JPS61230038A - Heat conductive vacuum gage - Google Patents

Abstract

PURPOSE:To detect the pressure of a gas at high accuracy irrespective of the type of the gas by disposing an exothermic body and a heat receiving body with the specific position relationship so as to face each other and calculating pressure with the use of both temperature detection values. CONSTITUTION:The exothermic body (heating plate) 13 and the heat receiving body 10 are faced and installed in parallel in a vacuum chamber 23 whose pressure is measured. The interval between the exothermic body 13 and the heat receiving body 10 is set smaller than the average free travel of the gas at a vacuum degree in the vacuum chamber 23. Then temperature detectors 11 and 12 such as a thermo-couple are fitted on the exothermic body 13 and the heat receiving body 10, and respective detecting signals are led to an arithmetic unit 19 so as to execute the prescribed arithmetic processing, whereby the pressure in the vacuum chamber 23 can be detected. Thus the pressure can be detected irrespective of the type of the gas, and calibration in accordance with the type of the gas is made unnecessary.

Description

[Detailed description of the invention] [Field of application of the invention j The present invention relates to a pressure measuring device for measuring gas pressure]
I am particularly interested in thermal conduction vacuum gauges that can measure the pressure of various gases with simple operation.

[Background of the Invention j In the manufacturing process of semiconductor devices, processing in a vacuum is essential, and various gases are used singly or in a mixture. In these processes, the pressure is usually from several Pa to 103 Pa.

Although the pressure of each gas needs to be accurately controlled, it often requires complicated calibration.

Conventionally, the gas pressure in the above range has been measured using a thermal conductivity vacuum gauge. This heat conduction vacuum gauge takes advantage of the fact that the thermal conductivity of gas depends on pressure.For the principle etc., for example, see "Vacuum Technology" by Gen Horikoshi (University of Tokyo Press, May 1983). P.

68-69, or Robert W. Berr7
At aj! .

[THIN FILM TECHNOLOGY J (
VAN N03TRANDRF! INHOLD COM
PANY, 196B), p. 82-85.

Conventional heat conduction vacuum gauges have the following problems: (a) The output is not linear with respect to pressure, as described in the above literature;
(b) The heat conversion efficiency (expressed by the thermal adaptation coefficient) between the filament and gas molecules changes depending on the surface condition of the filament, resulting in a change in sensitivity; and (o) The thermal conductivity varies depending on the type of gas. However, there was a problem in that the sensitivity of thermal conductivity gauges differed depending on the type of gas.

In particular, the fifth point has been a big problem when various gases are used.

[Object of the Invention j An object of the present invention is to provide a heat conduction vacuum gauge that can measure the pressure of various gases without having to calibrate each type of gas.

[Summary of the invention]

As a result of experiments conducted by the inventors of the present application, the ratio of the amount of heat exchange between two parallel surfaces of a solid placed in a vacuum atmosphere, that is, the exchange of heat between two surfaces per unit time, unit temperature difference, and unit area. The amount below the amount c is called the heat transfer rate.

Unit: W/m"・dog) is the distance between two surfaces, regardless of the type of gas intervening between the two surfaces, if the mean free path of the intervening gas molecules under that pressure is smaller. It was found that the h value is proportional to the gas pressure.

The present invention makes use of the above-mentioned properties to measure the heat transfer rate of different gases by installing two parallel solid surfaces sufficiently closer than the mean free path of the gas molecules to be measured and measuring the heat transfer rate between the two solid surfaces. This is a thermal conduction vacuum gauge configured to measure pressure.

Here, the principle of the present invention will be explained with reference to FIGS. FIG. 3 is a schematic diagram for explaining the present invention in detail.
0 is a constant temperature plate, 6 is a heat capacity plate with a small heat capacity, and 13 is a heating plate. Also, T1, T.

! , are the temperatures of the constant temperature plate 10, the heat capacity plate 6, and the heating plate 15, respectively, and K is the heat transfer rate between the heat capacity plate 6 and the heating plate 13. Further, %Kl is a coefficient related to heat transfer from the heat capacity plate 6 to the constant temperature plate 10 and the heating plate 13 by radiation, and will be explained later. Heat is transferred from the heating plate 13 by gas molecules interposed between the heating plate 13 and the heat capacity plate 6, but the dead rate ffl at this time is determined to be the fourth
As shown in the figure, it is proportional to the gas pressure P.

Figure 5 is a graph showing the experimental results of the heat transfer rate between two opposing solid surfaces plotted against the gas pressure using (a) the type of gas, and (b) the distance between the two surfaces as parameters. be. From this graph, it can be seen that in region 21, the heat transfer rate is independent of the type of gas and is proportional to the gas pressure. In addition, when the mean free path of the intervening gas is p smaller than the spacing between two surfaces (He10#m and He150μm in region 21
) is not dependent on the distance between the two surfaces. Therefore, in order for the above-mentioned linearity to be established, the gas interposed between the two surfaces must undergo free molecular motion. That is, the distance between the two surfaces needs to be sufficiently smaller than the mean free path of the intervening gas.

Now, heat is exchanged between the heat capacity plate 6, the constant temperature plate 10, and the heating plate 13 by thermal radiation. Here, since the temperature T of the heat capacity plate 6 is about 10,000 at most, the amount of heat exchanged between the heat capacity plate 6 and the constant temperature plate 10 due to heat radiation is calculated by the temperature difference ( T-T,)I
IC is approximately proportional. Let this proportionality coefficient be . In other words, the amount of heat transfer between the two is (amount of heat transfer), -. -((273+T)' -(27
3+T, )' ) Right 6111 = 275'i(1+
fi)'-(1+-Q)')1>253, so the right side U2754(4(1+,'7g)-4(1+,':
~ Monthly 4.273" (T - T, ) , °, (Heat transfer amount Ill YuKt (T T +) ・
...(1) On the other hand, between the heat capacity plate 6 and the heating plate 13, in addition to the amount of heat transfer due to thermal radiation as shown in the above equation (1), heat transfer t due to gas molecules is included. . The amount of heat transferred by the gas molecules is also proportional to the temperature difference between the two surfaces, so if this proportional coefficient is set to 2, the amount of heat transferred between the heat capacity plate 6 and the heating plate 13 is expressed as in the following equation (2). Become.

(Heat transfer amount) a-+s = (Kt +Kg) (T
(2) In this system, the heat capacity of the heat capacity plate 6 is sufficiently small, so that its temperature reaches a steady state in an extremely short time. In addition, the heat capacity plate 6 and the heating plate 13
Although the conductance with the outside is small, the pressure of the gas interposed between the inside and outside is small, so the pressure becomes equal to that of the outside, that is, the vacuum chamber, in a very short time.

In the above steady state, the amount of heat transferred between the heat capacity plate 6 and the constant temperature plate 10 is not equal to the amount of heat transferred between the heat capacity plate 6 and the heating plate 13), from equations (1) and (2). The following formula holds true.

K+ (T+ T) = (K, 2 in 10) (T Tt)
=l Gokoji K.

-T2 =Goto, 525K.

V-V.

Here, vl s vl vl are each temperature T1 *
Tt This is the voltage value obtained by measuring T2 with a thermocouple.

As described above, since K2 is proportional to the pressure P, the gas pressure P can be measured by the calculation process of equation (3).

Moreover, the constant temperature plate 13 can also be omitted. That is,
Even when there is no constant temperature plate 15, the heat radiation from the heat capacity plate 6 is considered to be approximately a constant value (assumed to be Q). From this, the gas pressure P can be measured using the following equation (4).

Q = K, (T-T,) ：に、＝” T-T.

σ P (4) [Embodiment of the Invention] Hereinafter, an embodiment of the heat conduction vacuum gauge according to the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing a cross section of the gauge section and a schematic diagram of the signal processing section of the embodiment, and FIG. 2 is a perspective view of the gauge section. As shown in FIG. 1, this embodiment includes a heating plate having a main body 14, a lamp heater 7 which is attached to the main body 14 via a spring 2 with a female screw 3, and is heated by a power source 18. 13, a heat capacity plate 6 with a small heat capacity attached to a heating plate 15 with a leaf spring 5, a constant temperature plate 10 supported by a constant temperature plate support rod 8, and a thermocouple 4.
．． 11.12 and thermocouple and lamp heater leads M
It consists of a heat conduction vacuum gauge gauge part made up of an insulator 15 for passing through, and a signal processing part made up of an arithmetic unit 19, an amplifier 20, and a voltmeter 21. The main body 14 is
It is sealed and fixed to the vacuum chamber 1 using a cone flat ring 17 and screws 22. In addition,
The side indicated by numeral 23 is inside the vacuum chamber, and the side indicated by 24 is the atmosphere side.

Next, details and operations of each part will be explained. heating plate 13
is heated to about 61oot by the lamp heater 7. At this time, since both the heating plate 13 and the lamp heater 7 are in a low-pressure atmosphere, there is little thermal contact, and the heating plate 13 is heated mainly by heat radiation from the lamp heater 7 heated to a high temperature. The heating plate 13 is made small and made of a material with high thermal conductivity and small heat capacity, such as aluminum, in order to minimize the heat capacity and achieve uniform temperature distribution. Furthermore, the surface 9 of the heating plate 13 in contact with the heat capacity plate 6 is made to have a surface roughness of 3.2S or more and a flatness of ±2 μm or less.

The heat capacity plate 6 is made of ceramic, glass, silicon, etc. in order to have high rigidity and to reduce the heat capacity 1k.
: Make it about 0.5mm. Further, the surface 9' in contact with the heating plate 13 is mirror finished and has a flatness of ±2 μm. This heat capacity plate 6 is fixed in contact with the heating plate 15 by a leaf spring 5.

The constant temperature plate 10 is fixed to the main body 14 by a constant temperature plate support rod 8. At this time, the distance between the constant temperature plate 10 and the heat capacity plate 6 is 3 to 5 m.
A gap of about m is provided, and the constant temperature plate 10 is sometimes made of polished aluminum that has been subjected to black alumite treatment. Book! i! In the monthly test, the same conditions as the heating plate 13 were used. The constant temperature plate 10 and the constant temperature plate support rod 8 and the constant temperature plate support rod 8 and the main body 14 need to be fixed by brazing or the like in order to improve thermal contact. As a result, the constant temperature plate 10 is maintained at the outside temperature.

In the above configuration, each temperature of the constant temperature plate 10, heat capacity plate 6, and heating plate 13 is measured by a thermocouple 11.4.12, and each thermocouple 11.4.12 has a voltage V, V, which is proportional to the temperature. Generate %v2. The generated voltage is calculated by the following equation (5) in an arithmetic unit 19 having an analog adder/subtractor and a multiplier.

The upper H-pi signal is amplified by the amplifier 20,
The voltage is displayed on the voltmeter 21 as a voltage. The voltage V displayed on the voltmeter 21 is proportional to the pressure P in the vacuum chamber 1 for the reason stated above, so when an appropriate coefficient is applied, the voltage V is expressed as pressure Pf.

[Effects of the Invention] According to the present invention, heat conduction between two parallel planes that does not depend on the type of gas, iM
Since the ratio is used, there is no need to calibrate according to the type of gas, and even when the type of gas is unknown or a mixture of two or more gases, it is easy to calculate the pressure with high accuracy. It becomes possible to perform measurements.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a cross section of a gauge part and a block diagram of a signal processing part of an embodiment of a heat conduction vacuum gauge according to the present invention;
Figure f42 is a perspective view of the gauge part of the embodiment, Figure 3 is a schematic diagram for explaining the present invention in detail, Figure 4 is a characteristic diagram showing the relationship between heat transfer rate and gas pressure, and Figure 5 is a diagram showing the relationship between heat transfer rate and gas pressure. Opposing solid 2
It is a graph showing experimental results in which the relationship between the heat transfer rate between surfaces and gas pressure is plotted using the type of gas and the distance between two surfaces as parameters. Explanation of symbols 1...Vacuum chamber 4...Thermocouple 5...
Leaf spring 6... Heat capacity plate 7... Lang heater 10... Temperature plate 11.12... Thermocouple 13... Heating plate 14... Main body
19... Arithmetic unit 20... Amplifier 21.
...Voltmeter Sai 10 Ta Sai Z Diasu 3 Dia.

Claims (1)

[Scope of Claims] 1. A heating element having a heating element that exchanges energy and heat when supplied with energy, which has an element that converts the temperature of the heating element into an electrical signal; and a vacuum to be measured. a heat receiving body disposed opposite to the heating element with a gap smaller than the mean free path of gas at a temperature of A heat conduction vacuum gauge comprising a pressure gauge that inputs an electric signal from the heat receiving body and an electric signal from the heat receiving body, performs predetermined calculations, and displays the pressure. 2. The heat conduction vacuum gauge according to claim 1, wherein the heating element is a second heat receiving element that is in close contact with the heating element, and includes an element that converts the temperature of the heat receiving element into an electrical signal. A heat conduction vacuum gauge that accompanies a device that has one. 3. The heat conduction vacuum gauge according to claim 1, wherein the heating element and the heat receiving element are flat on opposing surfaces, and the gap is 3 mm to 5 mm.