Patent Application
20110304025
The present invention relates to a nitride compound semiconductor element and a production method therefor.
A band gap of a nitride compound semiconductor whose composition is expressed by the general formula InxGayAlzN (where x+y+z=1, 0≦x≦1, 0≦y≦1, 0≦z≦1) may have a width corresponding to blue light or ultraviolet light through adjustment of the mole fraction of each element. Therefore, there have been vigorous research activities directed to light-emitting devices, e.g., semiconductor lasers, that comprise a nitride compound semiconductor as an active layer.
Due to this problem, it has conventionally been very difficult to fabricate a nitride compound semiconductor element having smooth resonator end faces.
Note that a sapphire substrate, which has conventionally been widely used as a substrate for nitride compound semiconductor elements, is not capable of cleaving. Therefore, when forming a semiconductor laser having a sapphire substrate, it has been practiced to perform scribing along the M-plane from the side of a nitride compound semiconductor layer that is grown on a sapphire substrate to thus form a scratch in the nitride compound semiconductor layer, this being an attempt to facilitate the formation of a cleavage plane.
Patent Document 1 discloses a method which involves performing an edge scribing for a nitride compound semiconductor layer, and thereafter performing a cleavage through breaking.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2000-058972
However, according to the aforementioned conventional technique, since scratches are formed in the nitride compound semiconductor layer through scribing or dicing, there is a problem in that “burrs”, “chipping”, “end-face cracks” and the like are likely to occur, thus resulting in a reduced production yield. There is also a problem in that, since the active layer is likely to suffer from strain and crystal defects, scratches and ruggednesses may occur in a resonator end face (light-outgoing surface), thus deteriorating the optical characteristics and reliability.
Furthermore, when a lateral crystal growth layer with a reduced defect density is formed on a substrate, the substrate may not be reached by a scratch even if an edge scribing is performed from the nitride compound semiconductor layer side. Moreover, an air gap and an insulative film layer which exist between the lateral crystal growth layer and the substrate are fragile regions with a low mechanical strength, and therefore are likely to experience crystal peeling and may be damaged. Therefore, especially in the case of growing a lateral crystal growth layer on a substrate, it has been difficult with the conventional method to obtain good resonator surfaces.
The present invention has been made in order to solve the aforementioned problems, and a main objective thereof is to provide a nitride compound semiconductor element which allows cleavage to be performed with a good yield, and a production method therefore.
A nitride compound semiconductor element according to the present invention is a nitride compound semiconductor element including a substrate having an upper face and a lower face and a semiconductor multilayer structure supported by the upper face of the substrate, such that the substrate and the semiconductor multilayer structure have at least two cleavage planes, comprising: at least one cleavage inducing member which is in contact with either one of the two cleavage planes, wherein a size of the cleavage inducing member along a direction parallel to the cleavage plane is smaller than a size of the upper face of the substrate along the direction parallel to the cleavage plane.
In a preferred embodiment, the upper face of the substrate has a rectangular shape, and the cleavage member is positioned in at least one of four corners of the upper face of the substrate.
In a preferred embodiment, the semiconductor multilayer structure has a laser resonator structure in which the cleavage planes function as resonator end faces; and a size of the cleavage inducing member along a resonator length direction is half or less of the resonator length.
In a preferred embodiment, the cleavage inducing member is smaller than a 180 μm×50 μm rectangle.
In a preferred embodiment, two or more cleavage inducing members are comprised, and arranged along a resonator length direction; and an interval between adjoining cleavage inducing members along the resonator length direction is 80% or more of the resonator length.
In a preferred embodiment, the cleavage inducing member is composed of a mask layer which is formed on the upper face of the substrate or in the semiconductor multilayer structure.
In a preferred embodiment, the cleavage inducing member is composed of a gap which is formed in the semiconductor multilayer structure.
In a preferred embodiment, a trench is formed on the upper face of the substrate; and the mask layer is positioned above the trench.
In a preferred embodiment, the mask layer is composed of a material which suppresses crystal growth of semiconductor layers composing the semiconductor multilayer structure.
In a preferred embodiment, the mask layer is formed of at least one material selected from the group consisting of: an oxide or nitride of silicon, aluminum, titanium, niobium, zirconia, or tantalum; gold; platinum; aluminum; nickel; palladium; and titanium.
In a preferred embodiment, the cleavage inducing members are located on both sides of a laser optical waveguide portion in the semiconductor multilayer structure.
In a preferred embodiment, the semiconductor multilayer structure includes: an n-type nitride compound semiconductor layer and a p-type nitride compound semiconductor layer; and an active layer interposed between the n-type nitride compound semiconductor layer and the p-type nitride compound semiconductor layer.
In a preferred embodiment, the substrate is a nitride compound semiconductor.
In a preferred embodiment, a pair of electrodes are formed on the upper face and the lower face of the substrate.
A production method for a nitride compound semiconductor element according to the present invention is a production method for a nitride compound semiconductor element including a substrate having an upper face and a lower face and a semiconductor multilayer structure supported by the upper face of the substrate, comprising: a step of providing a wafer to be split into the substrate; a step of growing semiconductor layers composing the semiconductor multilayer structure on the wafer; and a step of performing cleavage of the wafer and the semiconductor multilayer structure to form a cleavage plane of the semiconductor multilayer structure, further comprising a step of arranging a plurality of cleavage inducing members at positions where the cleavage plane is to be formed.
In a preferred embodiment, the step of arranging the cleavage inducing members includes: a step of depositing an insulative film; and a step of patterning the insulative film to form a plurality of mask layers being arranged along a line and defining positions at which the resonator end faces are to be formed.
In a preferred embodiment, the mask layers are formed on a principal face of the wafer.
In a preferred embodiment, the mask layers are formed in the semiconductor multilayer structure.
According to the present invention, since cleavage is induced along a cleavage inducing member, the problem of cracks being likely to occur in a 60° direction with respect to the M-plane in relation to cleavage of a hexagonal-system nitride compound semiconductor is solved, thus facilitating the formation of smooth resonator end faces.
Moreover, according to the present invention, burrs, chipping, scratches and ruggednesses in the resonator end faces, strain in the active layer, formation of crystal defects and the like, which are likely to occur upon cleavage, are suppressed. Therefore, there is provided an effect that the optical characteristics and electrical characteristics of the finally-obtained semiconductor laser are improved.
1 . . . wafer
3 . . . cleavage inducing member (mask layer)
18 . . . optical waveguide
23 . . . p-side wiring
24 . . . n-side wiring
27 . . . trench
30 . . . high defect-density region
40 . . . semiconductor multilayer structure
A nitride compound semiconductor element according to the present invention includes a substrate having an upper face and a lower face, and a semiconductor multilayer structure which is supported by the upper face of the substrate, such that the substrate and the semiconductor multilayer structure have at least two cleavage planes.
In the present invention, “cleavage inducing members” are provided in order to facilitate “cleavage” of a crystal during its production steps. Therefore, in most of the semiconductor elements that are finally fabricated, (at least a portion of) a cleavage inducing member(s) exists. Each cleavage inducing member in each semiconductor element is in contact with either one of two cleavage planes. In other words, the cleavage inducing member according to the present invention is not sized so as to extend from one of two parallel cleavage planes to the other. The size of the cleavage inducing member along a direction parallel to a cleavage plane is smaller than the size of an upper face of the substrate along the direction parallel to the cleavage plane. In other words, the cleavage inducing member according to the present invention is sized so as to be in contact with a portion of a cleavage plane, and does not extend from end to end on the cleavage plane along the lateral direction.
Hereinafter, with reference to the drawings, a first embodiment of the nitride compound semiconductor element according to the present invention will be described. The nitride compound semiconductor element according to the present invention is preferably a semiconductor laser whose cleavage planes are utilized as resonator end faces, but may be any other light-emitting device, e.g., an LED (Light Emitting Diode), or a transistor. Although a semiconductor element other than a semiconductor laser does not utilize its cleavage planes as resonator end faces, the ability to separate a hard nitride compound into chips with a good yield through cleavage produces advantages such as facilitated production.
First, with reference to
As shown in
By subjecting the photoresist film 2 to exposure and development through a known photolithography step, the photoresist film 2 is patterned as shown in
Next, as shown in
Next, a multilayer structure 40 of nitride compound semiconductor is formed on the GaN wafer 1 having the plurality of cleavage inducing members 3 periodically arranged on its upper face. In the present embodiment, a metal-organic vapor phase epitaxy (MOVPE) technique is used to grow layers of nitride compound semiconductor expressed as InxGayAlzN (where x+y+z=1, 0≦x≦1, 0≦y≦1, 0≦z≦1). Specifically, the semiconductor multilayer structure 40 as shown in
Hereinafter, with reference to
First, the GaN wafer 1 having the cleavage inducing members 3 formed on its upper face is retained on a susceptor in a reactor of MOVPE equipment. Then, the reactor is heated to about 1000° C., and source gases, i.e., trimethylgallium (TMG) supplied in an amount of 7 s ccm and ammonia (NH3) gas supplied in an amount of 7.5 slm, and a carrier gas of hydrogen are simultaneously supplied, and silane (SiH4) gas is supplied as an n-type dopant, thus allowing an n-type GaN layer 10 having a thickness of about 1 μm and an Si impurity concentration of about 1×1018 cm−3 to grow.
At this time, no growth of n-type GaN crystal directly occurs in the regions of the upper face of the GaN wafer 1 that are covered by the cleavage inducing members 3. However, the n-type GaN which has grown from the regions of the upper face of the GaN wafer 1 that are not covered by the cleavage inducing members 3 grows across the surface of the cleavage inducing members 3 in the lateral direction. Therefore, the surface of the cleavage inducing members 3 is also covered by the n-type GaN layer 10.
Thereafter, while also supplying trimethylaluminum (TMA), an n-type cladding layer 11 composed of n-type Al0.05Ga0.95N with a thickness of about 1.5 μm and an Si impurity concentration of about 5×1017 cm−3 is grown. Then, after growing a first optical guide layer 12 composed of n-type GaN with a thickness of about 120 nm and an Si impurity concentration of about 1×1018 cm−3, the temperature is lowered to about 800° C., the carrier gas is switched from hydrogen to nitrogen, and trimethylindium (TMI) and TMG are supplied, thus growing quantum wells (three layers) composed of In0.1Ga0.9N with a film thickness of about 3 nm and a multi-quantum well active layer 13 composed of In0.02Ga0.98N barrier layers (two layers) with a film thickness of about 9 nm.
The temperature within the reactor is again elevated to about 1000° C., the carrier gas is switched back from nitrogen to hydrogen, and while supplying a p-type dopant of biscyclopentadienylmagnesium (Cp2Mg) gas, a capping layer 14 composed of p-type Al0.15Ga0.85N with a film thickness of about 10 nm and an Mg impurity concentration of about 5×1017 cm−3 is grown.
Next, a second optical guide layer 15 composed of p-type GaN with a thickness of about 120 nm and an Mg impurity concentration of about 1×1018 cm−3 is grown. Thereafter, a p-type cladding layer 16 composed of p-type Al0.05Ga0.9N with a thickness of about 0.5 μm and an impurity concentration of about 5×1017 cm−3 is grown. Finally, a p-type contact layer 17 composed of p-type GaN with a thickness of about 0.1 μm and an Mg impurity concentration of about 1×1018 cm−3 is grown.
Note that, by adjusting the crystal growth conditions for the n-type GaN layer 10 and other semiconductor layers, it may be possible to leave the surface of the cleavage inducing members 3 exposed, rather than being completely covered.
Although
In the example shown in
The cleavage inducing members 3 do not need to be formed directly on the upper face of the wafer 1, but may be formed on any layer among the semiconductor layers 10 to 16 shown in
Thus, according to the present embodiment, periodic strain can be generated in the semiconductor multilayer structure 40 because of the arrangement of the cleavage inducing members 3. However, if the thickness of the cleavage inducing members 3 is too large, the active layer may also have a large strain due to their influence. In order to ensure that such strain does not become too large, the thickness of the cleavage inducing member 3 may be reduced to 0.5 μm or less.
However, depending on the shapes and positions of the cleavage inducing members 3, their thickness may be set to a value exceeding 0.5 μm. In particular, as shown in
Hereinafter, with reference to
The cleavage inducing members 3 according to the present embodiment are periodically arranged along the <11-20> direction, in a manner not to intersect any optical waveguide forming regions 18′ which are formed in the semiconductor multilayer structure 40. The distance between two adjoining cleavage inducing members 3 along the <11-20> direction is set to be substantially the same value as the size along the <11-20> direction of the finally-obtained laser device. In the present embodiment, the size along the <11-20> direction of each laser device is about 400 μm, and therefore the arraying pitch of the cleavage inducing members 3 along the <11-20> direction is also set at 400 μm.
On the other hand, the arraying pitch of the cleavage inducing members 3 along the <1-100> direction is set at a value which is equal to the resonator length of each laser device. In the present embodiment, the resonator length is about 600 μm, and therefore the arraying pitch of the cleavage inducing members 3 along the <1-100> direction is also set at about 600 μm.
The planar shape of each cleavage inducing member 3 is square (size: 10 μm×10 μm), for example. Thus, by arranging, along lines 25 and lines 26 on the wafer 1, the cleavage inducing members 3 which are sufficiently small relative to the size of each laser device, it becomes possible to perform primary and secondary cleavages at accurate positions. The cleavage inducing members 3 only need to be arranged in positions where cleavage is to be induced (i.e., the lines 25 and lines 26), and they do not need to be arranged with a constant period. However, since they are preferably located so as to avoid the optical waveguide forming regions 18′, it is preferable to place them in a periodical arrangement.
Since the primary cleavage is to take place along the <11-20> direction so as to expose the (1-100) plane as a cleavage plane, it is preferable that the size of the cleavage inducing members 3 along the <1-100> direction is sufficiently small relative to the resonator length. The reason is that, if the size of the cleavage inducing members along the <1-100> direction is too large, it becomes difficult to define the position (position along the <1-100> direction) of the cleavage plane. Therefore, the size of the cleavage inducing members 3 along the <1-100> direction should be half or less of the resonator length, and is preferably 20% or less of the resonator length. The absolute value of this size is preferably 150 μm or less, and more preferably 50 μm or less.
On the other hand, the size of the cleavage inducing members 3 along the <11-20> direction may be relatively larger than its size along the <1-100> direction. The size of the cleavage inducing members 3 along the <11-20> direction is to be determined from the standpoint of ensuring cleavage inducing effects while also reducing the strain occurring in the optical waveguide and the defect density. Therefore, it is preferable that the size of the cleavage inducing members 3 along the <11-20> direction is 5 μm or more, and is smaller than a value obtained by subtracting the width of the waveguide (i.e., size along the <11-20> direction) from the size along the <11-20> direction of the laser device. The typical size of the cleavage inducing members 3 along the <11-20> direction is no less than 5 μm and no more than 180 μm.
Note that each line 25 shown in
In the example shown in
In extreme cases, a given semiconductor laser may finally contain no cleavage inducing member 3 at all. In such cases, a semiconductor laser adjoining that semiconductor laser may contain at least one cleavage inducing member 3 which has been left unbroken.
The material of the cleavage inducing members 3 is not limited to SiO2, but may be an insulator such as silicon nitride. Preferably, they are formed of at least one material selected from the group consisting of: an oxide or nitride of silicon, aluminum, titanium, niobium, zirconia, or tantalum; gold; platinum; aluminum; nickel; palladium; and titanium.
The cleavage inducing members 3 may be what can cause selective growth of the nitride compound semiconductor which is stacked in layers so as to compose a laser structure, and may not only be an insulator but also a metal. Moreover, they may be semiconductors of different compositions in accordance with the nitride compound semiconductor crystal to be grown. Moreover, the cleavage inducing members 3 may be modified portions obtained by, e.g. implanting ions into the nitride compound semiconductor crystal layer. For example, if an aluminum gallium nitride (AlxGayN: where x+y=1, 0≦x≦1, 0≦y≦1) whose aluminum component differs from that of the nitride compound semiconductor crystal to be stacked is used for the cleavage inducing members 3, a difference in stress occurs at the interfaces because the nitride compound semiconductor crystal and the AlxGayN mask layer have different coefficients of thermal expansion, thus allowing the cleavages in the subsequent steps to progress more easily. It is preferable that the AlxGayN mask layer has a large Al mole fraction. The greater the Al mole fraction of the AlxGayN mask layer is, the greater coefficient of thermal expansion will exist in the c-plane, so that a greater difference in stress can be obtained.
Hereinafter, with reference to
First, as shown in
After removing the resist mask 20′ as shown in
Thereafter, the insulating layer 19′ is removed as shown in
Next, as shown in
Next, as shown in
Hereinafter, with reference to
First, the rear face of the GaN wafer 1 is polished, and the overall thickness of the semiconductor multilayer structure 40 and the wafer 1 is reduced to about 100 μm. Next, by using an apparatus which is not shown, stress is applied to effect a primary cleavage along the lines 25 shown in
Next, after a multilayered dielectric film composed of SiOx and TiOx is formed on both or either one of the resonator end faces of each laser bar (
Next, via solder, each semiconductor laser is placed in such a manner that its p-side portion is in contact with the upper face of a heat sink 28 which is composed of silicon carbide (SiC), and wiring is performed via wire bonding. At this time, by taking advantage of the cleavage inducing members 3 being in specific positions of the laser device, the cleavage inducing members 3 can exhibit a function as positioning markers during the packaging step.
As shown in
The laser device which has been produced by the above method has smooth resonator surfaces. At room temperature, continuous oscillation was confirmed at an operating current of 60 mA, with a threshold current of 30 mA and an output power of 50 mW, and a lifespan of 1000 hours or more was exhibited.
Moreover, in the laser device of the present embodiment, since tensile stress is released near the cleavage inducing members 3, a “window structure region” which has a relatively large band gap and in which light absorption is suppressed is formed near the resonator end faces. As a result, light emission at a high output power becomes possible. Note that, as the distance between each cleavage inducing member 3 and the ridge becomes shorter, the stress releasing effects will be enhanced, but the possibility of defects being introduced at the light-outgoing surface will also increase. Therefore, the distance between each cleavage inducing member 3 and the ridge stripe is to be set within a range from 2 to 50 μm, e.g. about 5 μm.
Although cleavage is also performed along the lines 26 in the above example, the faces other than the resonator end faces do not need to be cleavage planes. Therefore, cutting with laser, etc., may be performed along the lines 26.
a) and (b) show an experimental result where a primary cleavage is performed for a wafer which has been fabricated as a comparative example. This comparative example has been fabricated by the same method as the method described with respect to Embodiment 1 except that the cleavage inducing members 3 are not formed.
a) shows an upper face of the wafer of the comparative example. When a primary cleavage was performed in the direction of a line 25 in the figure by using a cleavage apparatus, a crack occurred in the 60° direction with respect to the M-plane, and the laser bar 50 was disrupted part of the way, as shown in
Next, with reference to
First, as shown in
By subjecting the photoresist film 2 to exposure and development through a known photolithography step, the photoresist film 2 is patterned as shown in
Next, as shown in
Thereafter, a lift-off is performed by removing the photoresist film 2 with an organic solution such as acetone, thus forming the cleavage inducing member 3 as shown in
Next, after a GaN layer 4 is grown on the GaN wafer having the plurality of cleavage inducing members 3 arranged on its upper face, the GaN wafer 1 is taken out of the reactor, and an insulative film 5 for selective growth is formed above the GaN layer 4. The insulative film 5 in the present embodiment is formed of SiO2, with a thickness of about 100 nm, that has been deposited in a plasma CVD apparatus.
Next, after the resist film 6 is applied on the insulative film 5 in a photolithography step, exposure and development is performed to form a resist film 6′ which is patterned in stripes, as shown in
Next, by using the resist film 6′ as an etching mask, the exposed portions of the insulative film 5 are removed with a hydrofluoric acid solution, thus forming a stripe-shaped insulation mask 5′ as shown in
Next, in order to selectively grow a GaN layer 7, the substrate having the stripe-shaped insulative film 5′ deposited thereon is again retained on a susceptor in a reactor of MOVPE equipment. Then the temperature is elevated to about 1000° C. in a hydrogen atmosphere at a pressure of 200 Torr, and by using 7 sccm TMG and 7.5 slm NH3 gas and simultaneously supplying a carrier gas of hydrogen, the GaN layer 7 is selectively grown on the selective growth mask pattern, as shown in
The exposed portions of the GaN layer 4 function as seeds 9 of crystal growth. The dislocation density of the seeds 9 is equal to the dislocation density of the GaN wafer 1, and is about 1×106/cm3. However, the dislocation density in the laterally-grown crystal region (wings) of the GaN layer 7 is reduced to about 1×105/cm3.
Thereafter, by performing steps similar to the steps described with respect to Embodiment 1, the semiconductor laser of the present embodiment is fabricated. In the present embodiment, since the direction in which the optical waveguides 18 extend is made parallel to the direction in which the stripe-shaped insulative film 5′ extends, the optical waveguides 18 are formed in the selective growth regions having a reduced dislocation density, so as to avoid the seeds 8 and the crystal coupling portions 9 having a high dislocation density. As a result, the operating current is reduced and the lifespan is extended.
According to the present embodiment, in addition to the effects of Embodiment 1, an effect of reducing the dislocation density in the selectively-grown layer is obtained, whereby the lifespan of the laser device is improved to 2000 hours or more.
Hereinafter, a third embodiment of the nitride compound semiconductor laser according to the present invention will be described.
In the present embodiment, on the GaN wafer 1 before a nitride compound semiconductor crystal is grown thereon, trenches are periodically formed so as to be perpendicular to but not intersecting the optical waveguides, and mask layers (cleavage inducing members 3) are formed on the trenches.
First, a resist film is deposited on the GaN wafer whose principal face is the (0001) plane. By using a photolithography technique, the resist is removed in the form of dotted lines with an interval of about 400 μm, along the <11-20> direction of a subsequently-formed nitride compound semiconductor layer, so as to be perpendicular to but not intersecting the optical waveguides. By using the resist film as an etching mask, the exposed portions of the GaN wafer are subjected to dry etching by using a dry etching apparatus, and an array of a plurality of trenches 27 are formed on the upper face of the GaN wafer 1 as shown in
Next, as shown in
The subsequent steps are similar to the steps described with respect to Embodiment 1, and the description thereof will not be repeated herein.
In the present embodiment, the trenches 27 are formed immediately under the cleavage inducing members 3, so that cleavage is more likely to be induced, and it is even easier to form smooth resonator end faces.
Hereinafter, a fourth embodiment of the nitride compound semiconductor laser according to the present invention will be described.
In the present embodiment, as shown in
Since an electrically conductive n-type GaN wafer 1 is used in the present embodiment, it is possible to form the n-side electrodes 24 directly on the rear face of the GaN wafer 1, as shown in
Note that, if the n-side electrodes 24 are patterned so as to avoid the regions where primary cleavage and secondary cleavage are to occur, peeling of the n-side electrodes 24 during cleavage can be prevented. However, the n-side electrodes 24 may be formed over the entire rear face of the n-type GaN wafer 1.
In the present embodiment, since electrodes are formed on the rear face of the GaN wafer 1, it is possible to reduce the size of the laser device, and the laser device can be produced at a low cost.
The shape and size of cleavage inducing members were changed in various manners, and soundness of cleavage was evaluated. Hereinafter, a production method for the samples used in the Example will be described.
First, a GaN wafer having a thickness of 400 μm was provided, and cleavage inducing members composed of an insulative film were formed on its principal face. Specifically, after cleaning the GaN wafer with acetone, solfine, methanol, and buffered hydrofluoric acid (BHF), an SiN layer (lower layer) and an SiO2 layer (upper layer) were sequentially deposited by using an ECR sputtering apparatus. The thicknesses of the SiO2 layer and the SiN layer were respectively set at 10 nm and 100 nm, or 10 nm and 500 nm.
Next, this multilayer was patterned by a photolithography technique and an etching technique. Etching of the SiN layer and the SiO2 layer was performed through a dry etching using CF4 (carbon tetrafluoride) gas. Thereafter, cleaning (acetone+sulfuric acid/hydrogen peroxide) was performed to form cleavage inducing members of a desired shape. The cleavage inducing members in the present Example function as mask layers for the selective growth in an epitaxial growth step to be next performed. Hereinafter, the cleavage inducing members in the present Example will be referred to as “mask layers”.
a) to (c) each shows a planar shape of a mask layer formed in the present Example.
In each of the mask layers shown in
Table 1 shows sizes for mask layers having the shape shown in
Note that each table shows the size along the <11-20> direction and the size along the <1-100> direction of each mask layer. For example, in sample No. 6 shown in Table 1, the mask layers have a size of 180 μm along the <11-20> direction and a size of 50 μm along the <1-100> direction.
In the present Example, a large number of mask layers having the aforementioned shapes and sizes were arranged on a wafer with a pitch of 400 μm. The number of mask layers arranged along a single line was thirty.
Next, selective epitaxial growth of a nitride compound semiconductor was performed by an MOVPE technique. Specifically, the wafer was cleaned with BHF, and SiO2 on the mask layers was subjected to wet etching to allow a clean SiN mask surface to be exposed. Thereafter, semiconductor multilayer structure having a double-hetero structure was formed in an MOVPE reactor. The growth conditions were similar to the conditions of the growth performed when forming the semiconductor multilayer structure 40 shown in
In the present Example, the surface of the mask layers was composed of SiN, and hardly any semiconductor layer grew on this surface. However, in the case of mask layers having a size of 5 μm or less, the upper face of the mask layers was almost covered by the semiconductor layer due to lateral growth. The thickness of the semiconductor multilayer structure covering the mask layers was not uniform, and depressions were formed on the upper face due to the presence of the mask layers.
The wafer having the semiconductor multilayer structure thus formed on its principal face was polished from the rear face, and the wafer thickness was adjusted to about 100 μm. Thereafter, cleavage was performed via edge scribing and breaking, and the soundness of cleavage was evaluated.
The rightmost column in Table 1 to Table 3 show evaluation results of sample Nos. 1 to 24. In the “results” column of each table, the “◯” symbol indicates that 12 mm-long bars were appropriately fabricated through cleavage. On the other hand, the “X” symbol indicates that the cleavage planes deviated from the mask layer rows, so that 12 mm-long bars could not be appropriately fabricated.
In Samples 13 to 15 of Table 3, cleavage was not appropriately performed. The reason is that the mask layer size was too small.
In the case where the mask layers had a rectangular shape, as shown in Table 3, cleavage was not properly performed when the size along the <1-100> direction was as large as 50 μm or more.
As can be seen from the above results, it is preferable that the mask layers are shaped so as to have a vertex pointing in a direction parallel to a cleavage plane. In the case of employing mask layers of a shape having no such vertices (e.g., rectangle or square), it is preferable to set their size to be within an appropriate range.
As has been described above, according to the present invention, cleavage inducing members are arranged in intermittent and linear manners on a wafer, whereby cleavage can be performed with a good yield.
As shown in
Note that, by removing the mask layers through etching after finishing the epitaxial growth step, gaps may be formed in the portions where the mask layers existed. When cleavage is performed after such an etching, the gaps will function as cleavage inducing members.
As lasers for short-wavelength light sources employing GaN substrates which are difficult to be cleaved, mass production of nitride compound semiconductor lasers according to the present invention is expected.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-300907 | Oct 2004 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11568481 | Oct 2006 | US |
| Child | 13213362 | US |
