JPH0870156A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE: To reduce the manufacturing cost of laser by drastically simplifying the manufacturing process of a semiconductor laser in ridge structure. CONSTITUTION: A ridge 31 is formed on a substrate 36 with the layer configuration of a semiconductor laser, an insulation film 37 is formed near the ridge, then a resist 38 is applied onto the insulation film, only the resist 38 on the ridge is selectively exposed and developed for elimination, and further the insulation film 37 on the ridge 31 is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser used for optical recording, optical communication, excitation of optical fiber amplifier and the like.

[0002]

2. Description of the Related Art Semiconductor lasers used for optical recording, optical communication, excitation of optical fiber amplifiers, etc.
Economicization is required. As a simple structure of a semiconductor laser, a ridge structure for confining light and current is adopted by forming a stripe ridge. In the manufacturing process of this ridge structure semiconductor laser, a ridge is formed on a substrate on which a layer structure of the semiconductor laser is formed, an insulating film is formed on the entire surface of the substrate, then the insulating film on the ridge is removed, and a current is injected. A contact with an electrode for forming. An example of the step of removing the insulating film on the ridge will be described with reference to FIG. In the figure (a), 11 is a ridge, 17 is a clad, 1
8 is a channel, 12 is an active layer, and 13 is a substrate. (B) As shown in the figure, an insulating film 14 is formed on the entire surface of the substrate on which the ridge 11 having a double channel structure having channels on both sides is formed by etching. As shown in (c), a first resist 15 thicker than the height of the ridge is applied thereon to flatten the ridge, and this is baked to fluidize and insolubilize the resist. (D) As shown in FIG.
6 is applied, and the second near the top of the ridge is subjected to photolithography.
The resist 16 is removed, the first resist 15 on the ridge is removed by oxygen plasma as shown in FIG. 7E, and then the insulating film 14 on the ridge is etched by etching as shown in FIG. Is removed, and finally, the resists 15 and 16 remaining by ashing are removed as shown in FIG.

In this conventional method, the number of steps is large, and
If the planarization is incomplete, the film thickness of the resist part on both sides of the ridge will decrease and the insulating film on both sides will be exposed, so that the side insulating film will be easily etched by etching, which will adversely affect the device characteristics. Bring Here, a situation where the insulating film on the side portion of the ridge disappears will be described with reference to FIG. In the figure (a), 21 is a ridge, 22 is a second resist, 23 is a first resist, 24 is an insulating film, 25
Is an active layer and 26 is a substrate. When the resist is not sufficiently flattened, the resist on the ridge is removed by oxygen plasma, so that the insulating films 24 on both sides of the ridge 21 are exposed. Therefore, as shown in FIG. 6B, when the insulating film on the ridge is removed by etching, the insulating film on the side portion of the ridge is over-etched. As shown in FIG. 6C, it can be seen that the insulating film on the ridge side has disappeared when the resist remaining by ashing is finally removed. Further, when wet etching is used for etching the insulating film in the state where the insulating film on the side is exposed (a), the etching solution may penetrate between the semiconductor and the insulating film or between the insulating film and the resist. , The side and bottom of the ridge may be etched (b), (c), and in order to prevent this, the insulating film is usually removed by dry etching, in which case the manufacturing process is more complicated. It has become.

[0004]

SUMMARY OF THE INVENTION The present invention has been proposed to solve the above-mentioned drawbacks, and an object of the present invention is to provide a simple method for manufacturing a semiconductor laser having a ridge structure.

[0005]

In order to achieve the above object, the present invention provides (1) a step of forming a ridge on a substrate having a layer structure of a semiconductor laser, and thereafter, at least on the surface of the substrate at least in the vicinity of the ridge. A step of forming an insulating film, a step of thereafter coating a resist on the insulating film and selectively removing only the resist on the ridge by exposure and development, and a step of thereafter removing the insulating film on the ridge by etching. A feature of the invention is a method of manufacturing a semiconductor laser including the above. (2) In the step of coating the insulating film with a resist and selectively removing the resist on the ridge by exposure and development, the resist width to be removed is made narrower than the ridge width, and then the insulating film on the ridge is etched. The method of manufacturing a semiconductor laser according to (1), which uses wet etching in the removing step, is a feature of the invention. (3) The method of manufacturing a semiconductor laser according to (1), wherein in the step of coating the insulating film with a resist and selectively removing the resist on the ridge by exposure and development, the exposure is selectively performed by electron beam exposure. It is a feature of the invention.

[0006]

After the ridge is formed on the substrate on which the layer structure of the semiconductor laser is formed, the insulating film is formed on at least the ridge and the channel portion of the substrate surface, and the insulating film on the ridge is removed. By using a method in which the resist is coated on the ridge, only the resist on the ridge upper part is selectively exposed and developed, and then the insulating film on the ridge upper part is removed by etching, the manufacturing process of the ridge structure semiconductor laser is significantly increased. The manufacturing cost of the laser can be greatly reduced.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to improve the drawbacks of the above conventional example, the present invention employs a method of selectively exposing and developing only the upper portion of a ridge coated with an insulating film to remove the resist on the ridge. FIG. 1 illustrates the process of the present invention. In the figure, 31 is a ridge, 32 is a clad, 33 is an active layer, 34 is a semiconductor, 35 is a channel, and 36 is a semiconductor substrate on which elements constituting a laser are formed. Then, the upper surface of the substrate on which the ridge is formed is coated with an insulating film 37, a resist 38 is further coated thereon, and then the ridge is selectively exposed and developed, and then only the insulating film on the ridge is etched. Then, the window 39 is formed, and then the remaining resist is removed.

This method greatly simplifies the process as compared with the conventional method. Since the conventional method does not have a highly accurate pattern alignment technique, the manufacturing method shown in FIG. 3 has been adopted. Normally, the ridge width is 1.5 ~
Since it is as narrow as 4.0 μm, an epitaxial substrate with poor substrate flatness is used for manufacturing a semiconductor laser, and a square small substrate obtained by cutting this is often used without using a circular full wafer. In a normal contact aligner used for manufacturing a semiconductor laser, it is difficult to accurately pattern the ridge over the entire substrate.

However, due to the recent improvement in the exposure technique, the alignment accuracy of the pattern is significantly improved, and it becomes possible to perform patterning with good uniformity over the entire substrate. The present invention is based on such a background. There are two types of exposure techniques used in the present invention: reduction projection exposure and electron beam exposure. In particular, in electron beam exposure, highly accurate alignment of 0.5 micron or less is possible without depending on the substrate shape or the flatness of the substrate. Therefore, the pattern size for selectively opening the window on the ridge can be formed into a shape like the window in FIG. 2 in which the pattern dimension is slightly narrower than the ridge width. In such a pattern shape, since both ends of the ridge are completely covered with the resist, the insulating film attached to both sides of the ridge does not recede by etching even if the insulating film is etched. Therefore, there is no problem in using wet etching accompanied by side etching. The wet etching not only does not require a dry etching apparatus, but also has the advantage that the final resist removal can be easily performed with a solvent because the quality of the resist does not change, and the process is further simplified. Next, examples will be described in detail.

(Embodiment 1) FIG. 1 is a view for explaining a first embodiment of the present invention, showing a manufacturing process of a ridge structure semiconductor laser. This embodiment relates to claim 1. In order to carry out this method, first, it is assumed that a semiconductor substrate in which each semiconductor layer forming a laser is formed on a GaAs substrate is prepared in advance as a semiconductor substrate for producing a semiconductor laser having a ridge structure. Semiconductor substrate 3
A mask layer made of photoresist was formed on No. 6 in a predetermined pattern by exposure and development. next,
To the semiconductor substrate 36, as a mask the mask layer by performing an etching process using a plasma of chlorine gas, the semiconductor substrate 3 processed ridge 31
Went up to 6 . Next, from the top of the semiconductor substrate 36 , N−
The mask layer was dissolved and removed using a solution of methylpyrrolidone. Further, the etching residue was processed using an oxygen asher (Fig. A). Next, the semiconductor substrate
For 36 , the insulating layer 37 was formed by using plasma CVD. Here, a nitride film was formed as the insulating film (FIG. B). Next, a photoresist 38 was applied to the semiconductor substrate 36 . After that, the resist 38 is
It was formed into a predetermined pattern by exposure and development, and was used as a mask layer so that the nitride film on the ridge 31 could be selectively etched. That is, a reduction projection exposure method was used to form a stripe pattern having the same width as the pattern used when the ridge 31 was formed so as to overlap directly on the ridge 31 (FIG. C). next,
The nitride film in the window opening portion 39 was removed by etching the semiconductor substrate 36 using plasma of fluorocarbon gas (FIG. D). Next, the mask layer was dissolved and removed from the semiconductor substrate 36 by using a liquid composed of N-methylpyrrolidone. Further, the etching residue was processed using an oxygen asher (Fig. E).
After this, p of Cr / Au or Ti / Pt / Au
An electrode and then an n-electrode such as Au / Ge / Ni were formed.
Further, ohmic sintering was performed to form the electrode portion. Next, the semiconductor substrate 36 is cleaved, divided into laser chips, and then assembled and mounted as a module to obtain a semiconductor laser device. The above is the first embodiment of the method for manufacturing a semiconductor laser according to the present invention. As described above, according to this embodiment, the insulating film on the ridge is selectively etched and removed, so that the insulating film on the side portion of the ridge is not etched unlike the conventional case. Moreover, the number of manufacturing steps can be reduced as compared with the conventional method.

(Embodiment 2) This embodiment relates to a method of manufacturing a semiconductor laser according to claim 2. In order to carry out this method, first, it is assumed that a semiconductor substrate in which each semiconductor layer forming a laser is formed on a GaAs substrate is prepared in advance as a semiconductor substrate for producing a semiconductor laser having a ridge structure. A mask layer made of photoresist was formed on the semiconductor substrate 36 in a predetermined pattern by exposure and development processing. Next, the semiconductor substrate 36 was subjected to etching treatment using plasma of chlorine-based gas using the mask layer as a mask to process the ridge 31 on the semiconductor substrate 36 . Next, the mask layer was dissolved and removed from the semiconductor substrate 36 by using a liquid composed of N-methylpyrrolidone. Furthermore, the etching residue was processed using an oxygen asher (FIG. 1a). Next, an insulating layer 37 was formed on the semiconductor substrate 36 by using plasma CVD. Here, a nitride film was formed as the insulating film (see FIG. 1).
b).

Next, a photoresist 38 is applied to the semiconductor substrate 36 , and when the resist on the ridge 31 is selectively removed by exposure and development, the nitride film on the ridge 31 can be selectively etched. This pattern was formed as a predetermined pattern. That is, a reduction projection exposure method was used to form a stripe pattern having a width slightly narrower than the pattern used when the ridge 31 was formed so that the ridge 31 and the center line overlapped with each other (FIG. 2).
a). Then, the semiconductor substrate 36 is subjected to an etching treatment using an etching solution composed of a hydrofluoric acid-based solution having a mixing ratio of hydrofluoric acid, ammonium fluoride, and water of 7:35:58, whereby a window is formed. The nitride film in the open portion 39 was removed (FIG. 2b). The resist 38 was then removed (Fig. 2c). The above is the second embodiment of the method for manufacturing a semiconductor laser according to the present invention. Thus, according to this embodiment, the resist width to be removed is made narrower than the ridge width.
Wet etching can be adopted, and the number of manufacturing steps can be further reduced.

(Embodiment 3) This embodiment relates to a method of manufacturing a semiconductor laser according to claim 3. In order to carry out this method, first, it is assumed that a semiconductor substrate in which each semiconductor layer forming a laser is formed on a GaAs substrate is prepared in advance as a semiconductor substrate for producing a semiconductor laser having a ridge structure. A mask layer made of photoresist was formed on the semiconductor substrate 36 in a predetermined pattern by exposure and development processing. Next, the semiconductor substrate 36 was subjected to etching treatment using plasma of chlorine-based gas using the mask layer as a mask to process the ridge 31 on the semiconductor substrate 36 . Next, the mask layer was dissolved and removed from the semiconductor substrate 36 by using a liquid composed of N-methylpyrrolidone. Furthermore, the etching residue was processed using an oxygen asher (FIG. 1a). Next, an insulating layer 37 was formed on the semiconductor substrate 36 by using plasma CVD. Here, a nitride film was formed as the insulating film (see FIG. 1).
b). Next, an electron beam resist 35 was applied to the semiconductor substrate 36 . When the resist on the ridge 31 was removed by selective exposure and development, selective exposure was performed by electron beam exposure. The subsequent manufacturing process is
The same procedure as in Example 1 was performed. The above is the third embodiment of the method for manufacturing a semiconductor laser according to the present invention. As described above, according to the present embodiment, since the selective exposure by the electron beam exposure is adopted, it is possible to perform highly accurate alignment and form the pattern with good uniformity over the entire substrate.

[0014]

As described above, the ridge is formed on the substrate on which the layer structure of the semiconductor laser is formed, and then the insulating film is formed on at least the ridge and the channel portion of the substrate surface, and the insulating film on the ridge is removed. In this step, a method of coating a resist on the insulating film to selectively remove only the resist on the ridge by exposure and development and then removing the insulating film on the ridge by etching is adopted. The manufacturing process of is greatly simplified, and the manufacturing cost of the laser can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a step of selectively processing an insulating film on a ridge according to the present invention, in which (a) to (e) show each step.

FIG. 2 is a cross-sectional view showing a process of selectively opening a window narrower than the ridge width of the present invention, in which (a) to (c) show each process.

FIG. 3 is a cross-sectional view showing a conventional process for removing an insulating film on a ridge, wherein (a) to (g) show each process.

FIG. 4 is a cross-sectional view showing a case where both side surfaces of a ridge are exposed by a conventional method, and (a) to (e) show respective steps.

[Explanation of symbols]

11 Ridge 12 Active Layer 13 Semiconductor Substrate 14 Insulating Film 15 First Resist 16 Second Resist 17 Cladding 18 Channel 21 Ridge Part 22 Second Resist 23 First Resist 24 Insulating Film 25 Active Layer 26 Semiconductor Substrate 27 Exposed Side surface of ridge 31 Ridge 32 Cladding 33 Active layer 34 Substrate 35 Channel 36 Semiconductor substrate 37 Insulating film 38 Resist 39 Window

Claims (3)

[Claims] 1. A step of forming a ridge on a substrate having a layer structure of a semiconductor laser, a step of forming an insulating film on the surface of the substrate at least in the vicinity of the ridge, and a resist is then coated on the insulating film. A step of selectively removing only the resist on the ridge by exposure and development, and thereafter,
And a step of removing the insulating film on the ridge by etching. 2. In the step of coating a resist on the insulating film and selectively removing the resist on the ridge by exposure and development, the resist width to be removed is made narrower than the ridge width, and the insulating film on the ridge is removed thereafter. 2. The method of manufacturing a semiconductor laser according to claim 1, wherein wet etching is used in the step of removing by etching. 3. The step of coating a resist on an insulating film and selectively removing the resist on the ridge by exposure and development, wherein the exposure is selectively performed by electron beam exposure. Manufacturing method of semiconductor laser.