JPS6019642B2 - Manufacturing method of thermistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a thermistor using a heat-sensitive resistor made of a silicon carbide film.

Widely used as a highly reliable thermistor external temperature sensor.

High-temperature semiconductors made of bulk single crystal silicon carbide are known to be useful for forming highly reliable thermistors, but they have high mechanical strength and are difficult to precisely process, so they have not been put to practical use industrially. It wasn't done. The inventors discovered that highly reliable thermistors could be manufactured by using a thin film of silicon carbide formed by a method called sputtering vapor deposition instead of bulk single crystal silicon carbide, and established a new manufacturing method for these ( The details are disclosed in Japanese Unexamined Patent Publication No. 53-63552 and Samurai Seki No. 53-63553). The present invention further improves this technique.

FIG. 1 shows the main structure of a thermistor formed by the thermistor manufacturing method according to the present invention.

That is, the thermistor includes a heat-resistant base 11 and a pair of heat-resistant electrodes 12A and 12B provided on the base 11.
and a heat-sensitive resistor 13 made of a silicon carbide film deposited on the base 11 so as to be in contact with the electrode pair. The heat-sensitive resistor 13 can be formed by sputtering deposition.

For example, when sputtering a cathode target of silicon carbide powder using a high-frequency sputtering device with the atmosphere inside the sputtering device set to argon gas and the pressure of the argon gas set to (1-5)×10-orr, the cathode target is sputtered. A heat-sensitive resistor made of a silicon film is formed on the substrate disposed in this manner. In this case, the substrate temperature during sputtering deposition is maintained at around the operating temperature or usage temperature of the thermistor, for example, the usage temperature is 40°C.
At 0-1000℃, the substrate temperature is 400-100030℃.
It was customary to hold it at The inventors investigated in detail the relationship between the heat resistance of silicon carbide thin film thermistors and the substrate temperature during sputtering deposition, and found that in order to increase the heat resistance of thermistors, sputtering deposition must be performed at an unexpectedly high temperature. It was discovered that there is no such thing as an optimum temperature, and based on this discovery, the manufacturing method of the present invention was completed. FIG. 2 is a basic characteristic diagram illustrating the method of manufacturing a thermistor according to the present invention.

That is, FIG. 2 shows the relationship between the change in substrate temperature during sputtering deposition and the time change in the thermistor resistance value while the thermistor is left at a high temperature.
In the figure, curves 21, 22, 23, and 24 show the time changes in the thermistor resistance during sputtering deposition when the substrate temperature is T, 2, T3, and T4 (T. < T2 x T3 x T4), respectively. It is shown in As shown in the figure, the thermistor resistance changes in the increasing direction when the substrate temperature is low (T,,2), and in the decreasing direction when the substrate temperature is high (T3, T4). It is in. In other words, the thermistor resistance, which determines the heat resistance characteristics of the thermistor, changes when left at high temperatures when the substrate temperature is lower than a certain degree during sputtering deposition.
This decreases as the substrate temperature increases (T, ~2 range), but when the substrate temperature is higher than a certain value (t ~ T4
range), as this substrate temperature increases, it increases in the opposite direction to the lower temperature range, and for the production of high temperature stable thermistors,
Although unexpected, the inventors have discovered that it is not necessarily appropriate to raise the substrate temperature too much. Taking these discoveries into account, if the substrate temperature is maintained within the range of, for example, a range of values, it is possible to manufacture a thermistor with excellent heat resistance and no change in the resistance value of the thermistor, as shown by the solid line 25. FIG. 3 is a characteristic diagram for more specifically explaining the method for manufacturing a thermistor according to the present invention.

That is, a curve 31 in the same figure shows an example of the relationship between changing the substrate temperature during sputtering deposition and changing the resistance value of the thermistor when left at high temperatures. In the same figure, the substrate temperature is set to 5000.
The temperature is varied between 0 and 900°C. Also, the change in resistance value is 100°C for a thermistor formed at 550℃ in the atmosphere
The value obtained when the sample was left for a period of time was compared with the value immediately after formation. As shown in the figure, the change in resistance value is zero when the substrate temperature during sputtering deposition is around 650 oo;
Below this temperature, the rate of change is positive; above this temperature, the rate of change is positive.
It can be seen that the rate of change is negative. As these characteristic curves show, a thermistor with a small resistance change rate, that is, a highly reliable thermistor is formed at a substrate temperature of around 650°C. In this case, it is practically desirable that the change in resistivity be 20% or less, and for this purpose, the substrate temperature must be adjusted to the curve 3.
As shown in No. 1, a range of 600oo to 750qo is suitable. However, since it is easier to design a substrate heating device when the substrate temperature is as low as possible, it has been confirmed that a substrate temperature in the range of 600° C. to 700 qo is optimal for manufacturing a thermistor that is stable at high temperatures. As is clear from the above description, the heat resistance characteristics of the thermistor change significantly depending on the temperature of the substrate during sputtering deposition of silicon carbide, and in particular, the characteristic of resistance value change is reversed at a certain temperature.

The details of the reason for this polarity reversal of resistance value change are not clear. However, it is presumed that lattice defects in the silicon carbide film formed by the manufacturing method of the present invention play an important role. Therefore, the polarity reversal phenomenon is related to the manufacturing conditions of the silicon carbide film according to the present invention, particularly to the sputtering deposition conditions. That is, the inventors have found that under sputtering deposition conditions, in addition to the substrate temperature, there is an optimum value for the formation rate of the silicon carbide film, and that value is in the range of 0.1 to 10 mm/hour. In this case, 0.1
If the speed is less than m/hour, impurity gases such as oxygen gas in the sputtering equipment will be mixed into the sputter-deposited silicon carbide film, which will cause the electrical resistance of the silicon carbide film to become abnormally high, making it impractical. . Further, in a range exceeding 10 m/hr, the adhesion of the silicon carbide film to the substrate becomes weak. In the above optimum range, the electric specific resistance p is 200
A heat-sensitive resistor with a thermistor constant of 2000 to 3000oK can be formed with good reproducibility. The silicon carbide film of the thermistor can normally be used as long as it has a thickness of 1 to 20 m, but for practical purposes, the optimum thickness is about 4 to 10 m.
If the thickness of the silicon carbide film is thinner than 4 mm, the degree of crystallinity of the silicon carbide film may lack reproducibility, and if it is thicker than 10 mm, the film may peel off from the substrate. The inventors have confirmed that the film formed under these manufacturing conditions is polycrystalline silicon carbide, and in this case, impurity elements such as aluminum and boron that significantly change the electrical resistance are not present. We have also confirmed that it does not contain any such items.
Therefore, it is considered that the various defects contained in pus are related to the electrical conduction of the silicon carbide film by the method of the present invention, rather than these impurity elements. In the above explanation, we have described the case where a silicon carbide film is obtained by sputtering deposition of a silicon carbide powder target in argon gas, but sputtering deposition takes longer with a silicon carbide burner target than with a powder target. It operates stably over time and is practical.

Note that it is also possible to form a silicon carbide film by so-called reactive sputtering using silicon as a target in a carbonizing atmosphere, such as a mixed gas of acetylene gas and argon, but in this case, the chemical composition ratio of silicon and carbon control is difficult, and direct sputtering deposition of the silicon carbide target described above in argon has higher utility value. In the method of the present invention described above, alumina, zirconia, titania, magnesia, silicon oxide, or a composite of one or more of these materials, which have high heat resistance, are used as the substrate.

It is also advantageous to use silicon whose surface is oxidized or nitrided as the substrate. The inventors have invented a method for manufacturing a thermistor with high precision by further improving the sputtering method of manufacturing thermistor using sputtering vapor deposition described above.

FIG. 4 explains this improvement.

That is, the main part lies in the sputtering deposition process. In FIG. 4A, sputtering deposition of the silicon carbide film is performed, for example, in a parallel disk bipolar high frequency sputtering apparatus. In this case, the main parts are composed of a silicon carbide disk target 41, a disk anode 42 facing the silicon carbide disk target, and a substrate heating holder 43 placed on the anode 42. When the base body 44 is brought into close contact with the base body holder 43 and silicon carbide is deposited as it is, the thickness of the silicon carbide formed is thick at the center and thin at the periphery. Therefore, the resistance value of the heat-sensitive resistive film made of silicon carbide film is different between the central portion and the peripheral portion. A curve 45 in FIG. 4B shows an example of the film thickness distribution on the substrate 44. However, a rotating mask plate 46 shown in FIG. 4A is placed between the target 41 and the substrate 44 so as to prevent part of the evaporated material from the target 41 from being deposited on the substrate 44. FIG. 4C shows a plan view of the mask plate 46 and its positional relationship with the target 41. As shown in FIG. It was confirmed that when the periphery is shaped like a wide propeller and the shape is adjusted, the film thickness distribution disappears, as shown by the solid line 47 in Figure 4B, and the distribution of the thermistor resistance within the base body 44 is significantly reduced. . In the above embodiments, a parallel bipolar sputtering apparatus having a disk-shaped target has been described, but the target does not need to be a disk-shaped target. However, it is only necessary to interlock the mask plate within a plane parallel to the base surface. The mask plate and the substrate are usually placed close to each other, but the distance is shorter than the mean free path of the evaporated substance of the target in the sputtering deposition atmosphere. In normal sputtering, the thickness should be less than 3 to 5 skins. Furthermore, in addition to this, the mask plate may be placed close to the target in reverse. In this case, the distance between the mask plate and the target is made shorter than the cathode fall distance of sputtering discharge. For example, it is usually 3 to 5 sides or less. In this case, since no discharge occurs between the mask plate and the target, sputtering evaporates do not adhere to the mask plate, which is advantageous for long-term sputtering deposition. As is clear from the above explanation, in the thermistor manufacturing method according to the present invention,
It is possible to manufacture a thermistor that has excellent heat resistance and has no change in thermistor resistance, which is an important characteristic of thermistor, especially when subjected to high-temperature dilation.

Further, in the thermistor manufacturing method of the present invention, by using a mask, a highly accurate thermistor with uniform thermistor characteristics and less thickness distribution during sputtering deposition can be manufactured.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional structural diagram of a thermistor formed by the manufacturing method of the present invention, Fig. 2 is a basic characteristic explanatory diagram for explaining the thermistor manufacturing method of the present invention, and Fig. 3 is a diagram of the thermistor manufacturing method of the present invention. FIG. 4A is a basic configuration diagram for explaining another embodiment of the thermistor manufacturing method of the present invention, and FIG. A basic characteristic diagram based on this diagram, C in the same figure, is a configuration diagram showing the main part of A in the same figure. 11...Heat-resistant base, 12A, 12B...
・Heat-resistant fin pole, 13... Heat-sensitive resistive film, 41...
... 4 silicon carbide target, 42 ... anode,
43... Base heating holder, 44... Base body,
46...Mask board. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. Carbonization using a silicon carbide target at a formation rate in the range of 0.1 to 10 μm/hour on a heat-resistant substrate maintained at a temperature of 600°C to 700°C in argon gas. A method for manufacturing a thermistor, comprising depositing silicon by high-frequency sputtering to form a heat-sensitive resistor made of a silicon carbide film. 2. The method for manufacturing a thermistor according to claim 1, characterized in that a sintered body of silicon carbide is used as the target. 3. Claim 1, characterized in that the substrate is made of one or more heat-resistant materials selected from alumina, zirconia, titania, magnesia, silicon oxide, and silicon whose surface is oxidized or nitrided. A method for manufacturing a thermistor. 4. A mask plate is installed between the target and the substrate close to the surface of the substrate to prevent part of the evaporated substance of the target from depositing on the substrate, and this mask plate is placed between the substrate and the target. 2. The method of manufacturing a thermistor according to claim 1, wherein the thermistor is moved parallel to the body surface. 5. The method of manufacturing a thermistor according to claim 4, characterized in that the distance between the mask and the substrate is made shorter than the mean free path of the evaporated material of the target. 6. Claim 4, characterized in that the distance between the mask and the target is made shorter than the cathode fall distance of sputtering discharge.
The method for manufacturing the thermistor described in Section 1.