Undercut process with isotropic plasma etching at package level

• US 6,686,291 B1
• Filed: 05/20/1997
• Issued: 02/03/2004
• Est. Priority Date: 05/24/1996
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Hortaleza, Edgardo R.
• Primary Examiner(s): KUNEMUND, ROBERT M
• Application Number:
  US08/859,407
• Time in Patent Office: 2,450 Days
• Field of Search: 438/51, 438/57, 438/67, 438/107, 438/110, 438/50
• US Class Current: 438/710
• CPC Class Codes: B81B 2201/042 Micromirrors, not used as optical switches
• CPC Class Codes: B81C 1/00896 Temporary protection during separation into individual elements
• CPC Class Codes: B81C 2203/0109 Bonding an individual cap on the substrate
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means

Abstract

A method (30) of fabricating a micromechanical device (10) by performing spacer layer undercutting (46) and passivation at the package level. A back-end assembly process utilizes a full-cut saw process to separate the partially fabricated micromechanical devices. The individual die are then attached by pick and place equipment to a lead frame and are wire bonded, before the die are undercut. This technique avoids the generation of any particles from becoming lodged under movable structure during the cut process, and further, reduces the susceptibility of the die to damage or particles generated during the pick and place process.

Claims

1. A method of fabricating a micromechanical device, comprising the steps of:

a) processing a wafer to form a plurality of partially fabricated devices, the devices having a micromechanical structure defined upon a first layer;

b) subdividing the wafer to separate the partially fabricated devices;

c) mounting the separated partially fabricated devices on a package with the first layer still in place;

d) undercutting the first layer from the mounted partially fabricated devices to free the micromechanical structure for movement; and

e) attaching a lid to the package.

2. The method as specified in claim 1 wherein step d) is performed by a plasma etch process.

3. The method as specified in claim 1 wherein the micromechanical structure comprises a beam and a hinge, the hinge supporting the beam above a well created after undercutting the first layer in step d).

4. The method as specified in claim 1 comprising the step of utilizing photoresist as the first layer.

5. The method as specified in claim 1 further comprising the step of performing a wire bond between the package and the mounted partially fabricated device before step d).

6. The method as specified in claim 1 further comprising the step of passivating the partially fabricated devices after step d) and before step e).