Method for hermetically encapsulating microsystems in situ

• US 20010004085A1
• Filed: 11/30/2000
• Published: 06/21/2001
• Est. Priority Date: 12/15/1999
• Status: Active Grant

• Current Assignee: The Swatch Group Research And Development Ltd (The Swatch Group AG)
• Original Assignee: Asulab SA (The Swatch Group AG)
• Inventors: Gueissaz, Fran?ccedil;ois
• Granted Patent: US 6,454,160 B2
• Time in Patent Office: Days
• US Class Current: 228/124.6
• CPC Class Codes: B81C 1/00293 maintaining a controlled atmosphere with processes not provided for in B81C1/00285
• CPC Class Codes: H01L 21/50 Assembly of semiconductor devices using processes or apparatus not provided for in a single one of the subgroups H01L21/06 - H01L21/326, e.g. sealing of a cap to a base of a container
• 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 23/315 the encapsulation having a cavity
• 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]
• CPC Class Codes: H01L 2924/09701 Low temperature co-fired ceramic [LTCC]
• CPC Class Codes: H01L 2924/16152 Cap comprising a cavity for hosting the device, e.g. U-shaped cap
• CPC Class Codes: H01L 2924/3025 Electromagnetic shielding

Abstract

The method for hermetically encapsulating microsystems in situ consists, in a first phase, of mounting on a common substrate (1), several microsystems (6) surrounded by a metal adhesion layer (4) deposited on the substrate (1). In a second phase, in a common deposition step a first metal layer (7) is deposited by electrolytic means on each microsystem (6) and on an annular zone (7a) of the adhesion layer (4) surrounding each microsystem (6), so as to completely cover each microsystem by overlap. Subsequently a second metal layer (9) is deposited by electrolytic means on the first metal layer (7) and on the adhesion layer so as to cover most of the first layer with the exception of at least one passage (10) per microsystem (6), providing access to the first layer (7). The metal of the first layer is different from the metals of the adhesion layer, the second layer and the microsystem. The first layer (7) is removed by selective chemical etching through the passages (10) which are closed to obtain metal capsules hermetically enclosing each microsystem.

Claims

1. A method for hermetically encapsulating microsystems in situ wherein, in a first phase, several microsystems are mounted on a common substrate, said microsystems being surrounded by a metal adhesion layer deposited on the substrate, the method wherein, in a second phase, in a common deposition step a first metal layer is deposited on each microsystem and on an annular zone of the adhesion layer surrounding each microsystem, so as to completely cover each microsystem by overlap, wherein a second metal layer is deposited by electrolytic means on the first metal layer and on the adhesion layer so as to cover the first layer over most of its surface leaving at least one passage per microsystem in the second layer to provide access to the first layer, the metal of the first layer being different from the metals of the adhesion layer, the second layer and the microsystem, wherein the first layer is removed by selective chemical etching through each passage of the second layer, and wherein said passages are then closed to obtain metal capsules hermetically enclosing each microsystem.

2. A method according to

claim 1

, wherein the first layer is deposited by electrolytic means.

3. A method according to

claim 1

, wherein the first layer coating each microsystem includes at least two openings each arranged between the microsystem and the corresponding passage of the second layer, and wherein the second layer extends into each of the openings as far as the adhesion layer so as to create a support pillar for the second layer between each passage and the corresponding microsystem.

4. A method according to

claim 1

, wherein said passages are formed by means of two extensions facing the first layer for each microsystem, said extensions coming out outside the second layer, the width of which does not vary between said extensions so as to create a reinforcing part at the passages.

5. A method according to

claim 1

, wherein the second layer is deposited so as to enclose the first layer with the exception of a multitude of passages of reduced dimensions arranged on the top portions of the second layer above each microsystem.

6. A method according to either of claims 3 and 5, wherein the passages arranged on the top portions of the second layer are closed by depositing a drop of solder to be solidified on each passage or by causing a wave of liquid solder to be solidified to close all said passages.

7. A method according to

claim 1

, wherein the passages are closed by heating and compressing portions of the second layer around each passage and by soldering them to the adhesion layer.

8. A method according to

claim 7

, wherein the adhesion layer includes bumps of a soldering metal arranged on a metal base layer of said adhesion layer and at the location of the passages of the second layer so as to close said passages when the portions of the second layer are thermocompressed.

9. A method according to

claim 1

, wherein the second layer rests on the soldering metal bumps of the adhesion layer distributed over the perimeter of each annular zone surrounding the corresponding microsystem, and wherein a portion of the first layer is arranged between neighbouring metal bumps to come out outside the second layer and to define several passages of the second layer per microsystem.

10. A method according to

claim 9

, wherein the passages for each microsystem are closed by heating the soldering metal bumps to cause the second layer to be lowered onto a base layer of the adhesion layer and to hermetically seal the capsules onto the microsystems.

11. A method according to

claim 10

, wherein guide elements for the capsules are secured to the adhesion layer before being coated by the first layer, said elements remaining after removal of the first layer and being used to guide the capsules vertically when the second layer is lowered to close the passages.

12. A method according to

claim 1

, wherein the metal of the first layer is copper or a copper alloy, and in that the metal of the second layer is gold or a gold alloy.

13. A method according to

claim 1

, wherein the metal base layer of the adhesion layer is made of a first metal fixing layer on the substrate made of titanium or chromium, a second metal layer made of nickel or palladium or rhodium or ruthenium or molybdenum or platinum as a diffusion barrier for the solder, and a third metal layer made of gold as oxidation protection.

14. A method according to

claim 1

, wherein a third metal layer is deposited on the second layer without closing the passages of the second layer, wherein a fourth metal layer is deposited on the third layer in order to completely enclose the third layer between the second layer and the fourth layer closing obstructing the passages of the second layer, the metal of the second layer being the same as the metal of the fourth layer, and wherein the first layer is removed by selective chemical etching through each passage.

15. A method according to

claim 1

, wherein, prior to mounting the microsystems, conductive strips for the external electric connection of each microsystem are made on the substrate, wherein an insulating layer is deposited on the median portion of the length of the strips, leaving their ends free for an electric connection, and wherein the adhesion layer is then deposited so as to pass over the insulation of the strips and structured so as to define metal paths connected to one of the ends of the conductive strips, the other end of the strips being connected to the corresponding microsystem.

16. A method according to

claim 1

, wherein, prior to mounting the microsystems, a series of conductive holes are made through an insulating part of the substrate for the external electric connection of each microsystem, and wherein metal pads are connected to the conductive holes on the surface of the substrate opposite the microsystems.

17. A method according to

claim 1

, wherein after closing the capsules, they are covered with a protective layer of resin.

18. A method according to

claim 1

, wherein after closing the metal capsules, the substrate is cut or diced in order to separate each encapsulated microsystem having metal contact pads which are accessible from the exterior.