JP4255586B2

JP4255586B2 - Sample inspection equipment

Info

Publication number: JP4255586B2
Application number: JP30252999A
Authority: JP
Inventors: 孝治大澤
Original assignee: Nidek Co Ltd
Current assignee: Nidek Co Ltd
Priority date: 1999-10-25
Filing date: 1999-10-25
Publication date: 2009-04-15
Anticipated expiration: 2019-10-25
Also published as: JP2001124532A

Description

【０００１】
【発明の属する技術分野】
本発明は、試料に投光された可干渉光により形成される干渉縞に基づいて試料の形状を検査する試料検査装置に関する。
【０００２】
【従来技術】
半導体ウェハ等の試料に対して可干渉光の測定光を投光し、試料表面と参照面で反射する反射光により生じる干渉縞を撮像した画像に基づいて試料の表面形状を検査する試料検査装置が知られている。このような装置では、平坦な基準平面を持つ載置台に試料裏面を密着させることで試料の裏面形状を平坦にして表面形状（平坦度）を計測している。
【０００３】
また、試料を透過する特性を有する測定光を投光し、試料の表面と裏面での反射光により干渉縞を形成させ、この干渉縞を検査することで厚さむらを検査する装置も提案されている。
【０００４】
【発明が解決しようとする課題】
しかしながら、前者の装置の場合、試料の裏面を載置台に吸着させて検査を行うと、試料自体が持つ反りや情報が修正された状態での検査となるため、厚み変動を伴わない自然な反り状態を含む表面形状を得ることができなかった。
【０００５】
自然な反り状態を含む表面形状の検査をするためには、試料の裏面を載置台に吸着せずに試料表面の形状を検査し、さらに後者の試料の表面と裏面での反射光による干渉縞に基づいて厚さむら情報を得る検査を組み合わせることで可能となるが、これを別々の検査装置で行うと、検査に手間が掛かり、検査者の負担となる。
【０００６】
両者の検査を一つの装置で行う場合、試料を透過する特性を有する光を使用すると、参照面と試料表面で形成される干渉縞と、試料の表裏面で形成される干渉縞の両方が現われるので、他方の干渉縞がノイズとして影響し、精度の高い検査を行うことを困難とする。これを避ける方法としては、表面形状の検査では試料を透過しない光を使用し、厚さむら検査では試料を透過する光を使用すると共に、両者の検査光路を分離することが考えられるが、この方法は構成が複雑になり、装置が大型化してしまう。
【０００７】
また、前者の装置では測定光を透過する試料の表面形状を高い精度で検査することは困難であった。例えば、Ｈｅ-Ｎｅレーザ等の可視光により半導体ウエハの表面形状を検査する装置を使用し、ガラスディスクの表面形状を検査しようとすると、ガラスディスクの表面と裏面で干渉縞が生じるので、これがノイズとなって精度の良い検査が困難となる。
【０００８】
本発明は上記従来技術を鑑み、装置構成を複雑とせずに、試料の表面形状及び厚さむらを精度良く検査することができる試料検査装置を提供することを技術課題とする。
【０００９】
また、測定光を透過する試料であっても、その表面形状を精度良く検査することができる試料検査装置を提供することを技術課題とする。
【００１０】
【課題を解決するための手段】
上記課題を解決するために、本発明は以下のような構成を備えることを特徴とする。
（１）測定光源からの可干渉光を試料に投光し、試料からの反射光により形成される干渉縞に基づいて試料を検査する試料検査装置において、試料表面に対向する位置に配置された参照面と、前記参照面と試料表面での反射光により形成される第１干渉縞，及び試料内部を透過した後に試料裏面で反射される反射光と試料表面で反射される反射光とにより形成される第２干渉縞を共に投影可能とするスクリーンと、該スクリーンに投影された干渉縞を撮像する撮像手段と、前記スクリーンに投影される前記第１干渉縞を実質的に除去する第１干渉縞除去手段であって、前記参照面に対して試料を相対的に傾斜させる傾斜手段を有し、該傾斜手段によって第１干渉縞の縞密度を前記撮像手段の解像度よりも小さくすることにより前記第１干渉縞を実質的に除去する第１干渉縞除去手段と、前記スクリーンに投影される前記第２干渉縞を実質的に除去する第２干渉縞除去手段であって、試料に投光される可干渉光の光量を調整する光量調整手段を有し、該光量調整手段により可干渉光を減光し、試料裏面からの反射光を減衰させることで前記第２干渉縞を実質的に除去するか、又は試料に投光される可干渉光の干渉性を調節する調節手段を有し、該調節手段により可干渉光の干渉性を低下させることで前記第２干渉縞を実質的に除去する第２干渉縞除去手段と、前記第１干渉縞除去手段により残った第２干渉縞画像及び前記第２干渉縞除去手段によって残った第１干渉縞画像に基づいてそれぞれ試料の形状を検査する検査手段と、を備えることを特徴とする。
（２）（１）の試料検査装置において、前記可干渉光は試料に対して斜め方向から投光され、前記傾斜手段は前記試料を可干渉光の投光光軸に対して試料表面上で直交する軸線方向に傾斜させることを特徴とする。
【００２１】
【発明の実施の形態】
本発明について一実施形態を挙げ、図面に基づいて以下に説明する。図１は実施形態である試料検査装置の要部概略図である。本装置は斜入射干渉計を使用している。
【００２２】
測定光源１から出射される可干渉光は、その一部が試料６を透過する特性（波長）を有しており、例えば、半導体ウェハの場合は赤外光を発する半導体レーザが利用でき、ガラスディスクの場合は可視光を発するＨｅ-Ｎｅレーザが利用できる。測定光源１より出射した光はエキスパンダレンズ２を通過した後、コリメータレンズ３により平行光束にされ、ロータリープリズム４を介してプリズム５に入射する。ロータリープリズム４は制御部１１により駆動制御され、ロータリープリズム４の駆動により測定光の試料６への入射角（投光角度）が変更される。試料６は載置台１３に吸着保持されるのではなく、試料６の端部が数箇所で保持されるように載置される。
【００２３】
プリズム５に入射した測定光の一部は参照面５ａで反射され、その他の光は参照面５ａを透過する。参照面５ａを透過した光の一部は試料表面６ａで反射し、残りの光は試料表面６ａを透過して試料裏面６ｂに至って反射する。スクリーン７には、参照面５ａと試料表面６ａでの反射光による干渉縞ＩＳと、試料表面６ａと試料裏面６ｂでの反射光による干渉縞ＩＴが形成される（図２参照）。参照面５ａと試料裏面６ｂでの反射光による干渉縞は、それぞれの反射光強度に大きな差があるため、スクリーン７上では観察されない。
【００２４】
スクリーン７上に形成された干渉縞像は撮像レンズ８によりＣＣＤカメラ９の撮像面に結像し、撮像される。ＣＣＤカメラ９で撮像された干渉縞像は解析装置１０に送信され、モニタ１４に表示される。解析装置１０では干渉縞を基に表面形状や厚さむらを得るための演算解析等が行われ、干渉縞像や各種情報はメモリ１５に記憶される。１７は試料６を載置する載置台１３の傾斜角度を変更する駆動装置であり、１２は測定感度の変更スイッチや駆動装置１７への駆動指令を行うスイッチ等を持つ入力部である。
【００２５】
以上のような構成を備える試料検査装置において、以下にその動作を説明する。図３は検査動作のフローチャート図である。
【００２６】
検査者は載置台１３に試料６を配置して検査を開始する。試料６は載置台１３に吸着保持されるのではなく、試料６の端部が数箇所で保持されるため、自然な反り状態を含む表面形状の平坦度を検査することができる。制御部１１が光源１を発光させると、スクリーン７上には２つの干渉縞ＩＳ，ＩＴが投影され、ＣＣＤカメラ９で撮像した画像はモニタ１４に表示される。
【００２７】
図２に示す２つの干渉縞像は、参照面５ａと試料表面６ａによる干渉縞ＩＳと、試料表面６ａと裏面６ｂによる干渉縞ＩＴであり、検査者はモニタ１４に表示される干渉縞ＩＳ，ＩＴを基に試料形状を検査する。また、解析装置１０はそれぞれの干渉縞ＩＳ，ＩＴを基に表面形状及び厚さむらを定量的に演算解析し、測定する。以下、表面形状検査と厚さむら検査について、各々説明する。
【００２８】
＜表面形状検査＞
表面形状検査では参照面５ａと試料表面６ａでの反射光による干渉縞ＩＳを利用する。この際、試料表面６ａと裏面６ｂでの反射光による干渉縞ＩＴはノイズとなるため、精度の良い表面形状を得るためには、干渉縞ＩＴの影響を取り除く、あるいは小さくすることが必要となる。
【００２９】
この方法としては、光源１の光量を調節することで、干渉縞ＩＴの影響を減少させることができる。具体的には図４の参照光の反射状況を説明する図に示すように、試料表面６ａを通過した光が試料６内で吸収されるか、あるいは試料裏面６ｂで反射した光が試料表面６ａを透過するまでの間に試料６内で吸収される程度の光量まで弱くする。光量の調節は検査者が手動により行うことができるが、干渉縞ＩＴの明るさ（輝度）情報を検出し、予め設定した閾値以下になるように制御部１１が光源１の光量を自動的に調節するようにすることも可能である。
【００３０】
これにより、試料裏面６ｂからの反射光は試料表面６ａでの反射光と干渉を起こすことなく試料６に吸収され、スクリーン７上に干渉縞ＩＴは形成されなくなる。一方、干渉縞ＩＴに対して干渉縞ＩＳのコントラストは遥かに高いため、光源１の光量を落としても参照面５ａと試料表面６ａの反射光による干渉縞ＩＳのみがＣＣＤカメラ９に撮像される。
【００３１】
また、試料６に投光される可干渉光の干渉性を低下させることでも裏面反射を除去することが可能である。例えば、測定光源１に半導体レーザ光源を用いる。半導体レーザ光源は通常１つのピーク波長を有しているが、温度が変化するとピーク波長が移行する特性がある。図５に示すように、通常１つのピーク波長λ１を有する参照光が（図５（ａ）参照）、温度変化によって波長λ１が弱まり、波長λ２が強くなり始める。一旦、２つの波長λ１，λ２の強度がほぼ等しくなった後（図５（ｂ）参照）、ピーク波長λ２を有するようになるモードジャンプが生じる。（図５（ｃ）参照）。
【００３２】
裏面反射を除去する際には、図５（ｂ）に示す２つの波長λ１，λ２がほぼ同じ強度を有する状態の参照光を利用する。ほぼ同じ強度を有する２つの波長λ１，λ２によるレーザ光の干渉性は弱まるため、干渉強度（コントラスト）が低い干渉縞ＩＴは除され、参照面と試料表面での干渉縞ＩＳが残るようになる。
【００３３】
図６は、光源１を半導体レーザ光源とし、参照光の一部をビームスプリッタ３０で分割し、センサ３１で波長スペクトルを検出しながら、半導体レーザ光源への供給電力により温度を調節し、２つの波長強度がほぼ等しい参照光を投光することで、裏面反射による干渉縞ＩＴを除去する例である。
【００３４】
なお、試料６に投光される可干渉光の干渉性を低下させる手段としては、上記の他、図１におけるレンズ２とレンズ３の間にスリガラス板を配置した構成でも可能である。レンズ２の焦点をスリガラス板の拡散面からずらすことによって、点光源を見かけ上広げてレーザ光の干渉性を低下させるように調整できる。
【００３５】
以上のように、干渉縞ＩＴを除去又は減衰させることができれば、ＣＣＤカメラ９には表面形状情報が含まれた干渉縞ＩＳだけが撮像されるので、干渉縞ＩＳを基に公知の位相シフト法により試料表面形状を定量的に算出することができる。表面形状を得るための位相シフト法では、図示なきピエゾ素子を制御部１１で駆動制御してプリズム５、又は載置台１３を微妙に移動させ、参照面５ａと試料表面６ａとの距離を変化させる。この距離変化に応じて位相の異なる干渉縞像が形成されるので、位相の異なる複数の干渉縞像をＣＣＤカメラ９で撮像し、メモリ１５に記憶する。解析装置１０では記憶された複数の干渉縞像を基に位相シフト法により試料表面形状を算出する。解析装置１０により得られた試料表面形状データは鳥瞰図や各種情報としてモニタ１４に表示される。
【００３６】
＜厚さむら検査＞
厚さむら検査について説明する。厚さむら検査では試料表面６ａと試料裏面６ｂでの反射光による干渉縞ＩＴを利用する。厚さむら検査の場合には、参照面５ａと試料表面６ａでの反射光による干渉縞ＩＳはノイズとなるため、厚さむらを精度良く検査する上で干渉縞ＩＳを取り除く、あるいは減衰させてやる必要がある。
【００３７】
検査者は干渉縞ＩＳを除去するために、入力部１２を操作して試料６が配置された載置台１３を参照面５ａに対して傾斜するように駆動する。その傾斜方向は、図７に示すように、試料表面６ａに斜め方向から投光される測定光の光軸Ｌ１に対して試料表面上で直交する軸線Ｌ２方向である矢印Ａ方向に傾斜させる。これにより、測定光の入射角度をほとんど変えることなく試料表面６ａと参照面５ａとの平行度を変更することができる。なお、載置台１３の傾斜駆動は制御部１１の制御により駆動装置１７によって行われるが、回転ノブの操作等によって手動調整する構成でも良い。
【００３８】
試料６を傾斜させると干渉縞ＩＳの濃淡の間隔が密になり、干渉縞の数が多く形成される。さらに試料６の傾斜を大きくしていくと、干渉縞密度が順次密になり、干渉縞の間隔がＣＣＤカメラ９の解像度（分解能）を越えると、ＣＣＤカメラ９では干渉縞ＩＳが撮像されなくなる。このように干渉縞ＩＳの間隔をＣＣＤカメラ９の解像度以下にすることで干渉縞ＩＳを実質的に除去することができる。また、試料６は測定光の光軸に対して試料表面上で直交する軸線方向に傾斜させているので、測定光の入射角は変更せず、傾斜による干渉縞ＩＴへの影響（測定感度の影響）は殆どない。これにより、干渉縞ＩＳのみが除去され、干渉縞ＩＴのみがＣＣＤカメラ９に撮像される。
【００３９】
以上のように、干渉縞ＩＳのみを除去することで、検査者はモニタ１４に映出される干渉縞ＩＴを基に精度良く検査を行うことができ、また、解析装置１０では干渉縞ＩＴを基に位相シフト法等を用いて演算解析することで、厚さむらを定量的に算出することができる。
【００４０】
なお、干渉縞像ＩＴに対して位相シフト法により演算解析する場合、干渉縞ＩＳのように干渉を起こす２つの反射面の距離を変更することができないため、本実施形態ではロータリープリズム４を回転駆動して入射角を変更させることにより干渉縞を位相シフトさせ、複数の干渉縞を基に厚さむら情報を定量的に算出する。例えば、４ステップの位相シフト法では、試料へ投光される測定光の角度変化は、スクリーン７上に形成される干渉縞がπ／２分の位相だけ移動するように制御する。このようにして干渉縞の位相をπ／２分ずつ変化させた４枚の干渉縞画像を順次撮像し、これをメモリ１５に記憶する。解析装置１０はメモリ１５に記憶した４枚の干渉縞画像から位相シフト法によって試料６の厚さむらの形状を解析する。
【００４１】
また、解析装置１０は定量的に算出した試料表面形状と厚さむら情報を基に、試料全体を三次元形状表示することが可能であり、検査者はモニタ１４に表示される検査試料の情報を基に容易に検査を行うことができる。
【００４２】
以上、１つの試料の表面形状と厚さむらの両方を検査する場合について説明したが、これに限らず本発明は次のように適用することができる。すなわち、半導体ウエハの表面形状を検査するために、測定光源１としてＨｅ-Ｎｅレーザ等の可視光を使用した装置において、可視光を透過するガラスディスクの表面形状を検査したい場合、前述した方法により光源１の光量を弱くしたり、または測定光の干渉性を低下させる。これにより、可視光を透過するガラスディスクであっても、その表面と裏面での反射光による干渉縞の影響を取り除くことができ、ガラスディスクの表面形状の検査が可能となる。
【００４３】
【発明の効果】
以上説明したように本発明によれば、装置構成を複雑とせずに、試料の自然な反り状態のままの表面形状、厚さむらを検査することができる。また、測定光を透過する試料であっても、ノイズとなる干渉縞を実質的に除去することで、表面形状を精度良く検査することができる。
【図面の簡単な説明】
【図１】実施形態である試料検査装置の要部概略図である。
【図２】スクリーン上に投影される干渉縞の説明図である。
【図３】検査動作のフローチャート図である。
【図４】参照光の反射状況を説明する図である。
【図５】半導体レーザ光源の温度変化による出射光の波長変化の説明図である。
【図６】裏面反射による干渉縞ＩＴを除去する場合の変容例の要部概略図である。
【図７】干渉縞ＩＳを除去する場合の試料（載置台）の傾斜方向を説明する図である。
【符号の説明】
１光源
５プリズム
５ａ参照基準面
６試料
６ａ試料表面
６ｂ試料裏面
９ＣＣＤカメラ
１０解析装置
１１制御部
１３載置台
１５メモリ
１７駆動装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sample inspection apparatus that inspects the shape of a sample based on interference fringes formed by coherent light projected onto the sample.
[0002]
[Prior art]
A sample inspection apparatus that projects measurement light of coherent light onto a sample such as a semiconductor wafer and inspects the surface shape of the sample based on an image obtained by imaging interference fringes generated by reflected light reflected from the sample surface and the reference surface It has been known. In such an apparatus, the back surface shape of the sample is made flat by bringing the back surface of the sample into close contact with a mounting table having a flat reference plane, and the surface shape (flatness) is measured.
[0003]
Also proposed is an apparatus that inspects thickness unevenness by projecting measurement light having the characteristics of transmitting through the sample, forming interference fringes by reflected light on the front and back surfaces of the sample, and inspecting the interference fringes. ing.
[0004]
[Problems to be solved by the invention]
However, in the case of the former apparatus, if the inspection is performed with the back surface of the sample adsorbed to the mounting table, the inspection itself is performed with the warpage and information of the sample corrected, so that natural warpage without thickness fluctuations occurs. The surface shape including the state could not be obtained.
[0005]
In order to inspect the surface shape including the natural warpage, the shape of the sample surface is inspected without adsorbing the back surface of the sample to the mounting table, and interference fringes caused by reflected light on the surface and back surface of the latter sample This is possible by combining inspections for obtaining thickness unevenness information based on the above, but if this is performed with separate inspection apparatuses, the inspection takes time and burdens on the inspector.
[0006]
When both inspections are performed with a single device, if light having the property of transmitting through the sample is used, both interference fringes formed on the reference surface and the sample surface and interference fringes formed on the front and back surfaces of the sample appear. Therefore, the other interference fringe influences as noise, making it difficult to perform a highly accurate inspection. As a method to avoid this, it is conceivable to use light that does not pass through the sample in the inspection of the surface shape, and use light that passes through the sample in the uneven thickness inspection, and separate the inspection optical paths of both. The method is complicated in configuration and the apparatus becomes large.
[0007]
In the former apparatus, it is difficult to inspect the surface shape of the sample that transmits the measurement light with high accuracy. For example, when using a device that inspects the surface shape of a semiconductor wafer with visible light such as a He-Ne laser and trying to inspect the surface shape of a glass disk, interference fringes are generated on the front and back surfaces of the glass disk. This makes accurate inspection difficult.
[0008]
An object of the present invention is to provide a sample inspection apparatus capable of accurately inspecting the surface shape and thickness unevenness of a sample without complicating the apparatus configuration in view of the above-described prior art.
[0009]
It is another object of the present invention to provide a sample inspection apparatus that can accurately inspect the surface shape of a sample that transmits measurement light.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, the present invention is characterized by having the following configuration.
(1) In a sample inspection apparatus that projects coherent light from a measurement light source onto a sample and inspects the sample based on interference fringes formed by reflected light from the sample, the sample is arranged at a position facing the sample surface. Formed by the reference surface, the first interference fringes formed by the reflected light on the reference surface and the sample surface, and the reflected light reflected on the sample back surface after passing through the inside of the sample and the reflected light reflected on the sample surface screen and, first interference substantially removed imaging means for imaging the projected interference pattern on the screen, the first interference fringes projected on the screen together with the possible projection of the second interference fringes The fringe removing unit includes a tilting unit that tilts the sample relative to the reference surface, and the tilting unit makes the fringe density of the first interference fringes smaller than the resolution of the imaging unit. First interference fringe A first interference fringe removing unit that substantially removes the second interference fringe and a second interference fringe removing unit that substantially removes the second interference fringe projected on the screen, the coherent light projected on the sample A light amount adjusting means for adjusting the light amount of the light beam, the coherent light is attenuated by the light amount adjusting means, and the reflected light from the back surface of the sample is attenuated to substantially remove the second interference fringes, or A second interference that has adjustment means for adjusting the coherence of the coherent light projected on the sample, and that substantially eliminates the second interference fringes by reducing the coherence of the coherent light by the adjustment means; A fringe removing unit, an inspection unit for inspecting the shape of each sample based on the second interference fringe image remaining by the first interference fringe removing unit and the first interference fringe image remaining by the second interference fringe removing unit; It is characterized by providing.
(2) In the sample inspection apparatus of (1), the coherent light is projected from an oblique direction with respect to the sample, and the tilting unit causes the sample to be projected on the surface of the sample with respect to the projecting optical axis of the coherent light. It is characterized by inclining in the direction of an orthogonal axis.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described below with reference to an embodiment. FIG. 1 is a schematic diagram of a main part of a sample inspection apparatus according to an embodiment. This device uses a grazing incidence interferometer.
[0022]
The coherent light emitted from the measurement light source 1 has a characteristic (wavelength) that part of the coherent light is transmitted through the sample 6. For example, in the case of a semiconductor wafer, a semiconductor laser that emits infrared light can be used. In the case of a disk, a He—Ne laser that emits visible light can be used. The light emitted from the measurement light source 1 passes through the expander lens 2, is converted into a parallel light beam by the collimator lens 3, and enters the prism 5 through the rotary prism 4. The rotary prism 4 is driven and controlled by the control unit 11, and the incident angle (light projection angle) of the measurement light to the sample 6 is changed by driving the rotary prism 4. The sample 6 is not sucked and held on the mounting table 13 but is placed so that the end of the sample 6 is held at several places.
[0023]
Part of the measurement light incident on the prism 5 is reflected by the reference surface 5a, and other light passes through the reference surface 5a. A part of the light transmitted through the reference surface 5a is reflected by the sample surface 6a, and the remaining light is transmitted through the sample surface 6a and reflected by the sample back surface 6b. On the screen 7, interference fringes IS caused by reflected light on the reference surface 5a and the sample surface 6a and interference fringes IT caused by reflected light on the sample surface 6a and the sample back surface 6b are formed (see FIG. 2). The interference fringes due to the reflected light on the reference surface 5a and the sample back surface 6b are not observed on the screen 7 because there is a large difference in the intensity of the reflected light.
[0024]
The interference fringe image formed on the screen 7 is imaged on the imaging surface of the CCD camera 9 by the imaging lens 8 and imaged. The interference fringe image captured by the CCD camera 9 is transmitted to the analysis device 10 and displayed on the monitor 14. In the analysis device 10, calculation analysis and the like for obtaining surface shape and thickness unevenness are performed based on the interference fringes, and the interference fringe image and various information are stored in the memory 15. Reference numeral 17 denotes a drive device that changes the tilt angle of the mounting table 13 on which the sample 6 is placed. Reference numeral 12 denotes an input unit having a measurement sensitivity change switch, a switch that gives a drive command to the drive device 17, and the like.
[0025]
The operation of the sample inspection apparatus having the above configuration will be described below. FIG. 3 is a flowchart of the inspection operation.
[0026]
The inspector places the sample 6 on the mounting table 13 and starts the inspection. Since the sample 6 is not held by suction on the mounting table 13, the end of the sample 6 is held at several places, so that the flatness of the surface shape including the natural warpage can be inspected. When the control unit 11 causes the light source 1 to emit light, two interference fringes IS and IT are projected on the screen 7, and an image captured by the CCD camera 9 is displayed on the monitor 14.
[0027]
The two interference fringe images shown in FIG. 2 are an interference fringe IS due to the reference surface 5a and the sample surface 6a, and an interference fringe IT due to the sample surface 6a and the back surface 6b. The sample shape is inspected based on IT. Further, the analysis device 10 quantitatively analyzes and measures the surface shape and thickness unevenness based on the interference fringes IS and IT. Hereinafter, the surface shape inspection and the thickness unevenness inspection will be described respectively.
[0028]
<Surface shape inspection>
In the surface shape inspection, interference fringes IS caused by reflected light from the reference surface 5a and the sample surface 6a are used. At this time, the interference fringes IT due to the reflected light on the sample surface 6a and the back surface 6b become noise, and in order to obtain a highly accurate surface shape, it is necessary to remove or reduce the influence of the interference fringes IT. .
[0029]
As this method, the influence of the interference fringe IT can be reduced by adjusting the light quantity of the light source 1. Specifically, as shown in the diagram explaining the reflection state of the reference light in FIG. 4, the light that has passed through the sample surface 6a is absorbed in the sample 6, or the light reflected by the sample back surface 6b is reflected in the sample surface 6a. Until the amount of light absorbed in the sample 6 is reduced. The light quantity can be adjusted manually by the inspector. However, the brightness (luminance) information of the interference fringe IT is detected, and the control unit 11 automatically adjusts the light quantity of the light source 1 so as to be below a preset threshold value. It is also possible to adjust.
[0030]
Thereby, the reflected light from the sample back surface 6b is absorbed by the sample 6 without causing interference with the reflected light on the sample surface 6a, and the interference fringes IT are not formed on the screen 7. On the other hand, since the contrast of the interference fringe IS is much higher than the interference fringe IT, only the interference fringe IS caused by the reflected light from the reference surface 5a and the sample surface 6a is picked up by the CCD camera 9 even if the light amount of the light source 1 is reduced. .
[0031]
Further, it is also possible to remove the back surface reflection by reducing the coherence of the coherent light projected on the sample 6. For example, a semiconductor laser light source is used as the measurement light source 1. A semiconductor laser light source usually has one peak wavelength, but has a characteristic that the peak wavelength shifts when the temperature changes. As shown in FIG. 5, the reference light normally having one peak wavelength λ1 (see FIG. 5A), the wavelength λ1 becomes weaker and the wavelength λ2 starts to become stronger due to the temperature change. Once the intensities of the two wavelengths λ1 and λ2 are substantially equal (see FIG. 5B), a mode jump that has a peak wavelength λ2 occurs. (See FIG. 5 (c)).
[0032]
When removing back surface reflection, reference light in a state where the two wavelengths λ1 and λ2 shown in FIG. 5B have substantially the same intensity is used. Since the coherence of the laser light by the two wavelengths λ1 and λ2 having substantially the same intensity is weakened, the interference fringe IT having a low interference intensity (contrast) is excluded, and the interference fringe IS on the reference surface and the sample surface remains. .
[0033]
In FIG. 6, the light source 1 is a semiconductor laser light source, a part of the reference light is divided by the beam splitter 30, and the temperature is adjusted by the power supplied to the semiconductor laser light source while detecting the wavelength spectrum by the sensor 31. This is an example in which interference fringes IT due to back surface reflection are removed by projecting reference light having substantially the same wavelength intensity.
[0034]
In addition to the above, as a means for reducing the coherence of coherent light projected on the sample 6, a configuration in which a ground glass plate is disposed between the lens 2 and the lens 3 in FIG. By shifting the focal point of the lens 2 from the diffusing surface of the ground glass plate, the point light source can be apparently expanded so that the coherence of the laser light is reduced.
[0035]
As described above, if the interference fringe IT can be removed or attenuated, only the interference fringe IS including the surface shape information is picked up by the CCD camera 9, so that a known phase shift method is used based on the interference fringe IS. Thus, the sample surface shape can be calculated quantitatively. In the phase shift method for obtaining the surface shape, a piezo element (not shown) is driven and controlled by the control unit 11 to slightly move the prism 5 or the mounting table 13 to change the distance between the reference surface 5a and the sample surface 6a. . Since interference fringe images having different phases are formed in accordance with the change in distance, a plurality of interference fringe images having different phases are picked up by the CCD camera 9 and stored in the memory 15. The analysis apparatus 10 calculates the sample surface shape by the phase shift method based on the plurality of stored interference fringe images. The sample surface shape data obtained by the analyzer 10 is displayed on the monitor 14 as a bird's eye view or various information.
[0036]
<Thickness unevenness inspection>
The thickness unevenness inspection will be described. In the thickness unevenness inspection, interference fringes IT caused by reflected light from the sample surface 6a and the sample back surface 6b are used. In the case of the thickness unevenness inspection, the interference fringes IS due to the reflected light on the reference surface 5a and the sample surface 6a become noises. Therefore, the interference fringes IS are removed or attenuated in accurately checking the thickness unevenness. I need to do it.
[0037]
In order to remove the interference fringes IS, the inspector operates the input unit 12 to drive the mounting table 13 on which the sample 6 is disposed so as to be inclined with respect to the reference surface 5a. As shown in FIG. 7, the tilt direction is tilted in the direction of arrow A, which is an axis L2 direction perpendicular to the sample surface with respect to the optical axis L1 of the measurement light projected on the sample surface 6a from an oblique direction. Thereby, the parallelism between the sample surface 6a and the reference surface 5a can be changed with almost no change in the incident angle of the measurement light. The tilting drive of the mounting table 13 is performed by the driving device 17 under the control of the control unit 11, but may be manually adjusted by operating a rotary knob or the like.
[0038]
When the sample 6 is tilted, the density of the interference fringes IS becomes dense, and the number of interference fringes is increased. When the inclination of the sample 6 is further increased, the interference fringe density is gradually increased. When the interference fringe interval exceeds the resolution (resolution) of the CCD camera 9, the CCD camera 9 does not capture the interference fringe IS. Thus, the interference fringes IS can be substantially removed by setting the interval of the interference fringes IS to be equal to or less than the resolution of the CCD camera 9. In addition, since the sample 6 is inclined in the axial direction orthogonal to the optical axis of the measurement light on the sample surface, the incident angle of the measurement light is not changed, and the influence on the interference fringe IT due to the inclination (measurement sensitivity) There is almost no influence. As a result, only the interference fringe IS is removed, and only the interference fringe IT is imaged by the CCD camera 9.
[0039]
As described above, by removing only the interference fringe IS, the inspector can accurately inspect based on the interference fringe IT displayed on the monitor 14, and the analysis apparatus 10 uses the interference fringe IT as a basis. Further, the thickness unevenness can be quantitatively calculated by performing a calculation analysis using a phase shift method or the like.
[0040]
Note that when the interference fringe image IT is calculated and analyzed by the phase shift method, the distance between the two reflecting surfaces that cause interference cannot be changed as in the interference fringe IS. Therefore, in this embodiment, the rotary prism 4 is rotated. By driving and changing the incident angle, the interference fringes are phase-shifted, and thickness unevenness information is quantitatively calculated based on the plurality of interference fringes. For example, in the four-step phase shift method, the change in the angle of the measurement light projected onto the sample is controlled so that the interference fringes formed on the screen 7 move by a phase of π / 2. In this way, four interference fringe images in which the phase of the interference fringe is changed by π / 2 are sequentially taken and stored in the memory 15. The analysis device 10 analyzes the shape of the uneven thickness of the sample 6 from the four interference fringe images stored in the memory 15 by the phase shift method.
[0041]
Further, the analysis apparatus 10 can display the entire sample in a three-dimensional shape based on the quantitatively calculated sample surface shape and thickness unevenness information, and the inspector can display information on the inspection sample displayed on the monitor 14. It is possible to easily inspect based on the above.
[0042]
The case where both the surface shape and the thickness unevenness of one sample are inspected has been described above, but the present invention is not limited to this and can be applied as follows. That is, in order to inspect the surface shape of the semiconductor wafer, in the apparatus using visible light such as a He—Ne laser as the measurement light source 1, when it is desired to inspect the surface shape of the glass disk that transmits visible light, the method described above is used. The light quantity of the light source 1 is weakened or the coherence of the measurement light is reduced. Thereby, even if it is a glass disk which permeate | transmits visible light, the influence of the interference fringe by the reflected light on the surface and back surface can be removed, and the surface shape of a glass disk can be test | inspected.
[0043]
【The invention's effect】
As described above, according to the present invention, it is possible to inspect the surface shape and thickness unevenness of a sample in a natural warpage state without complicating the apparatus configuration. Moreover, even if it is a sample which permeate | transmits measurement light, a surface shape can be test | inspected accurately by removing the interference fringe used as noise substantially.
[Brief description of the drawings]
FIG. 1 is a schematic view of a main part of a sample inspection apparatus according to an embodiment.
FIG. 2 is an explanatory diagram of interference fringes projected on a screen.
FIG. 3 is a flowchart of an inspection operation.
FIG. 4 is a diagram illustrating a reflection state of reference light.
FIG. 5 is an explanatory diagram of a wavelength change of emitted light due to a temperature change of a semiconductor laser light source.
FIG. 6 is a schematic diagram of a main part of a modification example in the case of removing interference fringes IT due to back surface reflection.
FIG. 7 is a diagram for explaining an inclination direction of a sample (mounting table) when interference fringes IS are removed.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light source 5 Prism 5a Reference reference plane 6 Sample 6a Sample surface 6b Sample back surface 9 CCD camera 10 Analyzing device 11 Control unit 13 Mounting table 15 Memory 17 Drive device

Claims

In a sample inspection apparatus that projects coherent light from a measurement light source onto a sample and inspects the sample based on interference fringes formed by reflected light from the sample, a reference surface disposed at a position facing the sample surface; The first interference fringes formed by the reference surface and the reflected light on the sample surface, and the first interference fringe formed by the reflected light reflected on the back surface of the sample after passing through the inside of the sample and the reflected light reflected on the sample surface A screen capable of projecting two interference fringes together, an imaging means for imaging the interference fringes projected on the screen, and a first interference fringe removing means for substantially removing the first interference fringes projected on the screen And an inclination means for inclining the sample relative to the reference surface, and the first interference is reduced by making the fringe density of the first interference fringes smaller than the resolution of the imaging means by the inclination means. Real streaks A first interference fringe removal means for removing the, a second interference fringe removal means for substantially removing the second interference fringes projected on the screen, the amount of coherent light projected on the sample A light amount adjusting means for adjusting, the coherent light is attenuated by the light amount adjusting means, and the reflected light from the back surface of the sample is attenuated to substantially remove the second interference fringes or to be projected on the sample. A second interference fringe removing unit that has an adjusting unit that adjusts the coherence of the coherent light that is emitted, and that substantially eliminates the second interference fringe by reducing the coherence of the coherent light by the adjusting unit; And inspection means for inspecting the shape of the sample based on the second interference fringe image remaining by the first interference fringe removal means and the first interference fringe image remaining by the second interference fringe removal means, respectively. Sample inspection device characterized by

2. The sample inspection apparatus according to claim 1, wherein the coherent light is projected from an oblique direction with respect to the sample, and the tilting unit causes the sample to be orthogonal to the projection optical axis of the coherent light on the sample surface. A sample inspection apparatus characterized by being inclined in a direction.