JPS6041848B2 - High temperature diffusion furnace - Google Patents

Description

[Detailed description of the invention] The present invention relates to a diffusion furnace that can operate at high temperatures.

For example, diffusion oxidation in the manufacture of power transistors, thyristors, etc. generally requires long hours of work, and there is a strong desire to shorten this time. Shortening work time increases production, and if production remains constant, less equipment is required, but since diffusion furnaces are often used in large quantities, reducing power consumption is a major advantage. Now, in the present invention, the time required for diffusion can be shortened by increasing the diffusion temperature, and also in the general use of a diffusion furnace.
) and cool down quickly, there is no need to keep the furnace at a predetermined temperature all the time, and the furnace only needs to be raised and maintained during work (this reduces lining costs). did.

This will be explained below with reference to the drawings. Figure 1 shows an example of the structure of a conventional diffusion furnace. 1 is a quartz process tube (reaction tube), 2 is an alumina liner tube (soaking tube), 3 is a heater, 4 is a heat insulating material, and 5 is a furnace body or It is the outer covering of the furnace.

The heat-treated product is taken in and out from one end of the reaction tube 1, and lb is an exhaust port that is led to an exhaust pump or the like. Conventionally, a resistance heating type furnace using a metal heating element (product name: Nichrome, Kanthal, etc.) as the heater 3 has been used, but the maximum operating temperature of the metal heating element is 1375°C, so it cannot be used regularly as an electric furnace. The maximum temperature that can be achieved is approximately 12,800C.

Therefore, in order to achieve deep diffusion and a thick oxide film, it is necessary to operate the furnace for a long time, which poses problems such as limited production and increased power costs. The present invention eliminates the above-mentioned drawbacks, and FIGS. 2 and 3 are schematic diagrams of structural examples of diffusion furnaces embodying the present invention, respectively.

In these figures, 1 is a reaction tube made of quartz J, and 3a is 1 to 3.
Divided auxiliary heater, 6 is a heat soaking tube using silicon carbide (silicon carbide, hereinafter abbreviated as SiC), 7 is a terminal, 8 is a transformer, 9 is a power supply, 10 is a power input controller (using a thyristor), 11 is a reaction tube made of SiC, and Fig. 3 is a reaction tube made of SiC.
The quartz reaction tube 1 shown in the figure is omitted, and a SiC soaking tube is used for the same purpose. As is clear from FIGS. 2 and 3, the furnace of the present invention is characterized in that the SiC soaking tube 6 or the SiC reaction tube 11 is used as the main heating element, and an auxiliary heating element 3a using a metal heating element is disposed outside thereof. By using these to perform precise temperature control and temperature distribution control, higher temperatures can be obtained in a shorter time than in electric furnaces that use conventional metal heating elements. The reason and method will be explained below. SlC has a high resistance value at low temperatures and a negative temperature coefficient of resistance (though smaller than metal resistance), so in order to use it as a heating element, it is necessary to first apply a high voltage to generate heat, then gradually apply it. The drawback was that a step was required to lower the voltage, and this control required complicated equipment.

In the present invention, an auxiliary heater 3a using a metal heating element is provided,
Initially, the auxiliary heater 3a is energized until the SiC tube 6 reaches a certain temperature.
Alternatively, after raising the temperature of 11, power is applied to the SlC tube whose resistance value has decreased so that a high temperature can be easily obtained. In a SiC tube, temperatures up to 2000'C can be obtained, but since the melting point of silicon Si is 1420°C, the temperature inside the furnace is 14°C.
The temperature is preferably around 00°C, and if the temperature can be maintained at this level, the time required for the diffusion process can be significantly shortened. FIG. 4 shows the temperature characteristics of the furnace according to the present invention, where 1 on the horizontal axis represents the distance from the inlet end of the furnace along the furnace axis, T1 represents the temperature of the SiC main heater, and TO represents the required temperature inside the furnace. Difference ΔTE between TO and T1,
ΔTO is the temperature that each heater of the divided heater 3a must share in raising. In addition, the temperature of the main heater is T.
. It is easy to raise the temperature to 100%, and in this case it is obvious that the central heater of the divided heaters 3a can be omitted, but as mentioned above, it is possible to save initial power or raise the temperature only during work. Generally necessary to take advantage of the benefits.
FIG. 5 is a configuration example diagram of a furnace temperature control device according to the present invention, in which each heater whose temperature is to be controlled has a temperature detector 13 such as a thermocouple, and a power controller (for example, a thyristor) 1 according to the output thereof.
It is well known that it is possible to perform predetermined temperature control by providing an automatic temperature controller 12 that controls 0, so a description thereof will be omitted.

As described above, since the furnace of the present invention can obtain a higher temperature than the conventional diffusion furnace, the time required for diffusion is shortened, and it is possible to reduce the power cost, improve the efficiency of equipment, and realize miniaturization. The effect is obvious.

[Brief explanation of the drawing]

FIG. 1 is a structural example of a conventional diffusion furnace, FIGS. 2 and 3 are structural examples of a furnace according to the present invention, FIG. 4 is a temperature characteristic diagram thereof, and FIG. 5 is a diagram of a temperature control device for a furnace according to the present invention. It is a configuration example diagram. 1... Reaction tube, 2... Soaking tube, 3...
...Heater, 3a...Split heater, 4...
... Insulation material, 5 ... Furnace enclosure, 6 ...
・・Soaking tube using SiC, 7・・・・Terminal, 8・
...Transformer, 9...Power supply, 10...
...Power controller, 11...Reaction tube using SiC, 12...Temperature automatic controller, 13...
Temperature detector.

Claims (1)

[Claims] 1. A silicon carbide tube that is heated by electricity is used as the main heating element of the furnace, and an auxiliary heater made of a metal heating element is arranged outside of the silicon carbide tube, and electric power is supplied to each of the two heating elements. A high-temperature diffusion furnace characterized in that the temperature inside the tube is maintained at a required high temperature by controlling the temperature. 2. The high-temperature diffusion furnace according to claim 1, characterized in that a quartz furnace core tube for storing a heat-treated material is provided inside a silicon carbide tube. 3. The high-temperature diffusion furnace according to claim 1, characterized in that the silicon carbide tube is configured to house a heat-treated material therein.