JP2825071B2 - Manufacturing method of semiconductor sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor sensor, and more particularly, to a method for manufacturing a semiconductor sensor for detecting pressure and acceleration by distortion of a thin beam.

[0002]

2. Description of the Related Art A conventional acceleration sensor or the like utilizes the fact that a weighted beam is distorted by receiving pressure or acceleration and the resistance value of a resistive element provided on the beam changes, so that the pressure or acceleration is measured. It is known to detect. Moreover, by forming these sensors from semiconductors, downsizing of the sensors is realized. For example, as an example of a semiconductor acceleration sensor, IEEE Electron Devices,
Vol. ED-26, no. 12, p1911, De
c. 1979 "A Batch-Fabricate
d Silicon Accelerometer "
And the like are known.

FIG. 4 is a perspective view of such a conventional semiconductor acceleration sensor. As shown in FIG. 4, this semiconductor acceleration sensor has a thick support portion 12, a thin beam portion 7, and a thick weight portion 10 formed by anisotropic etching from a single silicon substrate. . This sensor detects the magnitude of the impact by utilizing the fact that the weight 10 is displaced by inertia and the beam 7 is distorted when subjected to an impact. In this case, the shape of the weight 10 or the beam 7 directly affects the sensitivity of the sensor. In particular, regarding the thickness of the beam 7, both the acceleration sensor and the pressure sensor require high dimensional accuracy.

Therefore, a method of controlling the beam thickness in the sensor manufacturing process is a very important issue, and various methods are used. Hereinafter, some conventional examples will be described with emphasis on beam formation.

FIGS. 5A to 5C are cross-sectional views of a semiconductor sensor shown in the order of steps for explaining an example of the related art. First, as shown in FIG. 5A, in manufacturing a semiconductor sensor by anisotropic etching, an upper protective film 2 and a lower protective film 3 are formed on a silicon substrate 1 as an etching mask. Next, as shown in FIG. 5B, a beam hole 5a is formed in the lower protective film 3 on the back surface of the silicon substrate 1 by a photolithography process. Further, as shown in FIG.
The beam portion 7 is formed by performing anisotropic etching of about 400 μm.

In this manufacturing method, the thickness of the beam 7 is controlled by controlling the etching rate of an etching solution for performing anisotropic etching.

In addition to controlling the beam thickness, as a method of reducing the beam thickness variation, a semiconductor substrate composed of two crystal layers (p-type and n-type) having different conductivity types is used.
There is also a method of removing one conductive type crystal layer by electric field etching and using the other conductive type crystal layer as a beam portion.

FIGS. 6 (a) to 6 (c) are cross-sectional views of a semiconductor sensor shown in the order of steps for explaining another example of the related art. First, as shown in FIG. 6A, an n-type silicon layer 11 having the same thickness as a desired beam thickness is formed on a p-type silicon substrate 1. Thereafter, protective films 13 are formed on both surfaces of the laminated semiconductor substrate. Next, as shown in FIG. 6B, a beam opening 5a is formed in the protective film 13 protecting the lower surface of the p-type silicon substrate 1 by a photolithography process. Further, as shown in FIG. 6C, only the p-type silicon substrate 1 is etched by performing the electric field etching, and the beam portion 7 having a thickness substantially equal to that of the n-type silicon layer 11 is formed.

Here, the electric field etching is used for the purpose of etching only the p-type silicon substrate 1. That is, when a voltage is applied to the silicon substrate 1 (electric field etching) in the etching solution, the etching of the p-type silicon substrate 1 proceeds, and when the n-type silicon layer 11 is exposed, the surface of the exposed silicon layer 11 is It utilizes the principle that an oxide film is formed (anodic oxidation) and etching stops.

The two conventional examples based on FIGS. 5 and 6 described above are intended to obtain a desired beam thickness by one etching. However, these methods require a large amount of etching and a long time. Therefore, the variation in etching between wafers increases. Therefore, it is necessary to perform etching twice instead of once.
It is necessary to make fine adjustments while sequentially measuring the remaining etching amount.

Further, as a method for realizing highly accurate processing of the beam thickness, there is a method of alternately immersing a silicon substrate in an oxidizing agent and an oxide film removing agent. This method is disclosed in, for example,
It is disclosed in Japanese Patent Application Publication No. -10-54545.

FIGS. 7A to 7C are sectional views of a semiconductor sensor shown in the order of steps for explaining another example of the related art. First, as shown in FIG.
A thermal oxide film 6 as a protective film is formed on the silicon substrate 1 above and below, and the silicon substrate 1 is etched by the same etching method as in the above-described conventional example, so that the silicon substrate thin film is slightly thicker than a desired beam thickness. The part 4 is formed. Next, as shown in FIG.
Is measured, and the remaining etching amount is confirmed. Thereafter, the silicon substrate 1 is immersed in a nitric acid solution to oxidize the silicon surface, thereby forming an oxidized portion 15. At this time, the thickness of the oxide film 15 is determined by the concentration of nitric acid and the temperature.
Thereafter, as shown in FIG. 7C, the silicon substrate 1 is thoroughly washed with water so that no chemical remains, and then immersed in a hydrofluoric acid solution to remove the oxide film 15. FIG.
The process of (c) is repeated, and etching is performed until a desired beam thickness is obtained.

[0013]

As described above, several conventional methods for manufacturing a semiconductor sensor have been proposed for etching a silicon thin film. However, these conventional methods have the following disadvantages. is there.

First, in the manufacturing method of FIG. 5, when a very deep etching of 200 to 400 μm is performed on a silicon substrate, a desired beam thickness is obtained only by controlling an etching rate of an etching solution. Fluctuates depending on the liquid temperature during etching, the etching time, and the stirring state of the etching liquid. Therefore, not only variations occur in the wafer plane, but also variations of several tens of μm or more occur between wafers. For example, it is very difficult to suppress the beam thickness to the target variation of 1 μm or less.

In the conventional example of FIG. 6, the thickness variation at the time of forming the n-type silicon layer is about several μm.
This variation in the thickness of the n-type silicon layer directly affects the accuracy of the beam thickness. In addition, variations in the potential distribution due to differences in the position of the wafer in the etching solution during electric field etching, variations in the contact characteristics between the substrate and the voltage application terminal, and the like also affect the surface by several μm. For this reason, variations of at least about 2 μm are generated as a whole. Even if an attempt is made to adjust these variations by additional etching, as described above, the etching rate fluctuates depending on the liquid temperature during etching, the etching time, and the stirring state of the etching liquid. Therefore, it is difficult to obtain a target etching accuracy.

Further, in the conventional example of FIG. 7, although the etching accuracy is improved, the amount of one etching is as small as several tens of angstroms, so that several tens to several hundreds of etchings are required, and a great number of man-hours are generated. Resulting in.

An object of the present invention is to provide a method of manufacturing a semiconductor sensor having stable characteristics by controlling the beam thickness with high accuracy and efficiency.

[0018]

According to a method of manufacturing a semiconductor sensor of the present invention, a thick support portion and a thin beam portion connected to the support portion are formed on a silicon substrate, and distortion of the beam portion is utilized. In a method of manufacturing a semiconductor sensor for detecting acceleration or pressure, a step of forming a protective film serving as a mask for forming the support portion and the beam portion on the silicon substrate, and forming the silicon substrate anisotropically through the protective film. Wet etching, and the desired thickness is larger than the thickness of the beam portion .
Forming a substrate film of a thickness, the thickness of the substrate film unit after removing the protective film to form a thermal oxide film on the whole surface of the silicon substrate is thermally oxidized to the desired value And a step of etching and removing the thermal oxide film with hydrofluoric acid or the like.

In the method of manufacturing a semiconductor sensor according to the present invention, a thick support portion, a thin beam portion connected to the support portion, and a thick weight portion connected to the beam portion are formed on a silicon substrate. In a method of manufacturing a semiconductor sensor for detecting acceleration or pressure by utilizing a distortion of the beam part accompanying a displacement of a part or a displacement of the weight part, protection for forming the support part and the beam part on the silicon substrate forming a film, the silicon substrate is anisotropically wet etched through the protective film, thickness than the thickness of the beam portion
Forming a substrate thin film portion having a desired thickness, and removing the protective film and thermally oxidizing the entire surface of the silicon substrate until the thickness of the substrate thin film portion reaches a desired value, thereby forming a thermal oxide film. Forming, forming a gap window opening for forming a gap other than the beam portion between the support portion and the weight portion in the thermal oxide film, and forming the thermal oxide film through the thermal oxide film. The method includes a step of etching a silicon substrate to form a void portion while leaving a part of the thermal oxide film, and a step of etching and removing the thermal oxide film with hydrofluoric acid or the like.

Further, according to the method for manufacturing a semiconductor sensor of the present invention, a semiconductor substrate comprising a silicon substrate of one conductivity type and a silicon layer of the opposite conductivity type formed thereon is processed to provide a thick support portion and the support portion. Forming a thin beam that leads to
The method of manufacturing a semiconductor sensor for detecting acceleration or pressure by using a strain of the beam portion, and forming a reverse conductivity type silicon layer has thickness smaller than the thickness of the front Kihari portion to said one conductivity type silicon substrate, forming a protective film to be a mask for forming the supporting portion and the beam portion to the one conductivity type silicon substrate, said one conductivity type silicon substrate by anisotropic wet etching through said protective layer, the beam Forming a substrate thin film portion having a desired thickness larger than the thickness of the portion, and removing the protective film, and then heating the reverse conductivity type silicon layer until the thickness of the substrate thin film portion reaches a desired value. The method includes a step of forming a thermal oxide film on the entire surface by oxidation, and a step of etching and removing the thermal oxide film with hydrofluoric acid or the like.

[0021]

Next, the present invention will be described with reference to the drawings.

FIGS. 1A to 1D are sectional views of a semiconductor sensor shown in the order of steps for explaining a first embodiment of the present invention. In this embodiment, a thick support portion and a thin beam portion connected to the support portion are formed on a silicon substrate,
This is an example of manufacturing a semiconductor sensor that detects acceleration and pressure using the strain of a beam portion, and does not require a weight portion.

First, as shown in FIG. 1A, an upper protective film 2 and a lower protective film 3 are formed on both surfaces of a silicon substrate 1 so as to obtain an etching selectivity with respect to the silicon substrate 1. For example, an oxide film or a nitride film is used as the protective films 2 and 3 and serves as a mask for forming a support portion and a beam portion.

Next, as shown in FIG. 1B, a beam opening 5 for forming a beam in the lower protective film 3 is formed by a photolithography process. Thereafter, the anisotropic etching solution (for example, KOH20
% Aqueous solution, 90 ° C.)
The wet etching is performed for about m, and the etching is terminated when the thickness of the silicon substrate thin film portion 4 becomes larger than the desired thickness by about 2 μm. If necessary, the wet etching may be performed several times.

Here, while controlling the thickness of the silicon substrate thin film portion 4 to be about 2 μm thicker than the desired thickness,
When etching of about 400 μm is performed, thickness variation of several tens μm actually occurs. Therefore, FIG.
As shown in (c), after the protective films 2 and 3 are removed, the thickness of the silicon substrate thin film portion 4 is measured, and a difference from the desired beam portion thickness is confirmed. 1 is thermally oxidized by a thermal oxidation method to form a thermal oxide film 6 on the entire surface. At this time, the amount (thickness) of silicon consumed (oxidized) by the thermal oxidation is 44% of the formed oxide film thickness.

Finally, as shown in FIG. 1D, the thermal oxide film 6 is removed by etching with a buffered hydrofluoric acid or the like having an etching selectivity with respect to the silicon substrate 1. When the thermal oxide film 6 is removed, only the silicon portion remains, and the beam portion 7 having a desired thickness is obtained.

By using a thermal oxidation method in which the variation in film thickness between wafers is several tens nm or less for the above steps, particularly for adjusting the thickness of the beam part 7, the beam thickness can be controlled from several nm to several tens nm. Becomes possible.

FIGS. 2A to 2E are sectional views of a semiconductor sensor shown in the order of steps for explaining a second embodiment of the present invention. In this embodiment, a thick support portion, a thin beam portion connected to the support portion, and a thick weight portion connected to the beam portion are formed on the silicon substrate, and the displacement of the weight portion or the beam accompanying the displacement of the weight portion is formed. 7 is a manufacturing example of a semiconductor sensor that detects acceleration and pressure by using distortion of a part. The feature is that the thermal oxide film formed at the time of adjusting the beam thickness is used as an etching mask at the time of forming a void formed around the weight.

First, as shown in FIG. 2A, an upper protective film 2 and a lower protective film 3 serving as a first mask for forming a support portion and a beam portion on a silicon substrate 1 are formed.

Next, as shown in FIG. 2 (b), after forming a beam hole 5 for forming a beam and a void in the lower protective film 3 by a photolithography process, the lower protective film 3 is formed. Is used as a mask, the silicon substrate 1 is wet-etched by about 400 μm with an anisotropic etching solution from the perforated section 5 so that the thickness of the silicon substrate thin-film section 4 becomes about 2 μm thicker than a desired thickness.

Thereafter, as shown in FIG. 2C, the protective films 2 and 3 are removed, and then the silicon substrate 1 is thermally oxidized by a thermal oxidation method to form a thermal oxide film 6 on the entire surface. This thermal oxide film 6 is used as a mask when forming a void.
The steps up to the step of thermally oxidizing while leaving the thickness of the beam portion are the same as those in the first embodiment.

Next, as shown in FIG. 2D, a hole-forming portion 8 is formed from the upper surface of the silicon substrate 1 by a photolithography process, and the silicon substrate 1 is similarly formed through the hole-forming portion 8. Etch. The void 9 is formed by this etching.

Finally, as shown in FIG. 2E, by removing the thermal oxide film 6 by etching with hydrofluoric acid or the like, a beam portion 7 having a desired thickness combined with the weight portion 10 is obtained. .

FIGS. 3A to 3D are cross-sectional views of a semiconductor sensor shown in the order of steps for explaining a third embodiment of the present invention. First, as shown in FIG. 3A, in this embodiment, an n-type silicon layer 1 is formed on an upper surface of a p-type silicon substrate 1.
1 is formed 2 μm thicker than the desired thickness of the beam portion.
Further, a lower protective film 3 and an upper protective film 2 are formed on the silicon substrate 1 and the n-type silicon layer 11, respectively, with an oxide film or the like having an etching selectivity with respect to the silicon substrate 1.

Next, as shown in FIG. 3B, a beam opening 5 for forming a beam in the lower protective film 3 on the back surface of the p-type silicon substrate 1 is formed by a photolithography process. When the type silicon substrate 1 is subjected to electric field etching, the etching stops at the boundary surface (pn junction surface) between the silicon substrate 1 and the n-type silicon layer 11. Thus, only the substrate thin film portion 4 of the n-type silicon layer 11 which is about 2 μm thicker than the desired thickness of the beam portion is left. In the above-described electric field etching, a 20% aqueous KOH solution (temperature: 90 ° C.) is used, and the n-type silicon layer 11 is set to a positive potential and KOH
A voltage of about several volts is applied using the aqueous solution as a negative potential.

Further, as shown in FIG. 3C, even if an attempt is made to form a silicon layer about 2 μm thicker than the desired thickness of the beam portion, there is actually a wafer-to-wafer variation of about 2 μm. The thickness of the n-type silicon layer 11 is measured to confirm the desired thickness of the beam portion. Then, after removing the protective films 2 and 3, the silicon substrate 1 is oxidized by a thermal oxidation method by the difference to form a thermal oxide film 6.

Finally, as shown in FIG. 3 (d), the thermal oxide film 6 is removed by etching with a buffered hydrofluoric acid or the like having a high etching selectivity with respect to the silicon substrate 1.
Only the silicon portion remains, and the desired thickness of the beam portion 7 is obtained.

As described above, according to the present embodiment, the in-plane variation of the beam thickness can be reduced by using the electric field etching, and the adjustment etching can be performed on the silicon substrate by using the thermal oxidation method. Thereby, the desired thickness of the beam portion can be controlled with high accuracy. Note that the present embodiment can be similarly realized even when the conductivity types of the substrate and the silicon layer in the present embodiment are reversed to n-type and p-type, and can sufficiently cope with the case where the upper layer is formed by diffusion.

Although several embodiments have been described above, according to these embodiments, the beam thickness can be controlled with high accuracy, and the variation in the wafer surface can be reduced. In addition, since thermal oxidation can be controlled to a thickness of several μm, adjustment etching can be performed only once or several times, and an efficient manufacturing method can be realized.

[0040]

As described above, in the method of manufacturing a semiconductor sensor according to the present invention, after forming a substrate thin film portion thicker than a desired beam thickness by anisotropic wet etching, thermal oxidation is performed. Then, by removing the thermal oxide film by etching, the thickness of the beam portion can be accurately controlled, so that a semiconductor sensor having uniform characteristic sensitivity can be provided. Further, according to the present invention, since a thermal oxide film can be used as an etching mask at the time of forming a void portion required for an acceleration sensor or the like, there is no need to form a new mask, and there is an effect that manufacturing can be performed efficiently. further,
The present invention has the effect of reducing variations in the wafer plane by combining with electric field etching.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a semiconductor sensor shown in a process order for explaining a first embodiment of the present invention.

FIG. 2 is a sectional view of a semiconductor sensor shown in the order of steps for explaining a second embodiment of the present invention.

FIG. 3 is a cross-sectional view of a semiconductor sensor shown in a process order for explaining a third embodiment of the present invention.

FIG. 4 is a perspective view of a conventional semiconductor acceleration sensor.

FIG. 5 is a cross-sectional view of a semiconductor sensor shown in the order of steps for explaining an example of the related art.

FIG. 6 is a cross-sectional view of a semiconductor sensor shown in the order of steps for explaining another conventional example.

FIG. 7 is a cross-sectional view of a semiconductor sensor shown in the order of steps for explaining another conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2, 3 Protective film 4 Substrate thin film part 5 Beam drilling part 6 Thermal oxide film 7 Beam part 8 Void drilling part 9 Void part 10 Weight part 11 N-type silicon layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 29/84 G01L 9/04 101 G01P 15/12 H01L 21/306

Claims (3)

(57) [Claims] 1. A method of manufacturing a semiconductor sensor, comprising: forming a thick support portion and a thin beam portion connected to the support portion on a silicon substrate, and detecting acceleration and pressure by using distortion of the beam portion. forming a protective film to be a mask for forming the supporting portion and the beam portion in the silicon substrate, the silicon substrate is anisotropically wet etched through the passivation layer, optionally greater than the thickness of the beam portion
Forming a substrate film of a thickness of the thermally oxidized film of the silicon substrate on the entire surface by thermal oxidation to a thickness of the substrate film unit after removing the protective film becomes a desired value formation of And a step of etching and removing the thermal oxide film with hydrofluoric acid or the like. 2. A silicon substrate having a thick support portion, a thin beam portion connected to the support portion, and a thick weight portion connected to the beam portion, wherein a displacement of the weight portion or a displacement of the weight portion is formed. A method of manufacturing a semiconductor sensor for detecting acceleration and pressure by utilizing the distortion of the beam portion, a step of forming a protective film for forming the support portion and the beam portion on the silicon substrate; said silicon substrate to anisotropic wet etching, forming a desired thickness of the substrate film portion thicker than a thickness of the beam portion, the thickness of the substrate film unit after removing the protective film through Forming a thermal oxide film by thermally oxidizing the entire surface of the silicon substrate until a desired value is obtained, and forming a gap other than the beam portion between the support portion and the weight portion in the thermal oxide film; Window opening for opening Forming a void, leaving a part of the thermal oxide film by etching the silicon substrate through the thermal oxide film, and etching and removing the thermal oxide film with hydrofluoric acid or the like. A method for manufacturing a semiconductor sensor, comprising: 3. A semiconductor substrate comprising a silicon substrate of one conductivity type and a silicon layer of the opposite conductivity type formed thereon is processed to form a thick support portion and a thin beam portion connected to the support portion. the method of manufacturing a semiconductor sensor for detecting acceleration or pressure by using a strain of the beam portion, and forming a reverse conductivity type silicon layer has thickness smaller than the thickness of the front Kihari portion to said one conductivity type silicon substrate, forming a protective film to be a mask for forming the supporting portion and the beam portion to the one conductivity type silicon substrate, said one conductivity type silicon substrate by anisotropic wet etching through said protective layer, the beam Forming a substrate thin film portion having a desired thickness larger than the thickness of the portion, and removing the protective film, and then heating the reverse conductivity type silicon layer until the thickness of the substrate thin film portion reaches a desired value. Oxidizes and heats the entire surface A method for manufacturing a semiconductor sensor, comprising: a step of forming an oxide film; and a step of etching and removing the thermal oxide film with hydrofluoric acid or the like.