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 method for making a spatial light modulator, comprising:
providing a first wafer;
providing a second wafer;
forming circuitry and a plurality of electrodes on or in the first wafer;
forming a plurality of deflectable elements on or in either the first or second wafer;
bonding the first and second wafers together to form a wafer assembly; and
separating the wafer assembly into individual wafer assembly dies.
2 . The method of claim 1 , wherein each die comprises an array of deflectable reflective elements.
3 . The method of claim 2 , wherein the reflective elements correspond to pixels in a direct-view or projection display.
4 . The method of claim 3 , wherein the number of reflective elements in each die is from 6,000 to about 6 million.
5 . The method of claim 1 , wherein the first wafer is an optically transmissive wafer or a wafer having one or more layers that when removed result in an optically transmissive substrate.
6 . The method of claim 5 , wherein the first wafer is glass, borosilicate, tempered glass, quartz or sapphire.
7 . The method of claim 1 , wherein the second wafer is a dielectric or semiconductor wafer.
8 . The method of claim 7 , wherein the second wafer comprises GaAs or silicon.
9 . The method of claim 1 , wherein the first and second wafers are bonded together with an adhesive.
10 . The method of claim 9 , wherein the adhesive is an epoxy.
11 . The method of claim 10 , wherein the epoxy comprises balls or rods of predetermined diameter.
12 . The method of claim 1 , wherein the wafer assembly is separated into individual dies by scribing and breaking.
13 . The method of claim 1 , wherein the wafer assembly is tested for abnormalities prior to separation into the individual dies.
14 . The method of claim 1 , further comprising providing a spacing wafer between the first and second wafers.
15 . The method of claim 1 , further comprising providing microfabricated spacers on one or both of the first and second wafers prior to bonding.
16 . The method of claim 9 , wherein the adhesive is dispensed by automated controlled liquid dispensing through a syringe.
17 . The method of claim 9 , wherein the adhesive is dispensed by screen, offset or roller printing.
18 . The method of claim 16 , wherein the syringe is moved along X-Y coordinates for dispensing.
19 . The method of claim 1 , wherein the aligning comprises registration of substrate fiducials on opposite wafers.
20 . The method of claim 19 , wherein the registration is accomplished with a video camera having lens magnification.
21 . The method of claim 7 , wherein the second wafer is a glass or quartz wafer.
22 . The method of claim 1 , wherein the bonding of the wafers comprises the dispensing of a UV or thermal cure epoxy.
23 . The method of claim 22 , wherein the bonding further comprises application of a force of 10 kg force or more.
24 . The method of claim 1 , wherein the aligning comprises aligning each deflectable element on the first wafer with at least one electrode on the second wafer.
25 . The method of claim 1 , wherein the separation of the wafer assembly comprises forming scribes on the first and second wafers.
26 . The method of claim 25 , wherein the scribes are placed in an offset relationship to each other in at least one direction.
27 . The method of claim 25 , wherein the separation further comprises breaking the wafer assembly along the scribe lines with a guillotine or fulcrum breaking machine.
28 . The method of claim 1 , wherein the separation of the wafer assembly comprises sawing partially through each wafer followed by breaking along the sawed lines.
29 . The method of claim 1 , wherein the sawing is done in the presence of a high-pressure jet of water.
30 . The method of claim 1 , wherein the bonding comprises applying a sealant near the perimeter of each array on the wafer.
31 . The method of claim 30 , further comprising applying a sealant around the perimeter of at least one of the wafers.
32 . The method of claim 1 , wherein the bonding comprises applying an adhesive and spacers, the spacers having a size of from 1 to 100 microns.
33 . The method of claim 32 , wherein the spacers have a size of from 1 to 20 microns.
34 . The method of claim 1 , wherein the plurality of deflectable elements are reflective mirror elements and are formed on the second wafer which is a light transmissive wafer, at least with any surface coating removed therefrom.
35 . The method of claim 15 , wherein the microfabricated spacers comprise an organic material.
36 . The method of claim 32 , wherein the spacers are glass or plastic spacers.
37 . The method of claim 1 , wherein the forming of the deflectable element comprises surface or bulk micromachining.
38 . The method of claim 1 , wherein the plurality of deflectable elements are formed on or in the first wafer.
39 . The method of claim 38 , wherein the circuitry and plurality of electrodes are formed prior to forming the plurality of deflectable elements, wherein the plurality of deflectable elements are formed above the plurality of electrodes on the first wafer.
40 . The method of claim 39 , wherein a plurality of light blocking masks are formed on the second wafer.
41 . The method of claim 40 , wherein when the wafer assembly is singulated into wafer assembly dies, a light blocking mask is disposed on a second wafer portion within each wafer assembly die.
42 . The method of claim 1 , wherein the plurality of deflectable elements are formed on or in the second wafer.
43 . The method of claim 42 , wherein when the first and second wafers are aligned and bonded together, the deflectable elements on the second wafer are each disposed proximate to a corresponding electrode on the first wafer.
44 . The method of claim 1 , further comprising packaging the wafer assembly dies.
45 . The method of claim 1 , wherein the deflectable elements are micromirrors having jagged or zig-zag edges.
46 . The method of claim 1 , further comprising applying a stiction reducing agent to one or both wafers before or after bonding the two wafers together, but before singulating the wafer assembly into dies.
47 . The method of claim 1 , further comprising applying a getter to one or both wafers before bonding the two wafers together into a wafer assembly.
48 . The method of claim 47 , wherein the getter is a molecular, hydrogen and/or particle getter.
49 . The method of claim 47 , wherein the getter is a particulate and moisture getter.
50 . The method of claim 47 , wherein the getter is capable of absorbing moisture.
51 . The method of claim 46 , wherein the stiction reducing agent is a silane applied to the deflectable elements.
52 . The method of claim 46 , wherein the stiction reducing agent is a chlorosilane.
53 . The method of claim 1 , further comprising aligning the wafers prior to bonding.
54 . The method of claim 53 , wherein the aligning of the wafers has an accuracy of 10 microns or less.
55 . The method of claim 54 , wherein the accuracy is 3 micron or less.
56 - 123 . (canceled)
124 . A method for making a MEMS device, comprising:
providing a wafer;
providing a plurality of substrates that are transmissive to visible light, each smaller than said wafer, each substrate having a frame portion that is not transmissive to visible light;
forming circuitry and a plurality of electrodes on or in the wafer;
forming a plurality of deflectable elements on or in the wafer;
aligning the substrates with the wafer;
bonding the substrates and wafer together to form a wafer assembly; and
separating the wafer assembly into individual wafer assembly dies.
125 . A method of forming a microstructure device, comprising:
providing a substrate having a first material, a second material, and a sacrificial material between the first and second materials, wherein said sacrificial material comprises silicon;
exposing the substrate to a vapor-phase etchant comprising XeF 2 , which removes at least a portion of the sacrificial material from between the first and second materials, to leave a surface of the first material spaced from a surface of the second material by a gap, the surface of the first material being defined as a first surface and the surface of the second material being defined as a second surface; and
exposing at least one of the first and second surfaces to vapor-phase alkylsilane-containing molecules to form a coating over at least one of the first and second surfaces.
126 . The method of claim 125 , wherein the alkylsilane-containing molecules include an alkylsilane.
127 . The method of claim 125 , wherein the first material is different from than the second material.
128 . The method of claim 126 , wherein the alkylsilane is a alkylchlorosilane.
129 . The method of claim 126 , wherein the alkylsilane is a alkyltrichlorosilane.
130 . The method of claim 126 , wherein the alkylsilane is a octyldecyltrichlorosilane.
131 . The method of claim 126 , wherein the alkylsilane is a perfluorodecyltrichlorosilane.
132 . A method of forming a microstructure device, comprising:
providing a substrate having a first material, a second material, and a sacrificial material between the first and second materials;
exposing the substrate to a vapor-phase etchant which removes at least a portion of the sacrificial material from between the first and second materials, to leave a surface of the first material spaced from a surface of the second material by a gap, the surface of the first material being defined as a first surface and the surface of the second material being defined as a second surface;
exposing said at least one of the first and second surfaces to steam; and
exposing at least one of the first and second surfaces to vapor-phase alkylsilane-containing molecules to form a coating over at least one of the first and second surfaces.