Methods for depositing, releasing and packaging micro-electromechanical devices on wafer substrates
A method for forming a MEMS device is disclosed, where a final release step is performed just prior to a wafer bonding step to protect the MEMS device from contamination, physical contact, or other deleterious external events. Without additional changes to the MEMS structure between release and wafer bonding and singulation, except for an optional stiction treatment, the MEMS device is best protected and overall process flow is improved. The method is applicable to the production of any MEMS device and is particularly beneficial in the making of fragile micromirrors.
1 . A spatial light modulator comprising:
a lower semiconductor substrate comprising circuitry and electrodes;
an upper transparent substrate bonded in spaced apart relationship to the semiconductor substrate;
a spacer layer between the semiconductor and transparent substrates for holding the semiconductor and transparent substrates bonded together in spaced apart relation and defining a gap between the semiconductor substrate and the transparent substrate;
an array of reflective micromirrors disposed within the gap;
a light blocking rectangular mask disposed as a frame around the micromirrors;
wherein the micromirrors comprise substantially square micromirror plates and torsion hinges that allow the micromirror plates to move relative to the upper and lower substrates; and
wherein an edge of the transparent wafer is bonded offset from an edge of the semiconductor substrate such that a bond pad area is exposed on a top surface of the semiconductor substrate.
2 . The spatial light modulator of claim 1 , wherein the semiconductor substrate is a silicon substrate.
3 . The spatial light modulator of claim 2 , wherein the torsion hinges have a thickness of 50 Å to 2100 Å.
4 . The spatial light modulator of claim 1 , wherein the electrodes are designed to run at 0-5 V.
5 . The spatial light modulator of claim 2 , comprising an SRAM cell at each micromirror location.
6 . The spatial light modulator of claim 1 , that has XGA resolution.
7 . The spatial light modulator of claim 2 , wherein the substrates are bonded together with an adhesive.
8 . The spatial light modulator of claim 7 , wherein the substrates are bonded together with an epoxy.
9 . The spatial light modulator of claim 5 , wherein the mirror devices comprise a stiction treatment.
10 . The spatial light modulator of claim 1 , wherein the torsion hinges are disposed in a different plane than the micromirror plates.
11 . The spatial light modulator of claim 10 , wherein the micromirrors are formed on the semiconductor substrate.
12 . The spatial light modulator of claim 11 , wherein the semiconductor substrate is a silicon substrate.
13 . The spatial light modulator of claim 1 , further comprising a getter and lubricant within the gap.
14 . The spatial light modulator of claim 13 , wherein substrates are anodic bonded together.
15 . The spatial light modulator of claim 13 , wherein the substrates are solder bonded together.
16 . The spatial light modulator of claim 13 , wherein the substrates are compression bonded together.
17 . The spatial light modulator of claim 13 , wherein the micromirrors have an anti-stiction layer.
18 . The spatial light modulator of claim 1 , wherein the gap between the upper and lower substrate is from 1 to 10 um.
19 . The spatial light modulator of claim 7 , wherein the adhesive is a UV cured adhesive.
20 . The spatial light modulator of claim 8 , wherein the epoxy is a UV cured epoxy.
21 . The spatial light modulator of claim 1 , wherein the mask is formed on an underside of the transparent substrate.
22 . The spatial light modulator of claim 21 , wherein the mask blocks visible light around a perimeter of the micromirrors.
23 . The spatial light modulator of claim 1 , wherein bond wires are connected to the bond pads on the silicon substrate.
24 . The spatial light modulator of claim 23 , wherein the micromirrors are provided in an array of between 1 and 6 million micromirrors.
25 . The spatial light modulator of claim 24 , wherein the micromirrors are disposed within a rectangular area.
26 . The spatial light modulator of claim 1 , wherein the circuitry is DRAM circuitry.
27 . The spatial light modulator of claim 1 , further comprising a getter disposed on the light transmissive substrate.
28 . The spatial light modulator of claim 1 , further comprising a lubricant within the gap which is an organic lubricant.
29 . The spatial light modulator of claim 13 , wherein the lower semiconductor substrate is held on a lower packaging substrate.
30 . The spatial light modulator of claim 29 , wherein a distance between the upper and lower substrate is from 1 to 250 microns.
31 . The spatial light modulator of claim 1 , further comprising a getter disposed within the gap.
32 . The spatial light modulator of claim 31 , wherein the getter is a moisture getter.
33 . The spatial light modulator of claim 31 , wherein the getter is a particle getter.
34 . The spatial light modulator of claim 31 , wherein the getter is a hydrogen getter.
35 . The spatial light modulator of claim 31 , wherein the getter is a metal oxide getter.
36 . The spatial light modulator of claim 31 , wherein the getter is a zeolite getter.
37 . The spatial light modulator of claim 25 , wherein the micromirrors comprise a self assembled monolayer.
38 . The spatial light modulator of claim 1 , wherein the spacer layer is one or more intermediate substrates having an internal open area defining the gap.
39 . The spatial light modulator of claim 28 , further comprising a combination getter within the gap.
40 . The spatial light modulator of claim 1 , wherein the micromirrors correspond to pixels in a direct-view or projection display.
41 . The spatial light modulator of claim 13 , wherein the number of micromirrors is from 6,000 to about 6 million.
42 . The spatial light modulator of claim 41 , wherein the transparent substrate is glass.
43 . A spatial light modulator comprising:
a lower silicon substrate comprising circuitry, electrodes and deflectable micromirrors;
a glass substrate bonded in spaced apart relationship to the lower substrate;
one or more intermediate substrates bonded between the upper and lower substrates and having an open area for defining a cavity between the silicon substrate and the glass substrate, with the micromirrors deflectable within the gap;
wherein the micromirrors comprise substantially square micromirror plates and torsion hinges that allow the micromirror plates to move relative to the upper and lower substrates;
a RAM cell at each micromirror location; and
wherein an edge of the silicon substrate is bonded offset from an edge of the glass substrate.
44 . The spatial light modulator of claim 43 , wherein the RAM cell is an SRAM cell.
45 . The spatial light modulator of claim 44 , wherein the torsion hinges having a thickness of 50 Å to 2100 Å.
46 . The spatial light modulator of claim 45 , wherein the substrates are bonded together with an epoxy.
47 . The spatial light modulator of claim 43 , further comprising a lubricant within the gap for decreasing stiction of the micromirrors.
48 . The spatial light modulator of claim 47 , further comprising a getter within the gap.
49 . The spatial light modulator of claim 46 , wherein the epoxy is a UV cure epoxy.
50 . The spatial light modulator of claim 48 , wherein the glass substrate is bonded in an offset relation to the silicon substrate.
51 . The spatial light modulator of claim 50 , wherein bond pads are exposed on the silicon substrate due to the offset bond.
52 . The spatial light modulator of claim 51 , wherein bond wires are connected to the bond pads on the silicon substrate.
53 . The spatial light modulator of claim 43 , wherein the RAM cell is a DRAM cell.
54 . The spatial light modulator of claim 52 , wherein the getter is disposed on the glass substrate.
55 . The spatial light modulator of claim 48 , wherein the getter is disposed on the silicon substrate.
56 . The spatial light modulator of claim 47 , wherein the lubricant is an organic lubricant.
57 . The spatial light modulator of claim 48 , wherein the getter is a moisture getter.
58 . The spatial light modulator of claim 48 , wherein the getter is a particle getter.
59 . The spatial light modulator of claim 55 , wherein the getter is a hydrogen getter.
60 . The spatial light modulator of claim 54 , wherein the getter is a metal oxide getter.
61 . The spatial light modulator of claim 48 , wherein the getter is a zeolite getter.
62 . The spatial light modulator of claim 43 , further comprising a getter within the gap.
63 . The spatial light modulator of claim 62 , wherein the getter is a combination getter.
64 . The spatial light modulator of claim 56 , wherein the number of micromirrors is from 6,000 to about 6 million.
65 . The spatial light modulator of claim 43 , further comprising a light blocking rectangular mask.
66 . The spatial light modulator of claim 65 , wherein the light blocking mask is provided on an underside of the glass substrate.