JP2574818C

JP2574818C -

Info

Publication number: JP2574818C
Authority: JP
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Publication date: 1999-01-13

Description

【発明の詳細な説明】〔産業上の利用分野〕本発明は薄板を固定する技術に係り、特に薄板を平坦に固定するのに好適な真
空吸着固定台および真空吸着固定方法に関する。〔従来の技術〕従来の装置は特公昭60−15147に示されるように円筒状のピンを容器の中に組
立てる構造となっていた。また、特開昭60−99538号広報には、一体の結晶物質から構成され、ピークの
先端が同一平面上にある真空チャックについて開示されている。しかし、真空吸着固定台の複数の領域を独立に排気可能に構成すること、また
は、真空吸着固定台の表面に窒化膜を形成することについては開示がない。〔発明が解決しようとする問題点〕上記従来技術は、複数個の突起の形成を組立て構造としているため、その配列
間隔を狭めることが難しく、突起と突起の間のウエーハが大気圧によって変形す
ることに対する配慮がされておらず平坦度を高精る外周部が一つのリム構造であ
るため、外部から漏れて侵入する大気の影響について配慮されていないため、ウ
エーハ外周部の吸引力が弱くなって、吸引固定時にウエーハ周辺の平坦度が低下
する問題があった。本発明の目的は、多数の突起を用いて薄膜を支持する際の大気圧による変形と
、薄板を吸引固定する際のウエーハ外周の平坦度を良好にすることにある。〔問題点を解決するための手段〕上記目的は、基板の裏面に接して該基板を支持する複数の突起を有面に接する外周部と、を備えた真空吸着固定台において、前記突起の配列ピッチ
は２mm以下で、かつ、前記中心部と前記外周部とはそれぞれ真空排気可能に構成
されていることを特徴とする真空吸着固定台、また載置された基板を真空吸着固
定する際、前記基板の表面が±0.5μｍ以下の平坦度となるように、前記基板の
裏面に接して該基板を支持有した前記基板の裏面に接する外周部とを備えた真空吸着固定台上に基板を載置
する工程と、前記中心部と前記外周部とを真空排気し、前記真空吸着固定台に前
記基板を固定する工程とを有することを特徴とする真空吸着固定方法により達成
される。〔作用〕突起部を一つの母材から切削等により形成することにより突起部の間隔を小さ
くできるので、薄いウエーハが大気圧で押されてたわみ、変形することを防止で
きる。また、突起部の間隔が小さくなるため流量抵抗が増し、ウエーハ外周部か
らの大気浸入の影響をウエーハ裏面の負圧空間の中央の領域まで伝搬することを
防ぐことができる。従って、該負圧空間の外周部近傍に吸収孔を設けて、中央の
吸収孔よりも排気速度を大きくすることにより、大気浸入による吸引力の低下を
容易に防止可能となる。さらに外周部に連続した溝を設け、上述の負圧空間とは
独立に排気することにより、ウエーハ周辺からの大気の侵入の影響を完全に除去
することができる。従って、ウエーハの平坦度を極めて高精度に保持した状態で
吸引固定することが可能となる。〔実施例〕以下、本発明の一実施例を第１図により説明する。ａは本発明吸着台の平面図
、ｂは側面図、ｃは突起部と吸引孔との拡大平面図、ｄは突起部と吸引孔の断面
図、ｅは外周部の断面図であり、各々共通な部位には同一番号を付してある。吸着台４には、外周部２に包含された領域に複数個の突起部１がある。突起部
１はｃ，ｄ図に示すように、縦、横のピッチが２mmで断面の交差角度が90°をな
す四角錘状の形状である。突起部の先端の面積は0.0025mm²〜0.01mm²である。複
数の突起部のある領域の中央に吸引孔５があり、外周部近傍に８個の吸引力があ
る。吸収孔５は絞り弁10を介して、また吸引孔７は、絞り弁12を介して図示してい
ない排気系に接続している。外周部２は吸引固定するウエーハの輪郭に沿った平
面形状をしている。さらに、外周部２は溝部20を有し吸引孔６と絞り弁９を介し
て図示していない排気系に接続している。外周部２は断面図ｅに示してあるよう
に、その幅は３mmで、中央に幅1.5mm深さ２mmの溝20が形成されている。なお、吸引孔５,７の拡大図をｃ，ｄに示してあるが、その形状はいずれも等
しく、孔21の形状であり、その直径は１mmである。また突起部１と外周部２とは
図ｂ，ｅに示す通り同一の平面となるように平坦に加工されている。絞り弁9,10,12はウエーハの裏面を吸引固定する際の排気速度を変え、外周部
に近い所程吸引力を大きくするように吸引圧分布を生じている。絞り弁の流量抵
抗は絞り弁9,12,10の順で大きくなるように設定してある。従って、大気の侵入
洩れの大きいウエーハ外周部の吸引力が損なわれなくなる。第２図は、周辺部に溝部のない従来の吸着台で４インチウエーハを吸引固定し
た場合のウエーハ表面の直径上を片側の周辺部を含む領域の平坦度を３次元測定
機で測定した一例である。図中のスケールＷは吸着台から外側の部分でウエーハ
の平坦度が急激に悪化している領域を示しており、この例では約８mmに及んでい
る。Ｗの領域を除いた内側では、平坦度が±0.5μｍであるのに、Ｗの領域を含
めると５μｍ以上に悪化している。第３図は本発明による外周部に溝を設けた吸着台を用いて４インチウエーハを
吸引固定した場合の前図と同じ位置のウエーハ表面の平坦度の測定結果である。外周部におけるウエーハ表面の平坦度の悪化は認められず
、ウエーハ全面で±0.5μｍの平坦度が得られている。本発明の別の実施例の平面図を第４図に示す。吸着台40は、前述の発明例と同
一形状の四角錘状の突起部41とそれを包含する外周部42から構成される。外周部
42には溝が形成され吸引孔と絞り弁44を経て図示していない排気系に接続してい
る。複数の突起部の配列から成る領域は絞り弁43を経て図示していない排気系に
接続している。なお本例の吸着台は、ウエーハのオリエンテーションフラットを
用いてウエーハの位置決めを行うための回転支持部45,46,47,48を有している。
図示していない給気系に接続した駆動ピストンによって、支持部48を開閉させて
、吸着台上でウエーハを機械的に位置決めすることができる。なお、吸着台の逃げ部49は、図示していないウエーハ裏面吸引搬送アームの挿
入を可能とする領域である。以上述べた発明の吸着台の材質は耐磨耗性の良いアルミ合金A7075（日立製作
所製AHS）を用いた。しかし材質としては、吸着固定するウエーハと熱膨張率が
近いものが好ましく、他の材質を用いることも可能である。例えば、シリコンウ
エーハ用の吸着台としてはシリコン単結晶を用いて作製することが望ましい。シ
リコン単結晶製の吸着台の作り方としては、異方性エッチングを用いて四角錘状
の突起を作り、外周部は等方性エッチングを用いて形成することが可能である。
これらのエッチング技術は半導体プロセス分野で公知である。もちろん機械加工
も可能である。加工後の突起部と外周部に窒化膜形成処理を行うとウエーハ裏面
よりも硬度が高くなり耐磨耗性が向上する。次に複数の突起部分の配列ピッチについて述べる。突起部や外周部の先端で支
持されて真空吸引されるウエーハ面には大気圧が負荷され、支持の存在しない所
がたわみ変形する。ウエーハの変形量は、分布荷重の加わる両端支持梁として近
似計算することができる。幅をｂ、厚さをｈ、長さをｌ、縦弾性係数をＥ、断面
二次モーメントを等分布荷重をｗとするとこの梁の最大たわみ梁δはとなる。今幅ｂを突起部のピッチと仮定し、長さＩを正方配列の場合の対角長√
２・ｂとし、大気0.01kg/mm²（100KPa）が単位幅ｂに加わるもととすると、ｗは
0.01×ｂとなり式（１）はさらに４インチシリコンウエーハの場合Ｅ＝２×10⁴kg/mm、ｈ＝0.4mmとすと、
式（２）は δ＝５×10^-6・ｂ４ ……（３）従ってδ≦0.001mmとするにはより、４mm以下のピッチが望ましくなる。シリコンウエーハの裏面は、ポリッシ
ング後加工変質層を除去するためエッチング処理が施されているため、微少な凹
部が多く、突起部の先端部の面積を0.0025mm²〜0.01mm²とした場合でも、全ての
突起部の先端がウエーハ裏面に接触するのは困難と考えられるため、実際の突起
部の配列ピッチは余裕を見込んで２mm以下が望ましい。なお、この配列ピッチの
距離は、ウエーハの材質や厚さやたゆみ量の許容値により当然変わるが、パター
ンの微細化の進む、半導体分野においては、ウエーハのたわみ量が現在より一桁
小さくなることが要求されており、そのためにも、突起部のピッチは２mm以下に
することが必要である。（（４）式においてδ≦0.0001mmとするにはｂ≦２mmとなる）〔発明の効果〕本発明によれば、ウエーハを±0.5μｍ以下の平坦度で吸引固定でき、しかも突起状の支持点で支えるため、塵埃等の介在による平坦度の悪化も防止で
きるので、微細パターン形成を必要とする半導体プロセス試料台に適用する上で
効果がある。Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for fixing a thin plate, and particularly to a vacuum suction fixing base and a vacuum suction fixing method suitable for fixing a thin plate flat. [Prior Art] A conventional apparatus has a structure in which a cylindrical pin is assembled in a container as shown in JP-B-60-15147. In addition, Japanese Patent Application Laid-Open No. 60-99538 discloses a vacuum chuck composed of an integral crystalline substance and having peaks on the same plane. However, there is no disclosure about a configuration in which a plurality of regions of the vacuum suction fixing table can be independently evacuated or a method of forming a nitride film on the surface of the vacuum suction fixing table. [Problems to be Solved by the Invention] In the above prior art, since the formation of a plurality of projections is an assembly structure, it is difficult to reduce the arrangement interval, and the wafer between the projections is deformed by atmospheric pressure. The rim structure, which has a high degree of flatness and does not consider the effects of air that leaks in from the outside and does not enter, reduces the suction force of the wafer outer periphery. Therefore, there has been a problem that the flatness around the wafer is reduced at the time of suction fixing. An object of the present invention is to improve the deformation due to atmospheric pressure when a thin film is supported by using a large number of projections and to improve the flatness of the outer periphery of a wafer when a thin plate is fixed by suction. [Means for Solving the Problems] The object described above has a plurality of projections which are in contact with the back surface of the substrate and support the substrate. An outer peripheral portion that is in contact with a surface , wherein the arrangement pitch of the protrusions is 2 mm or less, and the central portion and the outer peripheral portion are each configured to be capable of evacuating. The vacuum suction fixing table to be fixed, and when the mounted substrate is fixed by vacuum suction, the surface of the substrate has a flatness of ± 0.5 μm or less .
Supports the substrate in contact with the back A step of placing the substrate on a vacuum suction fixing table having an outer peripheral portion that is in contact with the back surface of the substrate having, and evacuating the central portion and the outer peripheral portion, and placing the substrate on the vacuum suction fixing table. And a fixing step. [Operation] Since the interval between the projections can be reduced by forming the projections from one base material by cutting or the like, it is possible to prevent the thin wafer from being bent and deformed by being pressed at atmospheric pressure. Further, since the distance between the protrusions is reduced, the flow resistance increases, and the influence of the intrusion of the atmosphere from the outer peripheral portion of the wafer to the central region of the negative pressure space on the back surface of the wafer can be prevented. Therefore, by providing an absorption hole near the outer peripheral portion of the negative pressure space and making the exhaust speed higher than that of the central absorption hole, it is possible to easily prevent a decrease in suction force due to intrusion into the atmosphere. Further, by providing a continuous groove in the outer peripheral portion and evacuating independently of the above-mentioned negative pressure space, the influence of the intrusion of the atmosphere from around the wafer can be completely removed. Therefore, the wafer can be fixed by suction while maintaining the flatness of the wafer with extremely high precision. Embodiment An embodiment of the present invention will be described below with reference to FIG. a is a plan view of the suction table of the present invention, b is a side view, c is an enlarged plan view of the protrusion and the suction hole, d is a cross-sectional view of the protrusion and the suction hole, and e is a cross-sectional view of the outer peripheral portion. Common parts are given the same numbers. The suction table 4 has a plurality of protrusions 1 in a region included in the outer peripheral portion 2. As shown in FIGS. C and d, the protrusion 1 has a quadrangular pyramid shape having a vertical and horizontal pitch of 2 mm and a crossing angle of 90 °. The area of the tip of the projection portion is 0.0025mm ^² ~0.01mm ^2. There is a suction hole 5 in the center of the region having the plurality of protrusions, and eight suction forces are present in the vicinity of the outer peripheral portion. The absorption hole 5 is connected via a throttle valve 10 and the suction hole 7 is connected via a throttle valve 12 to an exhaust system (not shown). The outer peripheral portion 2 has a planar shape along the contour of the wafer to be fixed by suction. Further, the outer peripheral portion 2 has a groove portion 20 and is connected to an exhaust system (not shown) via the suction hole 6 and the throttle valve 9. As shown in the sectional view e, the outer peripheral portion 2 has a width of 3 mm, and a groove 20 having a width of 1.5 mm and a depth of 2 mm is formed in the center. The enlarged views of the suction holes 5 and 7 are shown in c and d. The shapes are the same, the shape of the hole 21 is 1 mm, and the diameter is 1 mm. Further, the projection 1 and the outer peripheral portion 2 are flattened so as to be on the same plane as shown in FIGS. The throttle valves 9, 10, and 12 change the exhaust speed at the time of suction-fixing the back surface of the wafer, and generate a suction pressure distribution so as to increase the suction force closer to the outer peripheral portion. The flow resistance of the throttle valve is set to increase in the order of the throttle valves 9, 12, and 10. Therefore, the suction force on the outer peripheral portion of the wafer, which has a large intrusion and leakage of the atmosphere, is not impaired. FIG. 2 shows an example in which the flatness of a region including one peripheral portion on the diameter of the wafer surface when a 4-inch wafer is suction-fixed by a conventional suction table having no groove portion in the peripheral portion is measured by a three-dimensional measuring machine. It is. The scale W in the figure indicates a region where the flatness of the wafer is sharply deteriorated in a portion outside the adsorption table, and in this example, it is about 8 mm. On the inside except for the region of W, the flatness is ± 0.5 μm, but when the region of W is included, the degree of deterioration is 5 μm or more. FIG. 3 shows the measurement results of the flatness of the surface of the wafer at the same position as in the previous figure when a 4-inch wafer is suction-fixed using the suction table provided with a groove in the outer peripheral portion according to the present invention. No deterioration in the flatness of the wafer surface in the outer peripheral portion was observed, and a flatness of ± 0.5 μm was obtained over the entire surface of the wafer. A plan view of another embodiment of the present invention is shown in FIG. The suction table 40 includes a quadrangular pyramid-shaped projection 41 having the same shape as that of the above-described invention, and an outer peripheral portion 42 including the same. The outer periphery
A groove is formed in 42 and connected to an exhaust system (not shown) via a suction hole and a throttle valve 44. A region composed of an array of a plurality of projections is connected to an exhaust system (not shown) via a throttle valve 43. Note that the suction table of this example has rotation support portions 45, 46, 47, and 48 for positioning the wafer using the wafer orientation flat.
The support portion 48 can be opened and closed by a drive piston connected to an air supply system (not shown) to mechanically position the wafer on the adsorption table. The escape portion 49 of the suction table is an area where a wafer back side suction transfer arm (not shown) can be inserted. The aluminum alloy A7075 (AHS manufactured by Hitachi, Ltd.) having good abrasion resistance was used as the material of the suction table of the invention described above. However, as the material, a material having a coefficient of thermal expansion close to that of the wafer to be fixed by adsorption is preferable, and other materials can be used. For example, it is desirable that the adsorption table for a silicon wafer be manufactured using a silicon single crystal. As a method of making the adsorption table made of silicon single crystal, it is possible to form a quadrangular pyramid-shaped projection using anisotropic etching, and to form the outer peripheral portion using isotropic etching.
These etching techniques are known in the semiconductor processing field. Of course, machining is also possible. When a nitride film is formed on the projection and the outer periphery after processing, the hardness becomes higher than that of the back surface of the wafer, and the wear resistance is improved. Next, the arrangement pitch of the plurality of protrusions will be described. Atmospheric pressure is applied to the wafer surface that is supported by the protrusions and the distal end of the outer peripheral portion and suctioned by vacuum, and a portion where there is no support is bent and deformed. The amount of deformation of the wafer can be approximately calculated as a beam supported at both ends to which a distributed load is applied. The width is b, the thickness is h, the length is l, the longitudinal elastic modulus is E, and the second moment of area is Assuming that the uniformly distributed load is w, the maximum deflection beam δ of this beam is Becomes Now, assuming that the width b is the pitch of the protrusions, the length I is the diagonal length in the case of a square arrangement √
Assuming that 2 · b and the atmosphere 0.01 kg / mm ² (100 KPa) is added to the unit width b, w is
Equation (1) becomes 0.01 × b. Further, in the case of a 4-inch silicon wafer, if E = 2 × 10 ⁴ kg / mm and h = 0.4 mm,
Equation (2) is calculated as follows: δ = 5 × 10 ⁻⁶ · b4 (3) Therefore, to make δ ≦ 0.001 mm Thus, a pitch of 4 mm or less is desirable. The back surface of the silicon wafer, the etching process for removing the polishing after the damaged layer is applied, many minute recess, the area of the tip portion of the protrusion even when a 0.0025mm ^² ~0.01mm ^2, Since it is considered that it is difficult for the tips of all the projections to come into contact with the back surface of the wafer, the actual arrangement pitch of the projections is desirably 2 mm or less in consideration of a margin. The distance of the arrangement pitch naturally changes depending on the material of the wafer, the allowable value of the thickness and the amount of sag, but in the field of semiconductors where pattern miniaturization is progressing, the amount of sag of the wafer may be one digit smaller than the current one. It is required that the pitch of the protrusions be 2 mm or less. (In the formula (4), b becomes 2 mm to satisfy δ ≦ 0.0001 mm) [Effect of the Invention] According to the present invention, the wafer can be suction-fixed with a flatness of ± 0.5 μm or less, and furthermore, a projection-like support is provided. Since it is supported at the point, it is possible to prevent the deterioration of the flatness due to the interposition of dust and the like, so that it is effective in application to a semiconductor process sample stage that requires formation of a fine pattern.

【図面の簡単な説明】第１図は本発明の実施例の図で、その（ａ）は平面図、（ｂ）は側面図、（ｃ
）は突起部の平面拡大図、（ｄ）及び（ｅ）は拡大断面図、第２図は従来例によ
る測定データを示す図、第３図は本発明による測定データを示す図、第４図は第
２の実施例の平面図である。１…突起部、２…外周部、４…吸着台、５…吸引孔、６…吸引孔、20…溝部。BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view of an embodiment of the present invention, in which (a) is a plan view, (b) is a side view, and (c).
) Is an enlarged plan view of the projection, (d) and (e) are enlarged cross-sectional views, FIG. 2 is a view showing measurement data according to the conventional example, FIG. 3 is a view showing measurement data according to the present invention, and FIG. Is a plan view of the second embodiment. DESCRIPTION OF SYMBOLS 1 ... Projection part, 2 ... Peripheral part, 4 ... Suction stand, 5 ... Suction hole, 6 ... Suction hole, 20 ... Groove part.

Claims

[Claims] 1. A center having a plurality of protrusions that contact the back surface of the substrate and support the substrate And an outer peripheral portion in contact therewith, the arrangement pitch of the projections is 2
mm, and the central portion and the outer peripheral portion are configured so as to be able to evacuate the vacuum, respectively. 2. A vacuum suction fixing base having a plurality of projections, wherein a nitride film is formed on a surface of each projection. 3. When vacuum mounting and fixing the mounted substrate, so that the surface of the substrate has a flatness of ± 0.5 μm or less, a central portion having a plurality of protrusions that support the substrate in contact with the back surface of the substrate , On the outer periphery of the plurality of protrusions A vacuum suction fixing method, comprising: mounting a substrate on a fixing table; and evacuating the central portion and the outer peripheral portion to fix the substrate to the vacuum suction fixing table. 4. 4. The vacuum suction fixing method according to claim 3, wherein the pumping speed of the outer peripheral portion is set higher than that of the central portion. 5. 5. The vacuum suction fixing method according to claim 3, wherein the surface of the plurality of projections has a higher hardness than the rear surface of the substrate. 6. A step of mounting a substrate on a vacuum suction fixing base having a plurality of protrusions and having a nitride film formed on the surface of the protrusion; and evacuating and fixing the substrate to the vacuum suction fixing base. And a step of fixing by vacuum suction.