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 7,067,763 B2
• Filed: 05/15/2003
• Issued: 06/27/2006
• 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
• Primary Examiner(s): ELVE, MARIA ALEXANDRA
• Application Number:
  US10/438,501
• Publication Number:
  US 20040060910A1
• Time in Patent Office: 1,139 Days
• Field of Search: 219/121.6, 219/121.67, 219/121.68, 219/121.69, 219/121.85, 219/121.11, 219/121.66
• 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 a semiconductor wafer during at least one step of a semiconductor manufacturing process, the wafer having a first side with circuit features, and a second side having a rough wafer surface portion to be marked, the method comprising:

generating a q-switched laser output for wafer marking, the output comprising an output wavelength less than an absorption edge of the semiconductor wafer material, a laser output power of at least about 3W at the wavelength, a plurality of pulses, each pulse having a pulse width less than about 50 ns, at least one pulse having a pulse width in the range of about 10–

15 ns, the temporal spacing between at least some consecutive pulses of the plurality of pulses corresponding to a repetition rate of at least 15 Khz; and

irradiating the semiconductor wafer with the output over at least one spot having a diameter in the range of less than about 60 microns to produce a shallow mark having sufficient contrast for machine readability, whereby the at least one pulse irradiates at least about 10⁸ W/cm² over the diameter while avoiding undesirable subsurface damage to the semiconductor wafer.

2. The method of claim 1 wherein the diameter is in the range of about 25–

40 microns.

3. The method of claim 1 wherein the energy of the at least one pulse is in the range of about 230–

250 microjoules, whereby the at least one pulse irradiates at least 10⁹ W/cm² over the at least one spot diameter.

4. The method of claim 1 wherein the laser output power is at least about 5 W at the wavelength.

5. The method of claim 1 wherein the output wavelength is a green wavelength.

6. 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.

7. The method of claim 1 wherein the at least one spot diameter is adjustable.