CN100495038C - Fabrication method of three-dimensional integrated micromachined acceleration sensor - Google Patents

Abstract

The invention relates to a three-dimensional integrated high-range acceleration sensor. It is characterized in that the three-dimensional acceleration sensor is composed of three mutually independent acceleration sensing elements; the structures of the acceleration sensing elements in the X and Y axis directions are the same, and their sensitive directions are in the direction of the silicon plane. The sensing elements of the structure are arranged perpendicular to each other; the acceleration sensing element in the Z-axis direction is another structure, and its sensitive direction is the vertical direction of the silicon chip, and one of the acceleration sensing elements arranged in parallel in the X and Y-axis directions Side; it is manufactured by MEMS conventional technology, and the process compatibility of two different sensing elements is considered, so that the sensitive elements in the three directions of the manufactured sensor have no interference phenomenon, and 10,000-100,000 g can be designed according to requirements. Three-dimensional high-shock acceleration sensors with different ranges.

Description

Fabrication method of three-dimensional integrated micromachined acceleration sensor

technical field

The invention relates to a three-dimensional integrated high-range micro-mechanical acceleration sensor and a manufacturing method thereof, belonging to the technical field of silicon micro-mechanical sensors.

Background technique

With the development of micro-mechanical system (MEMS) sensor technology, various MEMS sensors have attracted people's attention, among which micro-mechanical acceleration sensors have been widely used in different fields, such as automotive airbags, robot industry and automation control. However, in the monitoring process of various sports, the one-dimensional acceleration sensor can no longer meet the monitoring requirements well, so the three-dimensional acceleration sensor has become an important direction for the development of MEMS acceleration sensors.

In recent years, there have been continuous reports on the development of monolithic integrated 3D acceleration sensors. The common three-dimensional acceleration sensor is composed of a single sensitive element, and its sensitive element is a mass block-spring system composed of a sensitive mass block with multiple beams. This type of acceleration sensor is used in three directions in the same system. The minimum torsional mode that exists at the same time responds to the acceleration of the X, Y and Z axes at the same time. However, it has a high paraxial sensitivity, which leads to large coupling interference in the three directions, and the output of the signal is prone to interference. Therefore, the inventor proposed the idea of integrating three independent piezoresistive acceleration sensing elements on the same chip to form a three-dimensional acceleration sensor, so that this structure can simultaneously detect accelerations in the directions of the X, Y and Z axes. , there will be no mutual crosstalk, the acceleration information detection is relatively accurate, and the reliability is relatively high. Among them, the piezoresistive sensing element has great advantages over the capacitive acceleration sensing element in terms of manufacturing process and signal detection circuit. At the same time, the processes of these two different types of sensing elements are easier to integrate and reach a consensus .

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the existing three-dimensional acceleration sensor, and provide a three-dimensional integrated micro-mechanical acceleration sensor and a manufacturing method. In the present invention, the inventor proposes to integrate two existing one-dimensional piezoresistive high-impact acceleration sensing elements into a three-dimensional impact acceleration sensing device and the corresponding manufacturing process. A three-dimensional acceleration sensor with equivalent sensitivity and frequency bands in three axes is obtained, and the sensitive elements in the three directions hardly interfere with each other, and three-dimensional acceleration sensor devices with different range requirements can be designed according to needs.

The structural features of the existing two types of high-impact acceleration sensing elements integrated in the three-dimensional acceleration sensing device are firstly described below.

1. The characteristics of the basic structure design of the high impact acceleration sensing element in the X and Y axis directions:

The basic structure of the high-impact acceleration sensing element in the X and Y-axis directions is composed of a cantilever beam 5 , an anti-high overload impact surface 6 , a sensitive resistor 7 and a silicon frame 8 . The anti-high overload impact surface is located on the upper and lower sides of the cantilever beam; the high impact acceleration elements in the X and Y axis directions are respectively composed of two identical basic structures. When subjected to acceleration, the two resistors on the cantilever beam in the basic structure increase and decrease respectively. In order to facilitate the formation of a Wheatstone full bridge, a "several" resistor design is adopted, that is, two resistors are connected in series. The basic principle of work: its sensitive direction is in the silicon plane, when subjected to impact acceleration, the cantilever beam bends laterally, through the piezoresistive effect, the resistivity of the sensitive resistor changes, and the change signal is output through the Wheatstone bridge to determine the corresponding acceleration value. The sensitive direction of this structure is in the silicon plane, and it adopts a hyperboloid overload protection structure, so that the sensitive structure is well protected in the case of large impact overload, so as to meet the use in high impact environments; and the hyperboloid is also The film damping of the acceleration element is improved, the free vibration mode is effectively suppressed, and the measurement accuracy is improved; on the other hand, the designed sensitive structure cantilever beam has a length-thickness ratio of about 35:1 and a width-thickness ratio of about The ratio is 3:1, so that it has a wide frequency band while obtaining high sensitivity, and effectively suppresses the vibration effect perpendicular to the sensitive direction.

2. The characteristics of the structural design of the high-impact acceleration sensor element in the Z-axis direction:

The structure of the high-impact acceleration sensing element in the Z-axis direction is composed of a sensitive thin plate 1 , a quality block 2 , a sensitive resistor 3 and an outer frame 4 . The sensitive direction of this structure is perpendicular to the silicon plane. It adopts a double-mass structure supported by double ends, and the structure is symmetrical. At the same time, the width of the sensitive thin plate is basically the same as that of the mass. The basic principle of work: when subjected to impact acceleration, the relative movement of the mass block causes the deformation of the sensitive thin plate, which causes the resistivity of the piezoresistor on the sensitive thin plate to change, and the change signal is output through the Wheatstone bridge to determine the corresponding acceleration value . This structure makes the sensitive thin plate have a larger stiffness coefficient. When subjected to high impact, the stress on the sensitive thin plate is smaller than the silicon fracture stress, ensuring that the sensitive structure will not break and fail; on the other hand, the symmetrical structure can better control the lateral effect. , that is, the vibration effect in the non-sensitive direction is controlled; and the sensitive thin plate with a larger stiffness coefficient makes the high-impact acceleration sensing element in the Z-axis direction have a higher natural frequency.

In summary, it is not difficult to see that there are many similarities in performance between the two types of acceleration sensing elements, so the inventors of the present application can easily make the two compatible and integrated into a three-dimensional acceleration sensor through appropriate design integration; and Through process integration, the processes of the two are compatible with each other, and the production of three-dimensional devices can be completed by using the conventional process of silicon micromachining technology.

In the manufacture of three-dimensional integrated acceleration sensor devices, the key is to obtain a manufacturing process that is compatible with two different types of acceleration sensor elements. First of all, the sensing elements in the X and Y axis directions and the sensitive structure of the sensing element in the Z axis direction need to thin the silicon wafer in the vertical direction. According to the overall design of the three-dimensional device, the two achieve the same thinning thickness. , that is to achieve compatibility in the thinning process steps perpendicular to the direction of the silicon wafer, which can be carried out together without interfering with each other; secondly, it is necessary to form a proper The damping distance of the sensor element in the X and Y axis directions does not have this requirement. In order to achieve process compatibility, the method is to add a photolithography plate before thinning the silicon wafer in the vertical direction. The thinning area of this plate is larger than The thinning area in the vertical direction of the silicon wafer, that is, this version is to form a pre-thinning groove, and the thinning in the vertical direction of the silicon wafer is carried out in this groove. While forming the pre-thinning groove, the damping gap formed between the mass block and the lower cover plate in the sensing element structure in the Z-axis direction will not affect the sensing element structure in the X and Y directions in the Z-axis direction. The size is affected, so that the two are compatible in this step; third, the sensing element in the Z-axis direction needs the lower cover to form a damping gap. Here, the silicon glass bonding process is used for the original chip bonding, which not only It satisfies the requirements of the sensing element in the Z-axis direction, and also protects the back of the sensing element in the X-axis and Y-axis directions. The rest of the fabrication process such as resistors, leads, and the use of deep reactive ion etching (DRIE) to release sensitive structures are the same compatible process in both sensing elements and can be performed simultaneously. While the deep reactive ion etching process is used to release the sensitive structure in the X and Y axis directions, the overload protection curved surface structure corresponding to the cantilever beam is processed.

The basic manufacturing process of the present invention is as follows:

1. Use anisotropic etching solution to etch the back of the double-sided polished N-type (100) silicon wafer to form a pre-thinning groove, and at the same time etch to form a damping distance between the sensor element structure and the cover plate in the Z-axis direction .

2. Use anisotropic etching solution to thin the silicon wafer in the vertical direction in the pre-thinning tank, so as to achieve the size value of the sensitive structure of the two types of sensing elements on the vertical direction of the silicon wafer, and at the same time corrode to form a sensor in the Z-axis direction. The quality block of the sensing element.

3. Use the method of ion implantation of boron ions or diffusion of boron source to make sensitive resistors, the square resistance value of which is in the range of 80~90 ohms.

4. Make ohmic contact area and lead hole.

5. Deposit aluminum film on the surface of the silicon wafer, and form leads and pads.

6. Carry out anodic bonding of silicon glass to form the lower cover plate of the three-dimensional device. The damping required by the sensing element structure in the Z-axis direction is achieved, and the device is also protected.

7. Using deep reactive ion etching process to simultaneously release sensitive structures in X, Y and Z axis directions.

It can be seen that the three-dimensional integrated micro-mechanical acceleration sensor provided by the present invention is designed by utilizing two different types of acceleration sensing elements, specifically, it is formed by integrating three mutually independent acceleration sensing elements . The structures of the acceleration sensing elements in the X and Y axis directions are the same, and the sensitive direction is the silicon plane direction, and two sensing elements with the same structure are arranged perpendicular to each other; the acceleration sensing element in the Z axis direction has another structure, and its The sensitive direction is the vertical direction of the silicon chip, and one side of the acceleration sensing element in the X and Y axis directions is arranged in parallel. The arrangement of the specific three-dimensional acceleration sensor structure is shown in Fig. 3 . In terms of manufacturing process, the device adopts the silicon glass bonding process to form the lower cover plate of the device. While forming the damping gap required by the acceleration sensing element in the Z-axis direction, it also plays a role in the acceleration sensing element in the X and Y-axis directions. Protective effect: the method of making the thinning pattern perpendicular to the direction of the silicon wafer in the pre-thinning groove solves the problem of the difference in the technology of the two types of devices. In this method, the pre-thinning groove is firstly made, and at the same time, the gap between the acceleration sensing element in the Z-axis direction and the cover plate is formed. The whole device is made in the pre-thinning groove perpendicular to the thinned area of the silicon wafer. The corrosion and thinning of the corrosive solution meets the requirements of the size of the sensitive structure, and at the same time, the mass block of the acceleration sensing element in the Z-axis direction is made.

In summary, it is not difficult to see that the present invention utilizes the various advantages of two different types of acceleration sensor elements, which provides a good basis for the design of three-dimensional acceleration sensors for integration, and through appropriate design Adjustment can obtain a three-dimensional acceleration sensor with relatively consistent sensitivity and frequency band in the three-axis direction, which is very important for the performance of the three-dimensional acceleration sensor device; on the other hand, since the three-dimensional device is composed of three independent acceleration sensors The components are integrated, so the signals in the three directions will not interfere with each other, and the acceleration signals in each direction can be accurately output and extracted. And by properly designing and modifying the key dimensions of the sensitive structure, three-dimensional high-impact acceleration sensors with different ranges ranging from 10,000 to 100,000 can be obtained. In terms of the manufacturing process of the three-dimensional acceleration sensor, the acceleration sensing elements in the three directions can be well compatible with each other in the process, and the manufacturing process is a conventional process of micromachining, so the final realization of the device is also very easy. The production cost is not high, and it is easy to realize large-scale production.

Description of drawings

Figure 1: Schematic diagram of one-dimensional acceleration sensing elements with two different structures

(a): The sensitive direction is the one-dimensional acceleration transmission element of the Z axis

(b): One-dimensional sensing element whose sensitive direction is X or Y axis

Figure 2: Schematic diagram of the structural dimensions of one-dimensional acceleration sensing elements with two different structures

(a): Schematic diagram of the structural size of the one-dimensional acceleration transmission element whose sensitive direction is the Z axis

(b): Schematic diagram of the structural dimensions of the one-dimensional acceleration transmission element whose sensitive direction is the X and Y axes

Figure 3: Schematic diagram of the top view of the three-dimensional integrated acceleration sensor

(a): One-dimensional acceleration transmission element of X, Y axis

(b): One-dimensional acceleration transmission element of Z axis

Figure 4: Schematic diagram of <110> lobe compensation graphs

In the picture:

1—Sensitive thin plate 5—Cantilever beam

2—mass block 6—overload protection surface

3—Strip resistance 7—"Several" shape resistance

4—Silicon frame 8—Silicon frame

h—thickness of cantilever beam a ₁ —length of sensitive thin plate

L—length of cantilever beam h ₁ —thickness of sensitive thin plate

h ₂ —mass thickness

a ₂ —the total length of a single mass and a single sensitive thin plate

Detailed ways

The substantive characteristics and remarkable progress of the present invention are further illustrated below through specific examples, but the present invention is by no means limited to the examples described.

Design and manufacturing process of a three-dimensional integrated high-shock acceleration sensor with a measuring range of 50,000 g:

1. The structural size of the acceleration sensing element in the X and Y axis directions: the length of the cantilever beam is 515 μm, the thickness is 16 μm, and the width is 50 μm;

2. The structural size of the acceleration sensing element on the Z axis: the thickness of the thin plate is 50 μm, the length is 50 μm, the thickness of the mass block is 370 μm, the total length of the mass block and the thin plate is 670 μm, and the width of the entire structure is 1400 μm.

The dimensions of the entire three-dimensional integrated high-shock acceleration sensor are: length 4100 μm, width 3500 μm, thickness 920 μm. In this production process, the potassium hydroxide (KOH) corrosion solution with a mass concentration of 40% and a temperature of 50°C is used to form the width of the cantilever beam, the thickness of the thin plate and the mass block at the same time, so the KOH corrosion solution must be considered For the convex corner problem, we used the literature ("Etching front control of<110>strips for corner compensation"MHBao, C.Burrer, J.Bausells, J.Esteve, S.Marco.Sensors and Actuators A, 37-38, 727 -732, (1993).) In the convex corner compensation technology, the multi-branch <110> strip shape in the text is used for corrosion compensation on the side of the convex corner to be repaired. The effective compensation strip length formula is: L _eff = 2.7H _c =L ₁ +L ₂ +L ₃ +5.37B, H _c is the corrosion depth; B is the width of the <110> compensation strip. As shown in Figure 4. Therefore, this process also has requirements on the thickness of the entire silicon wafer. According to the needs, a silicon wafer with a thickness of 420 μm is selected here to design the effective length of the specific convex corner compensation strip.

Concrete process implementation steps are as follows:

1. The starting silicon wafer is an N-type (100) double-polished silicon wafer with a thickness of 420 μm.

2. After oxidation photolithography, use a KOH etching solution with a mass concentration of 40% and a temperature of 50°C to etch the back of the silicon wafer to form a 2.4 μm pre-thinning groove. 2.4 μm is the area between the structural mass block of the sensitive element in the Z-axis direction Damper spacing between cover plates.

3. Oxidize again, and make the required graphics in the pre-thinning tank. Use a KOH etching solution with a concentration of 40% and a temperature of 50°C to etch the back of the silicon wafer. In the pre-thinning tank, the acceleration in three directions The structural part of the sensitive element is thinned to 50 μm, and the mass block of the sensitive element in the Z-axis direction is made.

4. Using the method of boron ion implantation, boron ions are implanted on the front side of the silicon wafer to form a sensitive resistor with piezoresistive effect, and the resistance is 2.5~3kΩ.

5. Etching lead holes in the ohmic contact area.

6. Sputter an aluminum film with a thickness of 6500 angstroms on the front side of the silicon wafer, and form leads and pads.

7. Use a bonding machine to perform anodic bonding of silicon glass on the back of the silicon. The bonding temperature is 380°C. First apply a voltage of -600V for 3 minutes, then add a voltage of -1200V for 8 minutes, cool to room temperature and take it out.

8. Using deep reactive ion etching (DRIE) process to simultaneously release sensitive structures in X, Y and Z directions.

Explanation: The thickness and width of the sensitive structure mentioned in the invention are respectively, the dimension consistent with the direction of movement is the thickness of the structure, and the dimension perpendicular to the direction of movement is the width of the structure.

Claims (2)

1. the method for making of the integrated high-range acceleration transducer of a three-dimensional, it is characterized in that: described three dimension acceleration sensor is to be integral by three separate acceleration sensing sets of elements to constitute; A class X wherein, the structure of the acceleration sensing element of Y direction is identical, its sensitive direction is at the silicon in-plane, by semi-girder, anti high overload impacts curved surface, sensitive resistance and silicon frame constitute, anti high overload impact curved surface be positioned at semi-girder on, following two sides, the mutual vertical arrangement of the sensor element of above-mentioned two same structures, the acceleration sensing element of one class Z-direction is by responsive thin plate, mass, sensitive resistance and outside framework constitute, the double quality blocks structure that adopts both-end to prop up admittedly, its sensitive direction is the vertical direction of silicon chip, and parallel arrangement is in X, one side making step of the acceleration sensing element of Y direction is:

(a) corrosion forms pre-reducing thin groove at the N of twin polishing type (100) the silicon chip back side to adopt anisotropic etch solution, simultaneously also corrosion form Z-direction the sensing element structural requirement and cover plate between the damping spacing;

(b) adopt anisotropic etch solution in pre-reducing thin groove, to carry out the whole attenuate of silicon chip vertical direction, reach the structure of the acceleration sensing element of making X, Y direction and the size value of acceleration sensing component structure on the silicon chip vertical direction of Z-direction, corrosion simultaneously forms the mass of Z-direction sensing element;

(c) method in employing boron ion implantation ion or diffused with boron source is made sensitive resistance, and its square resistance is in 80～90 ohm of scopes;

(d) make ohmic contact regions and fairlead;

(e), and form lead-in wire and pad at silicon chip upper surface deposit aluminium film;

(f) carry out the anode linkage of silex glass, form the lower cover of three-dimension device; Reach the required damping of sensing element structure of Z-direction, simultaneously device has also been played protection;

(g) adopt deep reaction ion etching technology to discharge the sensitive structure of X, Y and Z-direction simultaneously; Before the silicon chip vertical direction is carried out attenuate, increase a reticle, the area of reticle attenuate forms a pre-reducing thin groove greater than the area that carries out attenuate in the silicon chip vertical direction, and the attenuate of two vertical silicon chip directions carries out in this groove; When forming pre-reducing thin groove, the damping gap that the mass in the sensing element structure of Z-direction forms between lower cover makes and reaches compatibility on both technologies.

2. press the method for making of the integrated high-range acceleration transducer of the described three-dimensional of claim 1, it is characterized in that having adopted the convex corner compensation technology at the whole attenuate that adopts anisotropic etch solution to carry out silicon chip, adopt multiple-limb＜110 being mended salient angle one side strip corrodes compensation.

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