Dendritic material sacrificial layer micro-scale gap...

Details Dendritic material sacrificial layer micro-scale gap... Dendritic material sacrificial layer micro-scale gap...

2000-01-14

2001-06-19

Fourson, George (Department: 2823)

Semiconductor device manufacturing: process

Chemical etching

Combined with coating step

C216S011000, C216S039000, C438S763000, C438S759000

Reexamination Certificate

active

06248668

ABSTRACT:

FIELD OF THE INVENTION
The present invention concerns micromechanical systems (MEMS) and microelectronics.
BACKGROUND OF THE INVENTION
MEMS have many applications including micro optical components, such as Fresnel lenses, optical gratings and corner cube reflectors. The structures are usually fabricated on a silicon substrate. Microelectronics encompass an even broader range of devices. In the field of microelectronics, micro-scale gaps are sometimes required for insulation between two materials.
Some MEMS require a microstructure, typically formed of polysilicon or nickel, to extend suspended, free standing in space, from another portion of the MEMS device. This is achieved in microfabrication by forming the microstructure around a sacrificial layer, which is later removed to release the microstructure. Conventionally, the selective release of a suspended microstructure is accomplished by a wet etch process to remove the sacrificial layer.
Wet etch release has the drawback of stiction, where the liquids used in etching cause adhesion between the suspended microstructure and other portions of the MEMS being fabricated. The stiction results from process induced capillary action. Often, the small microstructure possesses insufficient restoring forces to overcome the adhesion and the result is a useless device. Artisans have sought to overcome stiction in the wet etch process. Techniques have been developed with the use of diffusion etch holes and without, but such techniques slow the etch process and still suffer problems, though reduced, from stiction.
Hui et al, developed a dry release process described in “Carbonized Parylene as a Conformal Sacrificial Layer”, Proceedings from the Solid State Sensor and Actuator Workshop, Hilton Head Island, S.C., Jun. 6-11, 1998. This technique, being a dry release, avoids problems of stiction altogether. However, this technique embodies careful handling requirements and a limited process window. Specifically, the technique requires deposition of an adhesion layer, a flow prevention hardening step in a CHF
3
and He plasma, a pre-bake in N
3
, a carbonization step at 700° C.-1000° C. for an hour, and an oxidation step at 700° C. for an hour.
Accordingly, there is a need for an improved suspended microstructure release process which addresses some or all of the aforementioned problems. Applications requiring micro-scale gaps similar to those between a suspended microstructure and an opposing surface would similarly benefit from such a process. These needs are met by the present dendritic sacrificial layer dry release micro-scale gap formation method.
SUMMARY OF THE INVENTION
That and other needs are met or exceeded by the present micro-scale gap fabrication process using a dry releasable dendritic material sacrificial layer. The dendritic sacrificial layer is removed by decomposing the dendritic material, for example, by heating it past its decomposition point. This may release a formed microstructure, or create a gap between materials. The sacrificial layer may be applied to a wafer, for example, by spin coating a solution including the dissolved dendritic material. The sacrificial layer, after being formed, may be patterned and prepared for accepting structural material for the microstructure. After a desired microstructure or microstructures are formed around the sacrificial layer, the layer is dry releasable by heating or other dry decomposition technique.
In a preferred embodiment, a sacrificial layer of dendritic material is formed on a wafer. A mask pattern is then formed on the sacrificial layer and the sacrificial layer is patterned according to the mask, after which, the mask is removed. A photoresist layer is then formed in a pattern on the wafer. The photoresist layer permits a particularly configured microstructure to be formed, and the sacrificial layer is then dry released.


REFERENCES:
patent: 4371406 (1983-02-01), Li
E.E. Hui, C.G. Keller, R.T. Howe, “Carbonized Parylene as a Conformal Sacrificial Layer”, presented at Solid-State Sensor and Actuator Workshop, Hilton Head Island, South Carolina, Jun. 8-11, 1998, pp. 256-260.

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