JP2004138828A - Telecentric optical system and inspecting device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a telecentric optical system which has brightness capable of taking in the light from an object to be inspected sufficiently and can improve an inspection precision, and to provide an inspecting device using the optical system. <P>SOLUTION: The inspecting device has the both-side telecentric optical system 7 allowing emitted light emitted from the object 3 at a specified divergent angle to form an image at a specified position, and a CCD panel 9 arranged at the image forming position of the optical system 7 and picking up the image of the image-formed object 3, and inspects the uniformity of the emitted light from the object 3 based on image data obtained by the panel 9. The optical system 7 is equipped with a plurality of lens groups Gb and Gf arranged so that an optical axis 7A may be aligned therewith, and has an effective F value equal to or under the effective F value of the object 3 regulated by the specified divergent angle. <P>COPYRIGHT: (C)2004,JPO

Description

【００４２】
上記の諸元により、Ｆ値Ｆｔの値が１．２の両側テレセントリックな光学系を実現することができた。
表１に諸元を示した両側テレセントリック光学系７は、液晶パネル３のうちの画素が形成されている有効表示領域全面を一括して結像することができる。
図３は、液晶パネル３の表示領域を示す図である。図中、矩形の領域が表示領域３０を表わしている。矩形の表示領域３０の縦横比は一例として３：４である。光学系７は、一例として、表示領域３０の重心ＣＴを中心としたφ０．９インチ（約２２．８６ｍｍ）の範囲、即ち、対角線ＶＡの長さが０．９インチの表示領域３０を一括して撮像することができる。
以下に示す光学特性のグラフにおいて用いる物体高さとは、重心ＣＴから表示領域３０の角に向かう線ｄｓの長さによって規定する。
【００４３】
以下、表１に諸元を示した両側テレセントリック光学系７の光学特性について述べる。なお、以下では全て、カム機構によって光学系７の倍率を変化させない、規定倍率時の光学特性を調べている。
図４（ａ）〜（ｃ）は、光学系７の諸収差の計測結果を示すグラフである。各グラフにおいて、液晶パネル３から出射される光の波長が５８０．０ｎｍの場合を点線によって示し、５５０．０ｎｍの場合を実線によって示し、５２０．０ｎｍの場合を一点鎖線によって示している。
【００４４】
図４（ａ）は、球面収差を表わすグラフである。図４（ａ）において、横軸が球面収差量（ｍｍ）である。また、縦軸が開口、即ち絞りＳＴＯの相対的な大きさを表わしており、開口の最大の大きさを１としている。
図４（ａ）から、球面収差量は最大でも０．０１５ｍｍ程度であり、球面収差が非常に良好に補正されていることがわかる。開口の相対的な大きさが１のときにも、各波長の場合において、球面収差量の絶対値は０．０１ｍｍ以下であり、非常に良好に球面収差が補正されている。
【００４５】
図４（ｂ）は、非点収差を表わすグラフである。図４（ｂ）において、横軸が非点収差量（ｍｍ）を表わし、縦軸が物体高さ（ｍｍ）を表わしている。グラフＴ１は光学系７のメリジオナル面における非点収差を表わし、グラフＳ１はサジタル面における非点収差を表わしている。また、図４（ｂ）においては、波長が５５０．０ｎｍの場合の結果のみを示している。
図４（ｂ）から、表示領域３０の全面において非点収差の大きさが約０．００６ｍｍ以下と、非常に良好に非点収差が補正されていることが分かる。
【００４６】
図４（ｃ）は、歪曲率を表わすグラフである。図４（ｃ）において、横軸が歪曲率（％）を表わし、縦軸が物体高さ（ｍｍ）を表わしている。
図４（ｃ）から、表示領域３０の中心部においては、いずれの波長に対しても歪曲率がほぼ０％であることが分かる。また、表示領域３０の最周辺部においても、いずれの波長の場合にも歪曲率の大きさが０．１％以下であり、非常に良好に補正されていることが分かる。
歪曲率が大きいと、ＣＣＤパネル９に欠陥の位置が誤って結像され、欠陥画素の位置を誤って特定する原因となり得る。したがって、歪曲率が非常に小さい本実施形態の光学系７によれば、非常に高精度な欠陥検出が可能になることが分かる。
【００４７】
図５（ａ），（ｂ）および図６（ｃ），（ｄ）は、諸条件における光学系７の横方向の収差の計測結果を示すグラフである。図５および図６におけるｉ）およびｉｉ）は、メリジオナル方向とサジタル方向における横収差をそれぞれ示している。各グラフにおいて、液晶パネル３から出射される光の波長が５８０．０ｎｍの場合を点線によって示し、５５０．０ｎｍの場合を実線によって示し、５２０．０ｎｍの場合を一点鎖線によって示している。
各グラフにおいて、横軸は、焦点位置からの光軸７Ａに直交する横方向への距離を表わしている。また、縦軸が横収差量（ｍｍ）を表わしている。
なお、サジタル方向においては、縦軸に対してグラフが対称となるため、縦軸に対して片側のグラフのみを描いている。
【００４８】
図５および図６の（ａ）〜（ｄ）は、図３において物体高さを表わす線ｄｓの最大値ｄｓｌの大きさを１としたときの、相対的な物体高さが１．００，０．７５，０．５０，０．００（即ち、重心ＣＴ）の場合の結果をそれぞれ表わしている。
図５（ａ），（ｂ）および図６（ｃ），（ｄ）から、波長ごとの値にあまりばらつきがなく、横収差が良好に補正されていることが分かる。
また、横収差量の絶対値は最大でも０．０１２５ｍｍ以下であることも分かる。この値は、画素欠陥の検出に用いられる従来のテレセントリック光学系の横収差量の値よりも大幅に小さい。
以上から、本実施形態に係る両側テレセントリック光学系７においては、横収差が非常に良好に補正されていることが分かる。
【００４９】
横収差、即ち色収差が存在すると、得られる像にボケやにじみが発生し、欠陥位置が誤って特定される可能性がある。しかしながら、本実施形態に係る光学系７においては色収差が非常に良好に補正されているため、非常に高精度な欠陥検出が可能であることが分かる。
【００５０】
本実施形態に係る両側テレセントリック光学系７の総合的な光学特性を評価するために、ＭＴＦ（Ｍｏｄｕｌａｔｉｏｎ　Ｔｒａｎｓｆｅｒ　Ｆｕｎｃｔｉｏｎ：変調伝達関数）を調べた。その結果を図７に示す。
図７において、横軸は空間周波数（本／ｍｍ）を表わしており、縦軸は最大値を１とした場合の変調率を表わしている。
【００５１】
図７における各グラフは、波長５８０．０ｎｍの光と波長５５０．０ｎｍの光と波長５２０．０ｎｍの光を１：１：１に重み付けした光を、表１に諸元を示した光学系７に入射させたとした場合に、焦点位置における変調率を計算したシミュレーション結果である。
図中、グラフＬｍは理論上の回折限界を示しており、グラフＡ１は光軸７Ａにおける結果をそれぞれ示している。グラフＥは、前述の相対的な物体高さが１の場合の結果を示しており、グラフＥのうち、グラフＴ２がメリジオナル面における結果を表わしており、グラフＳ２がサジタル面における結果を表わしている。
図示はしないが、相対的な物体高さが１から０までの間の場合の結果は、グラフＡ１とグラフＴ２の間にほぼおさまっている。
【００５２】
一例として、投射型の液晶プロジェクターに用いられる投射光学系は、実効Ｆ値がＦ２．０程度であり、そのＭＴＦは、空間周波数が４０（本／ｍｍ）の場合に変調率０．６程度である。図７の結果から、本実施形態に係る光学系７によって得られたＭＴＦは、基準的な液晶プロジェクターの投射光学系よりも小さい実効Ｆ値を有しながらも、大幅に良い値が得られていることが分かる。
【００５３】
また、従来であれば空間周波数が２００（本／ｍｍ）程度まで増えると変調率が０．１以下となった。しかし、本実施形態においては、空間周波数が２８０（本／ｍｍ）の場合にも、それ以上の３００（本／ｍｍ）近い場合においても、変調率は０．１よりも大きい値が得られた。
【００５４】
図７の結果から、本実施形態に係る両側テレセントリック光学系７は、非常に高い解像度を有し、高精度な欠陥検出を可能にすることが分かった。また、欠陥がさらに微小になる場合にも欠陥検出が可能である。
【００５５】
図８は、本実施形態に係る両側テレセントリック光学系７を用いて、液晶パネル３の画素欠陥を結像させることにより、欠陥画素からの光量漏れを調べたシミュレーション結果である。
図８においても、図７の場合と同様に、波長５８０．０ｎｍの光と波長５５０．０ｎｍの光と波長５２０．０ｎｍの光を１：１：１に重み付けした光を、表１に諸元を示した光学系７に入射させたとしている。
【００５６】
図８の横軸が液晶パネル３における寸法（ｍｍ）を表わしている。シミュレーションにおいては、欠陥画素の透光部の大きさを一例として縦横１５μｍの正方形とした。ただし、欠陥画素が射出する光の強度は、透光部の全面において均一であると仮定し、シミュレーションにおいては、透光部の横方向の辺に沿った１次元シミュレーション結果を算出した。
前述のように、ノーマリーホワイトモードによって駆動される液晶パネル３においては、欠陥画素は光を透過し白く表示される。光の強度の最大値を１として、相対的に表わしたものが、図８のグラフにおける縦軸である。
したがって、図８における矩形Ｒの横線が、１つの欠陥画素の透光部の幅の、液晶パネル３における実際の位置を表わしている。
【００５７】
図８におけるグラフＡ２が、光軸７Ａ上に位置している欠陥画素を結像させた場合の、１次元の光の強度変化を示した結果である。
また、グラフＴ３およびグラフＳ３が、相対的な物体高さが１の位置の欠陥画素を結像させた場合の、光学系のタンジェンシャル方向とラジアル方向における１次元の光の強度変化の結果をそれぞれ示している。
各グラフは、横方向の寸法を、液晶パネル３における透光部の矩形Ｒの寸法に一致させて示している。
【００５８】
各グラフＡ２，Ｔ３，Ｓ３の形が矩形Ｒの形状に近いほど、画素輝点を忠実に結像できていることになり、欠陥検出上は都合が良い。特に、グラフＡ２，Ｔ３，Ｓ３のうち矩形Ｒの外部に位置している領域は、隣接する画素への光量漏れを意味するため、小さいほど良い。隣接する画素間の間隔は、一例として３μｍである。この場合には、図８の結果から、本実施形態においては光量漏れは実用上ほとんど問題ないレベルの値であるといえる。したがって、正確な欠陥検査が期待できる。
【００５９】
以上の結果から、本実施形態においては、被検査対象物である液晶パネル３の全面において諸収差が良好に補正されていることが分かる。したがって、本実施形態によれば、欠陥検査時の光量均一性を従来よりも大幅に向上可能である。また、解像度が高いため、検出可能欠陥のサイズの低減化、および欠陥位置特定精度の向上が可能になる。それゆえ、欠陥を高精度に検出することができる。
その結果、検査もれを低減することができ、被検査対象物の品質向上、不良率低減を図ることができる。
【００６０】
また、ある程度の大きさの被検査対象物を、ほとんど収差なく一括して撮像可能である。収差が少ないため、欠陥検出における画像処理の負担も軽減可能である。テレセントリックな光学系を採用しているため、検査時における被検査対象物の位置決めや温度変動等の検査条件誤差により生じる光軸方向の位置誤差を容易に吸収することができる。以上のことから、欠陥検査のタクトタイムを短縮することができる。
【００６１】
さらに、本実施形態においては、ＣＣＤパネル９によって欠陥検出を行なう場合に、用いる光学系は両側テレセントリック光学系７のみである。したがって、ＣＣＤパネル９において得られる像の劣化が少なく、高精度な欠陥検査が可能である。
【００６２】
両側テレセントリック光学系７において倍率調整を可能にした場合には、光学系７の加工誤差、製造誤差による倍率変化を吸収可能であり、高精度な欠陥検出が可能な光学系７を容易に確実に提供することが可能になる。倍率を調整する場合にも、収差変動は最小限に抑えられ、検査精度を確保することができる。
【００６３】
さらに、ビームスプリッタＢＳを設けた場合には、ＣＣＤパネル９による検査と、目視による検査の同時検査が可能になる。これにより、欠陥検査装置１による欠陥の自動検出の結果と、目視による結果とを比較して検討することも可能になる。
【００６４】
なお、本発明は、上記実施形態に限定されず、種々の変更が可能である。
たとえば、被検査対象物は、液晶パネルに限らず、プラズマディスプレイパネルやフィールドエミッションディスプレイ等の他の表示パネルであってもよい。表示パネルに限らず、光学ディスクや半導体ウェハ等の対象物の検査に本発明を適用してもよい。なお、これらの対象物においても、発光や反射によって光を出射する場合には、実効Ｆ値を規定することができる。
また、欠陥検出に限らず、フォトマスクの転写等の用途に本発明を適用することも可能である。
撮像手段としても、ＣＣＤに限らず、ＣＭＯＳ（Ｃｏｍｐｌｅｍｅｎｔａｒｙ　Ｍｅｔａｌ　Ｏｘｉｄｅ　Ｓｅｍｉｃｏｎｄｕｃｔｏｒ）等の他の撮像素子を用いることが可能である。
光学系の構成レンズについても、その枚数や形状、材料などの事項は、特許請求の範囲内において適宜変更可能である。
【００６５】
【発明の効果】
以上のように、本発明によれば、検査対象物からの光を十分に取込める明るさを有し、検査精度を向上可能なテレセントリック光学系を提供することができる。
また、テレセントリック光学系を備え、検査対象物からの光を十分に取込める明るさを有し、検査精度を向上可能な検査装置を提供することもできる。
【図面の簡単な説明】
【図１】図１は、本発明の一実施形態に係る欠陥検査装置の概略構成図である。
【図２】図２は、本発明の一実施形態に係る光学系のレンズ構成図である。
【図３】図３は、図１における検査対象物の一例としての液晶パネルの表示領域を表わす図である。
【図４】図４（ａ）〜（ｃ）は、図２に図解の光学系の諸収差を表わすグラフである。
【図５】図５（ａ），（ｂ）は、図２に図解の光学系の諸条件における横収差を表わすグラフである。
【図６】図６（ｃ），（ｄ）は、図５に続き、図２に図解の光学系の諸条件における横収差を表わすグラフである。
【図７】図７は、図２に図解の光学系のＭＴＦ（変調伝達関数）を示すグラフである。
【図８】図８は、図２に図解の光学系を用いて、液晶パネルの画素輝点を結像させた結果を示すグラフである。
【符号の説明】
１…欠陥検査装置、３…検査対象物（液晶パネル）、３ａ…パネル本体、３ｂ…偏光膜取付板、５…撮像カメラ、７…光学系、７Ａ…光軸、９…撮像手段（ＣＣＤパネル）、１１…モニター、１５…画像処理装置、３０…表示領域、３５…移動手段、Ｌ１〜Ｌ１０…レンズ、Ｒ１６〜Ｒ２７，Ｒ２９〜Ｒ４０…レンズ面、ＢＳ…ビームスプリッタ、ＳＤ…分光方向、ＮＦ…ＮＤフィルタ、ＳＴＯ…絞り、ＰＴ…保護ガラス、ｄｏ…後群焦点距離、ｄｆ…前群焦点距離[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical system used for photographing a liquid crystal panel when detecting a pixel defect of the liquid crystal panel, for example, and a defect inspection apparatus using the optical system. More specifically, the present invention relates to a telecentric optical system having a brightness capable of sufficiently capturing light emitted from an inspection object such as a liquid crystal panel, and a defect inspection apparatus using the optical system.
[0002]
[Prior art]
As an inspection device for inspecting pixel defects of a flat display device such as a liquid crystal display device (hereinafter, referred to as a liquid crystal panel), for example, a device that projects a liquid crystal panel on a screen and detects a defect based on the projected image is known. I have.
In a screen projection type apparatus, an image of a liquid crystal panel is enlarged and projected on a screen using an enlargement optical system. The inspector visually inspects the projected image to detect a pixel defect of the liquid crystal panel.
[0003]
In addition, there is also known an apparatus that captures an image of a liquid crystal panel with an imaging device such as a CCD (Charge Coupled Device) camera and detects a defect based on an image of the obtained liquid crystal panel.
There is also known a projection image capturing type inspection apparatus which captures not only the liquid crystal panel itself but also a projection image of the liquid crystal panel as described above using a CCD camera. In a projection image capturing type inspection apparatus, both a projection image on a screen and an image obtained by capturing a projection image by a CCD camera can be used for defect detection.
[0004]
An image pickup optical system for forming an image of a liquid crystal panel on an image forming surface of an image pickup device such as a CCD when an image of a liquid crystal panel is picked up by an image pickup device such as a CCD camera is disclosed in Patent Document 1 as an example. Such a telecentric optical system is used.
The telecentric optical system has the advantage that all principal rays travel in the object space or the image space in parallel to the optical axis, and errors in the size of an image taken or measured can be reduced. Therefore, it is used for object measurement and defect inspection.
[0005]
[Patent Document 1]
JP-A-9-33804
[0006]
[Problems to be solved by the invention]
However, in the inspection using the screen projection type device, the limit of the defects that can be found differs depending on the inspector. In addition, even for the same inspector, the limit of discoverable defects and the accuracy of detection of correctness of defect determination vary depending on factors such as physical condition.
Furthermore, as long as a human inspects, defects may be overlooked.
[0007]
In an apparatus that captures a liquid crystal panel with an imaging device and a projection image capturing type device that have been devised to realize an inspection that is not affected by the senses of the inspector, the F value of the imaging optical system is conventionally large, The imaging optics was dark. For this reason, the resolution limit may be low, and the defect may be overlooked.
In addition, since the F value is large, it is not possible to take in all the light from the liquid crystal panel, so that a defect may be overlooked.
[0008]
Conventionally, the telecentric optical system used for defect detection has a large F value and is dark. As a result, the change in magnification due to a position error occurring when the liquid crystal panel to be inspected is replaced is extremely reduced, and the uniformity of the light amount is high in order to realize a highly accurate unevenness inspection. There were no telecentric optics with the highest possible resolution.
[0009]
Accordingly, it is an object of the present invention to provide a telecentric optical system having sufficient brightness to receive light from an inspection object and capable of improving inspection accuracy.
It is another object of the present invention to provide an inspection apparatus that includes a telecentric optical system, has sufficient brightness to capture light from an inspection object, and can improve inspection accuracy.
[0010]
[Means for Solving the Problems]
The telecentric optical system according to the present invention includes a plurality of lens groups arranged so that optical axes coincide with each other, and emits light emitted at a predetermined divergence angle from an object at a predetermined position on the optical axis. A telecentric optical system for forming an image, the telecentric optical system having an effective F value equal to or less than an effective F value of the object defined by the divergence angle.
[0011]
Further, the inspection apparatus according to the present invention includes a plurality of lens groups arranged so that optical axes coincide with each other, and emits light emitted from the object at a predetermined divergence angle at a predetermined position on the optical axis. An optical system that forms an image, and an imaging unit that is arranged at an imaging position of the optical system so that an imaging surface is coincident with the imaging system.The imaging unit captures an image of the object through the optical system, An inspection apparatus for inspecting uniformity of the emitted light from the object, wherein the optical system is a telecentric optical system having an effective F value equal to or less than an effective F value of the object defined by the divergence angle. There is an inspection device.
[0012]
In the present invention, outgoing light is emitted from the object at a predetermined divergence angle. The effective F value of the object is defined by the emitted light having the predetermined divergence angle.
The constituent lenses of the plurality of lens groups that form the optical system are configured so that the effective F value of the optical system is smaller than the effective F value of the object and are telecentric, and are arranged with the optical axes coincident.
With this telecentric optical system, light emitted from the object is imaged. At an image forming position where the emitted light is formed, an image pickup means for picking up an image of the formed object is arranged.
The imaging unit captures an image of the object using the emitted light of the object formed by the telecentric optical system.
Based on the image data obtained by the imaging means, the uniformity of the emitted light of the object is inspected, and the presence or absence of a defect of the object is determined.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of a defect inspection apparatus according to an embodiment of the present invention.
The defect inspection device 1 illustrated in FIG. 1 includes an imaging camera 5, a monitor 11, and an image processing device 15. The imaging camera 5 further has an optical system 7 and an imaging unit 9.
[0014]
The defect inspection apparatus 1 is an inspection apparatus that images the inspection target 3 by the imaging unit 9 via the optical system 7 of the imaging camera 5 and inspects the defect of the target 3 based on the obtained image.
In the present embodiment, a liquid crystal panel will be described as an example of the target 3. Further, as the imaging means 9, for example, a CCD panel can be used. However, the present invention is not limited to these objects and imaging means.
[0015]
The liquid crystal panel 3 and the imaging camera 5 are arranged, for example, facing each other so that a defect of the liquid crystal panel 3 can be detected.
The liquid crystal panel 3 is placed on a stage (not shown) and positioned at the inspection position.
It is preferable that the entire surface of the liquid crystal panel 3 can be collectively imaged by the imaging camera 5 in order to improve the efficiency of the defect detection process.
The light emitted from the liquid crystal panel 3 enters the optical system 7 of the imaging camera 5. The CCD panel 9 is arranged at a position where the light emitted from the liquid crystal panel 3 incident on the optical system 7 forms an image.
An image processing device 15 is connected to the CCD panel 9. A monitor 11 can be connected to the CCD panel 9 in order to confirm an image obtained by the CCD panel 9.
[0016]
The liquid crystal panel 3 has a well-known structure in which, for example, a pair of substrates provided with electrodes formed in a predetermined shape such as a matrix shape is arranged with electrode forming surfaces facing each other and liquid crystal is sealed between the electrode forming surfaces. Having.
Each of the electrodes arranged in a matrix corresponds to a pixel for displaying an image. Each pixel has a light-transmitting portion through which light passes through a transparent electrode, a non-transparent electrode, a switching element such as a TFT (Thin Film Transistor), and a color filter to prevent color mixing of different color filters. There is a light-shielding portion where elements such as a black matrix are located.
[0017]
Due to the above conditions such as the area ratio and the shape of the light-transmitting portion and the light-shielding portion, the emitted light Lt from the liquid crystal panel 3 is, as shown in FIG. At a predetermined divergence angle θ.
With the divergence angle θ, the NA (Numerical Aperture: numerical aperture) of the liquid crystal panel 3 can be defined as NA = sin θ.
Further, by using the NA of the liquid crystal panel 3, the effective F value representing the brightness of the liquid crystal panel 3 can be defined as Fp = 1 / (2NA) = 1 / (2 sin θ).
[0018]
The value of the effective F value Fp of the liquid crystal panel 3 is F1.7 as an example.
The liquid crystal panel 3 may be provided with a microlens for converging and emitting light. Therefore, the effective F value Fp of the liquid crystal panel 3 may be smaller than F1.7, but hardly larger than F1.7.
As will be described later in detail, the optical system 7 according to the present embodiment has an effective F value smaller than the effective F value Fp of the liquid crystal panel 3 in order to sufficiently capture the light Lt emitted from the liquid crystal panel 3.
The optical system 7 takes in the emitted light Lt and forms an image of the liquid crystal panel 3 at a predetermined position.
[0019]
The CCD panel 9 has a plurality of CCDs arranged in a predetermined shape. The plurality of CCDs are arranged in a two-dimensional matrix as an example.
The imaging surface of the CCD panel 9 is formed by the light receiving units of the plurality of CCDs arranged in a two-dimensional matrix. The CCD panel 9 is arranged so that the image pickup surface coincides with the image forming position of the liquid crystal panel 3 by the optical system 7.
The CCD panel 9 converts the output light Lt from the liquid crystal panel 3 received by the imaging surface into an electric signal corresponding to the intensity and outputs the electric signal.
[0020]
The electric signal output from the CCD panel 9 is subjected to various kinds of signal processing by an electronic circuit (not shown) and transmitted to the image processing device 15 as image data.
The electric signal output from the CCD panel 9 can be directly transmitted to the image processing device 15 and converted into image data in the image processing device 15.
[0021]
The image processing device 15 performs predetermined signal processing on the input image data or the electric signal from the CCD panel 9, detects a defective pixel of the captured liquid crystal panel 3, and specifies its position.
As an example, consider a liquid crystal panel 3 driven in a normally white mode in which light can be transmitted and displayed white when no drive voltage is applied. In this case, if there is a defect in the pixel of the liquid crystal panel 3, the defective pixel is displayed as white even when a driving voltage is applied to the liquid crystal panel 3 to display it in black, and this is picked up by the CCD panel 9 as a bright point. Is done. That is, when a pixel defect exists in the liquid crystal panel 3, the light Lt emitted from the liquid crystal panel 3 is not uniform over the entire surface of the liquid crystal panel 3.
The image processing device 15 recognizes a pixel defect by determining the uniformity of the outgoing light Lt based on the input image data or the electric signal from the CCD panel 9, and automatically determines the position on the liquid crystal panel 3. It is programmed to be specific.
[0022]
In the present embodiment, defective pixels are automatically detected based on the output from the CCD panel 9. However, it is also possible to transmit the image data to the monitor 11 so that the image on the liquid crystal panel 3 can be visually checked by the inspector. This makes it possible to compare the inspection result by the inspector with the inspection result by the image processing device 15.
[0023]
The optical system 7 used in the imaging camera 5 has a brightness enough to take in the light Lt emitted from the liquid crystal panel 3 and has very little distortion to detect minute pixel defects with high accuracy. Is required to be high.
FIG. 2 shows an example of a detailed configuration of the optical system 7 used in the present embodiment.
[0024]
The optical system 7 shown in FIG. 2 includes ten lenses L1, L2,..., L10 arranged in order from the liquid crystal panel 3 which is the subject to the CCD panel 9 which is the image forming side, and a stop STO. have.
In FIG. 2, the liquid crystal panel 3 is illustrated as being divided into a panel main body 3a and a polarizing film mounting plate made of, for example, sapphire glass for mounting a polarizing film on the surface of the panel main body 3a.
A protective glass PT for protecting the CCD panel 9 is provided between the lens L10 closest to the image forming side and the CCD panel 9.
[0025]
The lenses L1 to L10 correspond to one embodiment of each constituent lens in the present invention.
The lenses L1 to L10 are arranged such that the optical axes 7A coincide.
The stop STO is arranged between the lens L5 and the lens L6. As the stop STO, for example, an aperture stop having a known structure is used. Hereinafter, the lenses L1 to L5 on the object side of the stop STO will be referred to as a rear group Gb, and the lenses L6 to L10 on the image forming side will be referred to as a front group Gf.
[0026]
The constituent lenses of the front group Gf and the rear group Gb have shapes and arrangements that are close to symmetrical with the stop STO interposed therebetween in order to minimize distortion. The constituent lenses of the front group Gf and the rear group Gb were combined after optimal color correction, and the shapes were determined by performing shape optimization again for suppressing aberration.
[0027]
In addition, it is necessary to obtain a power that can secure a relatively large lens back to enable the arrangement of the beam splitter BS described later, and that the arrangement of each lens is not completely symmetric with respect to the stop STO. Then, the glass material of each constituent lens is selected.
[0028]
As a result of taking the above conditions into consideration, in the present embodiment, as an example of a telecentric optical system, a front group Gf and a rear group Gb constitute a bilateral telecentric optical system. The double-sided telecentric optical system is, for example, a reduction optical system with a magnification of about 0.655.
With the above configuration, an effective F-number of F1.2 can be realized, for example, on the imaging side of the double-sided telecentric optical system shown in FIG. The effective F value Ft of the two-sided telecentric optical system is smaller than the effective F value Fp of the liquid crystal panel 3.
[0029]
Preferably, a concave meniscus lens L10b is arranged at a position closest to the image forming side with its concave surface R40 facing the image forming position.
The concave meniscus lens L10b may be arranged independently, or may be arranged as a doublet integrated with the lens L10a, like the lens L10 in FIG.
[0030]
The curvature radius rm of the concave surface R40 is designed so as to satisfy the following expression in relation to the focal length df from the stop STO of the front group Gf to the imaging plane of the CCD panel 9.
[0031]
[Equation 3]
0.3 <rm / df <0.45 (1)
[0032]
Since the F value Ft is as bright as about 1.2, if the ratio of the radius of curvature rm of the concave surface R40 to the focal length df is out of the range of the expression (1), the Petzval curvature is sufficiently corrected. And high optical characteristics cannot be achieved.
Within the range of the value of the expression (1), even if the value of the F value Ft is smaller than the value of the F value Fp, the Petzval curvature is sufficiently corrected to obtain high optical characteristics as described later. be able to.
[0033]
In addition, even when the ratio between the radius of curvature rm of the concave surface R40 and the focal length df is within the range of the expression (1), there is an upper limit and a lower limit in the value of the radius of curvature rm from the viewpoint of processing accuracy.
[0034]
In the optical system 7 which is telecentric on both sides as shown in FIG. 2, the distance from the liquid crystal panel 3 which is the subject to the optical system 7 and the distance from the liquid crystal panel 3 to the CCD panel 9 arranged at the image forming position are changed. However, the magnification of the liquid crystal panel 3 hardly changes. Therefore, the position error in the direction of the optical axis 7A generated when the liquid crystal panel 3 is arranged at the inspection position by the stage (not shown) at the time of the inspection is absorbed, and the inspection can always be performed at almost the same magnification.
[0035]
Further, the optical system 7 according to the present embodiment can be provided with a moving unit 35 that can move a predetermined lens of the optical system 7 along the optical axis 7A. By moving a predetermined lens using the moving means 35, it is possible to change the magnification of the optical system 7 whose magnification is hardly changed originally.
The magnification of the lens to be moved can be changed by moving the lens, and when the lens is moved, the image formed by the optical system 7 has an image quality such as various aberrations. Select a lens that has a smaller effect than other lenses. For example, in FIG. 2, the lens L7 is moved. However, it is not always necessary to move one lens.
[0036]
More specifically, as an example, as the moving unit 35, a lens barrel holding the lens L7 and a lens barrel holding the other lens are configured to be double with the optical axis 7A coincident. A well-known cam mechanism that converts the rotational movement of the lens barrel around the optical axis 7A into the movement of the lens barrel holding the lens L7 in the direction of the optical axis 7A is used.
[0037]
The above-mentioned cam mechanism makes it possible to change the magnification of the optical system 7 while keeping the distance from the liquid crystal panel 3 to the CCD panel 9 constant. Accordingly, even when a processing error or a manufacturing error occurs when the optical system 7 is created, and the magnification of the optical system 7 changes from a specified value, the change in the magnification can be easily corrected. As a result, a change in the defect inspection level can be suppressed.
In addition, when compensating for the magnification variation, it is possible to minimize the influence of various aberrations and the like on the image quality.
[0038]
In the present embodiment, a beam splitter BS can be provided between the rear group Gb and the liquid crystal panel 3. The beam splitter BS corresponds to one embodiment of the light splitting unit in the present invention.
The beam splitter BS splits the light emitted from the liquid crystal panel 3 in a direction along the optical axis 7A and in a different direction. The branching direction is, for example, a direction SD orthogonal to the optical axis 7A, which is indicated by an arrow in FIG.
The light emitted in the branching direction SD by the beam splitter BS is enlarged and projected onto a screen using, for example, another optical system, so that the liquid crystal panel 3 is imaged by the CCD panel 9 and also visually. Inspection becomes possible.
[0039]
When the amount of light from the liquid crystal panel 3 is too large and light equal to or more than the saturation light amount of the CCD panel 9 is incident on the CCD panel 9, the optical system 7 may be provided with an ND (Neutral Density) filter.
In FIG. 2, four ND filters ND filters N1 to N4 are arranged between the lens L1 closest to the subject and the beam splitter BS.
By providing the ND filter NF, the performance of the CCD panel 9 can be sufficiently exhibited.
In addition, the CCD panel 9 can image a defect other than a pixel defect that can be determined when the liquid crystal panel surface is irradiated with strong light, such as a scratch on the surface of the liquid crystal panel 3.
[0040]
Table 1 shows an example of lens specifications of the double-sided telecentric optical system 7 shown in FIG. As shown in FIG. 2, the lens surfaces in Table 1 are lens surfaces R16 to R27 defined in order from the subject-side lens surface R16 of the lens L1 to the aperture STO-side lens surface R27 of the lens L5 in the rear group Gb, In the group Gf, lens surfaces R29 to R40 defined in order from the lens surface R29 of the lens L6 on the stop STO side to the lens surface R40 of the lens L10 on the CCD panel 9 side are shown.
However, in Table 1, the specifications of the stop STO between the lens L5 and the lens L6 are also described.
The radius of curvature is the radius of curvature of each lens surface and the stop STO. When the center of each curvature is on the image forming side, it takes a positive value, and when it is on the subject side, it takes a negative value. Since the stop STO is planar, the radius of curvature is infinite.
The distance between lens surfaces is a distance on the optical axis 7A from the lens surface to the next lens surface.
In the optical system, if the ratio of each parameter is constant, the optical characteristics do not change, and hence no unit is added.
[0041]
[Table 1]

[0042]
With the above specifications, a bilateral telecentric optical system with an F-number Ft of 1.2 could be realized.
The double-sided telecentric optical system 7 whose specifications are shown in Table 1 can collectively form an image on the entire effective display area of the liquid crystal panel 3 where pixels are formed.
FIG. 3 is a diagram illustrating a display area of the liquid crystal panel 3. In the figure, a rectangular area represents the display area 30. The aspect ratio of the rectangular display area 30 is, for example, 3: 4. The optical system 7 collectively includes, for example, a display area 30 having a diameter of 0.9 inch (about 22.86 mm) around the center of gravity CT of the display area 30, that is, a display area 30 having a diagonal VA of 0.9 inch. Image.
The object height used in the graph of optical characteristics described below is defined by the length of a line ds from the center of gravity CT to the corner of the display area 30.
[0043]
Hereinafter, the optical characteristics of the double-sided telecentric optical system 7 whose specifications are shown in Table 1 will be described. In the following, the optical characteristics at a specified magnification without changing the magnification of the optical system 7 by the cam mechanism are examined.
FIGS. 4A to 4C are graphs showing measurement results of various aberrations of the optical system 7. In each graph, the case where the wavelength of the light emitted from the liquid crystal panel 3 is 580.0 nm is shown by a dotted line, the case of 550.0 nm is shown by a solid line, and the case of 520.0 nm is shown by a dashed line.
[0044]
FIG. 4A is a graph showing spherical aberration. In FIG. 4A, the horizontal axis represents the amount of spherical aberration (mm). The vertical axis represents the relative size of the aperture, that is, the stop STO, and the maximum size of the aperture is 1.
FIG. 4A shows that the spherical aberration amount is about 0.015 mm at the maximum, and that the spherical aberration is corrected very well. Even when the relative size of the aperture is 1, the absolute value of the amount of spherical aberration is 0.01 mm or less at each wavelength, and the spherical aberration is corrected very well.
[0045]
FIG. 4B is a graph showing astigmatism. In FIG. 4B, the horizontal axis represents the amount of astigmatism (mm), and the vertical axis represents the object height (mm). Graph T1 represents astigmatism on the meridional surface of the optical system 7, and graph S1 represents astigmatism on the sagittal surface. FIG. 4B shows only the result when the wavelength is 550.0 nm.
FIG. 4B shows that the magnitude of astigmatism is about 0.006 mm or less over the entire display area 30 and the astigmatism is corrected very well.
[0046]
FIG. 4C is a graph showing the distortion rate. In FIG. 4C, the horizontal axis represents the distortion rate (%), and the vertical axis represents the object height (mm).
From FIG. 4C, it can be seen that the distortion rate is almost 0% for any wavelength at the center of the display area 30. Also, at the outermost peripheral portion of the display area 30, the magnitude of the distortion is 0.1% or less at any wavelength, and it can be seen that the distortion is corrected very well.
If the distortion rate is large, the position of the defect is erroneously formed on the CCD panel 9 and may cause the position of the defective pixel to be erroneously specified. Therefore, according to the optical system 7 of the present embodiment having a very small distortion rate, it can be seen that very high-accuracy defect detection becomes possible.
[0047]
FIGS. 5A and 5B and FIGS. 6C and 6D are graphs showing the measurement results of the lateral aberration of the optical system 7 under various conditions. 5 and 6 show lateral aberrations in the meridional direction and the sagittal direction, respectively. In each graph, the case where the wavelength of the light emitted from the liquid crystal panel 3 is 580.0 nm is shown by a dotted line, the case of 550.0 nm is shown by a solid line, and the case of 520.0 nm is shown by a dashed line.
In each graph, the horizontal axis represents the distance from the focal point in the horizontal direction orthogonal to the optical axis 7A. The vertical axis represents the lateral aberration (mm).
In the sagittal direction, the graph is symmetrical with respect to the vertical axis, so that only one graph is drawn with respect to the vertical axis.
[0048]
FIGS. 5A to 6D show relative object heights of 1.00, 1 when the maximum value dsl of the line ds representing the object height in FIG. The results in the case of 0.75, 0.50, and 0.00 (that is, the center of gravity CT) are respectively shown.
5 (a) and 5 (b) and FIGS. 6 (c) and 6 (d) show that there is not much variation in the value for each wavelength, and that the lateral aberration is favorably corrected.
It can also be seen that the absolute value of the lateral aberration amount is at most 0.0125 mm. This value is significantly smaller than the value of the amount of lateral aberration of the conventional telecentric optical system used for detecting a pixel defect.
From the above, it can be seen that in the double-sided telecentric optical system 7 according to the present embodiment, the lateral aberration is corrected very well.
[0049]
If lateral aberration, that is, chromatic aberration, is present, the resulting image will be blurred or blurred, and the defect position may be erroneously identified. However, in the optical system 7 according to the present embodiment, since the chromatic aberration is corrected very well, it can be seen that very high-accuracy defect detection is possible.
[0050]
In order to evaluate overall optical characteristics of the double-sided telecentric optical system 7 according to the present embodiment, an MTF (Modulation Transfer Function) was examined. FIG. 7 shows the result.
In FIG. 7, the horizontal axis represents the spatial frequency (lines / mm), and the vertical axis represents the modulation rate when the maximum value is 1.
[0051]
Each graph in FIG. 7 shows the light obtained by weighting the light having a wavelength of 580.0 nm, the light having a wavelength of 550.0 nm, and the light having a wavelength of 520.0 nm in a ratio of 1: 1: 1. FIG. 9 is a simulation result of calculating a modulation factor at a focal position when it is assumed that light is incident on the focal point.
In the figure, a graph Lm shows a theoretical diffraction limit, and a graph A1 shows a result at the optical axis 7A. Graph E shows the result when the relative object height is 1 as described above. Of graph E, graph T2 shows the result on the meridional plane, and graph S2 shows the result on the sagittal plane. I have.
Although not shown, the result in the case where the relative object height is between 1 and 0 substantially falls between the graph A1 and the graph T2.
[0052]
As an example, a projection optical system used in a projection-type liquid crystal projector has an effective F value of about F2.0, and its MTF has a modulation rate of about 0.6 when the spatial frequency is 40 (lines / mm). is there. From the results of FIG. 7, the MTF obtained by the optical system 7 according to the present embodiment has a significantly better value while having an effective F-number smaller than the projection optical system of the reference liquid crystal projector. I understand that there is.
[0053]
Further, in the related art, when the spatial frequency is increased to about 200 (lines / mm), the modulation rate becomes 0.1 or less. However, in the present embodiment, the modulation rate is larger than 0.1 both when the spatial frequency is 280 (lines / mm) and when the spatial frequency is higher than 300 (lines / mm). .
[0054]
From the results of FIG. 7, it has been found that the double-sided telecentric optical system 7 according to the present embodiment has a very high resolution and enables highly accurate defect detection. Further, even when the defect becomes smaller, the defect can be detected.
[0055]
FIG. 8 is a simulation result obtained by imaging a pixel defect of the liquid crystal panel 3 using the double-sided telecentric optical system 7 according to the present embodiment to check for light quantity leakage from the defective pixel.
In FIG. 8 as well as in FIG. 7, the light obtained by weighting the light having a wavelength of 580.0 nm, the light having a wavelength of 550.0 nm, and the light having a wavelength of 520.0 nm to 1: 1: 1 is shown in Table 1. Is incident on the optical system 7 shown in FIG.
[0056]
The horizontal axis in FIG. 8 represents the dimension (mm) of the liquid crystal panel 3. In the simulation, the size of the light-transmitting portion of the defective pixel was a square of 15 μm in length and width as an example. However, assuming that the intensity of light emitted from the defective pixel is uniform over the entire surface of the light transmitting portion, a one-dimensional simulation result along a lateral side of the light transmitting portion was calculated in the simulation.
As described above, in the liquid crystal panel 3 driven in the normally white mode, the defective pixel transmits light and is displayed in white. The vertical axis in the graph of FIG. 8 relatively represents the maximum value of the light intensity as 1.
Therefore, the horizontal line of the rectangle R in FIG. 8 indicates the actual position of the width of the light transmitting portion of one defective pixel in the liquid crystal panel 3.
[0057]
A graph A2 in FIG. 8 is a result showing a one-dimensional light intensity change when a defective pixel located on the optical axis 7A is imaged.
The graphs T3 and S3 show the results of the one-dimensional light intensity change in the tangential direction and the radial direction of the optical system when a defective pixel at a relative object height of 1 is imaged. Each is shown.
In each graph, the horizontal dimension is shown so as to match the size of the rectangle R of the light transmitting portion in the liquid crystal panel 3.
[0058]
The closer the shapes of the graphs A2, T3, and S3 are to the shape of the rectangle R, the more faithfully an image of a pixel luminescent spot is formed, which is convenient for defect detection. In particular, in the graphs A2, T3, and S3, a region located outside the rectangle R means that light amount leaks to an adjacent pixel, and therefore the smaller the better. The distance between adjacent pixels is 3 μm as an example. In this case, from the results in FIG. 8, it can be said that in this embodiment, the light amount leakage is a value at a level that causes almost no problem in practical use. Therefore, accurate defect inspection can be expected.
[0059]
From the above results, it can be seen that in the present embodiment, various aberrations are satisfactorily corrected on the entire surface of the liquid crystal panel 3 which is the inspection target. Therefore, according to the present embodiment, the light amount uniformity at the time of the defect inspection can be significantly improved as compared with the related art. Further, since the resolution is high, it is possible to reduce the size of the detectable defect and to improve the defect position identification accuracy. Therefore, a defect can be detected with high accuracy.
As a result, inspection leakage can be reduced, and the quality of the inspection object can be improved and the defect rate can be reduced.
[0060]
In addition, an object to be inspected having a certain size can be collectively imaged with almost no aberration. Since the aberration is small, the load of image processing in defect detection can be reduced. Since a telecentric optical system is employed, it is possible to easily absorb a position error in the optical axis direction caused by an error in an inspection condition such as a positioning of an object to be inspected or a temperature variation during an inspection. As described above, the takt time of the defect inspection can be reduced.
[0061]
Further, in the present embodiment, when a defect is detected by the CCD panel 9, only the double-sided telecentric optical system 7 is used. Therefore, the deterioration of the image obtained in the CCD panel 9 is small, and a highly accurate defect inspection can be performed.
[0062]
When magnification adjustment is enabled in the double-sided telecentric optical system 7, a change in magnification due to a processing error and a manufacturing error of the optical system 7 can be absorbed, and the optical system 7 capable of detecting defects with high accuracy can be easily and reliably provided. Can be provided. Even when the magnification is adjusted, variation in aberration is minimized, and inspection accuracy can be ensured.
[0063]
Further, when the beam splitter BS is provided, simultaneous inspection of the inspection by the CCD panel 9 and the inspection by visual observation becomes possible. As a result, it is also possible to compare the result of the automatic detection of the defect by the defect inspection device 1 with the result of the visual inspection.
[0064]
Note that the present invention is not limited to the above embodiment, and various modifications are possible.
For example, the object to be inspected is not limited to a liquid crystal panel, but may be another display panel such as a plasma display panel or a field emission display. The present invention is not limited to the display panel, but may be applied to inspection of an object such as an optical disk and a semiconductor wafer. It should be noted that even in these objects, when light is emitted by light emission or reflection, the effective F value can be defined.
The present invention is not limited to defect detection, and can be applied to applications such as transfer of a photomask.
The imaging means is not limited to the CCD, but may be another imaging element such as a CMOS (Complementary Metal Oxide Semiconductor).
Matters such as the number, shape, and material of the constituent lenses of the optical system can be appropriately changed within the scope of the claims.
[0065]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a telecentric optical system that has sufficient brightness to capture light from an inspection object and that can improve inspection accuracy.
In addition, it is possible to provide an inspection apparatus that includes a telecentric optical system, has sufficient brightness to take in light from an inspection object, and can improve inspection accuracy.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a defect inspection apparatus according to an embodiment of the present invention.
FIG. 2 is a lens configuration diagram of an optical system according to an embodiment of the present invention.
FIG. 3 is a diagram illustrating a display area of a liquid crystal panel as an example of an inspection target in FIG. 1;
4 (a) to 4 (c) are graphs showing various aberrations of the optical system illustrated in FIG.
5 (a) and 5 (b) are graphs showing lateral aberrations under various conditions of the optical system illustrated in FIG.
6 (c) and 6 (d) are graphs showing lateral aberrations under various conditions of the optical system illustrated in FIG. 2, following FIG.
7 is a graph showing the MTF (modulation transfer function) of the optical system illustrated in FIG.
FIG. 8 is a graph showing a result of forming an image of a pixel bright point of a liquid crystal panel using the optical system illustrated in FIG. 2;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Defect inspection apparatus, 3 ... Inspection object (liquid crystal panel), 3a ... Panel body, 3b ... Polarizing film mounting plate, 5 ... Imaging camera, 7 ... Optical system, 7A ... Optical axis, 9 ... Imaging means (CCD panel) ), 11 monitor, 15 image processing device, 30 display area, 35 moving means, L1 to L10 lens, R16 to R27, R29 to R40 lens surface, BS beam splitter, SD spectral direction, NF ND filter, STO stop, PT protective glass, do focal length of rear group, df focal length of front group

Claims (8)

A telecentric optical system comprising a plurality of lens groups arranged so that optical axes coincide with each other, and emitting light emitted at a predetermined divergence angle from an object to form an image at a predetermined position on the optical axis. ,
A telecentric optical system having an effective F value equal to or less than an effective F value of the object defined by the divergence angle. An aperture is provided between the plurality of lens groups,
A lens including at least a concave meniscus lens is arranged by positioning the concave surface of the concave meniscus lens at a position closest to an image forming position,
2. The telecentric optical system according to claim 1, wherein the concave meniscus lens has a radius of curvature rm of the concave surface that satisfies the following expression with respect to a focal length df of the lens group on the image forming side from the stop. 3.

Among the constituent lenses of the plurality of lens groups, when moving along the optical axis, the constituent lens that has a smaller effect on the image quality of an image obtained by imaging than the other constituent lenses 3. The telecentric optical system according to claim 2, further comprising a moving unit that moves along the axis. On the optical axis, the emitted light is arranged between the object and the constituent lens arranged at a position closest to the object, and the direction of the optical axis is different from the direction of the emitted light. 4. The telecentric optical system according to claim 3, further comprising a light branching unit that branches light. An optical system comprising: a plurality of lens groups arranged so that optical axes coincide with each other; and an optical system that forms outgoing light emitted from an object at a predetermined divergence angle at a predetermined position on the optical axis; Imaging means arranged at an imaging position of the system and imaging the formed object, and inspecting uniformity of the emitted light from the object based on image data obtained by the imaging means. Inspection equipment,
The inspection device, wherein the optical system is a telecentric optical system having an effective F value equal to or less than an effective F value of the object defined by the divergence angle. An aperture is provided between the plurality of lens groups,
A lens including at least a concave meniscus lens is arranged with the concave surface of the concave meniscus lens located at a position closest to the imaging position,
The inspection device according to claim 5, wherein the concave meniscus lens has a curvature radius rm of the concave surface that satisfies the following expression with respect to a focal length df of the lens group on the image forming side from a stop.

Among the constituent lenses of the plurality of lens groups, when moving along the optical axis, the constituent lens that has a smaller effect on the image quality of an image obtained by imaging than the other constituent lenses The inspection device according to claim 6, further comprising a moving unit that moves along the axis. On the optical axis, the emitted light is arranged between the object and the constituent lens arranged at a position closest to the object, and the direction of the optical axis is different from the direction of the emitted light. The inspection apparatus according to claim 7, further comprising a light branching unit that branches light.

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