of the n-type InP substrate 600 (FIG. 7 (g)). . As a result, a Mach-Zehnder interferometric optical modulator could be manufactured. Mach-Zeh produced by this example
In the nder interferometer type optical modulator, since the Y-shaped branch portion is formed without distortion at an acute angle of 1 to 2 °, the loss of light due to the Y-shaped branch portion is extremely small and it has good characteristics.

[0018]

As described above, according to the present invention, it is possible to form a pattern having a Y-shaped branch branched at an acute angle of 1 to 4 ° or less. Therefore, the pattern is used as a mask. By processing the optical waveguide in this manner, it becomes possible to form an optical waveguide having a Y-shaped branch portion branched at an acute angle with small light loss.

[Brief description of drawings]

FIG. 1 is a process top view of a first embodiment.

FIG. 2 is a process top view of the second embodiment.

FIG. 3 is a process top view of the third embodiment.

FIG. 4 is a process top view of the fourth embodiment.

FIG. 5 is a top view of an optical waveguide of Example 5.

FIG. 6 is a process sectional view I of the fifth embodiment.

FIG. 7 is a process sectional view II of the fifth embodiment.

FIG. 8 is a Y-shaped branch pattern shape according to the related art.

FIG. 9 shows a first branch pattern and a second branch pattern on a photomask.

Claims (9)

[Claims] 1. A method of forming a Y-shaped pattern having a first branch and a second branch that branch at an acute angle, the step of forming a pattern including the first branch on a substrate, and then the second branch. A method for forming a Y-shaped pattern, which includes the step of forming a pattern including the pattern. 2. A desired Y-shaped pattern is formed by overlapping at least a part of the pattern including the first branch and the pattern including the second branch. Method for forming Y-shaped pattern. 3. A first substrate formed on a substrate by a lithographic technique.
Forming a resist pattern containing the second branch, then hardening the resist pattern containing the first branch, and then forming a resist pattern containing the second branch. The method for forming a Y-shaped pattern according to claim 1. 4. The method according to claim 3, wherein the step of curing the resist pattern including the first branch includes a step of subjecting the resist pattern to a heat treatment at a temperature higher or longer than an ordinary post bake. A method of forming a Y-shaped pattern. 5. The method of forming a Y-shaped pattern according to claim 3, wherein the step of curing the resist pattern including the first branch includes the step of irradiating the resist pattern with ultraviolet light. 6. The method of forming a Y-shaped pattern according to claim 3, wherein the step of curing the resist pattern including the first branch includes a step of irradiating the resist pattern with ions. 7. A method for forming a Y-shaped pattern having a first branch and a second branch that branch at an acute angle on the substrate,
The method includes forming a metal pattern including the first branch on the substrate by using a lift-off method, and then forming a metal pattern including the second branch by using a lift-off method. The method for forming a Y-shaped pattern according to claim 1. 8. A step of forming an insulating film on a semiconductor layer formed on a substrate, a step of forming a metal pattern including a first branch on the insulating film by using a lift-off method, and then a lift-off method. Forming a metal pattern including the second branch using the above, and then etching the insulating film using the metal pattern including the first branch and the metal pattern including the second branch as a mask. The method for forming a Y-shaped pattern according to claim 7, further comprising the step of etching the semiconductor layer using the insulating film as a mask. 9. A step of forming an insulating film of a silicon oxide film or a silicon nitride film on a III-V group compound semiconductor layer formed on a substrate, and a first branch on the insulating film by using a lift-off method. A step of forming an Al film pattern including the second branch, followed by a step of forming an Al film pattern including the second branch using a lift-off method, and then the first branch using a dry etching technique using an F-based gas. A step of etching the insulating film by using the Al film metal pattern including Al and the Al film pattern including the second branch as a mask, and then etching the III-V compound semiconductor layer by using the insulating film as a mask. The method for forming a Y-shaped pattern according to claim 7, further comprising: