JP2007258640A - Semiconductor element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor element in which high heat dissipating characteristics and high product yield are maintained by forming a metal layer having a sufficient film thickness as an upper electrode close to a light emitting end surface (cleaved end surface). <P>SOLUTION: In the semiconductor element comprising a semiconductor substrate 4 on which a plurality of semiconductor layers are laminated and an electrode formed on one surface in a lamination direction of the semiconductor substrate, the electrode 10 is so formed as to cover the entire surface of the one surface, and is comprised of at least one of a molybdenum (Mo) and a tungsten (W). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor device and a method for manufacturing the same, and more particularly, to a semiconductor device capable of obtaining a good resonator end face and improving yield while maintaining high heat dissipation.

2. Description of the Related Art In recent years, a semiconductor laser element, which is one form of a semiconductor element, has been widely used in an optical disk device that records / reproduces an optical disk such as a BD (Blu-ray Disk), a DVD (Digital Versatile Disk), and a CD (Compact Disk). Further higher output is desired.
One of the semiconductor laser elements corresponding to this high output is a resonator type semiconductor laser element. This resonator-type semiconductor laser device has a resonator composed of a light emitting surface and a reflecting surface that are substantially parallel to each other. When a current is applied to this resonator type semiconductor laser element, laser oscillation occurs in the active layer, and the oscillated laser light resonates between the light emitting surface and the reflecting surface, and the current exceeds the oscillation threshold value. When this happens, laser light is emitted from the light emission surface.

The heat dissipation characteristic of the heat accompanying this laser oscillation is determined by the structure around the light emitting part. In recent years, there has been proposed a structure in which a metal having high thermal conductivity is brought into contact with an active layer that emits light in order to improve heat dissipation (see Patent Document 1).
On the other hand, as a method of manufacturing such a semiconductor laser element, there is a technique of obtaining a good reflection surface (end face) by cleaving a semiconductor substrate on which the laser element is formed and easily separating each laser element. Generally adopted. In this cleavage, if a metal electrode exists on the cleavage line on the semiconductor substrate, burrs are generated due to the ductility of the metal, and the light emission characteristics are hindered. Therefore, a technique for patterning the metal electrode according to the element Is also widely used.

  For example, FIG. 6 is a schematic perspective view showing a conventional semiconductor laser device. In this semiconductor laser device 2, various layers including an active layer 6 are formed on a semiconductor substrate 4 such as a GaAs substrate, and a ridge portion 8 is formed with a convex upper surface. An upper electrode 10 and a lower electrode 12 are provided on the lower surface. One of the two ends of the semiconductor laser element 2 is a reflecting surface and the other is a light emitting surface. When a voltage is applied between the upper and lower electrodes 10 and 12 to cause laser oscillation, the end surface of the active layer 6 Laser light is emitted. Here, as described above, the upper electrode 8 is larger than the planar size of the laser element 2 so that the burrs generated by the ductility of the metal forming the upper electrode 8 at the time of cleavage do not hinder the light emission characteristics or reduce the product yield. It is formed in a slightly smaller pattern, and a slight gap 14 is formed between the end faces.

JP 2002-94181 A

  As described above, when the upper electrodes 10 are separated from each other by patterning, the metal layer as the upper electrode does not exist in the gap 14 on the upper surface near the end face of the semiconductor laser element. By the way, in this kind of semiconductor laser element, the heat generation amount of the active layer 6 in the vicinity of the end face is very large, and the fact that the metal layer made of the upper electrode 12 does not exist in the gap 14 as described above is a heat dissipation. Very disadvantageous in gender.

  On the other hand, when the metal layer of the upper electrode 12 is formed up to the position of the end face and the gap 14 is eliminated, the heat dissipation is improved, but the metal layer that inevitably becomes the upper electrode 12 on the semiconductor wafer at the time of cleavage. Will be divided by tension. Currently, the metal layer forming the upper electrode 12 often has a multi-layer structure centered on Au (gold) in terms of ohmic contact, stability, thermal conductivity, electrical conductivity, etc. Since the metal layer is a transition metal, the metal layer is highly ductile. As a result, burrs are generated when the metal layer is divided by tension, and the burrs may block the light emitting surface and hinder the light emitting characteristics. In particular, in the case of a semiconductor laser element called an air ridge structure as shown in Patent Document 1, since the distance between the upper electrode and the light emitting surface is very short, the generation of burrs causes a significant decrease in product yield.

In order to avoid the occurrence of such burrs, a method of reducing the thickness of the upper electrode 10 is sometimes used. In this case, however, it is expected that the heat dissipation is insufficient, the reliability is reduced due to an increase in stress, and the like. Is not desirable. In addition, there is a problem that the restriction by the solder material when mounting the laser element on the heat sink is strongly imposed, and the degree of freedom in design is reduced.
The present invention has been devised to pay attention to the above problems and to effectively solve them. An object of the present invention is to form a metal layer having a sufficient thickness as an upper electrode up to the vicinity of a light emitting end face (cleaved end face), maintain a high heat dissipation, and maintain a high product yield and its manufacture It is to provide a method.

  As a means for achieving the above object, according to the first aspect of the present invention, an active layer is formed on a semiconductor substrate sandwiched between electrodes made of metal layers from above and below, and a voltage is applied to both electrodes. Thus, in the semiconductor element in which laser light is emitted from the light emitting surface of the end surface of the active layer, both ends of the metal layer are formed to reach the cleavage end surface of the semiconductor substrate, and the metal layer is made of molybdenum. It is a semiconductor element characterized by including at least one of (Mo) and tungsten (W).

  According to a second aspect of the present invention, there is provided a step of forming a laser element block body by forming a second conductive type semiconductor layer on an active layer on a first conductive type semiconductor substrate, and the laser element Forming a metal layer serving as an electrode including at least one of molybdenum and tungsten on the second conductive type semiconductor layer of the block body; and a laser element block body on which the metal layer is formed. And cleaving the laser element block body in a cleavage direction of the semiconductor substrate in a state where the laser element block is cooled to a temperature lower than room temperature.

  According to the semiconductor element and the manufacturing method of the present invention, a metal layer having a sufficient thickness as an upper electrode is formed up to the vicinity of the light emitting end face (cleavage end face), and high heat dissipation can be maintained, and the product yield can be maintained high. Can do.

Hereinafter, an embodiment of a semiconductor device and a manufacturing method thereof according to the present invention will be described in detail with reference to the accompanying drawings.
1 is a schematic perspective view showing a semiconductor element according to the present invention, FIG. 2 is an enlarged cross-sectional view showing the semiconductor element shown in FIG. 1, and FIG. 3 is a situation when the semiconductor element of the present invention is separated by cleavage. It is explanatory drawing explaining these. Here, a semiconductor laser element will be described as an example of the semiconductor element.
The same components as those of the conventional semiconductor laser element shown in FIG. 6 will be described with the same reference numerals. Here, the first conductivity type of the semiconductor is described as n-type and the second conductivity type is defined as p-type, but the relationship between the two may be reversed.

  As shown in FIGS. 1 and 2, this semiconductor laser element 20 which is one form of a semiconductor element is formed on a semiconductor substrate 4 made of a compound semiconductor such as GaAs, for example, by MOCVD (chemical vapor phase using an organic metal material). N-AlGaInP first clad layer 22, n-AlGaInP second clad layer 24, active layer 6, and second conductivity type p-AlGaInP first clad using the vapor deposition method). A layer 26, an etching stopper layer 28, a p-AlGaInP second cladding layer 30, a barrier relaxation layer 32 made of n-GaInP, and a p-GaAs contact layer 34 are grown in this order, and are etched in the center as shown in FIG. A current confinement structure in which the convex ridge portion 8 is formed is produced. Here, below the active layer 6 is a semiconductor layer of the first conductivity type (n), and above is a semiconductor layer of the second conductivity type (p).

  An upper electrode 10 made of a metal layer is formed on the upper surface side, and a lower electrode 12 is formed on the lower surface side of the semiconductor substrate 4. In this case, the upper electrode 10 has a structure covering the upper surface of the ridge portion 8 and both the left and right side surfaces. Here, the metal layer of the upper electrode 10 includes at least one of Mo (molybdenum) and W (tungsten).

  Specifically, the upper electrode 10 made of this metal layer is formed by laminating a plurality of metal films, and here, for example, three layers of a Ti film 10A, a Mo film 10B, and an Au film 10C from the lower layer to the upper layer. Although it has a structure, the number of layers is not limited. Each of the above films is formed by sputtering or vapor deposition, and the thickness thereof is, for example, 500 nm for the Ti film 10A, 2 μm for the Mo film 10B, and 500 mm for the Au film. The Ti film 10A is an underlayer for ensuring ohmic contact with the barrier relaxation layer 32, and the Au film 10C functions as an anti-oxidation layer for preventing oxidation and an alloying layer for curing to a heat sink. To do. Both the Ti film 10A and the Au film 10C are desirably 1000 mm or less. In particular, by setting the Au film 10C to 1000 mm or less, burrs of the Au film 10C can be suppressed when cleaved. The Mo film 10B is desirably 5000 mm or more in order to ensure heat dissipation and relieve stress applied to the ridge portion 8. In this case, a W film may be provided instead of or in addition to the Mo film 10B. As will be described later, Mo and W are metals having a relatively high ductile brittle transition temperature compared to other metals.

  As shown in FIG. 3, the semiconductor laser element 20 is formed separately by cleaving a large semiconductor substrate (wafer) along its cleavage line 36. Here, the semiconductor substrate greatly spreads in a horizontal plane as will be described later. In this case, both end faces of the semiconductor laser element 20 are configured as cleaved end faces 38A and 38B, one cleaved end face 38A is a reflecting face, and the other cleaved end face 38B is a light emitting face, that is, a light emitting end face. The end surface of the active layer 6 immediately below the ridge 8, that is, the central region of the end surface of the active layer 6 becomes the light emitting surface 38 </ b> C. In this case, a resonator is formed between the two cleaved end faces 38A and 38B of the active layer 6, and laser oscillation is performed by applying a voltage between the upper and lower electrodes 10 and 12.

  Then, both end portions of the upper electrode 10 in the length direction of the semiconductor laser element 20 (left and right direction in FIG. 1) reach the both cleaved end faces 38A and 38B, that is, over the entire length direction of the laser element. As will be described later, the heat dissipation characteristics can be maintained high. In other words, the upper electrode 10 has a structure that covers the upper surface and both side surfaces of the ridge portion 8 as described above.

Next, a method for manufacturing the semiconductor laser element 20 will be described with reference to FIG.
First, as shown in FIG. 4A, on the large semiconductor substrate 4 made of a GaAs semiconductor wafer or the like, all the except for the upper electrode 10 and the lower electrode 12 shown in FIG. All layers 22, 24, 6, 26, 28, 30, 32, 34 from the thin film layer, that is, the n-AlGaInP first cladding layer 22 to the p-GaAs contact layer 34 thereabove (in FIG. (Omitted) are sequentially stacked, and the upper three layers 30, 32, and 34 are patterned and etched to form a plurality of parallel ridge portions 8. Thereby, the laser element block body 50 is formed as a whole.

  Next, as shown in FIG. 4B, the lower electrode 12 is formed on the entire lower surface of the laser element block body 50, and on the upper surface, for example, a Ti film 10A, a Mo film 10B, and an Au film 10C (see FIG. 2). The upper electrode 10 is laminated as a metal layer (metal layer forming step). In this case, the upper electrode 10 may be formed over the entire upper surface, or as a continuous pattern along the length direction of the ridge portion 8 as shown in FIG. It may be formed by patterning to some extent so as to be separated for each element in the direction to be performed. In any case, the upper electrode 10 is formed so that the upper surface and both side surfaces of the ridge portion 8 are completely covered along the longitudinal direction. The lower electrode 12 may be formed before the film formation process described with reference to FIG.

  Then, the laser element block body 50 in which both the upper and lower electrodes 10 and 12 are formed is cleaved along the cleavage line 36 of the large semiconductor substrate 4 to obtain a block bar as shown in FIG. 52 is formed (cleavage process). Here, when the cleavage shown in FIG. 4B is performed, as the characteristic treatment of the present invention, the cleavage is performed in a state where the laser element block body 50 is cooled to a temperature lower than room temperature. Preferably, the cleavage is performed in a state of cooling to a temperature near the ductile brittle transition temperature of molybdenum or tungsten contained in the metal layer of the upper electrode 10, and more preferably to a temperature lower than the ductile brittle transition temperature. Here, since the upper electrode 10 includes the Mo film 10B, the upper electrode 10 is formed at a temperature near or below the ductile brittle transition temperature of Mo. In the case where both the W film and the Mo film are included, it is performed at a temperature near or lower than the ductile brittle transition temperature of the lower temperature.

  Pure Mo forming the Mo film 10B is one of the most famous metals known to be brittle and deteriorate at low temperatures. This property is called low temperature brittleness, and the temperature at which the property is changed is called ductile brittle transition temperature (hereinafter also referred to as “DBTT”). The pure Mo has a DBTT of about −56 ° C. Therefore, by cleaving at a low temperature around −56 ° C., the Mo layer 10B exhibits low temperature brittleness and loses ductility, and can be divided without generating burrs regardless of its thickness. The DBTT of pure W is about -90 ° C.

  A simple example using dry ice is shown as an example of creating a low temperature environment. Since dry ice has a sublimation point of −78.5 ° C., the temperature can be easily lowered to −56 ° C. or lower, which is the DBTT of Mo. The laser element block body 50 with both electrodes shown in FIG. 4B, which is the target of cleavage, is fixed to a sheet and a predetermined jig, and a part of the separation line (cleavage line 36) to be cleaved is scribed. It is preferable that the sheet is fixed only by the adhesiveness of the surface, rather than the sheet fixed by the adhesive material. Then, leave it in a sealed space with dry ice for a sufficient amount of time, and then quickly apply pressure and cleave.

Next, when the block bar 52 shown in FIG. 4 (C) formed by the above cleavage is obtained, an end face protective film is formed on both the cleavage end faces before and after the block bar 52 by using a reactive sputtering method or the like. Then, by cutting in a direction orthogonal to the cleavage direction, the semiconductor laser device 20 as shown in FIG. 1 is completed by separating each device. Here, for example, an Al ₂ O ₃ film is formed on one cleavage end face of the laser element 20 to form a light emission end face, and an Al ₂ O ₃ film and amorphous Si are formed on the other cleavage end face. A reflective film is used.

  As described above, in the conventional semiconductor laser device, the upper electrode formed of a transition metal (Au, Pt, etc.) has its ductility, so that it reaches the cleavage end surface as in the semiconductor laser device 20 of the present invention shown in FIG. When the electrode is formed (in the state where there is no gap 14 in FIG. 6), a burr is generated at the time of cleavage, and this burr covers the light emitting surface (light emitting point) at the center of the ridge of the active layer 6 with a high probability. Therefore, the light emission characteristics of the semiconductor laser element are hindered and the yield is lowered. Even when the light emitting surface is not obstructed, the n electrode side and the p electrode side are short-circuited, and this point is also a cause of lowering the yield.

  On the other hand, as in the present invention, a Mo or W film that easily becomes brittle and denatured at low temperatures is used as a material for the metal layer of the upper electrode 10, and the metal layer is cleaved at a low temperature at which the ductility is not exhibited. Therefore, the metal layer does not generate burrs, and a good light emitting end surface in which the upper electrode 10 is formed up to the cleavage end surface can be obtained. As described above, since the metal layer is formed up to the cleaved end face, it is possible to sufficiently ensure the heat dissipation of the light emitting end face where the amount of heat generation is greatest in the resonator direction, and as a result, high heat resistance and reliability are obtained. I can do it.

  In particular, when a layer containing a metal having low temperature brittleness including Mo and W is used for the thick layer in the upper electrode 10, a low temperature environment that does not exhibit ductility can be easily created. As described above, for example, in the case of 100% Mo, the temperature showing low-temperature brittleness (ductile brittle transition temperature = DBTT) is about −56 ° C., and it is easy to use dry ice (sublimation point—78.5 ° C.) or the like. It is possible to cool down to DBTT.

<Evaluation by thermal simulation>
Next, the evaluation by thermal simulation was performed with and without the upper electrode up to the cleavage end face in the semiconductor laser element, and the evaluation result will be described.
FIG. 5 is a graph showing a temperature distribution when a thermal simulation of the semiconductor laser element is performed. In FIG. 5, curve A shows the characteristic along the active layer generation center line a of the conventional semiconductor laser device shown in FIG. 6, and curve B shows the active layer generation center line of the semiconductor laser device of the present invention shown in FIG. The characteristic along b is shown. The horizontal axis takes the position in the direction of the resonator formed between the two cleavage end faces, and the front end face (left end face in FIG. 1) is the reference (X = 0).

  Assuming that both were cured to a heat sink of AuSn wax material by junction down, the resonator length was 400 μm and the environmental temperature was 85 ° C. The upper electrode has a three-layer structure of Au (500 mm) / Mo (2 μm) / Ti (500 mm), and the length of the gap 14 where there is no metal layer in the vicinity of the cleaved end face in FIG. The conductivity values are Au: 310 (W / m · K), Mo: 140 (W / m · K), and Ti: 22 (W / m · K).

From FIG. 5, it can be seen that in the semiconductor laser element, the heat generation at the end face is the largest, and the heat dissipation is greatly improved by the presence of the metal layer in the upper part near the end face. For example, the temperature of the front end face in FIG. 6 of the conventional structure is 115.6 ° C., whereas the temperature of the front end face in the structure shown in FIG. 1 of the present invention is 105.7 ° C., which is about 10 ° C. It was confirmed that improvement can be made.
In the above embodiment, the configuration of the upper and lower semiconductor layers of the active layer 6 is merely an example, and it is needless to say that the present invention is not limited to this.

In the above embodiment, the upper electrode 10 has a laminated structure composed of the Ti film 10A, the Mo film 10B, and the Au film 10C. However, the present invention is not limited to this.
For example, the upper electrode 10 may be an alloy film made of three elements of Ti, Mo, and Au. In this case, the DBTT of the upper electrode 10 can be set to an arbitrary value depending on the composition ratio of each element. For example, the DBTT of the upper electrode 10 approaches −56 ° C. by increasing the Mo composition ratio, and the DBTT of the upper electrode 10 approaches −273 ° C. by increasing the Au composition ratio.
Further, the upper electrode 10 may be formed such that the composition ratio of the constituent elements gradually changes in the thickness direction. For example, the upper electrode 10 is formed by a vapor deposition method using two targets of a Mo target and an Au target, and the ratio of the amount of deposited Mo with respect to the amount of deposited Au is large at the start of film formation. The composition ratio of Mo with respect to Au in the thickness direction of the formed upper electrode 10 is decreased by gradually reducing the film thickness so that the deposition amount of Au is larger than the deposition amount of Mo at the end of deposition. Alternatively, it may be formed so as to be large on the semiconductor substrate side and small on the surface side of the upper electrode 10.

1 is a schematic perspective view showing a semiconductor element according to the present invention. It is an expanded sectional view which shows the semiconductor element shown in FIG. It is explanatory drawing explaining the condition when isolate | separating by cleavage when manufacturing the semiconductor element of this invention. It is explanatory drawing explaining the manufacturing method of a semiconductor laser element. It is a graph which shows temperature distribution when performing the thermal simulation of a semiconductor laser element. It is a schematic perspective view which shows the conventional semiconductor laser element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 4 ... Semiconductor substrate, 6 ... Active layer, 8 ... Ridge part, 10 ... Upper electrode, 10A ... Ti film, 10B ... Mo film, 10C ... Au film, 12 ... Lower electrode, 20 ... Semiconductor laser element (semiconductor element), 36 ... cleavage line, 38A, 38B ... cleavage end face, 38C ... light emitting surface, 50 ... laser element block.

Claims (3)

In a semiconductor element having a semiconductor substrate in which a plurality of semiconductor layers are stacked, and an electrode formed on one surface in the stacking direction of the semiconductor substrate,
The electrode is formed so as to cover the entire surface, and includes at least one of molybdenum (Mo) and tungsten (W). A metal layer forming step of forming a metal layer on a surface of a semiconductor substrate on which a plurality of semiconductor layers are stacked;
A cleavage step of cleaving in the thickness direction the semiconductor substrate on which the metal layer has been formed in a state of being cooled to a temperature equal to or lower than the ductile brittle transition temperature of the metal material constituting the metal layer;
A method for manufacturing a semiconductor device, comprising: 3. The method of manufacturing a semiconductor element according to claim 2, wherein in the metal formation step, the metal layer is formed to include at least one of molybdenum (Mo) and tungsten (W).

Images