Control of stress in metal films by controlling the temperature during film deposition
View Patent ↗Materials such as titanium are vapor-deposited to form a film on a substrate while the substrate is thermally coupled to a temperature-controlling thermal source. Varying the temperature conditions of the substrate when the film is deposited varies the intrinsic stress of the film, which varies the change in substrate shape caused by the presence of the film. A film having a desired intrinsic stress may be obtained by control of the substrate temperature when the film is deposited. A stress-controlled titanium film may be used, for example, as an adhesion layer between a silicon movable structure in an optical MEMS device and a gold layer serving as a reflecting surface.
1. A method of controlling the shape of a surface comprising:
depositing a film on a substrate having a surface with an initial shape, wherein:
the depositing step includes controlling temperature of the substrate so that intrinsic stress of the film causes a predetermined change in the shape of the surface with respect to the initial shape; and
the film consists essentially of titanium and oxygen.
2. The invention of claim 1 , wherein the substrate temperature is controlled so that the intrinsic stress of the film is substantially zero whereby the film causes substantially no change in the shape of the surface with respect to the initial shape.
3. The invention of claim 1 , wherein the depositing step includes:
coupling the substrate to a thermal source adapted to control the temperature of the substrate; and
depositing titanium from a vapor onto the substrate to form a film while the substrate temperature is controlled by the thermal source.
4. The invention of claim 3 , wherein the substrate temperature during deposition of the film is controlled by the thermal source to be less th about 20° C.
5. The invention of claim 3 , further comprising depositing a second film on the titanium-containing film.
6. The invention of claim 5 , wherein the second film is a gold film.
7. The invention of claim 3 , wherein the thermal source is an active source.
8. The invention of claim 3 , wherein the thermal source is a passive source.
9. The invention of claim 1 , wherein the substrate temperature during deposition of the film is controlled so as to cause the film to have a curvature of about zero.
10. The invention of claim 1 , wherein the substrate is silicon.
11. The invention of claim 1 further comprising disposing the substrate having the deposited film adjacent an electrostatic driving structure to provide an electro-mechanical device.
12. The invention of claim 1 , further comprising:
depositing a gold layer over the film, wherein the substrate, the film, and the old layer are parts of a MEMS device; and
maintaining temperatures of the substrate, the film, and the gold layer below about 70° C. during fabrication of said MEMS device.
13. The invention of claim 1 , further comprising depositing a metal layer over the film, wherein:
the titanium provides adhesion between the surface and the metal layer; and
the oxygen controls intrinsic stress of the film to provide the predetermined change in the shape of the surface.
14. The invention of claim 13 , wherein:
the substrate comprises silicon; and
the metal layer comprises gold.
15. The invention of claim 13 , wherein the metal layer has a reflective surface.