JPH0545294A - Foreign matter sensing system using floating threshold - Google Patents
Foreign matter sensing system using floating thresholdInfo
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- JPH0545294A JPH0545294A JP22882991A JP22882991A JPH0545294A JP H0545294 A JPH0545294 A JP H0545294A JP 22882991 A JP22882991 A JP 22882991A JP 22882991 A JP22882991 A JP 22882991A JP H0545294 A JPH0545294 A JP H0545294A
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- Prior art keywords
- foreign matter
- threshold value
- threshold
- pixel
- pixel signal
- Prior art date
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Abstract
Description
【0001】[0001]
【産業上の利用分野】この発明は、ウエハ異物検査装置
において、浮動閾値により異物を検出する方式に関する
ものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of detecting foreign matter by a floating threshold in a wafer foreign matter inspection apparatus.
【0002】[0002]
【従来の技術】半導体ICの製造においてはシリコンな
どの素材のウエハに対して、同一のパターンを有する多
数のICチップ(以下単にチップという)が形成され、
この段階で異物検査が行われる。異物検査はレーザビー
ムをウエハ面に投射し、その反射または散乱光を受光し
てなされるが、異物とともにパターンからも反射光が反
射されるので、これらを区別して異物のみを検出するこ
とが必要、かつ重要である。これに適応する方法には各
種のものが開発されているが、その一つとして互いに隣
接した2個のチップを相互に比較する方法がある。2. Description of the Related Art In the manufacture of semiconductor ICs, a large number of IC chips (hereinafter simply referred to as chips) having the same pattern are formed on a wafer made of a material such as silicon.
A foreign matter inspection is performed at this stage. The foreign matter inspection is performed by projecting a laser beam onto the wafer surface and receiving the reflected or scattered light, but since the reflected light is reflected from the pattern along with the foreign matter, it is necessary to distinguish them and detect only the foreign matter. , And is important. Various methods have been developed to adapt to this, and one of them is a method of comparing two chips adjacent to each other.
【0003】図2(a) 〜(c) は上記の異物検査装置の概
略構成と隣接チップの比較による異物検出方法を示す。
(a) に示すように、ウエハ1の表面にはオリエンティシ
ョン・フラット(OF)を基準線(X軸とする)とし
て、同一パターンを有する多数のチップ11がマトリック
ス状に形成されている。(b) において、ウエハは移動ス
テージ2に載置され、これに対して検査光学系3の光源
3a よりレーザビームLX をウエハの表面に照射する。
ウエハはX方向に往復移動されてレーザビームが各チッ
プ列を順次に走査し、その散乱光が対物レンズ3b を経
てCCDセンサ3c (他の光センサでも可)に入力す
る。ここで、チップ列中の隣接した任意の2個のチップ
を(c) の(イ) のように11a,11b とし、チップ11b には図
示の位置に異物p1,p2 が付着しているとする。まずチ
ップ11a の散乱光を受光し、CCDセンサの各画素の出
力信号(画素信号)は逐次に画素信号処理部4に入力
し、A/D変換器4a によりデジタル化され、メモリ
(MEM)4b に記憶される。ついでチップ11b の散乱
光より同様にえられる各画素信号が差分回路4c に入力
し、MEMに記憶されているチップ11a の各画素信号と
の差分データが出力される。(c) の(ロ) は両チップのパ
ターンPT および異物p1,p2 に対する各画素信号gn
(nは画素番号)よりなる画素データSa,Sb を示し、
パターンの無い基板面Kでは値が低く、パターンPT は
反射率が大きいので値が大きい。また、異物p1,p2 の
画素信号gはデータSb の上方に突出している。前記し
たように両パターンPT は同一であるので、両画素デー
タのパターン部分はほぼ同一となり、両者の差分をとる
とこれがほぼ消去されて、(ハ) に例示する差分データ
(Sb −Sa)がえられる。差分データは異物検出部4d
において適当な閾値Vthと比較されて異物p1,p2 が検
出される。なお、チップ11a にある異物は差分データ
(Sb−Sa)では負極となるが、前位のチップとの比較
においては反転し、または絶対値をとることにより正極
として上記と同様に検出される。以上により検出された
異物データはコンピュータ(CPU)4e により編集さ
れて表示器4f にマップ表示される。2 (a) to 2 (c) show a schematic structure of the above-mentioned foreign substance inspection apparatus and a foreign substance detecting method by comparing adjacent chips.
As shown in (a), a large number of chips 11 having the same pattern are formed in a matrix on the surface of the wafer 1 with the orientation flat (OF) as a reference line (X axis). In (b), the wafer is placed on the moving stage 2, and the surface of the wafer is irradiated with the laser beam L X from the light source 3 a of the inspection optical system 3.
The wafer is reciprocally moved in the X direction so that the laser beam sequentially scans each chip row, and the scattered light is input to the CCD sensor 3c (or another optical sensor) via the objective lens 3b. Here, arbitrary two adjacent chips in the chip row are set as 11a and 11b as shown in (c) of (a), and the foreign substances p 1 and p 2 are attached to the chip 11b at the illustrated positions. And First, the scattered light of the chip 11a is received, and the output signal (pixel signal) of each pixel of the CCD sensor is sequentially input to the pixel signal processing unit 4, digitized by the A / D converter 4a, and stored in the memory (MEM) 4b. Memorized in. Then, each pixel signal similarly obtained from the scattered light of the chip 11b is input to the difference circuit 4c, and the difference data with each pixel signal of the chip 11a stored in the MEM is output. (b) of (c) is the pixel signal g n for the patterns P T of both chips and the foreign substances p 1 , p 2 .
Pixel data S a , S b consisting of (n is a pixel number)
The value is low on the substrate surface K having no pattern, and the pattern P T has a large value because the reflectance is large. Further, the pixel signals g of the foreign substances p 1 and p 2 are projected above the data S b . As described above, since both patterns P T are the same, the pattern portions of both pixel data are almost the same, and when the difference between the two is taken, this is almost erased and the difference data (S b −S) illustrated in (c) a ) is obtained. The difference data is the foreign matter detection unit 4d.
Then, the foreign matters p 1 and p 2 are detected by comparing with an appropriate threshold value V th . Although the foreign matter on the chip 11a has a negative polarity in the difference data (S b −S a ), it is detected as a positive polarity in the same manner as above by reversing or taking an absolute value in comparison with the preceding chip. It The foreign matter data detected as described above is edited by the computer (CPU) 4e and displayed on the display 4f as a map.
【0004】[0004]
【発明が解決しようとする課題】上記においては、差分
データ(Sb −Sa)にはパターン部分が完全に消去され
ず、残留パターンRが残留している。この理由は、両チ
ップのパターンが同一であっても、例えば照射位置によ
るレーザビームの強度変化などにより対応した両画素信
号gがかならずしも同一とならないからである。一方、
チップパターンはプロセスの段階が進行するにつれて厚
さが逐次に厚くなって散乱光が増加するもので、このた
めに残留パターンRもプロセスの段階により変化する。
このような差分データより異物p1,p2 などを検出する
閾値Vthは、残留パターンRを検出することなく、異物
のみを検出するように最適値を設定することが必要であ
る。これに対して従来においては、プロセスごとに任意
の隣接チップをとってテストチップとし、手作業により
閾値を増減しながら異物検出を繰り返して最適値を求め
る方法が行われている。しかしこの方法では最適値がか
ならずしもえられず、また作業時間が長くかかる欠点が
あるので、これを自動化する提案もある。しかしなが
ら、いずれの方法によるとも閾値を固定値とする限り、
上記のように波高値が変動する差分データの各画素信号
に対して適切ではない。図3は固定閾値の欠点を説明す
るもので、(a) において、差分データの絶対値|(Sa
−Sb)|をとり、これに異物p1 〜p3 があるとする。
p1,p2 に対しては閾値Vth1 が適切であるが、これで
はp3 は検出されない。そこで、閾値をVth2 としてp
3 を検出するときは、残留パターンRが余分に検出され
て虚報となる。従って、各画素信号gn のレベルLV に
追従して値が変化する浮動閾値が望ましく、これにより
異物の検出性能を向上することができる。次に、パター
ンのエッジによる散乱光の問題がある。図3(b) の(イ)
において、レーザビームLの照射方向は、パターンPT
の表面Rの正反射光がCCDセンサに入射することを避
けるため、ウエハ1に対して低角度θとされている。し
かし、パターンのエッジEにおいては無指向性の強い散
乱光が散乱し、CCDセンサより(ロ)のような波高値と
幅が大きい画素信号が出力されるので、異物検出が妨害
される。このようなエッジ散乱光の画素信号を排除でき
る浮動閾値方式とすることが必要とされている。この発
明は以上に鑑みてなされたもので、残留パターンの各画
素信号に追従してレベルが変化する浮動閾値により、残
留パターンとエッジ散乱光の画素信号をともに排除でき
る異物検出方式を提供することを目的とする。In the above [0006] is not completely erased the pattern portion to the difference data (S b -S a), the residual pattern R is left. The reason is that even if the patterns of both chips are the same, the corresponding pixel signals g are not always the same due to, for example, the intensity change of the laser beam depending on the irradiation position. on the other hand,
The chip pattern has a thickness that increases successively as the process steps progress, and scattered light increases. Therefore, the residual pattern R also changes depending on the process step.
It is necessary to set the optimum value for the threshold value V th for detecting the foreign matter p 1 , p 2, etc. from such difference data so that only the foreign matter is detected without detecting the residual pattern R. On the other hand, conventionally, a method has been used in which an arbitrary adjacent chip is taken as a test chip for each process, and foreign matter detection is repeated while manually increasing or decreasing the threshold value to obtain an optimum value. However, this method has the drawback that the optimum value cannot always be obtained and the working time is long, so there is a proposal to automate this. However, as long as the threshold is fixed by either method,
As described above, it is not appropriate for each pixel signal of the difference data whose peak value varies. FIG. 3 illustrates the drawback of the fixed threshold. In (a), the absolute value of the difference data | (S a
-S b ) | is taken, and it is assumed that there are foreign matter p 1 to p 3 in this.
The threshold value V th1 is appropriate for p 1 and p 2 , but p 3 is not detected by this. Therefore, the threshold is set to V th2 and p
When 3 is detected, the residual pattern R is additionally detected and becomes a false alarm. Therefore, a floating threshold value whose value changes in accordance with the level L V of each pixel signal g n is desirable, which can improve the foreign matter detection performance. Second, there is the problem of scattered light due to the edges of the pattern. (A) in Fig. 3 (b)
, The irradiation direction of the laser beam L is the pattern P T
In order to prevent the specularly reflected light on the surface R of the wafer from entering the CCD sensor, it is set at a low angle θ with respect to the wafer 1. However, strong non-directional scattered light is scattered at the edge E of the pattern, and a pixel signal having a large peak value and a large width as shown in (b) is output from the CCD sensor, which hinders foreign matter detection. There is a need for a floating threshold method that can eliminate such pixel signals of edge scattered light. The present invention has been made in view of the above, and provides a foreign matter detection method capable of eliminating both a residual pattern and a pixel signal of edge scattered light by a floating threshold whose level changes in accordance with each pixel signal of the residual pattern. With the goal.
【0005】[0005]
【課題を解決するための手段】この発明は上記の目的を
達成する浮動閾値による異物検出方式であって、上記の
異物検査装置において、隣接チップの対応する両画素信
号の小さい方を選択し、選択された画素信号に対して1
より小さい一定の係数を乗じて第1の閾値とする。ま
た、両画素信号をそれぞれ微分した微分信号の小さい方
を選択し、選択された微分信号に対して、微分信号の大
きさが大きい程大きい値の非直線の係数を乗じて第2の
閾値とする。第1の閾値と第2の閾値を加算して浮動閾
値とし、浮動閾値に対して差分データの各画素信号を比
較して異物を検出するものである。SUMMARY OF THE INVENTION The present invention is a floating threshold foreign matter detection system that achieves the above object, wherein in the above foreign matter inspection apparatus, a smaller one of corresponding pixel signals of adjacent chips is selected, 1 for the selected pixel signal
The first threshold value is multiplied by a smaller constant coefficient. Also, a smaller one of the differential signals obtained by differentiating both pixel signals is selected, and the selected differential signal is multiplied by a non-linear coefficient having a larger value as the magnitude of the differential signal is increased to obtain a second threshold value. To do. The first threshold value and the second threshold value are added to make a floating threshold value, and each pixel signal of the difference data is compared with the floating threshold value to detect a foreign substance.
【0006】[0006]
【作用】上記の異物検出方式においては、比較される隣
接チップの対応する画素信号のうちの小さい方が選択さ
れ、これに1より小さい一定の係数を乗じたものが第1
の閾値とされる。ここで、両者のうちの小さい方を選択
する理由は、異物の画素信号はパターンのそれに比較し
て大きいので、画素信号の大きい方を選択すると異物が
検出されなくなるからである。これにより、異物が同一
位置に存在しない限り、浮動閾値は常に、ほぼパターン
の画素信号のレベルとなってパターンが排除され、異物
のみが検出される。In the foreign matter detecting method described above, the smaller one of the corresponding pixel signals of the adjacent chips to be compared is selected, and the one obtained by multiplying this by a constant coefficient smaller than 1 is the first.
Is set as the threshold value of. Here, the reason why the smaller one of the two is selected is that the pixel signal of the foreign matter is larger than that of the pattern, and therefore the foreign matter is not detected if the larger pixel signal is selected. As a result, as long as the foreign matter is not present at the same position, the floating threshold is always at the level of the pixel signal of the pattern, the pattern is eliminated, and only the foreign matter is detected.
【0007】次に第2の閾値は、両画素信号をそれぞれ
微分した微分信号の小さい方を選択し、これに対して上
記の非直線の係数を乗じて作成される。この場合微分信
号をとる理由は、変化が急峻なエッジ散乱光の画素信号
を微分すると、もとの画素信号の大きさに拘らず、その
傾斜角に相当した大きさの微分信号が、散乱光の幅の範
囲に亘ってえられるからである。これに対して大きい非
直線係数が乗ぜられた第2の閾値は、いわばエッジ散乱
光が強調されたものとなる。これによりエッジ散乱光の
幅の範囲にある画素信号の検出が排除される。一方、パ
ターンと異物の画素信号はエッジ散乱光のものより変化
率が小さく、従って微分信号もまた小さいので、これに
乗ぜられる非直線係数は小さくて第2の閾値は0に近い
小数となり、異物検出に支障しない。以上の第1および
第2の閾値は加算されて浮動閾値とされ、差分データの
各画素信号がこれに比較されて、残留パターンの画素信
号に対して第1の閾値が作用して異物が検出され、ま
た、エッジ散乱光の画素信号は第2の閾値により排除さ
れる。Next, the second threshold value is created by selecting the smaller one of the differential signals obtained by differentiating both pixel signals and multiplying it by the above-mentioned nonlinear coefficient. In this case, the reason why the differential signal is taken is that when a pixel signal of edge scattered light having a sharp change is differentiated, the differential signal of a size corresponding to the inclination angle of the scattered light is obtained regardless of the size of the original pixel signal. This is because it can be obtained over the range of width. On the other hand, the second threshold value multiplied by a large non-linear coefficient is, as it were, an edge scattered light is emphasized. This eliminates the detection of pixel signals in the range of the width of the edge scattered light. On the other hand, the pixel signal of the pattern and the foreign matter has a smaller rate of change than that of the edge scattered light, and therefore the differential signal is also smaller. Therefore, the non-linear coefficient multiplied by this is small, and the second threshold is a decimal number close to 0. Does not interfere with detection. The above first and second threshold values are added to each other to form a floating threshold value, each pixel signal of the difference data is compared with this, and the first threshold value acts on the pixel signal of the residual pattern to detect a foreign substance. The pixel signal of the edge scattered light is excluded by the second threshold.
【0008】[0008]
【実施例】図1はこの発明の一実施例を示し、(a) はこ
の発明を適用した異物検査装置の概略のブロック構成
図、(b) はモデル化した画素データと、これに対する第
1の閾値の作成方法の説明図、(c) はエッジ散乱光と、
これに対する第2の閾値の作成方法の説明図である。1 shows an embodiment of the present invention. (A) is a schematic block diagram of a foreign substance inspection apparatus to which the present invention is applied, (b) is modeled pixel data, and An explanatory diagram of the method of creating the threshold of, (c) is edge scattered light,
It is explanatory drawing of the preparation method of the 2nd threshold value with respect to this.
【0009】図1(a) において、異物検査装置は前記し
た図2(b)の異物検査装置の画素信号処理部4に閾値作
成部5を付加して構成される。すなわち、画素信号処理
部のA/D変換器4a とMEM4b がそれぞれ出力する
画素データSb とSa を分岐し、閾値作成部の比較選択
回路(A)5a と、2個の微分回路5d,5e にそれぞれ
入力する。比較選択回路(A)の出力側にMEM(A)
5b が、また、両微分回路には比較選択回路(B)5f
とこれにつづくMEM(B)5g がそれぞれ接続され、
両MEM(A),(B)の出力データは加算器5c を経て
画素信号処理部4の異物検出部4d に入力する。一方、
両画素データは従来と同様に差分回路4c に入力して差
分データが作られ、その絶対値|(Sa −Sb)|が異物
検出部4d に与えられる。In FIG. 1 (a), the foreign matter inspection apparatus is configured by adding a threshold value creating section 5 to the pixel signal processing section 4 of the foreign matter inspection apparatus of FIG. 2 (b) described above. That is, the pixel data S b and S a output by the A / D converter 4 a and the MEM 4 b of the pixel signal processing unit are branched, and the comparison / selection circuit (A) 5 a of the threshold generation unit and the two differentiating circuits 5 d, Enter each in 5e. MEM (A) on the output side of the comparison and selection circuit (A)
5b, and the comparison and selection circuit (B) 5f for both differentiation circuits.
And 5g of MEM (B) following this are connected,
The output data of both MEMs (A) and (B) are input to the foreign matter detection unit 4d of the pixel signal processing unit 4 via the adder 5c. on the other hand,
Both pixel data are input to the difference circuit 4c in the same manner as in the prior art to create difference data, and the absolute value | (S a −S b ) | is given to the foreign matter detector 4d.
【0010】以上の構成による異物検査装置の動作を、
図(a) に(b),(c) を併用して説明する。比較選択回路
(A)5a においては、(b) の(イ) に示した両画素デー
タSa,Sb の対応する画素信号を比較して小さい方のg
1,g2 〜g5 などを選択する。いま、画素データSb が
Saより全体として上側にあるとする。ここで、異物の
存在しない部分の代表として、Sa の画素信号g1 が選
択される。g2 〜g5 は異物が存在する位置の画素信号
を示し、画素信号Sa にある異物pa1はSb より突出し
ているのでSb の画素信号g2 が選択される。異物pb1
は画素データSbにあるが、小さい方のSa の画素信号
g3 が選択される。異物pa2, pb2についても同様に画
素信号g4,g5 が選択される。選択された画素信号の大
きさをアドレス番号としてMEM5b のアドレスを指定
する。MEM5b の各アドレスには、画素信号の大きさ
に、1より小さい適当な係数kを乗じた第1の閾値vs1
が記憶されている。係数kの値としては、もとの画素信
号と差分データの画素信号の比が適当であり、予めの実
験により定めておく。上記の指定により(ロ) に示す、差
分データ|(Sa −Sb)|に対する第1の閾値vth1
(kg1,kg2……)が出力されて加算器5c に入力す
る。一方、隣接チップの対応したパターンエッジに(c)
(イ)で示す散乱光ea,eb があるとし、その画素信号ge
を微分回路5d,5e によりそれぞれ微分すると、(ロ)
に示すレベルがLda,Ldbで、それぞれ複数個の微分信
号da,db がえられる。各微分信号は比較選択回路
(B)5f において比較されて小さい方のdb が選択さ
れ、選択された各微分信号db はその大きさをアドレス
番号としてMEM5g のアドレスを指定する。MEM5
g の各アドレスには、(ハ) に示した微分信号のレベルL
d が大きい程大きい値の非直線の係数ηを乗じた第2の
閾値vs2が記憶されており、上記の指定により(ニ) に示
すレベル(ηLdb)の第2の閾値vth2 が出力されて加
算器に入力する。この場合の非直線係数ηも予めの実験
により定める。以上により加算器5c に入力した第1お
よび第2の閾値vth1,vth2 は加算されて浮動閾値v
thf とされ、異物検出部4d に与えられる。差分データ
|(Sa−Sb)|の各画素信号ごとに浮動閾値が変化
し、両者の比較により異物が検出される。検出された異
物のデータはCPU4eに取り込まれて編集され、表示
器4f にマップ表示されることは従来と同様である。The operation of the foreign matter inspection apparatus having the above configuration
Explanation will be given by using (b) and (c) together with Fig. (A). In the comparison / selection circuit (A) 5a, the corresponding pixel signal of both pixel data S a and S b shown in (a) of (b) is compared and the smaller g
Select 1 , g 2 to g 5, etc. Now, it is assumed that the pixel data S b is above the S a as a whole. Here, the pixel signal g 1 of S a is selected as a representative of the portion where no foreign matter exists. g 2 to g 5 shows a pixel signal of the position where there is the foreign matter, the foreign matter p a1 in the pixel signal S a pixel signal g 2 of S b so protrudes from S b is selected. Foreign object p b1
Is in the pixel data S b , the smaller pixel signal g 3 of S a is selected. Similarly, the pixel signals g 4 and g 5 are selected for the foreign matters p a2 and p b2 . The address of the MEM 5b is designated with the size of the selected pixel signal as an address number. Each address of the MEM5b has a first threshold value v s1 obtained by multiplying the magnitude of the pixel signal by an appropriate coefficient k smaller than 1.
Is remembered. As the value of the coefficient k, the ratio of the original pixel signal and the pixel signal of the difference data is appropriate, and it is determined by an experiment in advance. The first threshold v th1 for the difference data | (S a −S b ) |
(Kg 1 , kg 2 ...) Is output and input to the adder 5c. On the other hand, at the corresponding pattern edge of the adjacent chip (c)
If there are scattered lights e a and e b shown in (a), the pixel signal g e
When is differentiated by differentiating circuits 5d and 5e respectively, (b)
The levels shown by are L da and L db , and a plurality of differential signals d a and d b are obtained respectively. Each differential signal is compared in the comparison / selection circuit (B) 5f and the smaller d b is selected, and each selected differential signal d b designates the address of the MEM 5g with its magnitude as an address number. MEM5
At each address of g, the level L of the differential signal shown in (C)
The second threshold v s2 obtained by multiplying the nonlinear coefficient η having a larger value is stored as d becomes larger, and the second threshold v th2 of the level (ηL db ) shown in (d) is output by the above designation. Is input to the adder. The non-linear coefficient η in this case is also determined by an experiment in advance. As described above, the first and second threshold values v th1 and v th2 input to the adder 5c are added to each other to obtain the floating threshold v
It is a thf, given to the foreign object detection section 4d. The floating threshold value changes for each pixel signal of the difference data | (S a −S b ) |, and a foreign substance is detected by comparing the two. The data of the detected foreign matter is taken in by the CPU 4e, edited, and displayed as a map on the display 4f, as in the conventional case.
【0011】[0011]
【発明の効果】以上の説明のとおり、この発明の浮動閾
値による異物検出方式においては、画素信号に追従して
レベルが変化する第1の閾値により、残留パターンが排
除されて異物のみが検出され、また微分信号より作られ
た第2の閾値により、パターンエッジの無指向性の強い
散乱光の画素信号が有効に排除されるもので、隣接チッ
プの比較方法による異物検査装置の性能の向上に寄与す
るところには大きいものがある。As described above, in the foreign matter detection method by the floating threshold value of the present invention, the residual pattern is eliminated and only the foreign matter is detected by the first threshold value whose level changes following the pixel signal. In addition, the second threshold value created from the differential signal effectively eliminates the pixel signal of scattered light having strong omnidirectionality at the pattern edge, which improves the performance of the foreign matter inspection apparatus by the comparison method of adjacent chips. There is a big contribution.
【図面の簡単な説明】[Brief description of drawings]
【図1】 この発明の一実施例を示し、(a) はこの発明
の浮動閾値を適用した異物検査装置の概略のブロック構
成図、(b) は第1の閾値の作成方法と作用の説明図、
(c) はパターンエッジの散乱光に対する第2の閾値の作
成方法と作用の説明図である。FIG. 1 shows an embodiment of the present invention, in which (a) is a schematic block diagram of a foreign matter inspection apparatus to which the floating threshold value of the present invention is applied, and (b) is a description of a first threshold value creating method and operation. Figure,
(c) is an explanatory view of a method and an operation of creating a second threshold value for scattered light at a pattern edge.
【図2】 (a) はウエハに形成されるICチップを示す
図、(b) は隣接チップの比較方法による異物検査装置の
概略構成図、(c) は比較される隣接チップとそれぞれの
画素データ、および差分データを示す図である。2A is a diagram showing an IC chip formed on a wafer, FIG. 2B is a schematic configuration diagram of a foreign matter inspection apparatus by a method of comparing adjacent chips, and FIG. 2C is an adjacent chip to be compared and each pixel. It is a figure which shows data and difference data.
【図3】 固定閾値で異物検出を行う場合の説明図であ
る。FIG. 3 is an explanatory diagram in a case where foreign matter detection is performed with a fixed threshold value.
1…ウエハ、11…ICチップ、チップ、11a,11b …隣接
チップ、2…移動ステージ、3…検査光学系、3a …光
源、3b …対物レンズ、3c …CCDセンサ、4…画素
信号処理部、4a …A/D変換器、4b …メモリ(ME
M)、4c …差分回路、4d …異物検出部、4e …コン
ピュータ(CPU)、4f …表示器、5…閾値作成部、
5a …比較選択回路(A)、5b …メモリ(MEM)
(A)、5c …加算器、5d,5e …微分回路、5f …比
較選択回路(B)、5g …メモリ(MEM)(B)、Sa,
Sb …画素データ、PT …パターン、R…残留パター
ン、Q…パターンの表面、E…パターンのエッジ、g,
gn …画素信号、e,ea,eb …エッジの散乱光 ge
…散乱光の画素信号、da,db …微分信号、k…一定の
係数、η…非直線の係数、Vth…閾値、vth1 …第1の
閾値、vth2 …第2の閾値、vthf …浮動閾値。1 ... Wafer, 11 ... IC chip, chip, 11a, 11b ... Adjacent chip, 2 ... Moving stage, 3 ... Inspection optical system, 3a ... Light source, 3b ... Objective lens, 3c ... CCD sensor, 4 ... Pixel signal processing unit, 4a ... A / D converter, 4b ... Memory (ME
M), 4c ... Difference circuit, 4d ... Foreign matter detection unit, 4e ... Computer (CPU), 4f ... Display device, 5 ... Threshold value creation unit,
5a ... Comparison selection circuit (A), 5b ... Memory (MEM)
(A), 5c ... Adder, 5d, 5e ... Differentiation circuit, 5f ... Comparison selection circuit (B), 5g ... Memory (MEM) (B), Sa ,
S b ... Pixel data, P T ... Pattern, R ... Residual pattern, Q ... Pattern surface, E ... Pattern edge, g,
g n ... Pixel signal, e, e a , e b ... Edge scattered light g e
... pixel signals of the scattered light, d a, d b ... differential signals, k ... constant factor, eta ... coefficient of nonlinearity, V th ... threshold, v th1 ... first threshold value, v th2 ... second threshold value, v thf ... Floating threshold.
Claims (1)
を有する複数のICチップを検査対象とし、該ウエハに
対してレーザビームを走査し、互いに隣接した2個の前
記ICチップの反射光を光センサにより受光し、該光セ
ンサの出力した該両ICチップの対応する画素信号の差
分データをとり、該差分データを適当な閾値に比較し
て、前記各ICチップに付着した異物を検出する異物検
査装置において、前記対応する両画素信号の小さい方を
選択し、該選択された画素信号に対して、1より小さい
一定の係数を乗じて第1の閾値とし、かつ前記両画素信
号をそれぞれ微分した微分信号の小さい方を選択し、該
選択された微分信号に対して、該微分信号の大きさが大
きい程大きい非直線の係数を乗じて第2の閾値とし、該
第2の閾値に前記第1の閾値を加算して浮動閾値とし、
該浮動閾値に対して前記差分データの各画素信号を比較
して前記異物を検出することを特徴とする、浮動閾値に
よる異物検出方式。1. A plurality of IC chips having the same pattern formed on a surface of a wafer are inspected, a wafer is scanned with a laser beam, and light reflected by two IC chips adjacent to each other is emitted. A foreign substance which is detected by a sensor and which takes difference data of pixel signals corresponding to both IC chips output from the photosensor and compares the difference data with an appropriate threshold value to detect a foreign substance adhering to each IC chip. In the inspection apparatus, the smaller one of the corresponding two pixel signals is selected, the selected pixel signal is multiplied by a constant coefficient smaller than 1 to obtain a first threshold value, and the two pixel signals are differentiated from each other. The smaller one of the differentiated signals is selected, and the selected differential signal is multiplied by a larger non-linear coefficient as the magnitude of the differentiated signal is larger to obtain a second threshold value. First To add a threshold of
A foreign matter detection method according to a floating threshold value, wherein the foreign matter is detected by comparing each pixel signal of the difference data with the floating threshold value.
Priority Applications (1)
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---|---|---|---|
JP3228829A JP3040013B2 (en) | 1991-08-14 | 1991-08-14 | Foreign object detection method using floating threshold |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP3228829A JP3040013B2 (en) | 1991-08-14 | 1991-08-14 | Foreign object detection method using floating threshold |
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JPH0545294A true JPH0545294A (en) | 1993-02-23 |
JP3040013B2 JP3040013B2 (en) | 2000-05-08 |
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JP3228829A Expired - Fee Related JP3040013B2 (en) | 1991-08-14 | 1991-08-14 | Foreign object detection method using floating threshold |
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Cited By (1)
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---|---|---|---|---|
US10578011B2 (en) | 2013-11-18 | 2020-03-03 | Kawasaki Jukogyo Kabushiki Kaisha | Motive-power transmission device for supercharger |
-
1991
- 1991-08-14 JP JP3228829A patent/JP3040013B2/en not_active Expired - Fee Related
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
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US10578011B2 (en) | 2013-11-18 | 2020-03-03 | Kawasaki Jukogyo Kabushiki Kaisha | Motive-power transmission device for supercharger |
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