JP4721497B2 - Silicon wafer processing method and semiconductor strain sensor manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for processing a silicon wafer that improves the adverse effects of microdefects that occur when a silicon wafer is directly wet etched , and, for example, in a manufacturing process of a piezoresistive pressure sensor. The present invention relates to a method for manufacturing a semiconductor strain sensor suitable for use in a process of forming a thin portion as the bottom of the recess .
[0002]
[Prior art]
As shown in FIGS. 2 and 3, a general piezoresistive pressure sensor 1 is provided with a recess 3 on the back side (lower side of FIG. 2) of a silicon substrate 2, and the bottom of the recess 3 is, for example, A diaphragm (thin wall portion) 4 having a thickness of about several μm is formed, and four piezoresistive portions 5 for strain detection are formed on the surface side. As shown in FIG. 3, the four piezoresistive portions 5 are arranged in a diamond shape in which two pairs are opposed to each other in two orthogonal directions, and one pair of the piezoresistive portions 5 is arranged so as to cover the edge of the diaphragm 4. The other pair of piezoresistive portions 5 are arranged near the center of the diaphragm 4. Although the detailed structure is omitted in FIGS. 2 and 3, pressure detection is performed on the surface of the silicon substrate 2 such as wiring that connects the four piezoresistors 5 so as to form a Wheatstone bridge circuit. A circuit is formed. Reference numeral 7 denotes an oxide film (for example, SiO ₂ ) as an insulating film for forming a detection circuit on the surface of the silicon substrate 2.
[0003]
The piezoresistive pressure sensor 1 is used by being bonded and fixed to a table 8 made of glass or the like, but the one that seals the recess 3 detects absolute pressure (vacuum pressure) and makes the recess 3 communicate with the outside. The one detects the relative pressure. In the piezoresistive pressure sensor 1, when pressure acts on the diaphragm 4 as shown by an arrow, the diaphragm 4 is dented by the pressure, and stress is generated in the piezoresistive portion 5 on the diaphragm 4, and the piezoresistive effect causes piezoresistance. The resistance of the part 5 changes. This change in resistance is electrically taken out as an output of a Wheatstone bridge circuit composed of four piezoresistors 5 and is converted into pressure to detect the pressure.
[0004]
The recess 3 for obtaining the diaphragm 4 is formed by etching (wet etching) a silicon wafer 2 ′, which is a thin disc of single crystal silicon, from the back side with an etching solution as shown in FIG. However, conventionally, the silicon wafer 2 ′ is simply etched and no special treatment is applied to the inner surface of the recess 3.
Each silicon substrate 2 is obtained by forming a large number of recesses 3 in a silicon wafer 2 ′ and then cutting it into square chips in a later step. Further, KOH or the like is used as an etchant, and the recess 3 having a desired aspect ratio is formed by anisotropic etching. Moreover, since the oxide film 7 on the back surface side is not preferable because it is bonded and fixed to the glass table 8, it is removed with a chemical solution in a subsequent process (FIG. 5B).
[0005]
[Problems to be solved by the invention]
When the recess 3 is formed by etching the silicon wafer 2 ′ with an etching solution, innumerable micro defects such as etch pits are usually generated on the inner surface of the recess 3. Therefore, innumerable micro defects exist on the back surface of the diaphragm 4 obtained by etching, and silicon breakdown is easily started from the micro defects as a starting point, and the diaphragm 4 is destroyed. That is, there is a problem that the minute defect formed at the time of etching reduces the breakdown voltage (breakdown strength) of the diaphragm 4.
This problem occurs not only in the case of a piezoresistive pressure sensor diaphragm, but also in various cases in which a silicon wafer is directly wet-etched.
[0006]
The present invention has been made to solve the above drawbacks, in advance, a silicon wafer having an oxide film formed was formed on the surface and back surface to be oxidation film as an insulating film covering the circuit formed on the silicon wafer surface Silicon wafer processing method and semiconductor strain sensor such as piezoresistive pressure sensor that can improve the adverse effect of minute defects generated on the inner surface of the recess when wet etching is performed on the back surface of the substrate In the process, when a recess is formed in a silicon wafer by wet etching and a thin portion is formed as the bottom of the recess, a method for manufacturing a semiconductor strain sensor capable of improving the fracture strength of the thin portion is provided. For the purpose.
[0007]
[Means for Solving the Problems]
Processing method of a silicon wafer of the present invention, in advance, a silicon wafer having an oxide film formed was formed on the surface and back surface to be oxidation film as an insulating film covering the circuit formed on the silicon wafer surface to solve the above problems In the silicon wafer processing method of forming a recess on the back surface of the, and forming a thin portion as the bottom of the recess,
Form a recess by wet etching in advance on the back surface of the silicon wafer on which an oxide film as an insulating film necessary for forming a circuit is formed on the front surface and the same oxide film is formed on the back surface,
Next, the inner surface of the recess is oxidized to form an oxide film on the inner surface of the recess,
Next, the previously formed oxide film on the back surface of the silicon wafer and the oxide film on the inner surface of the recess are removed by etching.
[0008]
A second aspect of the present invention is the method for processing a silicon wafer according to the first aspect, wherein the oxidation treatment for forming an oxide film on the inner surface of the recess is an oxidation treatment that is exposed to oxygen or water vapor in a high-temperature atmosphere. .
[0009]
According to a third aspect of the present invention, there is provided a semiconductor strain sensor for manufacturing a semiconductor strain sensor having a piezoresistive portion for strain detection on a surface side of a thin portion formed as a bottom portion of a recess provided on a back surface side of a silicon substrate. A manufacturing method comprising:
When forming the thin portion on the silicon wafer,
Previously, to form a recess by wet etching the back surface of the silicon wafer to form an oxide film formed by and oxidation film on the back surface to the surface that covers the circuit formed on the silicon wafer surface,
Next, the inner surface of the recess is oxidized to form an oxide film on the inner surface of the recess,
Next, the previously formed oxide film on the back surface of the silicon wafer and the oxide film on the inner surface of the recess are removed by etching.
According to a fourth aspect of the present invention, in the method for manufacturing a semiconductor strain sensor according to the third aspect, the oxidation treatment for forming an oxide film on the inner surface of the recess is an oxidation treatment that is exposed to oxygen or water vapor in a high-temperature atmosphere. To do.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS. FIG. 1 is a view for explaining a silicon wafer processing method according to the present invention. FIG. 1A shows a state in which a recess 3 is formed by wet etching on the back surface side of the silicon wafer 2 ′ (opposite the detection circuit surface side). It is a silicon wafer sectional view. The oxide film (for example, SiO ₂ ) 7 is formed in advance as an insulating film for forming a pressure detection circuit. When the recess 3 is etched, a mask (not shown) made of a silicon nitride film is formed outside the oxide film 7 on the lower surface side in a pattern corresponding to the recess 3 (the entire surface is formed as a protective film on the surface side). Then, etching is performed. As the etching solution, KOH or the like is used, and the recess 3 having a desired aspect ratio is formed by anisotropic etching.
Next, the silicon wafer 2 'shown in FIG. 1 (a) is subjected to an oxidation treatment by exposing it to oxygen or water vapor in a high-temperature atmosphere. As shown in FIG. 1 (b), the inner surface of the recess 3 of the silicon wafer 2' is formed. An oxide film (for example, SiO ₂ ) 9 is formed.
Next, as shown in FIG. 1C, the back surface side of the silicon substrate 2 is etched with an etching solution to remove the entire oxide films 7 and 9 on the back surface side .
Even when the oxide film is removed, it can be used as a protective film in another etching process by removing the oxide film at the end of the process.
[0011]
In the step of forming the oxide film 9 on the inner surface of the recess 3 in FIG. 1 (b), innumerable micro defects conventionally generated on the wet-etched surface are removed by oxidation treatment.
As described above, since the micro defect that is the starting point of the destruction is removed, the breaking strength of the diaphragm 4 is greatly improved. According to the result of the destructive pressure test in which the air pressure is increased until the diaphragm 4 breaks in the packaged state as the pressure sensor, the oxidized product of the present invention has a breakdown voltage of about 2 as compared with the conventional product that is not oxidized. It was twice. That is, in the product of the present invention, the diaphragm 4 was not destroyed until an air pressure about twice as high as that of the conventional product was applied.
[0012]
The present invention can be applied not only to the pressure sensor 1 described above but also to an acceleration sensor 11 as shown in FIG. Although the acceleration sensor 11 of FIG. 4 is shown in a simplified manner, a recess 13 is formed by wet etching around the central portion 20 on the back surface side (lower side of FIG. 4) of the silicon substrate 12. The thin-walled portion 14 is formed as the bottom portion of the glass 13, the glass weight 21 is fixed to the central portion 20, and the peripheral portion is similarly bonded and fixed to the glass base 22.
[0013]
When acceleration acts on the acceleration sensor 11, the portion of the weight 21 moves like a pendulum (moves in the left-right direction and other various directions in FIG. 4 in accordance with the direction of acceleration), thereby causing distortion in the thin-walled portion 14. Thus, the resistance value of the piezoresistive portion 5 formed on the upper surface (detection circuit surface) of the silicon substrate 12 changes, and this change in resistance value is electrically extracted and converted into an applied acceleration.
[0014]
In the manufacturing process of the acceleration sensor 11 described above, when the recess 13 is formed on the silicon wafer by wet etching to form the thin portion 14, an oxide film (SiO ₂ ) is formed on the inner surface of the recess 13 as described above. The countless minute defects generated on the inner surface of the recess 13 are removed.
In the case of the acceleration sensor 11 as well, if the thin portion 11 has a minute defect at the time of etching, the breaking strength of the thin portion 11 is reduced. However, since the minute defect is removed, the breaking strength of the thin portion 14 is improved. .
[0015]
The present invention is not limited to the pressure sensor 1 and the acceleration sensor 11 described above, and various types of resistance elements for strain detection are provided on the surface side of the thin portion formed as the bottom of the recess provided on the back surface side of the silicon substrate. can be applied to a case of manufacturing a semiconductor strain sensor, also in advance, the back surface of the silicon wafer to form an oxide film formed by and oxidation film on the back surface to the surface that covers the circuit formed on the silicon wafer surface The present invention can be applied to a case where a recess is formed in the bottom and a thin portion is formed as the bottom of the recess.
[0016]
【The invention's effect】
According to the processing method of a silicon wafer of the invention of claim 1, advance, concave to the rear surface of a silicon wafer to form an oxide film on the surface and was also form acid monolayer on the back surface for covering the circuit formed on the silicon wafer surface forming a Tokoro, in the processing method of a silicon wafer to form a thin portion as the bottom of the recess, in advance, the oxide film as an insulating film covering the circuit formed on the silicon wafer surface is formed on the surface and the back surface forming a recess by wet etching the back surface of the silicon wafer was also form acid monolayer, followed by oxidizing the inner surface of the recess to form an oxide film in the recess inner surface, then the silicon wafer back surface Since the oxide film formed in advance and the oxide film on the inner surface of the recess are removed by etching, the countless number generated on the inner surface of the recess by wet etching at the time of forming the recess Small defects are removed by oxidation of the can prevent strength reduction of the silicon by the minute defect, it was possible to significantly improve the fracture strength of the thin portion.
[0018]
Semiconductor strain diaphragm or thin wall portion of the pressure sensor, an acceleration sensor or the like is a sensor, since the influence of the very thin micro-defects is large thickness, it applied to the manufacture of semiconductor strain sensor as in the invention of claim 3, especially effective Is.
[Brief description of the drawings]
FIGS. 1A and 1B are diagrams for explaining a silicon wafer processing method according to the present invention, in which FIG. 1A shows a silicon wafer in which a recess is formed by wet etching on the back side of the silicon wafer (opposite to the detection circuit side). Sectional drawing, (B) is a sectional view of the silicon wafer at the stage where an oxide film is formed on the inner surface of the recess, and (C) is a sectional view of the silicon wafer at the stage where the entire oxide film on the back side is removed.
FIG. 2 is a schematic cross-sectional view of a piezoresistive pressure sensor to be manufactured by the method of the present invention.
FIG. 3 is a plan view of FIG. 2;
FIG. 4 is a schematic cross-sectional view of an acceleration sensor to be manufactured by the method of the present invention.
FIGS. 5A and 5B are diagrams for explaining a conventional silicon wafer processing method, wherein FIG. 5A is a cross-sectional view of a silicon wafer at a stage where a recess is formed by etching the back surface side (opposite the detection circuit surface side) of the silicon wafer. FIG. 4B is a cross-sectional view of the silicon wafer at the stage where the oxide film on the back surface is removed.
[Explanation of symbols]
1 Piezoresistive pressure sensor 2, 12 Silicon substrate 2 'Silicon wafer 3, 13 Recess 7 Oxide film 9 Oxide film 11 (formed on the inner surface of the recess) Acceleration sensor 14 Thin portion 21 Weight 22

Claims (4)

Previously, by forming a recess on the back surface of a silicon wafer to form an oxide film formed on the surface and back surface to be oxidation film as an insulating film covering the circuit formed on the silicon wafer surface, the bottom of the recess In the silicon wafer processing method for forming a thin portion as
Previously, to form a recess by wet etching the back surface of the silicon wafer to form an oxide film formed on the surface and back surface to be oxidation film as an insulating film covering the circuit formed on the silicon wafer surface,
Next, the inner surface of the recess is oxidized to form an oxide film on the inner surface of the recess,
Next, the silicon wafer processing method, wherein the previously formed oxide film on the back surface of the silicon wafer and the oxide film on the inner surface of the recess are removed by etching.   The method for processing a silicon wafer according to claim 1, wherein the oxidation treatment for forming an oxide film on the inner surface of the recess is an oxidation treatment in which the oxide film is exposed to oxygen or water vapor in a high-temperature atmosphere. A semiconductor strain sensor manufacturing method for manufacturing a semiconductor strain sensor including a piezoresistive portion for strain detection on a surface side of a thin portion formed as a bottom portion of a recess provided on a back surface side of a silicon substrate,
When forming the thin portion on the silicon wafer,
Previously, to form a recess by wet etching the back surface of the silicon wafer having an oxide film formed was formed on the surface and back surface to be oxidation film as an insulating film covering the circuit formed on the silicon wafer surface,
Next, the inner surface of the recess is oxidized to form an oxide film on the inner surface of the recess,
Next, the semiconductor strain sensor manufacturing method, wherein the pre-formed oxide film on the back surface of the silicon wafer and the oxide film on the inner surface of the recess are removed by etching.   4. The method of manufacturing a semiconductor strain sensor according to claim 3, wherein the oxidation treatment for forming an oxide film on the inner surface of the recess is an oxidation treatment which is exposed to oxygen or water vapor in a high temperature atmosphere.

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