JPS6129184A - Light emitting element and manufacture thereof - Google Patents

Abstract

PURPOSE:To enhance the manufacturing yield by disposing the peripheral edge except part of a cleaved surface of the uppermost layer of an electrode in coincidence with or inside the peripheral edge of the lower layer for supporting the uppermost layer. CONSTITUTION:A laser chip is formed of a multilayer grown layer 6 sequentially formed with a buffer layer 2 made of an N type InP, an active layer 3 made of InGaAsP, a clad layer 4 made of P type InP, and a cap layer 5 made of P type InGaAsP in a stripe shape on the main surface of an N type InP substrate 1. A blocking layer 7 made of P type InP, a buried layer 8 made of N type InP, and a cap layer 9 made of InGaAs are buried at both sides of the layer 6. The main surface side of the substrate 1 is coated with an insulating film 10 except the electrode contact region of the layer 6. An Au layer 12 of the upper layer of an anode electrode 13 is effectively placed on a Cr layer 11. Thus, the layer 12 is not short-circuited due to the contact with a P-N junction presented on the peripheral surface of the laser chip.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a light emitting device, for example, a semiconductor laser device that emits (emits) laser light from a resonator end of an end face, or an integrated optical device having such a semiconductor laser device portion. The present invention relates to light emitting elements such as devices (OE, IC elements) and methods for manufacturing the same.

[Background technology]

Light sources for optical communications or digital audio discs,
Regarding semiconductor laser elements that serve as light sources for information processing devices such as video discs, for example, see Sem1conductor World published by Press Journal.

Based on the figures etc. in May issue, 1982, pages 25-29. Discussed in the document entitled "Technical Innovations in Semiconductor Lasers".

In addition, prior art (Nikkei Electronics, published by Nikkei McGraw-Hill, September 14, 1'981, issue 138-15)
Page 2: Semiconductor lasers that meet the requirements of audio discs (for cutting trees, etc.), semiconductor laser chips (hereinafter simply referred to as laser chips) are manufactured by cutting (cleaving) a wafer on which electrodes are formed. It is also shown that the electrode has a multi-layered gold layer structure, and that gold (Au) is often used as the top layer material.

However, this technology does not solve the problem of show 1 failure and laser light shielding failure due to the hanging of the protruding Au portion (overhanging electrode portion) caused by the Au serving as the electrode extending and being torn off when the wafer is divided. I don't recognize it.

In other words, in conventional laser chips of this type, during manufacturing, etc., the electrodes provided on one side of the laser chip tend to protrude and sag due to the following reasons, and the phenomenon of overhanging and sagging of the electrodes provided on one side of the laser chip tends to occur. The inventors have found that short circuits are more likely to occur.

The laser chip has a structure in which a multilayer growth layer is formed on the main surface of a thick substrate of around 100 μm, and the laser beam is emitted from the end face (more precisely, the cavity end face) of the active layer, which is one of the constituent layers of this multilayer growth layer. It has a structure that emits . Shisode,
At least one electrode is provided on the upper surface side of the multilayer growth layer.

The distance between the electrode on this multilayer growth layer and the active layer is extremely short, for example, about 3 μm. Therefore, if the electrode on the multilayer growth layer overhangs and hangs down from the periphery of the laser chip, this hanging electrode portion will be
straddles the n-junction and contacts different electrocardiogram regions, or pn
This may come into contact with the bond, causing a short circuit or blocking the optical path of the laser beam.

By the way, as mentioned above, since the electrodes on the multilayer growth layer are made of highly malleable Au, when the wafer is divided, the Au stretches and is torn off, resulting in an overhanging electrode portion at the periphery of the laser chip. I end up.

[Purpose of the invention]

An object of the present invention is to provide a light emitting element having a structure in which short-circuit defects due to electrodes are unlikely to occur, and a method for manufacturing the same.

Another object of the present invention is to provide a method for manufacturing a light emitting device with high manufacturing yield.

The above and other objects and novel features of the present invention include:
It will become clear from the description of this specification and the accompanying drawings.

[Summary of the invention]

A brief overview of typical inventions disclosed in this application is as follows.

That is, in the present invention, when forming electrodes on the main surface of the wafer on which element patterns are formed, Cr is applied to the main surface of the wafer.
After sequentially forming the Au layer and the Au layer, the Au layer is partially etched by conventional photolithography using a photoresist as a mask, and then the Cr layer is etched using the Au layer covered with the photoresist as a mask. Then, using the photoresist as a mask, the Au layer is side-etched so that the periphery of the Au layer is the same as or inside the periphery of the Cr layer, and the wafer is separated by cleavage, scribing, and cracking, By preventing the Au layer from being torn into long pieces during cleavage of the wafer, the occurrence of shows 1 and optical path interruption due to electrode protrusion can be reduced.

〔Example〕

FIG. 1 is a perspective view showing a laser chip (light emitting element) according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of a wafer before electrode formation, also showing a method of manufacturing the laser chip, and FIG. FIG. 4 is a cross-sectional view showing the patterning state, FIG. 4 is a cross-sectional view showing the side etching state of the same<Au layer, and FIG. 5 is a cross-sectional view showing a laser chip obtained by dividing the wafer.

In this embodiment, an example in which the present invention is applied to a long wavelength semiconductor laser probe having a buried heterostructure (BH) will be described.

A laser chip is formed by cleaving a compound semiconductor thin plate (wafer) on which element patterns and electrodes have been formed, and then performing scribing and cranking along the cleavage direction to divide the wafer into a grid pattern vertically and horizontally. . The laser chip of this embodiment has a structure as shown in FIG.

Next, the structure of the laser chip will be explained.

The laser chip is mounted on the main surface of the n-type InP substrate 1 [Top surface: (
100) Buffer layer 2 made of n-type InP on the crystal plane]
, an active layer (resonator) made of InGaAsP, a 3° cladding layer 4 made of p-type InP, and a cap layer 5 made of p-type InGaAsP are sequentially formed to form a multilayer growth layer 6 in the form of a stripe. This multilayer growth layer 6 has an inverted triangular cross-sectional shape, and has a so-called inverted mesa structure.

Further, the portion below the lower end of this inverted mesa surface portion has a forward mesa structure that gradually expands. On both sides of this multilayer growth layer 6'', there are a blocking layer 7 made of P-type InP, a buried layer 8 made of N-type InP, and an InG layer.
A cap layer 9 made of aAsP is embedded in a stacked state. Further, the main surface side of the substrate 1 excluding the electrode contact area of the multilayer growth layer 6 is covered with an insulating film 10. Then, on the main surface side of the substrate 1, the lower layer is a Cr layer], 1, &
1. An anode electrode 13 made of an Au layer 12 is formed.

In addition, on the back side of the substrate 1 ^uGeNi / Pd /
A cathode electrode 14 is provided which is successively laminated with Au.

In addition, zinc (Zn) is diffused into the surface layer portions of the cap layer 9 and the cladding layer 4, and an ohmic contact Jfl] 5 (dotted region) consisting of a P1 type zinc diffusion region is provided. There is.

By the way, in the anode electrode 13, as shown in the figure, the Cr layer 1 along the direction in which the active layer 3 extends.
The periphery of 1 is more protruding than the periphery of the upper Au layer 12. This protrusion length is, for example, 0.1 to 0.5 μm.

The dimensions of such a laser chip are, for example, 40 mm wide.
0μm, length is 300μm, height is 100μm,
The width of the resonator is approximately 2 μm, and the thickness is approximately 0.15 μm.

Such a laser chip emits laser light 16 from the end face of the active layer (resonator) 3 when a predetermined voltage is applied to the pair of anode electrode 13 and cathode electrode 14 .

In such a laser chip, the anode electrode 13
The upper layer A u Ml 2 in is surely placed on the Cr layer 11 . Therefore, even if the Au layer 12 is accidentally contacted, there is a small probability that the Au layer 12 will crawl on the Cr layer 11 and extend outward to the periphery of the laser chip, and the Au layer 12 is present on the surface of the laser chip. The occurrence of short-circuit failures due to contact with the pn junction, or interruption of the optical path of laser light, is extremely reduced, and improvements in characteristics can be expected.

Next, a method for manufacturing a laser chip will be described with reference to FIGS. 2 to 5.

When manufacturing a laser chip, first a compound semiconductor thin plate (wafer) 17 as shown in FIG. 2 is prepared. This wafer 17 is formed by sequentially forming an n-type InP buffer layer 2, an InGaAsP active layer 3+a P-type InP layer on the (100) crystal plane of the n-type InP substrate 1 by liquid phase epitaxial method.
It has a structure in which a cladding layer 4 and a cap layer 5 of P-type InGaAsP are formed. Also, this board 2 has 200
The active layer 3 has a thickness of about 0.15 μm, and each of the other layers has a thickness of about 1 to 2 μm.

Further, on this wafer 17, a large number of striped portions j8 having a width of 5 to 6 μm are formed parallel to the <110> cleavage direction at intervals of, for example, about 400 μm, by photolithography. That is, the area between these striped portions 18 is removed by etching to a depth that reaches the buffer layer 2. In the groove portion dug by this etching, a blocking layer 7 made of n-type InP, a buried layer 8 made of p-type InP, and a cap layer 9 made of InGaAsP are sequentially buried by liquid phase epitaxial method. Further, the main surface portion of the wafer 17 excluding the portion corresponding to the stripe portion 18 and the region where the wafer is divided by scribing and cracking is 5i
02 film, phosphosilicate film (PSG film), or the like.

Further, the wafer 17 is provided with an ohmic contact layer 15 in which zinc (Zn) is diffused to a depth reaching the cladding layer 4 of the stripe portion 18 .

Such a wafer 17 has, for example, a Cr layer 1 with a thickness of 0.1 μm and an Au layer 12 with a thickness of 1 μm stacked on the Cr layer 1 formed on the entire main surface thereof by vapor deposition or the like. Ru. Further, as shown in FIG. 3, a mask 19 made of photoresist is formed on the Au layer 12 by conventional photolithography.

This mask 19 is provided along the stripe section 18 to be wider than the width of the stripe section 18 . For example, the width of the mask 19 is 200 to 300 μm.

Next, as shown in FIG. 3, the exposed Au layer 12 is etched away using an iodine-based etching solution using the mask 19, and the etching solution is replaced with ceric ammonium nitrate to remove the Au layer 12. Using 12 as a mask, the exposed Cr layer 1 is removed by etching. In these series of etchings, each object to be etched is side-etched, so that the width of the Au layer 12 is narrower than the width of the mask 19, and the width of the upper Cr layer 1 is narrower than the width of the Au layer 12.

By the way, in this state, remove the mask 19,
When the substrate 1 is back-etched, a cathode electrode J4 is formed on the back surface of the wafer 17, and the wafer 17 is divided into chips, 5 to 6 AuM12 are etched from both sides of the CrWJll.
Since it protrudes by about μm, the protruding A that is not directly supported by the Cr layer 11 when the wafer 17 is divided during cleavage.
u The WJ12 portion is torn as it stretches due to the malleability that is the original property of Au. According to experiments conducted by the present inventors, it has been confirmed that this extended length extends to a region where the active layer 3 that emits laser light is present, or to an extent that extends beyond the active layer 3. I wanted to do it, but the Au stuck out
The extended portion of the layer 12 may come into contact with a pn junction or the like to cause a short circuit, or may block the optical path of the laser beam, resulting in a light emission failure.

Therefore, in this embodiment, as shown in FIG.
After etching the upper layer 1, the etching solution is again replaced with an iodine-based etching solution without removing the mask 19, and the exposed peripheral surface of the Au layer 12 is etched (side etching). A
The side etching of the U layer 12 is performed so that the periphery of the Au layer 12 is made of Cr.
This is done so that it is aligned with or inside the periphery of layer 1. For example, the periphery of the Au layer 12 is etched so as to be recessed about 0.1 to 0.5 μm deeper than the periphery of the Cr layer 1.

Next, after removing the mask 19, the back surface of the wafer 17 is etched so that the thickness of the wafer 17 is about 100 μm. After that, AuGeNi/
A cathode electrode 14 is provided which is sequentially laminated with Pd/Au.

Next, such a wafer 17 is cleaved along a direction perpendicular to the extending direction of the striped portion 18, and is divided at the center of the striped portion 18 to form laser chips as shown in FIG. be done. The center portion of the stripe portion 18 is divided by scribing with a diamond tool and subsequent cranking.

〔effect〕

1. According to the present invention, the electrode on the wafer, which becomes the electrode (anode electrode 13) on the side close to the resonator of the laser chip, does not have an overhang structure because the surface layer is made of highly malleable Au. Since the entire bottom surface is bonded to the Cr layer, even when the wafer is cleaved, the Au layer is not bonded to the Cr layer.
The layer elongation phenomenon is less likely to occur, and when the laser chip is formed, the Au layer does not protrude and sag to come into contact with the pn junction, resulting in improved reliability.

2. The laser chip of the present invention does not have an anode electrode extending along the periphery of the laser chip except for the periphery of the laser chip corresponding to the end of the resonator that emits laser light, and also has a rectangular shape. The corners of the anode electrode corresponding to the corners of the laser chip are chamfered to move further away from the corners of the laser chip. Even if a corner of the laser chip were to be chipped, the probability that the chipped part would reach the anode electrode part is extremely low because the corner part of the laser chip is chamfered as described above.

Therefore, since the anode electrode portion does not break, the electrode does not sag due to chipping at the corner of the laser chip, and the short circuit occurrence rate due to the protruding electrode portion can be reduced.

3. When manufacturing the anode electrode, the laser chip of the present invention can form the electrode pattern as described above by changing the pattern of the evaporation mask or the pattern of the etching mask, thereby preventing a rise in manufacturing costs. The effect is that no hindrance occurs.

4. According to 1 to 3 above, the laser chip of the present invention improves the manufacturing yield when converting wafers into chips, and
Since the number of manufacturing steps is not too large and no special manufacturing equipment is required, a synergistic effect can be obtained in that the manufacturing cost can be reduced by 1 or more.

Although the invention made by the present inventor has been specifically explained based on Examples above, the present invention is not limited to the Examples described above, and it is understood that various changes can be made without departing from the gist of the invention. Needless to say. For example, as shown in FIG. 6, the periphery of A I3 F12 is
Etching is performed inside the periphery of the wafer 17 by removing the mask 19 and forming a new mask 20 on the Au layer 12 after etching the Au layer 12 and the Cr layer 11 at step 1 of the wafer 17. Even if the peripheral edge of the Au layer 12 is etched, the same effect as in the embodiment described above can be obtained.

The laser chip shown in FIG. 7 is an example in which the present invention is applied to a structure in which the pattern of the anode electrode 13 is not provided at the periphery of the laser chip except for the end of the resonator 3. Therefore, countermeasures against short-circuit defects caused by the anode electrode 13 are improved. That is, the anode electrode 13 in this laser chip has a structure in which the portions along each side of the laser chip are separated from the periphery of the laser chip by, for example, about 50 μm, and chamfered portions 21 are provided at the four corners. The reason why the anode electrode 13 is kept away from each side of the laser chip is to prevent a short circuit due to the extension of the anode electrode 13.
The reason for this provision is that when the wafer 17 is made into chips, even if the chip corners are chipped to some extent, the chips do not extend to the anode electrode 13, and the torn anode electrode 1
The objective is to prevent the three parts from coming into contact with the pn junction.

Note that the width of the anode electrode 13 portion corresponding to the resonator end (
The constriction width) is 10'Oμm.

The width of this constriction is determined so that the carrier injection efficiency and light emission efficiency of the resonator end face in the laser chip will not be reduced, and pulsation (self-excited pulse oscillation) will not occur.

[Application field]

In the above explanation, we have mainly explained the case where the invention made by the present invention is applied to long wavelength semiconductor laser device technology, which is the background field of application, but it is not limited to this. It can be applied to semiconductor laser technology that emits external light, etc., and edge-emitting diode technology that emits light from its edge.

The present invention can be applied at least to a light emitting element such as a semiconductor laser element that emits laser light from its end face, or an integrated optical device (○EIC element) having such a semiconductor laser element portion.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a laser chip according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of a wafer before electrode formation, also showing a method of manufacturing the laser chip, and FIG. 3 is a cross-sectional view showing the state of electrode patterning. Figure 4 is the same (cross-sectional view showing the side etching state of the A xi layer, Figure 5 is a cross-sectional view showing a laser chip similarly obtained by dividing the wafer, and Figure 6 is another embodiment of the present invention). 7 is a cross-sectional view showing a state of electrode formation according to an example. FIG. 7 is a perspective view showing a laser chip according to another example of the present invention. 1...Substrate, 2...Buffer layer, 3...Active layer (
resonator), 4... cladding layer, 5... cap layer,
6...Multilayer growth layer, 7...Blocking layer, 8...
- Buried layer, 9... Cap layer, 10... Insulating film, 11... Cr layer, 12... Au layer, 13... Anode electrode, 14... Cathode electrode, 15... Ohmic contact layer, 16... Laser light, 17...
- Wafer, 18... Stripe portion, 19... Mask, 20... Mask, 21... Chamfered portion.

Claims (1)

[Scope of Claims] 1. An electrode consisting of at least two layers provided on the main surface of a light emitting element in which at least one side surface is a cleavage plane, excluding a part of the cleavage plane of the uppermost layer of the electrode. A light-emitting element characterized in that the peripheral edge portion is located in alignment with or within the peripheral edge of a lower layer that supports the top layer. 2. The light emitting device according to claim 1, wherein the uppermost layer is made of a gold layer, and the four corners of the electrode are chamfered. 3. A method of forming an electrode in which the top layer is a gold layer in a method of manufacturing a light emitting device by cutting a wafer into chips with cleavage. forming a gold layer base layer and a gold layer overlapping the gold layer base layer over the entire surface of the wafer;
a step of partially etching the gold layer by photolithography; a step of etching the gold layer base layer using the patterned gold layer as a mask; and a step of etching the gold layer base layer using the patterned gold layer as a mask. A method for manufacturing a light emitting device, comprising the step of partially etching a gold layer so as to coincide with or inside the periphery. 4. Etching the gold layer, etching the gold layer base layer,
4. The method of manufacturing a light emitting device according to claim 3, wherein the side etching of the peripheral edge of the gold layer is performed continuously by changing the etching solution.