JPH01220436A - Vertical soaking furnace - Google Patents

Abstract

PURPOSE:To equalize a temperature gradient presented in a thermal space in a vertical soaking furnace not only at a normal time but at a transient time by mounting heat pipe near a cylindrical heater of the furnace along its longitudinal direction. CONSTITUTION:A furnace body 1 is composed of a cylindrical heater 2 and a heat insulating layer 3. A plurality of heat pipes 4 are mounted longitudinally near the heater 2 in the body 1. A soaking space is formed by supplying electric power from an exterior to the heater 2 in a thermal space of the body 1 to which a tube 5 is inserted. A pipe 4 so operates as to eliminate or reduce elevational difference of temperature distribution near the heat generating face of the furnace during temperature change. Generally, the longitudinal soaking property of the pipe 4 is caused by the large thermal conductivity. Accordingly, the elevational temperature difference of the space in the soaking furnace can be automatically eliminated or reduced rapidly without positive external control.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a vertical soaking furnace, and particularly to an improvement in the structure of a heating section.

(Prior art) In the semiconductor manufacturing process, horizontal furnaces have long been used as thermal oxidation furnaces to form thin silicon oxide films on wafer surfaces, but in recent years, the wafer diameter has increased and automation has increased. Based on the request, a vertical furnace is being considered. Its general structure consists of a cylindrical heater, a cylinder made of a layer of heat insulating material surrounding the outside, and a cover that holds and protects the outside as a structure.The wafer to be processed is
The cylindrical heater is inserted by boat through an opening provided with an opening/closing mechanism at the top or bottom, heated for a predetermined processing time, and exposed to a reaction gas (for example, 02) to form a silicon oxide film.

In such a furnace, it is required to maintain highly accurate thermal uniformity throughout the cylindrical space in which the wafer exists.

Therefore, in order to achieve this, when a cylindrical heater is divided longitudinally into three zones, for example, if a temperature deviation occurs between the top and bottom of the center, the heating energy applied from the outside is adjusted. Control is performed to ensure uniform heat distribution.

Moreover, in another example, the above-mentioned divisions are made into 3 to 5 zones, each having an independent cylindrical heater, and the supply of electric power to each zone is adjusted via a thyristor device.

The soaking furnace as described above is equipped with a power supply and a temperature controller corresponding to each section of the heater, forming an independent system to maintain the set temperature.

Therefore, in a steady state, when the heat balance of the entire furnace is balanced, it is relatively easy to achieve uniform heating, but during transients due to changes in the set temperature, variations in the characteristics of each heater, The rate of temperature change in each zone differs due to variations in the characteristics of the insulation material in the vicinity where it exists, variations in thermal conductivity, etc., and it is difficult to change the temperature of the thermal space while maintaining uniformity. It is.

In particular, when the prescribed heat treatment is completed and the wafer is taken out, it is necessary to lower the temperature of the internal section of the soaking furnace while maintaining its thermal uniformity. This is done by forced cooling by blowing air into the gap inside the air and blowing it out from above, but because the cooling space is vertically shaped, the so-called chimney effect causes a cooling effect in the vicinity of the air inlet. There was a large difference in the cooling effect near the outlet, making it impossible to uniformly cool the entire heat space while maintaining thermal uniformity.

(Problems to be Solved by the Invention) As mentioned above, in the conventional vertical soaking furnace, cooling gas is flowed in the longitudinal direction for cooling. Uniform cooling while maintaining thermal uniformity was not possible, and a solution to this problem was desired.

Therefore, an object of the present invention is to prevent temperature differences from occurring in the longitudinal direction when cooling by supplying cooling gas from the outside even though the device is vertical, or even if it occurs, the difference is so small that it can be practically ignored. The purpose of the present invention is to provide a vertical soaking furnace.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a vertical soaking furnace having a cylindrical heater, in which a heat pipe is installed along the longitudinal direction near the cylindrical heater. It is.

(Function) When performing heat treatment on semiconductors, etc., the temperature difference that occurs between the top, center, and bottom of the furnace body is automatically and without external control due to the extremely high heat conduction speed of the heat pipe. This makes it possible to equalize the temperature gradient existing in the heat space in the furnace not only during steady state but also during transient times associated with temperature rise, temperature fall, etc.

(Example) Hereinafter, an example of a vertical soaking furnace according to the present invention will be described with reference to the drawings. In the figure, reference numeral 1 denotes a furnace body, which is composed of a cylindrical heater 2 and a heat insulating layer 3, and has an opening provided at the bottom with an opening/closing mechanism.

A plurality of heat pipes 4 are attached to the furnace body 1 in the vicinity of the cylindrical heater 2 along the vertical (longitudinal) direction.

Here, the heat pipe 4 uses, for example, sodium or lithium as a working fluid. Reference numeral 5 denotes a tube made of quartz or the like and having a process gas inlet 5a7fipJ in the upper part, and a plurality of wafers (100 or more) supported by a wafer boat 6 having a wafer support rod 6a inside. -7 is inserted from the opening of the furnace body 1,
After heat treatment, it is transported outside.

The heat space of the furnace body 1 into which the JIKO-75 is inserted is provided with electric power supplied from the outside to the cylindrical heater 2 to form a uniform heating space. When the heat balance of the radiated thermal energy is balanced, the entire thermal space is kept uniformly heated and at a predetermined temperature.

The power supplied from the outside to the cylindrical heater 2 is controlled by inputting a signal from a temperature sensor (not shown) as a temperature control system heat back signal, thereby compensating for heat radiation disturbance.

In addition, when changing the currently stable temperature inside the furnace to another temperature, such as a low temperature suitable for carrying the wafer to be processed out of the furnace, the heat balance is destroyed and the heat balance is brought to a new level. Change the heat energy supplied and the heat energy released. For this purpose, the cooling medium 2, for example, air, is supplied from the suction port 8a and discharged from the discharge port 8b.

The supply of this cooling medium causes a temperature difference between the heat generating surfaces in the vertical direction inside the furnace, but this humidity difference is quickly eliminated or made small by the action of the heat pipe 4.

Generally, soaking furnaces have excellent heat retention and therefore have a large temperature time constant. However, the heat transfer rate due to the working fluid sealed in the heat pipe is extremely fast and is extremely small compared to the time constant for the entire furnace to reach a new level of balance temperature.

Therefore, the heat pipe 4 acts so that there is no or only a slight difference in the vertical direction with respect to the temperature distribution near the heat generating surface of the furnace during temperature change.

Generally, heat uniformity in the longitudinal direction of a heat pipe is good because it has a high heat conduction rate.

Therefore, the temperature difference between the upper and lower sides of the thermal space in the soaking furnace can be quickly and automatically eliminated or reduced to a small level without any active control from the outside. This results in
It is possible to obtain uniform heat in the heat space in the soaking furnace. Furthermore, even if the cooling medium is forced to flow, there is no difference in temperature between the suction port and the discharge port.

In the present invention, the structure of the heat pipe does not have to be cylindrical, and any suitable shape can be selected and used depending on the structure of the furnace.

[Effects of the Invention] As described above, the present invention eliminates the temperature difference in the vertical direction of a vertical soaking furnace by using the characteristics of the heat pipe. It is possible to maintain thermal uniformity even in the case of

In addition, unlike in conventional vertical diffusion furnaces for semiconductors, there is no need to divide the cylindrical heater installed between the upper and lower parts into 3 to 5 zones and control them; Since heat uniformity can be achieved in a similar manner, only one set of power supply and temperature control device is required, making the system economical and simple, and maintenance and inspection extremely easy.

[Brief explanation of the drawing]

The figure is a sectional view showing one embodiment of the present invention. 1...Furnace body 2...Cylindrical heater 4...Heat pipe 5...Tube 6...Wafer port 7...Wafer Agent: Patent Attorney Noriyuki Chika Ken Daikomaru

Claims (1)

[Claims] A vertical soaking furnace having a cylindrical heater, characterized in that a heat pipe is installed along the longitudinal direction near the cylindrical heater.