JP2501722B2 - Semiconductor capacitive pressure 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 semiconductor sensor which electrostatically detects a pressure change to be measured, and more particularly to a structure of its electrode portion.

[0002]

2. Description of the Related Art FIG. 5 is a constitutional view showing a conventional example of such a semiconductor sensor, (a) is a top view thereof, and (b) is a sectional view. In the figure, 1 is a metal layer, 2 and 9 are insulating layers, 3 is an opening, 4 is a metal electrode lead, 5 is a Si epitaxial layer, 6 is a low resistance buried layer, 7 is a P ⁺ layer, and 8 is a Si single crystal. Substrate 10, 10 is a surface stabilizing layer, 11 is a diaphragm portion, 1
2 is a cavity.

The main surface of the Si single crystal substrate 8 is a (100) plane, and a P ⁺ diffusion layer (concentration of about 10 ²⁰ per cm 3) 7 is formed on the main surface to form a diaphragm portion 11 and a cavity 12. It will be the stop layer for the occasion. An insulating layer 9 such as silicon nitride (Si ₃ N ₄ ) is formed on one surface of the substrate 8, and a surface stabilizing layer 10 such as glass is formed on the surface of the insulating layer 9 and the thin portion of the substrate 8. It An epitaxial layer 5 is formed on the other surface of the substrate 8, a part of which is hollowed out to form a cavity 12, and the P ⁺ diffusion layer 7 and the metal electrode portion 4 are brought into contact with each other in another part. A low resistance buried layer 6 is formed for this purpose.

An insulating layer 2 made of Si ₃ N ₄ or the like is formed on the Si epitaxial layer 5 similarly to the insulating layer 9, and a metal layer 1 is further formed thereon. Metal layer 1
The opening (hole) 3 formed through the insulating layer 2 and the insulating layer 2 is opened to supply the etching solution through the hollow portion 12 when the hollow portion 12 is formed by anisotropic etching. The shape of the opening 3 is, for example, a long and narrow groove as shown in FIG. 1 (a), and a plurality of “c” -shaped grooves are arranged and finally hollowed out into a shape like a broken line. Cavity 12
Is formed.

This is a mask of a closed pattern of arbitrary shape on a Si single crystal substrate 8 whose main surface is the (100) plane and whose lateral direction is the (011) plane. When anisotropic chemical etching is performed using a catechol-based etching agent, the final pattern is a pyramid shape in which four faces are surrounded by faces equivalent to the (111) face, and the pattern becomes a mask pattern. It is performed by utilizing the property of being inscribed.

Thus, the metal layer 1 and the diaphragm portion 11
A capacitance is formed between the two and when the diaphragm portion 11 is displaced by the measurement pressure, the capacitance changes accordingly, so that the pressure can be measured as a function of the capacitance.

[0007]

However, the semiconductor sensor having such a structure has the following drawbacks.

B) Since the opening 3 is formed by a thin groove, it is difficult for the etching liquid to enter, and therefore it takes time to form the cavity. If the groove is made larger, the effective area of the electrode portion becomes smaller, that is, the capacitance for detection becomes smaller, so there is a limit to widening the groove.

(B) Since the electrode portion is formed on the entire surface facing the diaphragm portion, the stray capacitance accompanying the detection capacitance in response to the pressure change is large, and therefore not only the measurement error increases but also the measurement sensitivity increases. descend.

The present invention has been made to eliminate such drawbacks, and provides a highly accurate semiconductor type electrostatic capacitance type pressure sensor having a small measurement error by improving the measurement sensitivity and reducing the stray capacitance. With the goal.

[0011]

To achieve the above object, in the present invention, a Si single crystal substrate and a P formed on the substrate are formed.
⁺ Diffusion layer, Si epitaxial layer formed on the diffusion layer, and the P ⁺ layer formed on a part of the epitaxial layer
A low resistance buried layer electrically connected to a diffusion layer, first and second insulating layers respectively formed on the epitaxial layer and on a surface of the Si substrate opposite to the epitaxial layer, and on the first insulating layer And a diaphragm portion formed by performing an anisotropic etching process through an opening penetrating the metal layer and the insulating layer and the opening on the side of the second insulating layer. In a semiconductor-type capacitance pressure sensor having a measuring capacitance formed between the diaphragm portion and the metal layer, the metal layer and the diaphragm portion are square in shape, and
The area of the metal layer is made slightly smaller than that of the diaphragm part, and the metal layer and the diaphragm part are arranged so that the respective sides are parallel to each other, while the square metal layer is provided with an arm part at the center of each side, respectively. Further, a fine groove portion was provided in the center of the metal layer.

[0012]

According to the present invention, in the semiconductor type pressure sensor, the area of the electrode portion which constitutes the measurement capacitance together with the diaphragm portion is made smaller than at least that of the diaphragm portion, and this is supported by the plurality of arm portions. As a result, the etching time is shortened, the detection sensitivity is improved, and the stray capacity is reduced.

[0013]

1 is a top view showing an embodiment of the present invention, FIG.
Is a sectional view of the same.

After the P ⁺ layer 7 is made to have the thickness of the diaphragm on the N or P type Si single crystal substrate 8 whose surface crystallographic direction is the (100) plane by an ion implantation method or a thermal diffusion method, The epitaxial layer 5 is grown by CVD (Chemical Vapor Deposition; a method of forming a thin film using a chemical reaction) or the like to a thickness in charge of the void of the capacitance (this layer does not have a low resistance and is susceptible to anisotropic chemical etching). Then, a buried layer 6 having a low resistance is formed so as to establish conduction with the P ⁺ layer 7, and an insulating layer such as Si ₃ N ₄ or SiO ₂ (silicon oxide) is formed so as to sandwich the integrated body thus formed. After forming about 0.5 to 1 μm, the process is the same as the conventional process from the opening of the insulating layer for forming the metal electrode lead 4 to the formation of the metal layer 1.

That is, the present invention is characterized by the shapes of the electrode portion and the diaphragm portion, as is apparent from FIG. 1, and how these are formed will be described below.

When making a square diaphragm, four trapezoids (shown as openings 3 in FIG. 1) as shown in FIG. 1 are formed on a Si substrate surface equivalent to a crystallographic (011) plane. , Two are parallel to each other and the other two
The metal layers are etched so that the individual pieces are at a right angle and the rectangles (the portions C surrounded by the alternate long and short dash lines) circumscribing the respective trapezoids overlap slightly. Next, the insulating layer 2 is etched using the opening 3 of the metal layer as a mask. At this time, the insulating layer 9 on the side without metal is also opened so that a square diaphragm portion is formed, and the etching is performed. To do. After that, the metal is left in the shape in which the arms 14 are attached to the square thus formed, and the metal in the other portions is removed by etching.

In this way, single crystal Si is formed in the opening.
Is exposed, so that when this is immersed in an anisotropic chemical etching solution such as KOH type or ethylenediamine / pyrocatechol type, anisotropic etching proceeds from the opening. Etching by the trapezoidal opening 3 first proceeds, but in the lateral direction, the etching proceeds to a portion C surrounded by a plane equivalent to the (111) plane and surrounded by a dashed line in FIG.

By the way, one of the properties of anisotropic chemical etching with respect to silicon is that "the etching of a portion where two (111) faces intersect in a concave shape is slower than that of the other portions". Etching progresses again from the overlapping portion of the two rectangles, and the bottom of the inner square is hollowed out to form the cavity 12 (see FIG. 2).

On the other hand, the surface opposite to the cavity is also etched in the same manner to form a recess in which four surfaces are surrounded by (111) surfaces, and the thin portion has a diaphragm as indicated by reference numeral 11 in FIG. It becomes a part. The second property for anisotropic chemical etching is that "the concentration per 1 cm ³ is 10
Due to the property that the P ⁺ layer of about ²⁰ is difficult to be etched, the vertical etching is stopped by the P ⁺ layer 7. Therefore, the thickness of the cavity 12 is limited by the thickness of the Si epitaxial layer 5, whereby the gap can be accurately formed.

Needless to say, the thickness of the diaphragm portion 11 is determined by the diffusion layer 7. In addition, of the metal layer (electrode portion) 1 and the diaphragm portion 11,
The side length ratio γ (= ae / a) of the outer square is chosen to be smaller than 1, in order to increase the sensitivity without reducing the detection capacity. That is, if the electrode is formed on the entire surface corresponding to the diaphragm portion, the sensitivity is lowered, and if the electrode is formed in the central portion of the diaphragm, the sensitivity is improved, but the detection capacitance is reduced and is easily affected by the stray capacitance. An appropriate ratio γ determined by these tradeoffs is selected.

FIG. 3 is a top view showing another embodiment of the present invention. In FIG. 1, the metal layer 1, that is, the electrode portion is (0
11) While being supported by the arm 14 which is inclined by 45 ° with respect to the plane direction, in this embodiment, (01
1) This is an example in which the arms are parallel to the surface and perpendicular to the surface.

Reference numeral 13 is an opening, which is an auxiliary opening for forming a cavity on the lower side of the arm portion 14. That is, L
Of the squares circumscribing the opening 3 in the shape of a letter, at least two diagonally arranged squares are overlapped by the auxiliary opening in the shape of a groove, whereby a cavity is formed under the arm portion 14. The time to do can be shortened. As is clear from the figure, the length of the opening 13 is formed to be larger than √2 times the width of the arm. Further, if the width of the opening 13 is widened, the time for forming the cavity is shortened, but the detection capacitance becomes small. Therefore, it is desirable to appropriately form in consideration of these.

FIG. 4 is a top view showing another embodiment of the present invention. That is, the same effect as described above can be expected by arranging the electrode portion with an inclination of 45 ° with respect to the diaphragm portion instead of the arrangement shown in FIG. Although the shape of the diaphragm portion and the electrode portion is square in the above, it is also possible to make it rectangular.

[0024]

According to the present invention, since the area of the electrode portion which constitutes the measurement capacitance together with the diaphragm portion is smaller than that of the diaphragm portion and is supported by a plurality of arms, the opening portion for forming the cavity portion is formed. Can be increased without decreasing the detection capacity,
Therefore, not only the etching time is shortened but also the detection sensitivity can be improved. Further, since the arm for supporting the electrode portion is slightly hung on the portion other than the diaphragm portion, there is an advantage that the stray capacitance associated with the detection capacitance can be reduced.

[Brief description of drawings]

FIG. 1 is a top view showing an embodiment of the present invention.

FIG. 2 is a sectional view showing a sectional structure of an embodiment of the present invention.

FIG. 3 is a top view showing another embodiment of the present invention.

FIG. 4 is a top view showing still another embodiment of the present invention.

FIG. 5 is a configuration diagram showing a conventional example of a semiconductor capacitive sensor.

[Description of sign]

1 ... Metal layer, 2, 9 ... Insulating layer, 3 ... Opening, 4 ... Metal electrode lead, 5 ... Si epitaxial layer, 6 ... Low resistance burying layer, 7 ... P ⁺ layer, 8 ... Si single crystal substrate, 10 ... Surface stabilizing layer, 11 ... diaphragm part, 12 ... cavity, 13 ... auxiliary opening, 14 ... arm

Claims (1)

(57) [Claims] And 1. A Si single crystal substrate, and the P ⁺ diffusion layer formed on the substrate, and the Si epitaxial layer formed on the diffusion layer, is formed on a part of the epitaxial layer and the P ⁺ diffusion A low resistance buried layer electrically connected to the layer, first and second insulating layers respectively formed on the epitaxial layer and on a surface of the Si substrate opposite to the epitaxial layer, and on the first insulating layer. And a diaphragm portion formed by performing an anisotropic etching process through an opening penetrating the metal layer and the insulating layer and an opening on the side of the second insulating layer. In a semiconductor-type capacitance type pressure sensor formed by forming a measuring capacitance between a diaphragm portion and the metal layer, the shape of the metal layer and the diaphragm portion is square, and the area of the metal layer is The size is slightly smaller than that of the ear diaphragm, and the sides of the metal layer and the diaphragm are parallel to each other, while the square metal layer has arms at the center of each side, and the center of the metal layer. A semiconductor type electrostatic capacitance type pressure sensor, characterized in that a thin groove portion is provided in the portion.