JP6742483B1 - Semiconductor pressure sensor and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly accurate semiconductor pressure sensor having high manufacturing stability. A semiconductor pressure sensor (100) has a first silicon substrate (1) having a concave portion (3) serving as a reference pressure chamber (10) formed on one main surface (1a), and an oxide film (8) on one main surface (1a) of the first silicon substrate (1). A second silicon substrate 2 that is bonded via the recess 3 to cover the recess 3, a diaphragm 5 formed on the second silicon substrate 2 located above the recess 3, and a gauge that is a pressure-sensitive element portion formed on the diaphragm 5. The concave portion 3 serving as the reference pressure chamber 10 is provided with the pressure detecting portion 20 including the resistor 6, and the edge portion 31 forming the contour of the opening region of the one main surface 1a of the first silicon substrate 1 and the edge thereof. The main concave portion 30 is formed deeper than the edge portion 31 in order to increase the volume of the reference pressure chamber 10 located inside the portion 31. [Selection diagram] Figure 2

Description

The present application relates to a semiconductor pressure sensor and a method for manufacturing the same.

As a conventional semiconductor pressure sensor, a reference pressure chamber is provided on one main surface of a first silicon substrate, and a pressure sensitive element section is provided on a second silicon substrate bonded to the first silicon substrate. There is disclosed an example in which a recess serving as a chamber is provided so as to have a constant depth deeper than the alignment mark (for example, Patent Document 1).
Further, the reference pressure chamber of the semiconductor pressure sensor is provided on the bonding surface of the second silicon substrate bonded to the first silicon substrate, and the pressure sensitive element section is provided on the back surface side of the second silicon substrate. An example is disclosed in which a recess serving as a pressure chamber is provided so as to have a constant depth (for example, Patent Document 2).

Japanese Patent No. 5639985 Japanese Patent No. 4250788

In the conventional technique, in order to secure the volume of the reference pressure chamber, the recess forming the reference pressure chamber is formed by digging down one main surface of the first silicon substrate to a certain depth. However, as the depth of the recess increases to secure the volume, the accuracy of the contour shape of the opening upper end of the recess that defines the outer shape of the diaphragm tends to decrease.

For example, in the case of a configuration in which a recess is formed in the upper surface of a first silicon substrate and a second silicon substrate is attached to the upper end side of the opening of the recess to provide a reference pressure chamber as in Patent Document 1, The diaphragm, the pressure sensitive element portion, and the like are formed by processing from the upper surface side of the silicon substrate. When the contour shape of the upper end of the opening of the recess is disturbed and distorted, abnormal stress concentration occurs at the end of the diaphragm when the pressure sensitive element is formed, and the breakdown strength of the diaphragm decreases. There was a problem.

The present application has been made in order to solve the above problems, and while improving the accuracy of the outer shape of the reference pressure chamber while securing the volume of the recess serving as the reference pressure chamber, the manufacturing stability is improved. Another object of the present invention is to obtain a highly reliable semiconductor pressure sensor and a method for manufacturing the same.

A semiconductor pressure sensor according to the present application includes a first silicon substrate having a concave portion serving as a reference pressure chamber hermetically sealed on one main surface and an alignment mark, and the one main surface of the first silicon substrate being oxidized. A second silicon substrate bonded through a film and covering the recess and the alignment mark, a diaphragm formed on the second silicon substrate above the recess, and a pressure-sensitive film formed on the diaphragm. A pressure detecting portion including an element portion, wherein the reference pressure chamber has an edge portion that defines the contour of an opening region of the one main surface of the first silicon substrate, and a main recess portion that is located inside the edge portion. And the main concave portion is formed deeper than the edge portion , and the alignment mark is formed in a region where the concave portion is not formed and at the same depth as the edge portion .

Further, in the method for manufacturing a semiconductor pressure sensor according to the present application, a step of forming a first concave portion by digging down a formation region of a reference pressure chamber on one main surface of a first silicon substrate, and forming a contour of the first concave portion. Leaving the edge portion to form a second concave portion constituting the main concave portion of the reference pressure chamber by digging down the bottom surface portion of the first concave portion inside the edge portion, the above-mentioned first silicon substrate A second silicon substrate is bonded to one main surface via an oxide film, and the reference pressure chamber is hermetically sealed by covering the recess formed by the first recess and the second recess with the second silicon substrate. to form a step, by processing the second silicon substrate, forming a diaphragm above the reference pressure chamber, it viewed including the step of forming the pressure-sensitive element unit in the second silicon substrate, the first Simultaneously with the formation of the concave portion, an alignment mark is formed at the same depth as the first concave portion in a region of the first principal surface of the first silicon substrate where the first concave portion is not formed. It is a thing.

According to the semiconductor pressure sensor of the present application, the recess serving as the airtightly sealed reference pressure chamber is constituted by the edge portion forming the contour of the reference pressure chamber and the main recess portion for securing the volume, and the outer periphery of the main recess portion. Since the portion is surrounded by the edge formed shallower than the main recess, the accuracy of the outer shape of the reference pressure chamber and the diaphragm can be improved, and the alignment mark is covered with the second silicon substrate. Therefore, it is possible to manufacture stability and reliability obtain high semiconductor pressure sensor.

Further, according to the method for manufacturing a semiconductor pressure sensor of the present application, after simultaneously forming the first concave portion and the alignment mark which form the edge portion of the hermetically sealed reference pressure chamber, the bottom surface of the first concave portion is dug down. Since the second concave portion constituting the main concave portion is formed by this, the mask member can be accurately formed on the processing surface before the second concave portion is formed, and the mask member is removed after the second concave portion is formed. ease rather, it is possible to suppress the number of manufacturing steps.

FIG. 3 is a cross-sectional view showing a state where the semiconductor pressure sensor according to the first embodiment is formed on a wafer. FIG. 2 is an enlarged cross-sectional view of a main part showing the semiconductor pressure sensor of FIG. 1 and a plan view of a reference pressure chamber. FIG. 9 is a diagram showing a manufacturing process of the semiconductor pressure sensor according to the second embodiment, which is a cross-sectional view and a plan view of the first recessed portion when forming the first recessed portion which constitutes the reference pressure chamber. FIG. 6A is a diagram showing a manufacturing process of the semiconductor pressure sensor, and is a cross-sectional view when forming a second recessed portion which constitutes the reference pressure chamber and a plan view of the recessed portion which becomes the reference pressure chamber. It is a figure showing a manufacturing process of a semiconductor pressure sensor, and is a sectional view at the time of oxide film formation. It is a figure which shows the manufacturing process of a semiconductor pressure sensor, Comprising: It is sectional drawing at the time of forming a pressure detection part.

Embodiment 1.
A semiconductor pressure sensor 100 according to Embodiment 1 of the present application will be described with reference to FIGS. 1 and 2. FIG. 1 is a cross-sectional view of one wafer 101 in which a large number of semiconductor pressure sensors 100 according to the first embodiment are built, and shows a state of a pre-stage for performing dicing to separate individual semiconductor pressure sensors 100 from the wafer 101. There is. FIG. 2 is an enlarged cross-sectional view of a main part showing the semiconductor pressure sensor 100 for one chip provided on the wafer 101 of FIG. 1 and a plan view of the reference pressure chamber 10 (pressure chamber, cavity).
As shown in FIG. 1, a large number of semiconductor pressure sensors 100 are arranged in a matrix on the plane of the wafer 101 (the surface other than the terrace 12 at the end of the wafer 101) before the dicing.

As shown in FIG. 2, one semiconductor pressure sensor 100 includes a first silicon substrate 1 provided with a concave portion 3 and an alignment mark 4 which form a reference pressure chamber 10, a pressure sensitive element such as a diaphragm 5 and a gauge resistor 6. The second silicon substrate 2 provided with the element portion is bonded via the oxide film 8. The pressure detection unit 20 includes a reference pressure chamber 10, a diaphragm 5, a gauge resistor 6 and the like. The recess 3 opened on the one main surface 1a of the first silicon substrate 1 is sealed by the second silicon substrate 2 in a vacuum atmosphere, so that the internal space of the recess 3 is maintained at a high vacuum serving as a reference pressure. Be drunk

Here, the shape of the diaphragm 5 is defined by the shape of the opening upper end of the opening of the recess 3 and the volume thereof, and the recess 3 and the formation region of the diaphragm 5 coincide with each other on the one main surface 1a. The shape and volume of the concave portion 3 provided on the one main surface 1a of the first silicon substrate 1 are set in consideration of the thickness of the diaphragm 5 to be formed in a later step, so that the semiconductor pressure sensor 100 has desired pressure-sensitive characteristics and breakdown voltage. And so on.
For example, when the measurement pressure is up to about 4 atm, the thickness of the diaphragm 5 can be set to 10 to 30 μm, and the planar shape of the diaphragm 5 can be set to a square with one side of about 200 to 500 μm.

As shown in the plan view of FIG. 2, the recessed portion 3 forming the reference pressure chamber 10 has a main recessed portion 30 and an edge portion 31 surrounding the main recessed portion 30 on the one main surface 1a. Both the main recessed portion 30 and the edge portion 31 indicate the internal space of the recessed portion 3. The edge portion 31 constitutes the contour of the opening region (the outer shape of the upper end portion of the opening) of the one main surface of the first silicon substrate 1, and the contour of the edge portion 31 becomes the outer shape of the diaphragm 5. The main recess 30 provided inside the edge 31 and deeper than the edge 31 is configured to earn the volume of the reference pressure chamber 10. The reference pressure chamber 10 is formed in two levels of depth, and the main concave portion 30 located inside the edge portion 31 is deeper than the edge portion 31 located at the inner peripheral portion of the formation region of the reference pressure chamber 10. Each of the bottom surfaces is formed as a flat surface parallel to the one main surface 1a.

The depth of the main recess 30 is typically provided in the range of about 50 to 300 μm, and the larger the depth of the main recess 30 dug down from the one main surface 1a of the first silicon substrate 1, the larger the reference pressure chamber. The volume of 10 can be secured large, and even if there is a slow leak or the like in the reference pressure chamber 10, there is an advantage that the pressure fluctuation can be reduced and the characteristic fluctuation can be reduced. A proper value is selected from the typical range to process the main recess 30.

If the reference pressure chamber 10 is composed of only the main concave portion 30, the deteriorated contour of the main concave portion 30 as shown in the plan view of FIG. The outer shape of the diaphragm 5 is defined by the contour including the abnormal portion. However, in the present application, the contour shape is defined by defining the outer shape of the reference pressure chamber 10 not by the main recess 30 but by the edge 31 located outside thereof. Suppresses the deterioration of. The edge portion 31 can be formed to have the same depth as that of the typical alignment mark 4, for example, about 1 to 2 μm. Needless to say, the alignment accuracy can be improved as the alignment mark 4 is provided, for example, in a region other than the region in which the recess 3 is formed and is arranged closer to the region to be processed.

As described above, the depth of the edge portion 31 of the reference pressure chamber 10 needs to be shallow from the viewpoint of suppressing the contour shape deterioration, and is typically about 1 to 2 μm which is the same depth as the alignment mark 4. It is possible to It is preferable that the size of the main recess 30 is set from the volume of the reference pressure chamber 10 to be secured, and the depth thereof is as shallow as possible from the viewpoint of processing load. Therefore, in order to secure a wide area for forming the main recess 30 on the one main surface 1a, the width of the edge 31 is made as narrow as possible, that is, the side lengths of the main recess 30 and the edge 31 are made as close as possible. Set to. For example, it is preferable to set one side of the main recess 30 to be shorter than one side of the edge 31 typically by about 10 to 20 μm. Further, it is suitable to dispose the main recess 30 in the center of the recess 3 so that the width of the edge 31 on the one main surface 1a is constant.

According to the semiconductor pressure sensor of the first embodiment, the main recess 30 that secures the volume of the reference pressure chamber 10 is provided inside the edge 31 that defines the shape of the diaphragm 5. It is possible to suppress the deterioration of the outer shape of the recessed portion 3 that becomes the above and to secure a sufficient volume. As a result, compared with the case where the recess 3 of the conventional structure is formed to a constant depth, abnormal stress concentration does not occur at the end of the diaphragm 5 when pressure is applied, and the breakdown withstand voltage of the diaphragm 5 can be improved. It is possible to obtain highly accurate products.

Therefore, since it is possible to prevent the diaphragm 5 from being destroyed in the manufacturing process of the semiconductor pressure sensor wafer, the yield of the semiconductor pressure sensor wafer can be improved, the manufacturing stability can be improved, and the semiconductor as a final product can be improved. The reliability of the pressure sensor can be improved. Further, by preventing the semiconductor pressure sensor wafer manufacturing equipment from being contaminated, it is possible to eliminate the influence on the manufacturing and quality of other products.

Embodiment 2.
Next, a method of manufacturing the semiconductor pressure sensor 100 according to the second embodiment of the present application will be described with reference to the process drawings of FIGS. Although there are various manufacturing methods for obtaining the semiconductor pressure sensor 100 shown in the above-described first embodiment, in the second embodiment, the most suitable manufacturing method is the order of forming the recesses 3 to be the reference pressure chambers 10. I will explain one.
In the method of manufacturing the semiconductor pressure sensor according to the second embodiment, when forming the concave portion 3, first, the first concave portion 3a is formed on the entire surface of the formation region of the concave portion 3 simultaneously with the formation of the alignment mark 4, and the reference pressure chamber 10 is formed. Then, the second recessed portion 3b is formed by digging the bottom surface of the first recessed portion 3a while leaving the edged portion 31, and the inner space of the second recessed portion 3b and the second recessed portion 3b are formed. It includes the step of obtaining the main recess 30 by the internal space of the first recess 3a located immediately above the recess 3b.

Hereinafter, description will be made step by step.
First, as shown in FIG. 3, the outer shape of the diaphragm 5 and the alignment mark 4 required for alignment when the gauge resistor 6 and the like are formed in the subsequent step is defined on the first silicon substrate 1 made of the wafer 101. The first concave portion 3a, which is a part of the reference pressure chamber 10, is simultaneously formed by plasma etching or the like. Both the alignment mark 4 and the concave portion 3 are formed to a depth of about 1 to 2 μm.
The first concave portion 3a and the alignment mark 4 can be formed in separate steps, but it goes without saying that by forming them simultaneously, an increase in the number of steps can be suppressed.

Next, as shown in FIG. 4, alignment is performed with the alignment mark 4 as a reference, leaving an edge 31 that constitutes the contour of the first recess 3a, and digging inside the edge 31 to form the main recess 30. To do. At this time, for example, a mask member (for example, a resist film) having an opening in a region to be the main recess 30 is formed on the upper surface of the first silicon substrate 1 by photolithography, and etching is performed using the mask member. A second recess 3b deeper than the first recess 3a is formed. The second recess 3b later constitutes a main part of the reference pressure chamber 10 as a pressure sensor. The depth of the second recess 3b is preferably about 50 to 300 μm, but since the depth is as deep as 50 μm or more, it is general to use a DRIE (Deep Reactive Ion Etching) device by the Bosch process. Wet etching using an alkaline etching solution such as (Tetramethyl ammonium hydroxide) can also be used.

The edge portion 31 forming the reference pressure chamber 10 corresponds to a contour portion that borders the first concave portion 3a, and the main concave portion 30 is a portion located inside the edge portion 31 of the first concave portion 3a. And the second concave portion 3b are combined.

Before opening the second concave portion 3b, a resist film serving as a mask member is applied and formed on the first concave portion 3a as described above. However, since the first concave portion 3a is as shallow as 1 to 2 μm, Since it is easy to apply the resist to the processed surface including the one concave portion 3a, the accuracy of forming the mask member can be increased and the patterning characteristics can be improved. Further, since the first concave portion 3a is formed shallowly, there is no resist remaining in the resist removing step, and it is possible to suppress subsequent foreign matter generation, contamination in the processing apparatus, and the like.

Here, if the edge portion 31 is formed on the outer peripheral upper end portion of the main concave portion 30 after the main concave portion 30 is formed, the resist remains as foreign matter inside the main concave portion 30 formed deeper than the edge portion 31. This is easy and causes problems in the subsequent manufacturing process. However, as described above, in the present application, the residual resist can be avoided by forming the concave portion 3 forming the reference pressure chamber 10 in the order of the edge portion 31 and the main concave portion 30, and the main concave portion 30 and the edge portion 31 can be formed in two steps. It is possible to form the reference pressure chamber 10 including the recessed portion 3 having a depth in a good state.

Next, as shown in FIG. 5, the first silicon substrate 1 is thermally oxidized to form an oxide film 8 on the entire front and back surfaces of the wafer 101. The thickness of the oxide film 8 is preferably about 0.2 to 1 μm. In order to simplify the description, the oxide film on the back surface 1b side of the first silicon substrate 1 which has no functional relationship is not shown.

Next, as shown in FIG. 6, the second silicon substrate 2 prepared in advance is overlaid on the one main surface 1a side of the first silicon substrate 1 in which the concave portion 3 is formed, and is placed in a vacuum chamber. Then, the first silicon substrate 1 and the second silicon substrate 2 are bonded by evacuating and thermally oxidizing under an environment of about 1100° C. By bonding the first silicon substrate 1 and the second silicon substrate 2 in this vacuum atmosphere, the recess 3 is completely hermetically sealed to form the reference pressure chamber 10.

Next, the exposed surface of the second silicon substrate 2 is ground by a grinder or the like to reduce the thickness, and further, the surface of the second silicon substrate 2 is mirror-finished, so polishing by CMP (Chemical Mechanical Polish) or the like is performed. To do. As a result, the diaphragm 5 is completed.
Next, the pressure detection part 20 is completed by aligning the alignment mark 4 with a stepper and forming a pressure sensitive element part such as a gauge resistor 6 at a predetermined position on the diaphragm 5.

Since the alignment mark 4 is completely covered with the second silicon substrate 2 when the pressure sensitive element is formed, it is not exposed on either the front or the back side, but the alignment mark is determined by using an infrared camera. 4 can be detected and alignment can be performed. Since infrared rays pass through the silicon substrate, the alignment mark 4 can be recognized from the second silicon substrate 2 side even when it is covered with the second silicon substrate 2. When the gauge resistor 6 and the like are formed, the alignment mark 4 close to the processing target area detected by the infrared camera is used for alignment, so that accurate processing can be performed.

After that, the protective film 7 is formed on the surface of the second silicon substrate 2 to protect the pressure detecting portion 20, so that the semiconductor pressure sensor 100 shown in FIG. 2 can be obtained. Here, as the protective film 7, a moisture-resistant nitride film having a thickness of about 1 μm can be used.
Since the illustrated semiconductor pressure sensor 100 is in a state before dicing built in the wafer 101, the semiconductor pressure sensor 100 is cut along the dicing line portion so as to have the dimensions of the individual semiconductor pressure sensors 100. Can be processed into chips. At this time, needless to say, the alignment mark 4 can be removed if the alignment mark 4 is arranged on the dicing line portion.

According to the method of manufacturing the semiconductor pressure sensor 100 according to the second embodiment, after the shallow first recess 3a is once formed, the second recess 3b deeper than the first recess 3a is formed therein. Since the concave portion 3 is formed, the mask member can be arranged on a flatter surface as compared with the case where the edge portion 31 is formed after the main concave portion 30 is formed, and the mask member when forming the concave portion 3 can be formed with high accuracy. The effect that the patterning characteristics can be improved is obtained. Further, since there are few irregularities of the base of the mask member, it is easy to remove the resist after processing the second recess 3b, and it is possible to suppress the foreign matter from remaining.

Further, in the manufacturing process of the semiconductor pressure sensor wafer, it is possible to prevent the resist from remaining in the recess 3 in advance, so that the yield of the semiconductor pressure sensor wafer can be improved, the manufacturing stability can be improved, and the final product can be obtained. The reliability of the semiconductor pressure sensor can be improved. Further, it is possible to prevent contamination of the semiconductor pressure sensor wafer manufacturing equipment.

Although the present application describes various exemplary embodiments and examples, various features, aspects, and functions described in one or more of the embodiments are applicable to particular embodiments. However, the present invention is not limited to this, and can be applied to the embodiments alone or in various combinations.
Therefore, innumerable variations not illustrated are envisioned within the scope of the technology disclosed herein. For example, it is assumed that at least one component is modified, added or omitted, and at least one component is extracted and combined with the components of other embodiments.

1 first silicon substrate, 1a one main surface, 1b back surface,
2 second silicon substrate, 3 recessed portion, 3a first recessed portion, 3b second recessed portion,
4 alignment mark, 5 diaphragm, 6 gauge resistance, 7 protective film,
8 oxide film, 10 reference pressure chamber, 12 terrace part, 20 pressure detection part,
30 main concave part, 31 edge part, 100 semiconductor pressure sensor, 101 wafer

Claims (3)

A first silicon substrate having a concave portion and an alignment mark, which are hermetically sealed reference pressure chambers , are formed on one main surface,
A second silicon substrate bonded to the one main surface of the first silicon substrate via an oxide film and covering the recess and the alignment mark ,
A pressure detection unit including a diaphragm formed on the second silicon substrate located above the recess, and a pressure sensitive element formed on the diaphragm;
The reference pressure chamber has an edge portion forming a contour of an opening region of the one main surface of the first silicon substrate, and a main concave portion located inside the edge portion, and the main concave portion is the edge. Formed deeper than the part ,
The semiconductor pressure sensor, wherein the alignment mark is formed in a region where the concave portion is not formed, at the same depth as the edge portion . The semiconductor pressure sensor according to claim 1, wherein the edge portion and the bottom surface portion of the main recess are flat surfaces parallel to the one main surface. A step of digging down the formation region of the reference pressure chamber on the one main surface of the first silicon substrate to form a first recess,
A step of forming a second concave portion that constitutes a main concave portion of the reference pressure chamber by leaving the edge portion that forms the contour of the first concave portion and digging down the bottom surface portion of the first concave portion inside the edge portion. ,
Bonding the second silicon substrate via the oxide film on the one main surface of the first silicon substrate, gas covers the first recess and the recess consisting of the second recess by the second silicon substrate A step of forming the reference pressure chamber which is tightly sealed ,
A step of processing the second silicon substrate to form a diaphragm above the reference pressure chamber,
Look including the step of forming the pressure-sensitive element unit in the second silicon substrate,
Simultaneously with the formation of the first recess, an alignment mark is formed at the same depth as the first recess in a region of the first main surface of the first silicon substrate where the first recess is not formed. A method for manufacturing a characteristic semiconductor pressure sensor.

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