CN1204434C - Method for fabricating an array of thin film actuated mirrors - Google Patents

Abstract

A method for making an array of thin film actuated mirrors (401) for use in an optical projection system, the method comprising the steps of: providing a substrate (310); depositing a thin film sacrificial layer atop the substrate; generating an array of MxN cavities on the thin film layer to be removed; depositing an elastic layer on top of the film sacrificial layer including the cavities; configuring the elastic layer into an array of M x N elastic members (335); forming an array of M x N switching devices (415) on the substrate; depositing a passivation layer (340) and an etchant stop layer (350) atop each of the resilient members and the switching devices; selectively removing the etchant stop layer and the passivation layer to expose the elastic members; successively forming an array of M x N second thin film electrodes (365) and an array of M x N thin film electrodisplacive members (375) atop each of the elastic members; forming an array of M x N first thin film electrodes and an array of contact features; removing the thin film sacrificial layer to form an array of M x N actuating structures; covering the array of M x N actuating mechanisms with a material to be removed; depositing a mirror layer on top of the material to be removed; configuring the mirror layer into an array of M x N mirrors; and removing the sacrificial material to form the array of M x N thin film actuated mirrors. To prevent thermal damage to the active matrix, in the method of the present invention, an array of M x N switching devices (415) is formed on the substrate (310) after all high temperature processing is completed, thereby reducing the likelihood of thermal damage occurring to the array of switching devices (415).

Description

Method for fabricating an array of thin film actuated mirrors

technical field

The present invention relates to an array of M×N thin film actuated mirrors used in an optical projection system; Contains the effects of high temperature processing.

Background technique

Among the various video display systems in the prior art, an optical projection system is known that can provide large-scale high-quality displays. In such an optical projection system, light from a lamp is uniformly illuminated, for example, on an array of M x N actuated mirrors, each mirror being connected to each actuator. These actuators may be made of electrodisplaceable materials that deform in response to an electric field applied thereto. Examples are piezoelectric or electrostrictive materials.

The reflected light beams from each mirror are incident on an aperture such as a diaphragm. By applying an electrical signal to each actuator, the relative position of each reflector to the incident beam is changed, thereby causing the optical path of the reflected beam from each reflector to be deflected. When the optical path of each reflected light beam changes, the amount of light reflected from each mirror passing through the small hole is changed, thereby modulating the intensity of the light beam, and the modulated light beam passing through the small hole is transmitted through a suitable optical device such as a projection lens onto a projection screen to display an image thereon.

In FIGS. 1A to 1I , there is shown a co-pending application, International Application No. PCT/KE96/00142, entitled "Thin Film Actuated Mirror Arrays for Use in Optical Projection Systems", made M The fabrication steps involved in the array 200 of xN thin film actuated mirrors 201, where M and N are integers.

The process of fabricating array 200 begins with fabricating an active matrix 110 comprising a substrate 112 with an array of M x N switching devices, such as metal-oxide-semiconductor (MOS) transistors 115, and a field formed atop it. oxide layer 116 . Each MOS transistor 115 has a source/drain region 117 , a gate oxide layer 118 and a gate 119 .

In a next step, a first passivation layer 120 made of eg PSG or silicon nitride with a thickness of 0.1-2 μm is deposited on top of the active matrix 110 by using eg CVD or spin coating.

Then, an etchant stop layer 130 made of nitride having a thickness of 0.1-2 μm is deposited on top of the first passivation layer 120 by using, for example, sputtering or CVD, as shown in FIG. 1A .

Then, a thin film sacrificial layer 140 is formed on top of the etchant stop layer 130 . If the thin-film sacrificial layer 140 is made of metal, the thin-film sacrificial layer 140 is formed by using sputtering or evaporation, if the thin-film sacrificial layer 140 is made of PSG, by CVD or spin coating, or if The thin film sacrificial layer 140 is made of silicon polymer (poly-Si) by CVD.

Next, by using dry or wet etching, an M×N cavity array (not shown) is formed on the thin film sacrificial layer 140 in such a manner that each cavity surrounds the source/drain in each MOS transistor 115 Polar Region 117.

In the next step, an elastic layer 150 made of an insulating material such as silicon nitride with a thickness of 0.1-2 μm is deposited on top of the thin-film sacrificial layer 140 including the cavities by using the CVD method.

Then, a second thin film layer 160 made of a conductive material such as Pt/Ta having a thickness of 0.1-2 μm is formed on top of the elastic layer 150 by using sputtering or vacuum evaporation. The second thin film layer 160 is then cut along the row direction etc. by using an etching method, as shown in FIG. 1B.

Then, on top of the second thin film layer 160 by using evaporation, Sol-Gel, sputtering or CVD, deposit a film made of a piezoelectric material such as PZT or an electrostrictive material such as PMN with a thickness of 0.1-2 μm. A thin film electrodisplacement layer (not shown).

Next, the thin film electrodisplacement layer is patterned into an array of M×N thin film electrodisplacement elements 175 by using photolithography or laser trimming, as shown in FIG. 1C .

In the next step, the second thin film layer 160 and the elastic layer 150 are respectively patterned into an array of M×N second thin film electrodes 165 and an array of M×N elastic members 155 by using an etching method, as shown in FIG. 1D shown.

In the next step, portions of the etchant stop layer 130 and the first passivation layer 120 formed on top of the source/drain region 117 in each MOS transistor 115 are removed by using an etching method while leaving them surrounding The gate 119 and the untouched portion 125 of the gate oxide layer 118 in each MOS transistor 115 are shown in FIG. 1E .

Next, an array of M×N first thin-film electrodes 185 and an array of contact members 183 are formed by the following steps: first, a layer of conductive material is formed by sputtering or vacuum evaporation to completely cover the above-mentioned mechanism ( not shown); this layer is then selectively removed using etching, as shown in FIG. 1F. Each first thin film electrode 185 is positioned on top of the thin film electrodisplacement element 175 . Each contact member 183 is positioned such that it electrically connects the second thin film electrode 165 with the source/drain region 117 in each MOS transistor 115 .

In the following steps, a second passivation layer 187 made of, for example, PSG or silicon nitride with a thickness of 0.1-2 μm is deposited by using CVD or spin coating, and then patterned by using etching such that It completely covers the contact members 183, forming an array 210 of MxN actuated mirror mechanisms 211, as shown in FIG. 1G.

Each actuated mirror mechanism 211 is then completely covered with a first thin film protective layer (not shown).

The thin film sacrificial layer 140 is then removed by using an etching method. Then, the first protective film is removed, thereby forming an array of M×N actuators 100, each actuator 100 having a proximal end and a distal end (not shown), as shown in FIG. 1H.

In a next step, the array of M x N actuation mechanisms 100 is covered with sacrificial material such that the top of the resulting mechanism (not shown) is fully formed when the thin film sacrificial layer 140 is removed. flat. An array (not shown) of M x N voids, each extending from the top of the resulting mechanism to the top of the distal end of each actuation mechanism 100, is then created on the resulting mechanism by using photolithography. .

After the above steps, a mirror layer (not shown) and a thin-film dielectric layer (not shown) made of light-reflecting material, such as Al, are deposited sequentially on the top of the material to be removed, including the cavities, and then by patterning the mirror layer and the thin-film dielectric layer into an array of M×N mirrors 190 and an array of M×N thin-film dielectric members 195, respectively, using photolithography or laser trimming to form An array of M x N semi-finished actuated mirrors (not shown), where each mirror 190 has a recessed portion 197 attached atop the distal end of the actuation mechanism 100 .

Each semi-finished actuated mirror is then completely covered with a second thin-film protective layer (not shown).

The material to be removed is then removed by using an etching method. Then, the second thin-film protective layer is removed, thereby forming the array 200 of the M×N thin-film actuated mirrors 201 , as shown in FIG. 1I .

The above method of fabricating the array 200 of M x N thin film actuated mirrors 201 has certain drawbacks. For example, the method includes multiple high temperature processes, especially during the early stages, e.g. the formation of the elastic layer 140 made of nitride requires a minimum temperature of 800°C, and the active matrix 110 usually cannot withstand such a high temperature, resulting in its thermal damage.

Contents of the invention

It is therefore an object of the present invention to provide a method for fabricating an array of thin film actuated mirrors for use in optical projection systems which reduces the effect of the high temperature processes involved in the fabrication.

According to the present invention, there is provided a method of fabricating a thin film actuated mirror array for use in an optical projection system, the method comprising the steps of: providing a substrate; depositing a thin film sacrificial layer on top of the substrate; creating an array of M x N cavities on the thin film sacrificial layer; depositing an elastic layer on top of the thin film sacrificial layer including the cavities; configuring the elastic layer into an array of M x N elastic members; An array of M x N switching devices is formed on the substrate; a passivation layer and an etchant stop layer are deposited on top of each spring member and switch device; the etchant stop layer and the passivation layer are selectively removed so that These elastic members are exposed; an array of M×N second thin film electrodes and an array of M×N thin film electrodisplacement members are continuously formed on top of each elastic member; an array of M×N first thin film electrodes is formed an array of arrays and contact elements; removing the sacrificial layer of the thin film to form an array of M x N actuating mechanisms; covering the array of M x N actuating mechanisms with a sacrificial material; on top of the sacrificial material depositing a mirror layer; configuring the mirror layer into an array of M×N mirrors; and removing the sacrificial material to form the array of M×N thin film actuated mirrors.

Description of drawings

The above and other objects and features of the present invention will become apparent through the following description of preferred embodiments in the accompanying drawings, in which:

Figures 1A to 1I present schematic cross-sectional views illustrating a previously disclosed method for fabricating an array of M x N thin film actuated mirrors; and

2A to 2J give schematic cross-sectional views illustrating a method for fabricating an array of MxN thin film actuated mirrors according to the present invention.

Detailed ways

2A to 2J present schematic cross-sectional views illustrating a method of fabricating an array 400 of MxN thin film actuated mirrors 401 for an optical projection system according to the present invention. It should be noted that the same components appearing in Figs. 2A to 2J are denoted by the same reference numerals.

The process of making the array 400 begins by preparing a substrate 310 made of insulating material, such as a silicon wafer.

In the next step, a thin film sacrificial layer 320 is formed on top of the substrate 310 . If the thin-film sacrificial layer 320 is made of metal, the thin-film sacrificial layer 320 is formed by using sputtering or evaporation, if the thin-film sacrificial layer 320 is made of PSG, by CVD or spin coating, or if The thin film sacrificial layer 320 is made of silicon polymer (poly-Si) by CVD.

Next, an array of M×N cavities 325 is formed on the thin film sacrificial layer 320 by using dry or wet etching, as shown in FIG. 2A .

In the next step, an elastic layer (not shown) made of insulating material such as nitride with a thickness of 0.1-2 μm is deposited on top of the thin film sacrificial layer 320 including the cavities by using the CVD method.

In the next step, the elastic layer is patterned into an array of M×N elastic members 335 by using an etching method at a high temperature, eg, 800° C., as shown in FIG. 2B .

Then, M×N switching devices 415 , such as an array of metal oxide semiconductor (MOS) transistors, are formed on the substrate 310 . Each MOS transistor 415 has a source/drain region 417, a gate oxide layer 418 and a gate 419 and is positioned between two consecutive elastic members 335 in the same row or column, as shown in FIG. 2C.

In a next step, a first passivation layer made of eg PSG or silicon nitride with a thickness of 0.1-2 μm is deposited on top of each spring member 335 and switching device 415 by using eg CVD or spin coating 340.

Then, an etchant stop layer 350 made of nitride having a thickness of 0.1-2 [mu]m is deposited on top of the first passivation layer 340 by using, for example, sputtering or CVD, as shown in FIG. 2D.

In a subsequent step, portions of the etchant stop layer 350 and the first passivation layer 340 are removed by using an etching method, while leaving the portion 345 untouched, as shown in FIG. 2E .

Then, a second thin film layer (not shown) made of a conductive material such as Pt/Ta having a thickness of 0.1-2 μm is formed on top of each elastic member 335 by using sputtering or vacuum evaporation. The second thin film layer is then cut in the column direction etc. by using an etching method.

Then, on top of this second thin film layer is deposited a film made of a piezoelectric material such as PZT or an electrostrictive material such as PMN with a thickness of 0.1-2 μm by using evaporation, Sol-Gel, sputtering or CVD method. A thin film electrodisplacement layer (not shown).

Next, the thin-film electrodisplacement layer and the second thin-film layer are respectively patterned into an array of M×N thin-film electrodisplacement components 375 and an array of M×N second thin-film electrodes 365 by using photolithography or laser trimming. array, as shown in Figure 2F.

Next, an array of M×N first thin-film electrodes 385 and an array of contact members 383 are formed through the following steps: first, a layer of conductive material is formed by sputtering or vacuum evaporation to completely cover the above-mentioned mechanism ( not shown); this layer is then selectively removed using etching, as shown in Figure 2G. Each first thin film electrode 385 is positioned on top of the thin film electrodisplacement element 375 . Each contact member 383 is positioned such that it electrically connects the second thin film electrode 365 with the source/drain region 417 in each MOS transistor 415 .

In the following steps, a second passivation layer 387 made of, for example, PSG or silicon nitride with a thickness of 0.1-2 μm is deposited by using CVD or spin coating, and then patterned by using etching such that It completely covers the contact members 383, forming an array 420 of MxN actuated mirror mechanisms 421, as shown in Figure 2H.

Each actuated mirror mechanism 421 is then completely covered with a first thin film protective layer (not shown).

The thin film sacrificial layer 320 is then removed by using an etching method. Then, the first film protection layer is removed, thereby forming an array of M×N actuating mechanisms 300, each actuating mechanism 300 having a proximal end and a distal end (not shown), as shown in FIG. 2I.

In the next step, the array of M x N actuation mechanisms 300 is covered with sacrificial material such that the tops of the resulting mechanisms (not shown) are completely flat. An array (not shown) of M x N voids, each extending from the top of the resulting mechanism to the top of the distal end of each actuation mechanism 300, is then created on the resulting mechanism by photolithography. .

After the above steps, a mirror layer (not shown) and a thin-film dielectric layer (not shown) made of light-reflecting material, such as Al, are deposited sequentially on the top of the material to be removed, including the cavities, and then by patterning the mirror layer and the thin film dielectric layer into an array of MxN mirrors 390 and an array of MxN thin film dielectric members 395, respectively, using photolithography or laser trimming to form An array of M x N semi-finished actuated mirrors (not shown), where each mirror 390 has a recessed portion 397 attached atop the distal end of the actuation mechanism 300 .

Each semi-finished actuated mirror is then completely covered with a second thin-film protective layer (not shown).

The material to be removed is then removed by using an etching method. Then, the second thin-film protective layer is removed, thereby forming the array 400 of the M×N thin-film actuated mirrors 401, as shown in FIG. 2J .

In contrast to previously disclosed methods for fabricating arrays of M x N thin film actuated mirrors, in the method of the present invention an array of M x N switching devices 415 is formed on substrate 310 after all high temperature processing is complete, This in turn reduces the likelihood of thermal damage occurring on the array of switching devices 415 .

Although the invention has been illustrated and described with reference to particular embodiments, it will be apparent that various changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (6)

1. A method of manufacturing a thin film actuated mirror array for use in an optical projection system, the method comprising the steps of: set a base; depositing a thin film sacrificial layer on top of the substrate; creating an array of M×N cavities on the sacrificial layer of the film; depositing an elastic layer on top of the sacrificial layer of the film including the cavities; configuring the elastic layer as an array of M x N elastic members; forming an array of M x N switching devices on the substrate; depositing a passivation layer and an etchant stop layer on top of each resilient member and switch device; selectively removing the etchant stop layer and the passivation layer to expose the resilient components; An array of M×N second film electrodes and an array of M×N thin film electrodisplacement components are formed on top of each elastic member; forming an array of M×N first thin film electrodes and an array of contact members; removing the sacrificial layer of the film, thereby forming an array of M×N actuation mechanisms; covering the array of M x N actuation mechanisms with a material to be removed; depositing a mirror layer on top of the material to be removed; configuring the mirror layer as an array of M x N mirrors; and removing the material to be removed, thereby forming the M×N thin film actuated mirror array, Wherein the switching device array is formed after all high temperature processing is completed. 2. The method according to claim 1, wherein the substrate is made of an insulating material. 3. The method of claim 2, wherein the substrate is a silicon wafer. 4. The method of claim 1, wherein each switching device is a metal oxide semiconductor (MOS) transistor. 5. A method according to claim 1, wherein each switching means is positioned between two consecutive resilient members in the same row or column. 6. The method of claim 1, further comprising the step of forming a thin film dielectric member atop each mirror after depositing the mirror layer.

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