JP-7855036-B2 - Carrier-assisted method for separating crystalline materials along laser damage regions

JP7855036B2JP 7855036 B2JP7855036 B2JP 7855036B2JP-7855036-B2

Inventors

ドノフリオマシュー
エドモンドジョン
コンファ－シュアン
バーカスエリフ

Assignees

ウルフスピードインコーポレイテッド

Dates

Publication Date: 20260507
Application Date: 20240903
Priority Date: 20190212

Claims (20)

The method involves temporarily bonding a rigid support having a thickness greater than 800 microns to a first surface of a crystalline material containing a semiconductor using an intervening adhesive material, wherein the crystalline material comprises a substrate having a subsurface laser-damaged region at a certain depth relative to the first surface. The crystalline material is fractured along or near the subsurface laser-damaged region so that a bonded assembly is obtained comprising the rigid carrier, the adhesive material, and the portion of the crystalline material removed from the substrate, wherein the portion of the crystalline material removed from the substrate in the bonded assembly has a thickness of at least 160 μm. Includes, A method for processing a crystalline material, wherein at least one of the maximum length or maximum width of at least a portion of the rigid carrier exceeds the corresponding maximum length or maximum width of the substrate, the crushing comprises applying a mechanical force in close proximity to at least one edge of the rigid carrier, the mechanical force is configured to impart a bending moment to at least a portion of the rigid carrier, the crystalline material comprises a hexagonal structure, and the bending moment is oriented within ±5 degrees from a direction perpendicular to the <11-20> direction of the hexagonal structure.
The crystalline material processing method according to claim 1, wherein the adhesive material includes a thermoplastic material.
The method for processing a crystalline material according to claim 1, wherein the adhesive material has a glass transition temperature Tg of at least 35°C.
The crystalline material processing method according to claim 1, wherein the adhesive material has a Shore D durometer value of at least 70 when the adhesive material is at 25°C.
The method for processing a crystalline material according to claim 1, wherein the adhesive material has an elastic modulus of at least 7 MPa when the adhesive material is at 25°C.
The method for processing a crystalline material according to claim 1, wherein the adhesive material has a thickness of less than 50 microns.
The rigid support comprises a first surface and a second surface opposite to the first surface. The adhesive material is positioned in contact with the first surface. The second surface contains no adhesive material and no stress generating material. The method for processing a crystalline material according to claim 1.
The method for processing a crystalline material according to claim 1, wherein the rigid support comprises a crystalline material.
The method for processing a crystalline material according to claim 1, further comprising performing at least one additional processing step on the portion of the crystalline material while the portion of the crystalline material remains part of the joined assembly.
The method for processing a crystalline material according to claim 1, further comprising bonding an additional rigid support having an elastic modulus of at least 20 GPa to the second surface of the crystalline material opposite to the first surface, prior to the crushing.
The crystalline material processing method according to claim 1, wherein the crystalline material includes SiC.
The method for processing a crystalline material according to claim 1, further comprising (i) roughening, textured, and/or etching at least one of the first surface of the crystalline material or (ii) an adjacent surface of the rigid support, before the temporary bonding of the rigid support to the first surface of the crystalline material using the adhesive material.
The crystal material processing method according to claim 1, wherein the portion of the crystal material removed from the substrate comprises a self-supporting wafer configured to grow at least one epitaxial layer thereon.
The crystal material processing method according to claim 1, wherein the portion of the crystal material removed from the substrate comprises a device wafer containing at least one epitaxial layer grown thereon.
The method for processing a crystalline material according to claim 1, wherein the portion of the crystalline material removed from the substrate in the joined assembly has a thickness of at least 240 μm.
Creating a subsurface damage region beneath the first surface of the crystalline material substrate, Bonding a support to the aforementioned crystalline material substrate, The fracture of the crystalline material substrate is to fracture the crystalline material substrate along the subsurface damage region such that the crystalline material portion separates from the rest of the crystalline material substrate, the crystalline material portion remains bonded to the carrier , and the fracture of the crystalline material substrate is achieved by at least one step including (i) applying a mechanical force close to at least one edge of the carrier to impart a bending moment to at least a portion of the carrier, or (ii) cooling the carrier if the carrier has a larger coefficient of thermal expansion than the crystalline material substrate. A method for processing a crystalline material, comprising performing a processing step on the crystalline material portion while the crystalline material portion remains bonded to the carrier.
The crystalline material processing method according to claim 16, wherein the processing step includes a grinding step.
The crystalline material processing method according to claim 16, wherein the processing step includes a cleaning step.
The crystalline material processing method according to claim 16, wherein the processing step includes providing an epitaxial layer to the crystalline material portion.
The crystalline material processing method according to claim 16, wherein the crystalline material substrate includes a SiC ingot.

Description

Detailed description of the invention [Description of related applications] This application claims priority to U.S. Patent Application No. 16/274,045 filed on 5 March 2019, U.S. Provisional Patent Application No. 62/803,333 filed on 8 February 2019, and U.S. Provisional Patent Application No. 62/786,335 filed on 29 December 2018, the entire disclosure of the said applications is thus incorporated herein by reference. [Technical Field] This disclosure relates to a method for processing crystalline materials, and more particularly to a carrier-assisted method for cutting or removing a relatively thin layer of crystalline material from a substrate such as a Boule or wafer that has subsurface laser damage. [background] Thin layers of crystalline materials are required as starting structures for fabricating various useful systems in a wide range of applications in microelectronics, optoelectronics, and microfabrication. Conventional methods for cutting thin layers (e.g., wafers) from large-diameter crystalline ingots of crystalline materials include the use of wire saws. Wire sawing techniques have been applied to various crystalline materials such as silicon, sapphire, and silicon carbide. Wire saw tools consist of extremely fine steel wires (typically less than 0.2 mm in diameter) that are passed through grooves in one or more guide rollers. Two slicing methods exist: free abrasive slicing and fixed abrasive slicing. Free abrasive slicing involves attaching a slurry (typically abrasive particles suspended in oil) to a steel wire moving at high speed, and the ingot is cut as the abrasive particles roll between the wire and the workpiece. Unfortunately, the environmental impact of the slurry cannot be ignored. To mitigate such effects, a wire with fixed diamond abrasive grains is sometimes used as a fixed abrasive slicing method, which requires only a water-soluble coolant (not a slurry). High-efficiency parallel slicing makes it possible to produce a large number of wafers in a single slicing procedure. Figure 1 shows a conventional wire saw tool 1, which includes a parallel wire section 3 that extends between rollers 4A to 4C and is arranged to simultaneously saw the ingot 2 into a plurality of thin sections (e.g., wafers 8A to 8G), each having a surface substantially parallel to the end face 6 of the ingot 2. During the sawing process, the wire section 3 supported by rollers 4A to 4C can be pushed downward 5 toward a holder 7 located below the ingot 2. If the end face 6 is parallel to the crystallographic c-plane of the ingot 2, and the wire region 3 saws the ingot 2 parallel to the end face 6, then each of the resulting wafers 8A to 8G will have an "on-axis" end face 6' that is parallel to the crystallographic c-plane. It is also possible to produce micro-slope wafers (also known as off-cut or "off-axis") that have end faces not parallel to the crystallographic c-plane. Micro-slope wafers with a 4-degree offcut (e.g., SiC) are often used as growth substrates for high-quality epitaxial growth of other materials (e.g., AlN and other Group III nitrides). Micro-slope wafer production can be carried out either by growing an ingot away from the c-axis (e.g., on a micro-slope species material) and sawing this ingot perpendicular to the ingot sidewall, or by starting the ingot from an on-axis species material and growing it and sawing this ingot at an angle away from the ingot sidewall perpendicular to the ingot sidewall. Wire sawing of crystalline materials has several limitations. Kerf loss, based on the width of material removed with each cut, is unavoidable in saw cutting and represents a significant loss of crystalline material. Wire saw cutting imparts relatively high stress to the wafer, resulting in non-zero bow and warp properties. Processing time for a single boule (or ingot) is very long, and events such as wire breakage can further extend processing time and lead to unwanted material loss. Chipping and cracking on the cut surface of the wafer can reduce wafer strength. At the end of the wire sawing process, debris must be removed from the resulting wafer. For silicon carbide (SiC), which possesses high wear resistance (and hardness comparable to diamond and boron nitride), wire sawing can require considerable time and resources, potentially resulting in significant manufacturing costs. SiC substrates enable the fabrication of desirable power electronics devices, radio frequency devices, and optoelectronic devices. SiC appears in many different crystalline structures called polytypes, and certain polytypes (e.g., 4H-SiC and 6H-SiC) have a hexagonal structure. Figure 2 is an oblique crystal plane view showing the coordinate system for hexagonal crystals such as 4H-SiC, where the c-plane (the (0001) plane, corresponding to the [0001] (perpendicular) direction of epitaxial crystal growth) is perpendicular to both the m-plane ((1-100) plane) and the a-plane ((11-20) plane), the (1-100) plane is perpendicular