MEMS device and method of forming MEMS device

0001The present invention relates to a MEMS device and to a method of forming a MEMS device.

0002Microelectromechanical systems or MEMS devices include micromachined substrates integrated with electronic microcircuits. Such devices may form, for example, microsensors or microactuators which operate based on, for example, electromagnetic, electrostrictive, thermoelectric, piezoelectric, or piezoresistive effects. MEMS devices have been formed on insulators or other substrates using micro-electronic techniques such as photolithography, vapor deposition, and etching.

0003An example of a MEMS device includes a micro-mirror device. The micro-mirror device can be operated as a light modulator for amplitude and/or phase modulation of incident light. One application of a micro-mirror device is in a display system. As such, multiple micro-mirror devices are arranged in an array such that each micro-mirror device provides one cell or pixel of the display.

0004A conventional micro-mirror device includes an electrostatically actuated mirror supported for rotation about an axis of the mirror. As such, rotation of the mirror about the axis may be used to modulate incident light by directing the incident light in different directions. To direct the incident light in different directions, the mirror may include a reflective surface which reflects the incident light. Unfortunately, variations in the reflective surface may lower the reflectivity of the mirror and/or produce light Interference, thereby lowering or diminishing a contrast ratio of the mirror.

0005The present invention seeks to provide an improved MEMS device.

0006According to an aspect of the present invention there is provided a method of forming a micro-mirror device as specified in claim 1.

0007According to another aspect of the present invention there is provided a micro-mirror device as specified in claim 10.

0008One embodiment provides a method of forming a MEMS device. The method includes depositing a conductive material on a substructure, forming a first sacrificial layer over the conductive material, including forming a substantially planar surface of the first sacrificial layer, and forming a first element over the substantially planar surface of the first sacrificial layer, including communicating the first element with the conductive material through the first sacrificial layer. In addition, the method includes forming a second sacrificial layer over the first element, including forming a substantially planar surface of the second sacrificial layer, forming a support through the second sacrificial layer to the first element after forming the second sacrificial layer, including filling the support, and forming a second element over the support and the substantially planar surface of the second sacrificial layer. As such, the method further includes substantially removing the first sacrificial layer and the second sacrificial layer, thereby supporting the second element relative to the first element with the support.

0009Embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which: <ul id="ul0001" list-style="none" compact="compact"><li>Figure 1 is a schematic cross-sectional view illustrating one embodiment of a portion of a micro-mirror device according to the present invention.</li><li>Figure 2 is a perspective view illustrating one embodiment of a portion of a micro-mirror device according to the present invention.</li><li>Figure 3 is a perspective view illustrating another embodiment of a portion of a micro-mirror device according to the present invention.</li><li>Figure 4 is a schematic cross-sectional view taken along line 4-4 of Figure 3 illustrating one embodiment of actuation of a micro-mirror device according to the present invention.</li><li>Figures 5A-5N illustrate one embodiment of forming a micro-mirror device according to the present invention.</li><li>Figure 6 is a block diagram illustrating one embodiment of a display system including a micro-mirror device according to the present Invention.</li></ul>

0010In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments. In this regard, directional terminology, such as "top," "bottom," "front," "back," "leading," "trailing," etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present. invention is defined by the appended claims.

0011Figure 1 illustrates one embodiment of a micro-mirror device 10. Micro-mirror device 10 is a micro-actuator which relies on electrical to mechanical conversion to generate a force and cause movement or actuation of a body or . element. In one embodiment, as described below, a plurality of micro-mirror devices 10 are arranged to form an array of micro-mirror devices. As such, the array of micro-mirror devices may be used to form a display. As such, each micro-mirror device 10 constitutes a light modulator for modulation of incident light and provides one cell or pixel of the display. In addition, micro-mirror device 10 may also be used in other imaging systems such as projectors and may also be used for optical addressing.

0012In one embodiment, as described below, micro-mirror device 10 is formed so as to minimize or reduce variations in a reflective surface of the device. For example, in one embodiment, a reflective element of micro-mirror device 10 is formed with a substantially planar surface over an entirety thereof. As such, reflectivity of micro-mirror device 10 may be enhanced and/or light interference from micro-mirror device 10 may be reduced. Thus, a contrast ratio of micro-mirror device 10 may be improved.

0013In one embodiment, as illustrated in Figure 1, micro-mirror device 10 includes a substrate 20, a plate 30, and an actuating element 40. Preferably, plate 30 is oriented substantially parallel to a surface 22 of substrate 20 and spaced from surface 22 so as to define a cavity 50 therebetween. Actuating element 40 is interposed between surface 22 of substrate 20 and plate 30. As such, actuating element 40 is positioned within cavity 50. In one embodiment, actuating element 40 is supported relative to substrate 20 by a support or post 24 extending from surface 22 of substrate 20.

0014In one embodiment, actuating element 40 is actuated so as to move between a first position 47 and a second position 48 relative to substrate 20 and plate 30. Preferably, actuating element 40 moves or tilts at an angle about an axis of rotation. As such, first position 47 of actuating element 40 is illustrated as being substantially horizontal and substantially parallel to substrate 20 and second position 48 of actuating element 40 is illustrated as being oriented at an angle to first position 47. Movement or actuation of actuating element 40 relative to substrate 20 and plate 30 is described in detail below.

0015Preferably, plate 30 is a transparent plate 32 and actuating element 40 is a reflective element 42. In one embodiment, transparent plate 32 is a glass plate. Other suitable planar translucent or transparent materials, however, may be used. Examples of such a material include quartz and plastic.

0016Reflective element 42 includes a reflective surface 44. In one embodiment, reflective element 42 is formed of a uniform material having a suitable reflectivity to form reflective surface 44. Examples of such a material include polysilicon or a metal such as aluminum. In another embodiment, reflective element 42 is formed of a base material such as polysilicon with a reflective material such as aluminum or silver disposed on one or more sides of the base material. In addition, reflective element 42 may be formed of a nonconductive material or may be formed of or include a conductive material.

0017As illustrated in the embodiment of Figure 1, micro-mirror device 10 modulates light generated by a light source (not shown) located on a side of transparent plate 32 opposite of substrate 20. The light source may include, for example, ambient and/or artificial light. As such, input light 12, incident on transparent plate 32, passes through transparent plate 32 into cavity 50 and is reflected by reflective surface 44 of reflective element 42 as output tight 14. Thus, output light 14 passes out of cavity 50 and back through transparent plate 32.

0018The direction of output light 14 is determined or controlled by the position of reflective element 42. For example, with reflective element 42 in first position 47, output light 14 is directed in a first direction 14a. However, with reflective element 42 in second position 48, output light 14 is directed in a second direction 14b. Thus, micro-mirror device 10 modulates or varies the direction of output light 14 generated by input light 12. As such, reflective element 42 can be used to steer light into, and/or away from, an optical imaging system.

0019In one embodiment, first position 47 is a neutral position of reflective element 42 and represents an "ON" state of micro-mirror device 10 in that light is reflected, for example, to a viewer or onto a display screen, as described below. Thus, second position 48 is an actuated position of reflective element 42 and represents an "OFF" state of micro-mirror device 10 in that light is not reflected, for example, to a viewer or onto a display screen.

0020In one embodiment, reflective element 42 is moved between first position 47 and second position 48 by applying an electrical signal to an electrode 60 formed on substrate 20. In one embodiment, electrode 60 is formed on surface 22 of substrate 20 adjacent an end or edge of reflective element 42. Application of an electrical signal to electrode 60 generates an electric field between electrode 60 and reflective element 42 which causes movement of reflective element 42 between first position 47 and second position 48. Preferably, when the electrical signal is removed from electrode 60, reflective element 42 persists or holds second position 48 for some length of time. Thereafter, restoring forces of reflective element 42 pull or return reflective element 42 to first position 47.

0021In one embodiment, a conductive via 26 is formed in and extends through post 24. Conductive via 26 is electrically coupled to reflective element 42 and, more specifically, conductive material of reflective element 42. As such, reflective element 42 is moved between first position 47 and second position 48 by applying an electrical signal to electrode 60 and reflective element 42. More specifically, electrode 60 is energized to one polarity and the conductive material of reflective element 42 is energized to an opposite polarity. Thus, application of an electrical signal of one polarity to electrode 60 and an electrical signal of an opposite polarity to reflective element 42 generates an electric field between electrode 60 and reflective element 42 which causes movement of reflective element 42 between first position 47 and second position 48.

0022In another embodiment, reflective element 42 is moved between first position 47 and second position 48 by applying an electrical signal to reflective element 42. More specifically, the electrical signal is applied to conductive material of reflective element 42 by way of conductive via 26 through post 24. As such, application of an electrical signal to reflective element 42 generates an electric field which causes movement of reflective element 42 between first position 47 and second position 48.

0023Additional embodiments of actuation of micro-mirror device 10 are described, for example, in U.S. Patent Application Serial No. 10/136,719, filed on April 30, 2002, entitled "Micro-Mirror Device", assigned to the assignee of the present invention and incorporated herein by reference.

0024Figure 2 illustrates one embodiment of reflective element 42 as an example of actuating element 40. Reflective element 42 has a reflective surface 44 and includes a substantially rectangular-shaped outer portion 80 and a substantially rectangular-shaped inner portion 84. In one embodiment, reflective surface 44 is formed on both outer portion 80 and Inner portion 84. Outer portion 80 has four contiguous side portions 81 arranged to form a substantially rectangular-shaped opening 82. As such, inner portion 84 is positioned within opening 82. Preferably, inner portion 84 is positioned symmetrically within opening 82.

0025In one embodiment, a pair of hinges 86 extend between inner portion 84 and outer portion 80. Hinges 86 extend from opposite sides or edges of inner portion 84 to adjacent opposite sides or edges of outer portion 80. Preferably, outer portion 80 is supported by hinges 86 along an axis of symmetry. More specifically, outer portion 80 is supported about an axis that extends through the middle of opposed edges thereof. As such, hinges 86 facilitate movement of reflective element 42 between first position 47 and second position 48, as described above (Figure 1). More specifically, hinges 86 facilitate movement of outer portion 80 between first position 47 and second position 48 relative to inner portion 84.

0026In one embodiment, hinges 86 include torsional members 88 having longitudinal axes 89 oriented substantially parallel to reflective surface 44, Longitudinal axes 89 are collinear and coincide with an axis of symmetry of reflective element 42. As such, torsional members 88 twist or turn about longitudinal axes 89 to accommodate movement of outer portion 80 between first position 47 and second position 48 relative to inner portion 84.

0027In one embodiment, reflective element 42 is supported relative to substrate 20 by support or post 24 extending from surface 22 of substrate 20. More specifically, post 24 supports inner portion 84 of reflective element 42, and outer portion 80 of reflective element 42 is supported by hinges 86 extending from inner portion 84. In one embodiment, post 24 is formed by conductive via 26 extending through inner portion 84 to a conductive layer of substrate 20.

0028Figures 3 and 4 illustrate another embodiment of a micro-mirror device 100. Micro-mirror device 100 is similar to micro-mirror device 10 and includes substrate 20, plate 30, and cavity 50 defined between substrate 20 and plate 30. In one embodiment, plate 30 includes transparent plate 32 and substrate 20 has one or more electrodes 60 formed on surface 22 of substrate 20, as described above.

0029As illustrated in the embodiments of Figures 3 and 4, micro-mirror device 100 includes an actuating element 140 supported between substrate 20 and plate 30. In one embodiment, actuating element 140 includes a hinge element 141 and a reflective element 142. As such, reflective element 142 includes a reflective surface 144. Thus, input light 12 (Figure 1) is reflected by reflective surface 144 of reflective element 142 in a manner similar to how input light 12 is reflected by reflective surface 44 of reflective element 42, as described above.

0030In one embodiment, reflective element 142 extends over and is supported from hinge element 141 by a support 124 and hinge element 141 extends over and is supported from substrate 20 by a support 125. In one embodiment, supports 124 and 125 constitute conductive vias extended between reflective element 142 and hinge element 141, and hinge element 141 and substrate 20, respectively.

0031In one embodiment, as illustrated in Figure 3, hinge element 141 is supported by a pair of supports 125 and includes a connecting portion or yoke 182 supported from supports 125 by hinges 186. In one embodiment, yoke 182 supports support 124 and, therefore, reflective element 142. As such, hinges 186 accommodate movement of yoke 182 relative to supports 125 so as to facilitate movement of reflective element 142, as described below.

0032Actuation of micro-mirror device 100 is similar to that of micro-mirror device 10, as described above, with the exception that both hinge element 141 and reflective element 142 of actuating element 140 are actuated. As such, hinge element 141 and reflective element 142 are both moved between a first position 147 and a second position 148 by applying an electrical signal to electrode 60 formed on substrate 20. Application of an electrical signal to electrode 60 generates an electric field between electrode 60 and hinge element 141 and/or reflective element 142 which causes movement of hinge element 141 and reflective element 142 between first position 147 and second position 148.

0033Figures 5A-5N illustrate one embodiment of forming micro-mirror device 100, including actuating element 140 of micro-mirror device 100. In one embodiment, as described above, actuating element 140 of micro-mirror device 100 includes hinge element 141 and reflective element 142. As such, Figures 5A-5N include one embodiment of forming hinge element 141 and reflective element 142.

0034In one embodiment, as illustrated in Figure 5A, micro-mirror device 100 is formed on a substructure 200. In one embodiment, substructure 200 includes a complementary metal oxide semi-conductor (CMOS) structure. As such, substructure 200 includes a base material 210 and at least one conductive layer 220 formed on a first side 212 of base material 210. Conductive layer 220 includes, for example, titanium (Ti), titanium nitride (TiN), copper (Cu), gold (Au), and/or aluminum (AI). Conductive layer 220 is formed, for example, by deposition, and patterned by photolithography and etching.

0035In one embodiment, substructure 200 includes a dielectric layer 214 formed on first side 212 of base material 210. As such, conductive layer 220 of substructure 200 is formed over dielectric layer 214. Dielectric layer 214 includes, for example, a silicon oxide such as tetraethylorthosilicate (TEOS): In one embodiment, deposited layers of substructure 200 including, for example, dielectric layer 214 are planarized during formation of substructure 200 to create a substantially planar substrate for micro-mirror device 10.

0036In one embodiment, conductive material of conductive layer 220 forms an electrical contact area 202 of substructure 200 and an actuating area 204 of substructure 200. Electrical contact area 202 defines an area where electrical connection to micro-mirror device 100 is to be made, and actuating area 204 defines an area where actuating element 140 of micro-mirror device 100 is to be formed, as described below. As such, conductive layer 220 of substructure 200 constitutes an interconnect level of the CMOS circuit.

0037As illustrated in the embodiment of Figure 5A, to form micro-mirror device 100 on substructure 200, a dielectric layer 222 is formed over conductive layer 220 of substructure 200. As such, dielectric layer 222 forms surface 22 of substrate 20, as described above. In one embodiment, dielectric layer 222 is formed by depositing a dielectric material over conductive layer 220. The dielectric material includes, for example, TEOS or other form of silicon oxide. In one embodiment, the dielectric material of dielectric layer 222 is planarized to create a substantially planar surface on which electrodes 60 are formed, as described below.

0038After dielectric layer 222 is formed over conductive layer 220, a conductive material 224 is deposited and patterned on dielectric layer 222. In one embodiment, conductive material 224 is deposited and patterned by photolithography and etching within actuating area 204 of substructure 200. As such, conductive material 224 defines electrodes 225 on dielectric layer 222. In one embodiment, conductive material 224 includes aluminum or an aluminum alloy such as an aluminum silicon alloy.

0039In one embodiment, conductive material 224 communicates with conductive layer 220 of substructure 200 by a conductive via 226 formed through dielectric layer 222. It is understood that Figure 5A is a schematic representation of substructure 200 and that the actual configuration of conductive layers and conductive vias formed between conductive layers may be more complicated than that illustrated.

0040In one embodiment, as illustrated in Figure 5A, conductive material of conductive layer 220 is patterned to form an electrical contact pad 221 for micro-mirror device 100. Electrical contact pad 221 is formed, for example, in electrical contact area 202 of substructure 200. As such, an opening 223 is formed through dielectric layer 222 to electrical contact pad 221. Thus, electrical contact pad 221 provides a point for electrical connection for micro-mirror device 100.

0041As illustrated in the embodiment of Figure 5B, to form actuating element 140 of micro-mirror device 100, a sacrificial layer 230 is formed over conductive material 224 and dielectric layer 222, including within opening 223. In one embodiment, sacrificial layer 230 is formed by depositing a sacrificial material over conductive material 224 and dielectric layer 222. The material forming sacrificial layer 230 is deposited, for example, by chemical vapor deposition (CVD) or plasma enhanced CVD (PECVD), or is spun on. In one embodiment, the material forming sacrificial layer 230 includes, for example, silicon, an oxide, such as TEOS, or photoresist. Sacrificial layer 230 is sacrificial in that the material forming sacrificial layer 230 is substantially removed during subsequent processing while forming actuating element 140, as described below.

0042After the material of sacrificial layer 230 is deposited over conductive material 224 and dielectric layer 222, the material is planarized to create a substantially planar surface 232 of sacrificial layer 230. In one embodiment, the material of sacrificial layer 230 is planarized by a chemical mechanical polishing (CMP) process.

0043Next, as illustrated in the embodiment of Figure 5C, a mask layer 240 is formed over sacrificial layer 230. In one embodiment, mask layer 240 is formed by deposition and patterned, for example, by photolithography or etching to expose areas of sacrificial layer 230 and define where openings 234 are to be formed through sacrificial layer 230 to conductive material 224.

0044In one embodiment, openings 234 through sacrificial layer 230 are formed by chemical etching. Thus, mask layer 240 is formed of a material which is resistant to the etchant used for etching openings 234. Examples of a material suitable for mask layer 240 include a hard mask material such as silicon dioxide or silicon nitride, or a photoimageable material such as photoresist. After openings 234 are formed, mask layer 240 is stripped or removed.

0045As illustrated in the embodiments of Figures 5D-5F, after openings 234 are formed through sacrificial layer 230 and mask layer 240 is removed, hinge element 141 of actuating element 140 is formed. Hinge element 141 is formed, for example, by depositing one or more layers of one or more materials over sacrificial layer 230, and patterning the materials to define hinge element 141. The materials are deposited, for example, by physical vapor deposition (PVD), CVD, or PECVD, and patterned, for example, by photolithography and etching.

0046As illustrated in the embodiment of Figure 5D, hinge element 141 of actuating element 140 is formed by depositing a first material 250 over sacrificial layer 230 and within openings 234 of sacrificial layer 230. In one embodiment, material 250 which is deposited within openings 234 forms conductive vias 251 through sacrificial layer 230 to conductive material 224. Thus, material 250 includes a conductive material. In one embodiment, for example, material 250 includes aluminum or an aluminum alloy such as an aluminum silicon alloy.

0047In one embodiment, conductive vias 251 form posts 125 (Figures 3 and 4) of micro-mirror device 100. As such, conductive vias 251 support hinge element 141 relative to substructure 200, as described below. In addition, in one embodiment, material 250 constitutes hinge material of hinge element 141 and forms hinges 186 (Figure 3) of micro-mirror device 100.

0048In one embodiment, as illustrated in Figure 5D, after material 250 is deposited over sacrificial layer 230, a protective material 252 is deposited and patterned on material 250. In one embodiment, protective material 252 is deposited by deposition and patterned by photolithography and etching to define where hinges 186 (Figure 3) of micro-mirror device 100 are to be formed. More specifically, protective material 252 is patterned to protect areas of material 250 which form hinges 186, as described below. In one embodiment, protective material 252 includes TEOS or other form of silicon oxide.

0049Next, as illustrated in the embodiment of Figure 5E, hinge element 141 is further formed by depositing a second material 254 over protective material 252 and material 250. In one embodiment, material 254 constitutes yoke material of hinge element 141 and forms yoke 182 (Figure 3) of micro-mirror device 100. In one embodiment, for example, material 254 includes aluminum or an aluminum alloy such as an aluminum silicon alloy.

0050In one embodiment, as illustrated in Figure 5E, after material 254 is deposited over protective material 252 and material 250, a mask layer 260 is formed over material 254. In one embodiment, mask layer 260 is formed by deposition and patterned, for example, by photolithography or etching to form openings 262 in mask layer 260 and expose areas of material 254. As such, the exposed areas of material 254 include areas which define where material 254 and protective material 252 are to be removed to form hinges 186 (Figure 3) of hinge element 141. In one embodiment, a dimension D1 of openings 262 is less than a dimension D2 of protective material 252. As such, protective material 252 protects material 250 during forming of hinges 186, as described below.

0051As illustrated in the embodiment of Figure 5F, hinges 186 are formed by forming openings 256 through material 254 and protective material 252 to material 250. In one embodiment, openings 256 are formed by chemical etching through openings 262 of mask layer 260. As such, protective material 252 protects and/or controls etching into material 250. After openings 256 are formed, mask layer 260 is stripped or removed,

0052Next, as illustrated in the embodiment of Figure 5G, after hinge element 141 is formed, a sacrificial layer 270 is formed over hinge element 141, including within openings 256. In one embodiment, sacrificial layer 270 is formed by depositing a sacrificial material over hinge element 141. The material forming sacrificial layer 270 is deposited, for example, by CVD or PECVD, or spun on. In one embodiment, the material forming sacrificial layer 270 includes, for example, silicon, an oxide, such as TEOS, or photoresist. Sacrificial layer 270 is sacrificial in that the material forming sacrificial layer 270 is substantially removed during subsequent processing while forming actuating element 140, as described below.

0053After the material of sacrificial layer 270 is deposited over hinge element 141, the material is planarized to create a substantially planar surface 272 of sacrificial layer 270. In one embodiment, the material of sacrificial layer 270 is planarized by a CMP process.

0054Next, as illustrated in the embodiment of Figure 5H, a mask layer 280 is formed over sacrificial layer 270. In one embodiment, mask layer 280 is formed by deposition and patterned, for example, by photolithography to expose an area of sacrificial layer 270 and define where an opening 274 is to be formed through sacrificial layer 270 to hinge element 141.

0055In one embodiment, opening 274 through sacrificial layer 270 is formed by chemical etching. Thus, mask layer 280 is formed of a material which is resistant to the etchant used for etching opening 274. Examples of a material suitable for mask layer 280 include a hard mask material such as silicon dioxide or silicon nitride, or a photoimageable material such as photoresist. After opening 274 is formed, mask layer 280 is stripped or removed.

0056As illustrated in the embodiments of Figures 5I and 5J, after opening 274 is formed through sacrificial layer 270 and mask layer 280 is removed, a plugged via 290 is formed in sacrificial layer 270, In one embodiment, plugged via 290 is conductive and forms post 124 (Figures 3 and 4) of micro-mirror device 100. As such, plugged via 290 provides conductivity between hinge element 141 and reflective element 142, and supports reflective element 142 relative to hinge element 141, as described below.

0057In one embodiment, as illustrated in Figure 5I, plugged via 290 is formed by depositing a protective material 292 over surface 272 of sacrificial layer 270 and within opening 274 of sacrificial layer 270. As such, protective material 292 contacts hinge element 141 and, in one embodiment, forms a conductive via 293 through sacrificial layer 270 to hinge element 141. Thus, in one embodiment, protective material 292 includes a conductive material. In one embodiment, for example, protective material 292 includes aluminum.

0058As illustrated in the embodiment of Figure 5I, after protective material 292 is deposited over surface 272 and within opening 274 (Figure 5H) of sacrificial layer 270, a plug material 294 is deposited over protective material 292, including within opening 274. As such, plug material 294 fills conductive via 293. In addition, protective material 292 protects plug material 294 during subsequent processing while forming actuating element 140, as described below.

0059In one embodiment, plug material 294 includes, for example, silicon, an oxide, such as TEOS, a metal, such as aluminum, copper, titanium, or tungsten, or photoresist. In one exemplary embodiment, when sacrificial layers 230 and 270 are formed of silicon, a suitable material for plug material 294 includes silicon, an oxide, a metal, or photoresist. In another exemplary embodiment, when sacrificial layers 230 and 270 are formed of photoresist, a suitable material for plug material 294 includes photoresist.

0060Next, as illustrated in the embodiment of Figure 5J, plug material 294 and protective material 292 are planarized. In one embodiment, plug material 294 and protective material 292 are planarized to sacrificial layer 270 so as to produce a substantially planar surface 295 of plug material 294 and recreate or reestablish substantially planar surface 272 of sacrificial layer 270. In one embodiment, plug material 294 and protective material 292 are planarized by a CMP process.

0061As illustrated in the embodiments of Figures 5K-5M, after substantially planar surface 272 of sacrificial layer 270 is formed, reflective element 142 of actuating element 140 is formed. Reflective element 142 is formed, for example, by depositing one or more layers of one or more materials over sacrificial layer 270 and plugged via 290, and patterning the materials to define reflective element 142. The materials are deposited, for example, by PVD, CVD, or PECVD, and patterned, for example, by photolithography and etching.

0062In one embodiment, as illustrated in Figure 5K, reflective element 142 of actuating element 140 is formed by depositing material 300 over sacrificial layer 270 and plugged via 290. More specifically, material 300 is deposited on substantially planar surface 272 of sacrificial layer 270 and substantially planar surface 295 of plug material 294. As such, reflective element 142 is formed with a substantially planar surface. More specifically, an entire surface of reflective element 142 is substantially planar.

0063In one embodiment, material 300 constitutes reflective material of reflective element 142 and forms reflective surface 144 of reflective element 142. Thus, material 300 includes a reflective material. In one embodiment, for example, material 300 includes aluminum.

0064As illustrated in the embodiment of Figure 5K, reflective element 142 is formed so as to contact plug material 294 of plugged via 290. As such, plug material 294 of plugged via 290 is enclosed by material 300 of reflective element 142 and protective material 292 of plugged via 290. Thus, plug material 294 is protected during subsequent processing while forming actuating element 140, as described below.

0065In one embodiment, as illustrated in Figure 5L, after material 300 is deposited over sacrificial layer 270 and plugged via 290, a mask layer 310 is formed over material 300. In one embodiment, mask layer 310 is formed by deposition and patterned, for example, by photolithography to expose areas of material 300 and define reflective element 142. Examples of material suitable for mask layer 310 include a hard mask material such as silicon dioxide or silicon nitride, or a photoimageable material such as photoresist.

0066As illustrated in the embodiment of Figure 5M, the exposed areas of material 300 are removed to define reflective element 142. In one embodiment, the exposed areas of material 300 are removed by chemical etching. As such, mask layer 310 protects reflective surface 144 of reflective element 142. After the exposed areas of material 300 are removed, mask layer 310 is stripped or removed.

0067Next, as illustrated in the embodiment of Figure 5N, sacrificial layers 230 and 270 are substantially removed. More specifically, the material of sacrificial layer 230 is removed from between hinge element 141 and conductive material 224 and dielectric layer 222, and the material of sacrificial layer 270 is removed from between reflective element 142 and hinge element 141. Thus, actuating element 140, including hinge element 141 and reflective. element 142 is released. As such, hinge element 141, including yoke 182 and hinges 186, is supported from substructure 200 by conductive vias 251, and reflective element 142, including reflective surface 144, is supported from hinge element 141 by plugged via 290. In addition, electrical contact pad 221 of electrical contact area 202 is exposed.

0068In one embodiment, sacrificial layers 230 and 270 are removed by a chemical etch process. As such, conductive layer 220, dielectric layer 222, conductive material 224, and the materials of actuating element 140 are selected so as to be resistant to the particular etchant used for removing sacrificial layers 230 and 270. In one embodiment, the etch process for removing sacrificial layers 230 and 270 is a dry etch, such as a plasma-based fluorinated etch using, for example, SF₆, CF₄, C₂F₆, or a combination of gases.

0069While the above description refers to the formation of a micro-mirror device, it is understand that the above processes are also applicable to the formation of other MEMS devices, including multi-layer MEMS devices. In addition, it is understood that Figures 5A-5N are schematic illustrations of one embodiment of forming a micro-mirror device according to the present invention and that the actual configuration of layers and vias of the micro-mirror device may be more complicated than that illustrated.

0070In one embodiment, as illustrated in Figure 6, micro-mirror device 10 (including micro-mirror device 100) is incorporated in a display system 500, Display system 500 includes a light source 510, source optics 512, a light processor or controller 514, and projection optics 516. Light processor 514 includes multiple micro-mirror devices 10 arranged in an array such that each micro-mirror device 10 constitutes one cell or pixel of the display.

0071In one embodiment, light processor 514 receives image data 518 representing an image to be displayed. As such, light processor 514 controls the actuation of micro-mirror devices 10 and the modulation of light received from light source 510 based on image data 518. The modulated light is then projected to a viewer or onto a display screen 520.

0072Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the claims and the equivalents thereof.

0073The disclosures in United States patent application No. 10/677,539, from which this application claims priority, and in the abstract accompanying this application are incorporated herein by reference.