JPS5816346B2 - Manufacturing method of semiconductor pressure transducer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a diaphragm-type semiconductor pressure transducer device mainly used for low pressure applications.

FIG. 1 shows the basic structure of the main parts of a diaphragm type semiconductor pressure transducer.

The illustrated one is an example in which N-type silicon is used as the semiconductor substrate 1, 2 is a P-type diffused resistance layer, 3 is an oxide film, 4 is a metal electrode, and 5 is a diaphragm.

Two important steps in manufacturing such a pressure transducer are the formation of a diffusion resistance layer (piezoresistance element) and the formation of a diaphragm.

The former is formed using silicon planar technology, similar to resistive elements used in conventional integrated circuits.

However, in the case of piezoresistive elements used in pressure transducers, the optimal position of the resistor is determined by the surface index of the silicon substrate used, and the performance is influenced by the geometric shape regardless of the resistance value. This is a major difference from resistive elements in ordinary integrated circuits.

On the other hand, methods for forming the latter diaphragm include machining, chemical etching, electrical discharge machining, etc.
Among these, chemical etching methods are often used.

Compared to other methods, this method does not create a fractured layer during processing, and the alignment accuracy of the resistor pattern on one side of the board and the diamond slam pattern on the other side is very good and simple. Due to reasons such as.

Etching solutions used in chemical etching methods include acid-based and alkaline-based ones, among which fluoronitric acid (HF-HNO3) and potassium hydroxide (KOH) are well known.

A silicon oxide film (Sin oxide film) is used as a mask when forming a diaphragm using these etching solutions.
2) and silicon nitride film (Si3N4) are commonly used.

In particular, it is known that the etching speed of the Si3N4 film with a chemical etching solution is much lower than that of the 5i02 film.

However, Si3N4 used as an etching mask
is a vapor-phase growth film that is formed at a high temperature of approximately 800°C, and due to the difference in thermal expansion coefficient with silicon, cracks and pinholes are very likely to occur when it is formed directly on silicon. It is usually formed through a membrane.

In this type of pressure transducer, the tire flam thickness becomes thinner as the pressure is lowered, and it must be etched deeply. Therefore, by annealing the grown SiN4 in N2 at 1000°C, the etching resistance of the SiN4 film is strengthened. It is common to use it as

For example, use HF-HNO3 based etching solution to remove silicon 200
For etching μ, it takes 2000 for grown Si3N4.
Although about λ is necessary, for annealed S i 3 N4, about 1500λ is sufficient.

If the mask is made of Si3N4 film annealed in this way, 2
Silicon etching at about 501° C. is possible, but in the case of chemical etching, side etching as shown in FIG. 2 inevitably occurs.

In FIG. 2, 6 is a mask for etching the 5i02 film, and 7 is a mask for etching the Si3N4 film.

It is known that side etching has a negative effect on linearity, which is one of the important characteristics of a pressure transducer.

This problem becomes more pronounced as the diaphragm becomes thinner and the degree of etching becomes deeper, making it extremely difficult to manufacture a low-pressure diaphragm type pressure transducer having good linearity.

Normally, the thickness of the wafer is almost determined by the size of the wafer, but this is because a certain thickness is required to minimize cracks and warpage of the wafer during oxidation, diffusion, and cleaning processes. It is.

On the other hand, in order to form a diaphragm using a chemical etching method and obtain a pressure transducer with good linearity, the depth of etching should be minimized as described above to minimize sag due to side etching. Bye.

Therefore, K can be achieved by reducing the thickness of the weber, but if this is done, the diameter of the weber must be made much smaller, resulting in one pellet per weber, resulting in a very poor productivity.

This is unavoidable in conventional techniques in which a piezoresistive element is formed by diffusion and a diaphragm is formed using SiO□ or Si 3 N4 formed at high temperature as an etching mask.

In order to eliminate the above-mentioned drawbacks, the present invention uses a gold (Au) layer as an etching mask when forming a diaphragm, thereby making it possible to easily obtain a pressure transducer with good linearity and to improve adhesion to the support base. It is an object of the present invention to provide a method for manufacturing a semiconductor pressure transducer that is reliable and can simplify the manufacturing process.

An embodiment of the present invention will be described below with reference to the drawings.

To explain the manufacturing order according to the order of FIG. Similarly, a plurality of P-type diffused resistance layers 12 which become pressure-sensitive elements are formed, and a metal electrode layer 13 made of aluminum is formed in conjunction therewith.

Note that 14 is an oxide film.

Next, as a second step, as shown in the figure, the low pressure (2
kg/cni), the thickness of the semiconductor substrate 11 is reduced to 150~2.
Thin it to about 00μ.

In the third step shown in C, gold (Au)/! is deposited on the other surface of the semiconductor substrate 11 by vacuum evaporation. 15, and then sintered at 300° C. for about 30 minutes in a hydrogen (N2) atmosphere to improve adhesion to the substrate 11.

Furthermore, as shown in FIG. 5, a diamond shim pattern is formed on the gold layer 15 by photolithography.

Finally, in the fourth step, a diaphragm 16 is formed by chemical etching using the gold layer 15 as an etching mask, as shown in FIG. 3e.

This etching mask of the gold layer 15 is used when adhering to the support base 17, as will be described later.

In this way, when chemically etching the semiconductor substrate 1
Since the thickness of the plate 1 can be made thinner in advance, sagging due to side etching is reduced compared to the conventional case, and a pressure transducer device with excellent linearity of characteristics can be obtained.

A feature of the manufacturing method of the present invention is that since a gold layer is used as the etching mask, this mask can be formed after the metal electrodes are formed.

Therefore, the thickness of the semiconductor substrate can be adjusted in advance after the metal electrodes are formed, and a thin diaphragm with less droop due to side etching can be easily obtained.

This is because the metal mask is formed at about 300°C, and unlike 5i02 or Si3N4, gold is not etched at all depending on the silicon etching solution such as HF-HNO3 or KOH, and it is not etched during vapor deposition. This is because even if the thickness of the silicon substrate is set to 200λ or less, the internal strain due to the formation of the gold mask can be ignored, for example because it is sufficient to have a thickness of about 1000λ without pinholes.

In contrast, conventional 5i02 and Si3N4 masks have 8
Since it can only be formed at a high temperature of 00° C. or higher, the thinner the silicon substrate is, the greater the warpage, and therefore the greater the strain inherent in the substrate itself, which adversely affects the characteristics.

For this reason, in the conventional case, a thick substrate must be used, deterioration of characteristics due to sagging during etching cannot be avoided, and the number of steps after forming the etching mask is required compared to the case of the present invention. There will be more.

Further, the pressure transducer according to the present invention has the advantage that bonding by the Au-8i eutectic method can be easily and reliably performed.

Since pressure cannot be applied with the structure shown in FIG. 3, it is necessary to create a structure as shown in FIG. 4.

In FIG. 4, numeral 17 is a support made of silicon or another material having the same thermal expansion coefficient as silicon, and 18 is a pipe for introducing fluid made of metal or glass.

Examples of methods for bonding the pressure transducer and the support base using the semiconductor substrate include methods using epoxy resin, glass, and Au-8i eutectic.

However, since the sink temperature of aluminum, which is generally used as an electrode, is around 500°C and long-term reliability is required, the bonding method using Au-8i eutectic (eutectic point 380°C) is recommended. Are suitable.

If conventional Si3N4 or SiO2 masks were used, these layers would be bonded with Au-8i eutectic.

This could only be done after removal.

However, in the case of the present invention, since a deposited gold film that has been previously sunk is used as an etching mask, bonding can be easily performed using this.

Due to this sinking Au film, an Au-8i eutectic layer containing no air bubbles is formed compared to the case where an Au-8i eutectic layer is formed directly between the silicon surface and the gold foil, and the adhesion is ensured. This can improve reliability.

Note that this invention is not limited to the above embodiments (
, it can be implemented with different configurations without changing the gist.

Although this invention is suitable for low pressure applications, it is not necessarily limited to this and can also be applied to high pressure applications.

Further, in the above embodiments, the case where the semiconductor substrate is N-type silicon has been described, but it goes without saying that the present invention can be practiced using P-type silicon.

As described above, according to the present invention, by using metal as an etching mask when forming a diaphragm, it is possible to easily obtain a pressure transducer with good linearity, simplify the manufacturing process, and moreover, A method for manufacturing a semiconductor pressure transducer with reliable adhesion can be provided.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view showing the basic structure of a diaphragm type semiconductor pressure transducer, FIG. 2 is a longitudinal cross-sectional view showing the structure of an example of a semiconductor pressure transducer manufactured by a conventional method, and FIG.
The figure is an explanatory diagram showing the manufacturing process of one embodiment of the present invention.
The figure is a longitudinal cross-sectional view for explaining how to bond a semiconductor substrate to a fixing base. DESCRIPTION OF SYMBOLS 1... Semiconductor substrate, 2... Diffused resistance layer, 3... Oxide film, 4... Metal electrode, 5
...Diaphragm, 6...Silicon oxide film, 7...Silicon nitride film, 11...
- Semiconductor substrate, 12... Diffused resistance layer, 13...
...Metal electrode layer, 14... Oxide film, 15.
...Gold (Au) layer, 16...Diaphragm, 17...Support stand, 18...Pipe.

Claims (1)

[Claims] 1. A first step of forming a diffused resistance layer and a metal electrode layer that will become a pressure-sensitive element on one surface of a semiconductor substrate, and a second step of processing the substrate to a predetermined thickness. A third step of forming a gold layer etching mask according to the pattern of the diaphragm on the other surface of the substrate, and a fourth step of forming a diaphragm of a predetermined thickness by chemical etching using this mask. □ A method for manufacturing a semiconductor pressure transducer device, characterized in that the etching mask for the gold layer is used when bonding the gold layer to the support base.