Method for separating sapphire wafer into chips using dry-etching

1. A method for separating a sapphire wafer serving as a substrate, on which semiconductor elements are formed, into unit chips, comprising the steps of:

(a) grinding a rear surface of the sapphire wafer so that the sapphire wafer has a designated thickness;

(b) lapping the rear surface of the ground sapphire wafer so that the sapphire wafer has a designated thickness;

(c) dry-etching the rear surface of the lapped sapphire wafer so that the sapphire wafer has a uniform thickness; and

(d) scribing the rear surface of the dry-etched sapphire wafer;

wherein said dry-etching is performed after said lapping without a polishing process between said lapping and said dry-etching.

2. The method as set forth in claim 1 , wherein the step (c) is performed by an RIE (Reactive Ion Etching) method.

3. The method as set forth in claim 1 , wherein the step (c) is performed for 50 seconds or more.

4. The method as set forth in claim 1 , wherein the sapphire wafer is dry-etched by 800 Å or more in the step (c).

5. The method as set forth in claim 1 , wherein an RF bias voltage of at most 26 W is imposed on the sapphire wafer in the step (c).

6. A method of separating a sapphire wafer, on which semiconductor elements are formed, into unit chips, said method comprising the steps of:

(a) grinding a rear surface of the sapphire wafer so that the sapphire wafer has a first designated thickness;

(b) lapping the rear surface of the ground sapphire wafer so that the sapphire wafer has a second designated thickness smaller than the first designated thickness;

(c) dry-etching the rear surface of the lapped sapphire wafer so that the sapphire wafer has a uniform thickness and a processing stress of the rear surface of the dry-etched sapphire wafer is maintained at a designated level; and

(d) scribing the rear surface of the dry-etched sapphire wafer;

wherein said dry-etching is performed after said lapping without a polishing process between said lapping and said dry-etching.

7. The method as set forth in claim 6 , wherein step (c) is performed by an RIE (Reactive Ion Etching) method.

8. The method as set forth in claim 6 , wherein step (c) is performed for 50 seconds or more.

9. The method as set forth in claim 6 , wherein the sapphire wafer is dry-etched by 800 Å or more in step (c).

10. The method as set forth in claim 6 , wherein an RF bias voltage of at most 26 W is imposed on the sapphire wafer in step (c).

11. The method as set forth in claim 6 , wherein the processing stress of the rear surface of the dry-etched sapphire wafer is higher than a processing stress obtainable by a polishing process, thereby facilitating cutting of said rear surface of the dry-etched sapphire wafer with a diamond tip in said scribing step.

12. The method as set forth in claim 11 , wherein

after said lapping, the rear surface of said lapped sapphire wafer includes at least one scratch; and

said dry-etching is performed to reduce a depth of said at least one scratch, without completely removing said at least one scratch.

13. The method as set forth in claim 12 , wherein

after said lapping, the rear surface of said lapped sapphire wafer includes at least one scratch; and

said dry-etching is performed to change said at least one scratch to a shallower scratch having a blunter shape, without completely removing said at least one scratch.

14. A method of separating a sapphire wafer, on which semiconductor elements are formed, into unit chips, said method comprising the steps of:

(a) grinding a rear surface of the sapphire wafer so that the sapphire wafer has a first designated thickness;

(b) lapping the rear surface of the ground sapphire wafer so that the sapphire wafer has a second designated thickness smaller than the first designated thickness;

(c) dry-etching the rear surface of the lapped sapphire wafer so that the sapphire wafer has a uniform thickness and a processing stress of the rear surface of the dry-etched sapphire wafer is maintained at a designated level; and

(d) scribing the rear surface of the dry-etched sapphire wafer with a diamond tip;

wherein

said dry-etching is performed after said lapping without a polishing process between said lapping and said dry-etching;

after said lapping, the rear surface of said lapped sapphire wafer includes at least one scratch; and

said dry-etching is performed to reduce a depth of said at least one scratch, without completely removing said at least one scratch, thereby maintaining a processing stress of the rear surface of the dry-etched sapphire wafer at a sufficiently high level that facilitates cutting of said rear surface of the dry-etched sapphire wafer with the diamond tip in said scribing step.

15. The method as set forth in claim 14 , wherein said dry-etching is performed to change said at least one scratch to a shallower scratch having a blunter shape, without completely removing said at least one scratch.

16. The method as set forth in claim 14 , wherein said lapping comprises using a diamond slurry having a particle size of 6 μm.

17. The method as set forth in claim 16 , wherein a processing stress of the rear surface of the dry-etched sapphire wafer is higher than a processing stress obtainable by a polishing process using a particle size of 3 μm, thereby facilitating cutting of said rear surface of the dry-etched sapphire wafer with a diamond tip in said scribing step.

18. A method of separating a sapphire wafer, on which semiconductor elements are formed, into unit chips, said method comprising the steps of:

(a) grinding a rear surface of the sapphire wafer so that the sapphire wafer has a first designated thickness;

(b) lapping the rear surface of the ground sapphire wafer so that the sapphire wafer has a second designated thickness smaller than the first designated thickness;

(c) dry-etching the rear surface of the lapped sapphire wafer so that the sapphire wafer has a uniform thickness and a processing stress of the rear surface of the dry-etched sapphire wafer is maintained at a designated level; and

(d) scribing the rear surface of the dry-etched sapphire wafer;

wherein the processing stress of the rear surface of the dry-etched sapphire wafer is higher than a processing stress obtainable by a polishing process, thereby facilitating cutting of said rear surface of the dry-etched sapphire wafer with a diamond tip in said scribing step.

19. The method as set forth in claim 18 , wherein

after said lapping, the rear surface of said lapped sapphire wafer includes at least one scratch; and

said dry-etching is performed to reduce a depth of said at least one scratch, without completely removing said at least one scratch.

20. The method as set forth in claim 19 , wherein

after said lapping, the rear surface of said lapped sapphire wafer includes at least one scratch; and

said dry-etching is performed to change said at least one scratch to a shallower scratch having a blunter shape, without completely removing said at least one scratch.