# US 5,698,474 A · High speed diamond-based machining of silicon semiconductor die in wafer and packaged form for backside emission microscope detection

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- Number: US 5,698,474 A
- Document ID: US5698474A
- Status: Granted
- Kind: A
- Application number: 08/606,638
- Filed: 1996-02-26
- Granted: 1997-12-16
- Earliest claimed: 1996-02-26
- Assignees: Hypervision, Inc.
- Inventors: Daniel T. Hurley
- Web page: https://patentgrep.com/patent/US5698474A

## CPC

- G01N 21/66: electrically excited, e.g. electroluminescence
- G01N 1/32: Polishing; Etching
- H10P 52/00: Grinding, lapping or polishing of wafers, substrates or parts of devices
- Y10S 148/135: Removal of substrate
- Y10S 438/977: Thinning or removal of substrate
- Y10T 408/03: Processes
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

Emission microscopy testing of semiconductor integrated circuits is accomplished from the back side of a packaged die or a wafer but selectively milling the back surface using high speed (e.g., 40,000-60,000 rpm) milling tool having a 150 grit 0.125 inch diameter laterally translated at 3 inches per minute and taking cuts up to approximately 0.00025 inch (6 microns). In milling a packaged die, a trench is first milled in the molding material holding the die in the package and surrounding the die so that the tool can momentarily pause to switch directions off the die face. The die or wafer can be thinned to less than 200 microns for the emission microscopy testing.

## Claims

### Claim 1

A method of machining a back surface of a semiconductor chip to permit backside emission microscopy of an integrated circuit in a front surface of the chip, said chip affixed by molding material in a package, comprising the steps of
a) mounting said package in a milling machine which permits movement of the package along three axes,
b) milling molding material of said package using a rotary tool operated at a first rotary speed thereby removing molding material over the back surface and forming a trench in the molding material around the semiconductor chip, and
c) milling semiconductor material from the back surface of the semiconductor chip using a rotary tool operating at a second rotary speed on the order of 60,000 rpm or greater.

### Claim 2 (depends on 1)

The method as defined by claim 1 and further including the step of
d) examining said semiconductor chip by backside emission microscopy.

### Claim 3 (depends on 1)

The method as defined by claim 1 and further including before step c) the step of milling a lead frame die paddle on the back surface using a rotary tool operating at a speed on the order of 60,000 rpm.

### Claim 4 (depends on 3)

The method as defined by claim 3 and further including the steps of
d) removing swirl marks on the back surface after step c), and
e) polishing the back surface with a polish paste.

### Claim 5 (depends on 4)

The method as defined by claim 4 wherein step c) is completed when the semiconductor chip thickness is reduced to 200 microns or less.

### Claim 6 (depends on 5)

The method as defined by claim 5 wherein step b) uses 0.005 inch cuts, the step of milling a lead frame paddle uses a 150 grit 0.125.diameter diamond end mill grinding tool traveling at 3 inches per minutes and taking 0.00025 inch each pass over the paddle, step c) uses 150 grit diamond, step d) uses 400 grit diamond end mill of 0.125 inch diameter traveling at 3 inches per minute and taking 0.0001 inch cuts in depth, and step e) uses 1 micron diamond paste with a buffing wheel at 2,400 rpm.

### Claim 7 (depends on 6)

The method as defined by claim 6 and further including the step of
f) examining said semiconductor chip by backside emission microscopy.

### Claim 8 (depends on 6)

The method as defined by claim 6 wherein step e) further uses 0.1 micron diamond paste and then 0.05 micron diamond paste.

### Claim 9 (depends on 1)

The method as defined by claim 1 and further including before step c) the step of milling a lead frame die paddle on the back surface using a rotary tool operating at a speed on the order of 60,000 rpm.

### Claim 10 (depends on 9)

The method as defined by claim 9 and further including the steps of
d) removing swirl marks on the back surface after step c), and
e) polishing the back surface with a polish paste.

### Claim 11 (depends on 10)

The method as defined by claim 10 wherein step c) is completed when the semiconductor chip thickness is reduced to 200 microns or less.

### Claim 12

A method of selectively thinning individual die from the back surface of a semiconductor wafer having integrated circuits formed in a front surface thereby maintaining structural integrity of the wafer for backside microprobing in an unsupported environment as required for backside emission microscopy of a die comprising the steps of:
a) mounting said wafer in a milling machine which permits movement of the wafer along three axes,
b) milling semiconductor from the back surface of said wafer opposite from an integrated circuit in the front surface using a rotary tool operating at a rotary speed on the order of at least 60,000 revolutions per minute (rpm) until said back surface is thinned to 200 microns or less, the thinning being restricted to a single integrated circuit thereby maintaining structural integrity of the wafer.

### Claim 13 (depends on 12)

The method as defined by claim 12 wherein step b) uses a 150 grit diamond 0.125 inch diameter diamond end mill grinding tool traveling at 3 inches per minute and taking 0.00025 inch of silicon each pass over the wafer in the presence of a constant flow of coolant.

### Claim 14 (depends on 13)

The method as defined by claim 13 and further including the steps of
c) removing swirl marks on the back surface after step b), and
d) polishing the back surface with a polish paste.

### Claim 15 (depends on 14)

The method as defined by claim 14 wherein step c) uses 400 grit diamond end mill of 0.125 inch diameter traveling at 3 inches per minute and taking 0.0001 inch cuts in depth, and step d) uses 1 micron diamond paste with a buffing wheel at 2,400 rpm.

### Claim 16 (depends on 15)

The method as defined by claim 15 wherein step d) further uses 0.1 micron diamond paste and then 0.05 micron diamond paste.