CN101119012B

CN101119012B - Method for fabrication of semiconductor device

Info

Publication number: CN101119012B
Application number: CN2007101490243A
Authority: CN
Inventors: 神川刚; 山田英司; 荒木正浩
Original assignee: Sharp Corp
Current assignee: Sharp Fukuyama Laser Co Ltd
Priority date: 2004-05-10
Filing date: 2005-05-10
Publication date: 2010-04-21
Anticipated expiration: 2025-05-10
Also published as: CN1697273A; CN101119011B; CN101119011A; CN101119012A; JP2005322786A; CN100392929C

Abstract

On a processed substrate having an engraved region as a depressed portion formed thereon, a nitride semiconductor thin film is laid. The sectional area occupied by the nitride semiconductor thin film filling the depressed portion is 0.8 times the sectional area of the depressed portion or less.

Description

Semiconductor device and method for manufacturing the same

The present application is a divisional application of chinese patent application No.200510070180.1 entitled "semiconductor device and method of manufacturing the same" filed on 5/10/2005.

Technical Field

The present invention relates to a semiconductor device such as a nitride semiconductor laser device, and a method of manufacturing such a semiconductor device.

Background

Nitride semiconductors such as GaN, AlGaN, GaInN, AlGaInN, and mixed crystals thereof have a characteristic of a larger band gap Eg and are direct transition semiconductor materials, compared with AlGaInAs-based and AlGaInP-based semiconductors. These properties make nitride semiconductors attractive materials for semiconductor light emitting devices, such as semiconductor lasers emitting light in the short wavelength range from ultraviolet to green and light emitting diodes covering a wide emission wavelength range from ultraviolet to red. Therefore, it is considered that nitride semiconductors will find wide application in high-density optical disks and full-color displays to the environmental and medical fields.

Also, nitride semiconductors have higher thermal conductivity than GaAs-based semiconductors and other semiconductors, and thus are expected to be widely used in high-temperature, high-output power devices. Further, the nitride semiconductor does not require the use of a material corresponding to arsenic (As) in an AlGaAs-based semiconductor, cadmium in a ZnCdSSe-based semiconductor, or a material such As arsine (AsH) for them₃) And thus is expected to be an environmentally friendly compound semiconductor material.

For a nitride semiconductor, one conventional problem is that: taking nitride semiconductor laser devices as an example, in the process of manufacturing nitride semiconductor devices, the yield, i.e., the ratio of the number of nitride semiconductor laser devices that normally operate to the total number of devices produced on a single wafer, is extremely low.

The reason is as follows. In order to separate the respective nitride semiconductor laser devices fabricated on the same wafer from each other, first, the wafer is cleaved in a direction perpendicular to the resonant cavity of the nitride semiconductor laser device, thereby dividing the wafer into strips, and the end faces of the resonant cavities are formed at the cleavage surfaces. Next, in order to further separate the respective nitride semiconductor laser devices which are now co-located on the mutually cleaved strip-shaped separation pieces of the nitride semiconductor substrate, the resulting strips are further cleaved in a direction parallel to the resonator. Here, in dividing the wafer into long strips, if the nitride semiconductor substrate is composed of a nitride semiconductor such as n-type GaN, the nitride semiconductor substrate and the nitride semiconductor growth layer located thereon have cleavage planes in a direction perpendicular to the resonant cavity, and thus cleavage is easy.

However, since a nitride semiconductor substrate composed of a nitride semiconductor such as n-type GaN has a hexagonal crystal structure and does not have a cleavage plane in a direction parallel to the direction of the resonator, it is difficult to further divide the bars into individual nitride semiconductor laser devices. Thus, the detachment here can lead to flaking and cracking, as well as cleavage in unintended directions, which can lead to low yields.

According to a conventional solution provided for this problem, after a nitride semiconductor growth layer covers the top of a substrate, a scribe machine is used to scribe from the surface of the nitride semiconductor growth layer to half the thickness of the substrate, then the substrate is polished to be thin, next, scribe lines are drawn on the surfaces of the trenches formed by the scribe machine, and finally, a load is applied to the substrate. This helps separate the individual nitride semiconductor laser devices from each other with excellent yield (see Japanese Patent Application Laid-Open No. h 5-315646).

Another cause of low yield is the generation of cracks. Such cracks may originate in the nitride semiconductor growth layer covering the top of the substrate. In particular, in the fabrication of a nitride semiconductor laser device, a nitride semiconductor growth layer is covered on top of a substrate, and this nitride semiconductor growth layer is composed of different types of films, such as GaN, AlGaN, and InGaN films. Here, different films forming the nitride semiconductor growth layer have different lattice constants, thereby causing lattice mismatch, resulting in the generation of cracks. In order to avoid this, according to a conventionally proposed method, a processed substrate is used, and after a nitride semiconductor growth layer is formed on top thereof, a depression is formed on the surface of the nitride semiconductor growth layer, instead of planarizing the surface. This helps to reduce cracking (see Japanese Patent Application Laid-Open No. 2002-246698). By adopting such a method, it is possible to reduce cracks caused by, for example, lattice constant mismatch between the respective films forming the nitride semiconductor growth layer on top of the substrate.

In fabricating a nitride semiconductor laser device using the technique disclosed in the above-mentioned Japanese Patent Application Laid-Open No.2002-246698 (Japanese Patent Application Laid-Open No.2002-246698), the structure of the nitride semiconductor growth layer may be as shown in FIG. 19, as an example.

Specifically, on the surface of a processed substrate 10 (see fig. 18a and 18b) formed of an etched n-type GaN substrate or the like, a nitride semiconductor growth layer 11 is formed, for example, the nitride semiconductor growth layer 11 is composed of the following layers stacked in the stated order: an n-type GaN layer 100 of 1.0 μm thickness; 1.5 μm thick n-type Al_0.062Ga_0.938N first clad layer (clad layer) 101; 0.2 μm thick n-type Al_0.1Ga_0.9N second cladding layer 102; 0.1 μm thick n-type Al_0.062Ga_0.938N third cladding layer 103; a 0.1 μm thick n-type GaN waveguide layer 104; a multiple quantum well active layer 105 composed of three InGaN well layers 4nm thick and four GaN barrier layers 8nm thick; 20nm thick p-type Al_0.3Ga_0.7An N evaporation prevention layer (evaporation prevention layer) 106; a 0.05 μm thick p-type GaN waveguide layer 107; 0.5 μm thick p-type Al_0.062Ga_0.938An N cladding layer 108; and a 0.1 μm thick p-type GaN contact layer 109. The multiple quantum well active layer 105 has layers stacked in the following order: the barrier layer, well layer, barrier layer, well layer and barrier layer.

In crystallography, the convention is: when the index indicating a crystal plane or orientation is negative, a horizontal line is added to the absolute value to indicate the index. In the following description, since such an index cannot be used, the minus sign "-" shown is used to indicate a negative index followed by the absolute value of the index.

In this specification, a "different substrate" means a substrate other than a substrate formed of a nitride semiconductor. Examples of different substrates include: sapphire substrate, SiC substrate and GaAs substrate.

The "processed substrate" means a substrate having engraved regions and ridges formed on the surface of a nitride semiconductor substrate or the surface of a nitride semiconductor thin film stacked on the surface of a nitride semiconductor substrate or a different substrate. In the following description, Mg-doped layers, i.e. p-type Al, are stacked in this order_0.3Ga_0.7N anti-evaporation layer 106, p-type GaN waveguide layer 107, and p-type Al_0.062Ga_0.938The layer formed by the N-cladding layer 108 and the p-type GaN contact layer 109 is referred to as a "p-layer".

On the processed surface of the processed substrate 10, a nitride semiconductor growth layer 11 is stacked by MOCVD (metal organic chemical vapor deposition) to form a nitride semiconductor wafer having a depression on the surface of the nitride semiconductor growth layer 11, as shown in fig. 18a and 18 b. In fig. 18a and 18b, the planar orientation is collectively shown.

In fig. 18b, an n-type GaN substrate is used as the substrate 10, and stripe-shaped engraved regions 16 and ridges 19 are formed in the [1-100] direction by dry etching such as RIE (reactive ion etching). The engraved regions were 5 μm wide and 3 μm deep, and the distance between two adjacent engraved regions was 15 μm. On top of the substrate 10 thus etched, a nitride semiconductor growth layer 11 structured as shown in fig. 19 is fabricated by a growth method such as MOCVD.

However, disappointingly, when a nitride semiconductor laser device is fabricated by epitaxially growing a nitride semiconductor growth layer 11 on an n-type GaN substrate by MOCVD or the like using a technique such as that disclosed in Japanese Patent Application Laid-Open No.2002-246698, with the n-type GaN substrate as the substrate 10, cracks can be reduced without significantly improving the yield. Specifically, a plurality of nitride semiconductor laser devices were manufactured by a technique as disclosed in Japanese Patent Application Laid-Open No.2002-246698, from which 100 were randomly extracted, and the FWHM (full width at half maximum) of the FFP (far field pattern) thereof was measured in the horizontal and vertical directions. Here, it is considered that a nitride semiconductor laser device exhibiting an FFP whose FWHM is within ± 1 ° of its design value is acceptable. As a result, the number of nitride semiconductor laser devices exhibiting an FFP with a FWHM satisfying the requirement is 30, and the yield is very low.

This is because leaving a depression on the nitride semiconductor growth layer 11 reduces the flatness of the film. The lowered flatness causes variations in the thickness of each layer in the nitride semiconductor growth layer 11, resulting in variations in the characteristics of the nitride semiconductor laser device from individual to individual, thereby reducing the number of devices whose characteristics fall within a required range. Therefore, to improve the yield, not only the cracks are reduced, but also the flatness of the film is improved.

In addition, the surface flatness in the surface of the nitride semiconductor wafer formed as shown in fig. 18a, 18b and 19 was also measured. The surface flatness measurements taken along the [1-100] direction are shown in FIG. 20. The conditions under which the measurements were carried out were as follows: measuring length: 600 μm; measuring time: 3 s; probe pressure: 30 mg; and horizontal resolution: 1 μm/sample. From the graph in fig. 20, it can be found that the difference in height between the highest portion and the lowest portion of the surface measured in a region 600 μm wide is 200 nm.

As shown in fig. 18b, the reason for this difference in flatness is: the thicknesses of the respective layers of the nitride semiconductor growth layer 11 disposed on top of the substrate 10 vary depending on the position on the wafer. Therefore, the characteristics of the nitride semiconductor laser device will greatly vary depending on the position on the wafer surface where the nitride semiconductor laser device is fabricated, and moreover, the thickness of the Mg-doped p layer (corresponding to the thickness of the p-type Al-doped p layer as shown in fig. 19) which has a great influence on the characteristics of the nitride semiconductor laser device_0.3Ga_0.7N anti-evaporation layer 106 to p typeThe sum of p-type layers in which the GaN contact layer 109 is arranged) varies greatly with position within the substrate surface.

After the ridge structure as a current confinement structure was formed, ridges in a stripe shape having a width of 2 μm remained, and the remaining portion was etched away by a dry etching technique using an ICP (inductively coupled plasma) apparatus or the like. Therefore, if the p-layer thickness varies depending on the position in the wafer surface before etching, the thickness of the remaining p-layer, which has the most significant influence on the characteristics of the nitride semiconductor laser device, varies depending on the position in the wafer surface after etching. As a result, not only the layer thickness of the nitride semiconductor laser device varies from one individual to another, but even in the same nitride semiconductor laser device, the remaining p-layer thickness may be almost zero in some portions, and considerably large in other portions. The difference in the thickness of the remaining p layer affects the laser emission lifetime of the nitride semiconductor laser device, and as described above, the characteristics such as the FWHM of the FFP.

The large distribution of layer thicknesses within the wafer surface is believed to be due to the following: the growth rate of a film obtained by epitaxial growth at the ridge on the processed substrate including the nitride semiconductor substrate will vary under the influence of the engraved region, resulting in non-uniformity of the growth rate in the wafer surface.

Specifically, as shown in fig. 21a, when the epitaxial growth is started from the substrate 10 having the engraved regions 16 formed thereon, the portions of the nitride semiconductor thin film grown on the bottom surface portions 124 and the side surface portions 126 of the engraved regions 16 at the initial stage of the growth are referred to as engraved region growth portions 122, and the engraved region growth portions 122 partially fill only the engraved regions 16. At this stage, the portion of the nitride semiconductor thin film grown on the surface of the top surface portion 123 of the ridge 19 is referred to as a top surface growth portion 121, and the surface of the nitride semiconductor thin film is kept flat while it is grown.

After the epitaxial growth of the nitride semiconductor thin film proceeds from the above-described stage shown in fig. 21a to the stage shown in fig. 21b, the engraved region growth portions 122, i.e., the portions of the nitride semiconductor thin film grown on the bottom surface portions 124 and the side surface portions 126 of the engraved region 16, almost completely fill the engraved region 16, and at this time, these portions are connected to the top surface growth portion 121, i.e., the portions of the nitride semiconductor thin film grown on the surface of the top surface portions 123 of the ridges 19, by the growth portions 125. At this stage, atoms and molecules of the raw material (for example, Ga atoms) that have adhered to the surface of the nitride semiconductor thin film grown on the top surface portions 123 of the ridges 19 are caused to migrate or move into the growth portions 125 and the engraved region growth portions 122 by the thermal energy. Such migration movement of atoms and molecules occurs very unevenly within the wafer surface, and the migration distance within the wafer surface is also unequal. As a result, as shown in fig. 21b, the surface flatness of the top growth part 121 is reduced.

The flatness of the nitride semiconductor thin film in the [1-100] direction is also reduced under the influence of the nonuniformity of the nitride semiconductor substrate itself, such as off-angle distribution in the wafer surface and substrate curvature distribution in the wafer surface, the nonuniformity of epitaxial growth rate in the substrate surface, the nonuniformity of the notching process in the substrate surface, and other factors. Specifically, the time required to fill the engraved regions 16 varies in the [1-100] direction, and therefore, at the position filled earlier, atoms and molecules of the raw material forming the nitride semiconductor thin film migrate or move from the top surface growth portions 121 of the ridges 19 into the growth portions 125 or the engraved region growth portions 122. Therefore, where those atoms and molecules migrate, it takes more time to form the nitride semiconductor thin film, resulting in a thickening of the nitride semiconductor thin film formed in the engraved region 16. On the other hand, at the position where the engraved region 16 is not completely filled, no atoms or molecules of the raw material forming the nitride semiconductor thin film move from the top surface growth portion 121 of the ridge 19 to the engraved region 16; even if such movement exists, less time is required to form the nitride semiconductor thin film. Therefore, the nitride semiconductor thin film formed in the engraved region 16 is thinner than the nitride semiconductor thin film that fills the position of the engraved region 16 earlier.

In a so-called supply control state, i.e., a state in which the growth rate is controlled by the flux of atoms and molecules, etc. supplied to the wafer surface, if atoms and molecules of the raw material forming the nitride semiconductor thin film migrate or flow into the engraved regions 16, since the flux of atoms and molecules of the raw material supplied to the entire wafer surface is fixed, the nitride semiconductor thin film grown on the top surface portions 123 of the ridges 19, i.e., the top surface growth portions 121, will be thinned. Otherwise, i.e., if none of the atoms or molecules of the raw material forming the nitride semiconductor thin film migrate or otherwise flow into the engraved regions 16, the nitride semiconductor thin film grown on the top surface portions 123 of the ridges 19, i.e., the top surface growing portions 121, will become thicker.

As a result, the thickness of the top growth portions 121 located on the top portions 123 of the ridges 19 varies within the wafer plane, thereby reducing the surface flatness of the nitride semiconductor thin films. Therefore, in order to improve the flatness, it is necessary to suppress atoms and molecules of the raw material forming the nitride semiconductor thin film from migrating or moving from the top surface growth portions 121 of the ridges 19 to the growth portions 125 or the engraved region growth portions 122 to form the nitride semiconductor thin film.

Further, it has been found that, when a semiconductor laser device is manufactured by the above-described technique disclosed in Japanese Patent Application Laid-Open No.2002-246698, if an electrode is formed in a recess on the surface of the nitride semiconductor growth layer 11, a current leakage path will be generated in the recess, and thus normal I-V characteristics cannot be obtained. Typically, a layer such as SiO is formed on the recess₂And then forming an electrode thereon. However, the depressions present here cause unevenness of the insulating film formed on the surface, leaving a large number of fine cracks, very thin regions, pinholes (pits), and the like. Therefore, a current leaks through the non-uniform portion of the insulating film formed.

On the other hand, it has also been found that, when the respective nitride semiconductor laser devices fabricated on the nitride semiconductor substrate by the above-described technique disclosed in Japanese Patent Application Laid-Open No. h5-315646 are separated from each other, since the grooves are formed by the dicing saw after the nitride semiconductor growth layers are stacked on top of the nitride semiconductor substrate, the nitride semiconductor growth layers may be damaged from the inside, thereby deteriorating the characteristics of the nitride semiconductor laser devices.

Disclosure of Invention

In view of the conventionally encountered problems discussed above, it is an object of the present invention to provide a semiconductor device and a method of manufacturing the same, in which, in manufacturing a semiconductor device such as a nitride semiconductor laser device by a method of arranging a nitride semiconductor growth layer on a substrate having a nitride semiconductor layer on at least a part of the surface thereof, generation of cracks is prevented, and furthermore, a nitride semiconductor growth layer having good surface flatness is formed by a method of suppressing formation of a nitride semiconductor thin film caused by migration or movement of atoms and molecules of a raw material forming the nitride semiconductor thin film from a top surface growth portion on a ridge surface to an engraved region, thereby eliminating a current leakage path and damage.

In order to achieve the above object, according to the present invention, a method of manufacturing a nitride semiconductor device includes: a first step of forming a processed substrate by forming a grooved region as at least one recessed portion and a ridge portion as a non-grooved region on a nitride semiconductor substrate at least a part of a surface of which is a nitride semiconductor or on a substrate formed by arranging a nitride semiconductor thin film on such a nitride semiconductor substrate; and a second step of arranging a nitride semiconductor layer portion composed of a plurality of nitride semiconductor thin films on the surface of the ridge portion and the engraved region formed on the processed substrate. Here, in the first and second steps, assuming that the sectional area of a region surrounded by the sectional portion of the recessed portion cut along a plane perpendicular to the extending direction of the recessed portion and a straight line extending from the surface of the ridge portion in parallel to the surface of the ridge portion is a and the sectional area covered by the nitride semiconductor thin film disposed in the recessed portion is B, then B/a representing the filling ratio of the nitride semiconductor thin film in the recessed portion is 0.8 or less.

In the above method for manufacturing a nitride semiconductor device, it is suggested that in the first step, the recess portions of the engraved regions are formed to have an opening width exceeding 100 μm, and in the second step, the total thickness from the surface of the ridge portion to the surface of the nitride semiconductor layer portion is 0.8 times or less the depth of the recess portions.

In the above method for manufacturing a nitride semiconductor device, it is suggested that in the first step, the recess portions of the engraved regions are formed to have an opening width exceeding 30 μm but less than or equal to 100 μm, and in the second step, the total thickness from the surface of the ridge portion to the surface of the nitride semiconductor layer portion is 2 times or less the depth of the recess portions.

In the above method for manufacturing a nitride semiconductor device, it is suggested that in the first step, the recess portions of the engraved regions are formed to have an opening width of 2 μm or more and 30 μm or less, and in the second step, the total thickness from the surface of the ridge portion to the surface of the nitride semiconductor layer portion is 3 times or less the depth of the recess portions.

In the above method of manufacturing a nitride semiconductor device, it is suggested that the method further includes: and a third step of forming an electrode pad on the portion of the nitride semiconductor layer disposed on the surface of the processed substrate formed in the second step, and performing wire bonding on the electrode pad to realize external connection, thereby forming a plurality of nitride semiconductor devices on the substrate. Here, in the third step, the electrode pad is not formed on the engraved region.

In the above method of manufacturing a nitride semiconductor device, it is suggested that in the third step, the electrode pad be formed 5 μm or more from the edge of the notch region.

In the above method for manufacturing a nitride semiconductor device, it is recommended that in the first step, the ridge portion have a width of 92 μm or more and 4mm or less.

In the above method of manufacturing a nitride semiconductor device, it is proposed to form one nitride semiconductor device, or a plurality of nitride semiconductor devices, in the ridge portion sandwiched between two adjacent engraved regions.

In the above method of manufacturing a nitride semiconductor device, it is suggested to perform dicing on the bottom or top surface of the portion of the nitride semiconductor substrate located just below the engraved region of the processed substrate, thereby achieving chip separation.

In the above method of manufacturing a nitride semiconductor device, it is suggested that the method further includes: a fourth step of cleaving the processed substrate in a direction perpendicular to the first direction with the direction in which the engraved regions of the nitride semiconductor devices extend being the first direction to form strips each having a plurality of nitride semiconductor devices thereon; and a fifth step of dividing the strip in a direction parallel to the first direction, and dividing each of the nitride semiconductor devices on the strip into individual chips, thereby achieving chip separation. Here, in the fifth step, after dicing processing is performed on the top surface of the portion of the nitride semiconductor layer arranged on the engraved region or on the bottom surface of the portion of the nitride semiconductor substrate located just below the engraved region to form a scribe line parallel to the first direction, chip separation is performed.

In the above method for manufacturing a nitride semiconductor device, it is suggested that the method includes the fourth and fifth steps, and that in the fifth step, a dicing process is performed on the top surface of the portion of the nitride semiconductor layer arranged on the engraved region or on the bottom surface of the portion of the nitride semiconductor substrate located just below the engraved region, and on the top surface of the portion of the nitride semiconductor layer arranged on the ridge portion or on the bottom surface of the portion of the nitride semiconductor substrate located just below the ridge portion, thereby achieving chip separation.

In the above method for manufacturing a nitride semiconductor device, it is suggested that the method includes fourth and fifth steps, and that, in the fifth step, the scribe line is formed in the form of a solid line from one end to the other end of each bar.

In the above method for manufacturing a nitride semiconductor device, it is suggested that the method includes fourth and fifth steps, and that, in the fifth step, a solid line-shaped scribe line is formed on a part of each strip.

In the above method for manufacturing a nitride semiconductor device, it is suggested that the method includes fourth and fifth steps, and that, in the fifth step, the scribe line is formed in the form of a broken line from one end to the other end of each bar.

In the above method of manufacturing a nitride semiconductor device, it is suggested that the method includes fourth and fifth steps, and that, in the fifth step, the scribe line is formed in the edge portion at the edge formed in the direction perpendicular to the first direction.

According to the present invention, a nitride semiconductor device is fabricated by one of the above-described methods of fabricating a nitride semiconductor device.

Alternatively, according to the present invention, a method of manufacturing a semiconductor device includes: in a first step, a grooved region formed as at least one recessed portion and a ridge portion formed as a non-grooved region are formed on a substrate having a nitride semiconductor layer in at least a part of the surface thereof, thereby forming a processed substrate. Here, the method further includes: a second step of forming inflow prevention walls as elevated portions along both edges of a ridge portion formed on the processed substrate; and a third step of forming a nitride semiconductor layer portion containing at least one nitride semiconductor thin film on the surface of the ridge portion and the engraved region formed on the processed substrate with the inflow prevention walls formed in the second step, thereby forming a nitride semiconductor layer portion on the inflow prevention walls formed along both sides of the ridge portion, thereby forming elevated inflow prevention portions so as to have a level difference with the surface of the flat portion of the nitride semiconductor layer portion disposed on the surface of the ridge portion.

In the above method of manufacturing a nitride semiconductor device, it is suggested that the recess portion as the engraved region is not completely filled when the nitride semiconductor layer portion is formed in the third step.

In the above method for fabricating a nitride semiconductor device, it is suggested that in the second step, the silicon nitride layer is made of SiO₂、Al₂O₃、TiO₂One of ZrO, and W forms the inflow prevention wall.

In the above method for manufacturing a nitride semiconductor device, it is recommended that when the inflow prevention wall is formed in the second step, the inflow prevention wall be made to have a thickness of 50nm or more and 3 μm or less in a direction perpendicular to itself and thus to the surface of the ridge portion.

In the above method for manufacturing a nitride semiconductor device, it is recommended that the inflow prevention walls have a width of 1 μm or more and 25 μm or less in a direction perpendicular to the length direction of the inflow prevention walls when the inflow prevention walls are formed in the second step.

In the above method of manufacturing a nitride semiconductor device, it is suggested that the method further includes: and a fourth step of forming an electrode pad on the portion of the nitride semiconductor layer arranged on the surface of the processed substrate and having the inflow prevention wall formed in the third step, and performing wire bonding on the electrode pad to realize external connection, thereby forming a plurality of semiconductor devices on the substrate. Here, in the fourth step, the electrode pad is not formed on the engraved region.

Alternatively, according to the present invention, a method of manufacturing a semiconductor device includes: a first step of forming a processed substrate by forming a grooved region formed as at least one recessed portion and a ridge portion formed as a non-grooved region on a substrate having a nitride semiconductor layer in at least a part of a surface thereof; and a second step of forming a nitride semiconductor layer portion composed of at least one nitride semiconductor thin film on the surface of the engraved region and the ridge portion formed on the processed substrate. Here, in the second step, the thickness of the nitride semiconductor layer portion disposed on both edge portions of the ridge portion near the engraved region is made larger than the thickness of the nitride semiconductor layer portion disposed outside both edges of the ridge portion, the former thickness being measured from the surface of the ridge portion to the surface of the nitride semiconductor layer portion and the latter thickness also being measured from the surface of the ridge portion to the surface of the nitride semiconductor layer portion, thereby forming the inflow prevention portion raised from the surface of the planar portion of the nitride semiconductor layer portion disposed on the surface of the region other than both edge portions of the ridge portion.

In the above method of manufacturing a nitride semiconductor device, it is suggested that the recess portion as the engraved region is not completely filled when the nitride semiconductor layer portion is formed in the second step.

In the above method of manufacturing a nitride semiconductor device, it is suggested that in the second step, a difference in height between a surface of a flat portion of a nitride semiconductor layer portion arranged on a surface of the ridge portion and an inflow prevention portion raised from the surface of the flat portion be 150nm or more.

In the above method for manufacturing a nitride semiconductor device, it is suggested that in the second step, the nitride semiconductor thin film in direct contact with the surface of the processed substrate is GaN having a thickness of 0.5 μm or less.

In the above method for manufacturing a nitride semiconductor device, it is suggested that in the second step, the nitride semiconductor thin film in direct contact with the surface of the processed substrate is AlGaN.

In the above method for manufacturing a nitride semiconductor device, it is suggested that in the second step, the nitride semiconductor thin film in direct contact with the surface of the processed substrate is GaN, and the temperature of the surface of the processed substrate is 1025 ℃ when the GaN is arranged on the surface of the processed substrate.

In the above method for manufacturing a nitride semiconductor device, it is suggested that in the second step, the nitride semiconductor thin film in direct contact with the surface of the processed substrate is GaN, and that, when arranging GaN, a ratio between a molar flow rate at which a raw material containing nitrogen atoms as a group V element is supplied per unit time and a molar flow rate at which a raw material containing gallium atoms as a group III element is supplied per unit time is 2000 or more.

In the above method for manufacturing a nitride semiconductor device, it is suggested that in the second step, the nitride semiconductor thin film forming the nitride semiconductor layer portion includes an AlGaN layer having an Al content of 0.02.

In the above method of manufacturing a nitride semiconductor device, it is suggested that the method further includes: and a fourth step of forming an electrode pad on the portion of the nitride semiconductor layer disposed on the surface of the processed substrate, which is formed in the second step, and performing wire bonding on the electrode pad to thereby realize external connection, thereby forming a plurality of semiconductor devices on the substrate. Here, in the fourth step, the electrode pad is not formed on the engraved region.

In the above method of manufacturing a nitride semiconductor device, it is suggested that in the fourth step, the electrode pad be formed 30 μm or more from the edge of the notch region.

In the above method of manufacturing a nitride semiconductor device, it is suggested to perform a dicing process on the top surface of the portion of the nitride semiconductor layer arranged on the engraved region or on the bottom surface of the processed substrate portion located just below the engraved region, thereby achieving chip separation.

In the above method for manufacturing a nitride semiconductor device, it is proposed that the recess portion has a depth of 1 μm or more and 20 μm or less when the engraved region as the recess portion is formed in the first step.

In the above method for manufacturing a nitride semiconductor device, it is proposed that the recess portion has an opening width of 1 μm or more when the engraved region as the recess portion is formed in the first step.

With any of the above-described methods, it is possible to prevent the engraved region from being filled with the nitride semiconductor thin film, and it is possible to prevent different portions of the nitride semiconductor thin film from meeting over the engraved region and forming a void.

In the above method for manufacturing a nitride semiconductor device, it is proposed that, when forming the engraved regions as the recessed portions in the first step, the ridge portions sandwiched between two adjacent engraved regions have a width of 140 μm or more and 4mm or less.

According to the present invention, a semiconductor device is manufactured by one of the above-described methods of manufacturing a semiconductor device.

Drawings

Fig. 1a is a schematic cross-sectional view of a nitride semiconductor laser device according to a first embodiment of the present invention;

fig. 1b is a schematic top view of a nitride semiconductor laser device of a first embodiment of the present invention;

FIG. 2a is a schematic cross-sectional view of a processed substrate having a grooved region formed thereon having a rectangular cross-sectional shape;

FIG. 2b is a schematic cross-sectional view of a processed substrate having a grooved region formed thereon having triangular and trapezoidal cross-sectional shapes;

FIG. 3a is a schematic top view of a processed substrate of a first embodiment of the present invention;

FIG. 3b is a schematic cross-sectional view of a processed substrate of the first embodiment of the present invention;

FIG. 4a is a schematic cross-sectional view of a processed substrate in an initial stage of growth of a nitride semiconductor thin film in the first embodiment of the present invention;

FIG. 4b is a schematic cross-sectional view of a processed substrate in a later stage of growth of a nitride semiconductor thin film in the first embodiment of the present invention;

FIG. 5 is a graph of the filling degree C versus the average deviation σ of the p-layer thickness in the first embodiment of the present invention;

fig. 6a is a schematic cross-sectional view of a processed substrate in a state where the engraved region is filled with a nitride semiconductor thin film in the first embodiment of the present invention;

fig. 6b is a schematic cross-sectional view of the processed substrate in a state where the engraved region is filled with a nitride semiconductor thin film in the first embodiment of the present invention;

fig. 6c is a schematic cross-sectional view of the processed substrate in a state where a void surrounded by the nitride semiconductor thin film is formed in the engraved region in the first embodiment of the present invention;

fig. 7a is a partial schematic top view of a nitride semiconductor substrate divided into strips in the first embodiment of the present invention;

fig. 7b is a partial schematic cross-sectional view of the nitride semiconductor substrate divided into strips in the first embodiment of the present invention;

fig. 8a is a schematic top view illustrating a chip detachment position on a nitride semiconductor laser device in the first embodiment of the present invention;

fig. 8b is a schematic cross-sectional view illustrating a chip detachment position on a nitride semiconductor laser device in the first embodiment of the present invention;

fig. 9 is a schematic cross-sectional view of a nitride semiconductor laser device divided into discrete chips in the first embodiment of the present invention;

fig. 10a is a schematic top view illustrating a chip separation position on a nitride semiconductor laser device in another example of the first embodiment of the present invention;

fig. 10b is a schematic cross-sectional view illustrating a chip separation position on a nitride semiconductor laser device in another example of the first embodiment of the present invention;

fig. 11a is a schematic cross-sectional view of a nitride semiconductor laser device according to a second embodiment of the present invention;

fig. 11b is a schematic top view of a nitride semiconductor laser device according to a second embodiment of the present invention;

FIG. 12a is a schematic top view of a processed substrate of a second embodiment of the present invention;

FIG. 12b is a schematic cross-sectional view of a processed substrate of a second embodiment of the present invention;

fig. 13 is a schematic cross-sectional view of a part of a wafer having a nitride semiconductor thin film grown on a processed substrate in a second embodiment of the present invention;

fig. 14a is a schematic cross-sectional view of a processed substrate in a state where the engraved region is filled with a nitride semiconductor thin film in the second embodiment of the present invention;

FIG. 14b is a schematic cross-sectional view of a processed substrate in a state where a void surrounded by a nitride semiconductor thin film is formed in a engraved region in the second embodiment of the present invention;

fig. 15a is a partial schematic top view of a nitride semiconductor substrate divided into strips in a second embodiment of the present invention;

fig. 15b is a partial schematic cross-sectional view of the nitride semiconductor substrate divided into strips in the second embodiment of the present invention;

fig. 16 is a partial schematic cross-sectional view of a wafer having a nitride semiconductor thin film grown on a processed substrate in a third embodiment of the present invention;

FIG. 17 is a graph of the height difference H versus the number of devices acceptable;

FIG. 18a is a schematic top view of a conventional wafer with a nitride semiconductor growth layer disposed on top of a processed substrate;

FIG. 18b is a schematic cross-sectional view of a conventional wafer with a nitride semiconductor growth layer disposed on top of a processed substrate;

fig. 19 is a schematic cross-sectional view of a nitride semiconductor growth layer;

FIG. 20 is a plot of surface height differences on a conventional wafer with a nitride semiconductor growth layer disposed on top of a processed substrate;

fig. 21a is a schematic cross-sectional view of a conventional processed substrate at an initial stage of growth of a nitride semiconductor thin film; and

fig. 21b is a schematic cross-sectional view of a conventional processed substrate at a later stage of nitride semiconductor thin film growth.

Detailed Description

First, some terms used in the present specification to express a key principle will be defined. The "engraved region" means a stripe-shaped depressed portion formed on the surface of a nitride semiconductor substrate or a different substrate, similar to that shown in fig. 2a and 2 b. Fig. 2a and 2b are schematic cross-sectional views of a substrate that has been subjected to a notching process, thereby forming notched regions 16 and ridges 19 thereon. The cross-sectional shape of such a scored region 16 need not necessarily be rectangular, but may be triangular or trapezoidal as shown in fig. 2 b; that is, it is only necessary to shape the engraved region 16 so that a height difference is generated between the depressed portion and the elevated portion. Each engraved region 16 is not necessarily formed with a single recessed portion, and each engraved region 16 may be composed of a plurality of recessed portions and a narrow flat portion sandwiched therebetween, as described later.

Likewise, "ridge" means a band-shaped elevated portion formed. In fig. 2a and 2b, the engraved regions 16 and the ridges 19 are formed in a striped pattern extending in one direction. The engraved regions 16 or ridges 19 may also be formed in a grid pattern extending in different directions across each other. The scored region 16 may be formed with different shapes, different depths, or different widths on a single substrate. The engraved regions 16 may be formed at different intervals on a single substrate.

"nitride semiconductor substrate" means a substrate made of Al_xGa_yIn_zAnd N (x is 0 to 1, y is 0 to 1, z is 0 to 1, and x + y + z is 1). Here, of the nitrogen elements contained in the nitride semiconductor substrate, about 10% or less of the nitrogen elements may be substituted by As, P, or Sb elements (provided that the substrate maintains a hexagonal crystal structure). Further, Si, O, Cl, S, C, Ge, Zn, Cd, Mg, or Be may Be doped in the nitride semiconductor substrate. Among these doping materials, Si, O, and Cl are particularly suitable for an n-type nitride semiconductor. Suitable for use as the principal plane direction of the nitride semiconductor substrate are the C plane {0011}, the A plane {11-20}, the R plane {1-102}, the M plane {1-100} or {1-101} plane. The surface morphology of the substrate can be satisfactory as long as the principal plane of the substrate deviates from the direction of any of those crystallographic planes by an angle of less than or equal to 2 °.

First embodiment

A first embodiment of the present invention will now be described with reference to the accompanying drawings. The present embodiment relates to a nitride semiconductor laser device as an example of a nitride semiconductor device. However, it should be understood that the present invention is applicable to any other type of nitride semiconductor device. Fig. 1a is a schematic cross-sectional view of the nitride semiconductor device of the present embodiment, and fig. 1b is a top view of fig. 1 a. Fig. 3b is a schematic cross-sectional view of the processed substrate 10 without growing a nitride semiconductor thin film on the processed substrate 10 in this embodiment of the present invention, and fig. 3a is a top view of fig. 3 b. In these figures, the plane directions are uniformly expressed. The nitride semiconductor laser device shown in fig. 1a and 1b is fabricated, for example, by disposing nitride semiconductor growth layer 11 having the structure shown in fig. 19 over processed substrate 10 shown in fig. 3a and 3 b.

The nitride semiconductor laser device of the present embodiment is fabricated by growing a nitride semiconductor growth layer 11 on a processed substrate 10 having a engraved region 16 formed thereon as a recessed portion. With regard to this nitride semiconductor laser device, first, how to manufacture the processed substrate 10 will be explained with reference to the drawings. In the present embodiment, it is assumed that an n-type GaN substrate is employed as the processed substrate 10.

First, SiO was sputter deposited to a thickness of 1 μm on the entire surface of an n-type GaN substrate₂A membrane or the like. Next, by a common photolithography process, along [1-100]]A stripe-shaped photoresist pattern is formed in a direction such that the photoresist pattern has an opening 5 μm wide and is extended from a certain stripe [11-20]]The distance from the center of the direction to the center of the adjacent stripe (hereinafter, this distance is referred to as pitch) is 400 μm. Next, the SiO is etched by a dry etching technique such as RIE (reactive ion etching)₂And an n-type GaN substrate, thereby forming a engraved region 16 having an engraved depth Y of 5 μm and an opening width X of 5 μm. Thereafter, using HF (hydrofluoric acid) or the like as an etchant, SiO is removed₂. The processed substrate 10 having the engraved regions 16 and the ridges 19 (i.e., non-engraved regions) as shown in fig. 3a and 3b formed thereon is fabricated using this method.

Vapor deposition of the above SiO₂The method used is not necessarily sputter deposition, but may be electron beam deposition, plasma CVD, or the like. The pitch of the photoresist pattern is not necessarily 400 μm as described above, and may be varied to suit the width of the nitride semiconductor laser device to be manufactured. Forming an etch on a processed substrate 10The etching method used for the trench region 16 may be dry etching or wet etching.

The processed substrate 10 may be formed by a method of forming the engraved region 16 directly on the surface of the n-type GaN substrate as described above, or may be formed by a method of first growing a nitride semiconductor thin film composed of GaN, InGaN, AlGaN, InAlGaN, or the like on the surface of the n-type GaN substrate, followed by engraving.

On the processed substrate 10 fabricated as described above, a nitride semiconductor growth layer 11 as shown in fig. 19 is epitaxially grown, suitably using a known technique such as MOCVD, to fabricate a nitride semiconductor laser device as shown in fig. 1a and 1 b.

Thus, the nitride semiconductor laser device shown in fig. 1a and 1b has a nitride semiconductor growth layer 11 formed on the processed substrate 10 having the engraved regions 16 fabricated as described above, the nitride semiconductor growth layer 11 having a plurality of nitride semiconductor thin films stacked in order as shown in fig. 19. Further, on the surface of the nitride semiconductor growth layer 11, a laser stripe (laser stripe)12 serving as a laser waveguide and SiO provided for sandwiching the laser stripe 12 and for current confinement are formed₂And a membrane 13. In the laser stripe 12 and SiO₂On the surface of the film 13, a p-side electrode 14 is formed. On the other hand, on the bottom surface of the processed substrate 10, an n-side electrode 15 is formed. Further, a surface portion of the p-side electrode 14 located just above the laser stripe 12 is formed as an elevated stripe (elevedated stripe) 18.

After forming the nitride semiconductor growth layer 11 over the processed substrate 10, a nitride semiconductor laser device having the ridge structure as described above is fabricated using an appropriate known technique. Therefore, a detailed description thereof will not be given. Thereafter, a plurality of nitride semiconductor laser devices formed by arranging nitride semiconductor growth layer 11 over processed substrate 10 (wafer) are divided into individual devices. Specifically, first, the wafer is cleaved in a direction parallel to the [11-20] direction (see fig. 1a and 1b) to be divided into strips as shown in fig. 7a and 7b, each strip having a plurality of nitride semiconductor laser devices. Here, in the present embodiment, the cavity length, i.e., the length in the cavity direction (i.e., [1-100] direction), is 600 μm. However, the cavity length does not necessarily have to be equal to the value, and the cavity length may be any value preferably in the range of 300 μm to 1200 μm. The thus-cleaved bar is then divided into chips, thereby separating the respective nitride semiconductor laser devices from each other. How the chip separation is performed will be described in detail later.

In accordance with the above description, the nitride semiconductor laser device shown in fig. 1a and 1b is manufactured. Here, the distance from the center of the laser stripe 12 to the edge of the engraved region 16 is referred to as "d". In this embodiment, let d be 40 μm. It should be noted that, in order to easily understand the cross-sectional structure, when the cross-sections of the nitride semiconductor laser devices shown in fig. 1a and 1b are generated, the positions where the chip separation is performed are different from the engraved regions where the chip separation is actually performed, which will be described in detail later.

In the nitride semiconductor laser device shown in fig. 1a and 1b, the p-side electrode 14 is formed of Mo/Au, Mo/Pt/Au, a single Au layer, or the like, starting from the side thereof closer to the nitride semiconductor growth layer 11. In the present embodiment, SiO is used₂The film 13 serves as an insulating film for current confinement. Alternatively, ZrO, TiO may be used₂Etc. as the material of the insulating film.

In this nitride semiconductor laser device, how to grow the nitride semiconductor thin film in the engraved regions 16 and the flatness of the nitride semiconductor thin film grown on the ridges have a correlation as described below.

When the epitaxial growth is started on the processed substrate 20 having the engraved regions 16 formed thereon, as shown in fig. 4a, a nitride semiconductor thin film is grown as top surface growth portions 21 on top surface portions 23 of the ridges and as engraved region growth portions 22 on side surface portions 24 and bottom surface portions 25 of the engraved regions 16. Before growing the nitride semiconductor thin film, the opening width and depth of the engraved region 16 formed on the processed substrate 20 are set to X and Y, respectively. Further, it is assumed that a line extending from the surface of the top surface portion 23 of the ridge in parallel to the surface forms a engraved-area boundary line 26. Here, in the engraved region 16, a cross-sectional area of a portion surrounded by the side surface portion 24, the bottom surface portion 25, and the engraved region boundary line 26 is set to a. Therefore, the sectional area a is equal to X × Y.

In the initial stage of epitaxial growth, as shown in fig. 4a, the top surface growth portions 21 formed of the nitride semiconductor thin film grown on the surfaces of the top surface portions 23 of the ridges are separated from the engraved region growth portions 22 formed of the nitride semiconductor thin film grown on the side surface portions 24 and the bottom surface portions 25 of the engraved region 16. As the nitride semiconductor thin film growth proceeds, as shown in fig. 4b, the top surface growth portion 21 grown on the top surface portion 23 is connected to the engraved region growth portion 22 grown in the engraved region 16 through the growth portion 27. Thus, the sectional area of the engraved-region growing part 22 thus grown in the engraved region 16 is set to B, and the ratio of the sectional area B to the above-described sectional area a is set to C. This ratio is used to indicate the degree to which the nitride semiconductor thin film fills the engraved region 16.

For example, as shown in fig. 6a, the nitride semiconductor thin film is arranged in the engraved region 16 until the latter completely fills the former regardless of whether the surface of the nitride semiconductor thin film thus grown is flat, at which time the filling degree C is considered to be 100%. On the other hand, as shown in fig. 6B, if the nitride semiconductor thin film (i.e., the trench region growing part 22) in which the engraved region 16 is not arranged is completely filled, the filling degree C is calculated according to the above-described calculation method so that C ═ B/a × 100%. In contrast, as shown in fig. 6c, if the top growth portions 21 grown in the lateral direction are grown so quickly that the voids 31 still remain in the engraved regions 16, different portions of the nitride semiconductor thin film (i.e., the top growth portions 21) will meet above those voids 31, and as a result, the surface flatness of the nitride semiconductor thin film is inferior, and there is little effect on reducing cracks. Therefore, the just-mentioned example is not considered in the present embodiment.

The flatness is estimated in the following manner. A wafer was produced by disposing a nitride semiconductor growth layer 11 composed of a plurality of nitride semiconductor thin films on a processed substrate 10 having a grooved region 16 formed thereon as shown in fig. 1a and 1b, and the resulting wafer was observed under an optical interference microscope to measure the p-layer thickness before etching was performed to form a ridge structure. The variation of the p-layer thickness within the wafer surface was used as an indicator of flatness. Specifically, assuming that the design value of the p-layer thickness is 0.670 μm, the p-layer thickness is measured at 20 points in the wafer plane, and the average deviation σ of the measurement results thus obtained is calculated. This average deviation σ represents the degree of variation between the thicknesses measured at the 20 points. The larger the average deviation σ is, the larger the variations in various characteristics of the nitride semiconductor laser device, such as FFP, threshold current, slope efficiency, and the like. In order to suppress the characteristic variation of the nitride semiconductor laser device, it is necessary to reduce the average deviation σ to 0.01 or less. Incidentally, the average deviation σ is calculated as follows: the difference between each thickness value measured at 20 points and the average of the 20 measurements is first determined, the absolute values of these differences are then added and summed, and the determined sum is finally divided by 20.

Fig. 5 shows the relationship between the degree of filling C of the nitride semiconductor thin film in the etched groove region 16 and the degree of variation in the thickness of the p layer before etching to form the ridge structure. The curves in fig. 5 are as follows. If the filling degree C is greater than 80%, the mean deviation sigma of the p-layer thickness increases suddenly; if the filling degree C is 80% or less, the mean deviation sigma of the p-layer thickness remains small. For example, when a nitride semiconductor laser device is manufactured with a filling degree C of 70%, the average deviation σ of the p-layer thickness is 0.0034 μm, which is an excellent result.

For example, the filling degree C of the engraved region 16 can be reduced to 80% or less by a method of controlling the total thickness of the nitride semiconductor thin film, or by a method of controlling the opening width X and depth Y of the engraved region 16. Here, ,the total thickness of the nitride semiconductor thin films (hereinafter simply referred to as the total thickness) represents the thickness from the surface of the portion thereof where the engraved region 16 is not formed to the surface of the nitride semiconductor growth layer 11 formed by stacking the respective nitride semiconductor thin films in order in the processed substrate 10 having the engraved region 16 formed thereon. That is, it indicates the thickness from the surface of the portion of the processed substrate 10 where the engraved region 16 is not formed to the surface of the laser stripe 12 located on the nitride semiconductor growth layer 11 after the laser stripe 12 (see fig. 1a) is formed. Here, SiO is not included₂A membrane 13 and a p-side electrode 14.

In order to obtain good film flatness, when the opening width X of the engraved region 16 is larger than 100 μm, the engraved region growth part 22 grown on the bottom surface part 25 of the engraved region 16 is grown at the same growth rate as the top surface growth part 21 grown on the surface of the top surface part 23 where the ridge of the engraved region 16 is not formed, thereby obtaining the same thickness as it. Therefore, when the total thickness is 0.8 times or less the depth Y of the engraved region 16, the filling degree C of the engraved region 16 is 80% or less.

When the opening width X of the engraved region 16 is 2 μm or more but 30 μm or less, the opening of the engraved region 16 is narrow, so that atoms and molecules of the raw material forming the nitride semiconductor thin film cannot sufficiently enter the engraved region 16. Therefore, the growth rate of the engraved region growth portions 22 grown on the bottom surface portions 25 of the engraved regions 16 is lower than the growth rate of the top surface growth portions 21 grown on the surfaces of the top surface portions 23 where the ridges at the engraved regions 16 are not formed, and therefore the former is smaller in thickness than the latter. Therefore, when the total thickness is 3 times or less the depth Y of the engraved region 16, the filling degree C of the engraved region 16 is 80% or less.

When the opening width X of the engraved region 16 is greater than 30 μm but less than or equal to 100 μm, the value of X falls between the above two ranges, and therefore, when the total thickness is twice or less the depth Y of the engraved region 16, the filling degree C of the engraved region 16 is 80% or less. Incidentally, if the opening width X of the engraved region 16 is less than 2 μm, an undesirable state as shown in fig. 6c will occur. Therefore, in the present embodiment, the opening width X of the engraved region 16 is 2 μm or more.

It is also estimated that cracks formed when the nitride semiconductor growth layer 11 composed of various nitride semiconductor thin films was disposed as described above on the processed substrate 10 on which the engraved regions 16 were formed. The results are as follows. When the filling degree C is 80% or less, the crack density in the film is 0 cracks/cm²(ii) a When the filling degree C is 80% or more, the crack density in the film is 3 to 4 cracks/cm²(ii) a And, when the degree of filling C is 100%, the crack density in the film is about 10 cracks/cm². That is, by lowering the filling degree C to be less than or equal to 80%, it is possible to manufacture a nitride semiconductor laser device in which the degree of variation in the thickness of the p layer is reduced, the flatness of the nitride semiconductor thin film is good, and the generation of cracks is reduced.

After that, the nitride semiconductor laser device thus manufactured is divided into separate chips. Before the chips are separated, the wafer is first cleaved to form the resonator end faces. This embodiment will now be described with reference to the drawings. Figure 7b shows a part of a schematic cross-sectional view of a wafer cleaved in a direction parallel to the 11-20 direction (see figures 1a and 1b) for the purpose of separating it into strips with resonator end faces formed at the cleaved surfaces, and figure 7a is a top view thereof.

On top of the processed substrate 10 having the engraved regions 16 formed thereon, a nitride semiconductor growth layer 11 is stacked, and on the surface thereof, p-side electrode pads 40 and p-side electrodes 14 (see fig. 1a) are formed, each of the p-side electrode pads 40 being made of, for example, SiO₂The insulating film of the film 13. Wire bonding is performed on these p-side electrode pads 40. The P-side electrode pad 40 is typically about 100nm to 1 μm thick. The nitride semiconductor growth layer 11 has a current confinement layer inside, and, in the "buried current confinement laser" in which current confinement is achieved using this layer, each p-side electrode pad 40 is constituted solely by one p-side electrode 14. In addition, on the top surface of the p-side electrode pad 40Elevated stripes 18 are formed thereon, and an n-side electrode 15 is formed on the bottom surface of the processed substrate 10. As shown in fig. 7a, the distances between the two edges of the p-side electrode pad 40 and the edges of the engraved regions 16 adjacent to those of the p-side electrode pad 40, respectively, are set to M and N, respectively.

As shown in fig. 7a and 7b, the p-side electrode pad 40 is not formed over the engraved region 16. This is because, since the surface of the nitride semiconductor growth layer 11 above the engraved region 16 is uneven, for example, SiO is formed on the surface₂The insulating film of (2) causes cracks, threading dislocations, holes, locally thin portions, and the like. These regions exhibit low electrical insulation compared to regions other than the regions above the engraved regions 16, and result in current leakage.

Further, even if no visible groove or depression is found when the engraved region 16 is completely filled, the nitride semiconductor thin film in the engraved region 16 may generate defects, dislocations, cracks, and the like during the gradual filling of the nitride semiconductor thin film in which the engraved region 16 is disposed. Thus, SiO is formed on the surface of nitride semiconductor growth layer 11 located above engraved region 16₂Etc. will result in low electrical insulation. Therefore, if the p-side electrode pad 40 is formed on the engraved region 16 or the depression, spontaneous emission light may be observed in those regions. This spontaneous emission light is generated when a leakage current flows through the nitride semiconductor laser device. When the p-side electrode pad 40 is formed at 5 μm or more from the edge of the engraved region 16, no spontaneous emission light is observed from a place other than the region of the laser stripe 12 (see fig. 1 a). Therefore, the distances M and N from the edge of the engraved region 16 to both edges of the p-side electrode pad 40 are each preferably equal to or greater than 5 μ M.

The present embodiment relates to a ridge-stripe (ridge-stripe) type laser by using, for example, SiO formed on a nitride semiconductor growth layer 11₂The present embodiment can also be applied to any other type of laser, for example, having electricity in the nitride semiconductor growth layer 11, realizing current confinementA VSIS (V-channel substrate internal stripe) type laser of the flow restriction layer. In this type of laser, there is no insulating film for current confinement on the surface of the nitride semiconductor growth layer 11, and the p-side electrode pad 40 is constituted by the p-side electrode 14 alone. It should be noted that, in this specification, the electrode pad means an electrode pad on an insulating surface or an electrode itself. Also, in this type of laser, when the p-side electrode pad 40 is formed in the engraved region 16, as in the ridge-stripe type laser, a large leakage current will flow, thereby degrading the characteristics of the nitride semiconductor laser device and causing it to fail to lase. It is considered that this is caused by the deterioration of the crystallinity of the current confinement layer located above the engraved region 16. Therefore, in the VSIS type or the like laser, the distances M and N from the edge of the engraved region 16 to both edges of the p-side electrode pad 40 are also preferably equal to or greater than 5 μ M.

The present embodiment relates to a structure in which an n-type GaN substrate is used as the processed substrate 10, and the electrode pad formed on the surface of the nitride semiconductor growth layer 11 is a p-side electrode pad, but the present embodiment can be applied to any other structure; for example, the present embodiment can also be applied to a nitride semiconductor laser device having the following configuration, that is: the processed substrate 10 is formed of a p-type semiconductor material, the surface of the nitride semiconductor growth layer 11 is formed of an n-type nitride semiconductor thin film, and the electrode pad formed on the surface thereof is an n-type electrode pad.

In wire bonding, although the diameter of the spherical portion at the tip of the wire depends on the structure of the nitride semiconductor laser device, it is generally about 80 μm, and therefore, the width of the p-side electrode pad 40 must be 80 μm or more. Therefore, the pitch T of the engraved region 16 needs to satisfy the formula T ≧ the formula [ the opening width X of the engraved region 16 (2 μ M or more) + the width of the p-side electrode pad 40 (80 μ M or more) +10 μ M (the minimum value of the sum of the distances M and N from both edges of the p-side electrode pad 40 to the edge of the engraved region 16) ]. When T is greater than 4mm, cracks may be generated in the arranged nitride semiconductor thin film. Therefore, the pitch T of the engraved region 16 is preferably 4mm or less. Therefore, the pitch T of the engraved regions 16 is preferably 92 μm or more but 4mm or less.

A plurality of nitride semiconductor laser devices fabricated on the processed substrate 10 are divided into long stripes as shown in fig. 7a and 7b, and then divided into discrete chips. Now, how the chip separation is performed will be described with reference to the drawings.

In fig. 7b, chip separation positions 41 and 42 are indicated. At the chip separation positions 41 and 42, a dicing operation is performed with a diamond pen or the like from the n-side electrode 15 side or from the nitride semiconductor growth layer 11 side. Thereafter, a blade having an acute-angled edge is placed on the scribed line (hereinafter referred to as a scribe line), and pressure is applied to the blade by using a breaking device, thereby causing the strip to be cleaved under the pressure. The score line preferably extends centrally along the score region 16. However, in the present embodiment, as described above, the filling degree C of the engraved region 16 is 80% or less, and therefore, the engraved region 16 is not completely filled, leaving a groove which plays a guide role for chip separation. Therefore, even if the scribe line is deviated from the center of the engraved region 16, there is no risk of peeling (chipping) or separation in an unintended direction as long as it extends within the engraved region 16.

Even if the score line extends outside the score region 16 and if the cleave deviates from the score line during chip separation, i.e. progresses in an unintended direction, once the crack reaches the score region 16, it proceeds down the groove in the score region 16. Thereby protecting the adjacent nitride semiconductor laser devices from damage. It is considered that the reason why the crack does not proceed outside the engraved region 16 is that the crystallinity, the plane orientation, and other properties of the nitride semiconductor thin film arranged in the engraved region 16 are different from those of the nitride semiconductor thin film grown on the flat portion of the non-engraved region.

In the present embodiment, as shown in fig. 7a and 7b, it is preferable to fabricate a nitride semiconductor laser device on each ridge, i.e., on the non-grooved region located between two adjacent grooved regions. However, it is also possible to adopt any other structure, for example, two or more nitride semiconductor laser devices are fabricated on each ridge, i.e., on a non-grooved region located between two adjacent grooved regions.

As shown in fig. 8a and 8b, the dicing operation can be performed at the chip separation positions 52 and 53, but only in the resonator end face side portion of the notch region 16, so that the scribe line 50 is formed only in the edge portion. A scribe line as shown by the dashed scribe line 51 may also be formed. Even when the dicing operation is performed by this method, it is possible to achieve chip separation with good yield. A scribe line may be formed as a solid line (not shown).

By the chip separation achieved as described above, a separate nitride semiconductor laser device as shown in fig. 9 is obtained. In the present embodiment, chip separation is performed using the trench located in the engraved region 16 as a result of the nitride semiconductor thin film in which the engraved region 16 is not arranged being completely filled. This method reduces damage to the nitride semiconductor thin film, prevents degradation of the characteristics of the nitride semiconductor laser device, and allows die separation to be performed with good yield, as compared with a conventional method in which a trench for die separation is newly formed in a die separation step.

Alternatively, as shown in fig. 10a and 10b, the chip separation may be performed by forming two stripe-shaped recessed portions 66, and thereafter, performing a dicing operation on the bottom surface of the wafer or the surface on the side of the nitride semiconductor growth layer 11 (shown in fig. 1a) in a flat area sandwiched by those two stripes. With this structure, even if the crack extends in an unintended direction during chip separation, the recessed portions 66 on both sides prevent the crack from extending to the outside thereof, thereby protecting the adjacent nitride semiconductor laser device from damage. In this manner, the dicing operation is performed in the flat areas of the chip separation positions 60 and 61 as indicated in fig. 10b sandwiched between the concave portions 66, without performing the dicing operation at the concave portions 66, so that it is possible to perform the chip separation with good yield. As shown in fig. 10a, the scribe line formed may be a dashed-line scribe line 62, or a scribe line 63 formed by performing a dicing process only on the side portion of the resonator end face, or a solid-line scribe line 64, or a solid-line scribe line 65 with an unpainted portion left.

Second embodiment

Next, a second embodiment example of the present invention will be explained with reference to the related drawings. The present embodiment and the following embodiments each relate to a nitride semiconductor laser device as an example of a semiconductor device. However, it should be understood that the present invention is applicable to any other kind of semiconductor device. Fig. 11a is a schematic cross-sectional view of the semiconductor device of the present embodiment, and fig. 11b is a top view of fig. 11 a. Fig. 12b is a schematic cross-sectional view of the processed substrate 10 before growing a nitride semiconductor thin film on the processed substrate 10 in this embodiment of the present invention, and fig. 12a is a top view of fig. 12 b. In fig. 11a, 11b, 12a and 12b, the crystal plane orientations are collectively indicated.

In the nitride semiconductor laser device of the present embodiment, the processed substrate 10, which is composed of the nitride semiconductor substrate on which the engraved regions 16 as the recessed portions are formed, further has [1-100] located along both sides of the ridge 19 (i.e., non-engraved regions)]Directionally elongated stripe-shaped SiO₂A wall. On top of this processed substrate 10, a nitride semiconductor growth layer 11 is grown, and thereby a nitride semiconductor laser device is manufactured. With regard to this nitride semiconductor laser device, how to manufacture the processed substrate 10 is first explained with reference to the drawings. In the present embodiment, it is assumed that an n-type GaN substrate is employed as the processed substrate 10.

First, SiO was sputter-deposited to a thickness of 1 μm on the entire surface of an n-type GaN substrate₂Films, and the like. Next, by a common photolithography process, along [1-100]]The direction was patterned to form a stripe-shaped photoresist pattern having an opening of 5 μm width and extending from the center of one stripe along [11-20]]The distance from the direction to the center of the next stripe was 250 μm. Then, byDry etching techniques such as RIE (reactive ion etching), etching of SiO₂And an n-type GaN substrate to form a notch region 16 having a notch depth Y of 5 μm and an opening width X of 5 μm. Thereafter, SiO is removed using HF (hydrofluoric acid) or the like as an etchant₂. The processed substrate 10 having the engraved regions 16 and the ridges 19 formed thereon is fabricated in this manner.

In this example, SiO is deposited by vapor deposition₂Forming SiO on the surface of an n-type GaN substrate₂And (3) a membrane. Alternatively, any other kind of dielectric film or the like may be formed on the surface of the n-type GaN substrate. Forming the above SiO₂The method of (2) is not necessarily sputter deposition but may be electron beam deposition, plasma CVD, or the like. The pitch of the photoresist pattern is not necessarily 250 μm as described above, and it may be varied to suit the width of the nitride semiconductor laser device to be manufactured. In the present embodiment, the engraved region 16 is formed by dry etching. Alternatively, the engraved region 16 may be formed by wet etching or the like.

The processed substrate 10 fabricated in this manner may be formed by forming the engraved regions 16 directly on the surface of the n-type GaN substrate as described above, or may be formed by first growing a nitride semiconductor thin film composed of GaN, InGaN, AlGaN, InAlGaN, or the like on the surface of the n-type GaN substrate, or a nitride semiconductor substrate other than the n-type GaN substrate, or on a different substrate, and then performing the engraving.

After forming the processed substrate 10 having the engraved regions 16 located thereon in this manner, SiO is vapor-deposited on the ridges 19 (i.e., non-engraved regions)₂To form SiO₂And (3) a membrane. Next, along both sides of the ridge 19, a common photolithography technique is used to form [1-100]]A striped photoresist pattern having a width D in the direction. Here, the photoresist pattern is formed in such a manner that: the side extension line of the engraved region 16 coincides with the sidewall surface of the photoresist pattern. Thereafter, SiO is etched by dry etching or wet etching with HF (hydrofluoric acid) or the like₂Film until n-type GaN liner is exposedThe surface of the bottom. The processed substrate 10 is formed in this manner, as shown in FIGS. 12a and 12b, with the engraved regions 16 and the ridges 19 formed thereon, and has a width D, a thickness T, and is located along both sides of the ridges 19 [1-100]]Directionally elongated striped SiO₂A wall 17.

In this example, SiO₂The wall 17 is made of SiO₂And (3) forming. Alternatively, the walls may be made of SiO₂Of any material other than, e.g. Al₂O₃、TiO₂ZrO or W. Such as Al₂O₃、TiO₂Any material of ZrO or W is selective in the sense that: in attempting to form a GaN or AlGaN film on its surface, the growth of GaN or AlGaN is either slow or completely non-existent. When walls composed of such selective materials are formed along both sides of the ridge 19, these walls prevent atoms and molecules of GaN or AlGaN raw material from flowing into the engraved regions 16. This makes it possible to use, for example, SiO₂、Al₂O₃、TiO₂A selective material for ZrO or W becomes a preferred material for the wall.

In forming SiO in the above manner₂If the walls 17 are formed of SiO on the ridges 19₂The film thickness T is less than 50nm, and it becomes difficult to form SiO with a uniform thickness in the range of the wafer surface₂And (3) a membrane. On the contrary, SiO is formed in the above manner₂If the walls 17 are formed of SiO on the ridges 19₂The thickness T of the film is greater than 3 μm, disadvantageously originating from SiO₂The stress of the film will act on the nitride semiconductor thin film. Thus, SiO is formed₂SiO formed on the ridge 19 in the case of the wall 17₂The thickness T of the film is preferably 50nm or more but 3 μm or less.

On the other hand, if parallel to [11-20]]SiO in the direction of the direction₂The width D of the wall 17 is less than 1 μm, disadvantageously, at this time, it is difficult to perform the process, and thus it is difficult to form SiO₂A wall 17. Conversely, if the width D is larger than 25 μm, it is not preferable, and in this case, it comes from SiO₂The stress of the film will act on the nitride semiconductorA film. Thus, in parallel to [11-20]]In the direction of the direction, SiO₂The width D of the wall 17 is preferably 1 μm or more but 25 μm or less.

Further, if the depth Y of the engraved region 16 formed in this way is less than 1 μm, the engraved region 16 is filled with the nitride semiconductor growth layer 11. This will result in that the strain occurring in the nitride semiconductor growth layer 11 cannot be released, thus resulting in the generation of cracks. On the contrary, if the depth Y is 20 μm or more, the wafer may be broken when the wafer is polished until its thickness is about 100 μm in a chip separation step to be performed later. Therefore, the depth Y of the engraved region 16 is preferably not less than 1 μm but not more than 20 μm.

On top of the processed substrate 10 fabricated as described above, a nitride semiconductor growth layer 11 composed of a plurality of nitride semiconductor thin films, exemplified by the structure shown in fig. 19, is epitaxially grown using a known technique such as MOCVD as appropriate to fabricate a nitride semiconductor laser device as shown in fig. 11a and 11 b.

FIG. 13 is a schematic cross-sectional view of a wafer on which a nitride semiconductor thin film is grown, with a view to arranging nitride semiconductor growth layer 11 on processed substrate 10 as described above, processed substrate 10 having engraved regions 16 and ridges 19 formed thereon and SiO formed along both sides of ridges 19 as described above₂A wall 17. As shown in fig. 13, a nitride semiconductor thin film is grown which functions as: a top surface growing portion 75 located at a central portion of the top surface portion 71 of the ridge 19; inflow prevention portions 74 at both edge portions of the top surface portion 71 of the ridge 19 where SiO is formed₂Walls 17a and 17b (corresponding to SiO in FIG. 11a)₂Walls 17); and a engraved region growing portion 77 located on the side surface portion 72 and the bottom surface portion 73 in the engraved region 16. The inflow prevention portion 74 is connected to the engraved region growth portion 77 through the growth portion 76.

As shown in FIG. 13, since the processed substrate 10 has SiO₂Walls 17a and 17b, so the inflow prevention portion 74 has a raised outer portionAnd (4) shaping. This allows SiO₂The walls 17a and 17b inhibit atoms and molecules of the raw material of the nitride semiconductor thin film from migrating from the top surface portions 71 of the ridges 19 and thus moving into the engraved regions 16. The inflow prevention portions 74 thus have a raised profile, contributing to more strongly suppressing the migration of atoms and molecules of the raw material of the nitride semiconductor thin film from the top surface portions 71 of the ridges 19 and thus into the engraved regions 16.

Specifically, even if atoms and molecules of the raw material of the nitride semiconductor thin film adhere to the surface of the top surface growth portion 75 grown on the top surface portions 17 of the ridges 19, the inflow prevention portions 74 will inhibit their migration and thus move to the top surface growth portions 75 and to the side surface portions 72 and the bottom surface portions 73 of the engraved regions 16. Therefore, atoms and molecules that have adhered to the surface of the top growth portion 75 migrate only on the surface of the top growth portion 75. This improves the surface flatness of the top growth portion 75 and contributes to the formation of a nitride semiconductor thin film of uniform thickness. The width of the inflow prevention portion 74 in the direction parallel to the [11-20] direction is about 10 μm to 30 μm.

In this embodiment and a third embodiment described later, "flatness" refers to the surface flatness of the top surface growth portions 75 and 95 (described below, see fig. 16) and the surface flatness of the nitride semiconductor thin films disposed over those top

surface growth portions

75 and 95. As shown in fig. 13, along the perpendicular to SiO₂The sectional shape of the plane cut in the extending direction of the walls 17a and 17b may be SiO₂The walls 17a are, for example, rectangular, or any other shape, such as SiO₂And a wall 17 b.

When the nitride semiconductor growth layer 11 is arranged in this manner, if the opening width X of the engraved region 16 is less than 1 μm, then the engraved region 16 will be completely filled with the engraved region growth part 77 as shown in fig. 14a, thereby generating cracks. Alternatively, as shown in fig. 14b, the top growth portions 75 grown on the surface of the ridges 19 grow in the lateral direction until different portions of the top growth portions 75 meet over the engraved regions 16, leaving the voids 51. This reduces the surface flatness of the top growth portion 75 and has little effect on reducing cracks. Therefore, the opening width X of the engraved region 16 needs to be 1 μm or more.

As described above, the inflow prevention portions 74 make it possible to obtain good surface flatness on the top surface growth portions 75 formed on the top surface portions 71 of the ridges 19. On the top surface growth portion 75 thus having good flatness, a plurality of nitride semiconductor thin films are stacked in order to form a nitride semiconductor growth layer 11 structured as shown in fig. 19, and in this way, a nitride semiconductor laser device as shown in fig. 11a is produced. The nitride semiconductor growth layer 11 is formed appropriately using a known technique such as MOCVD, and therefore, a detailed description thereof will not be given.

On the surface of this nitride semiconductor growth layer 11 formed over the processed substrate 10 as described above, laser stripes 12 and SiO are formed₂The film 13, the former functioning as a laser light guide, and the latter sandwiching the laser stripe 12 and functioning as a current limiter. In the laser stripe 12 and SiO₂On the surface of the film 13, a p-side electrode 14 is formed, and an n-side electrode 15 is formed on the bottom surface of the processed substrate 10. Here, the central portion of the surface of the p-side electrode 14 located just above the laser stripe 12 is formed as a rising stripe 18. Let the center of the laser stripe 12 go to SiO₂The wall 17 has an edge on one side of the laser stripe 12 at a distance "e". In the present embodiment, this distance "e" is equal to 40 μm.

Further, in this nitride semiconductor laser device, from its side close to nitride semiconductor growth layer 11, p-side electrode 14 is composed of Mo/Au, Mo/Pt/Au, a single Au layer, or the like. In the present embodiment, SiO is used₂The film 13 serves as an insulating film for limiting the current. Alternatively, it is possible to use ZrO, TiO₂Etc. as the material of the insulating film. It should be noted that fig. 11a and 11b show a cross section of a nitride semiconductor laser device for making the cross sectional structure easy to understand, the chip separation position adopted for fabricating the nitride semiconductor laser device being different from the actual implementation described belowThe location of the chip separation, namely the slot region 16.

After arranging nitride semiconductor growth layer 11 over processed substrate 10, suitably using known techniques, a nitride semiconductor laser device having the ridge structure as described above is fabricated, and therefore, a detailed description thereof will not be provided. Thereafter, the plurality of nitride semiconductor laser devices formed thereon by disposing nitride semiconductor growth layer 11 on processed substrate 10 (wafer) are separated into individual devices. Here, a portion of the processed substrate 10 is first removed, thereby making the wafer as thin as about 100 μm. Thereafter, an n-side electrode 15 is formed on the bottom surface of the processed substrate 10. Next, the parallel direction is [11-20]]The direction of the direction (see fig. 11a and 11b) cleaves the wafer to form the resonator end face, thereby dividing the wafer into strips each having a plurality of nitride semiconductor laser devices, as shown in fig. 15a and 15 b. Here, in the present embodiment, the cavity length, i.e., in the cavity direction (i.e., [1-100]]Direction) was 600 μm in length. However, the cavity length does not necessarily have to be equal to the value, but it may be any value preferably lying in the range of 300 μm to 1200 μm. Thereafter, on the resonator end face, SiO is vapor-deposited alternately by electron beam deposition or the like₂And TiO₂Forming a dielectric multilayer reflective film. The dielectric multilayer reflective film does not necessarily have to be made of SiO₂/TiO₂But may be formed of, for example, SiO₂/Al₂O₃And (4) forming.

In this way, a bar having a plurality of nitride semiconductor laser devices thereon as shown in fig. 15a and 15b is fabricated. Fig. 15b is a part of a schematic cross-sectional view of a bar obtained by cleaving a wafer in a direction parallel to the 11-20 direction (as shown in fig. 11a and 11b), the wafer being cleaved to form the resonator end face, and fig. 15a is a top view of fig. 15 b.

In the strip constructed as shown in fig. 15a and 15b, the engraved regions 16 are formed thereon and SiO is formed along both sides of the ridge 19₂On top of the processed substrate 10 of the wall 17, a nitride half is arrangedA conductor growth layer 11, a p-side electrode pad 80 and a p-side electrode 14 (shown in FIGS. 11a and 11b) are formed on the surface of the nitride semiconductor growth layer 11, each p-side electrode pad 80 being made of, for example, SiO₂The insulating film of the film 13. Since wire bonding is performed on the surface of the p-side electrode pad 80, the thickness thereof is generally set to be about 100nm to 1 μm. Here, the nitride semiconductor growth layer 11 has a current confinement layer inside, and in the "buried current confinement laser" in which current confinement is performed, each of the p-side electrode pads 80 is individually constituted by the p-side electrode 14. Further, on the top surface of the p-side electrode pad 80 structured as described above, the rising stripe 18 is formed, and on the bottom surface of the processed substrate 10, the n-side electrode 15 is formed. As shown in fig. 15a, distances from two sides of the P-side electrode pad 80 to edges of the engraved regions 16 adjacent to the two sides of the P-side electrode pad 80, respectively, are set to P and Q, respectively.

As shown in fig. 15a and 15b, the p-side electrode pad 80 formed as described above is not formed on the engraved region 16. This is because, since the surface of the nitride semiconductor growth layer 11 on the engraved region 16 is not flat, for example, SiO is formed on the surface at that position₂The insulating film of (2) will cause cracks, threading dislocations, holes, locally thin portions, etc. These regions exhibit low electrical insulation compared to regions other than above the engraved regions 16, resulting in current leakage.

Further, even if no visible groove or depression is found when the engraved region 16 is completely filled, the nitride semiconductor thin film in the engraved region 16 may generate defects, dislocations, cracks, and the like during the gradual filling of the nitride semiconductor thin film in which the engraved region 16 is disposed. Thus, SiO is formed on the surface of nitride semiconductor growth layer 11 located above engraved region 16₂Etc. will result in low electrical insulation. Therefore, if the p-side electrode pad 80 is formed on the engraved region 16 or the depression, spontaneous emission light may be observed in those regions. This spontaneous emission light is generated when a leakage current flows through the nitride semiconductor laser device. In addition, due toIn parallel to [11-20]]The inflow prevention portions 74 having a width in the direction of about 10 μm to 30 μm are formed along both sides of the ridge 19, and therefore, it is not preferable to form the p-side electrode pad 80 in those regions.

Based on the foregoing, when the p-side electrode pad 80 is formed at a distance of 30 μm or more from the edge of the engraved region 16, spontaneous emission light as described above is not observed from the region other than the region of the laser stripe 12 (see fig. 11 a). Therefore, the distances P and Q from the edge of the engraved region 16 to both edges of the P-side electrode pad 80 are each preferably equal to or greater than 30 μm.

The present embodiment relates to a ridge-stripe type laser formed by, for example, SiO formed on a nitride semiconductor growth layer 11₂The present embodiment can also be applied to any other type of laser, for example, a VSIS (V-channel substrate inner stripe) type laser having a current confinement layer located within nitride semiconductor growth layer 11. In this type of laser, there is no insulating film for current confinement on the surface of the nitride semiconductor growth layer 11, and the p-side electrode pad 80 is constituted by the p-side electrode 14 alone. Also, in this type of laser, when the p-side electrode pad 80 is formed in the engraved region 16, as in the ridge-stripe type laser, a large leakage current will flow, thereby degrading the characteristics of the nitride semiconductor laser device and causing it to fail to lase. This is believed to be due to the reduced crystallinity of the current confinement layer located over the engraved regions 16. Therefore, in the VSIS type or the like laser, distances P and Q from the edge of the engraved region 16 to both edges of the P-side electrode pad 80 are also preferably equal to or greater than 30 μm.

The present embodiment relates to a structure in which an n-type GaN substrate is used as the processed substrate 10, and the electrode pad formed on the surface of the nitride semiconductor growth layer 11 is a p-side electrode pad, but the present embodiment can be applied to any other structure; for example, the present embodiment can be applied to a nitride semiconductor laser device having the following configuration: the processed substrate 10 is formed of a p-type semiconductor material, the surface of the nitride semiconductor growth layer 11 is formed of an n-type nitride semiconductor thin film, and the electrode pad formed on the surface thereof is an n-type electrode pad.

In the wire bonding, the diameter of the spherical portion at the tip of the wire is generally about 80 μm although it depends on the structure of the nitride semiconductor laser device, and therefore, the width of the p-side electrode pad 80 must be 80 μm or more. Therefore, the pitch T between two adjacent engraved regions 16 must satisfy the formula T ≧ the width of the P-side electrode pad 80 (80 μm or more) +60 μm (the minimum value of the sum of the distance P and the distance Q between both sides of the P-side electrode pad 80 and the sides of the engraved regions 16). If the pitch T between adjacent engraved regions 16 is less than 140 μm, it is difficult to manufacture a nitride semiconductor laser device. Therefore, the pitch T between adjacent engraved regions 16 is preferably 140 μm or more. When T is greater than 4mm, cracks may be generated in the arranged nitride semiconductor thin film. Therefore, the pitch T between adjacent engraved regions 16 is preferably 140 μm or more, but 4mm or less.

After that, as in the first embodiment, the above-described bar shown in fig. 15a and 15b is subjected to chip separation to fabricate a discrete nitride semiconductor laser device. Now, how the chip separation is performed will be described with reference to the drawings.

In the present embodiment, first, the dicing process is performed at the chip separation position 81 or the chip separation position 82 as shown in fig. 15 b. The die-separating position 82 is located on the top surface of the nitride semiconductor growth layer 11 disposed in the engraved region 16 formed on the processed substrate 10, and the die-separating position 81 is located on the bottom surface of the portion of the processed substrate 10 located just below the engraved region 16. The score line is preferably located in the center of the score region 16. However, in the present embodiment, as described above, the engraved regions 16 are not completely filled with the nitride semiconductor growth layer 11, leaving trenches that serve as guides for chip separation. Therefore, even if the scribe line is deviated from the center of the engraved region 16, there is no risk of peeling or separation in an unintended direction as long as it extends within the engraved region 16.

In addition, when the scribe line extends outside the engraved region 16, the crack may deviate from the scribe line during the chip separation process, thereby extending in an unintended direction. Even if the crack extends in an unintended direction in this manner, once the crack reaches the adjacent scored region 16, it will extend along the groove inside the scored region 16. Thereby protecting the adjacent nitride semiconductor laser devices from damage.

In the present embodiment, as shown in fig. 15a and 15b, a nitride semiconductor laser device is fabricated on each ridge 19, i.e., on the non-grooved region located between the adjacent grooved regions 16. Alternatively, it is also possible to fabricate a plurality of nitride semiconductor laser devices thereat. In the present embodiment, each engraved area 16 is constituted by a recessed portion. Alternatively, it is also possible to form each engraved region to have a plurality of recessed portions and narrow flat portions sandwiched between the recessed portions.

With the above method according to the present embodiment, with SiO formed thereon₂The processed substrate 10 of the wall 17 makes a plurality of nitride semiconductor laser devices, the SiO₂The thickness T of the wall 17 is 500nm, in parallel to [11-20]]The width D in the direction of the direction was 3 μm. In the fabricated nitride semiconductor laser device, 100 were randomly extracted and the FWHM of the FFP in the vertical and horizontal directions thereof was measured. Here, it is considered that those nitride semiconductor laser devices exhibiting an FFP whose FWHM is within a range of ± 1 ° of their design value are acceptable. As a result, the number of nitride semiconductor laser devices exhibiting an FFP satisfying the requirement at the FWHM was 92. In contrast, in the nitride semiconductor laser devices fabricated by the conventional technique described earlier, only 30 were found to be acceptable. In contrast, the method of the present embodiment clearly provides a greatly improved yield.

The reason is that the inflow prevention portions 74 formed along both sides of the ridge 19 in the region where the nitride semiconductor laser device is fabricated help to suppress the migration of atoms and molecules of the raw material of the nitride semiconductor thin film into the engraved region 16. That is, the surface flatness is improved in the region where the nitride semiconductor laser device is fabricated, and therefore, the thickness of each nitride semiconductor thin film forming nitride semiconductor growth layer 11 is made uniform.

Further, with the processed substrate 10 on which the engraved regions 16 are formed, the strain existing in the nitride semiconductor growth layer 11 can be made uneven over the range of the wafer surface, thereby causing it to act in different directions. This allows the strain existing in the nitride semiconductor growth layer 11 to be relieved. Furthermore, making the engraved regions not completely filled with the nitride semiconductor growth layer 11 will promote the relief of strain. Therefore, no crack is generated.

Third embodiment

Next, a third embodiment example of the present invention will be explained with reference to the related drawings. Fig. 16 is a partial schematic cross-sectional view of a wafer having a nitride semiconductor thin film grown on the processed substrate 10 in the present embodiment. In the present embodiment, unlike the second embodiment, no SiO is formed along the edge of the ridge 19 (i.e., non-grooved region) on the processed substrate 10₂A wall.

Fig. 16 is a schematic cross-sectional view of a wafer having a nitride semiconductor thin film grown on such a processed substrate 10, on which a notch region 16 is formed on the processed substrate 10. As shown in fig. 16, a nitride semiconductor thin film is grown as a top surface growth portion 95 located in the central portion of the top surface portion 91 of the ridge 19, two inflow prevention portions 94 located at the edge portions of the top surface portion 91 of the ridge 19 near the engraved region 16, and an engraved region growth portion 97 located on the side surface portion 92 and the bottom surface portion 93 of the engraved region 16. The inflow prevention portion 94 is connected to the engraved region growth portion 97 through the growth portion 96.

As shown in FIG. 16, in the present embodiment, although SiO is not formed₂The walls, but in the raised profile form inflow prevention portions 94, in these inflow prevention portions 94, the grown nitrideThe thickness of the semiconductor thin film is larger than that of the top growth portion 95 to form a height difference. In the following description, this height difference is denoted by H. The reason why the difference in thickness between nitride semiconductor growth layer 11 in inflow prevention portion 94 and top surface growth portion 95 occurs is that: the growth rate of the nitride semiconductor thin film in the inflow prevention portions 94 (i.e., the both edge portions of the top surface portion 91 of the ridge 19 near the engraved region 16) is higher than the growth rate of the nitride semiconductor thin film in the top surface growth portions 95 (i.e., the regions on the top surface portion 91 of the ridge 19 not including the both edge portions thereof). The great difference in growth rate between the nitride semiconductor thin films in the inflow prevention portion 94 and the top surface growth portion 95 results from the difference in the probability of re-evaporation, that is, the probability that atoms and molecules of the raw material of the nitride semiconductor thin film once adsorbed on the growth surface of the nitride semiconductor thin film are re-evaporated from the growth surface without forming the nitride semiconductor thin film.

Specifically, the material atoms and molecules that have adhered to the surface of the nitride semiconductor thin film grown on the top surface portions 91 of the ridges 19 between the engraved regions 16 first migrate or otherwise move across the growth surface to an energy-stable region where the material atoms and molecules combine with the atoms and molecules of the surface to form the nitride semiconductor thin film. If these atoms and molecules cannot move to the energy stable region for a predetermined length of time, they will evaporate again from the growth surface. Further, it has been found that when the engraved regions 16 are formed on the surface of the substrate, as on the processed substrate 10, in the top surface portions 91 of the ridges 19 located between the engraved regions 16, the most energy-stable regions are the two edge portions thereof near the engraved regions 16. In these edge portions near the engraved region 16, the possibility of re-evaporation is low. Therefore, in both edge portions of the top surface portion 91 of the ridge 19 near the engraved region 16, the growth rate of the nitride semiconductor thin film is higher than that of the other portions of the top surface portion 91 of the ridge 19, and therefore, the inflow prevention portion 94 is formed where the thickness of the nitride semiconductor thin film grown is larger than that in the top surface growth portion 95.

These inflow prevention portions 94 are formed by growing a GaN or AlGaN layer over the processed substrate 10. The comparison between GaN and AlGaN shows that the raw material atoms and molecules of GaN have a more intense migration tendency when the GaN layer is disposed. Therefore, GaN raw material atoms and molecules that have adhered to the top surface portions 91 of the ridges 19 generally migrate and thus move into the engraved regions 16, which allows a thick GaN layer as the engraved region growth portions 97 to be grown on the surfaces of the side surface portions 92 and the bottom surface portions 93, and allows the inflow prevention portions 94 whose height difference H from the surface of the top surface growth portion 95 is as small as about 10nm or so to be formed. In contrast, when an AlGaN layer is arranged, AlGaN raw material atoms and molecules (particularly, Al) have only a weak migration tendency. Therefore, AlGaN raw material atoms and molecules that have adhered to the top surface portions 91 of the ridges 19 do not move into the engraved regions 16, but remain on the top surface portions 91 of the ridges 19. AlGaN raw material atoms and molecules that have remained on the top surface portions 91 of the ridges 19 migrate across the top surface portions 91 of the ridges 19. Here, since both edge portions of the top surface portion 91 of the ridge 19 are the energy stable regions as described above, atoms and molecules of the AlGaN raw material are bound in these regions and are not evaporated again, but a film is formed instead, and as a result, the thickness of the grown AlGaN layer is larger than the top surface growth portion 95, and the inflow prevention portion 94 is formed. When the Al content in AlGaN is 2% or more, the thickness of the grown inflow prevention portion 94 composed of an AlGaN layer is large. In this way, since the inflow prevention portions 94 are formed, AlGaN raw material atoms and molecules that have adhered to the surface of the top surface growth portion 95 migrate only on the surface of the top surface growth portion 95. This makes it possible to form the top growth portion 95 with good surface flatness. The width Z (see FIG. 16) of the inflow prevention section 94 thus formed in the direction parallel to the [11-20] direction is about 10 μm to 30 μm.

In this way, over the processed substrate 10 on which the engraved regions 16 and the ridges 19 are formed, the nitride semiconductor growth layer 11 composed of a plurality of nitride semiconductor thin films is arranged, thereby producing a plurality of nitride semiconductor laser devices, the nitride semiconductor growth layer 11 having the height difference H formed between the surface of the top surface growth portion 95 and the top end of the inflow prevention portion 94 as described above. In the fabricated nitride semiconductor laser device, 100 were randomly extracted and the FWHM of the FFP in the vertical and horizontal directions thereof was measured. Here, it is considered that those nitride semiconductor laser devices exhibiting an FFP whose FWHM is within a range of ± 1 ° of their design value are acceptable. Fig. 17 is a graph of the relationship between the height difference H and the number of nitride semiconductor laser devices evaluated as acceptable. As shown in fig. 17, when the height difference H is 150nm or more, the number of acceptable nitride semiconductor laser devices is 85 or more, thereby providing a high yield. On the other hand, when the height difference H is less than 150nm, the number of acceptable nitride semiconductor laser devices is 40 or less, and the yield is drastically reduced. The reason for this is that: in the nitride semiconductor laser device in which the height difference H is less than 150nm, the thickness of each nitride semiconductor thin film disposed above the top surface portion 91 of the ridge 19 varies not only over the wafer surface but also even in a single nitride semiconductor laser device. Therefore, in order to manufacture a nitride semiconductor laser device with high yield, it is necessary to make the height difference H between the surface of the top surface growth portion 95 and the top end of the inflow prevention portion 94 150nm or more. That is, with the height difference H of 150nm or more, when forming the nitride semiconductor growth layer 11 composed of a plurality of nitride semiconductor thin films over the processed substrate 10, it is possible to obtain good surface flatness in the surfaces of the respective nitride semiconductor thin films arranged on the top surface portions 91 of the ridges 19, thereby reducing thickness variations of the respective nitride semiconductor thin films.

Further, when the inflow prevention portions 94 are formed using AlGaN as described above, even if GaN having a strong migration tendency is grown thereafter, the inflow prevention portions 94 will suppress GaN raw material atoms and molecules from migrating and thus moving into the engraved regions 16. That is, since the AlGaN layer having a weak migration tendency is first arranged on the processed substrate 10, there is a large height difference H between the inflow prevention portion 94 and the surface of the top surface growth portion 95. Even if a GaN layer having a strong migration tendency is arranged thereafter, GaN will be confined from growing into the engraved region growth portions 97 located on the side face portions 92 and the bottom face portions 93 of the engraved region 16.

Even in the case where the GaN layer is first arranged on the processed substrate 10, if the thickness of the GaN layer is 0.5 μm or less, by subsequently stacking nitride semiconductor thin films in order, for example, from n-type Al as shown in fig. 19_0.062Ga_0.938The N first clad layer 101 to the p-type GaN contact layer 109 also makes it possible to form the inflow prevention portion 94 having a height difference H of 150nm or more. On the other hand, in the case where the GaN layer thickness is greater than 0.5 μm, GaN raw material atoms and molecules will migrate and thereby flow into the engraved regions 16, resulting in significant growth of the engraved region growth portions 97 on the side surface portions 92 and the bottom surface portions 93. Therefore, as shown in fig. 21b, the engraved region 16 is almost completely filled with GaN. This further promotes migration into the engraved region 16, so that the thickness of the GaN layer becomes uneven, reducing the surface flatness of the top growth portion 95. Based on these facts, in arranging nitride semiconductor growth layer 1l having a structure as shown in fig. l9, by making the thickness of n-type GaN layer l00 in contact with the surface of processed substrate 10 0.5 μm or less, it is possible to suppress the inflow of atoms and molecules of the raw materials forming n-type GaN layer 100. Can be prepared by reacting Al_0.062Ga_0.938The N first clad layer 101 starts to grow, and the nitride semiconductor growth layer 11 is formed in such a manner that the N-type GaN layer 100 is not disposed on the processed substrate 10. In this way, the nitride semiconductor growth layer 11 can also be formed with good surface flatness.

As described above, the inflow prevention portions 94 are formed by growing AlGaN on the processed substrate 10 on which the engraved regions 16 are formed. It has been found that even if GaN is grown instead, by controlling the substrate holder (susceptor) temperature and the molar ratio V/III of the raw material (NH provided as a raw material of a group V element N per unit time)₃Is supplied as a raw material of Ga of group III element per unit timeOf TMGa), it is also possible to suppress the migration of GaN raw material atoms and molecules, and thereby form the inflow prevention portions 94 having a height difference H of 150nm or more from the top surface growth portions 95. Given the following explanation of the growth conditions for growing GaN on the processed substrate 10 on which the engraved regions 16 are formed, the height difference H between the inflow prevention portions 94 and the surface of the top surface growth portion 95 formed is 150nm or more. The substrate holder temperature is approximately equal to the surface temperature of the processed substrate.

In general, when the n-type GaN layer 100 is grown on the processed substrate 10 (as shown in fig. 19), the substrate holder temperature on which the processed substrate 10 (wafer) is placed is 1075 ℃. Under this condition, atoms and molecules of the raw material of the n-type GaN migrate to flow into the engraved region 16 on a large scale, and therefore, it is impossible to form the inflow prevention portion 94 having a sufficiently large height difference H. To solve this problem, the temperature of the substrate holder was set to 1025 ℃, i.e., 50 ℃ lower than the normal substrate holder temperature, and, when n-type GaN was grown at this temperature, the height difference H between the inflow prevention portion 94 and the surface of the top surface growth portion 95 was formed to be 300nm, i.e., more than 150 nm. We believe that the reason for this is: the lower substrate holder temperature results in a lower surface temperature of the processed substrate 10, thereby suppressing migration of N-type GaN raw material atoms and molecules (Ga atoms, N atoms, etc.).

On the other hand, in terms of the molar ratio of the raw materials V/III, although the molar ratio of the raw materials V/III for growing the n-type GaN layer 100 is generally 1033, the molar ratio of the raw materials V/III for growing the n-type GaN layer 100 here is 2066, i.e., twice the normal molar ratio. Although the height difference H between the top surface growth portion 95 and the inflow prevention portion 94 is about 10nm in the usual molar ratio of the raw materials, the height difference H is about 320nm at a raw material molar ratio V/III of 2066, i.e., higher than 2000, thereby forming the inflow prevention portion 94 in which the height difference H is sufficiently large. This is because, when GaN raw material atoms and molecules attach to the growth film surface and migrate on the growth film surface under the action of thermal energy, NH is supplied in an extremely high amount if the raw material molar ratio V/III is high₃To make NH₃The N atoms in (a) and the Ga atoms in TMGa react rapidly and are absorbed into the film in the form of GaN. That is, when the raw material molar ratio V/III is high, migration of GaN raw material atoms and molecules (for example, Ga atoms and N atoms) on the surface of the grown film is restrained, and as a result, the inflow prevention portion 94 having a large height difference H is formed when the AlGaN layer is disposed. In contrast, when the molar ratio V/III of the raw material is low, NH is supplied in a small amount₃Therefore, Ga atoms that have adhered to the surface of the grown film cannot react rapidly with N atoms to form GaN. This lengthens the movement distance of GaN raw material atoms and molecules, such as Ga atoms, by migration, thereby facilitating the flow thereof into the engraved region 16. That is, setting the raw material molar ratio V/III to be equal to or higher than 2000 makes it possible to restrict migration of GaN raw material atoms and molecules on the surface of the grown film, and therefore, it is possible to form the inflow prevention portion 94 having a satisfactorily large height difference H, specifically, a height difference H of 150nm or more from the surface of the top surface growth portion 95.

As described above, in disposing the nitride semiconductor growth layer 11 composed of a plurality of nitride semiconductor thin films on the processed substrate 10, in order to dispose the n-type GaN layer 100 such that the height difference H between the inflow prevention portion 94 and the top surface growth portion 95 formed is 150nm or more, first, only the n-type GaN layer 100 is disposed under the condition that the substrate holder temperature is 1025 ℃, and then the substrate holder temperature is raised to 1075 ℃, and the slave Al layer except for the multiple quantum well active layer 105 is disposed_0.062Ga_0.938N first clad layer 101 to p-type GaN contact layer 109. Incidentally, the multiple quantum well active layer 105 is arranged at a temperature of 700 ℃ to 800 ℃, because at 1075 ℃, the vapor pressure of In is too high, so that In cannot be adsorbed into the film.

Alternatively, only the n-type GaN layer 100 is disposed under the condition that the molar ratio V/III of the raw materials is 2000 or more, and thereafter, at least from Al is disposed under the condition that the molar ratio V/III of the raw materials is 2000 or less_0.062Ga_0.938N first clad layer 101 to N type Al_0.062Ga_0.938N layers of third cladding 103.For the subsequently disposed layers from the n-type GaN waveguide layer 104 to the p-type GaN contact layer 109, the raw material molar ratio V/III may be 2000 or more, and may also be 2000 or less.

With this method, by disposing nitride semiconductor growth layer 11 over processed substrate 10 having n-type GaN layer 100 formed under specific conditions, it is possible to form inflow prevention portions 94 having a height difference H of 150nm or more from top surface growth portions 95. Finally, this makes it possible to form the nitride semiconductor growth layer 11 composed of nitride semiconductor thin films having good surface flatness stacked in order. In forming the n-type GaN layer 100, two conditions as described above may be combined; specifically, it can be formed at a substrate holder temperature of 1025 ℃ and at a raw material molar ratio V/III of 2000 or more.

Further, when the inflow prevention portions 94 are formed during the formation of the nitride semiconductor growth layer 11, making the width Z of the inflow prevention portions 94 in the direction parallel to the [11-20] direction smaller helps to widen the flat portions of the ridges 19, thereby making these portions more suitable for the fabrication of nitride semiconductor laser devices thereon. Further, the stronger the migration tendency of GaN raw material atoms and molecules, the narrower the width Z may be formed. However, too strong a migration tendency will result in implantation into the engraved regions 16, which is undesirable. Therefore, the width Z of the inflow prevention section 94 is preferably controlled to be between 10 μm and 30 μm.

This application claims priority to the patent application nos. 2004-.

Claims

1. A method of fabricating a semiconductor device, the method comprising:

a first step of forming a grooved region formed as at least one recessed portion and a ridge portion formed as a non-grooved region on a substrate having a nitride semiconductor layer in at least a part of the surface thereof, thereby forming a processed substrate; and

a second step of forming a nitride semiconductor layer portion composed of at least one nitride semiconductor thin film on both the surface of the engraved region and the surface of the ridge portion formed on the processed substrate,

wherein in the second step, a thickness of the nitride semiconductor layer portion arranged on both edge portions of the ridge portion near the engraved region as measured from the surface of the ridge portion to a surface of the nitride semiconductor layer portion is made larger than a thickness of the nitride semiconductor layer portion arranged outside both edge portions of the ridge portion as measured from the surface of the ridge portion to the surface of the nitride semiconductor layer portion, thereby forming an inflow prevention portion raised from a surface of a flat portion of the nitride semiconductor layer portion arranged on a surface of a region other than both edge portions of the ridge portion.

2. The method of claim 1, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein the recess portion formed as the engraved region is not completely filled when the nitride semiconductor portion is formed in the second step.

3. The method of claim 1, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein, in the second step, a difference in height between the surface of the flat portion of the nitride semiconductor layer arranged on the surface of the ridge portion and the inflow prevention portion rising therefrom is 150nm or more.

4. The method of claim 1, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein, in the second step, the nitride semiconductor thin film in direct contact with the processed substrate surface is CaN having a thickness of 0.5 μm or less.

5. The method of claim 1, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein, in the second step, the nitride semiconductor thin film that is in direct contact with the processed substrate surface is AlGaN.

6. The method of claim 1, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein in the second step, the nitride semiconductor thin film in direct contact with the processed substrate surface is GaN, and,

the surface of the processed substrate is at a temperature of 1025 ℃ when the GaN is disposed on the surface of the processed substrate.

7. The method of claim 1, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein, in the second step,

the nitride semiconductor thin film in direct contact with the processed substrate surface is GaN, and,

in disposing the GaN, a ratio between a molar flow rate at which a raw material containing nitrogen atoms as a group V element is supplied per unit time and a molar flow rate at which a raw material containing gallium as a group III element is supplied per unit time is 2000 or more.

8. The method of claim 1, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein, in the second step, the nitride semiconductor thin film forming the nitride semiconductor layer portion includes an AlGaN layer having an Al content of 0.02.

9. The method of claim 1, the method further comprising:

a fourth step of forming an electrode pad on the nitride semiconductor layer portion arranged on the surface of the processed substrate, formed in the second step, thereby forming a plurality of semiconductor devices on the substrate, on which wire bonding is to be performed to realize external connection.

Wherein, in the fourth step, the electrode pad is not formed on the engraved region.

10. The method of claim 9, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein, in the fourth step, the electrode pad is formed at a distance of 30 μm or more from the edge of the notch area.

11. The method of claim 1, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein a semiconductor device is formed in the ridge portion sandwiched between two adjacent engraved regions.

12. The method of claim 1, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein a plurality of semiconductor devices are formed in the ridge portion sandwiched between two adjacent engraved regions.

13. The method of claim 1, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein dicing is performed on a top surface of a portion of the nitride semiconductor layer arranged on the engraved region or on a bottom surface of a portion of the processed substrate located just below the engraved region, thereby achieving chip separation.

14. The method of claim 1, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein, when the engraved region as the depressed portion is formed in the first step, the depth of the depressed portion is specified to be 1 μm or more but 20 μm or less.

15. The method of claim 1, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein, when the engraved region is formed as the depressed portion in the first step, the depressed portion is specified to have an opening width of 1 μm or more.

16. The method of claim 1, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein, in forming the engraved regions as the recessed portions in the first step, the ridge portion specified to be sandwiched between two adjacent engraved regions has a width of 140 μm or more but 4mm or less.

17. A semiconductor device, comprising:

a processed substrate having formed on a nitride semiconductor substrate at least a part of the surface of which is a nitride semiconductor, a grooved region as at least one recessed portion and a ridge portion as a non-grooved region; and

a nitride semiconductor layer portion composed of at least one nitride semiconductor thin film formed on the surface of the engraved regions and the ridge portions formed on the processed substrate,

wherein,

a thickness of the nitride semiconductor layer portion arranged in both edge portions of the ridge portion near the engraved region as measured from the surface of the ridge portion to a surface of the nitride semiconductor layer portion is larger than a thickness of a nitride semiconductor layer portion arranged outside both edge portions of the ridge portion as measured from the surface of the ridge portion to the surface of the nitride semiconductor layer portion, and

in both edge portions of the ridge portion near the engraved region, inflow prevention portions are provided which rise from flat portions of the nitride semiconductor layer portion arranged on the surface of the region other than both edge portions of the ridge portion.

18. A semiconductor device, comprising:

a nitride semiconductor layer portion composed of at least one nitride semiconductor thin film formed on the surface of the engraved regions and the ridge portions on the processed substrate,

an optical waveguide formed in the nitride semiconductor thin film,

wherein,

a thickness of a nitride semiconductor layer portion arranged in both edge portions of the ridge portion near the engraved region, as measured from the surface of the ridge portion to a surface of the nitride semiconductor layer portion, is larger than a thickness of a nitride semiconductor layer portion arranged outside both edge portions of the ridge portion, as measured from the surface of the ridge portion to the surface of the nitride semiconductor layer portion,

in both edge portions of the ridge portion near the engraved region, inflow prevention portions are provided which rise from flat portions of the nitride semiconductor layer portion arranged on the surface of the region other than both edge portions of the ridge portion, and

in the processed substrate, at least part of the concave portion is formed on at least one of both sides of the optical waveguide.

19. The nitride semiconductor device according to claim 18,

wherein, in the processed substrate, the whole of the concave portion is formed on at least one of both sides of the optical waveguide.

20. A semiconductor wafer, comprising:

a nitride semiconductor layer portion composed of at least one nitride semiconductor thin film disposed on the surface of the engraved regions and the ridge portions on the processed substrate,

wherein,

a thickness of a nitride semiconductor layer portion arranged in both edge portions of the ridge portion near the engraved region as measured from the surface of the ridge portion to a surface of the nitride semiconductor layer portion is larger than a thickness of a nitride semiconductor layer portion arranged outside both edge portions of the ridge portion as measured from the surface of the ridge portion to the surface of the nitride semiconductor layer portion, and

21. A method of fabricating a semiconductor device, the method comprising:

a first step of forming a grooved region formed as at least one recessed portion and a ridge portion formed as a non-grooved region on a substrate having a nitride semiconductor layer in at least a part of the surface thereof, thereby forming a processed substrate,

a second step of forming inflow prevention walls as elevated portions along both edges of the ridge portion formed on the processed substrate; and

a third step of forming a nitride semiconductor layer portion containing at least one nitride semiconductor thin film on both of the groove-engraved portion formed on the processed substrate and the surface of the ridge portion formed on the processed substrate with the inflow prevention wall formed in the second step, so as to form the nitride semiconductor layer portion on the inflow prevention wall formed along both sides of the ridge portion, thereby forming a raised inflow prevention portion having a level difference from the surface of the flat portion of the nitride semiconductor layer portion disposed on the surface of the ridge portion.

22. The method of claim 21, wherein the step of,

wherein the recess portion formed as the engraved region is not completely filled in forming the nitride semiconductor layer portion in the third step.

23. The method of claim 21, wherein the step of,

wherein, in the second step, the inflow prevention wall is formed of one of SiO2, Al2O3, TiO2, ZrO, and W.

24. The method of claim 21, wherein the step of,

wherein, when the inflow prevention wall is formed in the second step, a thickness thereof is specified to be 50nm or more but 3 μm or less in a direction perpendicular to the inflow prevention wall and thus to the surface of the ridge portion.

25. The method of claim 21, wherein the step of,

wherein, when the inflow prevention wall is formed in the second step, a width thereof is specified to be 1 μm or more but 25 μm or less in a direction perpendicular to a longitudinal direction of the inflow prevention wall.

26. The method of claim 21, the method further comprising:

a fourth step of forming an electrode pad on the nitride semiconductor layer portion arranged on the surface of the processed substrate having the inflow prevention wall formed in the third step, thereby forming a plurality of semiconductor devices on the substrate, on which electrode pad wire bonding is to be performed to realize external connection,

27. The method of claim 21, wherein the step of,

wherein, in the fourth step, the electrode pad is formed at a distance of 30 μm or more from an edge of the notch area.

28. The method of claim 21, wherein the step of,

29. The method of claim 21, wherein the step of,

30. The method of claim 21, wherein the step of,

wherein dicing is performed on a top surface of the nitride semiconductor layer portion arranged on the engraved region or on a bottom surface of a portion of the processed substrate located just below the engraved region, thereby achieving chip separation.

31. The method of claim 21, wherein the step of,

32. The method of claim 21, wherein the step of,

33. The method of claim 21, wherein the step of,

34. A nitride semiconductor device comprising:

a processed substrate having, on a nitride semiconductor substrate having a nitride semiconductor in at least a part of a surface thereof, a grooved region formed as at least one recessed portion and a ridge portion formed as a non-grooved region; and

a nitride semiconductor layer portion composed of at least one type of nitride semiconductor thin film formed on the surface of the engraved regions and the ridge portions on the processed substrate,

wherein,

inflow prevention walls are provided as elevated portions between the processed substrate and the nitride semiconductor thin film along both edges of the ridge near the engraved portions, and

an inflow prevention portion is provided which is raised so as to have a height difference between the nitride semiconductor layer arranged on the inflow prevention wall and a surface of a flat portion of the nitride semiconductor layer portion arranged on a surface of the ridge portion.

35. A nitride semiconductor device comprising:

an optical waveguide formed in the nitride semiconductor thin film,

wherein,

the inflow prevention wall is provided as a raised portion between the processed substrate and the nitride semiconductor thin film along both edges of the ridge near the engraved portion,

an inflow prevention portion is provided which is raised so as to have a difference in height between the nitride semiconductor layer arranged on the inflow prevention wall and a surface of a flat portion of the nitride semiconductor layer portion arranged on a surface of the ridge portion, an

In the processed substrate, at least a part of the concave portion is formed on at least one of both sides of the optical waveguide.

36. The nitride semiconductor device according to claim 35,

37. A nitride semiconductor wafer comprising:

wherein,