Process for the production of gallium and nitrogen-bearing laser components with improved use of substrate material

Abstract

A method of manufacturing a gallium and nitrogen-containing laser diode device, the method comprising: Providing a gallium and nitrogen-containing substrate (100) having a surface region; Forming epitaxial material occupying the surface region, the epitaxial material comprising a sacrificial region (107) that can be selectively etched with a bandgap-selective photoelectrochemical etch, an n-type cladding region (101), an active region (102) comprising at least one active layer occupying the n-type cladding region (101), and a p-type cladding region (103) occupying the active layer region (102); Structuring the epitaxial material to form a plurality of dice, each of the dice corresponding to at least one laser device, characterized by a first spacing between a pair of dice, the first spacing being less than a nominal width; Transferring each of the plurality of dice to a carrier wafer (106) such that each pair of dice is configured with a second spacing between each pair of dice, the second spacing being greater than the first spacing corresponding to the nominal width, wherein transferring the dice comprises selective bonding to the carrier wafer (106), each die being configured to a bonding pad (108) on the carrier wafer (106), wherein the dice are undercut by a bandgap-selective photoelectrochemical etching of the sacrificial region prior to transfer to the carrier wafer (106), and the undercut bonded dice break in the area of ​​the sacrificial region (107) when the gallium and nitrogen-containing substrate (100) is removed.

Description

background

[0001] In 1960, the laser was first demonstrated by Theodore H. Maiman at Hughes Research Laboratories in Malibu.

[0002] US 2008 / 0 219 309 A1 describes a method for manufacturing a semiconductor laser diode device, comprising the steps of forming a plurality of first semiconductor laser diode sections on a first substrate at a prescribed pitch in a second direction intersecting a first direction in which cavities extend, connecting one or more of the first semiconductor laser diode sections to a second substrate, separating the first semiconductor laser diode sections connected to the second substrate from the first substrate; and dividing the second substrate along the second direction.

[0003] US 2013 / 0 214 284 A1 describes a method for reusing epitaxial gallium nitride (GaN) substrates, using a bandgap selective photoelectrochemical (PEC) etching to remove one or more epitaxial layers from bulk or freestanding GaN substrates without damaging the substrate.

[0004] US 2012 / 0 256 327 A1 describes a method for manufacturing a semiconductor device having a structure in which a semiconductor layer is bonded to a support substrate, comprising: a device region forming step of forming a device region including the semiconductor layer on a growth substrate through a lift-off layer; a columnar member forming step of forming a columnar member on the growth substrate; a bonding step of bonding the top surfaces of the semiconductor layer and the columnar member to a support substrate; a lift-off step of separating the bottom surface of the semiconductor layer from the growth substrate by removing the lift-off layer without separating the columnar member from the growth substrate; and a step of separating the columnar member from the support substrate. Brief description

[0005] The invention provides a method for manufacturing semiconductor laser diodes according to claims 1 to 11. Brief description of the drawings Fig. Figure 1 is a simplified illustration of a prior art laser diode. Fig. Figure 2 is a simplified illustration of a die-expanded laser diode obtainable by the method according to the invention. Fig. Figure 3 is a schematic cross-section of a prior art ridge laser diode. Fig. 4 is a plan view of a selective area bonding process in an example. Fig. Figure 5 is a simplified process flow for epitaxial fabrication in an example. Fig. Figure 6 is a simplified illustration of a side view of selective surface bonding in one example. Fig. Figure 7 is a simplified process flow of epitaxial fabrication with active region protection in an example. Fig. Figure 8 is a simplified process flow of epitaxial growth with active region protection and with ridge formation prior to bonding in an example. Fig. Figure 9 is a simplified illustration of anchored PEC undercutting (top view) in an example. Fig. Figure 10 is a simplified illustration of anchored PEC undercut (side view) in an example. Description in detail

[0006] Referring to Fig. Figure 1 illustrates a side view of a prior art GaN-based laser diode after processing. Laser diodes are fabricated on the original gallium and nitrogen-containing epitaxial substrate 100, typically with epitaxial n-GaN and n-side cladding layers 101, active region 102, p-GaN and p-side cladding 103, insulating layers 104, and contact / pad layers 105. The laser-die pitch is marked. Any epitaxial material not directly beneath the laser ridge is lost in this device construction. In one example, the n-type cladding can be GaN, AlGaN, or InAlGaN.

[0007] Referring now to Fig. 2, this illustration is a side view of the gallium and nitrogen-containing epitaxial wafer 100 before the die expansion process and the support wafer 106 after the die expansion process. This figure demonstrates an approximately five-fold expansion and thus a five-fold improvement in the number of laser diodes that can be fabricated from a single gallium and nitrogen-containing substrate and covering epitaxial material. Typical epitaxial and processing layers are included for example purposes and are n-GaN and n-side cladding layers 101, active region 102, p-GaN and p-side cladding 103, insulating layers 104, and contact / pad layers 105. Additionally, a sacrificial region 107 and bonding material 108 are used during the die expansion process.

[0008] Fig. 3 is a schematic cross-section of a ridge laser diode in one example and shows a simplified schematic cross-sectional diagram illustrating a prior art laser diode structure. This diagram is only an example and should not unduly limit the scope of the claims herein. As shown, the laser device includes gallium nitride substrate 203 having an n-type base metal backside contact 201. In one embodiment, the metal backside contact is made of a suitable material such as those listed below and others. In one embodiment, the device also has an n-type gallium nitride covering layer 205, which could alternatively be AlGaN, an active region 207, and a p-type gallium nitride covering layer structured as a laser stripe region 211, which could alternatively be AlGaN.Additionally, the device also includes an n-side separate confinement heterostructure (SCH) 206, a p-side conductive layer or SCH 208, and p-AlGaN EBL 209, among other features. In one embodiment, the device also includes a p++-type gallium nitride material 213 to form a contact region.

[0009] Fig. Figure 4 is a simplified top view of a selective area bonding process and illustrates a die expansion process via selective area bonding. The original gallium and nitrogen-containing epitaxial wafer 201 has an individual die of epitaxial material and release layers defined by processing. Dice of individual epitaxial material are marked 202 and spaced apart by a pitch of 1. A circular carrier wafer 200 with patterned bonding pads 203 has been fabricated. These bonding pads are spaced apart by a pitch of 2, which is an even multiple of pitch 1, so that selected rows of epitaxial die can be bonded during each iteration of the selective area bonding process. The iteration of the selective area bonding process continues until all epitaxial dice have been transferred to the carrier wafer 204.The gallium and nitrogen-containing epitaxial substrate 201 can now be prepared for reuse if necessary.

[0010] In one example, Fig. 5 shows a simplified schematic of the epitaxial growth process flow, including an illustration of a side view of an example of the epitaxial growth process flow for the die expansion process. The gallium and nitrogen-containing epitaxial substrate 100 and the covering epitaxial material are defined into individual dice, bonding material 108 is deposited, and sacrificial regions 107 are undercut. Typical epitaxial layers are included for example purposes and are n-GaN and n-side cladding layers, such as GaN or AlGaN 101, active region 102, and p-GaN and p-side cladding, such as GaN or AlGaN 103.

[0011] In one example, Fig. 6 is a simplified side view illustration of an example selective area bonding process. Fabricated gallium and nitrogen-containing epitaxial wafer 100 and fabricated carrier wafer 106 are the starting components of this process. The first iteration of selective area bonding transfers a fraction of the epitaxial dice, with additional iteration steps repeated as many times as necessary to transfer all epitaxial dice. Once the die expansion process is complete, laser processing can continue on the carrier wafer according to the prior art. Typical epitaxial and processing layers are included for example purposes and are n-GaN and n-side cladding layers such as GaN or AlGaN 101, active region 102, p-GaN and p-side cladding such as GaN or AlGaN 103, insulating layers 104, and contact / pad layers 105.Additionally, a sacrificial region 107 and bonding material 108 are used during the die expansion process.

[0012] In one example, Fig. Figure 7 is a simplified diagram of an epitaxial growth process with active region protection. Shown is a side-view illustration of an alternative epitaxial wafer growth process flow during which sidewall passivation is used to protect the active region during each PEC undercut step. This process flow allows for a wide range of sacrificial region materials and compositions. Typical substrate, epitaxial, and processing layers are included for example purposes and are the gallium and nitrogen-containing substrate 100, n-GaN and n-side cladding layers such as GaN or AlGaN 101, active region 102, p-GaN and p-side cladding layers such as GaN or AlGaN 103, insulating layers 104, and contact / pad layers 105. Additionally, a sacrificial region 107 and bonding material 108 are used during the die expansion process.

[0013] In one example, Fig. Figure 8 is a simplified diagram of the epitaxial growth process flow with active region protection and ridge formation prior to bonding. Shown is a side view illustration of an alternative epitaxial wafer growth process flow, during which sidewall passivation is used to protect the active region during each PEC undercut step, and laser ridges are defined on the denser epitaxial wafer prior to transfer. This process flow potentially allows for cost savings by performing additional processing steps on the denser epitaxial wafer. Typical substrate, epitaxial, and processing layers are included for example purposes and are the gallium and nitrogen-containing substrate 100, n-GaN and n-side cladding layers 101, active region 102, p-GaN and p-side cladding 103, insulating layers 104, and contact / pad layers 105.Additionally, a sacrificial region 107 and bonding material 108 are used during the die expansion process.

[0014] Fig. Figure 9 is a simplified example of anchored PEC undercut (top view). Shown is a top view of an alternative stripping process during selective area bonding. In this embodiment, a top-down etch is used to etch away area 300, followed by the deposition of bonding metal 303. A PEC etch is then used to undercut region 301. Sacrificial region 302 remains intact and serves as mechanical support during the selective area bonding process.

[0015] Fig. Figure 10 is a simplified view of an anchored PEC undercut (side view) in one example. A side view illustration of the anchored PEC undercut is shown. Posts of a sacrificial region are included at each end of the epitaxial die for mechanical support until the bonding process is complete. After bonding, the epitaxial material is cleaved at the unsupported thin film region between the bond pads and intact sacrificial regions, enabling the selective bonding process. Typical epitaxial and processing layers are included for example purposes and are n-GaN and n-side cladding layers such as GaN or AlGaN 101, active region 102, p-GaN and p-side cladding such as GaN or AlGaN 103, insulating layers 104, and contact / pad layers 105. In addition, a sacrificial region 107 and bonding material 108 are used during the die expansion process.Epitaxial material is transferred from the gallium and nitrogen-containing epitaxial wafer 100 to the carrier wafer 106. Further details of the present process and structures can be found in more detail below.

[0016] As further background for the reader, gallium nitride and related crystals are difficult to produce in bulk form. Growth technologies capable of producing large-area single-crystal bodies of GaN are still in their early stages, and costs for all orientations are significantly more expensive than similar wafer sizes of other semiconductor substrates, such as Si, GaAs, and InP. While freestanding large-area GaN substrates (e.g., with diameters of two inches or larger) are commercially available, the availability of large-area non-polar and semi-polar GaN substrates is very limited. Typically, these orientations are produced by growing a c-plane oriented single-crystal body, which is then sliced ​​into rectangular wafers at a somewhat steep angle relative to the c-plane.The width of these wafers is limited by the thickness of the c-plane oriented single crystal body, which in turn is limited by the method of single crystal body fabrication (e.g., typically hydride vapor phase epitaxy (HVPE) on a foreign substrate). Such small wafer sizes are limiting in several ways. The first is that epitaxial growth must be performed on such a small wafer, which increases the area fraction of the wafer that is unusable due to growth non-uniformity near the wafer edge. The second is that after epitaxial growth of optoelectronic device layers on a substrate, the same number of processing steps are required on the small wafers to produce the finished device as if it were performed on a large area wafer.Both of these effects drive up the cost of fabricating devices on such small wafers, as both the cost per fabricated device and the fraction of unusable wafer area increase with decreasing wafer size. The relative immaturity of bulk GaN growth techniques further limits the total number of substrates that can be fabricated, potentially limiting the feasibility of scaling up a device based on a non-polar or semi-polar GaN substrate.

[0017] Given the high cost of all GaN substrate orientations, the difficulty of scaling up wafer size, the inherent inefficiencies of processing small wafers, and potential supply limitations regarding semi-polar and non-polar wafers, it is highly desirable to maximize the utilization of substrates and epitaxial material. In lateral-cavity laser diode fabrication, it is typically the case that the minimum die length is determined by the laser cavity length, but the minimum die width is determined by other device components, such as wire bonding pads or considerations such as mechanical area for handling during die attachment processes. This means that while the laser cavity length limits the laser die length, the laser die width is typically much larger than the laser cavity width.Since the GaN substrate and epitaxial material are only critical in and near the laser cavity region, this presents a significant opportunity to develop new processes to form only the laser cavity region from these relatively expensive materials and to form the bond pad and the mechanical structure of the chip from a more cost-effective material. Typical dimensions for laser cavity widths are 1–30 µm, while wire bonding pads are ~100 µm wide. This means that if the wire bonding pad width limitations and mechanical handling concerns of the GaN chip size were eliminated, between >3 and 100 times more laser diode die could be fabricated from a single epitaxial gallium and nitrogen-containing wafer. This amounts to a >3 to 100-fold reduction in epitaxial and substrate costs.In conventional device structures, the relatively large bonding pads are mechanically supported by die epitaxial wafers, although they do not make use of the material properties of the semiconductor beyond the structure support.

[0018] In one example, the present invention is a method for maximizing the number of GaN laser devices that can be fabricated from a given epitaxial area on a gallium and nitrogen-containing substrate by spreading the epitaxial material onto a carrier wafer such that the wire bonding pads or other structural elements are mechanically supported by the relatively inexpensive carrier wafer while the light-emitting regions are further fabricated from the necessary epitaxial material. This invention will drastically reduce the chip costs for all gallium and nitrogen-based laser diodes and, in particular, could enable cost-effective nonpolar and semipolar laser diode technology.

[0019] These devices include a gallium and nitrogen-containing substrate (e.g., GaN) comprising a surface region oriented in either a semipolar or non-polar configuration, but may be different. The device also has a gallium and nitrogen-containing material, including InGaN, occupying the surface region. In a specific embodiment, the present laser device can be applied to either a semipolar or non-polar gallium-containing substrate, as described below. As used herein, the term "substrate" may mean the bulk substrate or may include occupying growth structures, such as a gallium and nitrogen-containing epitaxial region or functional regions, such as n-type GaN, combinations, and the like.We have also investigated epitaxial growth and cleavage properties on semipolar crystal planes oriented between the nonpolar m-plane and the polar c-plane. In particular, we have grown on the {30-31} and {20-21} families of crystal planes. We have achieved promising epitaxial structures and cleavages that will pave the way for efficient laser diodes operating at wavelengths from approximately 400 nm to green, e.g., 500 nm to 540 nm. These results include light-blue epitaxy in the 450 nm range, light-green epitaxy in the 520 nm range, and smooth cleavage planes orthogonal to the c-direction projection.

[0020] In a specific embodiment, the gallium nitride substrate component is a GaN bulk substrate characterized by having a semipolar or non-polar crystalline surface region, but may be different. In a specific embodiment, the GaN bulk nitride substrate comprises nitrogen and has a surface dislocation density between about 10E5 cm -2 and about 10E7 cm -2 or less than 10E5 cm -2 The nitride crystal or wafer can be Al x In y Ga 1-x-y N, where 0 ≤ x, y, x+y ≤ 1. In a specific embodiment, the nitride crystal comprises GaN. In one or more embodiments, the GaN substrate has threading dislocations at a concentration between about 10E5 cm -2 and about 10E8 cm -2in one direction, that is, essentially orthogonal or oblique with respect to the surface. As a consequence of the orthogonal or oblique orientation of the dislocations, the surface dislocation density is between about 10E5 cm -2 and about 10E7 cm -2 or below about 10E5 cm -2 In a specific embodiment, the device can be fabricated on a slight offcut of semipolar substrate, as described in US 8 422 525 B1.

[0021] The substrate is typically provided with one or more of the following epitaxially grown elements, but is not limited to: ◯ an n-GaN cladding region with a thickness of 50 nm to about 6000 nm with a Si or oxygen doping level of about 5E16cm -3 up to 1E19cm -3 ◯ an InGaN region of high indium content and / or thick InGaN layer(s) or super-SCH region; ◯ a higher bandgap stretch control region occupying the InGaN region; ◯ if applicable, an SCH region occupying the InGaN region; ◯ Multiple quantum well active region layers of three to five or four to six 3.0-5.5.0 nm InGaN quantum wells separated by 1.5-10.0 nm GaN barriers; ◯ optionally, a p-side SCH layer of InGaN with a mole fraction of indium between 1% and 10% and a thickness of 15 nm to 100 nm; ◯ an electron blocking layer of AlGaN with a mole fraction of aluminum between 5% and 20% and a thickness of 10 nm to 15 nm and doped with Mg; ◯ a p-GaN cladding layer with a thickness of 400 nm to 1000 nm with Mg doping height of 5E17 cm -3 up to 1E19 cm -3 ; ◯ a p++-GaN contact layer with a thickness of 20 nm to 40 nm with Mg doping height of 1E20 cm -3 up to 1E21 cm -3

[0022] Typically, each of these regions is formed using at least one epitaxial deposition technique of metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial growth techniques suitable for GaN growth. The active region may include one to twenty quantum well regions according to one or more embodiments. As an example, after deposition of the Al u In v Ga 1-u-v An active layer is deposited on an n-type N-layer for a predetermined period of time to achieve a predetermined thickness. The active layer may comprise a single quantum well or a multiple quantum well with 2-10 quantum wells. The quantum wells may comprise InGaN wells and GaN barrier layers. In other embodiments, the well layers and barrier layers comprise Al w In x Ga 1-w-x N or Al y- In z Ga 1-y-zN, where 0 ≤ w, x, y, z, w+x, y+z ≤ 1, where w < u, y and / or x > v, z, such that the band gap of the well layer(s) is less than that of the barrier layer(s) and the n-type layer. The well layers and barrier layers may each have a thickness between about 1 nm and about 15 nm. In another embodiment, the active layer comprises a double heterostructure with an InGaN or Al w In x Ga 1-w-x N-layer about 10 nm to 100 nm thick, surrounded by GaN or Al y In z Ga 1-y-z N-layers, where w < u, y and / or x > v, z. The composition and structure of the active layer are selected to provide light emission at a preselected wavelength. The active layer can remain undoped (or unintentionally doped) or can be n-type or p-type doped.

[0023] The active region may also include an electron-blocking region and a separate confinement heterostructure. In some embodiments, an electron-blocking layer is preferably deposited. The electron-blocking layer may be Al s In t Ga 1-s- tN, where 0 ≤ s, t, s+t ≤ 1, with a higher band gap than the active layer, and may be p-type doped, or the electron-blocking layer may comprise an AlGaN / GaN superlattice structure comprising alternating layers of AlGaN and GaN. Alternatively, there may be no electron-blocking layer. As noted, the p-type gallium nitride structure is deposited above the electron-blocking layer and active layer(s). The p-type layer may be doped with Mg to a level between about 10E16 cm -3 and 10E22 cm -3doped and can have a thickness between about 5 nm and about 1000 nm. The outermost 1-50 nm of the p-type layer can be more heavily doped than the rest of the layer to enable improved electrical contact.

[0024] The present invention is directed to the fabrication of optoelectronic devices from semiconductor wafers. In particular, the present invention increases the utilization of substrate wafers and epitaxial material by using a selective area bonding process to transfer individual dice of epitaxial material to a carrier wafer in such a way that the die pitch on the carrier wafer is increased relative to the original epitaxial wafer. The placement of epitaxial material enables device components that do not require the presence of the expensive gallium and nitrogen-containing substrate and covering epitaxial material, which is often grown on a gallium and nitrogen-containing substrate, to be fabricated on the low-cost carrier wafer, enabling more efficient use of the gallium and nitrogen-containing substrate and covering epitaxial material.

[0025] In one embodiment, mesas of gallium and nitrogen-containing laser diode epitaxial material are fabricated in a dense array on a gallium and nitrogen-containing substrate. This patterning spacing is referred to as the 'first spacing'. The first spacing is often a nominal width, that is, suitable for creating each of the epitaxial regions on the substrate, although not large enough for complete laser devices, for which larger non-active regions or regions for contacts and the like are often desired. For example, these mesas would have a first spacing in the range from about 5 micrometers to about 30 micrometers or to about 50 micrometers. Each of these mesas is a 'die'.

[0026] In one example, this die is then transferred to a carrier wafer at a second pitch such that the second pitch on the carrier wafer is greater than the first pitch on the gallium and nitrogen-containing substrate. In one example, the second pitch is configured with the die so that each die with a portion of the carrier wafer can represent a laser device, including contacts and other components. For example, the second pitch would be about 100 micrometers to about 200 micrometers or to about 300 micrometers. The second die pitch allows for easy mechanical handling and space for wire bonding pads positioned in the regions of the carrier wafer between epitaxial mesas, allowing a larger number of laser diodes to be fabricated from a given gallium and nitrogen-containing substrate and covering epitaxial material. The side view schematics of the prior art and die-expanded laser diodes are shown in Fig. 1 and Fig. 2. Typical dimensions for laser ridge widths and the necessary widths for mechanical and wire bonding considerations are from 1 µm to 30 µm and from 100 µm to 300 µm, respectively, allowing for significant improvements in utilization efficiency for gallium and nitrogen-containing substrate and covering epitaxial material in the present invention.

[0027] Fig. Figure 3 is a simplified schematic cross-sectional diagram illustrating a prior art laser diode structure. This diagram is merely an example and should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize other variations, modifications, and alternatives. As shown, the laser device includes gallium nitride substrate 203 having an n-type base metal backside contact 201. In one embodiment, the metal backside contact is made of a suitable material such as those listed below and others. Further details of the contact region can be found throughout the present description, and particularly below.

[0028] In one embodiment, the device also includes an n-type gallium nitride occupying layer 205, an active region 207, and a p-type gallium nitride occupying layer patterned as a laser stripe region 211. In addition, the device also includes an n-side separate confinement heterostructure (SCH) 206, a p-side conductive layer or SCH 208, p-AlGaN EBL 209, among other features. In one embodiment, the device also includes a p++ type gallium nitride material 213 to form a contact region. In one embodiment, the p++ type contact region has a suitable thickness and may be in the range of about 10 nm to 50 nm or other thicknesses. In one embodiment, the doping level may be higher than the p-type cladding region and / or the bulk region. In one embodiment, the p++ type region has a doping concentration in the range of about 10 19 up to 10 21 mg / cm 3and others. The p++ type region preferably induces tunneling between the semiconductor region and the occupying metal contact region. In one embodiment, each of the dense regions is formed using at least one epitaxial deposition technique of metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial growth techniques suitable for GaN growth. In one embodiment, the epitaxial layer is a high-quality epitaxial layer occupying the n-type gallium nitride layer. In some embodiments, the high-quality layer is doped, for example, with Si or O, to form n-type material, with a dopant concentration between about 10 16 cm -3 and 10 20 cm -3 .

[0029] The device has formed a laser stripe region that occupies part of the offcut of the crystalline orientation surface region.

[0030] In a specific embodiment, the method of faceting includes subjecting the substrates to a laser for pattern formation. In a preferred embodiment, the patterning is configured to form a pair of facets for one or more ridge lasers. In a preferred embodiment, the pair of facets face each other and are in parallel alignment with each other. In a preferred embodiment, the method uses a UV (355 nm) laser to scribe the laser stripes. In a specific embodiment, the laser is configured on a system that enables the precise scribing of lines configured in one or more different patterns and profiles. In one or more embodiments, the laser scribing can be performed on the backside, frontside, or both, depending on the application.Of course, there may be other variations, modifications and alternatives.

[0031] In a specific embodiment, the method uses backside laser scribing or the like. In backside laser scribing, the method preferably forms a laser scribe as a continuous line perpendicular to the laser stripe on the backside of the GaN substrate. In a specific embodiment, the laser scribe is generally 15-20 µm deep or of another suitable depth. Preferably, backside scribing may be advantageous. That is, the laser scribing process does not depend on the pitch of the laser stripes or other similar patterning. Consequently, a backside laser scribing may result in a higher density of laser stripes on each substrate according to a preferred embodiment. However, in a specific embodiment, backside laser scribing may result in residue from the stripe on one or more of the facets.In a specific embodiment, laser scribing of the backsides often requires the substrate side to face down on the tape. For laser scribing of the frontside, the backside of the substrate is in contact with the tape. Of course, other variations, modifications, and alternatives are possible.

[0032] Laser scribe patterning: The distance from the laser mask is approximately 200 µm, but can be varied. The process uses a 170 µm scribe with a 30 µm line for the 200 µm pitch. In a preferred embodiment, the scribe length is maximized or increased while keeping the heat-affected zone from the laser away from the heat-sensitive laser ridge.

[0033] Laser-Scribing Profiles: A sawtooth profile generally produces minimal facet roughness. The sawtooth profile shape is believed to create a very high stress concentration in the material, causing cleavage to proceed much more easily and / or efficiently.

[0034] In a specific embodiment, the method of faceting includes subjecting the substrates to mechanical scribing to form the pattern. In a preferred embodiment, the patterning is configured to form a pair of facets for one or more ridge lasers. In a preferred embodiment, the pair of facets face each other and are in parallel alignment with each other. In a preferred embodiment, the method uses diamond-tip scribing to physically scribing the laser stripes, although, as would be appreciated by one skilled in the art, scribing with a tip made of any material harder than GaN would be sufficient. In a specific embodiment, the laser is configured on a system configured for precise scribing of lines in one or more different patterns and profiles.In one or more embodiments, the mechanical scoring may be performed on the back, front, or both, depending on the application. Of course, other variations, modifications, and alternatives may exist.

[0035] In a specific embodiment, the method uses back-side scribing or the like. With mechanical back-side scribing, the method preferably forms a continuous line scribe that is perpendicular to the laser stripes on the back of the GaN substrate. In a specific embodiment, the laser scribing is generally 15-20 µm deep or has another suitable depth. Preferably, back-side scribing may be advantageous. That is, the mechanical scribing process does not depend on the pitch of the laser stripes or other similar patterning. Thus, according to a preferred embodiment, back-side scribing may result in a higher density of laser stripes on each substrate. However, in a specific embodiment, mechanical back-side scribing may result in residue from the stripe on one or more of the facets.In a specific embodiment, mechanical back-side scribing often requires the substrates to face down on the tape. With mechanical front-side scribing, the back of the substrate is in contact with the tape. Of course, other variations, modifications, and alternatives may exist.

[0036] It is well known that etching techniques such as chemically assisted ion beam etching (CAIBE), inductively coupled plasma (ICP) etching, or reactive ion etching (RIE) can produce smooth and vertically etched sidewall regions that could serve as facets in etched facet laser diodes. In the etched facet process, a masking layer is deposited and patterned on the surface of the wafer. The etch mask layer could be made of dielectrics such as silicon dioxide (SiO2), silicon nitride (Si x N y), a combination thereof, or other dielectric materials. Furthermore, the mask layer could consist of metal layers, such as Ni or Cr, but could also consist of metal combination stacks or stacks comprising metal and dielectrics. In another approach, photoresist masks can be used either individually or in combination with dielectrics and / or metals. The etch mask layer is patterned using conventional photolithography and etching steps. The alignment lithography could be preformed with a contact aligner or stepper aligner. Such lithographically defined mirrors provide a high degree of control for the designer. After the patterning of the photoresist mask on top of the etch mask is complete, the patterns are then transferred to the etch mask using a wet etch or dry etch technique.Finally, the facet patterning is etched into the wafer using a dry etching technique selected from CAIBE, ICP, RIE, and / or other techniques. The etched facet surfaces must be highly vertical, between approximately 87 and 93 degrees or between approximately 89 and 91 degrees of the wafer's surface plane. The etched facet surface region must be very smooth, with a root mean square edge of less than 50 nm, 20 nm, 5 nm, or 1 nm. CAIBE is known for providing very smooth and minimally damaged sidewalls due to the chemical nature of the etch, while it can provide highly vertical etches due to the ability to tilt the wafer stage to compensate for any inherent angle during etching.

[0037] The laser stripe is characterized by a length and width. The length ranges from approximately 50 micrometers to approximately 3000 micrometers, but is preferably between 10 micrometers and 400 micrometers, between approximately 400 micrometers and 800 micrometers, or between approximately 800 micrometers and 1600 micrometers, although this could be different. The stripe also has a width ranging from approximately 0.5 micrometers to approximately 50 micrometers, but is preferably between 0.8 micrometers and 2.5 micrometers for single-lateral mode operation or between 2.5 µm and 35 µm for multi-lateral mode operation, although it can have other dimensions. In a particular embodiment, the present device has a width in the range of about 0.5 micrometers to about 1.5 micrometers, a width in the range of about 1.5 micrometers to about 3.0 micrometers, a width in the range of 3.0 micrometers to about 35 micrometers, and others.In a specific embodiment, the width is substantially constant in dimension, although slight variations may occur. The width and length are often formed using a masking and etching process, which are common in the art.

[0038] The laser stripe is created by an etching process selected from dry etching or wet etching in either the p-type or n-type cladding layers. The device also has an occupant dielectric region exposing a p-type or n-type contact region. Overlying the contact region is a contact material, which may be metal or a conductive oxide, or a combination thereof. The p-type and n-type electrical contacts can be deposited by thermal evaporation, electron beam evaporation, electroplating, sputtering, or another suitable technique.

[0039] Given the high cost of gallium-nitrogen substrates and the difficulty of scaling up the gallium-nitrogen substrate size, the inefficiency, and potential supply limitations of polar, semi-polar, and non-polar gallium-nitrogen wafers, it is highly desirable to maximize the utilization of available gallium-nitrogen substrates and the supporting epitaxial material. In the fabrication of lateral-cavity laser diodes, it is typically the case that the minimum die size is determined by device components, such as wire bonding pads, or mechanical handling considerations, rather than by laser cavity widths. Minimizing the die size is critical for reducing manufacturing costs because smaller die sizes allow for a larger number of devices to be fabricated on a single wafer in a single processing pass.The present invention is a method for maximizing the number of devices that can be fabricated from a given gallium and nitrogen-containing substrate and the covering epitaxial material by spreading the epitaxial material onto a carrier wafer via a die expansion process.

[0040] A bottom plan view of a preferred embodiment of the die expansion process is shown in Fig. 4. The starting materials are patterned epitaxial and carrier wafers. Herein, the 'epitaxial wafer' or 'epitaxial wafer' is defined as the original gallium and nitrogen-containing wafer on which the epitaxial material constituting the active region was grown, while the 'carrier wafer' is defined as a wafer onto which epitaxial layers are transferred for easier processing. The carrier wafer can be selected based on a variety of criteria, including, but not limited to, cost, thermal conductivity, thermal expansion coefficient, size, electrical conductivity, optical properties, and processing compatibility. The patterned epitaxial wafer is fabricated in such a way that subsequent selective detachment of bonded epitaxial regions is possible.The patterned carrier wafer is fabricated such that bond pads are arranged to enable the selective area bonding process. These wafers can be fabricated using a variety of process steps, some embodiments of which are described below. In the first selective area bonding step, the epitaxial wafer is bonded to the pre-patterned bonding pads on the carrier wafer, and a combination of pressure, heat, and / or ultrasonication is used to bond the mesas to the bonding pads. The bonding material can be a variety of media, including, but not limited to, metals, polymers, waxes, and oxides. Only epitaxial die in contact with a bonding pad on the carrier wafer will bond. Sub-micrometer alignment tolerances are possible on commercial die bonders.The epitaxial wafer is then pulled away, fracturing the epitaxial material at a weakened epitaxial release layer, leaving the desired epitaxial layers on the carrier wafer. Herein, a 'selective area bonding step' is defined as a single repeat step of this process. In the process described in . Fig. In the example shown in Figure 4, one-quarter of the epitaxial die is transferred in this first selective bonding step, leaving three-quarters on the epitaxial wafer. The selective area bonding step is then repeated to transfer the second quarter, third quarter, and fourth quarter from the epitaxial die to the patterned carrier wafer. This selective area bonding can be repeated any number of times and is not limited to the four steps described in Fig. 4. The result is an array of epitaxial die on the carrier wafer with a wider die pitch than the original die pitch on the epitaxial wafer. The die pitch on the epitaxial wafer is referred to as Pitch 1, and the die pitch on the carrier wafer is referred to as Pitch 2, where Pitch 2 is greater than Pitch 1. At this point, standard laser diode processes can be performed on the carrier wafer. Side profile views of devices fabricated using prior art methods and the methods described in the present invention are shown in Fig. 1 or Fig. 2. The device structure enabled by the present invention contains the relatively expensive epitaxial material only where the optical cavity requires it and has relatively large bonding pads and / or other device components resting on a carrier wafer. Typical dimensions for laser ridge widths and bonding pads are <30 µm and >100 µm, respectively, allowing three or more times improved epitaxial utilization efficiency with the present invention.

[0041] There are many methods by which the extended die pitch can be achieved. One embodiment for the fabrication of GaN-based laser diodes is described in Fig. 5 and Fig. 6. This embodiment uses a bandgap-selective photoelectric chemical (PEC) etch to undercut an array of mesas etched into the epitaxial layers, followed by a selective area bonding process on a patterned carrier wafer. The fabrication of the epitaxial wafer is described in Fig. 5 and the selective surface bonding process is shown in Fig. 6. This process requires the inclusion of a buried sacrificial region that can be selectively PEC etched through the band gap. For GaN-based optoelectronic devices, InGaN quantum wells have proven to be an effective sacrificial region during PEC etching. The first in Fig. The step mentioned in Figure 5 is a top-down etching to expose the sacrificial layers, followed by a bonding metal deposition as in Fig. 5. In the exposed sacrificial region, a bandgap-selective PEC etch is used to undercut the mesas. The bandgaps of the sacrificial region and all other layers are selected such that during the PEC etch, only the sacrificial region will absorb light and therefore etch. With appropriate control of the etch rates, a thin strip of material can be left to weakly connect the mesas on the epitaxial substrate. This wafer is then aligned and bonded to a patterned carrier wafer, as shown in Fig. 6. Gold-gold metallic bonding is used as an example in this work, although a wide variety of oxide bonds, polymer bonds, wax bonds, etc. are potentially suitable. Submicrometer alignment tolerances are possible using commercially available die bonding equipment. The carrier wafer is patterned in such a way that only selected mesas come into contact with the metallic bond pads on the carrier wafer. When the epitaxial substrate is pulled away, the bonded mesas break away at the weakened sacrificial region, while the unbonded mesas remain attached to the epitaxial substrate. This selective area bonding process can then be repeated to transfer the remaining mesas into the desired configuration. This process can be repeated through a variety of iterative steps and is not limited to the two in Fig. 7. The carrier wafer can be of any size, including, but not limited to, 2 inches, 3 inches, 4 inches, 6 inches, 8 inches, and 12 inches. After all desired mesas have been transferred, a second bandgap-selective PEC etch can optionally be used to remove any remaining sacrificial region materials to achieve smooth surfaces. At this point, standard laser diode processes can be performed on the carrier wafer.

[0042] Another embodiment of the invention uses a sacrificial region with a higher band gap than the active region, so that both layers are absorbent during the band gap PEC etching process. In this embodiment, the active region can be prevented from etching during the band gap-selective PEC etching by using an insulating protection layer on the sidewall, as in Fig. 7. The first in Fig. The step shown in Figure 7 is an etch to expose the active region of the device. This step is followed by the deposition of a protective insulating layer on the mesa sidewalls, which serves to block the PEC etch of the active region during the later undercut PEC etch step of the sacrificial region. A second top-down etch is then performed to expose the sacrificial layers, and bonding metal is deposited, as shown in Fig. 7. In the exposed sacrificial region, a bandgap-selective PEC etch is used to undercut the mesas. At this point, the Fig. 6, selective area bonding techniques are used to continue the device formation.

[0043] Another embodiment of the invention involves the fabrication of device components on the dense epitaxial wafers prior to the selective area bonding steps. Fig. In the embodiment shown in Figure 8, the laser ridge, sidewall passivation, and contact metal are fabricated on the original epitaxial wafer prior to the die expansion process. This process flow is provided for example purposes only and is not intended to be limiting; the device components may be processed prior to the die expansion process. This workflow has potential cost advantages because additional steps are performed on the higher-density epitaxial wafer prior to the die expansion process. A detailed schematic of this process flow is shown in Fig. 8 is indicated.

[0044] In another preferred embodiment of the invention, the epitaxial gallium and nitrogen material is grown on a gallium and nitrogen containing substrate material from one of the following orientations: m-plane, {50-51}, {30-31}, {20-21}, {30-32}, {50-5-1}, {30-3-1}, {20-2-1}, {30-3-2} or offcuts from these planes in + / - 5 degrees against a-plane and / or c-plane.

[0045] In another embodiment of the invention, individual PEC undercut etchings are used after each selective bonding step to etch away the sacrificial release layer from only bonded mesas. Which epitaxial die is undercut is controlled only by etching down to expose the sacrificial layer of mesas to be removed in the current selective bonding step. The advantage of this embodiment is that only very coarse control of PEC etch rates is required. This comes at the expense of additional processing steps and geometry constraints.

[0046] In another embodiment of the invention, the bonding layers may be a variety of bonding pairs, including metal-metal, oxide-oxide, solder alloys, photoresists, polymers, wax, etc.

[0047] In another embodiment of the invention, the sacrificial region is completely removed by PEC etching, and the mesa remains anchored in place by any remaining defective columns. PEC etching is known to leave intact material around defects, which act as recombination centers. 2,3 Additional mechanisms by which a mesa might remain in place after a complete sacrificial etch include static forces or van der Waals forces.

[0048] In another embodiment of the invention, a mesa with an exposed shaped sacrificial region is etched to leave larger regions near the ends of each epitaxial die. Bonding metal is deposited only on the regions of epitaxy to be transferred. A PEC etch is then performed such that the epitaxial die to be transferred is completely undercut, while the larger regions near the end are only partially undercut. The intact sacrificial regions at the ends of the die provide mechanical stability through the selective area bonding step. Since only a few nanometers of thickness are undercut, this geometry should be compatible with standard bonding techniques. After the selective area bonding step, the epitaxial and carrier wafers are mechanically separated, with gaps at the weak points between the bonding metal and intact sacrificial regions. Example schematics of this process are shown in Fig. 9 and Fig.10. After the desired number of repetition steps has been performed, the prior art laser diode manufacturing processes can be applied to the expanded carrier wafer.

[0049] In another embodiment of the invention, the detachment of the epitaxial layers is carried out by means other than PEC etching, such as laser lift-off.

[0050] In another embodiment of the invention, the carrier wafer is another semiconductor material, a metallic material, or a ceramic material. Some potential candidates include silicon, gallium arsenide, sapphire, silicon carbide, diamond, gallium nitride, AlN, polycrystalline AlN, indium phosphide, germanium, quartz, copper, gold, silver, aluminum, stainless steel, or steel.

[0051] In another embodiment of the invention, the laser facets are fabricated by cleavage processes. If a suitable carrier wafer is selected, it is possible to use the carrier wafer to define cleavage planes in the epitaxial material. This could improve the yield, quality, ease, and / or accuracy of the cleavages.

[0052] In another embodiment of the invention, the laser facets are fabricated using etched facet processes. In the etched facet embodiment, a lithographically defined mirror pattern is etched in gallium and nitrogen to form facets. The etching process could be a dry etching process selected from inductively coupled plasma etching (ICP), chemically assisted ion beam etching (CAIBE), or reactive ion etching (RIE). The etched facet process can be used in combination with the die expansion process to avoid facet formation through cleaving, potentially improving yield and facet quality.

[0053] In another embodiment of the invention, dicing is achieved by cleavage techniques assisted by the selection of carrier wafers. For example, if silicon or GaAs carrier wafers are selected, there will be a system of common cubic cleavage planes available for dicing by cleavage. In this embodiment, there is no need to transfer the cleavages to the epitaxial material, since dicing will only take place in the carrier-wafer material regions.

[0054] In another embodiment of the invention, any of the above-mentioned process sequences can be used in combination with wafer laying. For example, 7.5 mm by 18 mm substrates can be laid on a 2-inch carrier wafer, allowing top-side processing and selective area bonding to be performed on multiple epitaxial substrates in parallel, resulting in further cost savings.

[0055] In another embodiment of the invention, the substrate wafer is reprocessed after the selective area bonding steps through replanarization and surface fabrication processes. The epitaxial wafer can be reused any number of times.

[0056] In one example, the present invention provides a method for increasing the number of gallium and nitrogen-containing laser diode devices that can be fabricated from a given epitaxial surface; wherein the gallium and nitrogen-containing epitaxial layers are overlain by gallium and nitrogen-containing substrates. The epitaxial material comprises at least the following layers: a sacrificial region that can be selectively etched using a bandgap-selective PEC etch, an n-type cladding region, an active region comprising at least one active layer occupying the n-type cladding region, and a p-type cladding region occupying the active layer region.The gallium and nitrogen-containing epitaxial material is patterned into die with a first die pitch; wherein the die of the gallium and nitrogen-containing epitaxial material is transferred to a carrier wafer with a first pitch to form a second die pitch on the carrier wafer; wherein the second die pitch is greater than the first die pitch.

[0057] While the foregoing is a complete description of the specific embodiments, various modifications, alternative constructions, and equivalents may be used. As an example, the packaged device may include any combination of elements described above and outside the present description. As used herein, the term "substrate" may mean the bulk substrate or may include the occupying growth structures, such as a gallium and nitrogen-containing epitaxial region or functional regions such as n-type GaN, combinations, and the like.

Claims

[1] A method of manufacturing a gallium and nitrogen-containing laser diode device, the method comprising: Providing a gallium and nitrogen-containing substrate (100) having a surface region; Forming epitaxial material occupying the surface region, the epitaxial material comprising a sacrificial region (107) that can be selectively etched with a bandgap-selective photoelectrochemical etch, an n-type cladding region (101), an active region (102) comprising at least one active layer occupying the n-type cladding region (101), and a p-type cladding region (103) occupying the active layer region (102); Structuring the epitaxial material to form a plurality of dice, each of the dice corresponding to at least one laser device, characterized by a first distance between a pair of dice, the first distance being less than a nominal width; Transferring each of the plurality of dice to a carrier wafer (106) such that each pair of dice is configured with a second spacing between each pair of dice, the second spacing being greater than the first spacing corresponding to the nominal width, wherein transferring the dice comprises selective bonding to the carrier wafer (106), each die being configured to a bonding pad (108) on the carrier wafer (106), wherein the dice are undercut by a bandgap-selective photoelectrochemical etching of the sacrificial region prior to transfer to the carrier wafer (106), and the undercut bonded dice break in the area of ​​the sacrificial region (107) when the gallium and nitrogen-containing substrate (100) is removed. [2] The method of claim 1, wherein each die is shaped as a mesa, and each die pair has the first pitch in the range between 1 µm and 10 µm, or between 10 micrometers and 50 micrometers in width, or between 50 and 3000 µm in length; and the patterning comprises an etching process; wherein the second pitch on the carrier wafer (106) is between 100 micrometers and 200 micrometers, or between 200 micrometers and 300 micrometers. [3] The method of claim 1, further comprising processing each of the die to form at least one laser device on each die after transferring or further comprising forming one or more laser diode cavities on each die of epitaxial material. [4] The method of claim 1, wherein each pair of dice occupying the carrier wafer (106) is defined by the second distance; and further comprising forming one or more components disposed overlying an area defined by the second distance, wherein the one or more components are selected from a contact region or a bonding pad. [5] The method of claim 1, wherein the carrier wafer is characterized by a conductive material for a contact region or regions; wherein each of the laser devices is characterized by a wavelength in the range between 200 and 2000 nm; and wherein each laser device comprises a pair of facets configured from a cleavage process or an etching process, wherein the etching process is selected from inductively coupled plasma etching, chemically assisted ion beam etching, or reactive ion beam etching. [6] The method of claim 1, further comprising singulating each of the die by separating each die pair in a region defined by the second distance; wherein the epitaxial material includes GaN, AlN, InN, InGaN, AlGaN, InAlN and / or InAlGaN. [7] The method of claim 1, wherein the gallium and nitrogen-containing material is grown on a polar, non-polar, or semi-polar plane; wherein the carrier wafer (106) comprises at least one of silicon, gallium arsenide, sapphire, silicon carbide, diamond, gallium nitride, AlN, indium phosphide, or metal. [8] The method of claim 1, wherein transferring comprises selectively bonding one or more die to the carrier wafer (106), and repeating the selective bonding N times for one or more other die on the carrier wafer (106), where N is an integer between 1 and 50. [9] The method of claim 1, wherein transferring comprises selectively bonding one or more die to the carrier wafer (106), and repeating the selective bonding N times for one or more other die on the carrier wafer (106), where N is an integer between 1 and 50, to remove each die to be bonded to the carrier wafer (106); wherein the carrier wafer (106) has a larger diameter than a diameter of the gallium and nitrogen-containing substrate (100); wherein each of the bonds is at least one of metal-metal pairs, oxide-oxide pairs, spin-on glass, solder alloys, polymers, photoresists, and / or wax. [10] The method of claim 1, wherein transferring comprises selectively bonding one or more die to the carrier wafer (106), and repeating the selective bonding N times for one or more other die on the carrier wafer (106), where N is an integer between 1 and 50, to remove each die to be bonded to the carrier wafer (106); wherein the carrier wafer (106) has a larger diameter than a diameter of the gallium and nitrogen-containing substrate (100); wherein each of the bonds is at least one of metal-metal pairs, oxide-oxide pairs, spin-on glass, solder alloys, polymers, photoresists, and / or wax; and further comprising stripping each of the die during each selective bonding by severing a stripping region connected to each die while leaving a portion of the epitaxial material intact. [11] The method of claim 1, wherein each of the die comprises one or more components, wherein the one or more components are selected from at least one of an electrical contact, a current spreading region, an optical cladding region, a laser ridge, a laser ridge passivation, or a facet pair, either individually or in any combination.

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