JPH06216397A - Manufacture of acceleration sensor - Google Patents

Abstract

(57) [Summary] [Object] To improve the dimensional accuracy of a support portion, a weight portion, and a beam portion of an acceleration sensor formed by processing a recess and a through hole in a silicon substrate. A dimensional accuracy of the recess is improved by digging a through hole portion having the same depth as the recess from the lower surface of the silicon substrate and then forming the remaining portion of the through hole by processing from the upper surface.
Further, the formation of the contact hole in the wiring and the processing of the through hole from the upper surface of the base body are simultaneously performed by the same mask, thereby improving the processing accuracy. Further, the pedestal is prevented from adhering to the weight portion by covering the lower surface of the weight portion with the insulating film or the passive metal film at the time of anodic bonding with the pedestal of the support portion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an acceleration sensor having a weight portion and a beam portion made of silicon, and a piezoresistor formed on the beam portion.

[0002]

2. Description of the Related Art An acceleration sensor for detecting an acceleration such as an impact or a centripetal force comprises a weight portion and a beam portion connected to the weight portion. 2 (a) and 2 (b) show the structure of a cantilever type acceleration sensor chip, in which an annular support portion 1 and its support portion are formed by processing a silicon plate to form a through hole 21 and a recess 22. It has a weight portion 2 supported through a thin beam portion 3, and piezoresistors 4 of different conductivity types are formed on the beam portion by impurity diffusion. Such a sensor chip is fixed on the pedestal 5 by the support 1. The piezoresistor 4 is bridge-connected by wiring on a chip (not shown).

Such an acceleration sensor is shown in FIG.
It is manufactured by the process shown in (g). That is, after a mask is formed on one surface of the silicon substrate 10 by photolithography, a piezoresistor 4 is formed by implanting impurities and driving, and a wiring 7 made of a metal such as Al that contacts the window portion of the oxide film 6 is formed. Provided by photolithography, a nitride film 8 for final passivation is formed by plasma CVD or the like [FIG. 3 (a)]. Next, after Al is deposited on both surfaces of the Si substrate 10 by vapor deposition or sputtering, an Al mask 11 for plasma etching is formed by photolithography using a double-sided aligner [FIG. 3 (b)]. Then, a concave portion 23 which becomes a part of the through hole 21 of FIG.
Protect with [Fig. 3 (c)]. Next, the Al mask 11 on the upper surface is removed by etching, a resist film 13 is formed on the exposed nitride film 8 by photolithography, and a window as a contact hole 24 is formed in the nitride film 8 by plasma etching [Fig. 3 (d)
]. Further, after protecting the upper surface with a resist film 13, the Al mask 11 on the lower surface is exposed and the recess 22 and the remaining portion 25 of the through hole 21 are formed by processing by plasma etching [FIG.
(e)]. After the support portion 1, the weight portion 2 and the beam portion 3 are formed in this manner, the Al mask 11 is etched to form a resist film.
13 is removed by ashing, and the stop and damping glass caps 9 and the glass pedestal 5 are bonded to the upper and lower surfaces by anodic bonding to prevent stress destruction of the thin beam portion 3 at the time of impact [Fig. 3 (f)]. . In this way, a large number of substrates having a three-layer structure are diced at the cut surface 14 into chips, which are then bonded to the substrate, and the wires 15 exposed to the contact holes 24 are bonded to the conductors 15 to form a power source for the bridge circuit. Make connections and make connections for extracting output signals [Fig. 3 (g)].

[0004]

The manufacturing method shown in FIG. 3 has the following problems. (1) In the case of a sensor for high acceleration detection of 20 to 50 G, the recess 23 formed in FIG. 7C has a depth of 20 to 30 μm. Therefore, the resist film 13 is applied in FIG. At this time, uneven coating of the resist occurs, resulting in poor pattern accuracy. (2) When plasma etching is performed from the bottom surface in FIG. 2E, the through hole 21 penetrates first and the resist film 13 applied from the top surface is exposed, so the processing depth of the recess 22 in the wafer is reduced. Variation occurs.
(3) In the same figure (f), at the time of anodic bonding with the glass pedestal 5, the weight portion 2 may be pulled by the electrostatic attractive force and adhere to the pedestal 5.

The object of the present invention is to solve these problems,
It is an object of the present invention to provide a method of manufacturing an acceleration sensor capable of simultaneously forming a large number of sensor chip structures with good dimensional accuracy on a single wafer.

[0006]

In order to achieve the above object, the present invention provides a wiring structure on one surface of a silicon substrate and then processes a recess and a through hole to form a supporting portion, a weight portion, and the supporting portion. In a method of manufacturing an acceleration sensor for forming a beam portion connecting both of them, a silicon substrate is processed from the other surface to form a part having the same depth as the recess and the recess of the through hole, and then processed from one surface to form the through hole. Shall form the rest of the. In addition, processing for forming a contact hole in an insulating film covering a wiring and forming a part of a through hole from one surface are performed at the same time. In that case, it is effective to form an oxide film as a mask used for processing for forming a part of the contact hole and the through hole. Furthermore, after forming the support portion, the weight portion, and the beam portion, when the surface of the support portion on the same side as the opening of the recess is bonded to the base by anodic bonding, the surface of the weight portion on the base side is an insulating film. Or covered with a passive metal film. It is effective that the insulating film is a silicon oxide film having a thickness of 0.6 μm or more and that the passivation metal is gold.

[0007]

According to the first aspect, since the through hole is not penetrated by performing the processing from the surface of the recess side first, the accuracy of the processing depth of the recess is improved. Then, if the through hole is formed by processing from the facing surface, the problem of processing depth does not occur in that case. The problem of resist film formation on the already formed through hole portion by simultaneously performing the processing for forming the contact hole on the insulating film covering the wiring according to claim 2 and the processing of a part of the through hole from the surface. It is possible to process with high accuracy. By forming the mask with an oxide film, it can be realized with better accuracy.

According to claims 4 and 6, when the weight portion is covered with the insulating film during the anodic bonding of the pedestal, the energy at the contact interface between the weight portion and the pedestal is reduced, and when the weight is covered with the passive metal film, the weight weight is reduced. Since the reaction between the silicon of the base and Si or O in the material of the base does not occur, the connection between the weight and the base does not occur.

[0009]

1 (a) to 1 (g) show a manufacturing process of an embodiment of the present invention, and the same parts as those in FIGS. 2 and 3 are designated by the same reference numerals. First, as in the case of FIG. 2A, a piezoresistor 4 is formed on one surface layer of the silicon substrate 10, an oxide film 6 and an Al wiring 7 are formed, bridge connection is performed, and then covered with a nitride film 8 [FIG. a)]. Next, the low temperature oxide film 12 is plasma C
It is formed on both sides by VD and a pattern is formed by photolithography [FIG. 1 (b)]. The pattern on the upper surface of the oxide film 12 has openings 31, 32 and 33 in the contact hole to the nitride film 8, the through hole portion and the bonding portion with the glass cap, and the pattern on the lower surface is the weight portion. It is open except where it is facing. Further, after the Al film 11 is formed on the lower surface by vapor deposition or sputtering, a pattern having openings 34 and 35 for forming recesses and through holes is formed, and the opening 33 on the upper surface is covered with the resist film 13. Figure 1 (c)]. Then, the recess 22 and the lower portion 25 of the through hole are processed by plasma etching from the lower surface [FIG. 1 (d)]. Next, after removing the Al mask 11 by etching, the silicon substrate 10 and the nitride film 8 are processed by plasma etching from the upper surface to form the upper portion 23 of the through hole and the contact hole 24. As a result, the supporting portion 1, the weight portion 2, and the beam portion 3 are generated [FIG. 1 (e)]. Then, the resist film 13 is removed by ashing, and the cap 9 is adhered to the exposed surface and the pedestal 5 is adhered to the lower surface of the support portion 3 by anodic bonding. At this time, since the lower surface of the weight 2 is covered with the low temperature oxide film 12, it does not adhere to the pedestal 5 [FIG. 1 (f)]. Both the cap 9 and the pedestal 5 are made of borosilicate glass.
Finally, the cutting surface 14 is diced into chips, and the conductors 15 are bonded to the wirings 7 to complete the acceleration sensor [Fig. 1 (g)]. In order to prevent the weight 2 and the pedestal 5 from adhering to each other in the process of FIG. 1 (f), the low temperature oxide film 12 has a thickness of 0.1.
It is necessary that the thickness is 6 μm or more. Further, instead of the oxide film, another heat resistant insulating film or a passive metal film such as gold can be used. A four-sided beam type acceleration sensor can be manufactured in the same manner.

[0010]

According to the present invention, the concave portion and the through hole for forming the weight portion and the beam portion of the acceleration sensor are dug at the same depth portion of the concave portion and the through hole from the lower surface first, and then the upper surface. By digging the remaining portion of the through-hole from the above, the processing accuracy of the depth of the recess can be improved. Further, the processing accuracy can be improved by simultaneously performing the processing from the upper surface of the through hole and the formation of the contact hole in the insulating film covering the wiring using the same mask. Further, by covering the lower surface of the weight portion with the insulating film or the passive metal film, it is possible to prevent the weight portion and the pedestal from adhering to each other during anodic bonding with the support portion of the pedestal.

[Brief description of drawings]

FIG. 1 shows a manufacturing process of an acceleration sensor according to an embodiment of the present invention.
Sectional views shown in order from (a) to (g)

2 (a) is a plan view and FIG. 2 (b) is a sectional view showing an acceleration sensor chip manufactured in the process of FIG.

[Figure 3] Conventional manufacturing process of acceleration sensor (a) to (g)
Sectional view showing in order

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Support part 2 Weight part 3 Beam part 4 Piezoresistive 5 Pedestal 6 Oxide film 7 Wiring 8 Nitride film 9 Cap 10 Silicon substrate 11 Al film 12 Oxide film 13 Resist film 14 Cut surface 15 Conductive wire 21 Through hole 22 Recess 23 Through hole Upper part 25 Lower part of through hole

Claims (7)

[Claims] 1. A method for manufacturing an acceleration sensor, comprising: providing a wiring structure on one surface of a silicon substrate; then processing a recess and a through hole to form a support portion, a weight portion, and a beam portion connecting both of them. A method of manufacturing an acceleration sensor, characterized in that the base body is processed from the other surface to form a recess and a part of the through hole having the same depth as that of the recess, and then processed from one surface to form the remaining part of the through hole. . 2. A method for manufacturing an acceleration sensor, comprising: forming a wiring structure on one surface of a silicon substrate; then processing a recess and a through hole to form a support portion, a weight portion, and a beam portion connecting both of them. A method for manufacturing an acceleration sensor, characterized in that a process for forming a contact hole in an insulating film covering the substrate and a process for forming a part of the through hole from one surface are performed at the same time. 3. The method of manufacturing an acceleration sensor according to claim 2, wherein a mask used for processing for forming a part of the contact hole and the through hole is formed of an oxide film. 4. A method of manufacturing an acceleration sensor, comprising: forming a wiring structure on one surface of a silicon substrate; then processing a recess and a through hole to form a support portion, a weight portion, and a beam portion connecting both of them. After the formation of the base portion, the weight portion, and the beam portion, when the surface of the support portion on the same side as the opening of the concave portion and the pedestal are bonded by anodic bonding, the surface of the weight portion on the pedestal side is covered with the insulating film. A method of manufacturing an acceleration sensor, comprising: 5. The method of manufacturing an acceleration sensor according to claim 4, wherein the insulating film is a silicon oxide film having a thickness of 0.6 μm or more. 6. A method of manufacturing an acceleration sensor, comprising: providing a wiring structure on one surface of a silicon substrate; then processing a recess and a through hole to form a support portion, a weight portion, and a beam portion connecting both of them. When the surface of the support part on the same side as the opening of the recess and the pedestal are bonded by anodic bonding after the formation of the weight part, the weight part and the beam part, the surface of the weight part on the pedestal side is formed of a passive metal film. A method of manufacturing an acceleration sensor, which is covered. 7. The method of manufacturing an acceleration sensor according to claim 6, wherein the passivation metal is gold.