JP4064533B2 - Wafer potential distribution measuring apparatus and potential distribution measuring method - Google Patents

Description

【００１６】
（数１）より、絶縁膜中の電荷分布をｑ０で一定とすると（数２）、（数３）となる。
【００１７】
【数２】

【００１８】
【数３】

【００１９】
（数２）、（数３）においてエアギャップＧは絶縁膜３の厚さよりもはるかに大きく、ｔ０＜＜ｔ１であるから、（数４）、（数５）となる。
【００２０】
【数４】

【００２１】
【数５】

【００２２】
よって（数３）は近似式（数６）となる。
【００２３】
【数６】

【００２４】
（数６）から、エアギャップＧが絶縁膜３の厚さよりかなり大きい場合、Ｑはｔ１（エアギャップ）には依存しないことになる。また、絶縁膜３の膜厚の変動がエアギャップＧを介して静電的に結合している電極５に検出される電圧に対しての影響を考えると、表裏両面に絶縁膜が付いている場合の図８の等価回路において、絶縁膜表面に誘起される電圧Ｖは（数７）となる。
【００２５】
【数７】

【００２６】
そして電極５に検出される電圧（測定電圧）Ｖ１は（数８）になる。
【００２７】
【数８】

【００２８】
ここで、（数８）よりエアギャップ、膜厚が変動した場合の変化をそれぞれの場合計算すると、仮にエアギャップを３ｍｍ、膜厚を４０００Åとして、その膜厚が１０％薄く変動した場合、電極５に検出される電圧の変化は０．０２％の減となり、また、エアーギャップが１０％近づいた場合は、電極５に検出される電圧の変化は１０％の増となる。従って、絶縁膜表面に誘起される電荷Ｑによる表面電位を所定以上のエアギャップを介して静電的に結合して測定することは、絶縁膜厚の変動による影響はほとんどなく、ウェハの反り等の影響でエアギャップの距離が変動した場合の電極に検出される電圧の変化のみが問題となり、その変動を補正しさえすれば、半導体ウェハ表面の絶縁膜がプラズマに曝される場合等により溜まった電荷に比例した電圧を正確に検出できることになる。
【００２９】
また、測定に用いる絶縁膜の厚さは、実デバイスの絶縁膜の厚さではかなり低い電圧になる為、４０００〜６０００オングストロームが好ましく、更には５０００オングストローム程度が望ましい。これは、絶縁膜表面に誘起される表面電位が最も大きくなるのは上記数値の膜厚であることが実験的に分かったことによる。
【００３０】
次に、図１〜図６を参照して、本発明の実施の形態を説明する。図１はウェハの電位分布測定装置の構成図であって、図７と同一要素には同一符号を付して説明は省略する。
【００３１】
テーブル３にはスイッチ部１１が接続されている。スイッチ部１１は可変接点１２と固定接点１３，１４があり、補正電圧電源１５と接地１６を選択的に切り換える。符号１１〜１６で示されるこれらの要素は、テーブル４を接地状態と電圧印加状態に選択的に切り換える電圧印加状態切り換え手段となっている。またテーブル４には校正用の電極１７が設けられている。電極１７は校正電源１８に接続されている。電極５は紙面に垂直な方向に複数個配置されている。校正電極１７はこれらの電極５のキャリブレーションを行う。
【００３２】
次に、ウェハ１の表面電位分布の測定方法を説明する。図１において、ウェハ１の表面電位の測定は、モータ９を駆動してウェハ１を電極５に対して水平方向へ往動（矢印Ａ）・復動（矢印Ｂ）させながら行う。往動時と復動時で接点を切り換える。すなわち往動時には可変接点１２を一方の固定接点１３側に投入してテーブル４を接地させ、接地状態での電圧を電極５で測定する。また復動時には可変接点１２を他方の固定接点１４側に投入し、テーブル４に電圧を印加する。この電圧の大きさはＶａであり、この電圧Ｖａを補正電圧という。勿論、往動時には固定接点１４側に投入し、復動時に固定接点１３側に投入してもよい。このように往動時と復動時で接地状態と電圧印加状態を切り換えることにより、電圧測定を作業性よく行うことができる。
【００３３】
図３は、図１において実線で示すウェハ１のように、ウェハ１に反りがない場合の電極５による電圧の測定結果を示しており、また図４は、図１において鎖線で示すウェハ１のように、ウェハ１に反りがある場合の電極５による電圧の測定結果を示している。移動距離とは電極５に対するウェハ１の相対的な移動距離である。なお本形態では、ウェハ１を電極５に対して移動させているが、電極５をウェハ１に対して移動させてもよい。
【００３４】
図３はウェハ１に反りがない場合であり、この場合接地状態の測定電圧Ｖｏ’と電圧印加状態の測定電圧Ｖａ’はウェハ１の場所的なばらつきはなく、一定である。ＶｄはＶａ’とＶｏ’の差であり、制御部６で演算して求める。
【００３５】
図４はウェハ１に反りがある場合である。この場合、図１において鎖線で示すウェハ１の端部のエアギャップＧ’は小さく、電極５との距離は小さいので、測定値は大きくなり、したがってＶｏ’とＶａ’は図４に示すカーブとなる。ＶｄはＶａ’とＶｏ’の差である。
【００３６】
そこでその比α＝Ｖｄ／Ｖａ’を補正係数として制御部６で演算して求める。図５および図６において、ウェハ１に反りがなくてエアギャップＧが一定の場合は、印加された電圧に比例した電圧Ｖａ’が電極５で検出され、その差として印加電圧Ｖａと同じ電圧を測定することになるので、α＝Ｖｄ／Ｖａ’＝１となる。
【００３７】
一方、ウェハ１に反りがあるとエアギャップＧは変動し、エアギャップが小さくなると、α＞１となり、これと反対にエアギャップが大きくなるとα＜１となる。
【００３８】
ここで、（数８）をエアギャップの距離をｄとして表し、その他の条件は一定として展開すると、測定電圧は次式となる。
Ｖ１＝６３３５．６３・Ｑ／ｄ
つまり、単純にエアギャップの距離ｄに反比例することになり、電極とウェハの反り等がなく表面との間に一定の間隔を隔てて平行に保持されているエアギャップの基準距離をｄ０、そしてウェハの反り等がある場合のエアギャップの距離をｄ１とすると、
α＝Ｖｄ／Ｖａ＝ｄ０／ｄ１
となる。そして、テーブル４が接地状態のときの測定電圧をＶｉとすると、
Ｖｉ＝６３３５．６３・Ｑ／ｄ１
であるから、エアギャップの距離の変動のない基準距離をｄ０の時の正確な電圧をＶｏとすると、
Ｖｏ＝６３３５．６３・Ｑ／ｄ０
となる。ここで、ｄ０＝α・ｄ１であるから、

となる。従って、印加電圧をＶａ、接地時の測定電圧と電圧印加時の測定電圧との差分の測定値をＶｄの比αを求め、移動可能なテーブル４が接地時の測定電圧をαで除する事で、エアギャップの距離の変動を補正した正確な電圧を求める事ができる。
【００３９】
以上酸化膜付きウェハについて説明したが、表面のみ酸化膜付きウェハの場合も同様に扱う事ができる。実際の測定では、エッチングやアッシング等に用いられているプラズマ処理や、イオン注入、プラズマＣＶＤ等の不純物導入、また洗浄処理を行う前に、被測定の酸化膜付きウェハの初期状態の電荷の蓄積状態を本測定装置で行った後、処理後、再び本測定装置で測定を行い、その二つの測定値の差で工程処理の際に蓄積した電荷による電位を求める様にするが、工程処理に依って、ウェハの反りの状態がたとえ変化しても、本測定装置の距離補正を用いる事で正確に工程処理の際に蓄積した電荷による電位を求める事が出来る。
【００４０】
この補正方法の特徴は、単一の電極の測定の補正であろうが、同一面に一列に配置した複数の電極での測定であろうが、補正のための機構は同一で、測定点数が増えても何ら付加する必要はなく、ただ各電極の出力毎にソフト上で補正を行うだけで良いことである。つまり、電極を複数使用した場合でも、同一条件で距離補正が出来る為、より精度向上がはかれる。以上の様に、半導体ウェハ表面の絶縁膜に蓄積した電荷による電位分布を高速に、且つ、正確に測定することができる。
【００４１】
【発明の効果】
以上説明したように本発明によれば、ウェハの反りに起因する表面電位分布のばらつきを検出・補正し、表面電位分布を高速度で精度良く測定することができる。また距離補正に着目することにより、ウェハの反りの状態も測定することができる。
【図面の簡単な説明】
【図１】ウェハの電位分布測定装置の構成図
【図２】ウェハの部分拡大断面図
【図３】ウェハに反りがない場合の電圧波形図
【図４】ウェハに反りがある場合の電圧波形図
【図５】ウェハに反りがある場合と反りがない場合の電位差波形図
【図６】電位差の比として求められる補正係数図
【図７】一般的なウェハの電位分布測定装置の構成図
【図８】ウェハと電極の等価回路図
【図９】（ａ）電圧測定の模型図
（ｂ）電荷分布図
【符号の説明】
１ ウェハ
２ 半導体ウェハ
３ 絶縁膜（酸化膜）
４ テーブル
５ 電極
６ 制御部
７ ナット
８ 送りねじ
９ モータ
１１ スイッチ部
１５ 補正電圧電源
１６ 接地
Ｇ，Ｇ’ エアギャップ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wafer potential distribution measuring apparatus and a potential distribution measuring method for measuring a potential distribution due to charges accumulated in an insulating film on a wafer surface.
[0002]
[Prior art]
Charges are accumulated in the insulating film on the surface of a semiconductor wafer in a plasma processing process used for etching or ashing, an impurity introduction process such as ion implantation or plasma CVD, or a cleaning process in a semiconductor manufacturing process. It has been known. This charge accumulation state varies depending on the individual processing apparatus, and also varies depending on the adjustment state of these apparatuses. Therefore, in order to monitor and manage the state of these apparatuses, insulation of the entire surface of the semiconductor wafer is performed. Measuring the charge distribution of the membrane is performed.
[0003]
[Problems to be solved by the invention]
In device management at the semiconductor manufacturing process site, conventionally, a surface potential probe was brought close to the wafer to be measured and the surface potential distribution due to the charge in the insulating film on the surface of the semiconductor wafer was measured. The surface potential distribution could not be measured accurately and accurately due to the warp of the wafer, such as the warp of the wafer before and after the process, or the warp of the table holding the wafer for measurement.
[0004]
Accordingly, an object of the present invention is to provide a wafer potential distribution measuring apparatus and a potential distribution measuring method capable of easily and accurately measuring the potential distribution due to the charge of the insulating film even when the wafer is warped. .
[0005]
[Means for Solving the Problems]
The present invention relates to a table for holding a wafer, an electrode for voltage measurement arranged with an air gap from the wafer, a moving means for moving the wafer relative to the electrode, and the table in a grounded state. And voltage application state switching means for selectively switching to the voltage application state, and a control for correcting the measurement voltage by calculating the difference between the measurement voltage in the ground state and the measurement voltage in the voltage application state and obtaining the ratio of the difference And a wafer potential distribution measuring apparatus.
[0006]
In the present invention, a wafer coated with an insulating film held on a table is moved relative to the electrode for voltage measurement with an air gap, and the table is brought into a grounded state during the movement. By selectively switching to the voltage application state, the difference between the measurement voltage in the ground state and the measurement voltage in the voltage application state is calculated by the control unit, and the ratio of this difference is obtained to obtain the measurement voltage caused by the warpage of the wafer. This is a method for measuring the potential distribution of a wafer, wherein the deviation of the wafer is corrected.
[0007]
Preferably, the wafer moves forward / backward with respect to the electrode, and selectively switches between a ground state and a voltage application state during forward movement and backward movement.
[0008]
Preferably, the insulating film has a thickness of 4000 to 5000 angstroms.
[0009]
[Action]
In the above configuration, the table is switched between the ground state and the voltage application state while moving the wafer relative to the voltage measurement electrode with an air gap, and the voltage in each case is measured. Then, the difference between the measurement voltage in the ground state and the measurement voltage in the voltage application state is calculated by the control unit, and the difference in the measurement voltage due to the warpage of the wafer is corrected by calculating the ratio of the difference.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 is a configuration diagram of a wafer potential distribution measuring apparatus according to an embodiment of the present invention, FIG. 2 is a partially enlarged sectional view of the wafer, FIG. 3 is a voltage waveform diagram when the wafer is not warped, and FIG. 4 is a warp of the wafer. FIG. 5 is a potential difference waveform diagram when the wafer is warped and when there is no warp, FIG. 6 is a correction coefficient diagram obtained as a ratio of potential differences, and FIG. 7 is a general wafer potential distribution. FIG. 8 is an equivalent circuit diagram of the wafer and electrodes, FIG. 9A is a model diagram of voltage measurement, and FIG. 9B is a charge distribution diagram.
[0011]
First, a general principle of measuring the potential distribution of a wafer will be described with reference to FIGS. In FIG. 7, a wafer 1 is formed by coating an entire surface of a semiconductor wafer 2 with an insulating film (oxide film) 3 (see FIG. 2). The wafer 1 is held on the table 4 in a horizontal posture. The table 4 is made of a conductive plate and is grounded 16.
[0012]
Above the wafer 1, an electrode 5, which is an element for measuring voltage, is provided with an air gap (distance) G. The electrode 5 is connected to the control unit 6. The control unit 6 performs necessary calculations. A nut 7 is attached to the lower surface of the table 4, and a feed screw 8 is screwed horizontally into the nut 7. When the feed screw 8 is rotated by driving the motor 9, the table 4 moves horizontally along the feed screw 8 and the wafer 1 moves horizontally with respect to the electrode 5. That is, the nut 7, the feed screw 8 and the motor 9 are moving means for moving the wafer 1 relative to the electrode 5. Reference numeral 17 is a calibration electrode, and 18 is a calibration power source.
[0013]
The apparatus wafer 1 and the electrode 5 in FIG. 7 are represented by the equivalent circuit in FIG. In the figure, C1 is the capacitance of the backside oxide film (insulating film) of the wafer 1, C0 is the capacitance of the wafer 1, C2 is the capacitance of the surface oxide film (insulating film), and C3 is the static air gap G. The capacitance C4 is the capacitance of the electrode 5.
[0014]
Since the charge in the insulating film is large at the interface and at the outermost surface and is almost uniformly distributed in the insulating film, the case where the wafer 1 to be measured and the electrode 5 for potential measurement are connected via the air gap G 9A has a structure as shown in FIG. 9A, and as shown in FIG. 9B, when an electrostatic charge is assumed, the charge Q induced on the surface of the insulating film becomes (Equation 1).
[0015]
[Expression 1]

[0016]
From (Equation 1), when the charge distribution in the insulating film is constant at q0, (Equation 2) and (Equation 3) are obtained.
[0017]
[Expression 2]

[0018]
[Equation 3]

[0019]
In (Equation 2) and (Equation 3), since the air gap G is much larger than the thickness of the insulating film 3 and t0 << t1, (Equation 4) and (Equation 5) are obtained.
[0020]
[Expression 4]

[0021]
[Equation 5]

[0022]
Therefore, (Equation 3) becomes an approximate expression (Equation 6).
[0023]
[Formula 6]

[0024]
From (Equation 6), when the air gap G is considerably larger than the thickness of the insulating film 3, Q does not depend on t1 (air gap). Considering the influence of the fluctuation of the film thickness of the insulating film 3 on the voltage detected by the electrode 5 that is electrostatically coupled through the air gap G, the insulating film is attached to both the front and back surfaces. In the equivalent circuit of FIG. 8 in this case, the voltage V induced on the surface of the insulating film is (Expression 7).
[0025]
[Expression 7]

[0026]
The voltage (measurement voltage) V1 detected by the electrode 5 is (Equation 8).
[0027]
[Equation 8]

[0028]
Here, when the change in the case where the air gap and the film thickness fluctuate are calculated from (Equation 8), if the air gap is 3 mm and the film thickness is 4000 mm, and the film thickness fluctuates 10%, the electrode The voltage change detected at 5 is reduced by 0.02%, and when the air gap approaches 10%, the voltage change detected at the electrode 5 is increased by 10%. Therefore, the surface potential due to the charge Q induced on the surface of the insulating film is measured by being electrostatically coupled through an air gap of a predetermined value or more, and is hardly affected by the variation of the insulating film thickness. The only problem is the change in the voltage detected at the electrodes when the air gap distance fluctuates due to the influence of the air gap, and if the fluctuation is corrected, it accumulates when the insulating film on the surface of the semiconductor wafer is exposed to plasma. Thus, a voltage proportional to the charged charge can be detected accurately.
[0029]
In addition, the thickness of the insulating film used for measurement is preferably 4000 to 6000 angstroms, more preferably about 5000 angstroms because the thickness of the insulating film of the actual device is a considerably low voltage. This is because it has been experimentally found that the surface potential induced on the surface of the insulating film is the largest in the above numerical values.
[0030]
Next, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of a wafer potential distribution measuring apparatus. The same components as those in FIG.
[0031]
A switch unit 11 is connected to the table 3. The switch unit 11 has a variable contact 12 and fixed contacts 13 and 14 and selectively switches between the correction voltage power supply 15 and the ground 16. These elements indicated by reference numerals 11 to 16 serve as voltage application state switching means for selectively switching the table 4 between a ground state and a voltage application state. The table 4 is provided with a calibration electrode 17. The electrode 17 is connected to a calibration power source 18. A plurality of electrodes 5 are arranged in a direction perpendicular to the paper surface. The calibration electrode 17 calibrates these electrodes 5.
[0032]
Next, a method for measuring the surface potential distribution of the wafer 1 will be described. In FIG. 1, the surface potential of the wafer 1 is measured while driving the motor 9 to move the wafer 1 forward (arrow A) / reverse (arrow B) with respect to the electrode 5 in the horizontal direction. Switch contacts between forward and backward movements. That is, at the time of forward movement, the variable contact 12 is inserted into the one fixed contact 13 side to ground the table 4, and the voltage in the grounded state is measured by the electrode 5. Further, at the time of reverse movement, the variable contact 12 is inserted into the other fixed contact 14 side, and a voltage is applied to the table 4. The magnitude of this voltage is Va, and this voltage Va is called a correction voltage. Of course, it may be supplied to the fixed contact 14 side during forward movement and may be input to the fixed contact 13 side during backward movement. Thus, voltage measurement can be performed with good workability by switching between the ground state and the voltage application state during forward movement and reverse movement.
[0033]
FIG. 3 shows the measurement result of the voltage by the electrode 5 when the wafer 1 is not warped like the wafer 1 shown by the solid line in FIG. 1, and FIG. 4 shows the wafer 1 shown by the chain line in FIG. Thus, the measurement result of the voltage by the electrode 5 when the wafer 1 is warped is shown. The moving distance is a relative moving distance of the wafer 1 with respect to the electrode 5. In this embodiment, the wafer 1 is moved with respect to the electrode 5, but the electrode 5 may be moved with respect to the wafer 1.
[0034]
FIG. 3 shows a case where the wafer 1 is not warped. In this case, the measurement voltage Vo ′ in the ground state and the measurement voltage Va ′ in the voltage application state are constant without variation in the location of the wafer 1. Vd is the difference between Va ′ and Vo ′ and is calculated by the control unit 6.
[0035]
FIG. 4 shows a case where the wafer 1 is warped. In this case, the air gap G ′ at the end of the wafer 1 indicated by the chain line in FIG. 1 is small and the distance from the electrode 5 is small, so that the measured value becomes large. Therefore, Vo ′ and Va ′ are the curves shown in FIG. Become. Vd is the difference between Va ′ and Vo ′.
[0036]
Therefore, the control unit 6 calculates the ratio α = Vd / Va ′ as a correction coefficient. 5 and 6, when the wafer 1 is not warped and the air gap G is constant, a voltage Va ′ proportional to the applied voltage is detected by the electrode 5, and the difference is the same voltage as the applied voltage Va. Since it is to be measured, α = Vd / Va ′ = 1.
[0037]
On the other hand, if the wafer 1 is warped, the air gap G fluctuates. If the air gap becomes smaller, α> 1. On the contrary, if the air gap becomes larger, α <1.
[0038]
Here, when (Expression 8) is expressed with the distance of the air gap as d and the other conditions are fixed, the measurement voltage is expressed by the following equation.
V1 = 633.63 · Q / d
That is, it is simply inversely proportional to the distance d of the air gap, d0 is the reference distance of the air gap that is held in parallel with a certain distance between the electrode and the surface without warping of the wafer, and the like. When the distance of the air gap when there is a warp of the wafer is d1,
α = Vd / Va = d0 / d1
It becomes. And when the measurement voltage when the table 4 is in the ground state is Vi,
Vi = 633.63 · Q / d1
Therefore, when the reference voltage without fluctuation of the air gap distance is d0 and the accurate voltage is Vo,
Vo = 633.63 · Q / d0
It becomes. Here, since d0 = α · d1,

It becomes. Therefore, the applied voltage is Va, the measured value of the difference between the measured voltage when the voltage is applied and the measured voltage when the voltage is applied is obtained as a ratio α of Vd, and the movable table 4 divides the measured voltage when grounded by α. Thus, it is possible to obtain an accurate voltage in which the variation of the air gap distance is corrected.
[0039]
Although the wafer with the oxide film has been described above, the wafer with the oxide film only on the surface can be handled in the same manner. In actual measurement, the initial charge accumulation of the wafer with oxide film to be measured is performed before the plasma treatment used for etching, ashing, etc., the introduction of impurities such as ion implantation and plasma CVD, and the cleaning treatment. After performing the state with this measuring device, after processing, measure again with this measuring device, and find the potential due to the electric charge accumulated during process processing by the difference between the two measured values. Therefore, even if the state of warping of the wafer changes, the potential due to the electric charge accumulated during the process processing can be accurately obtained by using the distance correction of this measuring apparatus.
[0040]
The feature of this correction method will be correction of measurement of a single electrode or measurement of multiple electrodes arranged in a line on the same plane, but the mechanism for correction is the same and the number of measurement points is the same. It is not necessary to add anything even if it increases, and it is only necessary to perform correction on the software for each output of each electrode. That is, even when a plurality of electrodes are used, since the distance can be corrected under the same conditions, the accuracy can be further improved. As described above, the potential distribution due to the charges accumulated in the insulating film on the surface of the semiconductor wafer can be measured at high speed and accurately.
[0041]
【The invention's effect】
As described above, according to the present invention, it is possible to detect and correct variations in the surface potential distribution caused by wafer warpage, and to measure the surface potential distribution with high speed and high accuracy. Further, by paying attention to the distance correction, the state of warpage of the wafer can also be measured.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a wafer potential distribution measuring apparatus. FIG. 2 is a partially enlarged sectional view of a wafer. FIG. 3 is a voltage waveform diagram when the wafer is not warped. FIG. 4 is a voltage waveform when the wafer is warped. FIG. 5 is a potential difference waveform diagram when the wafer is warped and when there is no warpage. FIG. 6 is a correction coefficient diagram obtained as a ratio of potential differences. FIG. 7 is a configuration diagram of a general wafer potential distribution measuring device. [Fig. 8] Equivalent circuit diagram of wafer and electrode [Fig. 9] (a) Model diagram of voltage measurement (b) Charge distribution diagram [Explanation of symbols]
1 Wafer 2 Semiconductor Wafer 3 Insulating film (oxide film)
4 Table 5 Electrode 6 Control part 7 Nut 8 Feed screw 9 Motor 11 Switch part 15 Correction voltage power supply 16 Ground G, G 'Air gap

Claims (4)

A table for holding the wafer, an electrode for voltage measurement arranged with an air gap from the wafer, a moving means for moving the wafer relative to the electrode, and a grounding state and a voltage application state of the table A voltage application state switching means for selectively switching to the control circuit, and a control unit for calculating a difference between the measurement voltage in the ground state and the measurement voltage in the voltage application state and correcting the measurement voltage by obtaining a ratio of the difference. An apparatus for measuring a potential distribution of a wafer. A wafer coated with an insulating film held on a table is moved relative to this electrode with an electrode gap for voltage measurement and an air gap, and during this movement, the table is selected between a ground state and a voltage application state. The difference between the measured voltage in the grounded state and the measured voltage in the applied voltage state is calculated by the control unit, and the deviation of the measured voltage caused by the warpage of the wafer is corrected by calculating the ratio of the difference. A method for measuring a potential distribution of a wafer. 3. The wafer potential according to claim 2, wherein the wafer moves forward and backward with respect to the electrode, and selectively switches between a ground state and a voltage application state during forward movement and backward movement. Distribution measurement method. 3. The wafer potential distribution measuring method according to claim 2, wherein a thickness of the insulating film is 4000 to 5000 angstroms.

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