JPH0536738B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to an improvement in a semiconductor pressure transducer in which a pressure sensitive pellet having a strain resistance gauge formed on a thin diaphragm surface of a semiconductor crystal is fixed to a base. [Technical background of the invention and its problems] Pressure transducers that utilize piezoresistance changes in semiconductors have been put into practical use as pressure transducers for detecting fluid pressure. As shown in the figure, this type of semiconductor pressure transducer has a basic configuration in which a thin diaphragm surface 2 that is sensitive to pressure is formed in the center of a semiconductor single crystal plate 1 made of, for example, silicon (Si). A diffused resistance layer 3 having a conductivity type opposite to that of the substrate 1 is formed on one side of the diaphragm surface, and is used as a strain resistance gauge. A window is provided in the SiO ₂ insulating film 4 provided to protect the surface of the substrate 1, and an electrode wiring 5 for the strain resistance gauge 3 is formed of aluminum or the like through this window. The pressure-sensitive pellet constructed in this way is fixed to the peripheral thick portion of the semiconductor single crystal plate 1 to the base 6 using an adhesive 7 or the like, and is fixed to the base 6 through a pressure introduction hole provided at the center of the base 6. The pressure P introduced through the pressure P is responsive to the pressure P introduced via the pressure P. Therefore, the strain resistance gauge 3 exhibits a resistance value change due to the diaphragm that is strained by the pressure P, and this resistance value change is caused by a full bridge circuit including the strain resistance gauge 3, etc. Detected by As a result, even weak pressure changes, for example, can be detected with high sensitivity. By the way, since such a semiconductor pressure transducer can detect even a weak pressure with high sensitivity due to the strain generated in the diaphragm as mentioned above, it goes without saying that the residual stress applied to the pressure-sensitive pellet is and temperature changes are a problem. For this purpose, base 6
It is also necessary to match the thermal expansion of the base 6 and the adhesive 7 with the silicon of the semiconductor crystal plate 1 so that no stress is applied to the pressure-sensitive pellet fixed to the substrate. For this reason, silicon has conventionally been generally used as the base 6. However, using silicon as the base 6 not only causes problems such as being expensive, but also requires the use of gold-silicon eutectic or low melting point solder glass as the adhesive 7. There was a problem that residual stress due to the material's expansion rate could not be removed. In contrast, recently, attempts have been made to use borosilicate glass known under trade names such as Pyrex as the base 6. If this borosilicate glass is used, bonding with the pressure-sensitive pellet can be performed by heating it to a temperature higher than its glass transition temperature, so the adhesive 7 described above is not required, and moreover, it can be bonded to the pressure-sensitive pellet over a wide range. The effect of matching thermal expansion can be achieved. However, generally the glass transition temperature of the above borosilicate glass is
The temperature is 500°C or higher, and in order to perform the above bonding, it is necessary to heat the glass to about 50 to 100°C higher than its glass transition temperature. At this time, the aluminum forming the electrode wiring 5 of the pressure-sensitive pellet changes in quality due to the heating and loses its role as an electrode. Therefore, expensive gold and
A problem arose in that a platinum-based material had to be used. It is also conceivable to form the electrode wiring 5 of aluminum after bonding and fixing the pressure-sensitive pellet to the base 6, but this poses problems such as complicating the manufacturing process. [Object of the Invention] The present invention has been made in consideration of the above circumstances, and its purpose is to provide an inexpensive method that allows electrode wiring to be made of aluminum, and which generates less residual stress on pressure-sensitive pellets. The object of the present invention is to provide a highly practical semiconductor pressure transducer. [Summary of the Invention] The present invention provides a base for fixedly supporting pressure-sensitive pellets, which has a glass transition temperature lower than 500°C and an average coefficient of thermal expansion up to the fixation temperature of 32 to 36 ×
Borosilicate glass having a temperature of 10 ^-7 /°C is used, and the electrode wiring of the pressure-sensitive pellet can be made of aluminum. The borosilicate glass as a base having the above characteristics contains 65 to 76% by weight of _SiO2 ,
13.5-20% by weight _{of B2O3} , 1.5-4.0% by weight _{of Al2O3} ,
2.0 to 4.0% by weight of Na ₂ O, 0 to 2% by weight of K ₂ O,
0 to 1% by weight of LiO ₂ (however, Na ₂ O, K ₂ O, Li ₂ O
total of 3.0 to 5.0% by weight), PbO of 0 to 5% by weight,
The composition contains 1% by weight or less of a clarifying agent. [Effects of the Invention] Thus, according to the present invention, a pressure-sensitive pellet can be directly bonded to a base made of borosilicate glass, and the generation of residual stress on the pressure-sensitive pellet can be effectively suppressed. Moreover, since the glass transition temperature of the borosilicate glass used as the base is low, even if aluminum is used as the electrode wiring of the pressure-sensitive pellets when the pressure-sensitive pellets are bonded by heating, this aluminum will not change in quality. do not have. In addition, since the average coefficient of thermal expansion of borosilicate glass up to the fixing temperature is 32 to 36 x 10 ^-7 /℃, it is sufficient to substantially tolerate the temperature change in residual stress that occurs when bonding with the pressure-sensitive pellet. becomes smaller,
Compensation becomes simple. Therefore, it is possible to easily create a semiconductor pressure transducer that is not affected by the adverse effects of residual stress.
Moreover, it can be manufactured at low cost, and has great practical effects. [Examples of the Invention] Hereinafter, consideration of the present invention and examples thereof will be described. The coefficient of thermal expansion of the silicon single crystal plate constituting the pressure-sensitive pellet increases as its temperature increases.
If the temperature at which this pressure-sensitive pellet and borosilicate glass are fixed is 500°C, then the average coefficient of thermal expansion of the silicon single crystal plate at this temperature is approximately 35.
×10 ^-7 /℃. On the other hand, the coefficient of thermal expansion of borosilicate glass, which is to be used as a base for fixedly supporting the pressure-sensitive pellets, differs somewhat depending on its composition, but it generally has a property of less temperature change compared to silicon. have. Therefore, it is completely impossible to match the coefficients of thermal expansion of the two in all temperature ranges below the fixing temperature.
However, the deviation in the resistance value of the strain resistance gauge on the pressure-sensitive pellet caused by a small amount of residual stress can be relatively easily compensated for electrically by shifting the zero point of the element. However, if the residual stress differs due to practical temperature changes of the transducer, the compensation becomes extremely difficult. Therefore, the present inventors experimentally investigated the range in which the temperature change of the residual stress mentioned above is practically acceptable for various glasses, and found that the average coefficient of thermal expansion up to the fixation temperature was 32 to 36 × 10 ^-7 /°C I have found that it is sufficient as long as it is possible. The glass used here is so-called alkali borosilicate glass, and the relationship between its composition, thermal properties such as thermal expansion and glass transition temperature, and its chemical durability are well known. However, in order to obtain borosilicate glass that satisfies the above-mentioned requirements regarding the coefficient of thermal expansion, it is necessary to suppress the total alkali concentration to 5% by weight or less. In order to create borosilicate glass with such a low alkali concentration, it is necessary to add boric acid to the glass at a concentration of 12 to 13% by weight. Conventionally, it has been generally accepted that if the concentration of boric acid is higher than this, the chemical resistance will be reduced. It is said to cause a significant decline in sexual performance. Moreover, it was also found that the glass transition temperature of borosilicate glass with such a boric acid concentration inevitably exceeds 500°C. Furthermore, in the low alkali concentration range mentioned above, the high-temperature viscosity of the glass increases significantly, and even when melting at 1600° C., which is the practical limit, problems such as a large amount of residual bubbles are expected. Therefore, in the present invention, we first examined the basic composition of borosilicate glass, tried adding Al ₂ O ₃ and PbO, etc., and achieved a borosilicate glass that exhibits various properties suitable as a base as shown below. First, the basic composition of borosilicate glass will be described. (i) SiO ₂ is a basic component of glass and greatly contributes to low expansion and improved chemical resistance, but on the other hand, it increases the glass transition temperature and high temperature viscosity.
If the composition ratio is less than 65% by weight, the coefficient of thermal expansion will exceed the above-mentioned optimum range, or the chemical durability will be significantly deteriorated. Also, if the composition ratio exceeds 75% by weight,
The glass transition temperature is 500°C or higher, and furthermore, it exhibits properties that make defoaming extremely difficult. (ii) B ₂ O ₃ is also one of the basic components of glass, and if its composition ratio is lower than 13.5% by weight, the glass transition temperature cannot be lowered to 500°C or less, and
If the content is 20.0% by weight or more, the chemical durability will be extremely deteriorated. (iii) Al ₂ O ₃ is an essential component for improving the chemical durability of glass, but in order to exhibit its effect, a composition ratio of 1.5% by weight or more is required. However, when the composition ratio becomes 4.0% by weight or more,
leading to an increase in the glass transition temperature and increasing the temperature
It becomes extremely difficult to keep the temperature below 500℃. (iv) Alkali oxides such as Na ₂ O, K ₂ O, Li ₂ O, etc.
It is necessary as a so-called network-type formed oxide for glass, and can lower the melting point of glass and improve its chemical durability. However, on the other hand, it has the property of increasing the thermal expansion coefficient of glass and also increasing the glass transition temperature. The effect varies somewhat depending on the type of alkali, but when Na ₂ O is used as the standard, K ₂ O has a small tendency to increase thermal expansion but is inferior in ability to lower melting temperature, and Li ₂ O has a high ability to reduce high temperature viscosity. However, it has the property that the effect of improving chemical durability is small. The total alkali concentration of these alkali oxides is preferably in the range of 3 to 5% by weight based on the glass composition; lower than this will cause a decrease in chemical durability, and higher than this will affect the required range of thermal expansion. It has the property of deviating from the . (v) PbO acts as a subcomponent to improve the low melting properties and chemical durability of glass, and is usually added in an amount not exceeding 5% by weight. The above is the basic composition and properties of borosilicate glass, but in addition to these, a small amount of fining agent is added as an essential component for defoaming the glass. This fining agent consists of As ₂ O ₃ , Sb ₂ O ₃ , NaCl, etc., and the higher the concentration, the greater the effect, but if it exceeds 1% by weight, it may cause adverse effects such as corrosion of the crucible in which the glass is melted and phase separation. invite. Therefore, its concentration can be suppressed to 1% by weight or less. The following table shows borosilicate glasses made by changing the concentrations of the above compositions, and are made by a normal glass melting method.

【table】

[Table] As shown in this table, by devising the composition ratio of borosilicate glass and adding As ₂ O ₃ , Sb ₂ O ₃ , and NaCl, it is possible to improve the composition of borosilicate glass. It was thought that it was impossible to reduce the transition temperature to 500°C or less, but now it has become possible to suppress the glass transition temperature of borosilicate glass to 500°C or less. Moreover, its thermal expansion coefficient is 32 to 36×10 ^-7 /℃
It is now possible to set the value within the range of . The present invention has such a composition, and has a glass transition temperature of 500°C or less and a thermal expansion coefficient of 32 to 36.
Based on borosilicate glass with a temperature of ×10 ^-7 /℃,
It is constructed by bonding pressure-sensitive pellets to this base. Incidentally, the above-mentioned pressure-sensitive pellet is a well-known one, and its electrode wiring is made of aluminum. Then, this pressure-sensitive pellet was placed on the base made of borosilicate glass mentioned above with the bonding surface aligned using a carbon jig, etc., and heated at 550°C using an electric furnace or the like. The bonding is performed by increasing the temperature and heating while applying a load to the following temperature. Thus, according to a semiconductor pressure transducer having such a structure, the base is made of an inexpensive glass material, and the pressure-sensitive pellet is bonded to a temperature that does not cause deterioration of the electrode wiring made of aluminum. It can be manufactured at low cost. In addition, since the influence of residual stress exerted on the pressure-sensitive pellet by the glass base is small, great practical effects such as being able to detect weak pressures with high sensitivity and high precision can be achieved. Next, one embodiment of the present invention will be described. First, as a pressure-sensitive pellet, an n-type [111] silicon substrate with both sides polished is prepared, and a P-type resistance layer is formed by a diffusion method. Thereafter, the aluminum deposited on this substrate is patterned using photolithography to form a bridge circuit using the P-type resistance layer as a strain resistance gauge. After forming a PSG protective film, the diaphragm surface is formed by etching. As a result, a pressure-sensitive pellet of 10×10 cm and 400 μm thick is produced, having a thin diaphragm of 8 mm in diameter and 150 μm thick. The sensitivity of this pressure-sensitive pellet is set to a maximum pressure of 4 kg/cm ² . On the other hand, the base is formed using borosilicate glass having the composition shown in the table above. This borosilicate glass is made by putting approximately 1 kg of glass raw materials such as refined silica sand, boric acid, alumina, soda carbonate, potassium carbonate, lead red, arsenic acid, and antimony oxide into a platinum crucible and heating it to 1500 to 1600°C. melt. The glass obtained by this melting is poured onto a stainless steel plate and solidified, then sufficiently slowly cooled to form a plate, which is then cut into a predetermined shape and drilled to form a base. . Furthermore, it was confirmed that even when the glass formed as described above was boiled in nitric acid diluted to approximately twice its original size, no surface deterioration occurred. Then, such a glass base and the pressure-sensitive pellet were aligned and bonded, and after applying a load of 3 kg, the glass transition temperature of the glass base was lowered.
Bond by heating to 50℃. When the aluminum electrode wiring of the semiconductor pressure transducer thus obtained was examined, no deterioration was observed. We also investigated the temperature change in residual resistance at zero pressure, the presence or absence of vacuum leaks, and the element breakdown pressure, and it was confirmed that all of them met the intended specifications. In other words, it has been confirmed that the temperature change in residual resistance is within 2% in the range of -30℃ to +100℃, there is no leakage even at a vacuum level of 10 ^-8 Torr or less, and the burst pressure is 10Kg/cm ³ or more. It was done. As described above, according to the present invention, it is possible to provide a semiconductor pressure transducer that is inexpensive, has high detection sensitivity, and is highly accurate, and its practical advantages are enormous.

[Brief explanation of the drawing]

The figure is a basic configuration diagram of a semiconductor pressure transducer. 1... Semiconductor crystal plate, 2... Thin diaphragm, 3
... Strain resistance gauge, 5... Electrode wiring, 6... Base.

Claims (1)

[Scope of Claims] 1. A pressure-sensitive pellet in which a strain resistance gauge is formed on the thin diaphragm surface of a semiconductor crystal plate, and aluminum electrode wiring is applied to the strain resistance gauge; the glass transition temperature is lower than 500°C. The base is made of borosilicate glass and is for supporting the peripheral thick portion of the semiconductor crystal plate, and has a pressure introduction hole in the center thereof for introducing pressure to the thin diaphragm surface. a base; the base is heated to about the glass transition temperature of the borosilicate glass, and the pressure-sensitive pellet and the base are directly bonded to their joint surfaces without intervening a foreign material layer; The borosilicate glass forming the base contains SiO ₂
65-76 wt% _{, B2O3 13.5-20} wt%, _Al2O3
1.5 to 4.0% by weight, 2.0 to 4.0% by weight of Na ₂ O, 0 to 2% by weight of K ₂ O, and 0 to 1% by weight of Li ₂ O (however, the above Na ₂ O, K ₂ O, Li ₂ O 3.0 to 5.0% by weight), 0 to 5% by weight of PbO, and 1% by weight or less of a clarifier.