JP2004358643A - Polishing method using fixed abrasive pad - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing method using a fixed abrasive pad capable of polishing a wafer without using a polishing liquid in a polishing step or deteriorating a processing characteristic such as increase of micro scratch or deterioration in uniformity in a face. <P>SOLUTION: A suspension type wettable fixed abrasive pad 3 is made into a sufficiently wet condition with pure water or processing liquid mainly composed of pure water. After the pad surface is adjusted into such a wet condition as capable of suspending abrasive from the pad in a polishing process, polishing is conducted without supplying the polishing liquid during polishing. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００４３】
加工特性として、加工レート、面内均一性及びマイクロスクラッチの発生個数を評価した。加工後の酸化膜ウェーハの残膜厚を、７２００型膜厚計（ナノメトリックス社製）でウェーハの任意の中心線（以下Ｘ軸という）上の２１点、及びＸ軸に直交する線（以下Ｙ軸という）上の８点について測定し、Ｘ軸上の除去膜量の平均値（加工時間を１分とした）を加工レートとした。また、面内均一性は、Ｘ軸とＹ軸上の残膜厚の平均値を求め、平均値と各測定点の差の百分率を測定点２９点について算出し、その標準偏差σで表した。マイクロスクラッチの発生個数の測定には、残膜を測定したウェーハを十分に洗浄し、ＳＰＩスクラッチカウンター（ＫＬＡ−Ｔｅｎｃｏｒ社製）を使用した。
【００４４】
図６に８インチブランケットウェーハにセミドライ加工方法を適用したときの、加工後の残膜厚の測定結果を示す。比較データとして純水加工、ｉｎ−ｓｉｔｕドレス加工及びスラリー加工の３種類の加工方法を適用したときの加工データも示した。図７には、残膜厚から算出した加工レートと面内均一性を示す。図７に示す４種類の加工方法には、同一の加工条件を適用したため単純な比較はできないが、本発明のセミドライ加工方法による加工特性が良好であることがわかる。
【００４５】
スラリー加工法では、高い加工レートを示すが面内均一性が悪く、図６に示すように加工特性がセンタースローであった。これは、供給したセリアスラリーの量がウェーハ面に対して偏った分布をし、特にウェーハ中央部に作用するスラリー量が少ないためと判断される。加工圧力を低くし、パッドとウェーハ間の相対速度を増加させるなどの加工条件の改善により、面内均一性の改善が図れるものと考えられる。
【００４６】
同様に純水加工、ｉｎ−ｓｉｔｕドレス加工方法では、加工圧力を増加させて加工レートを改善させることが可能であるがマイクロスクラッチが増加するので、本発明のセミドライ加工方法は、スラリーフリー加工方法として優れた加工方法と言える。
【００４７】
図８に加工後のウェーハ面内に存在するマイクロスクラッチ（０．２μｍ以上の微細打痕状キズ）の総数を示す。本発明のセミドライ加工方法を適用した加工では、マイクロスクラッチの発生数が少ないことがわかる。
【００４８】
砥粒加工によって生じるマイクロスクラッチは、マイクロスクラッチの直径の数倍以上の径を有する粗粒子によるものと考えられる。特に１μｍ以上の粗粒子（微粒子の凝集体も含まれる）個数とマイクロスクラッチの発生数には強い相関関係がある。
【００４９】
また加工条件が同一であれば、加工量が多いほど加工に作用した砥粒の量が多いと考えられるため、マイクロスクラッチの発生数が多くなることが予想される。しかし、図８は、最も加工量の多い本発明のセミドライ加工方法と、加工量の最も少ない比較例の純水加工方法とが同程度であることを示している。これは、固定砥粒パッドの表面近傍に存在する粗粒子が同程度に加工に作用すると仮定しても、本発明のセミドライ加工方法には、マイクロスクラッチの発生を緩和するメカニズムが働いていることを示すものである。
【００５０】
実施例２：セミドライ加工におけるパッド湿潤状態の測定
本実施例は、セミドライ加工方法を適用した場合のパッドの湿潤状態を数値化する目的で、外径１２インチのスパイラル型固定砥粒パッド（ＲＣ０１−＃３型）を使用し、パッドの湿潤状態の調整条件とパッド表面の水分量の関係を求め、同時に加工レートとの関係を測定した。また、本発明のＲＣ０１−＃３型パッドに樹脂含浸処理を行い、ＲＣ０１−＃３型パッドの固定砥粒層の微細気孔を閉鎖させた比較例のパッド（ＲＣ０１−＃４型）を試作し、同様にパッド表面の水分量と加工レートの関係を比較測定した。表２に適用した加工条件を示す。
【００５１】
加工試料には、膜厚１０００ｎｍのＰ−ＴＥＯＳ酸化膜の１８ｍｍ×１８ｍｍのウェーハチップを使用した。干渉式膜厚計（ＳＥＮＮＴＥＣＨ社製 ＦＴＰ５００）を用いて試料の膜厚さを測定し、加工前後の膜厚さの測定値をもとに、単位時間当たりの除去膜厚を加工レートとした。
【００５２】
【表２】

【００５３】
パッド湿潤状態は、赤外線式水分計（ＩＭ−３ＳＣＶ フジワーク社社製）を使用してパッドの表面近傍の水分量で数値化した。ただし、赤外線式水分計の指示値は、測定試料の材質や厚みに対して水分量の相対値を示すものである。
【００５４】
含水率の測定では、厚さ３ｍｍ、１００ｍｍ×１００ｍｍの固定砥粒パッドのカットサンプルを使用し、６０℃に設定したオーブン乾燥機（２−２０００１ＩＳＵＺＵ製作所製）で１０時間乾燥させた後のサンプル重量を測定（乾燥重量という）し、純水に１０時間浸漬した後、自然乾燥して重量を測定し、乾燥重量に対する重量増加率をパッドの含水率とした。
【００５５】
（１）パッド湿潤状態の水分量の測定
本実施例では、パッドの湿潤状態の調整方法として、プラテンの回転数を一定（１００ｒｐｍ）としてパッドの水切り時間を変化させる方法を採用し、パッドの湿潤状態を、赤外線式水分計を使用して数値化した。オン発明のＲＣ０１−＃３型パッドと比較例のＲＣ０１−＃４型パッドを使用して湿潤状態を調整した後、加工直前のパッド表面の水分量を赤外線式水分計で測定し、加工レートとの関係を２種類のパッドについて比較測定した。
【００５６】
図９に水切り時間を２分間隔で１０分間実施したときの水きり時間と加工レート及び水分計の指示値の関係を示す。
【００５７】
水きりを施すと、本発明のＲＣ０１−＃３型パッドの水分計指示値は、最初の２分間で３５００まで低下し、その後２５００までは徐々に低下していく。一方比較例のＲＣ０１−＃４型パッドの水分計指示値は、最初の２分間で１０００まで低下し、その後はほとんど変化がない。ＲＣ０１−＃４型パッドの加工レートは、水切り時間に対して変化がなく、低い値を示しているが、ＲＣ０１−＃３型パッドの加工レートは、水切り時間に対して増加傾向を示し、水切り時間８分にピーク値があることを示している。図１０は、水分計の指示値と加工レートとの関係を、図９を使用して再プロットしたものである。図１０より水分計指示値が２５００〜４０００の範囲で高い加工レートが得られることがわかる。
【００５８】
（３）パッド含水率と水分計指示値の関係
本実施例では、赤外線式水分計の指示値とパッドの湿潤状態の関係を調べるために、本発明のＲＣ０１−＃３型パッドと比較例のＲＣ０１−＃４型パッドのカットサンプルについて、パッドの含水率と水分計指示値の関係を測定した。
【００５９】
図１１に、２種類のパッドについて、パッド含水率と水分計指示値の関係を比較して示す。本発明のＲＣ０１−＃３型パッドでは、水分計指示値２５００で屈曲点を示す。この屈曲点は、パッドの乾燥条件の境界を示すもので、屈曲点以下の領域では、含水率の変化が著しく低下したため、自然乾燥からオーブン乾燥に変更した。同様に、ＲＣ０１−＃４型パッドでは、水分計指示値１０００以下で乾燥条件を変更した。
【００６０】
図１１から、自然乾燥の領域では２種類のパッドともに、含水率の変化率が同じであることがわかる。この水分計の指示値の領域（ＲＣ０１−＃３型パッドでは２５００以上、ＲＣ０１−＃４型パッドでは１０００以上）では、含水率の減少が、パッド表面に存在する水分の薄膜の減少に相対しているものと判断される。
【００６１】
図１０を考慮すると、パッド表面に存在する水分の薄膜が消滅する寸前に高い加工レートを得る条件があると判断される。メカノケミカル反応の低下を回避し、高い加工レートを安定して得るためには、使用するパッドが十分な含水率を有する必要がある。具体的には、好ましくは含水率３％〜１５％、特に好ましくは５％〜８％である。少なすぎると、メカノケミカル反応に必要な水分が不足し、多すぎるとパッド表面の水分を湿潤調整しても、パッドに吸水した水分が表面に移動するため、潤滑作用を低減させるのが困難となる。
【００６２】
本発明の効果の原因は、砥粒が加工試料に作用する新たな作用状態として、高粘性流動状態が生起しているためと考えられる。高粘性流動状態の砥粒が形成される条件は、固定砥粒層が摩擦力で破壊されて砥粒の遊離化が起こること、及びパッド表面の水分量が少ないことである。本発明のセミドライ加工法は、この２つの条件を同時に満たすように、加工前にパッドの湿潤状態を調整している。
【００６３】
このことは、水の薄膜による潤滑効果の影響がなくなる水分量の領域で高い加工レートが得られることと、この領域を過ぎると、パッドとウェーハ間に生じる摺動摩擦力が大きくなり、砥粒の遊離化に必要な摩擦力に達することから確認されている。従って、本発明によれば、多くの砥粒が遊離化することと、パッド表面の水分量が少ないことから、高粘性流動状態が生起していると判断される。
【００６４】
要するに本発明によれば、高濃度砥粒が高粘性流動状態に遊離化し、遊離化した砥粒が排出されずに加工に寄与するため、高い砥粒の利用効率が得られるものと考えられる。
【００６５】
【発明の効果】
以上述べた如く、本発明によれば、遊離化タイプの吸水性固定砥粒パッドを使用し、パッドから砥粒が遊離化し得る程度の湿潤状態に調整することによって、研磨中は一切の研磨液を使用しないで、マイクロスクラッチの増加や面内均一性の悪化などの加工特性が低下することなくウェーハを研磨することができる。これは従来なし得なかったことが達成できたものであるから、極めて画期的な効果である。
【００６６】
【図面の簡単な説明】
【図１】本発明の実施例を示す斜視図である。
【図２】本発明に使用する固定砥粒パッドの製法を説明する斜視図である。
【図３】本発明に使用する研磨装置の一例を示す斜視図である。
【図４】本発明のパッドのウェーハを載せた状態の断面図である。
【図５】図４の砥粒シートの断面図である。
【図６】ウェーハに本発明方法を適用した加工後の残膜厚の測定結果を示す線図である。
【図７】図６の残膜厚から算出した加工レートと面内均一性を示す棒グラフである。
【図８】本発明方法で加工後のマイクロスクラッチの総数を示す棒グラフである。
【図９】本発明のパッドと比較例のパッドについてのパッドの加工レートと水分計指示値の関係を示すグラフである。
【図１０】図９の結果を使用して再プロットした加工レートと水分計指示値の関係を示す線図である。
【図１１】本発明のパッドと比較例のパッドについて、水分計指示値と含水率との関係を示す線図である。
【符号の説明】
１………砥粒シート
２………繊維状シート
３………固定砥粒パッド
５………ウェーハ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polishing method for precision polishing for device wafers and hard disks, and more specifically, for polishing an oxide film on a wafer or the like by using a polishing pad for flattening CMP and applying a semi-dry processing method. On how to do it.
[0002]
[Prior art]
2. Description of the Related Art With the increase in integration and miniaturization of semiconductor integrated circuits, lamination of wiring has been performed. That is, a process is employed in which a wiring material is pattern-formed on the surface of a semiconductor wafer, the upper surface thereof is covered with an insulating film such as silicon oxide, the next wiring material is formed in a pattern, and the process is sequentially repeated.
[0003]
When the number of stacked wirings increases, a step occurs in an insulating film such as silicon oxide. Therefore, it is necessary to planarize the insulating film before forming a pattern of a next wiring material. ), A chemical mechanical polishing (hereinafter referred to as CMP) for polishing a wafer flat using a polishing pad.
[0004]
As a method of forming a wiring material pattern, a damascene method is employed in which a wiring material such as copper is deposited on the entire surface of a wafer, and thereafter, excess wiring material is removed by CMP.
[0005]
As described above, when polishing an insulating film or a wiring material by CMP, high polishing performance on the order of submicrons is required, such as securing the removal efficiency and securing the flatness of the entire wafer and the smoothness of the surface. In order to realize these high polishing performances, various fixed abrasive pads in which abrasive grains are fixed to pads have been proposed.
[0006]
CMP is a polishing method in which a mechanical removal action by particles such as abrasive grains and a chemical dissolution action by a polishing liquid are superimposed, and is roughly classified into a pad surface cleaning step and a polishing step. The step of cleaning the pad surface is a step of removing a polishing liquid and polishing debris attached to the pad in the previous polishing so that the history of the previous polishing does not remain. In this step, the pad surface is generally rinsed with pure water, but a brush and a dresser on which fine diamond particles are fixed are often used in combination. The polishing step is a step of sliding a wafer on the surface of a pad while supplying a polishing liquid. In this step, a dresser is often used in combination.
[0007]
Examples of the polishing liquid include fine particles such as silica and alumina mixed and dispersed in an alkaline or acidic chemical aqueous solution (referred to as a slurry) or ceria (cerium oxide) dispersed in a solvent such as water (slurry). Is used. Ceria slurry in which ceria (cerium oxide) is dispersed in a solvent such as water is used for CMP of a silicon oxide film. Since a mechanochemical reaction occurs between ceria and a silicon oxide film, ceria abrasive grains can use water instead of using a chemical aqueous solution as a solvent.
[0008]
The ceria fixed abrasive pad is a polishing pad used for CMP of a silicon oxide film, and uses a ceria slurry or pure water as a polishing liquid.
[0009]
However, although the above-mentioned conventional polishing method using a fixed abrasive pad is effective for improving the flattening performance, it has been a problem to reduce polishing scratches.
[0010]
The purpose of applying the fixed abrasive pad to CMP is to apply a slurry-free processing method (a method using a processing fluid that does not contain abrasive grains) to provide a good processing rate (MRR) and a high scratch-free surface. The object is to realize internal uniformity (WIWNU). In particular, if pure water can be used as the processing liquid, a device for managing the slurry such as a slurry supply device is not only unnecessary, but also a great advantage can be obtained since the consumption cost required for the slurry can be reduced. However, at present, when processing is performed using pure water, it is necessary to perform processing at a high processing pressure in order to obtain a good processing rate. There was a problem that the characteristics deteriorated.
[0011]
[Problems to be solved by the invention]
The present invention has been made by paying attention to such a point, and without using a polishing liquid in the polishing step, a wafer can be processed without deteriorating processing characteristics such as increase of micro scratches and deterioration of in-plane uniformity. An object of the present invention is to provide a polishing method using a fixed abrasive pad that can be polished. Conventionally, no polishing method using a polishing liquid in the polishing step has not been performed.
[0012]
[Means for Solving the Problems]
The configuration of the present invention that meets the above-mentioned object is to provide a liberated type water-containing fixed abrasive pad in a sufficiently wet state with pure water or a processing liquid containing pure water as a main component, and polishing the pad surface in a polishing step. It is characterized in that the polishing is performed without supplying a polishing liquid during the polishing after adjusting to a wet state in which the abrasive grains can be liberated.
[0013]
As the fixed abrasive pad, it is preferable to use a pad containing ceria abrasive as polishing abrasive (claim 2).
[0014]
The wet state may be adjusted so that the indicated value of the infrared moisture meter is in the range of 2500 to 4000, preferably 3000 to 3500 (claim 3).
[0015]
The fixed abrasive pad preferably has a water content of 3% to 15%, and particularly preferably 5% to 8% (claim 4).
[0016]
The adjustment of the wet state is preferably performed by draining using centrifugal force, air blowing, or water absorption by a water absorbing roller or the like (claim 5).
[0017]
It is preferable that the fixed abrasive pad is a polishing pad in which cut surfaces of an abrasive sheet and a fibrous sheet are spirally arranged on a polishing surface (claim 6).
[0018]
In short, the present invention is roughly divided into a cleaning step and a polishing step. In the cleaning step, the pad surface is adjusted to a wet state in which abrasive grains can be released from the pad in the polishing step, and sufficient lubricating friction is provided by a water film on the pad surface. After avoiding a state where force is not obtained, during polishing, polishing is performed without supplying any polishing liquid including pure water, so that processing characteristics such as increase of micro scratches and deterioration of in-plane uniformity decrease. The gist is that it has been eliminated.
[0019]
In addition, as a working liquid containing pure water as a main component, a working liquid obtained by adding abrasive grains, an acid, or an alkali to pure water can be used. By containing a small amount of abrasive grains, the abrasive grains can be easily released from the pad.
[0020]
Next, an embodiment of the present invention will be described.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
The polishing pad used in the present invention is used by attaching it to a rotating platen or a traveling belt of a polishing apparatus.
[0022]
The water-containing fixed abrasive pad used in the present invention is a water-absorbent polymer containing inorganic abrasive grains.As the inorganic abrasive grains, cerium oxide, silicon oxide, aluminum oxide, manganese dioxide, iron oxide, Zinc oxide, silicon carbide, boron carbide, synthetic diamond, and tourmaline powder may be used alone or in combination. In particular, it is preferable to use cerium oxide.
[0023]
As the fixed abrasive pad that can be used in the present invention, for example, a sheet containing one or more abrasive grains described in JP-A-2002-38129 is spirally wound, and the cut surface is used as a polished surface. Pad, a pad in which abrasive inorganic fine particles are dispersed in cellulose described in JP-A-2002-18731, a pad in which abrasive inorganic fine powder is dispersed in silicon rubber described in JP-A-2001-179609, and JP-A-2003-179609 No. 136397.
[0024]
The fixed abrasive pad for CMP is of the type where the abrasive is applied to the wafer while the abrasive is fixed, such as a grinding wheel, and the fixed abrasive is released due to sliding friction, etc. The fixed abrasive pad used in the present invention is classified into a type that acts on a wafer, and the latter type is a fixed abrasive pad.
[0025]
In the fixed abrasive pad used in the present invention, sufficient conditions for generating a sliding frictional force are necessary to release abrasive grains. In particular, when processing is performed using pure water, unlike the case of using a slurry as a processing liquid, the generation rate of the released abrasive grains depends on the frictional force between the pad and the wafer. However, when pure water is supplied during processing, a thin film of water is formed between the pad and the wafer, and a phenomenon occurs in which a sufficient sliding frictional force cannot be obtained due to the lubricating action of the thin film of water.
[0026]
Conversely, in the processing of ceria abrasive grains, if water is insufficient, the mechanochemical reaction that occurs in the solid phase between the silicon oxide film and the ceria abrasive grains does not proceed, and sufficient processing efficiency cannot be expected.
[0027]
In the present invention, since the processing is performed using a fixed abrasive pad that can contain water and a thin film of water is not generated, the above problem can be avoided. This state is an intermediate state between the wet processing method and the dry processing method, and a processing method that maintains this state is called a semi-dry processing method. In the method of the present invention, processing was performed in the following procedure as a semi-dry processing method.
(Procedure 1) Pure water or a working liquid containing no abrasive grains containing pure water as a main component is dropped onto the pad surface to make it sufficiently wet. When the abrasive grains are ceria abrasive grains, pure water is applied. When the abrasive grains are silica abrasive grains, pure water containing an alkali is used.
(Procedure 2) Draining is performed using centrifugal force due to rotation of the platen, and the wet state of the pad surface is adjusted.
(Procedure 3) Processing is performed. However, no polishing liquid such as pure water is supplied during the processing.
[0028]
As a method of adjusting the wet state of the pad surface, in addition to draining using centrifugal force due to rotation of the platen, use of an air blow or a water absorbing roller may be considered, but in the examples described later, draining is the simplest method. Adopted.
[0029]
The water-absorbing fixed abrasive pad of the present invention is preferably a polishing pad, as shown in FIG. 1, wherein cut surfaces of two types of sheets, an abrasive sheet 1 and a fibrous sheet 2, are spirally arranged on the polishing surface. Is used.
[0030]
In the embodiment of FIG. 1, a ceria-fixed abrasive layer is used as the abrasive sheet 1 and a polymer layer is used as the fibrous sheet 2, and these layers are arranged in a spiral shape and alternately arranged perpendicular to the processing surface. It has a structured structure. The ceria-fixed abrasive layer 1 of the above embodiment is obtained by uniformly mixing an acrylic thermoplastic resin (10% by weight) as a binder with ceria abrasive particles (30% by weight) having an average particle size of about 0.5 μm. It is formed into a long sheet having a thickness of 0.3 mm.
[0031]
The fixed abrasive pad shown in FIG. 1 is obtained by heating and coating a long sheet 1 of a ceria fixed abrasive layer with a thermoplastic thermoplastic resin 2 of polyurethane, and as shown in FIG. While forming a polymer layer, it is wound around a shaft core and is thickened to a predetermined pad diameter to form a columnar shape. After natural cooling, slice processing is performed with a predetermined thickness in a direction perpendicular to the axis, and a pressure-sensitive adhesive tape is attached to one of the slice surfaces to form a polishing pad.
[0032]
A release paper is preferably adhered to the back surface of the pad manufactured as described above, and when the pad is attached to a rotating platen or a traveling belt, the release paper is preferably peeled off and attached.
[0033]
Examples of the sheets 1 and 2 used for the pad include synthetic synthetic fibers, inorganic fibers, elastic polymer sheets, and the like, which are processed into a sheet in the form of a woven fabric, a nonwoven fabric, a felt, and a paper.
[0034]
As the abrasive grain sheet 1, it is preferable to use an abrasive grain sheet in which abrasive grains are dispersed and filled in a synthetic polymer, or an abrasive grain sheet in which an abrasive grain dispersed in a binder material is impregnated and filled in a fibrous sheet. After applying the abrasive liquid, for example, by passing the abrasive liquid through a roll, the content of the abrasive grains in the sheet can be made more uniform.
[0035]
The pad obtained as described above is fixed on a platen 4 with the cut surface (polishing surface) of the pad 3 facing upward, as shown in FIG. The wafer 5 is polished by being pressed from above with a dresser 6 and rotating a head 7 and a platen 4 erected on the dresser.
[0036]
FIG. 4 is a cross-sectional view of the pad 3 and the wafer 5, and the cut surface of the abrasive sheet 1 and the fibrous sheet 2 is spirally disposed on the polished surface.
[0037]
FIG. 5 is a cross-sectional view of the abrasive grain sheet 1 in which inorganic abrasive grains 9 are fixed on the sheet with a binder 10.
[0038]
【Example】
Next, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.
[0039]
Example 1 Measurement of Processing Characteristics Applying the Present Invention In order to evaluate the CMP processing characteristics applying the semi-dry processing method of the present invention, a spiral ceria fixed abrasive pad having an outer diameter of 24 inches shown in FIG. 1 was used. A processing experiment was performed using an 8-inch blanket wafer of a P-TEOS oxide film having a thickness of 1000 nm as a processing sample.
[0040]
As a processing method, a processing method using pure water as a processing liquid (hereinafter referred to as pure water processing), a processing method using 1% by weight ceria slurry as a processing liquid (hereinafter referred to as slurry processing), and using pure water as a processing liquid. Then, the processing characteristics when the three types of in-situ dressing methods (comparative examples) using a dresser and the semi-dry processing method of the present invention were applied were measured.
[0041]
The semi-dry processing method of the present invention is a method in which the pad is wetted with pure water before processing, and processing is performed without supplying pure water at all during processing, but processing is performed depending on the wet state of the pad before processing. The rate changes significantly. If the wet amount is too large or too small, a sufficient processing rate cannot be obtained, and an optimal wet state exists for processing. In the present embodiment, the supply of pure water was stopped after supplying sufficient pure water to the pad in an optimal wet state, and the pad was drained by rotating the platen at 100 rpm for 4 minutes. The processing conditions applied are shown in Table 1 below.
[0042]
[Table 1]

[0043]
As processing characteristics, a processing rate, in-plane uniformity, and the number of generated micro scratches were evaluated. The remaining film thickness of the processed oxide film wafer was measured at 21 points on an arbitrary center line (hereinafter referred to as X axis) of the wafer using a 7200 type film thickness meter (manufactured by Nanometrics) and a line perpendicular to the X axis (hereinafter referred to as X axis). The measurement was performed at eight points on the Y axis (referred to as the Y axis), and the average value of the removed film amount on the X axis (the processing time was 1 minute) was defined as the processing rate. The in-plane uniformity was calculated by calculating the average value of the remaining film thickness on the X-axis and the Y-axis, calculating the percentage of the difference between the average value and each measurement point for 29 measurement points, and expressing the standard deviation σ. . For the measurement of the number of generated micro scratches, the wafer on which the residual film was measured was sufficiently washed, and an SPI scratch counter (manufactured by KLA-Tencor) was used.
[0044]
FIG. 6 shows the measurement results of the remaining film thickness after processing when the semi-dry processing method is applied to an 8-inch blanket wafer. Processing data when three types of processing methods of pure water processing, in-situ dressing processing, and slurry processing are applied are also shown as comparative data. FIG. 7 shows a processing rate and in-plane uniformity calculated from the remaining film thickness. Since the same processing conditions were applied to the four types of processing methods shown in FIG. 7, a simple comparison cannot be made, but it can be seen that the processing characteristics by the semi-dry processing method of the present invention are good.
[0045]
The slurry processing method exhibited a high processing rate, but poor in-plane uniformity, and the processing characteristics were center slow as shown in FIG. This is considered to be because the amount of the supplied ceria slurry is unevenly distributed with respect to the wafer surface, and particularly the amount of the slurry acting on the central portion of the wafer is small. It is considered that in-plane uniformity can be improved by improving processing conditions such as lowering the processing pressure and increasing the relative speed between the pad and the wafer.
[0046]
Similarly, in the pure water processing and the in-situ dressing method, it is possible to improve the processing rate by increasing the processing pressure, but the micro-scratch increases. Therefore, the semi-dry processing method of the present invention is a slurry-free processing method. It can be said that this is an excellent processing method.
[0047]
FIG. 8 shows the total number of micro scratches (fine scratches of 0.2 μm or more) existing in the wafer surface after processing. It can be seen that the number of occurrences of micro scratches is small in the processing to which the semi-dry processing method of the present invention is applied.
[0048]
The micro scratches generated by the abrasive processing are considered to be due to coarse particles having a diameter several times or more the diameter of the micro scratches. In particular, there is a strong correlation between the number of coarse particles (including agglomerates of fine particles) of 1 μm or more and the number of generated micro scratches.
[0049]
Further, if the processing conditions are the same, it is considered that the larger the processing amount, the larger the amount of the abrasive grains acting on the processing. Therefore, it is expected that the number of generated micro scratches will increase. However, FIG. 8 shows that the semi-dry processing method of the present invention having the largest processing amount and the pure water processing method of the comparative example having the lowest processing amount are almost the same. This is because even if it is assumed that the coarse particles existing near the surface of the fixed abrasive pad affect the processing to the same extent, the semi-dry processing method of the present invention has a mechanism for mitigating the occurrence of micro scratches. It is shown.
[0050]
Example 2 Measurement of Pad Wet State in Semi-Dry Processing In this example, a spiral fixed abrasive pad (RC01-) having an outer diameter of 12 inches was used in order to quantify the wet state of the pad when the semi-dry processing method was applied. (# 3 type) was used to determine the relationship between the adjustment condition of the pad wet state and the amount of water on the pad surface, and at the same time, the relationship with the processing rate was measured. Further, a pad (RC01- # 4 type) of a comparative example in which the RC01- # 3 type pad of the present invention was subjected to a resin impregnation treatment to close the fine pores of the fixed abrasive layer of the RC01- # 3 type pad was produced. Similarly, the relationship between the water content on the pad surface and the processing rate was compared and measured. Table 2 shows the processing conditions applied.
[0051]
As the processed sample, a wafer chip of 18 mm × 18 mm made of a P-TEOS oxide film having a thickness of 1000 nm was used. The film thickness of the sample was measured using an interference type film thickness meter (FTP500 manufactured by SENTECH), and the film thickness removed per unit time was defined as the processing rate based on the measured values of the film thickness before and after processing.
[0052]
[Table 2]

[0053]
The pad wet state was quantified by the amount of water near the surface of the pad using an infrared moisture meter (IM-3SCV, manufactured by Fuji Work). However, the indicated value of the infrared moisture meter indicates a relative value of the water content with respect to the material and thickness of the measurement sample.
[0054]
In the measurement of the water content, a cut sample of a fixed abrasive pad having a thickness of 3 mm and 100 mm × 100 mm was used, and the sample weight after drying for 10 hours with an oven dryer (manufactured by 2-20001 ISUZU Seisakusho) set at 60 ° C. Was measured (referred to as dry weight), immersed in pure water for 10 hours, air-dried, and the weight was measured. The rate of weight increase relative to the dry weight was defined as the water content of the pad.
[0055]
(1) Measurement of Moisture Amount in Pad Wet State In this embodiment, as a method of adjusting the pad wet state, a method of changing the pad draining time while keeping the rotation speed of the platen constant (100 rpm) is adopted. The condition was quantified using an infrared moisture meter. After adjusting the wet state using the RC01- # 3 type pad of the invention and the RC01- # 4 type pad of the comparative example, the water content of the pad surface immediately before processing was measured with an infrared moisture meter, and the processing rate and Was measured for two types of pads.
[0056]
FIG. 9 shows the relationship between the drainage time, the processing rate, and the indicated value of the moisture meter when the draining time is performed at intervals of 2 minutes for 10 minutes.
[0057]
After draining, the moisture meter reading of the RC01- # 3 type pad of the present invention decreases to 3500 in the first two minutes, and then gradually decreases to 2500. On the other hand, the moisture meter indicated value of the RC01- # 4 type pad of the comparative example decreased to 1000 in the first two minutes, and hardly changed thereafter. The processing rate of the RC01- # 4 type pad does not change with respect to the draining time, and shows a low value. However, the processing rate of the RC01- # 3 type pad shows an increasing tendency with respect to the draining time. It shows that there is a peak value at time 8 minutes. FIG. 10 is a graph in which the relationship between the indicated value of the moisture meter and the processing rate is replotted using FIG. It can be seen from FIG. 10 that a high processing rate can be obtained when the moisture meter indicated value is in the range of 2500 to 4000.
[0058]
(3) Relationship between Pad Moisture Content and Moisture Meter Indicated Value In this example, the RC01- # 3 type pad of the present invention and the comparative example were examined in order to investigate the relationship between the indicated value of the infrared moisture meter and the wet state of the pad. For cut samples of RC01- # 4 type pads, the relationship between the moisture content of the pads and the indicated value of the moisture meter was measured.
[0059]
FIG. 11 shows a comparison of the relationship between the pad moisture content and the indicated value of the moisture meter for the two types of pads. In the RC01- # 3 type pad of the present invention, the inflection point is indicated by the moisture meter indicated value 2500. This inflection point indicates the boundary of the drying conditions of the pad. In a region below the inflection point, the change in moisture content was significantly reduced, so that the drying was changed from natural drying to oven drying. Similarly, in the RC01- # 4 type pad, the drying conditions were changed at a moisture meter indicated value of 1000 or less.
[0060]
From FIG. 11, it can be seen that the rate of change in the moisture content of the two types of pads is the same in the area of natural drying. In the region of the indicated value of the moisture meter (2,500 or more for the RC01- # 3 type pad and 1000 or more for the RC01- # 4 type pad), the decrease of the water content is relative to the decrease of the thin film of moisture existing on the pad surface. It is determined that it is.
[0061]
Considering FIG. 10, it is determined that there is a condition for obtaining a high processing rate just before the thin film of moisture existing on the pad surface disappears. In order to avoid a decrease in mechanochemical reaction and to stably obtain a high processing rate, it is necessary that a pad used has a sufficient moisture content. Specifically, the water content is preferably 3% to 15%, particularly preferably 5% to 8%. If the amount is too small, the moisture required for the mechanochemical reaction will be insufficient, and if the amount is too large, even if the moisture on the pad surface is adjusted, the water absorbed by the pad will move to the surface, making it difficult to reduce the lubrication effect. Become.
[0062]
The cause of the effect of the present invention is considered to be that a high viscous flow state has occurred as a new operation state in which the abrasive grains act on the processed sample. The conditions under which the abrasive grains in the highly viscous fluidized state are formed are that the fixed abrasive layer is broken by frictional force and liberation of the abrasive grains occurs, and the amount of water on the pad surface is small. In the semi-dry processing method of the present invention, the wet state of the pad is adjusted before processing so as to satisfy these two conditions simultaneously.
[0063]
This means that a high processing rate can be obtained in the region of the moisture content where the lubrication effect of the water thin film is not affected, and after this region, the sliding friction force generated between the pad and the wafer increases, and the abrasive grain It has been confirmed that the frictional force required for liberation is reached. Therefore, according to the present invention, it is determined that a high-viscosity flow state has occurred because many abrasive grains are liberated and the amount of water on the pad surface is small.
[0064]
In short, according to the present invention, it is considered that high-concentration abrasive grains are liberated into a highly viscous fluidized state, and the released abrasive grains are not discharged and contribute to processing, so that a high use efficiency of the abrasive grains can be obtained.
[0065]
【The invention's effect】
As described above, according to the present invention, by using a water-absorbing fixed abrasive pad of a release type and adjusting the wet state to such a degree that the abrasive particles can be released from the pad, any polishing liquid can be used during polishing. Without using, the wafer can be polished without lowering of processing characteristics such as increase of micro scratches and deterioration of in-plane uniformity. This is an extremely epoch-making effect because it has achieved what could not be achieved conventionally.
[0066]
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of the present invention.
FIG. 2 is a perspective view illustrating a method for producing a fixed abrasive pad used in the present invention.
FIG. 3 is a perspective view showing an example of a polishing apparatus used in the present invention.
FIG. 4 is a cross-sectional view of the pad of the present invention with a wafer mounted thereon.
FIG. 5 is a cross-sectional view of the abrasive sheet of FIG.
FIG. 6 is a diagram showing a measurement result of a residual film thickness after processing by applying the method of the present invention to a wafer.
FIG. 7 is a bar graph showing a processing rate and in-plane uniformity calculated from the remaining film thickness in FIG.
FIG. 8 is a bar graph showing the total number of micro scratches processed by the method of the present invention.
FIG. 9 is a graph showing a relationship between a pad processing rate and a moisture meter indication value for a pad of the present invention and a pad of a comparative example.
FIG. 10 is a diagram showing the relationship between the processing rate and the indicated value of the moisture meter replotted using the results of FIG. 9;
FIG. 11 is a diagram showing a relationship between a moisture meter indication value and a moisture content of a pad of the present invention and a pad of a comparative example.
[Explanation of symbols]
1 ... Abrasive sheet 2 ... Fibrous sheet 3 ... Fixed abrasive pad 5 ... Wafer

Claims (6)

The release-type fixed abrasive pad capable of containing water is made sufficiently wet with pure water or a working liquid containing pure water as a main component, and the pad surface is wetted to such an extent that abrasive grains can be released from the pad in the polishing step. A polishing method characterized in that after the state is adjusted, polishing is performed without supplying a polishing liquid during polishing. The polishing method according to claim 1, wherein the fixed abrasive pad includes ceria abrasive as polishing abrasive. 3. The polishing method according to claim 1, wherein the wet state is adjusted such that an indicated value of the infrared moisture meter is in a range of 2500 to 4000. 4. The polishing method according to claim 1, wherein the fixed abrasive pad has a water content of 3% to 15%. The polishing method according to any one of claims 1 to 4, wherein the adjustment of the wet state is performed by draining using centrifugal force, air blowing, or water absorption by a water absorbing roller or the like. The polishing method according to claim 1, wherein the fixed abrasive pad is a polishing pad in which cut surfaces of an abrasive sheet and a fibrous sheet are spirally arranged on a polishing surface.

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