JPS6154268B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor diaphragm for use in a semiconductor pressure transducer.

Semiconductor pressure transducers are made by applying stress to semiconductor crystals such as silicon or germanium.
This type of semiconductor pressure transducer utilizes the change in electrical resistance caused by the piezoresistance effect, and generally, in this type of semiconductor pressure transducer, a gauge resistor is formed in a silicon crystal substrate using selective diffusion technology, and this gauge resistor is The thickness of the forming part is reduced to form a diaphragm, and the diaphragm is deformed by external pressure, and the pressure is detected from the change in the resistance value of the gauge resistance due to the piezoresistance effect.

Therefore, in such a semiconductor pressure transducer, in order to improve its characteristics and reproducibility and reduce variations, it is necessary to form the diaphragm to a predetermined thickness with high precision. Conventionally, a chemical etching method has usually been applied to form the thickness of this diaphragm, but with this method, the etching speed is significantly affected by the temperature, composition, stirring state, etc. of the etching solution. ,
It was not possible to form the diaphragm to the desired thickness by one-time etching, so etching was repeated several times and the thickness was measured each time to obtain the desired thickness, which was extremely time-consuming. It was something like that.

In view of these conventional circumstances, the present invention makes it possible to detect when a diaphragm has been etched to a predetermined thickness, thereby making it easier to set the thickness of the diaphragm by etching.

Hereinafter, one embodiment of the method of this invention will be described in detail with reference to the accompanying drawings.

Figures 1a and 1b show the beginning and end of etching of the diaphragm according to this embodiment, and in each of these figures, 1 indicates n, which is the diaphragm.
2 is a surface protective film such as a silicon oxide film used as a diffusion mask, 3, 5 and 4, 6 are the n-type silicon semiconductor substrate 1 , and the diffusion depth from the surface is the desired diaphragm thickness. This is a p-type diffused region of boron, etc., which is selectively diffused relatively deeply to ensure a relatively deep diffusion, and its p-n junction. By doing so, settings can be made with relatively high accuracy and with good reproducibility and controllability. Further, reference numerals 7 and 8 refer to electrodes such as aluminum provided in the p-type diffusion regions 3 and 5, and reference numeral 9 refers to electrodes formed in the n-type silicon semiconductor substrate 1 , which have a diffusion depth deeper than that of the regions 3 and 5 and serve as gauge resistance. A shallow p-type diffusion region; 10 is an etching mask formed with an opening directly below each of these diffusion regions 3, 5, and 9; 11, 12, and 13 are lead wires between each of the electrodes 7 and 8; 14 is a DC power supply, an ammeter, and a variable resistor for controlling the current, which are connected in series; 15 is a hydrofluoric acid, nitric acid, or KOH,
This is an alkaline electrolyte etching solution such as NaOH.

Here, as shown in FIG. 1a, when etching is started while preventing the surface protection film 2, electrodes 7, 8, etc. from coming into direct contact with the etching solution 15, the deep p-type diffusion regions 3, 5 are not exposed. Since a DC voltage is applied to this with the polarity shown in the figure, the pn junction 4 in region 3 is forward biased, and the pn junction 6 in region 5 is biased in the reverse direction, resulting in a blocking junction. By keeping the applied voltage lower than the reverse breakdown voltage of the pn junction 6, the ammeter 12 does not swing.

When etching progresses in the above state and both the p-type diffusion regions 3 and 5 are exposed deeply and come into contact with the electrolyte etching solution 15 as shown in FIG.
6 no longer functions as a blocking junction, the current A flows easily through the etching solution 15, and the swing of the ammeter 12 indicates that etching has been carried out to the position of the deep p-type diffusion regions 3 and 5. Therefore, it can be detected. At this time, at the same time as the etching of the portion directly under the p-type diffusion regions 3 and 5, the etching of the portion directly under the p-type diffusion region 9, which is the gauge resistor, is also performed using the etching mask 1.
By keeping the opening shape and area of 0 the same, the same speed and similar operation can be performed. Therefore, if the diffusion depth of the deep p-type diffusion regions 3 and 5 from the substrate surface is set so that the desired diaphragm thickness is achieved, etching to a predetermined position can be performed according to the instruction from the ammeter 12. This makes it possible to detect that the diaphragm in the gauge resistance portion has reached a predetermined thickness.

In the above embodiment, in order to make the explanation easier to understand, the case where the gauge resistor is formed only in one place has been described, but it goes without saying that diaphragms with a large number of gauge resistors can be formed simultaneously on the same substrate. Further, in consideration of uniformity, it is desirable that the deep p-type diffusion region for monitoring etching be placed as close to the center of the substrate as possible.

Further, FIG. 2 shows a specific example of the etching apparatus in the above embodiment, in which an etching container 16 and a holding jig 17 are used to coat the surface protection film 2 side of the silicon semiconductor substrate 1 with an etching-resistant etching material. It is pasted and held on the holding jig 17 with wax 18,
This surface protection film 2 and each electrode 7, 8 are prevented from coming into contact with the etching liquid 15, and each lead wire 1 is
A protective coating 19 is also applied to 4, and an etching solution 15 is applied.
The material is charged into a container 16 filled with water, and a stirrer 20 is provided to improve the uniformity of etching, and etching is performed in this state.

As described in detail above, according to the present invention, when forming a diaphragm by etching a raw semiconductor substrate provided with a gauge resistor, even if the temperature, composition, stirring state, etc. of the etching solution change, for example, it can be easily etched. It is possible to form a diaphragm of a predetermined thickness by etching the semiconductor diaphragm used in this type of semiconductor pressure transducer, making it possible to manufacture semiconductor diaphragms with high precision, reproducibility, and controllability, thereby reducing costs. It has the following features:

[Brief explanation of the drawing]

FIGS. 1a and 1b are explanatory cross-sectional views showing the states at the start and end of etching of a diaphragm to which an embodiment of the method of the present invention is applied, and FIG. 2 is a cross-sectional view showing a specific example of the configuration of the same etching apparatus. It is. 1 ...N-type silicon semiconductor substrate, 2...Surface protective film, 3, 5...Deep p-type diffusion region (monitor region), 4,6...PN junction, 7, 8...Electrode, 9...
...shallow p-type diffusion region (gauge resistance region), 10...
... Etching mask, 15... Conductive etching liquid.

Claims (1)

[Claims] 1 A semiconductor substrate of one conductivity type with a gauge resistor formed on the surface side, and a part of this semiconductor substrate from the surface side with a diffusion depth equal to the thickness of the diaphragm to be obtained, and a conductivity type of the other conductivity type formed on the surface side. selectively controlling and forming at least one set of diffusion regions, and applying a voltage between these diffusion regions,
Etching is performed from the back side of the semiconductor substrate using a conductive etching solution, and as each of the diffusion regions is exposed during etching, the state of etching is confirmed by detecting current flow between these regions. A method for manufacturing a semiconductor diaphragm, characterized in that a diaphragm having a predetermined thickness is obtained by: