# US 10,319,594 B2 · Wafer thinning method

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- Number: US 10,319,594 B2
- Document ID: US10319594B2
- Status: Granted
- Kind: B2
- Application number: 15/212,513
- Filed: 2016-07-18
- Published: 2017-01-26
- Granted: 2019-06-11
- Earliest claimed: 2015-07-21
- Assignees: Disco Corporation
- Applicants: Disco Corporation
- Inventors: Kazuya Hirata
- Web page: https://patentgrep.com/patent/US10319594B2

## CPC

- H10P 50/00: Etching of wafers, substrates or parts of devices
- B23K 26/0006: {taking account of the properties of the material involved (B23K26/32, B23K26/40 take precedence)}
- B23K 26/032: {using optical means}
- B23K 26/0622: by shaping pulses
- B23K 26/0823: {Devices involving rotation of the workpiece}
- B23K 26/0853: {Devices involving movement of the workpiece in at least two axial directions, e.g. in a plane}
- B23K 26/53: for modifying or reforming the material inside the workpiece, e.g. for producing break initiation cracks
- B23K 26/60: Preliminary treatment
- B23K 26/702: {Auxiliary equipment}
- B24B 7/228: {for grinding thin, brittle parts, e.g. semiconductors, wafers (grinding edges of thin, brittle parts B24B9/065)}
- B28D 5/0011: {with preliminary treatment, e.g. weakening by scoring}
- H10D 62/8325: {Silicon carbide}
- H10P 34/42: with electromagnetic radiation, e.g. laser annealing (laser cutting H10P54/20)
- H10P 52/00: Grinding, lapping or polishing of wafers, substrates or parts of devices
- H10P 72/7402: {Wafer tapes, e.g. grinding or dicing support tapes}
- B23K 2101/40: Semiconductor devices
- B23K 2103/50: {Inorganic materials other than metals or composite materials}
- B23K 2103/56: {being semiconducting}
- H10P 72/0428: {Apparatus for mechanical treatment or grinding or cutting}
- H10P 72/7416: {used during dicing or grinding}
- H10P 72/7422: {used to protect an active side of a device or wafer}
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
- B23K: SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B24B: MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING (grinding of gear teeth B23F, of screw-threads B23G1/36; by electro-erosion B23H; abrasive or related blasting B24C; tools for grinding, buffing or sharpening B24D; polishing compositions C09G1/00; abrasives C09K3/14; electrolytic etching or polishing C25F3/00; grinding arrangements for use on assembled railway tracks E01B31/17); DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B28D: WORKING STONE OR STONE-LIKE MATERIALS
- H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES

## Abstract

Disclosed herein is a wafer thinning method for thinning a wafer formed from an SiC substrate having a first surface and a second surface opposite to the first surface. The wafer thinning method includes a separation start point forming step of applying the laser beam to the second surface as relatively moving the focal point and the SiC substrate to thereby form a modified layer parallel to the first surface and cracks inside the SiC substrate at the predetermined depth, thus forming a separation start point, and a wafer thinning step of applying an external force to the wafer, thereby separating the wafer into a first wafer having the first surface of the SiC substrate and a second wafer having the second surface of the SiC substrate at the separation start point.

## Claims

### Claim 1

A wafer thinning method for thinning a wafer to a predetermined thickness, the method comprising:
providing a wafer formed from an SiC substrate having a first surface, a second surface opposite to said first surface, a c-axis extending from said first surface to said second surface, and a c-plane perpendicular to said c-axis, where said c-plane is set in the SiC substrate at the molecular level, where said c-axis is inclined by an off angle with respect to a normal to said first surface, where said c-axis and said normal to the first surface intersect each other, and thereby said c-plane is inclined by said off angle with respect to the first surface, and said wafer having a plurality of devices formed on said first surface of said SiC substrate;
a separation start point forming step of setting the focal point of a laser beam having a transmission wavelength to said SiC substrate inside said SiC substrate at a predetermined depth from said second surface, which depth corresponds to a vertical position near said first surface of said SiC substrate, and next applying said laser beam to said second surface while relatively moving said focal point and said SiC substrate to thereby form a modified layer parallel to said first surface inside said SiC substrate at said predetermined depth and also form cracks extending from said modified layer along said c-plane, thus forming a separation start point; and
a wafer thinning step of applying an external force to said wafer after performing said separation start point forming step, thereby separating said wafer into a first wafer, of the predetermined thickness, having said first surface of said SiC substrate and a second wafer having said second surface of said SiC substrate at said separation start point;
said separation start point forming step including:
a modified layer forming step of relatively moving the focal point of said laser beam in a first direction, where the first direction is perpendicular to a second direction, and further wherein said second direction is defined as a direction parallel to a line connecting a point where said c-axis intersects said first surface to a point where said normal intersects said first surface, thereby linearly forming said modified layer extending in said first direction, and
an indexing step of relatively moving said focal point in said second direction to thereby index said focal point by a predetermined amount.

### Claim 2 (depends on 1)

The wafer thinning method according to claim 1, further comprising:
a grinding step of grinding a back side of said first wafer having said first surface on which the plural devices are formed after performing said wafer thinning step, thereby flattening the back side of said first wafer.

### Claim 3 (depends on 1)

The wafer thinning method according to claim 1, wherein said external force of said wafer thinning step comprises applying a torsional stress to said wafer.

### Claim 4 (depends on 2)

The wafer thinning method according to claim 2, wherein said external force of said wafer thinning step comprises applying a torsional stress to said wafer.