CN101604069B - Manufacturing process of three-layer continuous surface type MEMS deformable mirror based on bonding process - Google Patents

Abstract

A process for preparing three-layer continuous surface type MEMS deformable mirror based on bonding technique includes such steps as dry etching to form release hole on the upper surface of SOI wafer, partially releasing the oxide layer in the middle of SOI wafer, wet etching the lower surface of SOI wafer, depositing metal on another substrate (silicon wafer or glass) as electrode structure, and bonding the substrate with SOI wafer. The method is characterized in that a bulk silicon micromachining process and a surface micromachining process are combined, and an upper two-layer structure obtained by machining the bulk silicon process and a lower electrode structure layer obtained by adopting the surface micromachining process are bonded to obtain a three-layer micromechanical structure. The invention relates to a three-layer continuous surface type MEMS deformable mirror based on a bonding process, which has relatively easy manufacturing process, solves the problem that the traditional continuous surface micro mechanical deformable mirror has large difficulty in micro processing of three layers of surfaces, can obtain large out-of-plane displacement, eliminates the defect of short circuit caused by electrostatic pull-in by adding a silicon nitride insulating layer, and can be widely applied to the fields of optical communication and adaptive optics.

Description

A manufacturing process of three-layer continuous surface MEMS deformable mirror based on bonding process

technical field

The invention relates to the technical field of micro-opto-electromechanical systems, in particular to a manufacturing process of a three-layer continuous surface MEMS deformable mirror based on a bonding process suitable for an adaptive optical system.

Background technique

In the field of adaptive optics, electrostatically driven MEMS deformable mirrors have the advantages of small size, low power consumption, fast response, mass production, and good compatibility with integrated circuits, so they are favored in adaptive optics systems. The existing electrostatically driven MEMS deformable mirrors are generally processed by surface micromachining technology, which is difficult to process; and to obtain a large stroke, such as a stroke greater than 4 microns, due to the influence of the electrostatic pull-in effect, the stroke of the driver cannot If it exceeds one-third of the initial plate spacing, the thickness of the sacrificial layer needs to be greater than 10 microns, and the processing is more difficult. By adopting the manufacturing process of the three-layer continuous surface MEMS deformable mirror based on the bonding process, the difficulty of processing the continuous surface deformable mirror is reduced, and it is easy to process the deformable mirror with a large stroke. A layer of silicon nitride film is used to avoid the short circuit damage of the device due to electrostatic pull-in, and because it is continuous, the fill factor is close to 100%.

Contents of the invention

The technical problem to be solved by the present invention is: Aiming at the deficiencies of the prior art, a manufacturing process of a three-layer continuous surface MEMS deformable mirror based on a bonding process is designed, the processing process is relatively simple, and it is also easy to process a large-stroke continuous surface shape For deformable mirrors, the fill factor can reach close to 100%.

The technical solution adopted by the present invention to solve the technical problem is: a manufacturing process of a three-layer continuous surface MEMS deformable mirror based on a bonding process, which combines the bulk silicon processing technology with the surface micro-machining process, that is, the bulk silicon process. The upper two layers are bonded with the lower electrode structure layer processed by surface technology, so as to obtain a three-layer micro-mechanical structure.

Specifically, it consists of the following process flow:

(1) Take a piece of glass or silicon wafer as the substrate;

(2) Photolithography and etching to form grooves with a depth of 0.3 to 2.0 microns on the substrate;

(3) Deposit 0.3-2.0 micron thick polysilicon or amorphous silicon or metal film, then photolithography and etching, the etching depth is equal to the thickness of this layer of film, forming the lower electrode and lead of the deformable mirror;

(4) Deposit a silicon nitride film with a thickness of 0.1 to 1.0 microns, and then photolithography and etch. The etching depth is equal to the thickness of this film, so that the silicon nitride or silicon dioxide layer covers the lower electrode, thereby avoiding static electricity. The pull-in effect causes short-circuit damage to the device;

(5) Take an SOI wafer, the thickness of the silicon structure layer of the wafer is 0.3-20.0 microns, the thickness of the oxide layer is 0.3-10 microns, the thickness of the base is 300-1000 microns, or on an ordinary silicon wafer with a thickness of 300-1000 microns The surface is thermally oxidized with an oxide layer with a thickness of 0.3-10 microns, and then a silicon wafer is bonded on the surface of the oxide layer, and the silicon wafer is thinned to a thickness of 0.3-20 microns by mechanical or chemical methods and ground flat ;

(6) Deposit two layers of silicon dioxide and two layers of silicon nitride on the upper and lower surfaces of the wafer obtained in step (5), the order is silicon dioxide→silicon nitride→silicon dioxide→silicon nitride, which is the subsequent wet method Preparation for etching or dry etching;

(7) Perform photolithography and etching twice on the lower surface of the structure obtained in step (6) to form a stepped structure for subsequent wet etching;

(8) Perform wet or dry etching of the silicon substrate using the step-shaped silicon nitride and silicon dioxide obtained in step (7) as a mask, and stop the etching until it is 12 to 52 microns away from the upper surface of the substrate;

(9) Then wet or dry etch away one layer of silicon nitride and silicon dioxide, and use the remaining silicon nitride and silicon dioxide as a mask to wet or dry etch the silicon substrate, with a depth of 10 ~ 50 microns;

(10) The remaining silicon dioxide and silicon nitride on the upper and lower surfaces are removed by wet or dry etching;

(11) performing fusion bonding or anodic bonding or low-temperature bonding on the upper surface of the structure obtained in step (3) and the lower surface of the structure obtained in step (10);

(12) Photolithography and etching are performed on the upper surface of the structure obtained in step (10) to form a release hole, and then the oxide layer below the release hole is released, leaving only the connector connecting the first layer and the second layer .

Compared with the prior art, the present invention has the advantages that: the present invention mainly performs dry etching on the upper surface of the SOI wafer to form release holes, releases part of the oxide layer, and wet-etches the lower surface to process electrodes on another wafer. Structure and bond two wafers, combine bulk silicon processing and surface micromachining together, use bulk silicon to process the upper two layers and then bond the lower electrode made by micromachining the lower surface to obtain a three-layer mechanical structure, which solves the traditional continuous The surface micromechanical deformable mirror has the disadvantage that it is difficult to process the three-layer surface micromachining, and the distance between the upper and lower plates of the processed deformable mirror can be more than 20 microns, which can obtain a large out-of-plane displacement, and also by adding a silicon nitride insulating layer Eliminates the effect of electrostatic pull-in, and can be widely used in the field of adaptive optics.

Description of drawings

Fig. 1 is the realization flowchart of the inventive method;

Fig. 2 is a perspective view of a glass or silicon substrate in the present invention;

Fig. 3 is the perspective view after substrate etch groove among the present invention;

Fig. 4 is the structural diagram after depositing metal or polysilicon or amorphous silicon and etching in the present invention;

Fig. 5 is the structural diagram after depositing silicon nitride on it and etching in the present invention;

Fig. 6 is another piece of SOI wafer among the present invention or uses the thermal oxidation layer oxide layer on the upper surface of common silicon wafer, then bonds a piece of silicon wafer on the upper surface of oxide layer and this piece of silicon wafer is thinned with mechanical or chemical method and smooth it out;

Fig. 7 is the bottom view of all depositing 2 layers of silicon dioxide and two layers of silicon nitride on the upper and lower surfaces of the wafer obtained in Fig. 6;

FIG. 8 is a schematic bottom view of a mask for processing wet or dry etching in the present invention;

Fig. 9 is a bottom-view structural view of the present invention, where wet or dry etching is performed once, and the etching stops at a distance of 12 to 52 microns from the upper surface of the substrate;

Figure 10 is a bottom-view structure of silicon nitride and silicon dioxide etched away by a wet or dry method in the present invention, and then wet or dry etched again to etch away the remaining silicon nitride and silicon dioxide picture;

Figure 11a is a three-dimensional view of the upper two-layer structure before bonding in the present invention;

Figure 11b is a perspective view of the structure of the lower layer before bonding in the present invention;

Fig. 11c is a cross-sectional view of AA ₁ after bonding in the present invention.

In the figure: 1 is the first substrate, 2 is the electrode lead, 3 is the lower electrode, 4 is the silicon nitride covering the lower electrode, 5 is the structural layer used as a mirror, 6 is the oxide layer, 7 is the second substrate, 8 is silicon nitride, 9 is silicon dioxide, 10 is silicon nitride etched out to be used as a wet or dry etching mask, 11 is the upper electrode etched by wet method, and 12 is the bonding time 13 is a release hole, 14 is a thin plate beam structure, and 15 is a connecting body connecting the mirror surface and the driving beam.

specific embodiment

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. But the following examples are only limited to explain the present invention, and the protection scope of the present invention should include the entire content of the claims, and those skilled in the art can realize the entire contents of the claims of the present invention through the following examples.

Example 1

Taking the manufacturing process of a 3×3 unit three-layer continuous surface-shaped micromechanical deformable mirror as an example, the present invention will be described in detail in conjunction with the accompanying drawings, and the specific steps are shown in Figure 1.

1. Take a piece of 5-inch Pyrex7740 glass with a thickness of 500 microns as the first substrate 1, as shown in FIG. 2 .

2. Use the first mask for photolithography and wet etching with buffered hydrofluoric acid to form a 0.5 micron deep groove to prepare for the deposition of the lower electrode, as shown in Figure 3.

3. Evaporate 0.5 micron-thick gold on the upper surface of the glass substrate, then photolithography and dry etching, the etching depth is 0.5 micron, to form the lower electrode 3 and lead 2 of the deformable mirror, as shown in Figure 4.

4. Deposit a silicon nitride film 4 with a thickness of 0.5 microns by PECVD, then photolithography and dry etching, the etching depth is equal to the thickness of this film, so that the silicon nitride covers the lower electrode, thereby avoiding the electrostatic pull-in effect Damage to the device caused by a short circuit, as shown in Figure 5.

5. In the 4 inch N-type (100) 3-level double-sided polished Max silicon wafer with a thickness of 400 microns, thermally oxidize the oxide layer 6 with a thickness of 3 microns on the upper surface of the second substrate 7, and then bond on the surface of the oxide layer Combine a piece of the same silicon wafer and thin the silicon wafer to a thickness of 3 microns by mechanical or chemical methods and polish it with CMP as the structural layer of the mirror surface, as shown in Figure 6.

6. Use PECVD to deposit two layers of silicon dioxide 9 and two layers of silicon nitride 8 with a thickness of 300nm on both the upper and lower surfaces of the wafer obtained in the previous step, the order is silicon dioxide→silicon nitride→silicon dioxide→silicon nitride , to prepare for subsequent wet etching or substrate, as shown in FIG. 7 .

7. Perform two photolithography and two dry etching on the lower surface of the structure obtained in the previous step to form a stepped structure 10 to prepare for the subsequent wet etching of the substrate, as shown in FIG. 8 .

8. The step-shaped silicon nitride and silicon dioxide obtained in the above step are used as a mask to wet-etch the silicon substrate with 50% potassium hydroxide solution, and the etching stops at a distance of 20 microns from the upper surface of the substrate to form the upper electrode 11, as shown in Figure 9

9. Then dry etch away one layer of silicon nitride and silicon dioxide, use the remaining silicon nitride and silicon dioxide as a mask to wet etch the silicon substrate with 50% potassium hydroxide solution, and the etching depth is 10 microns, the connecting body 12 and the driver film 14 when forming the bonding, as shown in Figure 10

10. Perform anodic bonding of the upper surface of the structure obtained in step 3 and the lower surface of the structure obtained in step 9 under the conditions of 500V voltage, one standard atmospheric pressure and 300 degrees Celsius, and then photolithography on the upper surface and dry etching with SF ₆ Etch the release hole 13 and then use buffered hydrofluoric acid wet etching to release the oxide layer below the release hole, leaving only the connector 15 connecting the first layer and the second layer. The obtained structure is shown in FIG. 11 .

Example 2

Taking the manufacturing process of a 7×7 unit three-layer continuous surface-shaped micromechanical deformable mirror as an example, the present invention will be described in detail in conjunction with the accompanying drawings, and the specific steps are shown in Figure 1.

1. Take a piece of 5-inch Corning 7070 glass with a thickness of 1000 microns as the first substrate 1, as shown in FIG. 2 .

2. Use the first mask to lithography and wet-etch a groove with a depth of 2 microns with buffered hydrofluoric acid to prepare for laying the lower electrode, as shown in Figure 3.

3. Evaporate 2.0 micron-thick gold on the upper surface of the substrate, then photolithography and dry etching, the etching depth is 2 microns, to form the lower electrode 3 and lead 2 of the deformable mirror, as shown in Figure 4.

4. Deposit a silicon nitride film 4 with a thickness of 1 micron by LPCVD, then photolithography and dry etching, the etching depth is equal to the thickness of this film, so that the silicon nitride covers the lower electrode, thereby avoiding the electrostatic pull-in effect Damage to the device caused by a short circuit, as shown in Figure 5.

5. Get a 4-inch SOI wafer, the thickness of the silicon structure layer 5 of the wafer is 20 microns, the thickness of the oxide layer 6 is 10 microns, and the thickness of the second substrate 7 is 1000 microns, as shown in FIG. 6 .

6. Deposit two layers of silicon dioxide 9 and two layers of silicon nitride 8 with a thickness of 600nm on both the upper and lower surfaces of the wafer obtained in the previous step, and the order is silicon dioxide→silicon nitride→silicon dioxide→silicon nitride , to prepare for the subsequent wet etching of the substrate, as shown in FIG. 7 .

7. Perform two photolithography and two dry etching on the lower surface of the structure obtained in the previous step to form a stepped structure 10 to prepare for the subsequent wet etching of the substrate, as shown in FIG. 8 .

8. The step-shaped silicon nitride and silicon dioxide obtained in the above step are used as a mask to wet-etch the silicon substrate with 50% potassium hydroxide solution, and the etching stops at a distance of 52 microns from the upper surface of the substrate to form the upper electrode 11 , as shown in Figure 9

9. Then dry etch away a layer of silicon nitride and silicon dioxide, and use the remaining silicon nitride and silicon dioxide as a mask to wet etch the silicon substrate with a 50% potassium hydroxide solution to a depth of 50 microns. Connector 12 and driver film 14 when forming bonding, as shown in Figure 10

10. Perform anodic bonding of the upper surface of the structure obtained in step 3 and the lower surface of the structure obtained in step 9 under the conditions of 1000V, 500 degrees Celsius and a standard lower air pressure, then photolithography and dry etching of release holes with SF ₆ 13 and then use buffered hydrofluoric acid wet etching to release the oxide layer under the release hole, leaving only the connector 15 connecting the first layer and the second layer, and the obtained structure is shown in FIG. 11 .

Example 3

Taking the manufacturing process of a 10×10 unit three-layer continuous surface-shaped micromechanical deformable mirror as an example, the present invention will be described in detail in conjunction with the accompanying drawings, and the specific steps are shown in Figure 1.

1. Take a 4-inch N-type (100) double-sided polished Max silicon wafer with a thickness of 300 microns as the first substrate 1 with a resistivity of 10 ⁵ -2×10 ⁵ Ω·cm, as shown in FIG. 2 .

2. Use the first mask plate for photolithography and use 50% potassium hydroxide solution to wet-etch grooves with a depth of 0.1 micron to prepare for laying the lower electrode, as shown in Figure 3.

3. Deposit polysilicon with a thickness of 0.1 micron by LPCVD, then photolithography and dry etching, the etching depth is 0.1 micron, to form the lower electrode 3 and lead 2 of the deformable mirror, as shown in FIG. 4 .

4. Deposit a silicon nitride film 4 with a thickness of 0.1 micron by LPCVD, and then photolithography and etching. The etching depth is equal to the thickness of this film, so that the silicon nitride covers the lower electrode, thereby avoiding the electrostatic pull-in effect on the device Cause short circuit damage, as shown in Figure 5.

5. Get a 4-inch SOI wafer, the thickness of the silicon structure layer 5 of the wafer is 0.3 microns, the thickness of the oxide layer 6 is 0.3 microns, and the thickness of the second substrate 7 is 300 microns, as shown in FIG. 6 .

6. Use PECVD to deposit two layers of silicon dioxide 9 and two layers of silicon nitride 8 with a thickness of 800nm on both the upper and lower surfaces of the wafer obtained in the previous step, the order is silicon dioxide→silicon nitride→silicon dioxide→silicon nitride , to prepare for subsequent wet etching or dry etching, as shown in FIG. 7 .

7. Perform two photolithography and two dry etching on the lower surface of the structure obtained in the previous step to form a stepped structure 10 to prepare for the subsequent wet etching of the substrate, as shown in FIG. 8 .

8. The step-shaped silicon nitride and silicon dioxide obtained in the above step are used as a mask to wet-etch the silicon substrate with 50% potassium hydroxide solution, and the etching stops at a distance of 32 microns from the upper surface of the substrate to form the upper electrode 11 , as shown in Figure 9

9. Then dry etch away a layer of silicon nitride and silicon dioxide, and use the remaining silicon nitride and silicon dioxide as a mask to wet etch the silicon substrate with a 50% potassium hydroxide solution to a depth of 12 microns. Connector 12 and driver film 14 when forming bonding, as shown in Figure 10

10. Perform anodic bonding of the upper surface of the structure obtained in step 3 and the lower surface of the structure obtained in step 9 under the conditions of 600V, 1000 degrees Celsius and a standard lower air pressure, then photolithography and dry etching of release holes with SF ₆ Then use buffered hydrofluoric acid wet etching to release the oxide layer under the release hole, leaving only the connector connecting the first layer and the second layer, and the obtained structure is shown in FIG. 11 .

Claims (1)

1. manufacture craft based on the three-layer continuous surface type MEMS deformable mirror of bonding technology is characterized in that step is as follows:

(1) gets glass or silicon chip as substrate;

(2) photoetching and etching form 0.3～2.0 micron dark groove in substrate;

(3) polysilicon or the amorphous silicon or the metallic film of deposition 0.3～2.0 micron thickness, photoetching and etching then, etching depth equals the thickness of this layer film, forms the bottom electrode and the lead-in wire of distorting lens;

(4) deposit thickness is 0.1～1.0 micron a silicon nitride film, photoetching and etching then, and etching depth equals the thickness of this layer film, makes silicon nitride film that bottom electrode is covered, thereby avoids static to draw in effect causes short circuit to device infringement;

(5) get a SOI wafer, the silicon structure layer thickness of wafer is 0.3～20.0 micron, oxidated layer thickness is 0.3～10 micron, silicon base thickness is 300～1000 microns, perhaps in the oxide layer of 0.3～10 micron of upper surface thermal oxide one bed thickness of the common silicon chip silicon base of thick 300-1000 micron, be thinned to 0.3～20 micron thickness at silicon chip of oxide layer upper surface bonding and with this piece silicon chip with machinery or chemical method then and it is polished;

(6) the wafer upper and lower surface that step (5) is obtained all deposits two-layer silicon dioxide and two-layer silicon nitride, and order is silicon dioxide → silicon nitride → silicon dioxide → silicon nitride, for follow-up wet etching or dry etching are prepared;

(7) the structure lower surface that step (6) is obtained carries out Twi-lithography and etching, forms step-like structure, for follow-up wet etching is prepared;

(8) step-like silicon nitride and the silicon dioxide that obtains with step (7) is that mask carries out wet method or dry etching silicon base, and 12～52 microns places of upper surface that are etched to apart from silicon base stop;

(9) then the structure wet method or the dry etching of step (8) gained fallen one deck silicon nitride and silicon dioxide, carry out wet method or dry etching silicon base with residual silicon nitride and silicon dioxide as mask, the degree of depth is 10～50 microns;

(10) resulting structure upper and lower surface remaining silica and silicon nitride in the step (9) are removed with wet method or dry etching;

(11) lower surface with the structure that obtains in the upper surface of the structure that obtains in the step (3) and the step (10) carries out fusion bonding or anode linkage or low-temperature bonding;

(12) upper surface to the structure that obtains in the step (10) carries out photoetching and etching, forms release aperture, then the oxide layer below the release aperture is discharged, and only keeps and sees the connector that ground floor is connected with the second layer from the top down.

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