CN101733703B - Process method for reducing deformation of micro suspension structure in chemically mechanical thinning and polishing process - Google Patents

Abstract

The invention is a process method for reducing the deformation of a micro-suspension structure in chemical mechanical thinning and polishing. It is characterized in that the wafer used for chemical mechanical thinning and polishing is a three-dimensional two-layer wafer formed by a bonding process. The device design requires that there is a cavity array formed by wet etching or dry etching on the back of the wafer that needs to be thinned and polished, and the cavity array forms a bonding surface with the substrate wafer; It is released in a dry etching or wet etching process to form an array of movable suspension structures supported by thin beam structures such as straight beams or folded beams; by introducing an auxiliary support structure as a compensation structure for the cavity structure before the release of the suspension structure. Advantages: This method is simple in process, easy to implement, does not cause any impact on the device, and makes the warping deformation of the suspension structure very small, improves the performance of MEMS devices, and can be widely used in the manufacture of micro-inertial devices, micro-fluids, and micro-radio frequency and other MEMS devices.

Description

A process method for reducing deformation of micro-suspension structure in chemical mechanical thinning and polishing

technical field

The invention relates to a process for reducing the deformation of a micro-suspension structure in chemical-mechanical thinning and polishing, which belongs to the field of micro-electro-mechanical system (MEMS) processing, and in particular to a method for reducing the deformation of a three-dimensional micro-mechanical structure with a large-area suspension structure. Chemical Mechanical Thinning of Devices by Polishing Stress and Strain Methods.

Background technique

MEMS sensors are usually composed of three-dimensional micro-mechanical structures, detection circuits and signal processing circuits. The microstructure processed by the MEMS bulk silicon process has the advantages of high aspect ratio, large sensitive mass, and high sensitivity, so it is widely used in the processing of three-dimensional microstructures.

The three-dimensional micro-mechanical structure processed by the MEMS bulk silicon process usually uses single crystal silicon as the structural material, and the three-dimensional structure is formed by bonding technology, and then the thickness of the silicon structure layer is thinned according to the design requirements. Currently, there are two methods for thinning the silicon structural layer, one is chemical wet etching, and the other is chemical mechanical polishing (CMP). The advantage of chemical wet etching thinning is fast thinning rate and low cost, but the disadvantage is that the flatness and roughness of the structure are poor, which will affect the subsequent process and device performance. The CMP technology combines the advantages of chemical and mechanical polishing. The microstructure after thinning and polishing has the advantages of high surface finish and flatness, low damage, and good polishing consistency. The sheet is prone to warping and deformation, which affects the performance of the microsensor.

Three-dimensional micromechanical structures usually have movable parts in the form of suspended structures, such as micro-accelerometers, micro-gyroscopes, micro-oscillators, etc. The residual stress generated by chemical mechanical thinning and polishing will cause the structure to warp and deform. Therefore, it is necessary to use reasonable techniques to reduce residual stress and warp deformation of the structure, thereby improving the performance of the microsensor.

Contents of the invention

The invention proposes a process method for reducing the deformation of the micro-suspension structure in chemical mechanical thinning and polishing. The method is to add an auxiliary support structure to the cavity structure before the suspension structure is released. Due to the effect of the auxiliary support structure, the stress introduced by the cavity structure is greatly reduced during the thinning and polishing process. After thinning and polishing, the auxiliary support structure is removed by wet etching or dry etching process, and the suspension structure is released at the same time. The warping deformation of the released suspension structure is greatly reduced, and it becomes an independent movable structure.

The technical solution of the present invention: a process method for reducing the deformation of the micro-suspension structure in chemical mechanical thinning and polishing, which is characterized in that the wafer used for chemical mechanical thinning and polishing is a three-dimensional two-layer circle formed by a bonding process According to the design requirements of MEMS devices, there is a cavity array formed by wet etching or dry etching on the back of the wafer that needs to be thinned and polished. The cavity array and the substrate wafer form a bonding surface; the cavity structure array It is released in the subsequent dry etching or wet etching process to form an array of movable suspension structures supported by thin beam structures such as straight beams or folded beams; by introducing an auxiliary support structure as the cavity structure before the release of the suspension structure compensation structure.

The technical effect of the present invention: overcomes the problem of warping deformation caused by stress in the thinning and polishing process of the suspension structure, and provides a process compensation method, that is, adding an auxiliary support structure on the cavity structure before the release of the suspension structure, due to The role of the auxiliary support structure, during the thinning and polishing process, the stress introduced by the cavity structure is greatly reduced. After thinning and polishing, the auxiliary support structure is removed by wet etching or dry etching process, and the suspension structure is released at the same time. The warping deformation of the released suspension structure is greatly reduced, and it becomes an independent movable structure. The cross-section of the compensation structure occupies a very small proportion of the cross-section of the suspension structure, which will not have any impact on device performance. This process compensation technology can be applied to the processing technology of micro-inertial devices, which greatly improves the performance of three-dimensional micro-machines with large-area suspension structures. Device performance and yield.

Description of drawings

The present invention will be described in detail below in conjunction with the accompanying drawings.

Figure 1 is a bonded wafer requiring thinning and polishing.

Figure 2 is a three-dimensional view of the cavity array.

Fig. 3 is a schematic diagram of chemical mechanical thinning and polishing.

Fig. 4 is a schematic diagram of the warping deformation of the cavity structure.

Figure 5 is a schematic illustration of a cross-sectional type of compensation structure.

Fig. 6 is a schematic diagram of distribution types of compensation structures.

Fig. 7 is a schematic diagram of a small deformation of the cavity structure with the addition of the compensation structure.

Fig. 8 is a schematic diagram of the suspension structure unit after the release of the compensation structure is added.

In the figure, 1 is the cavity structure, 2 is the compensation structure, 3 is the polishing pad, 4 is the rotating chassis, 5 is the polishing liquid, 6 is the fixture disc, 7 is the wax, and 8 is the wafer.

Detailed ways

1. The process sheet in this process is a two-layer bonded wafer, as shown in Figure 1, where the front side of the wafer to be thinned and polished is the thinned surface, and the back side is the bonded surface. According to design requirements, wet etching or dry etching is used on the back to form a cavity structure array, as shown in Figure 2. Figure 3 is a schematic diagram of chemical mechanical thinning and polishing. Cavity structure In the chemical mechanical thinning and polishing process, due to the pressure of the grinding block, the cavity structure will be warped and deformed, as shown in FIG. 4 . After thinning and polishing, the cavity structure is released by wet etching or dry etching to form a movable suspension structure that is only connected to the anchor area through thin beams. Due to the stress introduced by thinning and polishing, it cannot be effectively released in the suspension structure. There will be a large residual deformation in the suspension structure, thereby affecting the performance of the device.

2. In order to reduce the impact of the stress introduced by thinning and polishing on the performance of the suspension structure, process compensation technology is adopted, that is, an auxiliary support structure is added to the cavity structure before the release of the suspension structure, and the support structure is bonded to another wafer. It is also an anchor region structure in the thinning polishing process. The cross-section of the auxiliary support structure can be in the shape of a circle, a rectangle, a regular polygon, etc., as shown in Figure 5, the number of auxiliary support structures can be one or more, and multiple support structures can be distributed in a ring or a regular polygon, as shown in Figure 5 6.

3. The wafer with auxiliary structure will become the anchor structure in the cavity array after wet etching or dry etching. After bonding with another wafer, the bonded wafer will be chemically mechanically thinned polishing. Due to the supporting role of the anchor region structure formed by the auxiliary support structure in the thinning and polishing process, the stress introduction of the cavity structure in the thinning and polishing process is reduced, and the deformation of the cavity structure is small after the thinning and polishing process, and there is almost no warping curved deformation, as shown in Figure 7.

4. After thinning and polishing, the anchor region structure formed by the auxiliary support structure has become a redundant structure of the device. In the process of releasing the suspension structure by dry etching or wet etching, the auxiliary support structure can be removed at the same time to obtain The independently movable suspension structure and the tiny residual stress of the cavity structure will also be fully released, as shown in Figure 8, the suspension structure has no deformation, and the device performance is greatly improved.

Claims (3)

1. one kind reduces the process that micro suspension structure is out of shape in chemically mechanical thinning and polishing, it is characterized in that being used for disk two layers of disk of three-dimensional of chemically mechanical thinning and polishing for adopting bonding technology to form, designing requirement according to the MEMS device, the array of cavities that has wet etching or dry etching to form at the disk back side that needs attenuated polishing, array of cavities and substrate disk form bonding face; The array of cavities structure is released in the dry etching of postorder or wet corrosion technique, and the thin beam structure that is formed by straight beam or folded beam supports movable suspension structure array; By introducing the collocation structure of the cavity body structure before auxiliary support structure discharges as suspension structure.

2. a kind of process that micro suspension structure is out of shape in chemically mechanical thinning and polishing that reduces according to claim 1, the cross sectional shape that it is characterized in that collocation structure is circle, rectangle or regular polygon, the collocation structure number is one or more, and many collocation structures are that annular spread or regular polygon distribute.

3. a kind of process that micro suspension structure is out of shape in chemically mechanical thinning and polishing that reduces according to claim 1, it is characterized in that collocation structure is after attenuated polishing technology is finished, collocation structure becomes the redundancy structure of device, adopting dry etching or wet etching to carry out in the process of suspension structure release, can remove collocation structure simultaneously, thereby obtain independent movable suspension structure, the small residual stress of cavity body structure also will fully be discharged.

Images