JP2966686B2 - Manufacturing method of semiconductor laser - Google Patents

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 using a substrate oriented in a direction deviating from a certain crystallographic direction.

[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-GaAs
On an s substrate 1, an n-AlGaAs cladding layer 2, an undoped AlGaAs active layer 3, and a p-AlGaAs cladding layer 4 are formed. The p-AlGaAs cladding layer 4 and the p-GaAs cap layer 8 formed thereon are etched to form a mesa-shaped ridge A as shown. On both sides of the mesa-shaped ridge A, n-GaAs current blocking layers 9 are formed.
Further, a p-GaAs contact layer 10 is formed above the p-GaAs cap layer 8 and the n-GaAs current block layer 9. Electrodes 11, 11 'are formed on the upper and lower surfaces of the wafer in which the respective layers are stacked on the substrate 1 as described above. By the way, in manufacturing the ridge-embedded semiconductor laser, usually, a mother wafer 13 shown in a plan view in FIG. Each semiconductor laser is manufactured by cutting at a portion indicated by a chain line C.

The electrodes formed on the upper surface are formed only on the upper surface of one semiconductor laser chip in FIG. 3, as indicated by reference numeral 11, on the cleavage surface and on the surface separated from the adjacent semiconductor laser. Is formed in a size that cannot be reached. Further, the electrode 11 has windows 11a, 11a. The windows 11a, 11a are provided to indicate that the mesa-shaped ridge A described above, that is, the oscillation region is located below the windows 11a. That is, if wire bonding is performed on the electrode 11 above the oscillation region, the oscillation region will be damaged by the impact of the wire bonding. Therefore, the window portions 11a and 11 are used as positioning marks for performing wire bonding while avoiding the oscillation region.
a is formed. 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 such that the oscillation region D is located below the windows 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, so that the raised portion on the upper surface of the wafer is positioned in the windows 11a and 11a. The electrode 11 may be formed.

However, when a GaAs substrate oriented in the direction off from the (100) plane to the <011> direction is used as the n-GaAs substrate 1, for example, a raised portion on the upper surface of the wafer, that is, a stripe-shaped portion is used. The electrode 11 could not be formed on the basis of. This is the case where a substrate oriented in a direction deviating from a certain crystal orientation (hereinafter referred to as an off-substrate) is used, as shown in the sectional view and the partially cutaway plan view in FIGS. The thickness of each layer grown on the substrate 1 does not become as shown in FIG. 2 due to the crystallinity of the off-substrate 1.

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

Therefore, even if the window 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 portion 15a. For this reason, the windows 11a and 11a could not be used as marks for specifying the oscillation region position.

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

[0009]

As described above, in the conventional method of manufacturing a ridge-embedded semiconductor laser using an off-substrate, a complicated etching process must be performed in order to expose the mesa-shaped ridge A. did not become.

In addition, since the above-mentioned etching must be adjusted depending on the thickness of the contact layer to be removed, in order to cope with wafers having different thicknesses and materials of the contact layer, experiments must be repeated again to find the optimum etching conditions. did not become.

An object of the present invention is to omit the complicated etching step for positioning when forming an electrode, and therefore to easily cope with the manufacture of a semiconductor laser having contact layers having different thicknesses. It is an object of the present invention to provide a method of manufacturing a ridge-embedded semiconductor laser.

[0012]

According to the present invention, at least a first conductive type clad layer, an active layer, and a second conductive type clad layer are directly or indirectly formed on a first conductive type off-substrate. And manufacturing a semiconductor laser comprising a step of forming a contact layer and a wafer having a mesa-shaped ridge formed on the cladding layer of the second conductivity type, and forming electrodes on the upper and lower surfaces of the wafer. The method is characterized by comprising the following configuration.

That is, according to the present invention, when forming the electrode, the thickness of the contact layer at the position where the stripe-shaped portion is formed is x, based on the stripe-shaped portion formed on the upper surface of the wafer.

[0014]

(Equation 2)

An electrode pattern for indicating that the center position of the oscillation region exists at a position separated from the stripe-shaped portion by the distance y determined by the above is formed.

[0016]

When each layer for forming a semiconductor laser is crystal-grown thereon using an off-substrate, a stripe portion is formed on the upper surface of the contact layer, that is, on the upper surface of the wafer. As described above, it is formed at a position shifted from the lower oscillation region. However,
It has been experimentally confirmed by the inventors of the present invention that the distance y between the stripe-shaped portion and the center of the lower oscillation region is separated by the distance y represented by 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 away from the position where the stripe-shaped portion is formed by the above distance y, the electrode pattern is formed. The position where the oscillation region exists below is displayed on the electrode. Therefore, wire bonding can be performed while reliably avoiding the portion where the oscillation region is located below.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings to clarify the present invention.

In this embodiment, 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 of FIG. 2, each layer will be described using the reference numerals used in FIG. The production of the wafer was performed as follows.

An n-GaAs substrate 1 was prepared which was 4 ° off from the (100) plane in the <011> direction. This n-GaAs
n-Al _0.4 Ga having a thickness of 2 μm on the s-off substrate 1
_0.6 As cladding layer 2, undoped Al _0.1 Ga _0.9 As active layer 3 having a thickness of 0.07 μm 3, _0.8 μm
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
The layers were sequentially grown using Method D (metal organic chemical vapor deposition).
Next, a mesa-shaped ridge A was formed by etching the p-Al _0.4 Ga _0.6 As clad layer 4 and the p-GaAs cap layer 8. The mesa-shaped ridge A
The thickness of the p-Al _0.4 Ga _0.6 As cladding layer on both sides of the substrate is 0.3 μm.

Next, 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 were grown by MOCVD 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 is prepared as the wafer.

FIG. 1 is a partially cutaway plan view of the mother wafer 15 prepared as described above. Wafer 15
Is divided into individual semiconductor laser elements by cleaving along a dashed-dotted line B and cutting along a dashed-dotted line C after an electrode forming step described later.

On the upper surface of the wafer 15, reference numeral 20 shown in FIG.
And an electrode was 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 another semiconductor laser element. And these are interconnected and integrated.

On the upper surface of the wafer 15, a stripe portion 15a is formed. As shown in FIG. 3 described above, the striped portion 15a is formed at a position deviated from immediately above the region D where the lower mesa ridge is formed. On the other hand, in the present embodiment, 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 positioning marks are formed, and the through holes 20c, 2c are formed using the scales E, F.
A position separated by a predetermined distance from 0c in the direction in which the side edges 20a and 20b extend can be determined.

In this embodiment, the through holes 20c, 20c
The electrode forming mask 20 is arranged using the scales E and F so that the distance between the electrode and the stripe-shaped portion 15a is separated by the distance y that satisfies the above formula (1). It is formed. FIG. 6 shows the formed electrodes. Since the electrode 11 is formed using the electrode forming mask 20, the above-described 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 correspond to the striped portions 15a.
Is formed at a position separated by a distance y from. In addition, the oscillation region D is located below the positioning marks 12a. The reason will be described with reference to FIG.

Referring to FIG. 7, the distance between the stripe-shaped 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 considers that there is some relationship between the distance y and the thickness x of the p-GaAs contact layer 10, and makes the thickness x of the p-GaAs contact layer 10 different,
A wafer having a structure similar to that of the above-described embodiment is manufactured,
The distance y was measured. FIG. 8 shows the results. As is clear from FIG. 8, an extremely high correlation is observed between the distance y and the thickness x of the p-GaAs contact layer 10, and the expression (1)
It was confirmed that a = approximately 4.4 to 5 and 0 <b ≦ 10. Also, a plurality of types of semiconductor lasers were constructed in exactly the same manner as described above, except that only the off-angle was varied, and the relationship between the distance y and the thickness x was examined. It was confirmed that a in 1) was in the range of 0 <a ≦ 6 and 0 <b ≦ 10.

Accordingly, the electrode forming mask 2 shown in FIG.
0 through holes 20c, 20 for forming positioning marks.
When the electrode 11 is formed by arranging the electrode forming mask 20 so that c is positioned at a distance y from the stripe portion 15a, the positioning mark 12a (electrode material) is enlarged as shown in FIG. Part where is not given)
The oscillation region is surely located below. Therefore, in the manufacturing method of the present embodiment, since the positioning marks 12a, 12a indicating the oscillation region are formed below the electrode 11, the wire bonding can be performed while avoiding the portion where the oscillation region exists below.

In the above-described embodiment, the electrode forming mask 20 shown in FIG. 1 is used to provide the positioning mark, but the electrode forming mask that can be used is not limited to this. For example, as shown in FIG. 9A, an electrode forming mask 23 having rectangular through holes 23c, 23c may be used to indicate the positions where wire bonding may be performed. That is, the present invention is characterized in that an electrode is formed so as to specify a wire bonding position in order to avoid performing wire bonding above a portion where a 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 (in FIG. 9A, a region between the marks 23c, 23c) is displayed. The electrodes may be formed so as to form the positioning marks as described above.

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

[0031]

According to the present invention, the oscillation region is provided on the upper surface of the ridge-embedded semiconductor laser wafer constituted by using the off-substrate at a position away from the stripe-shaped portion formed on the upper surface of the wafer by the distance y. The electrode is formed so as to have a positioning display portion for displaying the existence 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 that is less likely to damage the oscillation region and has excellent characteristics.

In addition, when forming the positioning mark on the electrode as described above, it is not necessary to perform a complicated etching step as in the conventional method, so that the entire electrode forming step can be performed efficiently and the contact layer can be formed efficiently. It is possible to easily cope with the manufacture of semiconductor lasers having different thicknesses. Therefore, mass productivity of the ridge-embedded semiconductor laser can be effectively improved.

[Brief description of the 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 embodiment.

FIG. 2 is a cross-sectional view illustrating 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 in a conventional method.

FIGS. 4A and 4B are a cross-sectional view and a partially cutaway plan view illustrating a main part of a wafer when an off-substrate is used.

FIG. 5 is a partially cutaway plan view for explaining a state in which a mesa-shaped ridge is exposed by 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 partially 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 thickness x of a contact layer.

FIGS. 9A and 9B are plan views each illustrating another example of the electrode forming mask used in the present invention.

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-33885 (JP, A) JP-A-5-145177 (JP, A) JP-A-4-72787 (JP, A) 79172 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01S 3/18

Claims (1)

(57) [Claims] At least a first conductive type cladding layer, an active layer, and a second conductive type are provided on a first conductive type substrate oriented in a direction deviating from a certain crystal orientation. A semiconductor comprising a lamination of a cladding layer and a contact layer, wherein a wafer having a mesa-shaped ridge formed on the cladding layer of the second conductivity type is provided, and electrodes are formed on the upper and lower surfaces of the wafer. In the laser manufacturing method, when the thickness of the contact layer in the striped portion is x with respect to the striped portion formed on the upper surface of the wafer, 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 a distance y determined by the following formula.