JPH06310800A - Fabrication of semiconductor laser - Google Patents

Abstract

PURPOSE:To eliminate the etching process for alignment at the time of formation of an electrode by forming an electrode indicating the central position of an oscillation region at a position separated by a predetermined distance from a stripe part. CONSTITUTION:At least a clad layer 2 of first conductivity type, an active layer 3, a clad layer 4 of second conductivity type, and a contact layer 10 are formed on an OFF substrate 1 of first conductivity type and electrodes are formed on the upper and lower faces of a wafer 15 where a mesa ridge A is formed on the clad layer 4 of second conductivity type. In this regard, an electrode pattern indicating the central position of an oscillation region is formed at a position separated by a distance Y from a stripe part 15a formed on the upper face of the wafer 15, where (x) represents the thickness of a contact layer 10 at the position where the stripe part 15a is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor laser, and more particularly to a method for manufacturing a ridge-embedded semiconductor laser constructed by using a substrate oriented in a direction deviated from a certain crystal orientation.

[0002]

2. Description of the Related Art FIG. 2 is a sectional view showing an example of a conventionally known ridge-embedded semiconductor laser. n-GaA
An n-AlGaAs clad layer 2, an undoped AlGaAs active layer 3, and a p-AlGaAs clad layer 4 are formed on the s substrate 1. The p-AlGaAs clad layer 4 and the p-GaAs cap layer 8 formed thereon are etched so as to form the mesa-shaped ridge A as shown in the figure. N-GaAs current blocking layers 9 are formed on both sides of the mesa-shaped ridge A,
Further, a p-GaAs contact layer 10 is formed above the p-GaAs cap layer 8 and the n-GaAs current blocking layer 9. Electrodes 11 and 11 'are formed on the upper and lower surfaces of the wafer in which each layer is laminated on the substrate 1 as described above. By the way, in the manufacture of the ridge-embedded semiconductor laser, usually, a mother wafer 13 shown in a plan view in FIG. , Individual semiconductor lasers are manufactured by cutting at the portion indicated by the alternate long and short dash line C.

It should be noted that the electrode formed on the upper surface is formed on the cleavage plane and the surface divided between adjacent semiconductor lasers, as indicated by reference numeral 11 only on the upper surface of one semiconductor laser chip in FIG. Is formed to a size that does not reach. Further, the electrode 11 is formed with windows 11a and 11a. The windows 11a, 11a are provided below the mesa-shaped ridge A, i.e., the oscillation region. That is, if wire bonding is performed on the electrode 11 above the oscillation region, the oscillation region is damaged by the impact during wire bonding. Therefore, the window portions 11a, 11 serve as positioning marks for performing wire bonding while avoiding the oscillation region.
a is formed. Note that, in FIG. 3, a portion where the mesa-shaped ridge is formed, that is, an oscillation region is indicated by a broken line D.

As described above, when forming the electrode 11, the electrode 11 must be formed so that the oscillation region D is located below the windows 11a, 11a. Usually, in the ridge-embedded semiconductor laser, the portion where the mesa-shaped ridge A is located has a raised shape on the upper surface of the wafer. The electrode 11 may be formed.

However, when the GaAs substrate oriented in the direction of <011> off from the (100) plane is used as the n-GaAs substrate 1, a raised portion on the upper surface of the wafer, that is, a striped portion is used. It was not possible to form the electrode 11 on the basis of. This is the case where a substrate (hereinafter referred to as an off-substrate) oriented in a direction deviating from a certain crystal orientation is used, as shown in the sectional views and partially cutaway plan views of FIGS. 4 (a) and 4 (b). Due to the crystallinity of the off-substrate 1, the thickness of each layer grown on the substrate 1 does not become as shown in FIG.

As a result, as shown in FIGS. 4A and 4B, stripe-shaped portions 15a are formed on the surface of the wafer 15 in parallel to the direction in which the mesa-shaped ridge A extends. The striped portion 15a was formed at a position laterally displaced from the portion where the oscillation region extends.

Therefore, even if the window portion 11a of the electrode 11 shown in FIG. 3 is positioned with reference to the stripe 15a formed on the upper surface of the wafer 15, the lower oscillation region is located immediately below the stripe-shaped portion 15a. Therefore, the windows 11a and 11a cannot be used as marks for identifying the oscillation region position.

Therefore, when manufacturing a ridge-embedded semiconductor laser using an off substrate, as shown in a partially enlarged plan view of FIG. Exposing the light emitting region portion where the mesa-shaped ridge A is formed,
Based on the exposed mesa-shaped ridge A, an electrode pattern is formed on another semiconductor laser element portion on the wafer. That is, a plurality of electrodes are patterned on the upper surface of the wafer 15 by using the exposed mesa-shaped ridge A as a clue so that the mesa-shaped ridge A is located immediately below the window on another semiconductor laser device. It was

[0009]

As described above, in the conventional method for manufacturing a ridge-embedded semiconductor laser using an off-substrate, a complicated etching process is required to expose the mesa-shaped ridge A. did not become.

Further, the above etching must be adjusted according to the thickness of the contact layer to be removed. Therefore, in order to cope with wafers having different contact layer thicknesses and materials, the experiment must be repeated to find the optimum etching conditions. did not become.

The object of the present invention is that the complicated etching process for positioning when forming electrodes can be omitted, and therefore, it is possible to easily deal with the manufacture of semiconductor lasers having contact layers of different thicknesses. Another object of the present invention is to provide a method of manufacturing a ridge-embedded semiconductor laser that can be manufactured.

[0012]

According to the present invention, at least a first-conductivity-type cladding layer, an active layer, and a second-conductivity-type cladding layer are directly or indirectly provided on a first-conductivity-type off-substrate. And a contact layer, and a step of preparing a wafer in which the mesa-shaped ridge is formed in the second conductive type clad layer, and forming electrodes on the upper and lower surfaces of the wafer. The method is provided with the following structure.

That is, in the present invention, when forming the electrode, when the thickness of the contact layer at the position where the striped portion is formed is x with reference to the striped portion formed on the upper surface of the wafer,

[0014]

[Equation 2]

It is characterized in that an electrode pattern indicating that the center position of the oscillation region is present is formed at a position separated from the stripe-shaped portion by the distance y determined by.

[0016]

When each layer for forming a semiconductor laser is crystal-grown on an off-substrate, a stripe-shaped portion is formed on the upper surface of the contact layer, that is, the upper surface of the wafer. As described above, it is formed at a position displaced from the lower oscillation region. However,
It has been experimentally confirmed by the inventors of the present application that the distance y between the stripe-shaped portion and the center of the lower oscillation region is separated by the distance y shown in the above formula (1).

Therefore, as in the present invention, by forming an electrode pattern configured to display the oscillation region position at a position separated by the distance y from the position where the striped portion is formed, the electrode pattern is formed. The position where the oscillation region exists below will be displayed on the electrode. Therefore, it is possible to reliably avoid the portion where the oscillation region is located below and perform the wire bonding.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be clarified by explaining embodiments of the present invention with reference to the drawings.

In this example, a wafer similar to that shown in FIG. 2 was first prepared except that an off substrate was used. Since the cross-sectional structure of the wafer is the same as that in FIG. 2, each layer will be described using the reference numerals used in FIG. The wafer was manufactured as follows.

An n-GaAs substrate 1 was prepared which was turned off by 4 ° in the <011> direction from the (100) plane. This n-GaA
n-Al _0.4 Ga having a thickness of 2 μm is formed on the s-off substrate 1.
_0.6 As clad layer 2, undoped Al _0.1 Ga _0.9 As active layer 3 having a thickness of 0.07 μm, _0.8 μm
Of the p-Al _0.4 Ga _0.6 As cladding layer 4 having a thickness of 0.2 μm and the p-GaAs cap layer 8 having a thickness of 0.2 μm are
Sequential growth was performed using the D method (metalorganic vapor phase epitaxy).
Next, the p-Al _0.4 Ga _0.6 As cladding layer 4 and the p-GaAs cap layer 8 were etched to form a mesa-shaped ridge A. The mesa-shaped ridge A
The thickness of the p-Al _0.4 Ga _0.6 As cladding layers on both sides of is 0.3 μm.

Next, the MOCVD method was also used to grow an n-GaAs current blocking layer 9 having a thickness of 1.0 μm and a p-GaAs contact layer 10 having a thickness of 6.0 μm to obtain a wafer.

Although FIG. 2 shows only the cross-sectional structure of one semiconductor element, a mother wafer having a plurality of semiconductor laser elements arranged in a matrix was prepared as the wafer.

FIG. 1 is a partially cutaway plan view of the mother wafer 15 prepared as described above. Wafer 15
After being subjected to an electrode forming step described later, the element is cleaved along the alternate long and short dash line B and divided along the alternate long and short dash line C to be divided into individual semiconductor laser elements.

On the upper surface of the wafer 15, reference numeral 20 is shown in FIG.
The electrode forming mask shown in 1 was placed, and the electrodes were formed by a thin film forming method such as vapor deposition. Although FIG. 1 shows a state in which the electrode forming mask 20 is arranged only on the upper surface of one semiconductor laser element portion, the electrode forming mask is also placed on other semiconductor laser elements. And these are connected and integrated with each other.

By the way, a striped portion 15a is formed on the upper surface of the wafer 15. As shown in FIG. 3 described above, the striped portion 15a is formed at a position deviating from just above the region D where the lower mesa-shaped ridge is formed. On the other hand, in this embodiment, the scales E and F are formed on the side edges 20a and 20b of the electrode forming mask 20, respectively. Further, through holes 20c, 20c for forming the positioning marks are formed, and the through holes 20c, 2 are formed using the scales E, F.
It is arranged to be able to determine a position separated from the 0c by a predetermined distance in the extending direction of the side edges 20a, 20b.

In this embodiment, the through holes 20c, 20c are provided.
The electrode forming mask 20 is arranged by using the scales E and F so that the distance between the stripe-shaped portion 15a and the stripe-shaped portion 15a is separated by the distance y that satisfies the above-described formula (1). It is formed. The formed electrode is shown in FIG. Since the electrode 11 is formed using the electrode forming mask 20, the positioning through hole 20c,
Positioning marks 12a, 12a to which no electrode material is applied are provided in the portion where 20c was located. The positioning marks 12a, 12a have stripe-shaped portions 15a.
Is formed at a position separated by a distance y from. Further, the oscillation region D is located below the positioning marks 12a, 12a. The reason for this will be described with reference to FIG.

Referring to FIG. 7, the distance between the striped portion 15a on the surface and the center of the oscillation region is y, p-Ga.
The thickness of the As contact layer 10 is x. The inventor of the present application believes that there is some relation between the distance y and the thickness x of the p-GaAs contact layer 10, and thus the thickness x of the p-GaAs contact layer 10 is made different,
A wafer having the same structure as that of the above-described embodiment is manufactured,
The distance y was measured. The results are shown in Fig. 8. As is clear from FIG. 8, there is a very high correlation between the distance y and the thickness x of the p-GaAs contact layer 10, and the equation (1)
It was confirmed that the relation of a = about 4.4 to 5 and 0 <b ≦ 10 holds. Further, when a plurality of types of semiconductor lasers were configured and the relationship between the distance y and the thickness x was investigated in exactly the same manner as above except that only the off angle was changed, the expression ( It was confirmed that a of 1) was in the range of 0 <a ≦ 6 and in the range of 0 <b ≦ 10.

Therefore, the electrode forming mask 2 shown in FIG.
0, and the through holes 20c, 20 for forming the positioning marks are used.
When the electrode 11 is formed by disposing the electrode forming mask 20 so that c is located at a position separated by the distance y from the stripe portion 15a, as shown in an enlarged view in FIG. (The part where is not attached)
The oscillation region will be surely positioned below. Therefore, in the manufacturing method of this embodiment, since the positioning marks 12a, 12a indicating the oscillation region are formed on the electrode 11 below, the wire bonding can be performed while avoiding the portion where the oscillation region is below.

Although the electrode forming mask 20 shown in FIG. 1 is used to provide the positioning mark in the above-described embodiment, the electrode forming mask that can be used is not limited to this. For example, as shown in FIG. 9A, in order to display the position where wire bonding may be performed, an electrode forming mask 23 having positioning through holes 23c, 23c for square holes may be used. That is, the present invention is characterized in that the electrode is formed so as to specify the wire bonding position in order to avoid performing the wire bonding above the portion where the mesa-shaped ridge is formed. As shown in FIG. 9A, a region other than the portion where the mesa-shaped ridge is located below, that is, a region where wire bonding may be performed (region between the marks 23c and 23c in FIG. 9A) is displayed. The electrodes may be formed so as to form the positioning marks.

Further, as shown in FIG. 9B, in the electrode forming mask 24, through holes 24a, 24a in the shape of square holes are formed.
Further, as for the scale, the scale is not directly formed on the mask, but stepwise portions 24b and 24b having a predetermined width are formed at the corner portions forming a pair of the mask 24, and the width of each step of the stepwise portion is formed. May be used as a scale.

[0031]

According to the present invention, the oscillation region is formed on the upper surface of the ridge-embedded type semiconductor laser wafer formed by using the off-substrate at a position separated by the distance y from the stripe-shaped portion formed on the upper surface of the wafer. The electrodes are formed so as to have a positioning display portion that indicates that the presence of the. Therefore, wire bonding can be reliably performed on the electrode while avoiding the oscillation region. Therefore, it is possible to obtain a ridge-embedded semiconductor laser with excellent characteristics in which the oscillation region is unlikely to be damaged.

Moreover, in forming the positioning mark on the electrode as described above, it is not necessary to carry out a complicated etching process as in the conventional method, so that the entire electrode forming process can be efficiently carried out and the contact layer is formed. It is possible to easily deal with the manufacturing of semiconductor lasers having different thicknesses. Therefore, mass productivity of the ridge-embedded semiconductor laser can be effectively enhanced.

[Brief description of drawings]

FIG. 1 is a partially cutaway plan view for explaining a state in which an electrode forming mask is arranged on a wafer in an example.

FIG. 2 is a sectional view for explaining an example of a ridge-embedded semiconductor laser.

FIG. 3 is a plan view for explaining a state in which electrodes are formed on the upper surface of a wafer by a conventional method.

4A and 4B are a cross-sectional view and a partially cutaway plan view for explaining an essential part of a wafer when an off-substrate is used.

FIG. 5 is a partially cutaway plan view for explaining a state where a mesa-shaped ridge is exposed by performing etching from the upper surface side of a wafer in a conventional method.

FIG. 6 is a partially cutaway plan view for explaining electrodes formed on the upper surface of the wafer in the manufacturing method according to the embodiment.

FIG. 7 is a partial cutaway sectional view for explaining a distance y between a stripe-shaped portion and the center of an oscillation region and a thickness x of a contact layer.

FIG. 8 is a diagram showing a relationship between a distance y and a contact layer thickness x.

9A and 9B are plan views for explaining another example of the electrode forming mask used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... n-AlGaAs clad layer 3 ... Active layer 4 ... p-AlGaAs clad layer 10 ... p-GaAs contact layer 11 ... Electrode 12a, 12a ... Positioning mark 15 ... Wafer 15a ... Striped part A ... Mesa ridge

Claims (1)

[Claims] 1. A substrate of the first conductivity type oriented in a direction deviating from a certain crystal orientation, directly or indirectly, of at least a cladding layer of the first conductivity type, an active layer, and a second conductivity type. A semiconductor including a step of preparing a wafer in which a clad layer and a contact layer are laminated and having a mesa-shaped ridge formed on the second conductive type clad layer, and forming electrodes on the upper surface and the lower surface of the wafer. In the laser manufacturing method, when the thickness of the contact layer in the striped portion is x with reference to the striped portion formed on the upper surface of the wafer, from the striped portion, A method of manufacturing a semiconductor laser, comprising forming an electrode on the upper surface of the wafer by forming an electrode indicating that the center position of the oscillation region is located at a position separated by the distance y determined by.