JP2004042215A

JP2004042215A - Polishing stone, and apparatus and method for mirror-finishing cut surface

Info

Publication number: JP2004042215A
Application number: JP2002204679A
Authority: JP
Inventors: Naoto Minagawa; 皆川　直人
Original assignee: Disco Abrasive Systems Ltd
Current assignee: Disco Corp
Priority date: 2002-07-12
Filing date: 2002-07-12
Publication date: 2004-02-12

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing stone, etc., which improves its straightness during mirror-finishing, and also prevents a burn mark produced on a cut surface. <P>SOLUTION: The polishing stone is provided with a stone part 52 arranged at least on an outer peripheral part of at least one side face, and a plurality of grooves 58 formed by cutting off a part of the stone part. A contact area of the polishing stone with a workpiece during polishing is sufficiently minimized by providing the stone part on the outer peripheral part of the side face of the polishing stone and further by providing a plurality of grooves on the stone part according to this configuration. Therefore, the sufficient straightness during polishing is achieved even if the polishing stone is thin, and as a result, the accuracy of the mirror finishing is improved. Further, because a sufficient coolant is supplied to the polishing point through a plurality of the grooves formed on the stone part, the polishing point is satisfactorily cooled. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は，研磨砥石，切断面鏡面加工装置および切断面鏡面加工方法にかかり，特に，切断砥石によって切断された基板の切断面を切削研磨する研磨砥石等に関する。
【０００２】
【従来の技術】
近年，表面に光導波路などの回路が形成された基板をダイシングして，複数のチップ（光学素子）を切り出す際には，光信号が通過，反射等する部分となる切断面を鏡面加工することが要求されるようになった。
【０００３】
かかる切断面の鏡面加工方法としては，特開平１１一１９５６２７号公報に記載のように，光学素子の切断面を回転ディスクによって研磨する方法が提案されている。しかし，かかる手法では，基板の切断加工と，切断面の研磨加工とが別工程で行われるため，生産効率が低下してしまう。
【０００４】
このため，切断加工された基板を移送することなく，そのままの位置で切断面を研磨加工して，切断加工と研磨加工とを同工程で行う手法が提案されている。かかる手法としては，特開平２−３０３０５０号公報に記載のように，切断砥石で基板を切断して切溝（カーフ）を形成した後，厚さが切断砥石より厚く（つまり，切溝の幅よりも厚く）かつ微粒砥石からなる研磨砥石で切溝を所定幅に拡幅し，切断面の両面を同時に切削研磨する手法が提案されている。しかし，このような手法では，微粒砥石で構成された研磨砥石は摩耗が著しく，切断面の研磨に必要な厚さを維持することが困難であるという問題があった。このように研磨砥石の寿命が短いため，頻繁に研磨砥石を交換する必要があるので，生産性を大きく低下させる原因となっていた。
【０００５】
これらの問題を解決するために，本願発明者らは，鋭意努力して，新規かつ改良された切断面鏡面加工方法を想到した。かかる手法とは，特願２００２−１０４８８８号に記載のように，切断砥石より薄い研磨砥石によって，切断面の一方の面を研磨砥石の一側面で切削研磨し，その後，研磨砥石の他側面が切断面の他方の面に接触するように研磨砥石を移動させ，この切断面の他方の面を研磨砥石の他側面で切削研磨するという方法である。
【０００６】
【発明が解決しようとする課題】
しかしながら，上記従来の切断面鏡面加工方法では，薄い研磨砥石を使用しているため，研磨砥石に硬質の基台部を設けて剛性を高めるとともに，研磨砥石の両側面に側面逃げを形成して鏡面加工時の側面抵抗を低減させたとしても，加工中に研磨砥石が切断面によって押圧されて歪んでしまい，研磨砥石の直進性を十分に保つことができないという問題があった。このため，研磨した切断面に歪みが生じてしまい，加工精度が不十分なものとなる場合があった。
【０００７】
このような従来の切断面鏡面加工方法により生じた切断面の歪みを，模式図を用いてより詳細に説明する。図１０（ａ）に示すように，研磨後の切断面は，垂直方向（即ち，基板表面に対して垂直方向）には，切断面の下部にいくほど膨らむように湾曲してしまっていた。また，図１０（ｂ）に示すように，水平方向（即ち，基板表面に対して平行な切溝の長手方向）には，切断面の中央付近ほど膨らむように湾曲してしまっていた。実際には，このような切断面の歪みは，ミクロンレベルの歪みであり目視できるものではないが，精密装置であるチップの性能上では大きな支障を来す場合がある。
【０００８】
また，上記のような問題に加え，研磨時に切断面と研磨砥石との間で生じる摩擦熱によって面焼けと呼ばれる現象が起こり，鏡面加工後の切断面が黒ずんでしまうという問題も生じた。
【０００９】
本発明は，上記問題点に鑑みてなされたものであり，本発明の目的は，切断面の鏡面加工時に，研磨砥石の直進性を維持して加工精度を向上できるとともに，切断面に生ずる面焼けを抑制することも可能な，新規かつ改良された切断面鏡面加工方法およびこれを実現する研磨砥石，切断面鏡面加工装置を提供することである。
【００１０】
【課題を解決するための手段】
上記課題を解決するため，本発明の第１の観点によれば，少なくとも一側面の少なくとも外周部に設けられる砥石部と，砥石部の一部を削り取って形成される複数の溝と，を備えることを特徴とする，研磨砥石が提供される。
【００１１】
かかる構成により，微粒砥石からなり実際に切断面と干渉して切削研磨する機能を有する砥石部を，研磨砥石の側面の外周部に突出するような形状で設けることができる。換言すると，研磨砥石の側面に当該外周部を残して陥没するような側面逃げを形成できる。さらに，当該外周部は複数の溝によって削り取られて複数の領域に分断されているので，突出している砥石部の面積をさらに小さくすることができる。このような側面逃げと複数の溝を備えることにより，高速回転させた研磨砥石の側面を用いて被加工物を切削研磨して鏡面加工するときには，被加工物と研磨砥石の側面との接触面積を小さくすることができる。このため，加工中に被加工物から受ける側面抵抗（反発力）が低減されるため，薄い研磨砥石であっても，加工中の歪みやぶれが抑制され，直進性を向上させることができる。従って，鏡面加工後の平坦度が向上し，鏡面加工精度を高めることができる。また，加工時には砥石部に形成された複数の溝を通って加工点に十分な量の切削水が供給されるので，加工点を十分に冷却できる。
【００１２】
また，上記研磨砥石は，金属製の基台部と，基台部の少なくとも一側面に取り付けられた砥石部と，を備える，如く構成すれば，硬質な基台部を設けることで研磨砥石全体の剛性を高めることができる。このため，鏡面加工時における研磨砥石の直進性をさらに高めることができる。また，上記基台部は超硬合金からなるように構成して，研磨砥石の剛性をより高めてもよい。さらに，砥石部の一部を削り取って形成される溝の深さを，中心にある基台部にまで至らないような深さにする（即ち，基台部には当該溝が形成されないようにする）ことで，略円板状若しくは略リング状の基台部が比較的大きい径を確保することができる。従って，砥石部を削り取って複数の溝を形成することに伴う，研磨砥石の強度の低下を抑制できる。
【００１３】
さらに，上記溝は，それぞれ，砥石部の外周部に，研磨砥石側面の略直径方向に延びるように形成されてもよい。即ち，複数の上記溝が，研磨砥石側面の中央部を中心として略放射状に延びるような方向に形成されてもよい。
【００１４】
また，複数の上記溝が，研磨砥石側面の円周方向に沿って略等間隔で配置されるようにしてもよい。
【００１５】
また，上記課題を解決するため，本発明の別の観点によれば，基板を切断砥石で切断することによって形成された切断面の双方を，高速回転する研磨砥石で切削研磨して鏡面加工する切断面鏡面加工装置であって：両側面の少なくとも外周部に設けられる砥石部と，砥石部の一部を削り取って形成される複数の溝とを有し，厚さが切断砥石より薄い研磨砥石と；研磨砥石を移動させる移動機構と；研磨砥石が，一側面を用いて切断面の一方を鏡面加工し，他側面を用いて切断面の他方を鏡面加工するよう，移動機構を制御する制御装置と；を備えることを特徴とする切断面鏡面加工装置が提供される。
【００１６】
かかる構成により，上記のような特徴を有する研磨砥石を用いて，被加工物である切断面の双方を好適に鏡面加工することができる。即ち，研磨砥石の両側面には上記側面逃げと複数の溝が形成されているので，研磨砥石の一側面を用いて切断面の一方を鏡面加工し，他側面を用いて切断面の他方を鏡面加工する場合に，切断面と研磨砥石の側面との接触面積が小さくなり，研磨砥石の直進性を高めて鏡面加工精度を向上させることができる。また，側面逃げを備えることにより，研磨砥石が摩耗して砥石部の先端形状が崩れたとしても，崩れた砥石形状が切断面に転写することを防止できるとともに，深く切り込んだ研磨砥石を切溝から引き出す際に切断面を傷つけないようにできる。
【００１７】
また，上記研磨砥石は，金属製の基台部と，基台部の両側面に取り付けられた砥石部と，を備える，如く構成すれば，研磨砥石の剛性が高まり，加工時の研磨砥石の直進性がより向上する。
【００１８】
また，上記課題を解決するため，本発明の別の観点によれば，基板を切断砥石で切断することによって形成された切断面の双方を，高速回転する研磨砥石で切削研磨して鏡面加工する切断面鏡面加工方法であって：両側面の少なくとも外周部に設けられる砥石部と，砥石部の一部を削り取って形成される複数の溝とを有し，厚さが切断砥石より薄い研磨砥石の一側面を用いて，切断面の一方を鏡面加工する第１の工程と；切断面の他方を切削研磨可能な位置まで，研磨砥石を移動させる第２の工程と；研磨砥石の他側面を用いて，切断面の他方を鏡面加工する第３の工程と；を含むことを特徴とする，切断面鏡面加工方法が提供される。
【００１９】
かかる構成により，切断砥石によって形成された切溝の内部に研磨砥石を挿入することができる。この研磨砥石を高速回転させながら研磨砥石のいずれか一側面を切断面のいずれか一方の面に微小な切り込み幅で切り込ませた状態で，かかる研磨砥石を切溝が延長形成された方向に沿って移動させることにより，切断面を一端から多端にかけて連続的に削り取るようにして切削研磨できる。かかる加工方法で，研磨砥石の一側面で一方の切断面を鏡面加工し，研磨砥石の他側面で他方の切断面を鏡面加工できるので，切断面の鏡面加工を片方ずつ行うことができる。従って，摩耗しやすい研磨砥石の幅を維持する必要がなく，鏡面加工精度が向上する。
【００２０】
さらに，砥石部を研磨砥石の両側面の少なくとも外周部に設ける（即ち，研磨砥石の両側面の内周部には側面逃げを形成する）ことで，加工時における研磨砥石と切断面との接触面積を小さくできる。加えて，かかる砥石部に複数の溝を設けることで，切断面と接触する砥石部が複数の領域に分断される。このため，研磨砥石と切断面との接触面積をより小さくできるので，加工時に研磨砥石が切断面から受ける側面抵抗を小さくできる。従って，薄い研磨砥石であっても十分な加工直進性を得られるので，鏡面加工精度がより高まる。さらに，加工時には砥石部に形成された複数の溝を通って加工点に十分な量の切削水が供給される。このため，加工点を十分に冷却して，切断面と砥石部の間で生ずる摩擦熱による温度上昇を抑制できるので，切断面の面焼け現象を防止できる。
【００２１】
さらに，上記第１の工程と第３の工程の少なくともいずれか一方の工程では，上記研磨砥石は，基板の厚み方向に複数段階で，切断面を鏡面加工する，如く構成すれば，１段階で切削研磨する切断面の領域を小さくできるので，鏡面加工精度がより向上する。
【００２２】
【発明の実施の形態】
以下に添付図面を参照しながら，本発明の好適な実施の形態について詳細に説明する。なお，本明細書及び図面において，実質的に同一の機能構成を有する構成要素については，同一の符号を付することにより重複説明を省略する。
【００２３】
（第１の実施の形態）
以下に，本発明の第１の実施形態にかかる切断面鏡面加工方法，切断面鏡面加工装置および研磨砥石について説明する。本実施形態にかかる切断面鏡面加工方法は，特に，切断面を切削研磨する際に適用される研磨砥石の形状に特徴を有し，この特徴によって鏡面加工中の研磨砥石の直進性を向上させることができるものである。そこで，以下では，まず，被加工物である基板について説明した後，かかる基板の切断面を鏡面加工する切断面鏡面加工装置および研磨砥石の構成について詳細に説明する。次いで，この切断面鏡面加工装置および研磨砥石を用いた切断面鏡面加工方法について，詳細に説明することとする。
【００２４】
まず，本実施形態にかかる被加工物である基板について説明する。基板は，例えば，シリコンなどの半導体基板上に，例えば石英ガラス層が積層された半導体ウェハなどである。この基板は，例えば略円盤形状を有し，その大きさは，外径が例えば４インチであり，厚さが例えば約１ｍｍである。なお，以下では，基板の表面とは，ガラス層が積層された側の面をいい，基板の裏面とは，半導体基板側の面をいうものとする。
【００２５】
かかる基板の表面のガラス層には，例えば略同一のパターンおよび特性を有するの複数の素子（例えば光導波路などの回路）が形成されている。かかる基板を，素子間のストリートに沿ってダイシングして複数片に分割することで，例えば光学素子などのチップを得ることができる。このチップは，例えば光学素子として機能する場合，その側面（即ち，切断面）のうち例えば光信号が通過または反射する部分が，高精度で平坦化されていなければならない。しかし，ダイシングされた基板の切断面は平坦度が十分ではないので，ダイシング後にかかる切断面を研磨して鏡面加工する必要がある。そこで，本実施形態では，以下のような切断面鏡面加工装置を用いて，かかる切断面を鏡面加工する。
【００２６】
次に，本実施形態にかかる切断面鏡面加工装置について説明する。本実施形態にかかる切断面鏡面加工装置は，基板に形成された切断面の双方を高速回転する研磨砥石で切削研磨して鏡面加工する機能を有しており，例えばダイシング装置で構成できる。このダイシング装置（ダイシングソーまたはダイサーともいう。）は，高速回転するブレードを用いて半導体ウェハなどの被加工物を切削してダイシング加工する際に用いられる一般的な装置である。
【００２７】
ここで，図１に基づいて，本実施形態にかかるダイシング装置について説明する。図１は，本実施形態にかかるダイシング装置１０の全体斜視図である。
【００２８】
図１に示すように，ダイシング装置１０は，例えば，基板１２を切断加工する第１の切削ユニット２０−１と，基板１２の切断面を鏡面加工する第２の切削ユニット２０−２と，基板１２を載置するチャックテーブル１５と，例えばチャックテーブル１５を移動させる移動機構（図示せず。）と，移動機構の動作を制御する制御装置１６とを有する。このように，ダイシング装置１０は，例えば，２つの切削ユニット２０−１，２を具備する例えば対面型のデュアルダイサーである。
【００２９】
第１の切削ユニット２０−１は，端部に設けられた切断砥石を用いて，加工面上のストリートに沿って基板１２を切断して，極薄の切溝（カーフ）を形成する機能を有するが，詳細は後述する。また，第２の切削ユニット２０−２は，端部に設けられた研磨砥石を用いて，上記切溝の両側面である切断面を鏡面加工する機能を有するが，詳細は後述する。
【００３０】
チャックテーブル１５は，基板１２を載置・固定するテーブルであり，その上面に例えば真空チャック機構が設けられている。基板１２は，かかるチャックテーブル１５上に，例えば治具１４を介して載置される。この際，基板１２の裏面と治具１４とは，例えば，接着剤，両面テープまたはシールなどで貼り付け固定されている。
【００３１】
この治具１４は，例えば，プラスチック等の合成樹脂または金属などで形成された略平板状の部材であり，その上面に載置された基板１２を支持する機能を有する。
【００３２】
また，この治具１４の表面（基板１２と接する面）には，後述する切断砥石および研磨砥石が通過する位置に，複数の砥石通過用溝１３が形成されている。かかる砥石通過用溝１３は，幅が少なくとも切断砥石の幅より広く，深さが研磨砥石の外周部を十分に挿入可能な深さとなるよう調整されている。また，砥石通過用溝１３は，切断方向が２方向（例えば基板１２を格子状にダイシングする場合など）である場合には，図１に示すように，各々の切断方向に沿って例えば２方向に複数設けられるが，基板１２の切断方向が１方向である場合には，切断方向と略平行な例えば１方向にのみ複数設けてもよい。このような砥石通過用溝１３は，切断加工または鏡面加工時に，切断砥石または研磨砥石が基板１２にのみ作用し，基板１２を支持する治具１４とは干渉しないようにする機能を有する。
【００３３】
移動機構（図示せず。）は，上記のように基板１２を載置したチャックテーブル１５を，第１の切削ユニット２０−１および第２の切削ユニット２０−２（以下では，単に切削ユニット２０という場合もある。）に対し，相対的に移動させる機能を有する。より詳細には，移動機構は，高速回転する切断砥石または研磨砥石を基板１２の表面に所定量切り込ませた状態で，かかる基板１２ごとチャックテーブル１５を移動させることができる。これにより，切断砥石をストリートに沿って所定の送り速度で移動させて，基板１２の切断加工を進行させることができる。また，研磨砥石を切断面に沿って所定の送り速度で移動させて，切断面の鏡面加工を進行させることもできる。なお，移動機構は，かかる例に限定されず，固定的に配されたチャックテーブル１５に対し，切削ユニット２０を相対移動させるように構成してもよい。
【００３４】
制御装置１６は，例えばダイシング装置１０の内部に配され，例えばＣＰＵ等の演算処理装置，ＲＡＭ等の記憶装置などで構成される。この制御装置１６は，切断砥石による切断加工や，研磨砥石による鏡面加工が好適に行われるよう，上記移動機構の動作を制御する機能を有する。なお，かかる制御装置１６は，必ずしも，ダイシング装置１０に内蔵されなくともよく，例えば，ダイシング装置１０の外部に設置して，例えば有線または無線などでダイシング装置１０の移動機構に制御信号を送信するように構成してもよい。
【００３５】
次に，図２に基づいて，本実施形態における第１の切削ユニットに設けられた切断砥石について説明する。なお，図２（ａ）および図２（ｂ）は，本実施形態にかかる切断砥石４０を示す平面図および断面図である。
【００３６】
図２（ａ）に示すように，切断砥石４０は，例えば略リング形状を有する極薄の切断ブレードであり，ダイヤモンド，ＣＢＮ等の砥粒を，電鋳タイプの金属（例えばニッケル）やレジンなどの結合剤（ボンド剤）で結合して形成される。この切断砥石４０は，後述する研磨砥石よりも粗い砥粒で構成することが好ましく，この粒度は例えば＃８００程度である。このため，切断砥石４０は比較的硬質であり，切削性能や耐摩耗性に優れるが，平坦加工精度が劣る。また，切断砥石４０の厚さは，図２（ｂ）に示すように，例えば約０．３２ｍｍである。なお，本実施形態にかかる切断砥石４０は略リング形状を有するが，かかる例に限定されず，略円盤形状を有したり，例えばハブ（Ｈｕｂ）と切刃部を一体形成したハブブレードなどであったりしてもよい。
【００３７】
かかる切断砥石４０は，フランジ（図示せず。）に挟持された状態でスピンドル（図示せず。）に軸着され，例えば３００００Ｒ．Ｐ．Ｍ．で高速回転可能である。高速回転する切断砥石４０が，その外周を基板１２の加工面に所定量切り込ませながら，ストリートに沿って加工面を切削することで，加工面に極薄の切溝を形成できる。この際，十分な切り込み深さを維持することにより，基板１２を完全に切断することができ，切溝の両側面が基板１２の裏面にまで達することで，対向する２つの切断面が形成される。なお，かかる切削加工中には切削水が供給され，切断砥石４０及び加工点が冷却される。
【００３８】
次に，図３に基づいて，本実施形態にかかる第２の切削ユニット２０−２に設けられた研磨砥石５０について詳細に説明する。なお，図３（ａ）は，本実施形態にかかる研磨砥石５０を示す平面図であり，図３（ｂ）は，図３（ａ）のＡ−Ａ’線での断面図である。
【００３９】
図３に示すように，研磨砥石５０は，全体としては例えば略リング形状を有する極薄の研磨用の砥石であり，切断面を切削研磨して鏡面加工する機能を有する。この研磨砥石５０の大きさは，外径が例えば５２ｍｍ，内径が例えば４０ｍｍであり，厚さが例えば約０．３０ｍｍで上記切断砥石４０よりも若干薄い。この研磨砥石５０は，中心に配された例えば金属製の基台部５４と，基台部５４の両側面に貼り付けられた砥石部５２とからなる。
【００４０】
基台部５４は，厚さが例えば０．１ｍｍ程度の例えば略リング状の部材であり，例えば，タングステン炭化物，チタン炭化物またはモリブデン炭化物などを含む焼結合金である超硬合金などからなる。かかる基台部５４は，非常に硬質であるため，鏡面加工時において研磨砥石５０全体の剛性を高める補強材として機能する。
【００４１】
砥石部５２は，基台部５４の両側に例えば接着剤等で貼り付けられた例えば微粒砥石であり，基台部５４の一側に貼り付けられた左砥石部５２ａと，他側に貼り付けられた右砥石部５２ｂとからなる。かかる左砥石部５２ａと右砥石部５２ｂは略対称な形状を有しており，双方の厚さは外周部で例えば約０．１ｍｍである。
【００４２】
この砥石部５２を構成する砥石は，緑色炭化ケイ素（ＧＣ）砥粒またはダイヤモンド（Ｄ，ＳＤ）砥粒，ＣＢＮ砥粒などを各種の結合剤で結合して形成されており，その粒度は細かい方が好ましく例えば＃１０００〜＃８０００などである。このため，砥石部５２は，例えば，切断砥石４０よりも軟質であり，耐摩耗性が劣るが，平坦加工精度に優れるので，被加工物を高精度で鏡面加工できる。
【００４３】
また，双方の砥石部５２の外側面（即ち，研磨砥石５０の両側面）には，外周部を残して陥没するよう形成された側面逃げ５６が形成されている。この側面逃げ５６の深さ（即ち，砥石部５２の外周部と側面逃げの底部のレベルの差）は，例えば約０．０２ｍｍなどである。かかる側面逃げ５６を形成することにより，図３（ｂ）に示すように，左砥石部５２ａおよび右砥石部５２ｂの外周部が，外側に突出した形状となる。このため，左砥石部５２ａおよび右砥石部５２ｂは，外周部では厚さが例えば０．１ｍｍと厚くなっているのに対し，側面逃げ５６が形成された外周部の内側から内周部にかけては，厚さが側面逃げ５６の深さの分だけ薄くなっている。研磨砥石５０がこのような側面逃げ５６を具備することにより，切断面の鏡面加工時に，実質的には砥石部５２の外周部（幅が例えば約０．７ｍｍ）のみが切断面に対して作用することとなる。
【００４４】
さらに，研磨砥石５０の例えば両側面には，本実施形態にかかる大きな特徴である溝５８が形成されている。以下に，図３および図４に基づいて，かかる溝５８について詳細に説明する。なお，図４（ａ）は，本実施形態にかかる溝５８周辺の研磨砥石５０を示す部分拡大平面図であり，図４（ｂ）は，本実施形態にかかる溝５８周辺の研磨砥石５０を示す部分拡大正面図であり，図４（ｃ）は，図４（ａ）のＢ−Ｂ’線での断面図であり，図４（ｄ）は，図４（ａ）のＣ−Ｃ’線での断面図である。
【００４５】
図３（ａ）に示すように，研磨砥石５０の側面には複数の溝（スリット）５８が形成されている。この溝５８は，例えば工作機械などを用いて，砥石部５２側面の一部を例えば直径方向に直線的に削り取って形成された切り欠き部である。かかる溝５８は，左砥石部５２ａと右砥石部５２ｂの外側面に，例えば略同一のパターンでそれぞれ例えば８つずつ形成されている。この例えば８つの溝５８は，砥石部５２外側面の円周方向に沿って略均等な間隔で配置されており，砥石部５２の外側面を例えば略同一の形状を有する例えば８つの領域に分割している。
【００４６】
また，各々の溝５８は，図４（ａ）および図４（ｂ）に示すように，例えば厚さに比べて幅が広い形状を有しており，具体的には幅が例えば２ｍｍ，深さが例えば０．０５ｍｍなどである。このように，ある程度の溝５８幅を確保することによって，溝５８は，砥石部５２の外周部を十分な距離を隔てて分断することができる。砥石部５２の外周部のうち，このような比較的広い幅の溝５８が形成された部分は，加工時に切断面と接触しない。従って，加工時における切断面と砥石部５２の外周部との接触面積をさらに小さくできるので，研磨砥石５０に作用する側面抵抗をより低減できる。
【００４７】
また，溝５８の深さが，例えば，上記側面逃げ５６の深さより深くなるように設定されているので，溝５８は，砥石部５２の外周部のみならず側面逃げ５６が形成されている部分をも削り取って形成されることとなる。このため，研磨砥石５０において，溝５８が形成されている部分（図４（ｃ）参照）は，溝５８が形成されていない部分（図４（ｄ）参照）と比して，砥石部５２の厚さが薄くなっている。このように溝５８を形成することにより，加工時に純水等の切削水が，かかる溝５８内に侵入しやすくなる。このため，摩擦熱が生じている加工点を好適に冷却できる。
【００４８】
なお，溝５８の深さは，上記の例に限定されず，例えば，上記側面逃げ５６の深さより浅くなるように設定して，砥石部５２の外周部のみを削り取って溝５８を形成するようにしてもよい。このように溝５８の深さを浅くするほど，研磨砥石５０の強度を大きくできる。
【００４９】
このような溝５８の設置数，幅，深さ，砥石部５２の側面全体に占める面積などは，例えば基板１２の材質，硬度や，求められる鏡面加工精度，加工速度などに応じて，好適に設定されるものであり，上記の例に限定されない。
【００５０】
以上のような構成の研磨砥石５０は，フランジ（図示せず。）に挟持された状態でスピンドル（図示せず。）に軸着され，例えば２００００Ｒ．Ｐ．Ｍ．で高速回転可能である。かかる研磨砥石５０は，高速回転しながらその一側面を所定の切り込み幅（例えば０．０１〜００１５ｍｍ）だけ一方の切断面に切り込ませた状態で，切溝の長手方向（即ち，切断方向）に切溝内を平行移動することにより，切断面の一方をその一側面で切削研磨して鏡面加工することができる。なお，かかる鏡面加工中には，例えばシャワーノズルや側面ノズル（図示せず。）などによって切削水が供給され，研磨砥石５０及び加工点が冷却される。
【００５１】
また，研磨砥石５０は，補強材として基台部５４が設けられているため，上記のような鏡面加工時において，切断面から受ける側面抵抗によるぶれや蛇行などが低減され，直進性を高めることができる。また，上記溝５８は，砥石部５２の例えば側面のみを削り取って形成されるものであり，基台部５４を切り取ったり，基台部５４に貫通孔を設けたりするものではない。このため，比較的面積が大きい基台部５４を設けることができるので，研磨砥石５０の強度をより高めることができる。
【００５２】
さらに，研磨砥石５０は，側面逃げ５６が形成されているので，鏡面加工時において，研磨砥石５０の外周部以外の側面は切断面と接触しない。このため，研磨砥石５０の側面と切断面との接触面積を小さくして，研磨砥石５０が切断面から受ける側面抵抗を低減できるので，研磨砥石５０の直進性の向上を図ることができる。さらに，研磨砥石５０が摩耗して砥石部５２の先端形状が崩れたとしても，側面逃げ５６の下端が基板１２裏面外に達するような深さまで研磨砥石５０を切り込ませることで，崩れた砥石形状が切断面に転写されないようにできる。
【００５３】
加えて，本実施形態の特徴である溝５８が，研磨砥石５０の両側面に複数形成されているので，側面逃げ５６と相まって，研磨砥石５０の側面と切断面との接触面積をさらに小さくできる。これにより，研磨砥石５０の直進性を十分に確保することができるので，図１０に示したような切断面の歪みが生ずることを抑制できる。よって，鏡面加工後の切断面を，基板１２表面に対して略垂直な平坦面とすることができる。
【００５４】
次に，図５〜図８に基づいて，上記ダイシング装置１０を用いた本実施形態にかかる切断面鏡面加工方法について説明する。なお，図５は，本実施形態にかかる切断面鏡面加工方法の動作フローを示すフローチャートである。また，図６は，本実施形態にかかる左切断面鏡面加工サブルーチンの動作フローを示すフローチャートである。また，図７および図８は，本実施形態にかかる切断面鏡面加工方法の各工程における，基板１２等の態様を示す断面図である。
【００５５】
図５に示すように，まず，ステップＳ１０では，切断砥石４０によって基板１２が切断される（ステップＳ１０）。図７（ａ）に示すように，ガラス層１２ａと半導体基板１２ｂからなる基板１２が，第１の切削ユニット２０−１に設けられた切断砥石４０によって切断される。この際，切断ラインが治具１４の砥石通過用溝１３と重なるようにして，基板１２が切断される。
【００５６】
かかる切断加工により，基板１２には極薄の切溝が形成される。この切溝の幅は，切断砥石４０の幅と略同一若しくは若干大きく，例えば約０．３２ｍｍである。かかる切溝の両側面が切断面であり，以下では左切断面７０ａおよび右切断面７０ｂということとする。この左切断面７０ａおよび右切断面７０ｂ（以下では，単に切断面７０という場合もある。）は平坦度が粗いので，このままでは例えば光信号が通過等する光学面としては利用できない。
【００５７】
このような切断加工を各ストリートに沿って繰り返し一方向に複数の切溝を形成した後，チャックテーブル１５を例えば９０度回転させて，同様にして切断加工を行い，例えば直交する２方向に複数の切溝を形成する。これにより，基板１２が例えば格子状にダイシングされ，個々のチップに分割される。
【００５８】
次いで，ステップＳ２０では，研磨砥石５０を水平方向に移動させ，左切断面７０ａを鏡面加工可能な位置に配置させる（ステップＳ２０）。制御装置１６からの制御信号に基づいて移動機構（図示せず。）を動作させて，図７（ｂ）に示すように，第２の切削ユニット２０−２に設けられた研磨砥石５０を，上記左切断面７０ａを切削研磨可能な位置に移動させる。より具体的には，研磨砥石５０の左砥石部５２ａが左切断面７０ａに例えば約０．０１ｍｍの切り込み幅で切り込むことができるように，研磨砥石５０の水平方向の位置が調整される。このように，本ステップは研磨砥石５０によって左切断面７０ａを鏡面加工するための準備工程である。
【００５９】
さらに，ステップＳ３０では，図６に示す左切断面鏡面加工サブルーチンを行って，左切断面７０ａが鏡面加工される（ステップＳ３０）。
【００６０】
図６に示すように，まず，ステップＳ３２では，研磨砥石５０が基板１２に対して下降される（ステップＳ３２）。上記ステップＳ２０で左切断面７０ａに対する水平位置が合わせられた研磨砥石５０を，垂直方向に所定距離下降させる。本ステップは，研磨砥石５０が左切断面７０ａを切削研磨する際の，基板１２に対する研磨砥石５０の基板１２厚み方向への切り込み深さ（以下では，垂直切り込み深さという。）を決定する工程である。この垂直切り込み深さは，ガラス層１２ａを切削研磨する場合には例えば０．１〜０．０４ｍｍであり，半導体基板１２ｂを切削研磨する場合には例えば０．１〜０．２ｍｍである。
【００６１】
次いで，ステップＳ３４では，左切断面７０ａが切削研磨される（ステップＳ３４）。図７（ｃ）に示すように，高速回転する研磨砥石５０を，左砥石部５２ａを左切断面７０ａに水平方向に例えば約０．０１ｍｍの切り込み幅で切り込ませながら，切溝が延長形成された方向（図７（ｃ）の紙面垂直方向）に所定送り速度で移動させる。これにより，左砥石部５２ａの外周部が，左切断面７０ａの一側端から他側端にかけて徐々に干渉していき，粗い左切断面７０ａを薄く削り取るようにして切削研磨する。これにより，左切断面７０ａのうち上記垂直切り込み深さの分だけが，切溝が延長形成された方向に沿って連続して鏡面加工される。
【００６２】
なお，かかる切削研磨時には，上記説明したように側面逃げ５６，基台部５４および複数の溝５８が好適に機能するので，研磨砥石５０は，左切断面７０ａからの側面抵抗により，ぶれたり蛇行したりすることなく，好適に切溝内を直進できる。
【００６３】
次いで，ステップＳ３６では，左切断面７０ａの全てが鏡面加工されたか否かが判定される（ステップＳ３６）。
【００６４】
研磨砥石５０の下端が未だ基板１２の裏面より下方に達しておらず，左切断面７０ａの全てが切削研磨されていない場合には，ステップＳ３２に戻り，再び研磨砥石５０を所定の垂直切り込み深さ分だけ下降させ，さらにステップＳ３４で再び左切断面７０ａが切削研磨される。かかる研磨砥石５０の下降と切削研磨は，左切断面７０ａの全てが鏡面加工されるまで繰り返される。
【００６５】
このように本実施形態にかかる切断面鏡面加工方法では，垂直切り込み深さを基板１２厚み以上として一回の切削研磨（１ｐａｓｓ）で切断面７０の全てを切削研磨するのではなく，例えば，一段階（１ｓｔｅｐ）あたりの垂直切り込み深さを基板１２厚み以下として基板１２厚み方向に複数の段階（例えば１４ｓｔｅｐ）で切断面７０を順次切削研磨していく手法（以下では，多段鏡面加工という。）を採用している。
【００６６】
かかる多段鏡面加工は，例えばダイシング方法のステップカット（多段切り）のような手法であるといえ，切断面７０を基板１２厚み方向に多段階で切削研磨することにより，被加工領域を小さくして鏡面加工精度を高めることができる。この加工精度は，多段階であるほどより高くなる。
【００６７】
本実施形態では，一段階当たりの垂直切り込み深さを例えば０．０４ｍｍとし例えば２段階でガラス層１２ａを切削研磨し，一段階当たりの垂直切り込み深さを例えば０．１ｍｍとし例えば１２段階で半導体基板１２ｂを切削研磨するよう設定している。このように，半導体基板１２ｂよりガラス層１２ａを細かく切削研磨するのは，例えば光学素子が形成されているガラス層１２ａの鏡面加工精度を高めるためである。また，研磨砥石５０の送り速度は，半導体基板１２ｂを切削研磨する場合には例えば２．０ｍｍ／ｓであるのに対し，ガラス層１２ａを切削研磨する場合には例えば０．５ｍｍ／ｓと小さく設定されている。これは，ガラス層１２ａの加工時には加工精度を優先させる一方，半導体基板１２ｂの加工時には加工速度を優先させるためである。
【００６８】
このような多段鏡面加工によって，左切断面７０ａを基板１２厚み方向に徐々に鏡面加工していき，研磨砥石５０の下端が基板１２の裏面より下方に達している場合には，左切断面７０ａの全てが鏡面加工されたと判定され，左切断面鏡面加工サブルーチンを終了して，ステップＳ４０に進む。
【００６９】
このように左切断面鏡面加工サブルーチンを終了する場合には，図７（ｄ）に示すように，左砥石部５２ａの例えば外周部下端が治具の砥石通過用溝１３に十分挿入され，側面逃げ５６の少なくとも一部が基板１２の裏面より下方に現れるような状態となっていることが好ましい。このように研磨砥石５０を砥石通過用溝１３内に深く挿入した状態で切削研磨しておくことにより，左砥石部５２ａの外周部が摩耗により崩れていたとしても，上記側面逃げ５６が機能して，崩れた砥石形状が左切断面７０ａに転写されないようにできる。また，研磨砥石５０を引き出す際に，左砥石部５２ａが接触して左切断面７０ａを傷つけたり，左砥石部５２ａの端部が欠けたりしないようにできる。
【００７０】
その後，図５に示すステップＳ４０では，研磨砥石５０を移動して，右切断面７０ｂを鏡面加工可能な位置に配置する（ステップＳ４０）。まず，図７（ｄ）に示したような治具１４および切溝に挿入されている研磨砥石５０を，左切断面７０ａを傷つけないように切溝から引き出す。次いで，制御装置１６からの制御信号に基づいて移動機構（図示せず。）を動作させて，研磨砥石５０を水平方向に移動させ，図８（ａ）に示すように，右砥石部５２ｂが右切断面７０ｂに例えば約０．０１ｍｍだけ切り込むことができるような位置に配置する。このように，本ステップは右切断面７０ｂを鏡面加工するための準備工程である。
【００７１】
次いで，ステップＳ５０では，右切断面７０ｂが鏡面加工される（ステップＳ５０）。図８（ｂ）〜（ｃ）に示すように，上記左切断面７０ａの鏡面加工と同様にして，多段鏡面加工で右切断面７０ｂが鏡面加工される。かかる右切断面７０ｂの鏡面加工は，左切断面７０ａの鏡面加工の場合と比して，左砥石部５２ａの代わりに右砥石部５２ｂを用いる点で相違するのみであり，その他の機能構成は略同一であるので，詳細な説明は省略する。
【００７２】
上記までのステップにより，図８（ｄ）に示すように，左切断面７０ａおよび右切断面７０ｂの双方が鏡面加工される。これにより，切溝の幅は，鏡面加工前の例えば約０．３２ｍｍと比して若干広く，例えば０．３４ｍｍとなる。
【００７３】
このような切溝内の切断面鏡面加工を，他の切溝についても同様な手法で繰り返し行うことで，例えば全ての切断面７０を鏡面加工できる。この際，まず，１方向の切溝内の切断面７０を順次鏡面加工し，次いで，他方向（即ち，例えば直交する方向）の切溝内の切断面７０を順次鏡面加工することが好ましい。
【００７４】
以上のように，本実施形態にかかる切断面鏡面加工方法は，ダイシングにより得られたチップをピックアップして搬送してから個々にその切断面を鏡面加工するのではなく，切断された基板１２を搬送せずにそのままの位置で切断面７０を鏡面加工できる。このため，基板１２若しくはチップのアライメントを２回行う必要がないだけでなく，基板１２搬送作業を省略でき，工程数も削減できるので，生産効率が向上する。
【００７５】
また，本実施形態にかかる切断面鏡面加工方法は，従来のように切断面７０の双方を同時に鏡面加工するのではなく，研磨砥石５０の両側面を片方ずつ用いて，切断砥石４０によって形成された２つの切断面を別々に鏡面加工することができる。より具体的には，切溝内に挿入された研磨砥石５０は，左砥石部５２ａを用いて左切断面７０ａを鏡面加工する一方，右砥石部５２ｂを用いて右切断面７０ｂを鏡面加工することができる。これにより，鏡面加工時に，研磨砥石５０の厚さを維持する必要がなくなる。即ち，鏡面加工を繰り返して砥石部５２が摩耗し，研磨砥石５０の厚さが薄くなったとしても，制御装置１６と移動機構が研磨砥石５０を好適に位置調整することにより，研磨砥石５０は双方の切断面７０を好適に鏡面加工できる。従って，研磨砥石５０の交換回数を低減して，生産効率の向上が図れる。また，研磨砥石５０の寿命を長期化できるので，低コスト化が図れる。
【００７６】
また，鏡面加工に用いられる研磨砥石５０は，硬質な基台部５４を具備しているので比較的大きい強度を有する。また，両側面に側面逃げ５６が形成されているので，研磨砥石５０の側面と切断面７０との接触面積が小さくなる。
【００７７】
さらに，かかる研磨砥石５０の例えば両側面には，好適な本数，幅，深さ，側面全体に占める面積を有する溝５８が設けられているので，切断面７０に対する研磨性能を低下させることなく，研磨砥石５０と切断面７０との接触面積をさらに小さくすることができる。このため，鏡面加工時に切断面７０から受ける側面抵抗（反発力）を十分に低減することができる。従って，研磨砥石５０は，極薄であったとしても加工中にぶれたり歪んだりすることなく，十分な加工直進性を得ることができる。よって，鏡面加工後の切断面７０は，従来のように湾曲することなく，垂直方向の平坦度（直角度）および水平方向の平坦度（真直度）が向上する。このように本実施形態にかかる切断面鏡面加工方法は，溝５８を具備しない研磨砥石を用いた従来の切断面鏡面加工方法と比べて，切断面７０を高精度で鏡面加工することができ，直角度および真直度の誤差である切断面の歪みを例えば半分以下に抑えることも可能である。
【００７８】
また，上記溝５８を設けることにより，加工点に供給される切削水の量を増加させることができる。このため，加工点を十分に冷却して，切断面７０と研磨砥石５０との間の摩擦熱による温度上昇を抑えることができるので，切断面７０が黒ずんでしまう面焼け現象を防止することもできる。
【００７９】
（実施例）
次に，上記のような第１の実施形態にかかる溝５８が形成された研磨砥石５０を用いて，基板１２の切断面７０を鏡面加工する実験を行った結果について説明する。また，対照実験として，溝５８が形成されていない従来の研磨砥石を用いて，基板１２の切断面７０を鏡面加工した実験結果についても，併せて説明する。
【００８０】
まず，以下の表１に，本実施例にかかる鏡面加工実験の実験条件を示す。
【００８１】
【表１】

【００８２】
本実施例にかかる鏡面加工実験では，表１に示すような実験条件で基板１２の切断面７０を鏡面加工し，鏡面加工された切断面７０の平坦度を測定した。この平坦度を表すパラメータとしては，直角度誤差と，真直度誤差の２つを採用した。直角度誤差とは，湾曲した切断面７０の垂直方向の歪みを最上部と最下部との高低差で表したものであり，真直度誤差とは，湾曲した切断面７０の水平方向（切溝の長手方向）の歪みを最上部と最下部との高低差で表したものである。これらの値が大きいほど鏡面加工後の切断面７０が歪んでおり平坦でないことになる。
【００８３】
なお，溝５８が形成されていない従来の研磨砥石を用いた鏡面加工実験の場合には，溝５８に関する条件以外は，上記本実験と同じ条件で切断面７０を鏡面加工して，同様にして平坦度を測定した。
【００８４】
次に，図９に基づいて，本実施例にかかる切断面の鏡面加工実験の実験結果について説明する。なお，図９は，本実施例にかかる鏡面加工実験の実験結果を示すグラフである。
【００８５】
図９（ａ）に示すように，直角度誤差は，溝５８が形成されていない研磨砥石で鏡面加工した場合には，平均で１．０μｍ，最大値で２．０μｍと比較的大きい。これに対して，溝５８が形成された研磨砥石５０で鏡面加工した場合には，直角度誤差は，平均で０．３μｍ，最大値で１．０μｍであり，溝５８が形成されていない場合と比して，平均値で約３分の１，最大値で半分というように非常に小さくなっている。
【００８６】
また，図９（ｂ）に示すように，真直度誤差は，溝５８が形成されていない研磨砥石で鏡面加工した場合には，平均で１．８μｍ，最大値で２．２μｍと比較的大きい。これに対して，溝５８が形成された研磨砥石５０で鏡面加工した場合には，真直度誤差は，平均で０．６μｍ，最大値で１．１μｍであり，溝５８が形成されていない場合と比して，平均値で３分の１，最大値で半分というように非常に小さくなっている。
【００８７】
このように，本実施例にかかる鏡面加工実験では，研磨砥石５０の側面に溝５８を形成した場合には，溝５８を形成していない場合と比べて，直角度誤差および真直度誤差の双方が大幅に小さくなっている。かかる実験結果によれば，研磨砥石５０の側面に溝５８を形成することによって，鏡面加工した切断面７０の平坦度を大幅に向上できるといえる。従って，上記本実施形態にかかる切断面鏡面加工方法により，切断面７０の鏡面加工精度を大幅に向上できることが実証されたといえる。
【００８８】
以上，添付図面を参照しながら本発明の好適な実施形態について説明したが，本発明はかかる例に限定されない。当業者であれば，特許請求の範囲に記載された技術的思想の範疇内において各種の変更例または修正例に想到し得ることは明らかであり，それらについても当然に本発明の技術的範囲に属するものと了解される。
【００８９】
例えば，本実施形態にかかる被加工物である基板１２は，半導体基板１２ｂの上にガラス層１２ａが積層された半導体ウェハを用いたが，本発明は，かかる例に限定されず，例えば，ガラス層１２ａが積層されていなくともよい。また，基板１２としては，例えば，上記以外の各種半導体基板や，サファイヤ基板，水晶，ガラス，セラミック等の難加工材，複合材，各種金属材料，脆性材料からなる基板，ＶＴＲやＦＤＤ等の磁気ヘッドなどであってもよい。また，基板１２の表面には上記光学素子以外にも，ＬＳＩなどの半導体デバイスを構成する各種の配線，電極，絶縁膜，トランジスタ構造等が，多様な態様で形成されていてもよい。また，基板１２は，略円盤形状に限られず，例えば略方形，略扇形等の平板形状などであってもよい。
【００９０】
また，上記実施形態では，基板１２は，治具１４を介してチャックテーブル１５上に載置されたが，かかる例に限定されず，ウェハテープ，粘着テープ，フレーム，サブストレートなどを介して設置されてもよい。ただし，切断砥石４０や研磨砥石５０の切り込み深さを十分に確保できる素材および厚さであることが好ましい。
【００９１】
また，上記実施形態では，切断面鏡面加工装置として，ダイシング装置１０を用いた。この場合には，切断ブレードの代わりに研磨砥石５０を適用するだけでよく，その他の装置本体の設計変更などは不要であるで，高性能の切断面鏡面加工装置を容易に提供でき，かつ，切断加工と鏡面加工を同時に行えるというメリットがあった。しかし，本発明にかかる切断面鏡面加工装置は，かかる例に限定されない。例えば，基板１２を切断する切断砥石４０を具備する切断装置と，切断面鏡面加工装置とを別体に構成してもよい。この場合，切断面鏡面加工装置として，例えば各種のグラインダー等の研磨装置などを用いてもよい。
【００９２】
また，上記実施形態では，切断面鏡面加工装置であるダイシング装置１０として，２つの切削ユニット２０を備えた対面型デュアルダイサーを用いたが，本発明はかかる例に限定されない。例えば，ダイシング装置１０として，例えば２つの切削ユニット２０を並列的に配置したデュアルダイサーを用いてもよい。また，切削ユニット２０を１つだけ具備したシングルダイサーを用いてもよい。この場合には，切断砥石４０による切断加工後に，例えば，切断砥石４０を研磨砥石５０に交換して，鏡面加工を行うようにしてもよい。
【００９３】
また，上記実施形態では，研磨砥石５０の基台部５４は，超硬合金からなるが，本発明はかかる例に限定されず，例えばステンレス鋼等の比較的硬質な各種金属や，硬質な切断ブレード（補強用砥石）などで構成してもよい。
【００９４】
また，研磨砥石５０は，基台部５４を必ずしも具備しなくともよい。研磨砥石５０は，切断砥石４０の幅（切溝の幅）より薄い砥石であれよく，全体が超微粒砥石からなるものや，各種の電鋳ブレード，メタルブレードまたはレジンブレード，回転ディスクなどであってもよい。
【００９５】
また，上記実施形態では，研磨砥石５０は，両側面に砥石部５２および溝５８を備えていたが，かかる例に限定されず，一側面にのみ砥石部５２および溝５８を具備するようにしてもよい。
【００９６】
また，研磨砥石５０の厚さ，砥石部５２の粒度若しくは厚さ，砥石部５２の外周部の幅，溝５８の設置数，幅若しくは深さ，側面逃げ５６の幅若しくは深さ，研磨砥石５０の回転速度若しくは送り速度などの各数値は，上記実施形態の例に限定されず，被加工物である基板１２の種類や，求められる鏡面加工精度等に応じて好適に変更することができる。
【００９７】
特に，本実施形態にかかる特徴である溝５８に関していえば，例えば，溝５８の設置数を多くする，或いは，溝５８の幅および研磨砥石５０の側面面全体に占める面積等を大きくするほど，研磨砥石５０と切断面７０の接触面積を低減できるが，研磨効率は低下してしまう。このため，上記のように被加工物の種類や所望の加工精度に応じて，かかる溝５８の形成条件を好適に設定することが好ましい。
【００９８】
例えば，溝５８の設置数は，複数であればよく，必ずしも８つに限定されない。また，溝５８の幅は，例えば溝５８の設置数等に応じて増減させてもよい。また，それぞれの溝５８は，上記実施形態のように略同一幅でなくともよく，例えば，砥石部５２の外周部に近いほど広い幅とするなどしてもよい。
【００９９】
また，上記実施形態では，略同一形状の溝５８が等間隔で設けられていたが，かかる例に限定されず，例えば，多様な形状を有する溝５８を任意の配置で設けてもよい。より具体的には，例えば，幅が太い溝５８と細い溝５８を交互に配置したり，深さが浅い溝５８と深い溝５８とをランダムに配置したりしてもよい。また，溝５８の断面形状は，上記実施形態のようにコの字形に限定されず，例えば略Ｕ字形，略Ｖ字形，略Ｗ字形などの任意の断面形状であってもよい。
【０１００】
また，溝５８の深さを深くするほど溝５８内に切削水が入り込みやすくなるので，加工点に多くの切削水を供給することができるが，研磨砥石５０が薄くなるので強度が低下してしまう。このため，上記のように被加工物の種類や所望の加工精度に応じて，かかる溝５８の深さも好適に設定することが好ましい
【０１０１】
また，上記実施形態では，溝５８を形成する方向は，研磨砥石５０側面の直径方向であったが，かかる例に限定されず，例えば，すべての溝５８を１つの所定方向に平行に並べて形成するなど，任意の方向で形成してもよい。
【０１０２】
また，上記実施形態にかかる切断面鏡面加工方法では，基板１２厚み方向に複数の段階で切削研磨して切断面を鏡面加工（多段鏡面加工）したが，本発明は，かかる例に限定されない。例えば，研磨砥石５０の垂直切り込み深さを大きくして，一方の切断面７０の全てを１ｐａｓｓで切削研磨してもよい。
【０１０３】
【発明の効果】
以上説明したように，本発明によれば，研磨砥石の側面に複数の溝を設けることで，鏡面加工時において，研磨砥石の側面と切断面との接触面積を低減できるので，薄い研磨砥石であっても十分な直進性を得ることができる。従って，鏡面研磨後の切断面の歪みが低減され，鏡面加工精度が大幅に向上する。
【０１０４】
また，かかる溝を介して十分な量の切削水が加工点に供給されるので，加工点を好適に冷却して切断面に生ずる面焼けを防止できる。
【図面の簡単な説明】
【図１】図１は，第１の実施形態にかかるダイシング装置の全体斜視図である。
【図２】図２（ａ）は，第１の実施形態にかかる切断砥石を示す平面図である。
図２（ｂ）は，第１の実施形態にかかる切断砥石を示す断面図である。
【図３】図３（ａ）は，第１の実施形態にかかる研磨砥石を示す平面図である。
図３（ｂ）は，図３（ａ）のＡ−Ａ’線での断面図である。
【図４】図４（ａ）は，第１の実施形態にかかる溝周辺の研磨砥石を示す部分拡大平面図である。
図４（ｂ）は，第１の実施形態にかかる溝周辺の研磨砥石を示す部分拡大正面図である。
図４（ｃ）は，図４（ａ）のＢ−Ｂ’線での断面図である。
図４（ｄ）は，図４（ａ）のＣ−Ｃ’線での断面図である。
【図５】図５は，第１の実施形態にかかる切断面鏡面加工方法の動作フローを示すフローチャートである。
【図６】図６は，第１の実施形態にかかる左切断面鏡面加工サブルーチンの動作フローを示すフローチャートである。
【図７】図７は，第１の実施形態にかかる切断面鏡面加工方法の各工程における，基板等の態様を示す断面図である。
【図８】図８は，第１の実施形態にかかる切断面鏡面加工方法の各工程における，基板等の態様を示す断面図である。
【図９】図９は，実施例にかかる切断面の鏡面加工実験の実験結果を示すグラフである。
【図１０】図１０（ａ）は，従来の切断面鏡面加工方法により生じた切断面の垂直方向の歪みを示す模式図である。
図１０（ｂ）は，従来の切断面鏡面加工方法により生じた切断面の水平方向の歪みを示す模式図である。
【符号の説明】
１０　：　ダイシング装置
１２　：　基板
１３　：　砥石通過用溝
１４　：　治具
１５　：　チャックテーブル
１６　：　制御装置
２０−１　：　第１の切削ユニット
２０−２　：　第２の切削ユニット
４０　：　切断砥石
５０　：　研磨砥石
５２　：　砥石部
５２ａ　：　左砥石部
５２ｂ　：　右砥石部
５４　：　基台部
５６　：　側面逃げ
５８　：　溝
７０　：　切断面
７０ａ　：　左切断面
７０ｂ　：　右切断面[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polishing grindstone, a cut surface mirror-finish apparatus, and a cut surface mirror-finish method, and more particularly to a polishing grindstone for cutting and polishing a cut surface of a substrate cut by a cutting grindstone.
[0002]
[Prior art]
In recent years, when dicing a substrate on which a circuit such as an optical waveguide is formed on its surface and cutting out multiple chips (optical elements), it is necessary to mirror-process the cut surface, which is where optical signals pass and reflect. Came to be required.
[0003]
As a mirror surface processing method of such a cut surface, a method of polishing a cut surface of an optical element using a rotating disk has been proposed as described in Japanese Patent Application Laid-Open No. 11-195627. However, in such a method, the cutting process of the substrate and the polishing process of the cut surface are performed in different processes, so that the production efficiency is reduced.
[0004]
For this reason, a method has been proposed in which the cut surface is polished at the same position without transferring the cut substrate, and the cutting and polishing are performed in the same step. As such a technique, as described in JP-A-2-303050, after cutting a substrate with a cutting grindstone to form a kerf, the thickness is larger than that of the cutting grindstone (that is, the width of the kerf). A method has been proposed in which the cutting groove is widened to a predetermined width by a polishing grindstone made of a fine-grained grindstone and both sides of the cut surface are cut and polished at the same time. However, in such a method, there is a problem that the polishing wheel made of the fine-graining wheel is extremely worn, and it is difficult to maintain a thickness necessary for polishing the cut surface. Since the life of the grinding wheel is short, it is necessary to frequently replace the grinding wheel, which causes a great decrease in productivity.
[0005]
In order to solve these problems, the inventors of the present application have made intensive efforts and came up with a new and improved method for processing a mirror surface of a cut surface. As described in Japanese Patent Application No. 2002-104888, one side of the cut surface is cut and polished by one side of the grinding wheel with a polishing wheel thinner than the cutting wheel, and then the other side of the grinding wheel is grounded. In this method, a grinding wheel is moved so as to contact the other surface of the cut surface, and the other surface of the cut surface is cut and polished by the other side surface of the grinding wheel.
[0006]
[Problems to be solved by the invention]
However, in the above-mentioned conventional method for processing a mirror surface of a cut surface, a thin grinding wheel is used, so that a rigid base is provided on the grinding wheel to increase rigidity, and side clearances are formed on both side surfaces of the grinding wheel. Even if the side surface resistance at the time of mirror finishing is reduced, the grinding wheel is pressed by the cut surface during processing and is distorted, so that there is a problem that the straightness of the grinding wheel cannot be sufficiently maintained. For this reason, distortion may occur in the polished cut surface, and the processing accuracy may be insufficient.
[0007]
The distortion of the cut surface caused by such a conventional method for mirror-cutting the cut surface will be described in more detail with reference to a schematic diagram. As shown in FIG. 10A, the cut surface after polishing was curved in a vertical direction (that is, in a direction perpendicular to the substrate surface) so as to expand toward the bottom of the cut surface. Further, as shown in FIG. 10B, in the horizontal direction (that is, in the longitudinal direction of the cut groove parallel to the substrate surface), the curved portion was curved so as to expand toward the center of the cut surface. Actually, such a cut surface distortion is a micron-level distortion which is not visible, but may seriously hinder the performance of a chip as a precision device.
[0008]
Further, in addition to the above-mentioned problems, a phenomenon called surface burn occurs due to frictional heat generated between the cut surface and the polishing wheel during polishing, and a problem also arises in that the cut surface after mirror finishing is darkened.
[0009]
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to improve the processing accuracy by maintaining the straightness of a polishing grindstone when mirror-cutting a cut surface, and to improve a surface generated on the cut surface. An object of the present invention is to provide a new and improved cut surface mirror processing method capable of suppressing burn, and a grinding wheel and a cut surface mirror processing device for realizing the method.
[0010]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a grindstone portion provided on at least one outer peripheral portion of at least one side surface, and a plurality of grooves formed by cutting off a part of the grindstone portion. A grinding wheel is provided, characterized in that:
[0011]
With such a configuration, a grindstone portion made of fine-grain grindstones and having a function of actually cutting and polishing while interfering with the cut surface can be provided in a shape protruding from the outer peripheral portion of the side surface of the grindstone. In other words, it is possible to form a side relief that is depressed while leaving the outer peripheral portion on the side surface of the grinding wheel. Further, since the outer peripheral portion is cut off by the plurality of grooves and divided into a plurality of regions, the area of the protruding grindstone portion can be further reduced. By providing such a side clearance and a plurality of grooves, the contact area between the workpiece and the side surface of the grinding wheel when the workpiece is cut and polished using the side surface of the grinding wheel rotated at a high speed and mirror-finished. Can be reduced. For this reason, the side resistance (repulsive force) received from the workpiece during processing is reduced, so that even with a thin abrasive grindstone, distortion and blur during processing can be suppressed, and straightness can be improved. Therefore, the flatness after mirror processing is improved, and the mirror processing accuracy can be increased. Further, at the time of machining, a sufficient amount of cutting water is supplied to the machining point through a plurality of grooves formed in the grindstone portion, so that the machining point can be sufficiently cooled.
[0012]
In addition, when the above-mentioned polishing whetstone is provided with a metal base and a whetstone part attached to at least one side surface of the base, the whole whetstone is provided by providing a hard base. Rigidity can be increased. For this reason, the straightness of the grinding wheel during mirror finishing can be further enhanced. Further, the base may be made of a cemented carbide to further increase the rigidity of the grinding wheel. Furthermore, the depth of the groove formed by scraping off a part of the grindstone should be such that it does not reach the center base (that is, the groove is not formed in the base). By doing so, a relatively large diameter of the substantially disk-shaped or substantially ring-shaped base portion can be secured. Therefore, it is possible to suppress a decrease in the strength of the polishing grindstone caused by shaving the grindstone portion to form a plurality of grooves.
[0013]
Further, each of the grooves may be formed in the outer peripheral portion of the grindstone portion so as to extend substantially in the diametrical direction of the side surface of the polishing grindstone. That is, the plurality of grooves may be formed so as to extend substantially radially from the center of the side surface of the grinding wheel.
[0014]
Further, the plurality of grooves may be arranged at substantially equal intervals along the circumferential direction of the side surface of the grinding wheel.
[0015]
According to another aspect of the present invention, in order to solve the above-described problems, both of the cut surfaces formed by cutting the substrate with a cutting grindstone are mirror-polished by cutting and polishing with a high-speed rotating polishing grindstone. A cutting surface mirror-finishing device, comprising: a grinding wheel portion provided on at least outer peripheral portions of both side surfaces, and a plurality of grooves formed by shaving off a part of the grinding wheel portion, wherein the thickness of the grinding wheel is thinner than the cutting wheel. A moving mechanism for moving the polishing wheel; and a control for controlling the moving mechanism such that the polishing wheel mirror-processes one of the cut surfaces using one side surface and mirror-processes the other of the cut surface using the other side surface. And a device for processing a mirror-surface with a cut surface, the device comprising:
[0016]
With this configuration, both of the cut surfaces, which are the workpieces, can be suitably mirror-finished using the polishing grindstone having the above characteristics. That is, since the above-mentioned side clearance and a plurality of grooves are formed on both side surfaces of the grinding wheel, one of the cut surfaces is mirror-polished using one side of the grinding wheel, and the other is cut using the other side surface. When performing mirror finishing, the contact area between the cut surface and the side surface of the grinding wheel is reduced, so that the straightness of the grinding wheel can be increased and the mirror finishing accuracy can be improved. In addition, even if the grinding wheel is worn and the tip shape of the grinding wheel is broken by providing the side clearance, it is possible to prevent the broken wheel shape from being transferred to the cutting surface and to cut the deeply cut grinding wheel. The cut surface can be prevented from being damaged when it is pulled out.
[0017]
In addition, if the above-mentioned polishing whetstone is provided with a metal base portion and whetstone portions attached to both side surfaces of the base portion, the rigidity of the polishing whetstone increases, and the polishing whetstone at the time of processing is increased. Straightness is further improved.
[0018]
According to another aspect of the present invention, in order to solve the above-described problems, both of the cut surfaces formed by cutting the substrate with a cutting grindstone are mirror-polished by cutting and polishing with a high-speed rotating polishing grindstone. A method for mirror-cutting a cutting surface, comprising: a grindstone portion provided on at least outer peripheral portions of both side surfaces, and a plurality of grooves formed by shaving off a part of the grindstone portion, wherein the thickness of the polishing grindstone is thinner than the cutting grindstone. A first step of mirror-finishing one of the cut surfaces using one side surface; a second step of moving a polishing grindstone to a position at which the other of the cut surfaces can be cut and polished; And a third step of mirror-polishing the other of the cut surfaces using the method.
[0019]
With this configuration, the polishing grindstone can be inserted into the kerf formed by the cutting grindstone. While rotating this grinding wheel at a high speed, either side of the grinding wheel is cut into one of the cut surfaces with a small cutting width, and the grinding wheel is moved in the direction in which the kerf is extended. By moving the cut surface along one end, the cut surface can be cut and polished continuously from one end to multiple ends. With this processing method, one cut surface can be mirror-finished on one side surface of the grinding wheel, and the other cut surface can be mirror-finished on the other side surface of the grinding wheel, so that the mirror surface processing of the cut surface can be performed one by one. Therefore, it is not necessary to maintain the width of the abrasive wheel, which is easily worn, and the precision of mirror finishing is improved.
[0020]
Further, by providing the grinding wheel portion at least on the outer peripheral portion of both sides of the polishing wheel (that is, forming a side clearance on the inner peripheral portion of both side surfaces of the polishing wheel), the contact between the grinding wheel and the cut surface during processing is achieved. The area can be reduced. In addition, by providing a plurality of grooves in the grindstone portion, the grindstone portion in contact with the cut surface is divided into a plurality of regions. For this reason, the contact area between the grinding wheel and the cut surface can be made smaller, so that the side resistance that the grinding wheel receives from the cut surface during processing can be reduced. Therefore, even with a thin grinding wheel, sufficient processing straightness can be obtained, and the mirror processing accuracy is further improved. Further, during processing, a sufficient amount of cutting water is supplied to the processing point through a plurality of grooves formed in the grindstone portion. For this reason, the working point can be sufficiently cooled and the temperature rise due to the frictional heat generated between the cut surface and the grindstone portion can be suppressed, so that the surface burn phenomenon of the cut surface can be prevented.
[0021]
Further, in at least one of the first step and the third step, the polishing grindstone performs mirror finishing of the cut surface in a plurality of steps in the thickness direction of the substrate. Since the area of the cut surface to be cut and polished can be reduced, the mirror finishing accuracy is further improved.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted.
[0023]
(First Embodiment)
Hereinafter, a method for mirror-cutting a cut surface, a mirror-cutting device for a cut surface, and a grinding wheel according to a first embodiment of the present invention will be described. The method for mirror-cutting a cut surface according to the present embodiment is particularly characterized by the shape of a polishing grindstone applied when cutting and polishing a cut surface, and this feature improves the straightness of the polishing grindstone during mirror-finish processing. Is what you can do. Therefore, in the following, first, a substrate which is a workpiece will be described, and then, a configuration of a cutting surface mirror processing apparatus and a polishing grindstone for mirror-processing a cut surface of the substrate will be described in detail. Next, a method for mirror-cutting a cut surface using the apparatus for mirror-cutting a cut surface and a grinding wheel will be described in detail.
[0024]
First, a substrate as a workpiece according to the present embodiment will be described. The substrate is, for example, a semiconductor wafer in which, for example, a quartz glass layer is laminated on a semiconductor substrate such as silicon. This substrate has, for example, a substantially disk shape, and has an outer diameter of, for example, 4 inches and a thickness of, for example, about 1 mm. Hereinafter, the surface of the substrate refers to the surface on which the glass layer is laminated, and the back surface of the substrate refers to the surface on the semiconductor substrate side.
[0025]
A plurality of elements (for example, circuits such as optical waveguides) having substantially the same pattern and characteristics are formed on the glass layer on the surface of such a substrate. By dicing such a substrate along a street between elements and dividing it into a plurality of pieces, a chip such as an optical element can be obtained. When the chip functions as, for example, an optical element, a portion of the side surface (that is, a cut surface) through which an optical signal passes or reflects, for example, must be flattened with high precision. However, since the cut surface of the diced substrate has insufficient flatness, the cut surface after dicing must be polished and mirror-finished. Therefore, in the present embodiment, such a cut surface is mirror-finished using a cut surface mirror-finishing apparatus as described below.
[0026]
Next, the cut surface mirror processing apparatus according to the present embodiment will be described. The apparatus for mirror-cutting a cut surface according to the present embodiment has a function of performing mirror-polishing by cutting and polishing both of the cut surfaces formed on a substrate with a polishing grindstone rotating at a high speed, and can be configured by, for example, a dicing device. The dicing apparatus (also referred to as a dicing saw or dicer) is a general apparatus used for cutting a workpiece such as a semiconductor wafer using a high-speed rotating blade for dicing.
[0027]
Here, a dicing apparatus according to the present embodiment will be described with reference to FIG. FIG. 1 is an overall perspective view of a dicing apparatus 10 according to the present embodiment.
[0028]
As shown in FIG. 1, the dicing apparatus 10 includes, for example, a first cutting unit 20-1 that cuts a substrate 12, a second cutting unit 20-2 that mirror-cuts a cut surface of the substrate 12, It has a chuck table 15 on which the chuck 12 is placed, a moving mechanism (not shown) for moving the chuck table 15, for example, and a control device 16 for controlling the operation of the moving mechanism. As described above, the dicing apparatus 10 is, for example, a facing-type dual dicer having two cutting units 20-1 and 20-2, for example.
[0029]
The first cutting unit 20-1 has a function of cutting the substrate 12 along a street on a processing surface using a cutting grindstone provided at an end to form an extremely thin kerf. The details will be described later. Further, the second cutting unit 20-2 has a function of mirror-finishing the cut surfaces, which are both side surfaces of the above-mentioned kerf, using a polishing grindstone provided at an end portion, which will be described later in detail.
[0030]
The chuck table 15 is a table on which the substrate 12 is placed and fixed, and has, for example, a vacuum chuck mechanism on its upper surface. The substrate 12 is placed on the chuck table 15 via, for example, a jig 14. At this time, the back surface of the substrate 12 and the jig 14 are attached and fixed with, for example, an adhesive, a double-sided tape, a seal, or the like.
[0031]
The jig 14 is a substantially flat member formed of, for example, synthetic resin such as plastic or metal, and has a function of supporting the substrate 12 mounted on the upper surface thereof.
[0032]
On the surface of the jig 14 (the surface in contact with the substrate 12), a plurality of grindstone passage grooves 13 are formed at positions where cutting whetstones and polishing whetstones to be described later pass. The width of the grindstone passage groove 13 is at least wider than the width of the cutting grindstone, and the depth is adjusted to be a depth at which the outer peripheral portion of the polishing grindstone can be sufficiently inserted. When the cutting direction is two directions (for example, when the substrate 12 is diced in a lattice), the grindstone passage grooves 13 are formed in two directions along each cutting direction as shown in FIG. In the case where the cutting direction of the substrate 12 is one direction, the plurality may be provided only in, for example, one direction substantially parallel to the cutting direction. Such a grindstone passage groove 13 has a function of preventing the cutting grindstone or the polishing grindstone from acting on only the substrate 12 and not interfering with the jig 14 supporting the substrate 12 at the time of cutting or mirror finishing.
[0033]
The moving mechanism (not shown) moves the chuck table 15 on which the substrate 12 is mounted as described above to the first cutting unit 20-1 and the second cutting unit 20-2 (hereinafter simply referred to as the cutting unit 20). Has a function to move relatively. More specifically, the moving mechanism can move the chuck table 15 together with the substrate 12 in a state where a cutting wheel or a polishing wheel that rotates at a high speed is cut into the surface of the substrate 12 by a predetermined amount. Thus, the cutting wheel can be moved along the street at a predetermined feed speed, and the cutting of the substrate 12 can be advanced. Further, it is also possible to move the polishing grindstone at a predetermined feed speed along the cut surface, and to proceed with the mirror finishing of the cut surface. The moving mechanism is not limited to this example, and may be configured to move the cutting unit 20 relatively to the chuck table 15 that is fixedly arranged.
[0034]
The control device 16 is disposed, for example, inside the dicing device 10 and includes, for example, an arithmetic processing device such as a CPU and a storage device such as a RAM. The control device 16 has a function of controlling the operation of the moving mechanism so that cutting with a cutting grindstone and mirror finishing with a polishing grindstone are suitably performed. Note that the control device 16 does not necessarily have to be built in the dicing device 10, and is installed outside the dicing device 10, for example, and transmits a control signal to a moving mechanism of the dicing device 10 by wire or wireless. It may be configured as follows.
[0035]
Next, a cutting grindstone provided in the first cutting unit in the present embodiment will be described with reference to FIG. 2 (a) and 2 (b) are a plan view and a cross-sectional view illustrating a cutting grindstone 40 according to the present embodiment.
[0036]
As shown in FIG. 2 (a), the cutting grindstone 40 is, for example, an ultra-thin cutting blade having a substantially ring shape, and is formed by polishing an abrasive such as diamond or CBN with an electroformed metal (eg, nickel) or resin. Formed by bonding with a bonding agent (bonding agent). The cutting grindstone 40 is preferably made of abrasive grains coarser than a polishing grindstone described later, and the grain size is, for example, about # 800. For this reason, the cutting grindstone 40 is relatively hard and has excellent cutting performance and wear resistance, but is inferior in flattening accuracy. The thickness of the cutting grindstone 40 is, for example, about 0.32 mm as shown in FIG. Although the cutting grindstone 40 according to the present embodiment has a substantially ring shape, the present invention is not limited to this example. The cutting grindstone 40 may have a substantially disc shape, for example, a hub blade integrally formed with a hub (Hub) and a cutting blade portion, or the like. It may be.
[0037]
The cutting grindstone 40 is axially mounted on a spindle (not shown) while being held between flanges (not shown). P. M. And can rotate at high speed. The cutting wheel 40 that rotates at a high speed cuts the processing surface along the street while cutting the outer circumference of the processing surface of the substrate 12 by a predetermined amount, thereby forming an extremely thin kerf on the processing surface. At this time, by maintaining a sufficient notch depth, the substrate 12 can be completely cut, and since both side surfaces of the cut groove reach the back surface of the substrate 12, two opposing cut surfaces are formed. You. During the cutting, cutting water is supplied to cool the cutting wheel 40 and the processing point.
[0038]
Next, the polishing grindstone 50 provided in the second cutting unit 20-2 according to the present embodiment will be described in detail with reference to FIG. FIG. 3A is a plan view showing the polishing grindstone 50 according to the present embodiment, and FIG. 3B is a cross-sectional view taken along line AA ′ in FIG. 3A.
[0039]
As shown in FIG. 3, the polishing grindstone 50 is a very thin grindstone having a substantially ring shape, for example, and has a function of cutting and polishing a cut surface to perform mirror finishing. The size of the polishing grindstone 50 is, for example, 52 mm in outer diameter and 40 mm in inner diameter, and is, for example, about 0.30 mm and is slightly thinner than the cutting grindstone 40. The polishing grindstone 50 includes a metal base 54 arranged at the center, for example, and a grindstone 52 attached to both side surfaces of the base 54.
[0040]
The base 54 is, for example, a substantially ring-shaped member having a thickness of, for example, about 0.1 mm, and is made of, for example, a cemented carbide that is a sintered alloy containing tungsten carbide, titanium carbide, molybdenum carbide, or the like. Since the base 54 is very hard, the base 54 functions as a reinforcing material for increasing the rigidity of the entire polishing grindstone 50 during mirror polishing.
[0041]
The grindstone portion 52 is, for example, a fine-grained grindstone stuck on both sides of the base portion 54 with, for example, an adhesive or the like. The left grindstone portion 52a stuck on one side of the base portion 54 and the other side are stuck. And the right whetstone portion 52b. The left grindstone portion 52a and the right grindstone portion 52b have a substantially symmetrical shape, and the thickness of both is, for example, about 0.1 mm at the outer peripheral portion.
[0042]
The grindstone constituting the grindstone portion 52 is formed by bonding green silicon carbide (GC) abrasive grains, diamond (D, SD) abrasive grains, CBN abrasive grains, and the like with various binders, and has a fine particle size. More preferably, for example, # 1000 to # 8000. For this reason, the grindstone portion 52 is softer than the cutting grindstone 40, for example, and is inferior in abrasion resistance, but is excellent in flattening accuracy, so that the workpiece can be mirror-finished with high accuracy.
[0043]
In addition, side reliefs 56 are formed on the outer side surfaces of both grindstone portions 52 (that is, both side surfaces of the polishing grindstone 50) so as to be depressed while leaving the outer peripheral portions. The depth of the side clearance 56 (that is, the difference in level between the outer peripheral portion of the grindstone portion 52 and the bottom of the side clearance) is, for example, about 0.02 mm. By forming the side relief 56, as shown in FIG. 3B, the outer peripheral portions of the left grindstone portion 52a and the right grindstone portion 52b have a shape protruding outward. For this reason, the left grindstone portion 52a and the right grindstone portion 52b have a thickness of, for example, 0.1 mm at the outer peripheral portion, whereas the inner portion of the outer peripheral portion where the side clearance 56 is formed extends from the inner peripheral portion. The thickness is reduced by the depth of the side relief 56. Since the polishing grindstone 50 is provided with such a side clearance 56, substantially only the outer peripheral portion (for example, a width of about 0.7 mm) of the grindstone portion 52 acts on the cut surface during the mirror finishing of the cut surface. Will be done.
[0044]
Further, grooves 58 which are a major feature of the present embodiment are formed on, for example, both side surfaces of the polishing grindstone 50. Hereinafter, the groove 58 will be described in detail with reference to FIGS. FIG. 4A is a partially enlarged plan view showing the polishing grindstone 50 around the groove 58 according to the present embodiment, and FIG. 4B is a plan view showing the polishing grindstone 50 around the groove 58 according to the present embodiment. FIG. 4C is a sectional view taken along line BB ′ of FIG. 4A, and FIG. 4D is a sectional view taken along line CC ′ of FIG. It is sectional drawing in a line.
[0045]
As shown in FIG. 3A, a plurality of grooves (slits) 58 are formed on the side surface of the polishing grindstone 50. The groove 58 is a notch formed by, for example, cutting a part of the side surface of the grindstone portion 52 linearly in a diametric direction using, for example, a machine tool. For example, eight such grooves 58 are formed on the outer surfaces of the left grindstone portion 52a and the right grindstone portion 52b, for example, each having approximately the same pattern. The eight grooves 58 are arranged at substantially equal intervals along the circumferential direction of the outer surface of the grindstone portion 52, and the outer surface of the grindstone portion 52 is divided into, for example, eight regions having substantially the same shape. are doing.
[0046]
Further, as shown in FIGS. 4A and 4B, each groove 58 has a shape wider than the thickness, for example, and specifically, the width is 2 mm, for example, and the depth is 2 mm. Is, for example, 0.05 mm. Thus, by securing a certain width of the groove 58, the groove 58 can divide the outer peripheral portion of the grindstone portion 52 at a sufficient distance. The portion of the outer peripheral portion of the grindstone portion 52 where such a relatively wide groove 58 is formed does not contact the cut surface during processing. Accordingly, since the contact area between the cut surface and the outer peripheral portion of the grindstone portion 52 during processing can be further reduced, the side resistance acting on the polishing grindstone 50 can be further reduced.
[0047]
Further, since the depth of the groove 58 is set to be deeper than, for example, the depth of the side relief 56, the groove 58 is formed not only at the outer peripheral portion of the grindstone portion 52 but also at the portion where the side relief 56 is formed. Is also shaved off. Therefore, in the polishing grindstone 50, the portion where the groove 58 is formed (see FIG. 4C) is compared with the portion where the groove 58 is not formed (see FIG. 4D). Has become thinner. By forming the grooves 58 in this manner, cutting water such as pure water easily enters the grooves 58 during processing. For this reason, the processing point where frictional heat is generated can be suitably cooled.
[0048]
The depth of the groove 58 is not limited to the above example. For example, the groove 58 is formed by setting the depth to be shallower than the depth of the side relief 56 and shaving only the outer peripheral portion of the grindstone portion 52. It may be. As described above, the strength of the polishing grindstone 50 can be increased as the depth of the groove 58 is reduced.
[0049]
The number of the grooves 58, the width, the depth, the area occupying the entire side surface of the grindstone portion 52, and the like are suitably determined according to, for example, the material and hardness of the substrate 12, the required mirror finishing accuracy, and the processing speed. It is set and is not limited to the above example.
[0050]
The polishing grindstone 50 having the above-described configuration is mounted on a spindle (not shown) while being held between flanges (not shown). P. M. And can rotate at high speed. The grinding wheel 50 is rotated at a high speed and one side surface is cut into one cut surface by a predetermined cut width (for example, 0.01 to 0015 mm). By parallel movement in the cut groove, one of the cut surfaces can be cut and polished on one side surface and mirror-finished. During the mirror polishing, cutting water is supplied by, for example, a shower nozzle or a side nozzle (not shown) to cool the polishing grindstone 50 and the processing point.
[0051]
In addition, since the polishing whetstone 50 has the base portion 54 as a reinforcing material, in the above-described mirror finishing, the deviation or meandering due to the side resistance received from the cut surface is reduced, and the straightness is improved. Can be. The groove 58 is formed by cutting only the side surface of the grindstone portion 52, for example, and does not cut off the base portion 54 or provide a through hole in the base portion 54. For this reason, since the base 54 having a relatively large area can be provided, the strength of the polishing grindstone 50 can be further increased.
[0052]
Furthermore, since the side surface relief 56 is formed in the polishing grindstone 50, the side surfaces other than the outer peripheral portion of the polishing grindstone 50 do not come into contact with the cut surface during mirror polishing. For this reason, the contact area between the side surface of the polishing grindstone 50 and the cut surface is reduced, and the side resistance that the polishing grindstone 50 receives from the cut surface can be reduced, so that the straightness of the polishing grindstone 50 can be improved. Further, even if the polishing grindstone 50 is worn and the tip shape of the grindstone portion 52 collapses, the grinding grindstone 50 is cut into a depth such that the lower end of the side relief 56 reaches the outside of the back surface of the substrate 12. The shape can be prevented from being transferred to the cut surface.
[0053]
In addition, since a plurality of grooves 58 which are features of the present embodiment are formed on both side surfaces of the polishing grindstone 50, the contact area between the side surface of the polishing grindstone 50 and the cut surface can be further reduced in combination with the side clearance 56. . Thereby, the straightness of the polishing grindstone 50 can be sufficiently ensured, so that the distortion of the cut surface as shown in FIG. 10 can be suppressed. Therefore, the cut surface after mirror finishing can be a flat surface substantially perpendicular to the substrate 12 surface.
[0054]
Next, a method for mirror-cutting a cut surface according to the present embodiment using the dicing apparatus 10 will be described with reference to FIGS. FIG. 5 is a flowchart showing an operation flow of the method for mirror-cutting a cut surface according to the present embodiment. FIG. 6 is a flowchart showing an operation flow of a left-cut-surface mirror-surface machining subroutine according to the present embodiment. FIGS. 7 and 8 are cross-sectional views showing aspects of the substrate 12 and the like in each step of the method for mirror-cutting a cut surface according to the present embodiment.
[0055]
As shown in FIG. 5, first, in step S10, the substrate 12 is cut by the cutting grindstone 40 (step S10). As shown in FIG. 7A, the substrate 12 including the glass layer 12a and the semiconductor substrate 12b is cut by the cutting grindstone 40 provided in the first cutting unit 20-1. At this time, the substrate 12 is cut such that the cutting line overlaps the grindstone passage groove 13 of the jig 14.
[0056]
By such a cutting process, an extremely thin kerf is formed in the substrate 12. The width of this kerf is substantially the same as or slightly larger than the width of the cutting grindstone 40, for example, about 0.32 mm. Both side surfaces of such a kerf are cut surfaces, and are hereinafter referred to as a left cut surface 70a and a right cut surface 70b. The left cut surface 70a and the right cut surface 70b (hereinafter sometimes simply referred to as the cut surface 70) have a rough flatness and cannot be used as such as optical surfaces through which optical signals pass.
[0057]
After such a cutting process is repeated along each street to form a plurality of kerfs in one direction, the chuck table 15 is rotated, for example, by 90 degrees, and cut in the same manner. Is formed. Thus, the substrate 12 is diced into, for example, a lattice and divided into individual chips.
[0058]
Next, in step S20, the polishing grindstone 50 is moved in the horizontal direction, and the left cut surface 70a is arranged at a position where mirror finishing can be performed (step S20). By operating a moving mechanism (not shown) based on a control signal from the control device 16, as shown in FIG. 7B, the polishing grindstone 50 provided in the second cutting unit 20-2 is moved. The left cut surface 70a is moved to a position where cutting and polishing can be performed. More specifically, the horizontal position of the polishing grindstone 50 is adjusted so that the left grindstone portion 52a of the polishing grindstone 50 can cut into the left cut surface 70a with a cutting width of, for example, about 0.01 mm. Thus, this step is a preparation process for mirror-finishing the left cut surface 70a with the polishing grindstone 50.
[0059]
Further, in step S30, the left-cut surface mirror processing subroutine shown in FIG. 6 is performed to mirror-process the left cut surface 70a (step S30).
[0060]
As shown in FIG. 6, first, in step S32, the polishing grindstone 50 is lowered with respect to the substrate 12 (step S32). In step S20, the polishing grindstone 50 whose horizontal position is aligned with the left cutting surface 70a is lowered vertically by a predetermined distance. This step is a step of determining a cutting depth (hereinafter, referred to as a vertical cutting depth) of the polishing grindstone 50 with respect to the substrate 12 in the thickness direction of the substrate 12 when the polishing grindstone 50 cuts and polishes the left cut surface 70a. It is. The vertical cutting depth is, for example, 0.1 to 0.04 mm when the glass layer 12a is cut and polished, and is, for example, 0.1 to 0.2 mm when the semiconductor substrate 12b is cut and polished.
[0061]
Next, in step S34, the left cut surface 70a is cut and polished (step S34). As shown in FIG. 7 (c), while the polishing grindstone 50 which rotates at a high speed, the left grindstone portion 52a is cut into the left cut surface 70a in the horizontal direction at a cut width of, for example, about 0.01 mm, and the cut groove is formed to be extended. Is moved at a predetermined feed speed in the direction (vertical direction in FIG. 7C). Accordingly, the outer peripheral portion of the left grindstone portion 52a gradually interferes from one side end to the other side end of the left cut surface 70a, and the rough left cut surface 70a is thinly polished. As a result, only the vertical cut depth of the left cut surface 70a is continuously mirror-finished along the direction in which the cut groove is formed.
[0062]
At the time of such cutting and polishing, the side relief 56, the base 54 and the plurality of grooves 58 function suitably as described above, so that the grinding wheel 50 is displaced or meandered by the side resistance from the left cut surface 70a. It is possible to favorably go straight in the incision groove without dropping.
[0063]
Next, in step S36, it is determined whether or not all of the left cut surface 70a has been mirror-finished (step S36).
[0064]
If the lower end of the polishing grindstone 50 has not yet reached the lower side of the back surface of the substrate 12 and the entire left cut surface 70a has not been cut and polished, the process returns to step S32, and the polishing grindstone 50 is again moved to the predetermined vertical cutting depth. Then, the left cut surface 70a is cut and polished again in step S34. The lowering of the polishing grindstone 50 and the cutting and polishing are repeated until all of the left cut surface 70a is mirror-finished.
[0065]
As described above, in the method for mirror-cutting the cut surface according to the present embodiment, the vertical cut depth is set to be equal to or greater than the thickness of the substrate 12, and the entire cut surface 70 is not cut and polished by one cutting and polishing (1 pass). A method of sequentially cutting and polishing the cut surface 70 in a plurality of stages (for example, 14 steps) in the thickness direction of the substrate 12 by setting the vertical cutting depth per stage (1 step) to be equal to or less than the thickness of the substrate 12 (hereinafter, referred to as multi-step mirror finishing). Is adopted.
[0066]
Such multi-step mirror surface processing can be said to be, for example, a method such as step cutting (multi-step cutting) of a dicing method. By cutting and polishing the cut surface 70 in multiple steps in the thickness direction of the substrate 12, the area to be processed is reduced. Mirror finishing accuracy can be improved. This processing accuracy increases as the number of steps increases.
[0067]
In the present embodiment, the vertical cutting depth per step is, for example, 0.04 mm, and the glass layer 12a is cut and polished in, for example, two steps, and the vertical cutting depth per step is, for example, 0.1 mm. The substrate 12b is set to be cut and polished. The reason why the glass layer 12a is finely cut and polished from the semiconductor substrate 12b in this way is, for example, to increase the mirror finishing accuracy of the glass layer 12a on which the optical element is formed. The feed speed of the polishing grindstone 50 is, for example, 2.0 mm / s when the semiconductor substrate 12b is cut and polished, whereas it is as small as 0.5 mm / s when the glass layer 12a is cut and polished. Is set. This is because the processing accuracy is prioritized when processing the glass layer 12a, while the processing speed is prioritized when processing the semiconductor substrate 12b.
[0068]
By such multi-step mirror finishing, the left cut surface 70a is gradually mirror-finished in the thickness direction of the substrate 12, and when the lower end of the polishing grindstone 50 reaches below the back surface of the substrate 12, the left cut surface 70a Is determined to have been mirror-finished, the left-cut-surface mirror-finishing subroutine ends, and the routine proceeds to step S40.
[0069]
As shown in FIG. 7D, when the left cut surface mirror finishing subroutine is completed, the lower end of the left grindstone portion 52a, for example, is sufficiently inserted into the grindstone passage groove 13 of the jig as shown in FIG. It is preferable that at least a part of the escape 56 be in a state where it appears below the back surface of the substrate 12. By cutting and polishing the grinding wheel 50 in such a state that the grinding wheel 50 is inserted deeply into the groove 13 for grinding wheel passage, even if the outer peripheral portion of the left grinding wheel portion 52a is broken by abrasion, the side relief 56 functions. Thus, the collapsed whetstone shape can be prevented from being transferred to the left cut surface 70a. Further, when the polishing grindstone 50 is pulled out, it is possible to prevent the left grindstone portion 52a from contacting and damaging the left cut surface 70a, or the end of the left grindstone portion 52a from being chipped.
[0070]
Thereafter, in step S40 shown in FIG. 5, the polishing grindstone 50 is moved to arrange the right cut surface 70b at a position where mirror finishing can be performed (step S40). First, the polishing grindstone 50 inserted in the jig 14 and the kerf as shown in FIG. 7D is pulled out from the kerf so as not to damage the left cut surface 70a. Next, a moving mechanism (not shown) is operated based on a control signal from the control device 16 to move the polishing grindstone 50 in the horizontal direction, and as shown in FIG. It is arranged at a position where it can be cut into the right cut surface 70b by, for example, about 0.01 mm. Thus, this step is a preparation process for mirror-finishing the right cut surface 70b.
[0071]
Next, in step S50, the right cut surface 70b is mirror-finished (step S50). As shown in FIGS. 8 (b) to 8 (c), the right cut surface 70b is mirror-finished by multi-stage mirror polishing in the same manner as the mirror finish of the left cut surface 70a. The mirror finishing of the right cut surface 70b is different from the mirror finishing of the left cut surface 70a only in that the right grindstone portion 52b is used instead of the left grindstone portion 52a. Since they are substantially the same, detailed description is omitted.
[0072]
By the above steps, both the left cut surface 70a and the right cut surface 70b are mirror-finished as shown in FIG. As a result, the width of the kerf is slightly wider than, for example, about 0.32 mm before mirror finishing, and becomes, for example, 0.34 mm.
[0073]
The mirror processing of the cut surface in such a kerf is repeated for other kerfs in the same manner, so that, for example, all the cut surfaces 70 can be mirror-finished. At this time, it is preferable that first, the cut surface 70 in the cut groove in one direction is sequentially mirror-finished, and then, the cut surface 70 in the cut groove in the other direction (that is, for example, a direction perpendicular to) is sequentially mirror-finished.
[0074]
As described above, in the method for mirror-cutting the cut surface according to the present embodiment, the chips obtained by dicing are picked up and conveyed, and then the cut surfaces of the cut substrate 12 are not individually mirror-processed. The cut surface 70 can be mirror-finished at the same position without being transported. Therefore, not only is it unnecessary to perform the alignment of the substrate 12 or the chip twice, but also the operation of transporting the substrate 12 can be omitted, and the number of steps can be reduced, so that the production efficiency is improved.
[0075]
Further, in the method for mirror-cutting the cut surface according to the present embodiment, instead of simultaneously performing mirror-polishing on both of the cut surfaces 70 as in the related art, the cutting surface 40 is formed by the cutting grindstone 40 using both side surfaces of the polishing grindstone 50 one by one. The two cut surfaces can be separately mirror-finished. More specifically, the polishing grindstone 50 inserted into the kerf mirror-processes the left cut surface 70a using the left grindstone portion 52a and mirror-processes the right cut surface 70b using the right grindstone portion 52b. be able to. This eliminates the need to maintain the thickness of the polishing grindstone 50 during mirror finishing. That is, even if the grindstone portion 52 is worn due to repeated mirror finishing and the thickness of the polishing grindstone 50 becomes thin, the polishing device 50 is adjusted by the control device 16 and the moving mechanism so that the polishing grindstone 50 is suitably adjusted. Both the cut surfaces 70 can be suitably mirror-finished. Therefore, the number of replacements of the polishing grindstone 50 can be reduced, and the production efficiency can be improved. In addition, since the life of the polishing grindstone 50 can be extended, the cost can be reduced.
[0076]
The polishing grindstone 50 used for mirror finishing has a relatively large strength because it has the hard base portion 54. Further, since the side clearances 56 are formed on both side surfaces, the contact area between the side surface of the polishing grindstone 50 and the cut surface 70 is reduced.
[0077]
Further, grooves 58 having a suitable number, width, depth, and area occupying the entire side surface are provided on, for example, both side surfaces of the polishing grindstone 50, so that the polishing performance for the cut surface 70 is not reduced. The contact area between the grinding wheel 50 and the cut surface 70 can be further reduced. For this reason, the side surface resistance (repulsive force) received from the cut surface 70 during mirror finishing can be sufficiently reduced. Therefore, even if the polishing grindstone 50 is extremely thin, it can obtain sufficient processing straightness without being shaken or distorted during processing. Accordingly, the cut surface 70 after the mirror finishing is improved in the flatness in the vertical direction (square angle) and the flatness in the horizontal direction (straightness) without being curved unlike the related art. As described above, the method for mirror-cutting the cut surface according to the present embodiment can mirror-process the cut surface 70 with higher precision as compared with the conventional method for mirror-cutting the cut surface using a grinding wheel having no groove 58. It is also possible to reduce the distortion of the cut surface, which is an error between the squareness and the straightness, to, for example, less than half.
[0078]
Further, by providing the groove 58, the amount of cutting water supplied to the processing point can be increased. For this reason, since the processing point can be sufficiently cooled and the temperature rise due to the frictional heat between the cut surface 70 and the polishing grindstone 50 can be suppressed, the surface burn phenomenon in which the cut surface 70 darkens can also be prevented. it can.
[0079]
(Example)
Next, a description will be given of the result of an experiment in which the cut surface 70 of the substrate 12 is mirror-finished using the polishing grindstone 50 having the groove 58 according to the first embodiment as described above. In addition, as a control experiment, an experimental result in which the cut surface 70 of the substrate 12 is mirror-finished using a conventional polishing grindstone having no groove 58 will also be described.
[0080]
First, Table 1 below shows experimental conditions of a mirror finishing experiment according to the present embodiment.
[0081]
[Table 1]

[0082]
In the mirror finishing experiment according to the present example, the cut surface 70 of the substrate 12 was mirror-finished under the experimental conditions shown in Table 1, and the flatness of the mirror-finished cut surface 70 was measured. As a parameter representing the flatness, two parameters, a squareness error and a straightness error, are employed. The squareness error is the vertical distortion of the curved cut surface 70 expressed by the height difference between the uppermost portion and the lowermost portion, and the straightness error is the horizontal direction (cut groove) of the curved cut surface 70. (Longitudinal direction) is expressed by the height difference between the uppermost part and the lowermost part. The larger these values are, the more the cut surface 70 after mirror finishing is distorted and not flat.
[0083]
In the case of a mirror polishing experiment using a conventional polishing grindstone having no groove 58, the cut surface 70 is mirror-polished under the same conditions as those of the above-described experiment except for the conditions relating to the groove 58, and similarly. The flatness was measured.
[0084]
Next, based on FIG. 9, an experimental result of a mirror finishing experiment on a cut surface according to the present embodiment will be described. FIG. 9 is a graph showing experimental results of a mirror finishing experiment according to the present embodiment.
[0085]
As shown in FIG. 9A, the squareness error is relatively large at 1.0 μm on average and 2.0 μm at maximum when mirror-polished with a polishing grindstone having no groove 58 formed. On the other hand, when mirror polishing is performed with the polishing grindstone 50 in which the groove 58 is formed, the squareness error is 0.3 μm on average and 1.0 μm in the maximum value. The average value is very small, such as about one third of the average value and half of the maximum value.
[0086]
Further, as shown in FIG. 9B, the straightness error is relatively large at 1.8 μm on average and 2.2 μm at maximum when mirror-polished with a polishing grindstone having no groove 58 formed. . On the other hand, when mirror polishing is performed with the polishing grindstone 50 in which the groove 58 is formed, the straightness error is 0.6 μm on average and 1.1 μm in the maximum value, and when the groove 58 is not formed. The average value is very small, such as one third at the average value and half at the maximum value.
[0087]
As described above, in the mirror finishing experiment according to the present embodiment, when the groove 58 is formed on the side surface of the polishing grindstone 50, both the squareness error and the straightness error are compared with the case where the groove 58 is not formed. Is significantly smaller. According to such experimental results, it can be said that the flatness of the mirror-finished cut surface 70 can be significantly improved by forming the groove 58 on the side surface of the polishing grindstone 50. Therefore, it can be said that it has been proved that the mirror surface machining accuracy of the cut surface 70 can be greatly improved by the method for mirror surface cutting of the present embodiment.
[0088]
The preferred embodiment of the present invention has been described with reference to the accompanying drawings, but the present invention is not limited to this example. It is obvious that a person skilled in the art can conceive various changes or modifications within the scope of the technical idea described in the claims, and those changes naturally fall within the technical scope of the present invention. It is understood to belong.
[0089]
For example, as the substrate 12 which is a workpiece according to the present embodiment, a semiconductor wafer in which a glass layer 12a is laminated on a semiconductor substrate 12b is used. However, the present invention is not limited to this example. The layer 12a may not be laminated. Examples of the substrate 12 include various semiconductor substrates other than those described above, sapphire substrates, difficult-to-process materials such as quartz, glass, and ceramics, composite materials, substrates made of various metallic materials, brittle materials, and magnetic materials such as VTRs and FDDs. It may be a head or the like. In addition to the above-described optical elements, various wirings, electrodes, insulating films, transistor structures, and the like constituting a semiconductor device such as an LSI may be formed on the surface of the substrate 12 in various forms. Further, the substrate 12 is not limited to a substantially disk shape, and may be, for example, a flat plate shape such as a substantially square shape or a substantially sector shape.
[0090]
Further, in the above embodiment, the substrate 12 is placed on the chuck table 15 via the jig 14, but the present invention is not limited to this example, and the substrate 12 may be placed via a wafer tape, an adhesive tape, a frame, a substrate, or the like. May be done. However, it is preferable that the material and the thickness are such that the cutting depth of the cutting grindstone 40 and the polishing grindstone 50 can be sufficiently secured.
[0091]
In the above embodiment, the dicing device 10 is used as the cut surface mirror processing device. In this case, it is only necessary to apply the polishing grindstone 50 instead of the cutting blade, and it is not necessary to change the design of the other apparatus main body. Therefore, it is possible to easily provide a high performance cut surface mirror processing apparatus, and There is an advantage that cutting and mirror finishing can be performed simultaneously. However, the cut surface mirror finishing apparatus according to the present invention is not limited to such an example. For example, a cutting device provided with a cutting grindstone 40 for cutting the substrate 12 and a cut surface mirror processing device may be configured separately. In this case, for example, a polishing device such as various grinders may be used as the cut surface mirror finishing device.
[0092]
Further, in the above-described embodiment, the facing dual dicer including the two cutting units 20 is used as the dicing device 10 that is a mirror-surface processing device for a cut surface, but the present invention is not limited to this example. For example, as the dicing apparatus 10, for example, a dual dicer in which two cutting units 20 are arranged in parallel may be used. Further, a single dicer having only one cutting unit 20 may be used. In this case, after cutting by the cutting grindstone 40, for example, the cutting grindstone 40 may be replaced with a polishing grindstone 50 to perform mirror finishing.
[0093]
Further, in the above embodiment, the base 54 of the polishing grindstone 50 is made of a cemented carbide, but the present invention is not limited to such an example, and for example, various kinds of relatively hard metals such as stainless steel and hard cutting. A blade (reinforcement grindstone) or the like may be used.
[0094]
In addition, the polishing grindstone 50 does not necessarily need to include the base 54. The polishing grindstone 50 may be a grindstone thinner than the width of the cutting grindstone 40 (the width of the kerf), and may be composed entirely of ultrafine grindstones, various types of electroformed blades, metal blades or resin blades, and rotating disks. You may.
[0095]
In the above-described embodiment, the polishing grindstone 50 has the grindstone portions 52 and the grooves 58 on both side surfaces. However, the present invention is not limited to such an example. Is also good.
[0096]
In addition, the thickness of the polishing grindstone 50, the grain size or thickness of the grindstone portion 52, the width of the outer peripheral portion of the grindstone portion 52, the number of grooves 58, the width or depth, the width or depth of the side clearance 56, the polishing grindstone 50 Numerical values such as the rotation speed and the feed speed of the substrate are not limited to the examples of the above-described embodiment, but can be suitably changed according to the type of the substrate 12 which is the workpiece and the required mirror finishing accuracy.
[0097]
In particular, regarding the groove 58 which is a feature of the present embodiment, for example, as the number of grooves 58 is increased, or as the width of the groove 58 and the area occupying the entire side surface of the polishing grindstone 50 are increased, Although the contact area between the grinding wheel 50 and the cut surface 70 can be reduced, the polishing efficiency is reduced. For this reason, it is preferable to appropriately set the conditions for forming the groove 58 according to the type of the workpiece and the desired processing accuracy as described above.
[0098]
For example, the number of the grooves 58 may be plural, and is not necessarily limited to eight. Further, the width of the groove 58 may be increased or decreased according to, for example, the number of grooves 58 to be installed. Further, the respective grooves 58 do not have to have substantially the same width as in the above-described embodiment, and may have, for example, a wider width closer to the outer peripheral portion of the grindstone portion 52.
[0099]
In the above embodiment, the grooves 58 having substantially the same shape are provided at equal intervals. However, the present invention is not limited to such an example. For example, grooves 58 having various shapes may be provided in an arbitrary arrangement. More specifically, for example, the groove 58 having a large width and the groove 58 having a small width may be alternately arranged, or the groove 58 having a small depth and the groove 58 may be arranged at random. Further, the cross-sectional shape of the groove 58 is not limited to the U-shape as in the above-described embodiment, and may be any cross-sectional shape such as a substantially U-shaped, a substantially V-shaped, or a substantially W-shaped.
[0100]
Further, as the depth of the groove 58 becomes deeper, the cutting water easily enters the groove 58, so that a larger amount of cutting water can be supplied to the processing point. However, since the polishing grindstone 50 becomes thinner, the strength decreases. I will. For this reason, it is preferable to appropriately set the depth of the groove 58 according to the type of the workpiece and the desired processing accuracy as described above.
[0101]
In the above-described embodiment, the direction in which the grooves 58 are formed is the diameter direction of the side surface of the polishing grindstone 50. However, the present invention is not limited to this example. For example, all the grooves 58 are formed in parallel in one predetermined direction. For example, it may be formed in any direction.
[0102]
In the method for mirror-cutting the cut surface according to the embodiment, the cut surface is mirror-polished (multi-step mirror-finished) by cutting and polishing in a plurality of stages in the thickness direction of the substrate 12, but the present invention is not limited to this example. For example, the vertical cutting depth of the polishing grindstone 50 may be increased, and the entire cut surface 70 may be cut and polished at 1 pass.
[0103]
【The invention's effect】
As described above, according to the present invention, by providing a plurality of grooves on the side surface of the grinding wheel, the contact area between the side surface of the grinding wheel and the cut surface can be reduced during mirror polishing, so that a thin grinding wheel can be used. Even if it is, sufficient straightness can be obtained. Therefore, the distortion of the cut surface after mirror polishing is reduced, and the mirror processing accuracy is greatly improved.
[0104]
Further, since a sufficient amount of cutting water is supplied to the processing point via such a groove, the processing point can be suitably cooled to prevent surface burn occurring on the cut surface.
[Brief description of the drawings]
FIG. 1 is an overall perspective view of a dicing apparatus according to a first embodiment.
FIG. 2A is a plan view showing a cutting grindstone according to the first embodiment.
FIG. 2B is a cross-sectional view illustrating the cutting grindstone according to the first embodiment.
FIG. 3A is a plan view showing a grinding wheel according to the first embodiment.
FIG. 3B is a cross-sectional view taken along line AA ′ of FIG.
FIG. 4A is a partially enlarged plan view showing a polishing grindstone around a groove according to the first embodiment.
FIG. 4B is a partially enlarged front view showing the polishing grindstone around the groove according to the first embodiment.
FIG. 4C is a cross-sectional view taken along line BB ′ of FIG. 4A.
FIG. 4D is a cross-sectional view taken along line CC ′ of FIG. 4A.
FIG. 5 is a flowchart illustrating an operation flow of the method for processing a cut surface mirror surface according to the first embodiment;
FIG. 6 is a flowchart illustrating an operation flow of a left-cut-surface mirror polishing subroutine according to the first embodiment;
FIG. 7 is a cross-sectional view illustrating an aspect of a substrate or the like in each step of the method for mirror-cutting a cut surface according to the first embodiment;
FIG. 8 is a cross-sectional view showing an aspect of a substrate or the like in each step of the method for mirror-cutting a cut surface according to the first embodiment.
FIG. 9 is a graph showing an experimental result of a mirror finishing experiment on a cut surface according to the example.
FIG. 10 (a) is a schematic view showing a distortion in a vertical direction of a cut surface caused by a conventional method for mirror-cutting a cut surface.
FIG. 10B is a schematic diagram showing horizontal distortion of a cut surface caused by a conventional method for processing a mirror surface of a cut surface.
[Explanation of symbols]
10: Dicing device
12: Substrate
13: Groove for whetstone passage
14: Jig
15: Chuck table
16: Control device
20-1: First cutting unit
20-2: Second cutting unit
40: Cutting whetstone
50: Polishing whetstone
52: Whetstone part
52a: Left whetstone part
52b: Right whetstone part
54: Base
56: Side escape
58: Groove
70: Cut surface
70a: Left cut surface
70b: Right cut surface

Claims

A polishing whetstone comprising: a whetstone portion provided on at least an outer peripheral portion of at least one side surface; and a plurality of grooves formed by cutting off a part of the whetstone portion.

The polishing wheel according to claim 2, wherein the polishing wheel includes a metal base and the wheel mounted on at least one side surface of the base.

A cutting surface mirror-finishing apparatus, wherein both of a cut surface formed by cutting a substrate with a cutting grindstone are mirror-polished by cutting and polishing with a high-speed rotating grinding wheel:
A grinding wheel having at least outer circumferential portions of both side surfaces and a plurality of grooves formed by shaving off a portion of the grinding wheel, the polishing wheel having a thickness smaller than that of the cutting wheel;
A moving mechanism for moving the polishing wheel;
A control device that controls the moving mechanism so that the polishing grindstone mirror-processes one of the cut surfaces using one side surface and mirror-processes the other of the cut surfaces using the other side surface;
A mirror processing apparatus for a cut surface, comprising:

4. The apparatus according to claim 3, wherein the polishing grindstone includes a base made of metal and the grindstones attached to both side surfaces of the base. 5.

A cutting surface mirror polishing method, wherein both of a cut surface formed by cutting a substrate with a cutting whetstone are mirror-polished by cutting and polishing with a high speed rotating polishing whetstone:
It has a grindstone portion provided at least on the outer peripheral portion of both side surfaces, and a plurality of grooves formed by shaving off a part of the grindstone portion, and using one side surface of the polishing grindstone having a thickness smaller than that of the cutting grindstone. A first step of mirror-finishing one of the cut surfaces;
A second step of moving the polishing wheel to a position where the other of the cut surfaces can be cut and polished;
A third step of mirror-finishing the other of the cut surfaces using the other side surface of the polishing grindstone;
A mirror surface processing method for a cut surface, comprising:

In at least one of the first step and the third step,
6. The method according to claim 5, wherein the polishing grindstone mirror-processes the cut surface in a plurality of steps in a thickness direction of the substrate.