JP2004186300A - Method of heat treatment of semiconductor wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure the temperature of a wafer whose emissivity is hardly measured and to treat the wafer normally, in a system for directly measuring the temperature of the wafer upon the heat treatment of the semiconductor wafer. <P>SOLUTION: When an emissivity in the rear surface of the wafer is within the detecting range of an optical detector in a process of irradiating light to the rear surface of the wafer to measure the temperature of the wafer based on the emissivity ε, the temperature is operated based on the emissivity ε measured in the process of heat treatment. On the other hand, when the emissivity in the rear surface of the wafer is out of the detecting range of the optical detector, the temperature is operated based on an emissivity ε<SB>0</SB>measured before the heat treatment process. As a result, an error upon measuring the temperature can be minimized whereby the wafer temperature can be measured correctly and the heat treatment can be effected with a good accuracy. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２２】
次に、ウェハ処理中の反射エネルギーＶ_Ｗ（ｚ，Ｔ）、熱放射エネルギ−Ｉ（Ｔ）、及び先に求めた反射率の炉内補正係数Ｋ（ｚ）に基づいて、次の関数（２）及びプランクの法則式（３）より、熱処理中における実際のウェハ温度Ｔが得られる。なお、放射率ε（Ｔ）と反射率Ｒ（Ｔ）は、ε（Ｔ）＝１−Ｒ（Ｔ）に示される関係にある（ここでは、透過率はゼロである。フィルタリングにより、透過率がゼロになる波長帯の放射エネルギーをパイロメータに読ませている。）。
【００２３】
【数２】

【００２４】
ここで、Ｉは熱放射エネルギー（Ｗ／ｍ^２）、εは物体の放射率、λは熱放射の波長（ｍ）、Ｔは物体の温度（Ｋ）、Ｃ_１、Ｃ_２はそれぞれプランクの第１、第２定数である。
【００２５】
以上より、光検出器を用いて放射率補正を行うことにより、パイロメータを用いてウェハ処理中の温度測定を行うことが出来る。
【００２６】
【特許文献１】
特開２００１−１９４０７５号公報（段落番号００６５〜００６７）
【特許文献２】
特開平１０−５５９７４号公報（段落番号００１８〜００３２）
【００２７】
【発明が解決しようとする課題】
しかしながら、実際に熱処理をする際にウェハの放射率εが低いと、放射率測定誤差が温度測定に与える影響が大きくなる。
【００２８】
具体的には、式（３）のεにウェハの放射率そのものを用いる場合の温度誤差と放射率誤差の関係を表わすと図５のようになる（式（３）のεにウェハの放射率そのものを用いない場合もある。例えば特開平１０−５５９７４号公報）。図５より、放射率εが低いほど、少しの放射率誤差でも温度誤差としては大きく影響してしまうことが分かる。
【００２９】
しかし放射率εが高すぎると、図１に示したホットウォールタイプの装置では、光を用いてウェハ裏面の放射率を直接測定するシステムを用いているため、温度測定エラーが発生する。それは、放射率εと反射率Ｒの関係式ε（Ｔ）＝１−Ｒ（Ｔ）から、放射率εが高いということは反射率Ｒが低いということであり、ウェハからの光の反射量が微弱となるためである。その結果、光検出器に発生する電圧信号が、ノイズの大きさと同様かまたはそれ以下になるため、正確に放射率を算出することが出来ない。
【００３０】
よって本発明では、図１に示した装置のように、ウェハの放射率を直接測定するシステムにおいて、光検出器自体のノイズの影響を受けにくい範囲でウェハ裏面の放射率εを測定することにより、正確かつ正常にウェハを処理する方法を提供することを目的とする。
【００３１】
【課題を解決するための手段】
上記課題を解決するために、本発明では、ウェハに光を照射し、その放射率からウェハ温度を算出するシステムを有する熱処理装置において、ウェハ裏面における放射率が光検出器の検出範囲内にある場合は、熱処理工程中に測定した放射率に基づいて温度を算出し、ウェハ裏面における放射率が光検出器の検出範囲外にある場合は、熱処理工程前に測定した放射率に基づいて温度を算出することを特徴とする、半導体ウェハの製造方法を提供する。
【００３２】
その結果、ウェハ裏面の反射率が低すぎる場合においても、より正確にウェハ処理時の温度を求めることができるため、温度測定エラーの発生を抑え、精度良く熱処理を行うことが出来る。
【００３３】
【発明の実施の形態】
本発明の実施形態について、図面を参照しながら説明する。
【００３４】
本発明は、図１〜３のような光検出器などを用いてウェハの反射率（または放射率）を測定する装置の場合、ウェハの反射率の値によって実際の温度測定で用いない反射率を選択することに特徴がある。その場合、熱処理温度は、主に２つのパラメータである、パイロメータにより測定される熱放射エネルギーＩと、光検出器により測定される熱放射率ε（つまり、反射率Ｒ）に基づいて導き出される。なお、ウェハを透過しない波長帯の熱放射エネルギーを用いることにより、放射率εと反射率Ｒは、ε＝１−Ｒの式で表わされる関係にある。以下、図４のフロー図を用いて具体的に説明する。
【００３５】
まず、図４（ａ）の工程前において、ウェハ裏面に膜の堆積、あるいは膜の除去等により、低反射率の膜、例えばＳｉＮ，ＴＥＯＳ、又はＳｉＣ等の膜を表面に露出させ、熱処理装置に搬入する。
【００３６】
次に、図４（ｂ）の工程において、熱処理装置の炉内に導入される前に、室温におけるウェハ裏面の反射率を測定する。本工程は、図３（ａ）に示すステップに該当し、積分球６により、炉外におけるウェハ裏面の反射率Ｒ_０を測定する。
【００３７】
その後、図４（ｃ）の工程において、ウェハ裏面の反射率Ｒがしきい値と比較して大きいか小さいかを確認する。しきい値は、図５に示した温度エラーと放射率エラーの関係、及び光検出器の検出限界に基づいて設定する。
【００３８】
具体的には、放射率誤差が比較的大きくなったとしても、温度誤差としてはほとんど変化しない値で、光検出器で測定可能な反射率の範囲の値であることが望ましい。それは、図５より放射率εが高いほど、つまり反射率Ｒが低いほど、反射率Ｒに基づく温度エラーの値は小さくなるが、反射率Ｒが小さすぎるとパイロメータに反射してくる光も弱くなるためである。
【００３９】
ここで、図３に示す装置において、パイロメータはウェハからの熱放射エネルギーＩを読み取る働きをし、ウェハの放射率εは光検出器により感知され、温度測定はこれら２つのパラメータ、つまり熱放射エネルギーＩと放射率εから計算される。よって、ウェハの反射率Ｒが小さすぎて、反射光があまりにも弱いと、得られる変換電圧が光検出器自体の誤差範囲内に含まれてしまい、正確な測定ができない。従って、光検出器の測定可能範囲内である値のしきい値を、例えば放射率０．９８以上、つまり反射率０．０２以下に設定する。
【００４０】
その結果、放射率ε、もしくは反射率Ｒがしきい値より大きいか小さいかによって、最適な温度測定方法が異なってくる。
【００４１】
まず、図４（ｄ）に示すように、しきい値より反射率Ｒが小さい場合、つまり放射率εが大きい場合について説明する。
【００４２】
しきい値より反射率Ｒが小さい場合は、つまり図５でいうと放射率εが大きいほど、反射率の誤差が温度の誤差に対してほとんど影響を及ぼさなくなる。しかし、反射率Ｒが小さすぎるとウェハからの反射光が弱くなり、光検出器の検出限界を超えて誤差範囲に含まれてしまう。よって、熱処理中のウェハにおいて、光検出器を用いて放射率を測定することが出来ない、もしくは測定できたとしても、正確な値を得られる可能性が大変低くなる。
【００４３】
従って、反射率Ｒがしきい値以下である場合は、熱処理前のウェハにより測定した反射率Ｒ_０を、熱処理中のウェハにおける反射率Ｒとする。図５より、反射率Ｒが低い、つまり放射率εが高い場合は放射率εの値に関わらず、ほぼ温度誤差は一定であるので、実測値を用いなくても正確な温度測定が出来る。この理由について、以下より具体的に説明する。
【００４４】
熱放射を利用する温度計測では、物体の表面から放射される熱放射量が物体の温度の他に、物体の性質と光学的な要因によって決まる放射率εの影響を受ける。物体の表面から放射される熱放射エネルギーＩは、温度と波長の関数（プランクの法則）で下記式（３）のように表わされる。
【００４５】
【数３】

【００４６】
ここで、Ｉは熱放射エネルギー（Ｗ／ｍ^２）、εは物体の放射率、λは熱放射の波長（ｍ）、Ｔは物体の温度（Ｋ）、Ｃ_１、Ｃ_２はそれぞれプランクの第１、第２定数である。
【００４７】
波長が一定ならば、上式（３）において熱放射の強さＩと物体の放射率εは温度Ｔのみの関数となる。
【００４８】
パイロメータでは、熱放射エネルギーＩと熱放射によって得られる電流値が一次の関係にあり、波長が既知であると、物体の放射率εが分かれば温度Ｔが求められる。温度測定に使用する熱放射の波長λのオーダーは１０^−３ｍ、Ｔのオーダーは１０^３Ｋ程度であるので、ｅ^ｃ２／λ^Ｔ≒１となる。したがって式（３）は下記式（４）のように近似できる（ウィーンの公式）。
【００４９】
【数４】

【００５０】
上式（４）の左辺はパイロメータの読み値であるから、一定としてＴについて微分すると下式（５）が得られる。
【００５１】
【数５】

【００５２】
上式（５）においてウェハ放射率εの誤差ｄε及びウェハ温度Ｔの誤差ｄＴの関係をグラフで表わした結果が、先でも説明した図５である。図５より放射率εが大きい場合は、温度誤差ｄＴが小さくなることが分かる。高放射率のウェハを処理する場合、室温での放射率εと処理中（高温）での放射率εの変化は非常に小さいため、室温での放射率εを処理中の放射率εとして見なしても、大きな誤差は発生しない。
【００５３】
例えば、放射率が０．９８〜０．９９のウェハを処理する場合は、放射率誤差ｄε＝０．００５程度となることが分かっている。その場合、図５よりｄＴ＝−５．０程度の温度誤差となる。従って、熱処理前に測定した放射率εを処理中のウェハの放射率εと見なしても大きな誤差を生じることはなく、実測値の代わりに用いることが出来る。
【００５４】
次に、図４（ｅ）に示すように、しきい値より反射率Ｒが大きい場合、つまり放射率εが小さい場合について説明する。
【００５５】
反射率Ｒがしきい値より大きい場合は、つまり図５で言うと放射率εが小さいほど、反射率エラーが温度エラーに対して大きな影響を及ぼす。よって、先で説明したように処理前の反射率Ｒ_０を代わりに使用することは出来ず、処理中の反射率Ｒを正確に測定する必要がある。この場合、熱処理中の反射率Ｒは、光検出器の測定限界であるしきい値以上の値であるため、基本的には正確に熱処理中の温度測定することが出来る。
【００５６】
本実施形態におけるしきい値は、光検出器の検出限界に基づいて求められた反射率Ｒであり、裏面につける膜の種類や熱処理時の温度によって、ある程度影響され変化する。よって、本実施形態では仮に、しきい値はＲ＝０．０２としたが、これらの値に限定されるものではない。
【００５７】
また本発明では、放射率に基づいて温度を算出する方法について説明したが、放射率から反射率を求めることが出来るので、反射率を用いて温度を算出することも出来、放射率の測定に限定されるものではない。よって、初めに反射率を測定して、反射率に基づいて温度を求めることも出来る。
【００５８】
【発明の効果】
以上本発明によると、ウェハに光を照射し、その反射率及び反射光強度に基づいてウェハ温度測定をする場合において、ウェハ裏面における反射率によって、温度測定方法を変えることにより、温度測定誤差を最小限に抑えることが出来る。例えば、ウェハ裏面の反射率が低すぎて、光検出器の検出限界を超えて、放射率の測定が不可能である場合は、その代わりに熱処理前の放射率を用いて温度を求めることが出来る。
【図面の簡単な説明】
【図１】ホットウォールタイプの熱処理装置を示す図
【図２】ホットウォールタイプの装置におけるウェハの位置と炉内温度の関係を示す図
【図３】ホットウォールタイプの熱処理装置を示す図
【図４】ホットウォールタイプの装置における測定フローを示す図
【図５】温度エラーと放射率エラーの関係を示す図
【符号の説明】
１ トランスファーロボット
２ ヒーター
３ エレベーター
４ パイロメータ
５ 光検出器
６ 積分球
７ ウェハ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor wafer, and more particularly to a method for measuring a wafer temperature.
[0002]
[Prior art]
2. Description of the Related Art In recent years, in the process of manufacturing a semiconductor wafer, the number of steps using rapid thermal processing (Rapid Thermal Annealing) is increasing.
[0003]
Apparatuses used for the rapid heat treatment can be classified into those that measure the temperature of a wafer during processing and those that measure the temperature of a heat source such as a heater without directly measuring the wafer temperature.
[0004]
In order to perform rapid thermal processing with high accuracy, it is necessary to accurately measure and control the wafer temperature during processing, and the former is a more effective system for rapid thermal processing.
[0005]
There are two methods of measuring the wafer temperature: a thermocouple method and a pyrometer method. In particular, the pyrometer method is becoming the mainstream of rapid thermal processing equipment because it can measure the temperature of a wafer more accurately than a thermocouple.
[0006]
Here, there are two types of heat sources used in the rapid heat treatment apparatus: a lamp and a heater. The former is generally called a cold wall type device, and the latter is a hot wall type device.
[0007]
At present, the mainstream is a lamp type device, but in recent years, a hot wall type device is also being used.
[0008]
Hereinafter, a typical hot wall type apparatus and a method for measuring the temperature thereof will be described.
[0009]
First, a typical structure of a hot wall type heat treatment apparatus is shown in FIG. As shown in FIG. 1, the wafer 7 is introduced into the furnace of the heat treatment apparatus by the transfer robot 1. In the furnace of this heat treatment apparatus, a heater 2 exists along a side wall portion.
[0010]
Next, the wafer 7 introduced into the furnace is moved upward by the elevator 3 to a certain height, heated by the heater 2 on the side wall in the furnace, and heat-treated. In the case of this device, the emissivity ε from the back surface of the wafer is measured by a photodetector (photodetector) 5 installed at the bottom of the elevator 3 in addition to the pyrometer 4.
[0011]
In this heat treatment apparatus, as shown in FIG. 2, a temperature change in the wafer itself is controlled by providing a temperature distribution in the furnace.
[0012]
Specifically, as shown in the graph of FIG. 2 in which the horizontal axis indicates the furnace temperature (° C.) and the vertical axis indicates the wafer position (mm), the furnace has a higher temperature in the upper part of the furnace. The higher the temperature of the wafer, the higher the temperature of the wafer. Therefore, the temperature of the wafer is controlled to an arbitrary temperature by adjusting the position of the wafer in the furnace by moving the elevator up and down and changing the time the wafer stays at that position.
[0013]
Subsequently, a method of measuring a temperature in a heat treatment apparatus equipped with a photodetector and a pyrometer will be described with reference to FIG.
[0014]
First, in the integrating sphere 6 of FIG. 3A, the reflectance R ₀ of the wafer at room temperature before being introduced into the furnace is measured.
[0015]
Specifically, the reflected energy V _W from the wafer and the energy V _REF of the light source are measured by the photodetector as converted voltage values by the photodiode. Further, the influence constant C of the integrating sphere 6 itself is measured using a wafer or the like whose reflectance is known. Then, by substituting the value into the relational expression R ₀ = C (V _W / V _REF ), the wafer reflectance R ₀ at room temperature is obtained.
[0016]
Next, in the furnace of FIG. 3 (b), the elevator 3 is swept without a wafer, so that stray light energy V ₀ (z) in a state where a wafer is not introduced into the furnace is converted into each height in the furnace. Is measured using a photodetector (z represents height).
[0017]
Thereafter, the wafer is introduced into the furnace, and the elevator-3 is swept while the wafer is placed thereon, so that the stray light energy _VW0 (z) in the furnace is _measured using a photodetector for each height in the furnace. And measure. Here, since the elevator 3 is swept in a short time, the wafer temperature hardly rises, and the wafer temperature is about 150 ° C. or less.
[0018]
Subsequently, the wafer is actually heat-treated while the wafer is placed on the elevator 3, and the reflected energy V _W (z, T) of the wafer during the heat treatment is detected by the photodetector, and the thermal radiation energy I (T) is measured by the pyrometer. Is measured.
[0019]
Using the above measurement results, the actual wafer temperature T during the heat treatment can be derived.
[0020]
Specifically, based on the wafer reflectance R ₀ , stray light energy V ₀ (z) when there is no wafer in the furnace, and stray light energy V _W0 (z) when there is a wafer in the furnace, the following relational expression is used. Using (1), the in-furnace correction coefficient K (z) of the reflectance at each height is obtained.
[0021]
(Equation 1)

[0022]
Next, based on the reflected energy V _W (z, T) during the wafer processing, the thermal radiation energy −I (T), and the furnace correction coefficient K (z) of the reflectance previously obtained, the following function ( From 2) and Planck's law equation (3), the actual wafer temperature T during the heat treatment is obtained. Note that the emissivity ε (T) and the reflectance R (T) have a relationship expressed by ε (T) = 1−R (T) (here, the transmittance is zero. The pyrometer reads the radiant energy in the wavelength band where is zero.)
[0023]
(Equation 2)

[0024]
Here, I is the thermal radiation energy (W / m ² ), ε is the emissivity of the object, λ is the wavelength of the thermal radiation (m), T is the temperature of the object (K), and C ₁ and C ₂ are each of Planck. These are the first and second constants.
[0025]
As described above, by performing the emissivity correction using the photodetector, the temperature can be measured during the wafer processing using the pyrometer.
[0026]
[Patent Document 1]
JP-A-2001-194075 (Paragraph Nos. 0065 to 0067)
[Patent Document 2]
JP-A-10-55974 (paragraph numbers 0018 to 0032)
[0027]
[Problems to be solved by the invention]
However, when the emissivity ε of the wafer is low during the actual heat treatment, the influence of the emissivity measurement error on the temperature measurement increases.
[0028]
Specifically, the relationship between the temperature error and the emissivity error when the emissivity of the wafer itself is used for ε in equation (3) is as shown in FIG. It may not be used in some cases (for example, JP-A-10-55974). From FIG. 5, it can be seen that as the emissivity ε is lower, even a small emissivity error has a greater effect on the temperature error.
[0029]
However, if the emissivity ε is too high, the hot-wall type apparatus shown in FIG. 1 uses a system that directly measures the emissivity on the back surface of the wafer using light, so that a temperature measurement error occurs. From the relational expression ε (T) = 1−R (T) between the emissivity ε and the reflectivity R, the higher the emissivity ε, the lower the reflectivity R, and the amount of light reflected from the wafer. Is weak. As a result, the voltage signal generated in the photodetector is equal to or less than the magnitude of the noise, so that the emissivity cannot be accurately calculated.
[0030]
Therefore, in the present invention, as in the apparatus shown in FIG. 1, in a system for directly measuring the emissivity of the wafer, the emissivity ε of the back surface of the wafer is measured in a range that is hardly affected by the noise of the photodetector itself. It is an object of the present invention to provide a method for accurately and normally processing a wafer.
[0031]
[Means for Solving the Problems]
In order to solve the above problems, in the present invention, in a heat treatment apparatus having a system for irradiating light to a wafer and calculating a wafer temperature from the emissivity, the emissivity on the back surface of the wafer is within a detection range of a photodetector. In the case, the temperature is calculated based on the emissivity measured during the heat treatment step, and when the emissivity on the back surface of the wafer is out of the detection range of the photodetector, the temperature is calculated based on the emissivity measured before the heat treatment step. There is provided a method for manufacturing a semiconductor wafer, wherein the method is calculated.
[0032]
As a result, even when the reflectivity of the back surface of the wafer is too low, the temperature at the time of processing the wafer can be obtained more accurately. Therefore, the occurrence of a temperature measurement error can be suppressed, and the heat treatment can be performed accurately.
[0033]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the drawings.
[0034]
The present invention relates to an apparatus for measuring the reflectivity (or emissivity) of a wafer using a photodetector or the like as shown in FIGS. There is a feature in selecting. In that case, the heat treatment temperature is derived based on two main parameters, the thermal radiation energy I measured by the pyrometer and the thermal emissivity ε (ie the reflectance R) measured by the photodetector. In addition, the emissivity ε and the reflectance R have a relationship represented by the equation of ε = 1−R by using thermal radiation energy in a wavelength band that does not pass through the wafer. Hereinafter, a specific description will be given with reference to the flowchart of FIG.
[0035]
First, before the step of FIG. 4A, a film having a low reflectance, for example, a film of SiN, TEOS, or SiC is exposed on the front surface by depositing a film on the back surface of the wafer or removing the film. Carry in.
[0036]
Next, in the step of FIG. 4B, the reflectance of the back surface of the wafer at room temperature is measured before being introduced into the furnace of the heat treatment apparatus. This step corresponds to the step shown in FIG. 3A, and the reflectance R _{0 of the} back surface of the wafer outside the furnace is measured by the integrating sphere 6.
[0037]
Thereafter, in the step of FIG. 4C, it is checked whether the reflectance R on the back surface of the wafer is larger or smaller than the threshold value. The threshold value is set based on the relationship between the temperature error and the emissivity error shown in FIG. 5 and the detection limit of the photodetector.
[0038]
Specifically, even if the emissivity error becomes relatively large, it is desirable that the temperature error be a value that hardly changes, and that the value be in the range of the reflectivity that can be measured by the photodetector. As shown in FIG. 5, the higher the emissivity ε, that is, the lower the reflectance R, the smaller the value of the temperature error based on the reflectance R. However, if the reflectance R is too small, the light reflected on the pyrometer is also weak. It is because it becomes.
[0039]
Here, in the apparatus shown in FIG. 3, the pyrometer serves to read the thermal radiation energy I from the wafer, the emissivity ε of the wafer is sensed by the photodetector, and the temperature measurement is based on these two parameters, namely the thermal radiation energy. Calculated from I and emissivity ε. Therefore, if the reflectance R of the wafer is too small and the reflected light is too weak, the obtained converted voltage is included in the error range of the photodetector itself, and accurate measurement cannot be performed. Therefore, the threshold value within a measurable range of the photodetector is set to, for example, emissivity of 0.98 or more, that is, reflectance of 0.02 or less.
[0040]
As a result, the optimum temperature measurement method differs depending on whether the emissivity ε or the reflectance R is larger or smaller than the threshold.
[0041]
First, the case where the reflectance R is smaller than the threshold value, that is, the case where the emissivity ε is large, as shown in FIG.
[0042]
When the reflectance R is smaller than the threshold value, that is, in FIG. 5, as the emissivity ε increases, the reflectance error hardly affects the temperature error. However, if the reflectance R is too small, the light reflected from the wafer will be weak, exceeding the detection limit of the photodetector and included in the error range. Therefore, the emissivity cannot be measured using the photodetector on the wafer during the heat treatment, or even if the emissivity can be measured, the possibility of obtaining an accurate value is very low.
[0043]
Therefore, when the reflectance R is equal to or less than the threshold value, the reflectance R ₀ measured on the wafer before the heat treatment is defined as the reflectance R on the wafer during the heat treatment. According to FIG. 5, when the reflectance R is low, that is, when the emissivity ε is high, the temperature error is almost constant regardless of the value of the emissivity ε, so that accurate temperature measurement can be performed without using an actually measured value. The reason will be described more specifically below.
[0044]
In temperature measurement using thermal radiation, the amount of thermal radiation radiated from the surface of an object is affected not only by the temperature of the object but also by the emissivity ε determined by the properties of the object and optical factors. The thermal radiation energy I radiated from the surface of the object is represented by the following equation (3) as a function of temperature and wavelength (Planck's law).
[0045]
[Equation 3]

[0046]
Here, I is the thermal radiation energy (W / m ² ), ε is the emissivity of the object, λ is the wavelength of the thermal radiation (m), T is the temperature of the object (K), and C ₁ and C ₂ are each of Planck. These are the first and second constants.
[0047]
If the wavelength is constant, the intensity I of the thermal radiation and the emissivity ε of the object in the above equation (3) are functions of only the temperature T.
[0048]
In the pyrometer, the thermal radiation energy I and the current value obtained by the thermal radiation have a linear relationship. If the wavelength is known, the temperature T can be obtained by knowing the emissivity ε of the object. Order ¹⁰ -3 m of the wavelength of the thermal radiation to be used for temperature measurement lambda, since the order of T is about 10 ^{3 K,} the ^{e c2 /} λ ^T ≒ 1. Therefore, equation (3) can be approximated as equation (4) below (Wien's formula).
[0049]
(Equation 4)

[0050]
Since the left side of the above equation (4) is a pyrometer reading, the following equation (5) is obtained by differentiating T with a fixed value.
[0051]
(Equation 5)

[0052]
FIG. 5 is a graph illustrating the relationship between the error dε of the wafer emissivity ε and the error dT of the wafer temperature T in the above equation (5). FIG. 5 shows that when the emissivity ε is large, the temperature error dT becomes small. When processing a wafer with a high emissivity, the change in the emissivity ε at room temperature and the emissivity ε during processing (high temperature) are very small, so the emissivity ε at room temperature is regarded as the emissivity ε during processing. However, no large error occurs.
[0053]
For example, when processing a wafer having an emissivity of 0.98 to 0.99, it is known that the emissivity error dε is about 0.005. In this case, a temperature error of about dT = -5.0 is obtained from FIG. Therefore, even if the emissivity ε measured before the heat treatment is regarded as the emissivity ε of the wafer being processed, no large error occurs, and the emissivity ε can be used instead of the actually measured value.
[0054]
Next, a case where the reflectance R is larger than the threshold value, that is, a case where the emissivity ε is small, as shown in FIG.
[0055]
When the reflectance R is larger than the threshold value, that is, as the emissivity ε is smaller in FIG. 5, the reflectance error has a greater effect on the temperature error. Therefore, as described above, the reflectance R ₀ before processing cannot be used instead, and the reflectance R during processing needs to be accurately measured. In this case, since the reflectance R during the heat treatment is equal to or higher than the threshold value, which is the measurement limit of the photodetector, basically, the temperature during the heat treatment can be accurately measured.
[0056]
The threshold value in the present embodiment is the reflectance R obtained based on the detection limit of the photodetector, and varies to some extent depending on the type of film applied to the back surface and the temperature during heat treatment. Therefore, in the present embodiment, the threshold value is set to R = 0.02, but is not limited to these values.
[0057]
Further, in the present invention, the method of calculating the temperature based on the emissivity has been described.Since the reflectance can be obtained from the emissivity, the temperature can be calculated using the reflectance, and the emissivity can be measured. It is not limited. Therefore, the reflectance can be measured first, and the temperature can be determined based on the reflectance.
[0058]
【The invention's effect】
According to the present invention, when a wafer is irradiated with light and the wafer temperature is measured based on the reflectance and the reflected light intensity, the temperature measurement error is reduced by changing the temperature measurement method depending on the reflectance on the back surface of the wafer. Can be minimized. For example, if the reflectivity of the backside of the wafer is too low and the emissivity cannot be measured because it exceeds the detection limit of the photodetector, the temperature can be calculated using the emissivity before heat treatment instead. I can do it.
[Brief description of the drawings]
FIG. 1 is a view showing a hot wall type heat treatment apparatus. FIG. 2 is a view showing a relationship between a wafer position and a furnace temperature in the hot wall type heat treatment apparatus. FIG. 3 is a view showing a hot wall type heat treatment apparatus. FIG. 4 is a diagram showing a measurement flow in a hot wall type device. FIG. 5 is a diagram showing a relationship between a temperature error and an emissivity error.
Reference Signs List 1 transfer robot 2 heater 3 elevator 4 pyrometer 5 light detector 6 integrating sphere 7 wafer

Claims (5)

In the system that measures the wafer temperature based on the emissivity obtained by irradiating the light on the back surface of the wafer and the thermal radiation energy from the wafer,
When the emissivity on the back surface of the wafer is outside the detection range of the photodetector, the wafer temperature is measured using the emissivity measured before the heat treatment step. In the system that measures the wafer temperature based on the emissivity obtained by irradiating the light on the back surface of the wafer and the thermal radiation energy from the wafer,
If the emissivity on the back side of the wafer is within the detection range of the photodetector, measure the wafer temperature using the emissivity measured during the heat treatment step,
When the emissivity on the back surface of the wafer is outside the detection range of the photodetector, the wafer temperature is measured using the emissivity measured before the heat treatment step. The method according to claim 1, wherein the photodetector is out of a detection range when the emissivity is 0.98 or more. 3. The method according to claim 1, wherein the lower surface of the wafer has a low-reflectance film exposed. The method according to claim 4, wherein the low-reflectivity film is made of SiN, TEOS, or SiC.

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