Apparatus and method of wafer bonding using compatible alloy

• US 7,943,411 B2
• Filed: 05/04/2009
• Issued: 05/17/2011
• Est. Priority Date: 09/10/2008
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Martin, John R., Tsau, Christine H., Frey, Timothy J.
• Primary Examiner(s): Luu; Chuong A.
• Application Number:
  US12/434,772
• Publication Number:
  US 20100059835A1
• Time in Patent Office: 743 Days
• Field of Search: 438/50, 438/51, 438/52, 438/53, 438/455, 438/406
• US Class Current: 438/50
• CPC Class Codes: B81C 1/00269 Bonding of solid lids or wafers to the substrate
• CPC Class Codes: B81C 2203/0118 Bonding a wafer on the substrate, i.e. where the cap consists of another wafer
• CPC Class Codes: H01L 23/10 characterised by the material or arrangement of seals between parts, e.g. between cap and base of the container or between leads and walls of the container
• 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
• CPC Class Codes: H01L 2924/01079 Gold [Au]

Abstract

A method of forming an inertial sensor provides 1) a device wafer with a two-dimensional array of inertial sensors and 2) a second wafer, and deposits an alloy of aluminum/germanium onto one or both of the wafers. The alloy is deposited and patterned to form a plurality of closed loops. The method then aligns the device wafer and the second wafer, and then positions the alloy between the wafers. Next, the method melts the alloy, and then solidifies the alloy to form a plurality of conductive hermetic seal rings about the plurality of the inertial sensors. The seal rings bond the device wafer to the second wafer. Finally, the method dices the wafers to form a plurality of individual, hermetically sealed inertial sensors.

Claims

1. A method of bonding a MEMS device wafer to a second wafer, the method comprising:

forming an aluminum layer on the MEMS device wafer;

forming a germanium layer on the second wafer;

bringing the aluminum layer on the device wafer into contact with the germanium layer on the second wafer;

heating the aluminum layer and the germanium layer,

heating at least in part causing the aluminum layer and germanium layer to form a eutectic material, heating being initiated either before or after the aluminum layer is in contact with the germanium layer; and

cooling the wafers to form a plurality of hermetic seal rings between the wafers,

wherein at least one of the seal rings has varying concentrations of aluminum, germanium, or aluminum/germanium eutectic, the region of the seal ring adjacent to the device wafer having a higher concentration of aluminum than the region of the seal ring adjacent to the second wafer, the region of the seal ring adjacent to the second wafer having a higher concentration of germanium than the region of the seal ring adjacent to the device wafer.

2. The method as defined by claim 1 wherein forming an aluminum layer comprises using sputter deposition processes to form the aluminum layer on the device wafer.

3. The method as defined by claim 1 wherein forming a germanium layer comprises using sputter deposition processes to form the germanium layer on the second wafer.

4. The method as defined by claim 1 wherein the device wafer comprises a two dimensional array of MEMS inertial sensors, the second wafer comprising a corresponding two-dimensional array of caps.

5. The method as defined by claim 1 wherein heating comprises heating to between about 349 and 424 degrees C.

6. The method as defined by claim 1 wherein heating comprises heating to between about 424 and 499 degrees C.