JPH02128487A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of steps in a waveguide layer to improve a semiconductor device in performance by a method wherein a negative photoresist and a positive photoresist forming a periodic stripe-like pattern are exposed to light and developed, and a semiconductor substrate is etched using both residual resist films as mask. CONSTITUTION:A positive photoresist film 2 is applied onto a semiconductor substrate 1, which is exposed to laser rays to form a periodic stripe-like pattern of the resist film 2. Next, a negative photoresist film 3 is applied to fill the gap of the stripe-like pattern of the film 2. Then, the resist films 2 and 3 are exposed to light through a mask 4. In this process, the mask 4 is so arranged as to make its ends parallel with the stripes. Next, the resist films 2 and 3 are developed respectively to remove the exposed resist film 2 and the non- exposed resist film 3. And, the substrate 1 is etched using the resist films 2 and 3 left unremoved as a mask, and a waveguide layer 5, an active layer 6, and a clad layer 7 are formed, consequently a phase shift distributed feedback type laser can be improved in performance.

Description

[Detailed Description of the Invention] [Summary] Regarding a method of manufacturing a semiconductor device, particularly a method of manufacturing a phase-shifted distributed feedback laser that oscillates at a single wavelength, the present invention relates to a method of manufacturing a phase-shifted distributed feedback laser that oscillates at a single wavelength. A process of coating a positive photoresist film on a semiconductor substrate and forming a periodic striped pattern of the positive photoresist film using an exposure means, and a process of coating a negative photoresist film on a semiconductor substrate. , a step of filling in the spaces between the periodic striped patterns, and a step of exposing negative photoresist and positive photoresist substantially parallel to the periodic striped pattern, covering a part of the periodic stripe pattern and exposing the other part. and developing the negative photoresist film and the positive photoresist film respectively, removing the exposed positive photoresist, and removing the unexposed negative photoresist, and masking the remaining positive and negative photoresist films. and a step of etching the semiconductor substrate.

[Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor device, and particularly to a method for manufacturing a phase-shift distributed feedback laser that oscillates at a single wavelength.

Recently, distributed feedback type (D F B
: D 1tributed FeedBack)
As the demand for lasers increases, phase (for example, λ/4) shifted DFB lasers have been developed to exhibit even higher performance laser characteristics.

λ/4 shift DFB laser
Perot) laser, it is characterized by oscillating the laser by using the reflection of the diffraction grating without using the edge reflection.
In addition, in order to obtain a single wavelength laser, the reflective wall at the interface between the waveguide layer and the substrate adjacent to the active layer that emits the laser has periodicity parallel to the direction of laser propagation, and has a phase approximately at the center of the device. is reversed, that is, the left and right phases are approximately 10Δ/4Δ/4 at approximately the center of the diffraction grating of a normal DFB laser.
The diffraction grating is formed to have a shifted diffraction grating (A is the length of one period of the diffraction grating).

By doing so, it is possible to obtain a laser beam that stably oscillates with a single wavelength of only the Bragg wavelength, which is the main mode, and with the lowest dark value gain.

When forming a diffraction grating using this technique, it is extremely important to form the diffraction grating with a uniform shape (period, shape size, etc.).

[Conventional technology] Next, a conventional manufacturing method will be explained with reference to the drawings.

FIGS. 3(a) to 3(h) are cross-sectional views illustrating a conventional method of manufacturing a λ/4DFB laser.

In the same figure (a), a negative photoresist film 102
and positive photoresist film 103 as nInP101.
It is formed by sequentially coating and baking on In.

Next, as shown in the same figure (b), the positive photoresist film 1
Pattern 03 and leave a portion.

Next, as shown in the same figure (c), the positive photoresist film 1
03 as a mask, negative photoresist film 102
, sulfuric acid CII□SO4:l/hydrogen peroxide (H20□)
It is dissolved in a system solution and patterned.

Next, as shown in FIG. 4D, after removing the positive photoresist film 103, a new positive photoresist film 104 is again applied and baked over the entire surface.

Next, as shown in the same figure (e), a He-Cd laser beam (λ
, = 3250 people), interference fringes with a bright/dark period of 2000 to 2400 people are transferred onto the photoresist film.

Thereafter, as shown in FIG. 2F, first the positive photoresist film 104 is developed, and then the negative photoresist film 102 is developed to form a periodic striped pattern.

This striped pattern is formed by the positive photoresist film 10.
4 (indicated by P in the figure) and the negative photoresist film 102 part (indicated by N in the figure), there is a shift of half a period. This is due to the opposite photoreaction properties of each photoresist film, that is, the positive photoresist film 10
4 utilizes the property that the exposed portion is removed, whereas the negative photoresist film 102 utilizes the property that the exposed portion remains.

Note that the striped pattern extends in a direction perpendicular to the paper surface.

Next, as shown in FIG. 6(g), the n-InP groups vi, 1 are exposed using the negative photoresist film 102 as a mask.
01 is etched to a certain depth. The unevenness of the n-TnP substrate 101 formed by etching at this time is the same as the above-mentioned periodic striped pattern.

Next, as shown in the same figure (h), n −1nGaAs
P layer 105 (waveguide layer), InGaAsP layer 106
(Active layer) A pJnP layer 107 (cladding layer) is deposited to form the main part of a predetermined λ/4 shift DFB laser.

[Problem to be solved by the invention]

However, according to the above-mentioned conventional method, the following problems occur.

That is, as shown in FIG. 3(c), when removing the negative photoresist film 103, in order to completely remove it,
The immersion time in the H2SO4/H20□ system solution is slightly excessive. However, in this case, the n-1nP substrate 101 directly under the negative photoresist film 102 is also exposed to H2S.
It is etched by exposure to an O4/H2O2 solution.

As a result, a positive photoresist film (indicated by P) and a negative photoresist film (indicated by N) are shown in FIG.
There is a step on the board at the boundary (shown by the broken line in Figure (c)).
occurs.

This step is the ndnGaAsP layer (waveguide layer) shown in the figure.
It remains even after the formation of 105.

If the waveguide layer 105 has a step as described above, it is equivalent to having a semi-transparent mirror there, and causes unnecessary reflected waves, and the oscillation wavelength of each mode and the corresponding darkness The value gain fluctuates and deviates from the value it should take when it is normally manufactured without any steps. In such a state, the dark value gain difference becomes small as shown by the black circles in Figure 2, and the laser oscillates with two wavelengths, making it impossible to obtain a single predetermined wavelength. .

The present invention was created in view of the problems of the conventional example, and aims to improve the performance of a phase-shifted DFB laser by preventing the step difference in the waveguide layer.

[Means to solve the problem]

The above problem consists of a step of applying a positive photoresist film on a semiconductor substrate and forming a periodic striped pattern made of the positive photoresist film using an exposure means, and a step of applying a negative photoresist film and forming a periodic striped pattern of the positive photoresist film using an exposure means. a step of exposing a negative photoresist and a positive photoresist that cover a part of the periodic striped pattern and expose the other part, substantially parallel to the periodic striped pattern; Developing the film and the positive photoresist film, removing the exposed positive photoresist, removing the unexposed negative photoresist, and using the remaining positive and negative photoresist films as a mask, the semiconductor substrate is This is achieved by a method for manufacturing a semiconductor light emitting device, which is characterized in that it includes a step of etching.

[For production]

According to the present invention, a striped pattern consisting of a negative photoresist film and a positive photoresist film, in which Al1 is shifted from one side to the other at the boundary, without going through the step of etching the hardened negative photoresist that causes the formation of steps on the substrate surface. It is possible to create a striped pattern consisting of

Therefore, by etching using these resists as a mask, it is possible to form a diffraction grating in a predetermined shape without steps that would cause unnecessary reflections.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to an illustrated embodiment.

FIGS. 1(a) to (g) show λ/4 according to the embodiment of the present invention.
FIG. 3 is a cross-sectional view illustrating a method of manufacturing a shifted DFB laser.

As shown in the figure (a), after coating and baking a positive photoresist film 2 on an n-1nP substrate 1,
- The bright/dark period is 2000 to 240 by two-beam interference exposure method using Cd gas laser light (λ1 = 3250 people).
0 person's interference fringes are transferred to the positive photoresist film 2.

Note that the above-mentioned period is the same for two Hs separated from the same light source.
It can be varied by changing the incident angle of the e-Cd gas laser beam onto the n-TnP substrate 1.

Next, as shown in FIG. 2B, the positive photoresist film 2 is developed to form a periodic striped pattern.

Thereafter, as shown in FIG. 2C, a negative photoresist film 3 is applied to the entire surface to fill in the recesses between the striped patterns of the positive photoresist film 2.

Next, using the mask 4, the positive and negative photoresist films 2.3 on the n-TnP substrate 1 are exposed. At this time, the end of the mask 4 is arranged so as to be parallel to the direction of the stripes of the resist pattern.

Next, as shown in FIG. 3(d), first, the negative photoresist film 3 is developed. As a result, the negative photoresist film 3 in the non-exposed areas is removed.

Next, as shown in FIG. 2(e), the positive photoresist film 2 is developed. As a result, the positive photoresist film 2 in the exposed area is removed.

Thereafter, as shown in FIG. 2(f), the remaining negative resist film 3 and positive resist Jl! are developed.
2 as a mask, the n-TnP substrate 1 is etched with a saturated bromine water-based etching solution to form a striped pattern. The striped pattern has a period on the positive photoresist film 2 side and on the negative photoresist film 3 side, and the period is shifted by Δ/2 from one side at the boundary thereof.

Next, as shown in the same figure (g), an n-TnGaAsP layer 5 (
Waveguide layer) 9 composition wavelength 1.55 μm, thickness 0.1-0.
15 μm InGaAsP layer 6 (active layer) and p-1
An nP layer 7 (cladding layer) is sequentially formed by liquid phase epitaxial method.

As described above, λ/4 shift InP/InGaAs
Compound semiconductor wafer for P-based DFB laser is completed.

Next, the laser characteristics of the laser manufactured by the manufacturing method of the embodiment of the present invention and the laser manufactured by the conventional manufacturing method will be compared.

FIG. 2 is a diagram comparing dark value gain characteristics between the embodiment of the present invention and the conventional example.

In the figure, the horizontal axis is the deviation from the normalized Bragg wavelength, that is, C・(λ1−λ)/(λ,・λ) (C is a constant determined by the dimensions of the device and the refractive index of the waveguide layer. , λ1 indicates a variable representing the wavelength at which oscillation occurs), and the vertical axis indicates the dark value gain, that is, the minimum gain necessary for laser light to oscillate.

In addition, white circles connected by solid lines in the figure indicate the characteristics of the λ/4 shift DFB laser of the present invention, where λ is the Bragg wavelength of fundamental mode oscillation, and λ8. and λ8- represents the oscillation wavelength of the secondary mode.

The black circles connected by dotted lines represent the threshold gain of the conventional λ/4 shift DFB laser with a step in the waveguide layer.
The dark value gain fluctuates due to the difference in level, and shows a state where it deviates to the left from the value it should take when normally manufactured.

In the figure, the amount of current flowing through the laser is kept constant.

As shown in the figure, the λ/4-shifted DFB laser of the present invention does not generate a step at the boundary of the Δ/4-shifted diffraction grating, and no unnecessary reflection occurs, so it has a dark value gain that is not as high as that of the conventional example. There is no change in Therefore, the dark value gain difference between λ, λ1, and λo- can be made quite large, and laser light oscillated at a single wavelength of only the Bragg wavelength λ can be stably extracted.

In the embodiment, a λ/4 shift DFB laser has been described, but it goes without saying that the present invention can also be applied to other phase shift DFB lasers.

〔Effect of the invention〕

As described above, according to the manufacturing method of the present invention, a phase-shifted DFB laser having a diffraction grating having a predetermined appropriate shape can be created because a step that causes unnecessary reflection is not generated.

As a result, it is possible to stably extract a single wavelength oscillation mode, which is a characteristic of phase-shifted DFB lasers, and improve the performance and yield of semiconductor light-emitting devices.

[Brief explanation of drawings]

FIGS. 1(a) to (g) show λ/4 according to the embodiment of the present invention.
2 is a cross-sectional view illustrating the manufacturing method of a shifted DFB laser, FIG. 2 is a diagram comparing the dark value gain characteristics of the embodiment of the present invention and a conventional example, and FIGS. 3(a) to (h) are conventional examples. λ/4 shift) D
FIG. 3 is a cross-sectional view illustrating a method of manufacturing an FB laser. [Explanation of symbols] 1, 101-n-1nP base material, 2, 102
．． 104...Positive photoresist film, 3.103
... Negative photoresist film, 4... Mask, 5, 105-n-1nGaAsP layer (waveguide layer),
6, 106-1nGaAsP layer (active layer), 7, 10
7.=p-1nP layer (cladding layer), 111... overetching region, N... positive photoresist section, P... negative photoresist section.

Claims (1)

[Scope of Claims] A step of applying a positive photoresist film on a semiconductor substrate and forming a periodic striped pattern of the positive photoresist film using an exposure means; a step of exposing a negative photoresist and a positive photoresist substantially parallel to the periodic striped pattern, covering a part of the periodic striped pattern and exposing the other part; Developing the photoresist film and the positive photoresist film, removing the exposed positive photoresist, and removing the unexposed negative photoresist, using the developed and remaining positive and negative photoresist films as a mask. A method for manufacturing a semiconductor device, comprising the step of etching the semiconductor substrate.