JP2004301614A - Radiation temperature measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation temperature measuring apparatus capable of highly accurately measuring radiation temperatures. <P>SOLUTION: In the radiation temperature measuring apparatus, light having a measuring wavelength not transmitting through an object to be measured 3 is projected from a light source 16 to the object to be measured, and reflected light from the object to be measured is captured at two different solid angles or more. On the basis of the differences in the moduli of capturing reflected light among them, the n of an approximate expression cos<SP>n</SP>θ of a bi-directional reflectance distribution function is computed to estimate directional hemispherical reflectance and determine emissivity. Then the temperature of the object to be measured is computed by an arithmetic means 14. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

式（３）
【００１４】
一方、２方向反射率分布係数をｆ＝ｋｃｏｓ^ｎθで近似（第２２回ＳＩＣＥ学術講演会（昭和５８年）予稿集１９２頁）する。ｎ、ｋは定数である。ｎ＝０の場合が完全拡散面であり、鏡面反射の場合はｎ≫１である。θは測定部に対するロッドの立体角で、石英ロッドの径および測定距離ｌは既知であるので見込み角θは容易に算出可能である。よって入力信号の差の比Ｒと定数ｎの関係は一義的に決定できｎ＝Ｇ（Ｒ）となる。図４は入力信号の差の比Ｒと定数ｎの関係を示すグラフである。
【００１５】
入力信号の差の比Ｒは計測量から算出できるので、Ｒから定数ｎを求めることができ、次式でＦ（θ）を算出できる。

式（４）
Ｆ（θ_１）が求まることから、

式（５）

式（６）
の式から温度Ｔを求めることができる。
【００１６】
図３は、距離可変手段により、１つの石英ロッド１と測定対象３の距離を異なるようにしたときの説明図である。距離可変手段は測定対象３をあるいは石英ロッド１を移動させる。距離ｌ_１、ｌ_２において、２つの立体角θ_１、θ_２が設定される。放射率、温度の算出は上述の手順でと同様に行われる。
【００１７】
図５は、石英ロッド１、２の先端をレンズ状に加工したロッドレンズ１１、１２としたときの説明図である。ロッドレンズを用いることにより、ロッド内で散乱する光の集光精度を高められ、より高精度の温度測定が可能となる。
【００１８】
【発明の効果】
拡散反射面、鏡面反射面によらず、測定対象の表面状態を予め知ることなしに、その場測定により方向半球反射率を推定して、高精度の放射率測定、放射温度測定が可能となる。また、測定対象基板内に温度分布があったり、表面状態が部分的に異なる場合には、基板を回転（回転信号より）、あるいは移動させて同一個所を受光径の異なる２つのロッドで測定することで温度測定が可能である。
【図面の簡単な説明】
【図１】この発明の実施の形態を示す構成説明図。
【図２】立体角の説明図。
【図３】この発明の他の実施の形態を示す説明図。
【図４】入力信号の差の比Ｒと定数ｎの関係を示すグラフ。
【図５】この発明の他の実施の形態を示す説明図．
【符号の説明】
１，２ 石英ロッド
３ 測定対象
５ 光ファイバ
８ 光路切換手段
１０ 検出器
１４ 演算手段
１６ 光源[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a radiation temperature measuring device for measuring emissivity and temperature of a measurement object. In particular, the present invention relates to a radiation temperature measuring device useful for in-situ measurement of emissivity and temperature of a semiconductor substrate such as silicon.
[0002]
[Prior art]
It is important in a process to measure the surface temperature of a measurement object such as a silicon substrate during various kinds of processing. Since various processes such as CVD (Chemical Vapor Deposition) are performed, a radiation temperature measuring device of a measurement object whose emissivity fluctuates due to a change in state such as a change in surface roughness or a deposit is known. For example, as shown in Japanese Patent Publication No. 6-69922 by the present applicant, a measurement object (Si wafer) is irradiated with light (I ₀ ), its reflected light Ir is measured, and the reflectance _r is calculated from r = I _r / I _0. According to Kirchhoff's law, ε = 1−r, emissivity ε was obtained, emissivity correction was performed, and the temperature T of the measurement object was determined. More specifically, there is a radiation temperature measuring device in which an emissivity is calculated based on radiant energy from a back surface of a measurement target, and thereafter, the temperature of the measurement target is calculated by a calculation unit using the emissivity. .
[0003]
[Problems to be solved by the invention]
However, in the above method, the correct emissivity can be obtained only in the case of diffuse reflection. There is a problem that the measurement temperature error is increased because the measurement object whose mirror surface is a mirror surface cannot capture (delete) reflected light. In addition, when the object to be measured is heated, the emissivity measured before heating is used even during heating, so that if the emissivity greatly changes during heating, there is a problem that a temperature error increases. On the other hand, in the semiconductor manufacturing process, in-situ measurement of emissivity and temperature is required for the purpose of precise temperature control. The present invention is intended to solve such a problem, and the emissivity and the surface state of an object to be measured are unknown, in particular, even for a semiconductor substrate having a fluctuating surface state such as a silicon substrate, the emissivity is measured by in-situ measurement. It is an object of the present invention to provide a radiation temperature measuring device capable of performing highly accurate radiation temperature measurement.
[0004]
[Means for Solving the Problems]
The present invention captures reflected light from a measurement target at two or more different solid angles, and a light source that emits light of a measurement wavelength that does not pass through the measurement target to the measurement target. This is a radiation temperature measuring device that calculates the approximate expression cos ⁿ θ of the two-way reflectance distribution function, estimates the directional hemispherical reflectance, obtains the emissivity, and calculates the temperature of the measurement target by the calculating means. .
[0005]
In order to obtain two or more different solid angles, at least two quartz rods having different light receiving diameters for capturing the reflected light from the object to be measured are provided.
[0006]
Further, in the invention of claim 2, a rod for capturing the reflected light from the object to be measured and a variable means for changing the distance between the rod and the object to be measured are provided.
[0007]
A third aspect of the present invention is the radiation temperature measuring apparatus, wherein the object to be measured is a silicon substrate, and the measurement wavelength is 0.9 μm which does not transmit through the silicon substrate.
[0008]
According to a fourth aspect of the present invention, there is provided a radiation temperature measuring apparatus including an optical fiber for transmitting two optical signals, ie, light emission and light reception, between a rod and a detector.
[0009]
A fifth aspect of the present invention is a radiation temperature measuring device in which a rod is a rod lens whose tip is processed into a lens shape in order to enhance the light-collecting accuracy.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a configuration explanatory view showing an embodiment of the present invention. In FIG. 1, reference numeral 3 denotes an object to be measured such as a silicon substrate, which is heated by a heating device 4 and controlled at a predetermined process temperature. Numerals 1 and 2 denote rods for transmitting light and reflected light in proximity to the object to be measured, which are quartz rods in this embodiment and are located at a predetermined distance from the object to be measured. An optical fiber 5 transmits an optical signal between the quartz rod and the optical connector 6. Reference numeral 7 denotes a lens for collecting the reflected light. Reference numeral 8 denotes an optical path switching means such as a beam splitter that is provided between the lens 7 and a detector 10 such as a photodiode and reflects light, and a measurement wavelength is provided between the optical path switching means 8 and the detector 10. Is provided. Between an amplifier 11 for amplifying a signal from the detector 10 and an analog / digital signal converter 13, a multiplexer 12 for converting several input signals into one output signal in such a manner as to be able to reproduce each input signal is provided. The calculating means 14 calculates the emissivity and the temperature of the object to be measured based on the digital signal by a calculating method described later. The calculation means 14 is connected to a control circuit 15 such as a microprocessor, and performs on / off control of a light source 16 that irradiates light to a measurement target. FIG. 1 shows an example in which two quartz rods 1 and 2 having different light receiving diameters are used.
[0011]
FIG. 2 is an enlarged view of FIG. 1 in which two solid angles θ ₁ and θ ₂ are set by quartz rods having _two diameters (d ₁ and d ₂ ) different from those to be measured. As the measurement wavelength, a wavelength that does not transmit the measurement object is used. In the case of a silicon substrate, a measurement wavelength λe = 0.9 μm is used. As the light source, for example, an LED (light emitting diode), an LD (laser diode), or a tungsten lamp is used. In order to measure the radiation from the silicon substrate to be measured, the light source can be turned on or off or the measurement wavelength can be shielded. The calculation of the emissivity and the temperature of the present invention will be described below by taking as an example the case where there are two quartz rods.
[0012]
The signals received through the quartz rods 1 and 2 and input to the arithmetic means are as follows: when the light source is off (OFF), the input signal V, the emissivity ε of the object to be measured, and the radiant energy L (λ, T) are as follows. It is represented by an equation. λ is the measurement wavelength, and T is the temperature of the measurement target.
Quartz rod 1 V ₁₀ = α ₁ · εL (λ, T) Equation (1)
Quartz rod 2 V ₂₀ = α ₂ · εL (λ, T) Equation (2)
When the light source is on,
Quartz rod 1 V ₁₁ = α ₁ {εL (λ, T) + (1−ε) F (θ ₁ ) β ₁ · I ₀ }
Quartz rod 2 V ₂₁ = α ₂ {εL (λ, T) + (1−ε) F (θ ₂ ) β ₂ · I ₀ }
F (θ ₁ ) and F (θ ₂ ) are quantities determined by the geometrical quantities and the two-way reflectance distribution of the surface to be measured, and are called capture rates of reflected light. α ₁ , α ₂ , β ₁ , and β ₂ are optical constants, and I ₀ is irradiation energy.
[0013]
The ratio R of the difference between the input signals is given by the following equation.

Equation (3)
[0014]
On the other hand, the two-way reflectance distribution coefficient is approximated by f = kcos ⁿ θ (192 pages of proceedings of the 22nd SICE Academic Lecture (1983)). n and k are constants. The case of n = 0 is a perfect diffusion surface, and the case of specular reflection is n≫1. θ is the solid angle of the rod with respect to the measuring unit, and the expected angle θ can be easily calculated because the diameter of the quartz rod and the measurement distance l are known. Therefore, the relationship between the ratio R of the difference between the input signals and the constant n can be uniquely determined, and n = G (R). FIG. 4 is a graph showing the relationship between the ratio R of the difference between the input signals and the constant n.
[0015]
Since the ratio R of the difference between the input signals can be calculated from the measured amount, the constant n can be obtained from R, and F (θ) can be calculated by the following equation.

Equation (4)
Since F (θ ₁ ) is obtained,

Equation (5)

Equation (6)
The temperature T can be obtained from the following equation.
[0016]
FIG. 3 is an explanatory diagram when the distance between one quartz rod 1 and the measuring object 3 is made different by the distance varying means. The distance varying means moves the measuring object 3 or the quartz rod 1. At the distances l ₁ and l ₂ , two solid angles θ ₁ and θ ₂ are set. Calculation of emissivity and temperature is performed in the same manner as in the above-described procedure.
[0017]
FIG. 5 is an explanatory view when the ends of the quartz rods 1 and 2 are formed into lens lenses 11 and 12 formed into lenses. By using a rod lens, the accuracy of condensing light scattered in the rod can be increased, and more accurate temperature measurement can be performed.
[0018]
【The invention's effect】
Irrespective of the diffuse reflection surface and the specular reflection surface, it is possible to estimate the directional hemispherical reflectivity by in-situ measurement without knowing the surface condition of the measurement object in advance, and it is possible to measure the emissivity and radiation temperature with high accuracy . If there is a temperature distribution in the substrate to be measured or the surface state is partially different, the substrate is rotated (from a rotation signal) or moved to measure the same portion with two rods having different light receiving diameters. This enables temperature measurement.
[Brief description of the drawings]
FIG. 1 is a configuration explanatory view showing an embodiment of the present invention.
FIG. 2 is an explanatory diagram of a solid angle.
FIG. 3 is an explanatory view showing another embodiment of the present invention.
FIG. 4 is a graph showing a relationship between a ratio R of a difference between input signals and a constant n.
FIG. 5 is an explanatory view showing another embodiment of the present invention.
[Explanation of symbols]
Reference numerals 1 and 2 Quartz rod 3 Measurement target 5 Optical fiber 8 Optical path switching means 10 Detector 14 Operation means 16 Light source

Claims (5)

A light source that emits light having a measurement wavelength that does not pass through the measurement target to the measurement target, at least two quartz rods having different light receiving diameters that capture reflected light from the measurement target, and a detector that detects the received reflected light, Calculate ⁿ of the approximate expression cos ⁿ θ of the two-way reflectance distribution function from the difference in the capture rates of at least two different quartz rods, estimate the directional hemispherical emissivity, obtain the emissivity, and calculate the temperature of the measurement target. A radiation temperature measuring device provided with a calculating means. A light source that emits light of a measurement wavelength that does not pass through the measurement target to the measurement target, a rod that captures reflected light from the measurement target, a variable unit that changes a distance between the rod and the measurement target, and receives the reflected light. From the detector to be detected and the difference in the capture ratio of the reflected light at at least two different distances, ⁿ of the approximate expression cos ⁿ θ of the two-way reflectance distribution function is calculated to estimate the directional hemispherical reflectance, and the emissivity is determined. And a calculating means for calculating the temperature of the object to be measured. The radiation temperature measuring device according to claim 1, wherein the measurement target is a silicon substrate, and the measurement wavelength is 0.9 μm. 4. The radiation temperature measuring device according to claim 1, further comprising an optical fiber for transmitting two optical signals of light emission and light reception between the rod and the detector. The radiation temperature measuring device according to claim 1, wherein the rod is a rod lens whose tip is processed into a lens shape.

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