JPH0527971B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for electrochemically etching silicon substrates. In particular, it relates to electrochemical etching when forming a diaphragm of a diaphragm type silicon pressure sensor.

(Prior Art) Conventionally, the diaphragm of a diaphragm type silicon pressure sensor has been formed by chemical etching, electrical discharge machining, or electrochemical etching.

However, it is difficult to accurately control the thickness of the diaphragm using chemical etching or electrical discharge machining.
Electrochemical etching techniques, in which etching stops when a predetermined thickness is reached, have begun to be used (IEEE ELECTRON DEVICE LETTERS).
VOL.EDL-2, No.2, FEB., 1981, 44-45)).

Figures 3a and 3b show a conventional electrochemical etching method.

The silicon substrate 100 is composed of a P-type layer and an N-type layer, and a metal film 101 is attached to the N-type layer side. A positive polarity voltage is applied to the metal film 101, and a platinum electrode 102 is used on the negative polarity side. The etching liquid 103 is stirred by a rotor 104 so that etching proceeds uniformly.
Ethylenediamine/pyrocatechol is used as the etching solution. The metal film 101 serves as an electrode for applying voltage and also as a protective film against etching. In FIG. 3a, the N-type layer is protected and the P-type layer is etched. When the P-type layer is completely etched and the N-type layer is exposed, the etching stops and only the N-type layer remains. The applied voltage is
It is 0.5V.

FIG. 3b shows an example in which a diaphragm of a diaphragm type silicon pressure sensor is formed using this electrochemical etching.

An N-type silicon layer 106 is formed on the surface of the P-type silicon substrate 105 by thermal diffusion or epitaxial growth.
A P-type diffused resistor 107 which becomes a pressure sensitive element is formed. A portion of the back surface of the P-type silicon substrate 105 that will not be etched is protected with an oxide film 108. When ethylenediamine-pyrocatechol is used as the etching solution, the P-type silicon substrate 105 is anisotropically etched. For example, if the plane orientation of the board is (100)
When considered as a plane, the inclined part forms an angle of 54.7° with the (111) plane. Once the P-type silicon substrate is removed and the N-type silicon layer is exposed, etching stops, leaving the N-type layer.

Since the pressure-to-electrical conversion sensitivity of a diaphragm type silicon pressure sensor is inversely proportional to the square of the diaphragm thickness, it is necessary to accurately control the diaphragm thickness in order to reduce sensitivity variations. Using the electrochemical etching technique, the thickness of the diaphragm is precisely defined by the thickness of the N-type silicon layer 106. If the N-type silicon layer 106 is formed by epitaxial growth technology, the thickness can be controlled with an accuracy of within 10%, and a diaphragm pressure sensor with less variation in sensitivity can be obtained.

(Problems with the Prior Art) As shown in FIG. 3a, in the past, a metal film was deposited by vapor deposition or the like in order to obtain an electrode contact. Then, after etching the P-type layer, this metal film must be removed so as not to cause unnecessary strain. Further, the metal film has the disadvantage that it must be made of a material that is resistant to corrosion by the etching solution.

(Objective of the Invention) An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a method by which electrode contact can be obtained without using a metal film.

(Structure of the Invention) According to the present invention, a high concentration diffusion of the same conductivity type as the first conductive layer of a two-layer silicon substrate consisting of a first conductive layer and a second conductive layer of the opposite conductivity type. A method of etching is provided, characterized in that a layer is formed in a non-active area of the first conductive layer as an electrode, and the second conductive layer is removed by electrochemical etching, leaving the first conductive layer. It will be done.

(Example) Next, the present invention will be described by giving examples with reference to the drawings.

FIGS. 1a and 1b show the structure of a silicon substrate showing a first embodiment of the present invention. Silicon substrate specific resistance 1
is the thick (100) P-type single crystal silicon layer 4 and the thickness
It is a two-layer silicon substrate consisting of an N-type epitaxial layer 3 of 20 μm and 4 Ω·cm. An N-type high concentration diffusion layer 2 is formed in the peripheral portion of the silicon substrate 1 by thermal diffusion of phosphorus, etc., and serves as a low resistance electrode region.
To form a diaphragm, electrode wiring is applied to the N-type heavily doped diffusion layer, and the P-type silicon layer is removed by conventional electrochemical etching as shown in Figure 3a, leaving the N-type epitaxial layer. . Since the periphery of the silicon substrate is damaged when handled with tweezers or the like, good products cannot be obtained, so there is no loss by using it as an electrode region. Furthermore, if hydrazine hydrate is used as the etching solution, the protective film may be a silicon oxide film, and a thermal oxide film is formed on the surface of the N-type high concentration diffusion layer during the indentation oxidation during formation of the diffusion layer. , there is no need to apply a protective film again.
In the N-type epitaxial layer (not shown in FIG. 1), a P-type diffused resistor is formed which becomes a pressure-sensitive element as shown in the conventional example shown in FIG. Electrode connection parts and wiring parts must be insulated and protected with resin, wax, etc.

The N-type high-concentration diffusion layer can be provided in one place on the periphery of the silicon substrate, but as the thickness of the N-type epitaxial layer becomes thinner, the resistance increases and it becomes difficult for current to flow, so it is recommended to place it in a place far from the electrode connection area. In this case, a sufficient current is not supplied, making it difficult to form an anodic oxide film, and etching does not stop, making it impossible to obtain a uniform film thickness, so a circular shape is better.

FIG. 2 shows the structure of a silicon substrate showing a second embodiment of the present invention. The same reference numerals as in FIG. 1 indicate the same components. The difference from FIG. 1 is that the N-type heavily doped diffusion layer 2 is provided not only in the periphery of the silicon substrate but also in the cut region, which is an inactive region. The width of the cutting region is usually 20 to 80 μm, and if the sheet resistance of the N-type heavily doped diffusion layer is several Ω/□, a sufficient current can be supplied even to the center of the silicon substrate. This embodiment is particularly effective when the diameter of the substrate is large. The cross-sectional structure is the same as that in FIG.

(Effects of the Invention) If the etching method of the present invention is used, a uniform current can be generated within the plane of the silicon substrate without using a metal film when manufacturing diaphragm silicon pressure sensors or other thin film devices using an electrochemical method. can be supplied and a uniform film thickness can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a structural diagram of a silicon substrate according to a first embodiment of the present invention, and FIG. 2 is a structural diagram of a silicon substrate according to a second embodiment of the present invention. Figure 3a,
b is a diagram showing a conventional electrochemical etching method. 1... Silicon substrate, 2... N-type high concentration diffusion layer, 3
...N type epitaxial layer, 4...P type silicon layer,
100...Silicon substrate, 101...Metal film, 102
...Platinum electrode, 103...Etching liquid, 104
...Rotor, 105...P-type silicon substrate, 106...
N-type silicon layer, 107...P-type diffused resistance, 108
…Oxide film.

Claims (1)

[Claims] 1 A high concentration diffusion layer of the same conductivity type as the first conductive layer of a two-layer silicon substrate consisting of a first conductive layer and a second conductive layer of the opposite conductivity type is added to the first conductive layer. An etching method characterized in that the second conductive layer is formed in a non-active region to serve as an electrode, and the second conductive layer is removed by electrochemical etching, leaving the first conductive layer.