# US 10,319,593 B2 · Wafer thinning method

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- Number: US 10,319,593 B2
- Document ID: US10319593B2
- Status: Granted
- Kind: B2
- Application number: 15/209,292
- Filed: 2016-07-13
- Published: 2017-01-26
- Granted: 2019-06-11
- Earliest claimed: 2015-07-21
- Assignees: Disco Corporation
- Applicants: Disco Corporation
- Inventors: Kazuya Hirata; Yoko Nishino; Hiroshi Morikazu; Karl Priewasser
- Web page: https://patentgrep.com/patent/US10319593B2

## 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}
- 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
- 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 an annular groove forming step of forming an annular groove on the second surface of the SiC substrate in an annular area corresponding to the boundary between a device area and a peripheral marginal area in the condition where a thickness corresponding to the finished thickness of the wafer after thinning is left, and a separation start point forming step of applying the laser beam to the second surface as relatively moving a focal point and the SiC substrate to thereby form a modified layer and cracks inside the SiC substrate at the predetermined depth.

## Claims

### Claim 1

A wafer thinning method for thinning a wafer to a finished thickness 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, said first surface of said SiC substrate having a device area where a plurality of devices are formed and a peripheral marginal area surrounding said device area, said wafer thinning 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 first surface of said SiC substrate having a device area where a plurality of devices are formed and a peripheral marginal area surrounding said device area;
an annular groove forming step of forming an annular groove on said second surface of said SiC substrate in an annular area corresponding to the boundary between said device area and said peripheral marginal area in a condition where a thickness corresponding to the finished thickness is left;
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 in a central area surrounded by said annular groove at a predetermined depth from said second surface, which depth corresponds to the finished thickness, 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 inside said SiC substrate at said predetermined depth in said central area 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 at said separation start point into a first wafer of the finished thickness and having said first surface of said SiC substrate and a second wafer having said second surface of said SiC substrate, and wherein a ring-shaped reinforcing portion is formed on a back side of said first wafer in a peripheral area corresponding to said peripheral marginal area;
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 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 the back side of said first wafer having said first surface except said ring-shaped reinforcing portion after performing said wafer thinning step, thereby flattening the back side of said first wafer except said ring-shaped reinforcing portion.

### 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.