JPS61228637A - Method and device for temperature measurement of semiconductor substrate - Google Patents

Abstract

PURPOSE:To effect the temperature measurement of a wafer without contact with the wafer accurately and to eliminate the need of any process for a heat reactor itself by detecting the quantity of transmitted light by irradiating a surface of the wafer with the temperature measuring light of necessary wavelength. CONSTITUTION:A surface of a semiconductor substrate 1 in a heat reactor 3 is irradiated with the temperature measuring light of necessary wavelength to detect the quantity of transmitted light. Then the temperature is worked out from the light transmittance characteristic of the semiconductor substrate. For example, one end of a light emitting means and that of a light accepting means are arranged oppositely above and under the heat reactor 3. The light emitting means is composed of a light emitting element 11 such as a light emitting diode, an optical fiber 12, and a collimater lens 13, and the light accepting means is composed of a condenser lens 18, an optical fiber 17, an optical filter 19, a lens 20 and a light accepting element 16 such as Ge photo diode. The influence of the light energy radiated from a light source or walls of the heat reactor is eliminated by switching on and off the light emitting means by a predetermined period.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method and apparatus for measuring the temperature of a semiconductor substrate (hereinafter referred to as a "wafer"), and particularly to an apparatus for heat-treating a wafer using a heating means. The present invention relates to a method and apparatus for measuring the temperature of a wafer without contacting the wafer.

[Conventional technology]

In various heat treatments performed in the manufacturing process of semiconductor substrates, it is necessary to accurately measure the surface temperature of the wafer and perform the heat treatment. Conventionally, the wafer temperature measurement method is 1.
For example, as disclosed in Japanese Patent Application Laid-Open No. 56-100412, there is a method of measuring the surface temperature of a wafer by bringing a thermocouple into contact with the surface of the wafer, and International Publication WO 301005
As disclosed in Japanese Patent Application Publication No. 55-500701 related to No. 22, there is a known method of measuring the temperature of a wafer by utilizing changes in conductivity due to heat of the wafer. However, in such conventional measurement methods, a temperature measurement contact must be provided on the wafer surface, and this contact measurement may damage the wafer surface or damage the temperature measurement contact itself. There are disadvantages such as a rise in temperature becoming a disturbance factor that affects the wafer surface temperature.

Therefore, the applicant proposed a method for accurately measuring the surface temperature of a wafer without contacting the wafer.

Specification of Japanese Patent Application No. 58-240474 and Utility Application No. 1987-65
As described in the specification of No. 931, there is a method of detecting the radiant energy emitted by the wafer itself heated by light irradiation through a filter, and a method of detecting the radiant energy by focusing only the radiant light on the wafer surface with a lens. I suggested it earlier.

[Problem that the invention seeks to solve]

Specification of Japanese Patent Application No. 58-240474 and Utility Application No. 1987-65
In the wafer temperature measurement method as described in the specification of No. 931, it is necessary to insert a detection means or a guide tube into the heat treatment furnace in which the wafer is housed, and for this purpose, a through hole is drilled in the wall of the heat treatment furnace. The processing requires time and effort. Another method is to provide a through hole in the wall of the heat treatment furnace and insert the detection means or guide cylinder into the furnace through the through hole.

As a result, the atmosphere within the heat treatment furnace may change depending on the location, which poses a problem of adversely affecting the results of heat treatment of the wafer.

This invention solves these problems and provides a novel method for temperature measurement of semiconductor substrates that accurately measures the temperature of a wafer without contacting the wafer, and does not require any processing on the heat treatment furnace itself. We have attempted to provide a method and apparatus.

[Means for solving problems]

This invention aims to solve the above problems by utilizing the fact that the light transmittance of a semiconductor changes depending on the wavelength of irradiated light and also changes depending on the temperature of the semiconductor itself. Utilizing the above principle, a fiber temperature sensor is disclosed in Japanese Patent Laid-Open No. 58-13903, which has a structure in which light emitting and light receiving elements are arranged at both ends of an optical fiber, and a semiconductor material is connected in between.
No. 8, JP-A-59-168328, "Electronic Materials J December 1983 issue (p.

44-P, 49), etc., but this invention
The above principle is applied to a method and apparatus for measuring the temperature of a wafer in a heat treatment apparatus in which a wafer is housed in a heat treatment furnace and the wafer is heated by light irradiation from a light source.

That is, the wafer temperature measurement method according to the present invention is characterized in that the surface of the wafer is irradiated with temperature measurement light of a required wavelength, the amount of transmitted light is detected, and the temperature of the wafer is determined from the light transmittance characteristics of the wafer. shall be.

Further, there is a wafer temperature measuring device according to the present invention.

A means for determining the temperature of the wafer from a light transmittance characteristic of the wafer based on an output signal from the light emitting means and the light receiving means and an output signal from the light emitting means and the light receiving means. The present invention is characterized in that the wafer temperature detection means is constructed by the following. More specifically, means for blinking the light from the light emitting means at a predetermined period (frequency) is provided, and the light receiving means is provided with a circuit for removing the DC component of the output signal from the light receiving means. Connected.

(Function) In the wafer temperature measuring method and apparatus according to the present invention, temperature measuring light is irradiated onto the surface of the wafer by the light emitting means, the amount of transmitted light is detected by the light receiving means, and a signal is output from the light receiving means. This detects the light transmittance characteristics that change in response to the wafer temperature, and determines the wafer temperature from the light transmittance characteristics, making it possible to measure the wafer temperature without contacting the wafer.

The method for determining the temperature change of the wafer from the change in the light transmittance of the wafer will be explained in detail below with reference to FIGS. 2 and 3.

When a semiconductor is irradiated with light having an energy equivalent to or greater than the forbidden band width (energy gap) Eg of the semiconductor, intrinsic absorption occurs due to excitation inside the semiconductor. The wavelength λ of the light at this time. is λ. =hc/Eg (where h is a blank constant and C is the speed of light). Here, the forbidden band width Eg differs depending on the type of semiconductor, and becomes smaller as the temperature of the semiconductor increases. Therefore, the characteristic absorption wavelength λ. varies depending on the type of semiconductor, and shifts to longer wavelengths as the temperature of the semiconductor increases.

The absorption of light by a semiconductor is at this specific absorption wavelength λ. as a boundary.

Its λ. It increases rapidly as the wavelength shifts slightly to the shorter wavelength side, until almost no light passes through the semiconductor. On the other hand, for light having a wavelength longer than the characteristic absorption wavelength λ1, the semiconductor absorbs almost no light, and the semiconductor becomes almost transparent.

FIG. 2 is a graph showing the relationship between the wavelength of light and the transmittance in silicon, as well as the temperature characteristics of the intrinsic absorption wavelength.
It shows the change in transmittance in the case of K, and at this temperature, the wavelength is 1.
Most of the light with a wavelength of 0.07 μm or less is absorbed by silicon, and most of the light with a wavelength of 1.09 μm or more is transmitted.

In addition, curve T shows the change in transmittance when the absolute temperature T is 600"K; at this temperature, most of the light with a wavelength of 1°17 μm or less is absorbed by silicon, and the light with a wavelength of 1.19 μm or more is almost completely absorbed by silicon. To Penetrate.

Figure 3 is a graph showing the relationship between the wavelength of light and the intensity of light emitted and received light when the surface of a silicon substrate is irradiated with light by a light emitting element and the transmitted light is detected by a light receiving element. 1 curve a is the intensity distribution of the light emitting element,
The curve S represents the intensity distribution of the light-receiving element, and the curve C represents the temperature T of the silicon substrate interposed between the light-emitting element and the light-receiving element, = 60
Each shows the change in light transmittance at 0@K, and the shaded area A shows the light emitted from the light emitting element that is transmitted through the silicon substrate.

It shows the amount of light. Since the intensity distribution of the light-receiving element generally has a wider wavelength range than that of the light-emitting element, the light emitted by the light-emitting element is irradiated onto the silicon substrate, and some of the light is transmitted through the silicon substrate. By detecting the amount of light with a light receiving element, the light transmittance characteristics of the silicon substrate at that temperature can be known, and the temperature of the silicon substrate can be determined from the light transmittance characteristics. For example, in FIG. 3, when the light receiving element detects the light transmittance characteristic indicated by the shaded area A surrounded by the intensity distribution curve a of the light emitting element and the transmittance curve C at the temperature T3 of the silicon substrate, and outputs the signal. Since the output signal decreases as the temperature rises, if the relationship is calibrated in advance, the temperature indicator can display the temperature of the silicon substrate in correspondence with the output signal value.

The temperature of a wafer (silicon substrate, etc.) is measured in the manner described above.

Next, an oscillation circuit is connected to one light emitting means to blink the light emitting means at a predetermined period, and a synchronous rectification circuit is connected to the other light receiving means to synchronize and rectify the output signal from the light receiving means with the period of the oscillation circuit. In this case, for light other than measurement moonlight, such as light from a heating light source with almost no periodic changes or light emitted from a heated heat treatment furnace, wafer, etc., the output signal of the light receiving means is determined. The signals of the parts are blocked, and only the signal regarding the light from one light emitting means can be taken out.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of a temperature measuring device for a semiconductor substrate, which is an embodiment of the present invention, together with a schematic diagram of a heat treatment furnace.゛The heat treatment furnace (3) is made of quartz glass, and heating light sources (4) such as halogen lamps are arranged in rows on both upper and lower surfaces of the furnace, facing each other.
) is provided with a reflective plate (5). A wafer (1) such as a silicon substrate is placed on a supporter (2) and accommodated inside the heat treatment furnace (3). Support (
Like the heat treatment furnace (3), the heat treatment furnace (3) is made of quartz glass, and is carried into the heat treatment furnace (3) via an arm (6) by a drive device (not shown), and is moved back and forth horizontally to uniformly heat the furnace. . In addition, the negative side of the heat treatment furnace (3) is
It can be opened and closed by the furnace wall (7), and wafers (1) are loaded and unloaded through the opening.

Above and below the heat treatment furnace (3), a light emitting means and one end of a light receiving means are arranged facing each other.The light emitting means includes a light emitting element (11) such as a light emitting diode (LED),
This light emitting element (11) is connected to one end of an optical fiber (12), the other end of which is guided to the top surface of a heat treatment furnace (3), and a collimator lens (13) arranged at the other end of the optical fiber (12). It is configured. Note that the collimator lens (13) allows the optical fiber (12) to
The light emitted from the surface hardly spreads and becomes almost parallel.

On the other hand, the light receiving means includes an optical fiber (17) whose one end is guided to the lower surface of the heat treatment furnace (3) and which is disposed opposite to the end surface of the optical fiber (12), and which is disposed opposite to the other end of the optical fiber (17). Optical filter (19
), a lens (20), and a light receiving element (16) such as a Ge photodiode or a PbS photoconductive cell.

A condenser lens (18) may be attached to one end of the optical fiber (17) on the heat treatment furnace (3) side as shown in the figure, if necessary.
) may be placed facing each other.

The optical filter (19) blocks light in wavelength ranges that are unnecessary for temperature measurement of Ueno This was installed to improve measurement accuracy by eliminating the effects of

Furthermore, rather than using a too wide wavelength range, it is better to limit the wavelength range useful for measuring the temperature of the wafer (1) to the light receiving element (16) so that the wafer (1) can be measured with higher sensitivity. It was installed based on the reason that it was possible to measure the temperature of In addition, as the light receiving element (16), for example, G
It is not necessary to use an optical filter (19) for a device such as an e-photodiode that hardly detects light in a wavelength range of 1.5 to 1.6 μm or more.

By the way, the temperature measuring method and device according to the present invention measure the temperature of the wafer (1) by irradiating the surface of the wafer (1) with measurement light and detecting the transmitted light. The heating light source (4) of the furnace (3) also uses a halogen lamp that emits light in a wavelength range of 1 to 2 μm that is easily absorbed by the substrate to be processed 1, for example, a wafer such as a silicon substrate. Further, the wall surface of the heat treatment furnace (3) is made of quartz glass and transmits light of 0.5 to 4 μm well.

Therefore, light that interferes with temperature measurement other than the measurement moonlight from the light emitting means also enters the light receiving element (16).

It is desirable to eliminate the harmful effects of unnecessary light and accurately measure the temperature of the wafer (1). This will be explained below with reference to (V).

An oscillation circuit (14) is connected to the light emitting element (11) via an amplifier (15). This oscillation circuit (14)
The output is as shown by line (a) in FIG. 4(1).

Due to its function, the light emitting element (11) can generate several hundred to several tens of KH.
Figure 4 (II) shows the output from the light receiving element (16) that receives the light emitted from the light emitting means that repeats blinking at a predetermined frequency of z onto the surface of the wafer (1) and that passes through the wafer (1). It becomes an alternating current shape as shown by the curve (b). Note that the output signal represented by the curve (b) includes light from light 1 (4),
Contains unnecessary output based on light radiated from the heated heat treatment furnace (3) wall, support (2), and wafer (1), as well as light transmitted through the wafer (1), etc. .

Here, although the light from the heating light source (4) and various radiant lights change over time due to temperature rise and fall, they are almost constant compared to the blinking light from the light emitting element (11) whose frequency is several KHz. This is a negligible periodic change. Therefore, a capacitor (22) is connected to the output side of the light emitting element (16) via an amplifier II (21), and this capacitor (22) absorbs the DC component contained in the signal output from the light emitting element (16). An oscillation circuit (
A tuned amplifier (2) whose center frequency is the oscillation frequency of (14)
3) is connected, and the DC component and parts with small periodic changes in the output signal are cut off, resulting in the curve (III) in Figure 4 (III).
As shown in c), signals based on light that does not change periodically, such as light from the light source (4), light radiated from the heated heat treatment furnace (3), wafer (1), etc., are blocked. be done. The light emitting element (11) then illuminates the wafer (1).
Only the high frequency alternating current signal based on the light that has passed through is extracted. The tuned amplifier (23) further includes a synchronous rectifier circuit (24) that performs full-wave rectification of the output signal in synchronization with the oscillation circuit (14), and a low-frequency filter that eliminates unnecessary AC components and noise contained in the signal. The wave circuit (25) is connected,
The synchronous rectifier circuit (24) synchronously rectifies the signal from the tuned amplifier (23) as shown by curve (d) in Figure 4 (TV), and the low-pass filter circuit (25) removes unnecessary alternating current. components and noise are removed.

The output of only the DC component represented by the line (E) in FIG. 4(V) is taken out. Curve (e) Kt: $1, for example, the output V at time t is 1, for example, the shaded area A in FIG. The temperature of (1) will be displayed. The change in the output value at each time indicated by the line (E) in Figure 4 (V) corresponds to the change in the optical transmittance characteristics of a wafer such as a silicon substrate depending on the temperature, as shown in Figure 2. It is something. Incidentally, as the temperature of the wafer rises, it becomes difficult for light with short wavelengths to pass through as shown in Figure 2, and the area shown by the shaded area A in Figure 3 (
Since the amount of light transmitted through the wafer decreases, the amount of light transmitted through the wafer decreases.
The line (E) slopes downward to the right. Also, if the type of wafer is different, the characteristic absorption wavelength λ of the semiconductor will be different.

The temperature dependence of TL and T in FIG.
, , T3, etc., will of course also change.

In addition to blinking the light emitting means itself as in the illustrated embodiment, for example, a tungsten lamp containing light in the absorption wavelength range of a wafer such as a silicon substrate may be used as the light source of the light emitting means, and the light source may be connected to an optical fiber. A mechanical chopper may be provided, and the chopper may be driven by chopper driving means to block and pass light from the light source at a frequency of several KHz.

1. Optical fibers (12) and (17) for emitting and receiving light.
) does not necessarily have to be attached to the outer wall surface of the heat treatment furnace (3).

It may be placed in the heat treatment furnace (3) by penetrating the wall surface,
Conversely, the reflector (
5) may be placed immediately inside.

Furthermore, it is not always necessary to use optical fibers as the light emitting means and the light receiving means, and these may be directly attached to the heat treatment furnace. The optical filter (19), lens (20), condenser lens (18), etc. attached to the light receiving means are not necessarily used, and may be replaced with other ones depending on the design aspect.

The tuned amplifier (23) does not necessarily need to synchronize and amplify only the blinking frequency of the light from the light emitting means.

It is only necessary to amplify the signal of such a frequency, and it is not necessary to use a synchronous rectifier circuit (
24) and low-pass filter circuit (25) are not necessarily necessary,
If these are not used, for example, the maximum values of the curve (c) in FIG. 4 (II) and the curve (d) in FIG. 4 (rV) may be evaluated and studied.

The heating means is not limited to a light irradiation lamp that irradiates light including infrared rays, but may be any other means as long as it heats the wafer.

〔effect〕

Since the semiconductor substrate temperature measuring method and device according to the present invention are configured as described above, the following effects can be achieved.

i) It is possible to measure temperature more accurately than conventional methods without contacting the wafer.

if) Since there is no contact with the wafer, the temperature of the wafer can be measured without shaking or rotating the wafer in a horizontal plane during heat treatment.

1ii) Temperature measurement of the wafer can be performed in a non-contact manner without necessarily forming holes in the wall surface of the heat treatment furnace.

iv) Since there is no need to install a guide tube or sensor close to the wafer in the heat treatment furnace, the atmosphere inside the heat treatment furnace can be maintained uniformly, and there is no need to worry about adverse effects on the heat treatment effect due to temperature measurement. do not have.

V) The temperature measuring device can be made small, lightweight and inexpensive.

In addition, if the output signal from the light receiving means is made into an alternating current state by blinking the light emitting means at a predetermined period, and the signal is processed appropriately, the influence of the light energy emitted from the light source of the heat treatment furnace, the furnace wall, etc. It is possible to accurately measure only the temperature of the wafer.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a semiconductor substrate temperature measuring device according to an embodiment of the present invention, together with a schematic diagram of a heat treatment furnace. Figure 3 is a graph showing the relationship between the wavelength of light, transmittance, and □ in a silicon semiconductor, and the temperature characteristics of the characteristic absorption wavelength.
In the case where the surface of a silicon substrate is irradiated with light and the transmitted light is detected. 4 is a graph showing the relationship between the wavelength of light and the intensity of light emission and light reception, and FIGS. It is a graph showing the state of an output signal. 1... Semiconductor substrate (wafer) 3... Heat treatment furnace 4...
・Heating light source 11...Light emitting elements 12, 17
...Optical fiber 13...Collimator lens 14...Oscillation circuit 1
6... Light receiving element 18... Condenser lens 19... Optical filter 23... Tuning amplifier 24... Synchronous rectifier circuit 25... Low pass filter circuit Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. In a method for measuring the temperature of a semiconductor substrate housed in a heat treatment furnace and heat-treated by a heating means, the surface of the semiconductor substrate is irradiated with temperature measurement light of a desired wavelength. A method for measuring the temperature of a semiconductor substrate, comprising detecting the amount of transmitted light and determining the temperature from the light transmittance characteristics of the semiconductor substrate. 2. A temperature measuring device for a semiconductor substrate, which is housed in a heat treatment furnace and includes a detection means for detecting the temperature of a semiconductor substrate heat-treated by a heating means, which is attached opposite to the front and back surfaces of the semiconductor substrate. It consists of a light emitting means, a light receiving means, a means for blinking the light from the light emitting means at a predetermined frequency, and a DC component removal circuit connected to the light receiving means,
A temperature measuring device for a semiconductor substrate, characterized in that the temperature of the semiconductor substrate is determined from the light transmittance characteristics of the semiconductor substrate based on an output signal from a light receiving means. 3. The temperature of the semiconductor substrate according to claim 2, wherein the light emitting means comprises a light emitting element, an optical fiber connected to one end of the light emitting element, and a collimator lens disposed at the other end of the optical fiber. measuring device. 4. The temperature measuring device for a semiconductor substrate according to claim 3, wherein the light emitting element is a light emitting diode. 5. The light emitting means comprises a lamp and an optical fiber connected to one end of the lamp, as claimed in claim 2 or 4.
A temperature measuring device for a semiconductor substrate as described in 1. 6. The means for blinking the light from the light emitting means at a predetermined frequency comprises an oscillation circuit connected to the light emitting means and controlling the blinking of the light emitting means according to any one of claims 2 to 5. Temperature measuring device for semiconductor substrates. 7. The device according to any one of claims 2 to 5, wherein the means for blinking the light from the light emitting means at a predetermined frequency comprises a mechanical chopper disposed between the light emitting means and the heat treatment furnace. Temperature measuring device for semiconductor substrates. 8. The light receiving means includes a condenser lens, an optical fiber with the condenser lens arranged at one end, an optical filter and a light receiving element arranged opposite to each other at the other end of the optical fiber, and an amplifier connected to the output side of the light receiving element. A temperature measuring device for a semiconductor substrate according to any one of claims 2 to 5.