High speed, laser-based marking method and system for producing machine readable marks on workpieces and semiconductor devices with reduced subsurface damage produced thereby

• US 20040060910A1
• Filed: 05/15/2003
• Published: 04/01/2004
• Est. Priority Date: 05/17/2002
• Status: Active Grant

• Current Assignee: Electro Scientific Industries Incorporated (MKS Instruments Incorporated)
• Original Assignee: GSI Group Corporation (Novanta Inc.)
• Inventors: Schramm, Rainer
• Granted Patent: US 7,067,763 B2
• Time in Patent Office: Days
• US Class Current: 219/121.69
• CPC Class Codes: B23K 2101/007 Marks, e.g. trade marks
• CPC Class Codes: B23K 2101/40 Semiconductor devices
• CPC Class Codes: B23K 2103/50 Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
• CPC Class Codes: B23K 26/04 Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
• CPC Class Codes: B23K 26/042 Automatically aligning the laser beam
• CPC Class Codes: B23K 26/043 along the beam path, i.e. alignment of laser beam axis relative to laser beam apparatus
• CPC Class Codes: B23K 26/0853 Devices involving movement of the workpiece in at least in two axial directions, e.g. in a plane
• CPC Class Codes: B23K 26/361 for deburring or mechanical trimming B23K26/351 takes precedence
• CPC Class Codes: B23K 26/40 taking account of the properties of the material involved
• CPC Class Codes: B23K 26/705 Beam measuring device
• CPC Class Codes: G06K 1/126 by photographic or thermographic registration recording apparatus for measuring instruments G01D15/00
• CPC Class Codes: H01C 17/242 by laser trimming by laser in general B23K26/351
• CPC Class Codes: H01L 21/67282 Marking devices
• CPC Class Codes: H01L 21/681 using optical controlling means
• CPC Class Codes: H01L 2223/5442 comprising non digital, non alphanumeric information, e.g. symbols
• CPC Class Codes: H01L 2223/54453 for use prior to dicing
• CPC Class Codes: H01L 2223/54473 for use after dicing
• CPC Class Codes: H01L 2223/5448 Located on chip prior to dicing and remaining on chip after dicing
• CPC Class Codes: H01L 23/544 Marks applied to semiconductor devices or parts, e.g. registration marks, alignment structures, wafer maps test patterns for characterising or monitoring manufacturing processes H01L22/00
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 : Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Abstract

An improved method of laser marking semiconductor wafers is provided wherein undesirable subsurface damage to a silicon semiconductor wafer is avoided while providing a relative improvement in marking speed for a predetermined spot diameter. A laser pulse of a laser beam has a predetermined wavelength, pulse width, repetition rate, and energy. The method further includes irradiating a semiconductor wafer with the pulsed laser beam over a spot diameter to produce a machine readable mark on the semiconductor wafer. The mark has a mark depth. The pulse width is less than about 50 ns, and the step of irradiating irradiates over the spot diameter to produce a mark having a mark depth substantially less than about 10 microns.

Claims

1. A method of laser marking semiconductor wafers comprising:

generating a pulsed laser beam, the beam having a laser pulse with a wavelength, pulse width, repetition rate, and energy; and

irradiating a semiconductor wafer with the pulsed laser beam over a spot diameter to produce a machine readable mark on the semiconductor wafer, the mark having a mark depth, wherein the pulse width is less than about 50 ns, and wherein the step of irradiating irradiates over the spot diameter to produce a mark having a mark depth substantially less than about 10 microns wherein undesirable subsurface damage to a semiconductor wafer is avoided.

2. The method of claim 1 wherein the mark depth is in the range of about 3-4.5 microns.

3. The method of claim 1 wherein pulse energy incident on the surface is in a range of about 230-250 microjoules, the pulse width is in a range of about 10-15 nanoseconds, and the repetition rate is in a range of about 15-30 KHz.

4. The method of claim 1 wherein the step of irradiating is carried out at a plurality of locations and wherein the spot diameter is in a range of about 25-40 microns and the marking speed is at least 150 mm/sec.

5. The method of claim 1 wherein the step of irradiating is carried out at a plurality of locations and wherein the spot diameter is in a range of about 30-35 microns and the marking speed is at least 150 mm/sec.

6. The method of claim 1 wherein the spot diameter is in a range of about 25-40 microns and a marking field size is in a range of about 75-100 mm.

7. The method of claim 1 wherein the semiconductor wafer comprises a silicon wafer and wherein the step of generating is carried out using a frequency doubled Nd:

YVO₄ laser having a green output wavelength.

8. The method of claim 1 wherein the laser repetition rate is at least 10 KHz.

9. The method of claim 1 wherein the laser repetition rate is at least 15 KHz.

10. The method of claim 1 wherein the undesirable subsurface damage includes microcracking.

11. A pulsed laser system including a laser for carrying out the method of claim 1.

12. The system of claim 11 wherein the laser is a Nd:

YVO₄ frequency doubled laser having a green output wavelength.

14. A semiconductor device having a machine readable mark with a depth of about 3-4.5 microns produced by the method of claim 1.

13. A semiconductor device having a machine readable mark with a depth of about 3-4.5 microns.