JP4847682B2 - Nitride semiconductor device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a nitride semiconductor device such as a semiconductor laser, which is expected to be applied to the field of optical information processing, and a method for manufacturing the same.

  In order to increase the recording density of the optical disc, it is required to shorten the wavelength of the laser beam necessary for reading / writing data. In DVD players and recorders that are currently in widespread use, a red semiconductor laser with a wavelength of 660 nm is widely used. This red semiconductor laser is manufactured, for example, by epitaxially growing an InGaAlP-based compound semiconductor on a GaAs substrate.

  In recent years, next-generation optical discs have been actively developed in order to increase the recording density compared to DVD. As a light source for such a next-generation optical disc, it is required to stably emit blue-violet laser light (wavelength 400 nm band) having a shorter wavelength than red light.

  A group III-V nitride semiconductor containing nitrogen (N) as a group V element has a larger band gap than a GaAs-based semiconductor, and has a large emission energy, and thus has a short emission wavelength. For this reason, nitride semiconductors are considered promising as light emitting materials for short wavelength light.

Among nitride semiconductors, gallium nitride-based compound semiconductors (GaN-based semiconductors: Al _x Ga _y In _z N (0 ≦ x, y, z ≦ 1, x + y + z = 1)) have been actively studied, and blue light-emitting diodes (LED) and green LED are put into practical use. In addition, in order to increase the capacity of an optical disk device, a semiconductor laser having an oscillation wavelength in the 400 nm band is required, and development of a semiconductor laser using a GaN-based semiconductor as a material is underway.

  However, unlike a GaAs semiconductor laser, such a GaN semiconductor laser has been manufactured using a sapphire substrate or a low dislocation substrate on sapphire without using a semiconductor substrate. This is because it is difficult to produce a high-quality GaN-based semiconductor substrate. However, since the quality of GaN-based semiconductor substrates has recently been improved, it has begun to consider the production of nitride semiconductor elements using GaN-based semiconductor substrates.

  FIG. 9 is a perspective view showing the structure of a conventional semiconductor laser having a laminated structure on a GaN substrate. Such a semiconductor laser is disclosed in, for example, Patent Document 1 and Patent Document 2. A method for manufacturing the semiconductor laser shown in FIG. 9 will be described with reference to FIGS.

  First, an n-type GaN substrate 301 shown in FIG. 10 is prepared. The n-type GaN substrate 301 is composed of a hexagonal single crystal, and its main surface (upper surface) is a (0001) surface.

Next, as shown in FIG. 11, an n-type nitride semiconductor 303 and a p-type nitride semiconductor 304 are deposited on the n-type GaN substrate 301 by metal organic chemical vapor deposition (MOCVD). The n-type nitride semiconductor 303 includes an n-AlGaN cladding layer and an n-GaN light guide layer from the side close to the n-type GaN substrate 301, and the p-type nitride semiconductor 304 is from the side close to the n-type GaN substrate 301. _{, Ga 1-x In x N} / Ga 1-y In y N (0 <y <x <1) multiple quantum well (MQW) active layer, p-GaN optical guide layer, p-AlGaN cladding layer, and p- Includes a GaN contact layer.

  Next, as shown in FIG. 12, the upper surface of the p-type nitride semiconductor 304 is processed to form a plurality of ridge stripes each having a width of about 2 μm. FIG. 12 shows a cross section taken along a plane perpendicular to the resonator length direction.

  Thereafter, as shown in FIG. 13, both sides of each ridge stripe formed in the p-type nitride semiconductor 304 are covered with an insulating film 305. The upper surface of the ridge stripe is exposed through a stripe-shaped opening formed in the insulating film 305. Thereafter, a p-electrode 306 made of, for example, Ni / Au is formed so as to be in contact with the p-type nitride semiconductor 304 at the top of the ridge stripe. An n-electrode 307 made of, for example, Ti / Al is formed on the back surface of the substrate 301 after performing a polishing process as necessary.

  Next, primary cleavage is performed along the <11-20> direction of the substrate 301 to form a resonator end face made of a (1-100) plane. More specifically, a large number of bars are formed from one wafer by primary cleavage. Each bar has a resonator end face parallel to the paper surface of FIG. Thereafter, each bar is separated into multiple chips by secondary cleavage. More specifically, secondary cleavage is performed along the <1-100> direction, and the chips are separated as shown in FIG. The <1-100> direction is perpendicular to the resonator end surface composed of the (1-100) plane, and the surface exposed by secondary cleavage is perpendicular to both the resonator end surface and the substrate main surface (11-20). Surface.

9 is operated, the n-electrode 307 is grounded, and a voltage is applied to the p-electrode 306 by a drive circuit (not shown). Then, holes are injected from the p-electrode 306 side toward the MQW active layer, and electrons are injected from the n-electrode 307 side toward the MQW active layer. As a result, an inversion distribution is formed in the MQW active layer and an optical gain is generated, so that laser oscillation in the oscillation wavelength band of 400 nm is caused.
JP-A-11-330622 JP 2001-148357 A

  When manufacturing a semiconductor laser chip by the above-described method, there is a problem that the yield of secondary cleavage for chip separation is poor. This is a problem resulting from the crystal structure of a nitride semiconductor substrate such as GaN.

  In general, in the hexagonal nitride semiconductor, the (1-100) plane is easily cleaved, and the (11-20) plane perpendicular thereto is less likely to be cleaved than the (1-100) plane. Therefore, in the case of a semiconductor laser using a GaN substrate, in order to obtain a high-quality resonator end surface, a primary cleavage is usually performed along the <11-20> direction, and the resonator end surface composed of (1-100) planes. Form. Thereafter, secondary cleavage for chip separation is performed along the <1-100> direction. However, when cleaving along the <1-100> direction, it is often cracked along a direction shifted by 30 degrees with respect to the <1-100> direction, for example, along the <2-1-10> direction, resulting in a decrease in yield. To do.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a nitride semiconductor device having a high production yield and a method for producing the same.

  A method of manufacturing a nitride semiconductor device according to the present invention includes a nitride semiconductor substrate that is divided into a plurality of chip substrates, and a plurality of element portions that function as the substrate for each chip after the division, and the element portions are combined. A step (A) of preparing a nitride semiconductor substrate having an inter-element portion having an average thickness of the inter-element portion smaller than the thickness of the element portion; and a stripe-shaped opening on the element portion. Forming a mask layer on the upper surface of the nitride semiconductor substrate; and a nitride semiconductor on a region of the upper surface of the nitride semiconductor substrate exposed through the opening of the mask layer. A step (C) of selectively growing the layers, and cleaving the nitride semiconductor substrate from a portion between the elements of the nitride semiconductor substrate, and comprising a plurality of nitride semiconductor devices each having a chip substrate divided individually Form Degree and a (D).

  In a preferred embodiment, the step (A) includes a step (a1) of preparing a nitride semiconductor substrate having a flat top surface, and an average thickness of the inter-element portion by forming a groove on the top surface of the substrate. And a step (a2) of making the thickness smaller than the thickness of the element portion.

  In a preferred embodiment, in the step (a1), a GaN-based compound semiconductor substrate having an upper surface of (0001) is prepared, and in the step (a2), a groove extending in the <1-100> direction is formed.

  In a preferred embodiment, the step (a2) includes a step of forming the groove by etching the upper surface of the substrate by 0.1 μm or more.

  In a preferred embodiment, in the step (C), a stacked structure including a GaN-based compound semiconductor layer is formed by a selective growth method.

  In a preferred embodiment, the total thickness of the nitride semiconductor layers present on the inter-element portion of the nitride semiconductor substrate at the time of dividing the step (D) is present on the element portion. Smaller than the total thickness of the nitride semiconductor layers.

  The semiconductor light emitting device of the present invention is formed on the main surface of the nitride semiconductor substrate having a stripe-shaped convex portion extending in the resonator length direction and selected on the upper surface of the stripe-shaped convex portion. A mask layer having a stripe-shaped opening on the region; and a nitride semiconductor multilayer structure grown on a selected region on the upper surface of the stripe-shaped convex portion, the thickness of the nitride semiconductor multilayer structure being , Greater than the thickness of the nitride semiconductor present on the mask layer.

  In a preferred embodiment, the nitride semiconductor multilayer structure includes a p-type semiconductor layer and an n-type semiconductor layer.

  In a preferred embodiment, the substrate is a GaN-based compound semiconductor substrate having an upper surface of (0001) plane, and the resonator end surface is a (1-100) plane.

  In a preferred embodiment, the width of the protrusion is 50 μm or more and 500 μm or less, and the width of the stripe-shaped opening of the mask layer is 30 μm or more and 480 μm or less, and is narrower than the width of the protrusion.

  The width of the nitride semiconductor multilayer structure is larger than the width of the stripe-shaped opening of the mask layer, and the nitride semiconductor multilayer structure includes a portion grown laterally on the mask layer.

  In a preferred embodiment, the mask layer covers both side surfaces of the convex portion of the substrate.

  In a preferred embodiment, the height of the step existing on both sides of the convex portion of the substrate on the main surface of the nitride semiconductor substrate is 0.1 μm or more.

  In general, the crystal structure of a nitride semiconductor substrate is a hexagonal crystal and it is difficult to cleave in the <1-100> direction. However, in the present invention, a nitride in which the average thickness of the inter-element portion is smaller than the thickness of the element portion. Since a semiconductor substrate is used and a nitride semiconductor multilayer structure is selectively grown on the element portion, cleavage at the element portion is facilitated. According to the present invention, since a nitride semiconductor device can be mass-produced with a high yield using a nitride semiconductor substrate, a short wavelength light source such as a blue semiconductor laser can be supplied at low cost.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  First, refer to FIG. FIG. 1 is a perspective view showing the structure of the nitride semiconductor laser of this embodiment. As shown in the drawing, the substrate 101 in this embodiment is formed of an n-type GaN single crystal having a hexagonal crystal structure. The main surface (upper surface) of the n-type GaN substrate 101 is the (0001) surface. The n-type GaN substrate 101 is cleaved and divided into chips so that the resonator end face is the (1-100) plane and the side face of the element is the (11-20) plane.

  In the present embodiment, an n-type GaN substrate is used as the substrate 101, but the conductivity type may be inverted depending on the element structure. In addition, as long as the nitride semiconductor substrate has a hexagonal crystal structure, an AlGaN substrate, an AlN substrate, or the like may be used.

  As shown in FIG. 1, stripe-like convex portions extending along the resonator length direction <1-100> are formed on the main surface of the n-type GaN substrate 101. In a preferred embodiment, the width of the convex portion is set in a range of, for example, 50 μm or more and 500 μm or less. The resonator length is set, for example, in the range of 400 μm to 800 μm.

  On both sides of the main surface of the n-type GaN substrate 101 where the stripe-shaped convex portions are formed, there are surfaces located at a level lower than the upper surface level of the convex portions, and there are steps (0.1 to 10 μm). Is formed. For this reason, when the resonator end surface of the n-type GaN substrate 101 is viewed from the resonator length direction, it is observed that the upper portion of the n-type GaN substrate 101 is raised in a convex shape.

  An insulating film 102 that functions as a mask layer for selective growth is formed on the main surface of the n-type GaN substrate 101. The insulating film 102 is formed of, for example, a silicon nitride film and has a stripe-shaped opening on a selected region on the upper surface of the stripe-shaped convex portion, but covers the other region of the main surface of the substrate. The width of the stripe-shaped opening is 30 μm or more and 480 μm or less, and is preferably designed to be narrower than the width of the projection.

  The insulating film 102 may be formed of any material as long as the nitride semiconductor does not easily grow on the insulating film 102, but is preferably silicon nitride, silicon oxynitride, silicon oxide, oxide It is formed from aluminum or the like. Note that the mask layer does not necessarily have an insulating property as long as it is a material that functions as a mask for selective growth; therefore, the mask layer can be formed from a semiconductor or metal.

  In this embodiment, a nitride semiconductor multilayer structure is formed on the upper surface of the stripe-shaped convex portion of the n-type GaN substrate 101. As will be described in detail later, this stacked structure is selectively grown on an n-type GaN substrate 101 whose main surface is partially covered by an insulating film 102. In the drawing, it is described that no nitride semiconductor is deposited on the insulating film 102, but the entire insulating film 102 is covered as long as the layer is thinner than the thickness of the nitride semiconductor multilayer structure. You may do it. Although a nitride semiconductor may grow on the insulating film 102 depending on the conditions of selective growth, the thickness of the nitride semiconductor existing on the insulating film 102 is the thickness (height of the stacked structure of nitride semiconductors). If it is smaller than), there is no problem.

  More specifically, the stacked structure of nitride semiconductors formed on the stripe-shaped protrusions of the n-type GaN substrate 101 is more specifically the n-type nitride semiconductor 103 grown on the substrate 101 and the n-type nitride semiconductor 103. The grown p-type nitride semiconductor 104 is included, and these semiconductors 103 and 104 further include nitride semiconductor layers having various compositions.

  The upper portion of the p-type nitride semiconductor 104 is processed into a ridge stripe shape, and is covered with an insulating film 105 having an opening at the top of the ridge stripe. A p-electrode 106 is formed so as to be in contact with the p-type compound semiconductor 104 at the top of the ridge stripe, and an n-electrode 107 is formed on the back side of the substrate 101.

  The width of the nitride semiconductor stacked structure may be wider than the width of the stripe-shaped opening of the insulating film 102. The laminated structure of the nitride semiconductor in the illustrated example includes a portion grown in the lateral direction on the insulating film 102. The width at the bottom of the laminated structure is set in a range of 40 μm or more and 490 μm or less, for example.

  In the semiconductor laser shown in FIG. 1, the width of the opening provided in the insulating film 102 is constant in the resonator length direction, but the insulating film 102 is patterned so that the width of the opening varies depending on the position. Also good. By adjusting the shape, size, and position of the opening in the insulating film 102, the shape, size, and position of the nitride semiconductor stacked structure formed by selective growth can be controlled. Even if the pattern of the openings in the insulating film 102 is the same, the width of the nitride semiconductor multilayer structure can be changed by adjusting the conditions for selective growth.

  1, the n electrode 107 is grounded and a voltage is applied to the p electrode 106 to inject holes from the p electrode 106 side into the multiple quantum well active layer, and from the n electrode 107 side to the multiple quantum well. Electrons are injected into the active layer. Thus, an optical gain can be generated in the multiple quantum well active layer, and laser oscillation with an oscillation wavelength band of 400 nm can be caused.

  Next, a method for manufacturing the semiconductor laser shown in FIG. 1 will be described with reference to FIGS.

  First, as shown in FIG. 2, an n-type GaN substrate 101 having a hexagonal crystal structure and having a principal surface 10 of (0001) plane is prepared. The thickness of the substrate 101 is, for example, 400 μm. The n-type GaN substrate 101 at this stage is not divided into chips, and has a wafer shape with a diameter of about 2 inches, for example. FIG. 2 is a partially enlarged view schematically showing a part of the substrate 101.

  Next, as shown in FIG. 3, grooves 12 are formed in the main surface of the substrate 101. In this embodiment, the groove 12 has a width of 50 μm and a depth of 500 nm, and the direction in which the groove extends (the direction perpendicular to the drawing sheet) is the <1-100> direction of the substrate 101 (see FIG. 1). This groove 12 is formed to facilitate secondary cleavage. Accordingly, the groove 12 is formed in the inter-element portion 16, and the element portion 14 cut out from the substrate 101 as the final chip substrate is located in a region between the two adjacent grooves 12.

  In the present embodiment, the interval between the grooves 12 (size approximately corresponding to the width of the element portion 14) is set to 450 μm, for example. The grooves 12 are periodically arranged, and the pitch defines the chip size of each element that is finally cut out from the substrate 101. In order to facilitate secondary cleavage, the lower limit of the depth of the groove 12 is preferably set to 0.1 μm or more. On the other hand, the upper limit of the depth of the groove 12 is about 10% of the substrate thickness at the start of the process. If the depth of the groove 12 is excessively larger than the above-mentioned ratio compared to the substrate thickness, the mechanical strength of the substrate 101 is lowered, and the substrate 101 may be damaged during the manufacturing process.

  Such grooves 12 are easily formed by forming a resist pattern (not shown) on the main surface 10 of the substrate 101 by photolithography and then etching the substrate 101 using the resist pattern as a mask. The groove 12 can be preferably formed by, for example, reactive ion etching. In this case, the depth of the groove 12 is managed by the etching time.

  Next, an insulating film 102 made of a silicon nitride film is deposited on the main surface of the substrate 101 by sputtering. The thickness of the insulating film 102 is arbitrary as long as the thickness functions as a mask for selective growth. There is no need to consider the withstand voltage of the insulating film 102. In this embodiment, the insulating film 102 made of a silicon nitride film having a thickness of about 50 nm is formed. Thereafter, as shown in FIG. 4, the insulating film 102 is patterned to form an opening of the insulating film 102 at a position between the groove 12 and the groove 12 (a convex portion of the substrate main surface). A part of the convex portion of the substrate 101 is exposed through the opening. The groove 12 is entirely covered with the insulating film 102. The planar shape of the opening is a stripe shape having a longitudinal direction in the resonator length direction.

Next, as shown in FIG. 5, a nitride semiconductor multilayer structure 30 is formed using MOCVD. The stacked structure 30 includes an n-type nitride semiconductor 103 and a p-type nitride semiconductor 104 from the side close to the substrate 101. More specifically, the n-type nitride semiconductor 103 includes an n-Al _0.07 Ga _0.93 N cladding layer and an n-GaN light guide layer, and the p-type nitride semiconductor 104 includes a multiple quantum well active layer and a p-GaN light guide. Layer, p-Al _0.07 Ga _0.93 N clad layer, p-GaN layer. The details of each semiconductor layer constituting the stacked structure 30 may be different depending on the type of the semiconductor laser.

  The laminated structure 30 is composed of a nitride semiconductor layer selectively grown from the opening of the insulating film 102. Since the nitride semiconductor is difficult to grow on the insulating film 102 by the selective growth, the thickness of the stacked structure formed on the opening of the insulating film 102 is larger than the thickness of the nitride semiconductor deposited on the insulating film 102. (The thickness is zero in FIG. 5).

  Next, as shown in FIG. 6, a ridge stripe having a width of about 2 μm is formed on the p-type nitride semiconductor 104. Next, as shown in FIG. 7, after covering both sides of the ridge stripe with the insulating film 105, a current injection region is formed on the top of the ridge stripe. Then, a p-electrode 106 made of, for example, Ni / Au is formed by a lift-off method so as to contact the surface of the p-type nitride semiconductor 104 exposed at the top of the ridge stripe. For example, an n-electrode 107 made of Ti / Al is formed on the back surface of the substrate 101 after performing a polishing process as necessary.

  Thereafter, primary cleavage is performed along the <11-20> direction of the substrate 101 to form a resonator end face made of a (1-100) plane. The resonator end face is parallel to the paper surface of FIG. By this primary cleavage, a large number of bars are formed from one wafer. In each bar, a plurality of elements are connected in series as shown in FIG.

  Next, secondary cleavage is performed from the portion of the substrate 101 where the groove 12 is formed along the <1-100> direction perpendicular to the resonator end face. Thus, as shown in FIG. 8, an element divided into chips can be obtained. In FIG. 8, only three elements are shown, but in reality, many elements are formed from each bar. In FIG. 8, the (11-20) planes generated by the secondary cleavage of adjacent elements are shown to face each other.

  The device shown in FIG. 1 is formed by the method described above. Each element has an element portion of the substrate 101 originally in a single wafer state as a chip substrate.

  The p-electrode 106 is desirably formed only on the opening of the insulating film 102. In this case, since the p-electrode 106 does not exist in the chip division region (inter-element portion) due to secondary cleavage, defects such as separation of the p-electrode due to chip division are unlikely to occur.

  According to the present embodiment, for example, as shown in FIG. 7, the groove-like void 40 extending in the <1-100> direction is formed between the adjacent laminated structures 30. On the other hand, in the conventional example, as shown in FIG. 13, since the laminated structure is continuously present on the substrate 101 even in the portion between the elements, the above groove-like gap does not exist. The presence of such a groove-like void 40 also has an effect of facilitating secondary cleavage in the <1-100> direction.

  In this embodiment, the groove 12 is formed on the main surface 10 of the substrate 101 to facilitate secondary cleavage in the <1-100> direction. However, such a groove 12 is formed on the main surface 10 of the substrate 101. Even if not, there is a possibility that the secondary cleavage in the <1-100> direction can be executed with a high yield due to the presence of the groove-like gap 40 extending in the <1-100> direction. In such a case, it is not necessary to form the groove 12 on the main surface of the substrate 101. In the case where a groove is not formed in the main surface of the substrate 101 as described above, it is preferable to increase the selectivity during selective growth and to sufficiently reduce the thickness of the semiconductor deposited on the insulating film 102. However, when the substrate 101 has a thickness exceeding 100 μm, it is preferable to provide the groove 12 in addition to the groove-shaped gap 40.

  In the above-described embodiment, the average thickness in the inter-element portion of the substrate 101 is made thinner than the other portions by forming the grooves 12 continuous in the <11-20> direction. Instead of forming 12, a plurality of pit rows may be formed. The grooves and pit rows may be formed on the back side of the substrate.

  The present invention greatly contributes to the practical application of a short wavelength semiconductor laser expected to be applied to the field of optical information processing.

It is a perspective view which shows the structure of embodiment of the nitride semiconductor element by this invention. FIG. 3 is a process cross-sectional view illustrating a method for manufacturing the nitride semiconductor device of FIG. 1. FIG. 3 is a process cross-sectional view illustrating a method for manufacturing the nitride semiconductor device of FIG. 1. FIG. 3 is a process cross-sectional view illustrating a method for manufacturing the nitride semiconductor device of FIG. 1. FIG. 3 is a process cross-sectional view illustrating a method for manufacturing the nitride semiconductor device of FIG. 1. FIG. 3 is a process cross-sectional view illustrating a method for manufacturing the nitride semiconductor device of FIG. 1. FIG. 3 is a process cross-sectional view illustrating a method for manufacturing the nitride semiconductor device of FIG. 1. FIG. 3 is a process cross-sectional view illustrating a method for manufacturing the nitride semiconductor device of FIG. 1. It is a perspective view which shows the structure of the conventional nitride semiconductor laser. FIG. 10 is a process cross-sectional view illustrating the method for manufacturing the nitride semiconductor laser of FIG. 9. FIG. 10 is a process cross-sectional view illustrating the method for manufacturing the nitride semiconductor laser of FIG. 9. FIG. 10 is a process cross-sectional view illustrating the method for manufacturing the nitride semiconductor laser of FIG. 9. FIG. 10 is a process cross-sectional view illustrating the method for manufacturing the nitride semiconductor laser of FIG. 9. FIG. 10 is a process cross-sectional view illustrating the method for manufacturing the nitride semiconductor laser of FIG. 9.

Explanation of symbols

101 n-type GaN substrate 102 insulating film 103 n-type nitride semiconductor 104 p-type nitride semiconductor 105 insulating film 106 p-electrode 107 n-electrode 301 n-type GaN substrate 302 insulating film 303 n-type nitride semiconductor 304 p-type nitride semiconductor 305 Insulating film 306 p-electrode 307 n-electrode

Claims (3)

A step (A) of preparing a nitride semiconductor substrate having a main surface of (0001) plane;
Forming a stripe-shaped groove extending in the <1-100> direction on the main surface side of the nitride semiconductor substrate (B);
Forming a mask layer to cover the groove (C);
A step (D) of selectively growing a nitride semiconductor multilayer structure in a region of the main surface of the nitride semiconductor substrate that is not covered with the mask layer;
The <1-100> along the direction, seen including a step (E) cleaving the nitride semiconductor substrate from said groove,
In the step (C), the mask layer is formed so as to cover the entire groove portion . The method for manufacturing a nitride semiconductor device according to claim 1, further comprising a step of cleaving the nitride semiconductor substrate along a <11-20> direction between the step (D) and the step (E). .   The method for manufacturing a nitride semiconductor device according to claim 1, wherein the nitride semiconductor multilayer structure includes a p-type semiconductor layer and an n-type semiconductor layer.