JPH03245576A - Manufacture of pressure sensor - Google Patents

Abstract

PURPOSE:To enable a recess which is uniform in depth and provided with an opening optional in diameter to be surely formed by a method wherein a semiconductor substrate is formed as thin as prescribed in thickness by grinding after a wafer process in which a gauge resistor and an attached integrated circuit are formed is finished. CONSTITUTION:Impurities are introduced into an Si board 1 through one of its sides to form a gauge resistor 4 and integrated circuit elements 51 and 52, and then a layer 14 on the rear side of the Si board is removed by grinding to make the Si board 1 as thin as prescribed. Then, a plasma etching mask 7 is formed into a prescribed pattern, a plasma etching is executed to form a recess 8, a diaphragm is formed as thick as prescribed, a protective film 61 is deposited on a gauge surface, the mask 7 is removed, and then a pedestal 10 is joined. As mentioned above, the Si board 1 subjected to a wafer process while it stays thick is formed thin by grinding, whereby a plasma etching method can be applied to form a recess, so that the recess can be accurately formed.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides a pressure sensor that has a gauge resistance in a diaphragm portion formed in a semiconductor piece, and detects pressure generated by a change in gauge resistance caused by deformation of the diaphragm portion. The present invention relates to a method of manufacturing a sensor.

[Conventional technology]

In pressure sensors that utilize deformation of the diaphragm,
In order to obtain high pressure detection accuracy of several percent or less, the thickness of the diaphragm must be several tens of tens of cents. Recent trends in pressure sensors include the use of a semiconductor substrate that forms the diaphragm, in addition to the main element gauge. In recent years, there has been a shift toward compact, high-performance sensors that integrate amplifier circuits, compensation circuits, etc. using the IC process. In the IC process, film formation.

Because it is exposed to a lot of heat and mechanical strain during processes such as film peeling, etching, and ion implantation, the concave machining for forming the diaphragm is done after these processes are completed.
This is generally done from the opposite side of the semiconductor substrate.

FIG. 2 1m1 to +61 shows a conventional pressure sensor manufacturing process, in which a buried layer 2 is placed on a silicon plate 1 having an etch stop layer 11 with different dopant concentrations and resistance values on the negative side.
A layer 3 of epitaxial medium is laminated through the layer 3, and a gauge resistor 4 of different conductivity type, an amplifier circuit, and a compensation circuit element 5 are formed on this layer.
1.52 is integrated and the surface is covered with a wiring protection film 6 (second
Then, on the opposite side, a mask 71 consisting of a single or composite layer of oxide film, nitride film, gold, pitch, resist, etc. A mask 72 for protecting the gauge surface is formed on the gauge surface side by using a similar material or glass glued with wax (Fig. 1 (bl)), and wet etching using butic acid, nitric acid, strong alkali, etc. Stop etching is performed up to the layer 11 by the method to form the recess 8 (FIG. 1 (C1), after this, the mask 7
1.72 was removed and Au, Cr,
A metallized layer 9 made of TI etc. is deposited (see Fig. 1).
d)) Similarly, the metallized layer 9 is bonded to the base 10 using the solder 12 (FIG. 1 1el). For the stop etching to form the recess 8, silicon is used as an anode and There is also a method of performing electrolytic etching by anodic oxidation using a solution.Normally, such a recess 8 is 1
A plurality of sensor chips are formed on a single SI wafer and divided to obtain individual sensor chips.

[Problem to be solved by the invention]

As shown in FIG. 2, processing the recess 8 for forming the diaphragm is different from etching such as mask buttering in a normal wafer process. Since etching is used, not only is the material selection and formation method for the patterning mask 71 complicated, but additional consideration must be given to protecting the surface of the gauge 4 that has already been formed.

In addition, it is necessary to form the etching stop layer 11 in advance, and when applying electrolytic etching using anodic oxidation to stop etching, the process control is difficult.
The process becomes more complicated.

Furthermore, a basic problem with wet etching and electrolytic etching is that as the recesses formed become deeper, they are more susceptible to the effects of gas generated within the recesses, and unevenness of the recesses also occurs. There is also the problem that the limit value of is large and the joint surface with the pedestal becomes small.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and to reliably form four parts of uniform depth with arbitrary opening dimensions from one surface of a semiconductor substrate, thereby producing a diaphragm part of a desired thickness and having a gauge resistance. It is an object of the present invention to provide a method for manufacturing a pressure sensor that leaves no problems.

[! ! l! Means to solve the problem]

To achieve the above object, the present invention introduces impurities from one side of a semiconductor substrate to form a gauge resistor and an attached integrated circuit, and then grinds and polishes the other side of the substrate to a predetermined thickness. Then, a recess is formed by plasma etching from that surface to form a diaphragm portion provided with a gauge resistance.

[Effect]

After completing the wafer process for forming gauge resistors and attached integrated circuits, the semiconductor substrate is ground and thinned to a predetermined thickness. By optimizing parameters such as high-frequency power, gas type, gas mixture ratio, pressure, temperature, electrode spacing, and mask shape under etch mode, isotropic etching is performed to precisely form recesses with uniform shape and reproducibility. Can be formed well. In addition, in the wafer process for IC production, damage etching is performed on the back surface of the substrate for the purpose of gettering impurities, so there are many defects on that surface, and there is a risk of abnormal etching occurring during concave processing, and surface roughness. Due to the high degree of roughness, the bottom surface of the recess becomes rough. However, since the defect layer is removed by grinding to thin the substrate, and the surface roughness is improved by the subsequent polishing, plasma etching improves the uniformity within the concave bottom surface. Plasma etching, which was not previously used, makes it possible to form a recess for forming the diaphragm of the pressure sensor, and because the opening size can be made smaller, it is possible to increase the bonding area with the pedestal.

〔Example〕

FIG. 1 (al~+61 shows the manufacturing process of an embodiment of the present invention, and the same parts as in FIG. 2 are given the same reference numerals. An epitaxial layer 3 is laminated on the substrate via a buried layer 2, a gauge resistor 4 of different conductivity type, an amplifier circuit, and a compensation circuit element 51, 52 are integrated in this layer, and the surface is covered with a wiring protective film 6 (
As shown in FIG. 1(al), a rough surface 3 is formed on the back surface of the Si plate 1 for impurity gettering and the like. This S1
Grind the layer 14 on the back side of 1 by surface grinding or the like (
In FIG. 1 (bl), the thickness after grinding is set to 200μ or more to prevent damage during grinding and damage in subsequent processes. Grinding surface 15
Steps 5 to 15 were performed to remove the strained layer on the surface caused by grinding, to ensure surface roughness for bonding to the pedestal, and to obtain uniformity of the concave bottom surface by plasma etching. Zero-order finishing to a surface roughness of 10n@rs+s or less by polishing about n,
M.

A film of metal such as Cu, Au, or StO is formed by vapor deposition, sputtering, CVD, etc., and a plasma etching mask 7 having a desired pattern is formed by photolithography or the like (FIG. 1(C)). Then, CF□S
Using gas such as P&, 01, high frequency power, pressure.

Plasma etching is performed under optimal parameters such as temperature and electrode spacing to form the recess 8 and finish the diaphragm to the desired thickness (FIG. 1 td)).

In order to improve the uniformity of the plurality of recesses 8 provided in order to obtain a plurality of sensor chips from one substrate, the etching value is calculated by dividing half of the difference between the recess opening dimension and the mask opening dimension by the recess depth. Isotropic etching with a factor of 0.5 or more is effective. FIG. 3 shows the variations in the recess processing time and recess depth when plasma etching was performed on one side of St wafers having different thicknesses to leave a diaphragm portion with a thickness of 50 mm. As the wafer thickness increases and the machining depth b increases, the concave machining time a increases nonlinearly,
As a result, the variation A in recess depth increases non-linearly. The concave processing accuracy, that is, the in-wafer thickness accuracy of the diaphragm, can be compensated to some extent by the amplification factor of the gauge output of the sensor chip, etc., but in the case of highly functional sensors, it is necessary to maintain miniaturization. Figure 3 shows that in order to form a 50μ diaphragm with an A5μ or less, that is, an in-plane accuracy of 10% or less, the wafer thickness must be 350β or less. Recognize.

After the recess machining, a protective film 61 made of resist etc. is applied to the gauge surface.
After removing the mask 7, it is bonded to a pedestal 10 made of Pyrex glass, etc., which has a coefficient of thermal expansion similar to that of Si (Fig. 1(e)). Because of its roughness, it can be directly bonded to the pedestal 10 by electrostatic bonding or the like, and there is no need for metallization or soldering.

(Effects of the Invention) According to the present invention, the wafer process for forming gauge resistors and integrating auxiliary circuits is performed by grinding and polishing the semiconductor substrate, which is made thick to prevent warping, to make it thinner. Concave machining using plasma etching, which is extremely simple compared to the wet method, can be applied, and the effect of reducing man-hours and improving yield can be achieved with the same machining accuracy as conventional methods.In addition, the opening size can be made smaller. By increasing the bonding area between the sensor chip and the pedestal, it has become possible to further improve yield and improve reliability.Furthermore, the sensor chip has a bonding surface that can be directly bonded to the pedestal. Therefore, it is possible to improve reliability through direct bonding without significantly increasing the number of processes.

[Brief explanation of drawings]

Figure 1 shows the manufacturing process of a pressure sensor according to an embodiment of the present invention (8
) to Tel, FIG. 2 is a cross-sectional view showing the conventional pressure sensor manufacturing process in the order of (al to tal), and FIG. 3 shows the thickness of the silicon wafer to be processed, the concave processing time during plasma etching, and It is a relationship diagram with the variation in the depth of the recess. 1: silicon plate, 3: epitaxial layer, 4: gauge resistor, 51.527 integrated circuit element, 7: mask for plasma etching, 8: recess, 1o: pedestal. -'22, 〆jutsu 1 illustration 2 flash

Claims (1)

[Claims] 1) After introducing impurities from one side of the semiconductor substrate to form a gauge resistor and an attached integrated circuit, the other side of the substrate is ground and polished to a predetermined thickness, and then a recess is formed by plasma etching from that side. A method for manufacturing a pressure sensor, comprising processing to form a diaphragm portion provided with a gauge resistance.