JPWO2004047156A1 - Position measuring method, position measuring apparatus, exposure method, and exposure apparatus - Google Patents

Abstract

High-precision focus adjustment is performed by eliminating the adverse effect caused by the reflectance distribution. The measurement light on the substrate is irradiated with the detection light, the reflected light reflected at the measurement position is received, and the position information in the normal direction of the substrate surface is measured. The method includes a step of measuring an error component of position information generated by a reflectance distribution of detection light at a measurement position on the substrate, and a step of correcting position information in the normal direction based on the measured error component.

Description

INDUSTRIAL APPLICABILITY The present invention is used in a position measuring method and a position measuring device for measuring position information in the normal direction of a substrate surface by irradiating the substrate with detection light, and a manufacturing process of a device such as a semiconductor element or a liquid crystal display element. The present invention relates to an exposure method and an exposure apparatus.
This application is based on Japanese Patent Application No. 2002-336778, the contents of which are incorporated herein.

Various devices such as semiconductor elements, liquid crystal display elements, and thin film magnetic heads have been conventionally formed by applying a planar technology, and a photolithography technology is indispensable for the planar technology. When manufacturing these devices using photolithography technology, a pattern image of a mask or reticle is exposed through a projection optical system onto a photosensitive substrate such as a wafer or glass substrate coated with a photosensitive material such as photoresist. The exposure device is used.
Generally, an exposure apparatus uses a projection optical system having a large numerical aperture (NA) and a shallow depth of focus in order to obtain a resolution necessary for forming a fine pattern. Therefore, in order to transfer a fine circuit pattern with high resolution, it is necessary to align the surface of the photosensitive substrate more accurately and surely with the image plane of the projection optical system (within the depth of focus (DOF)). For this reason, the exposure apparatus includes a focus detection system that detects the position and inclination of the photosensitive substrate surface in the optical axis direction of the projection optical system (direction normal to the substrate surface), and the exposure device based on the detected height and inclination. The focusing mechanism includes an adjusting mechanism that adjusts the posture of the photosensitive substrate including the position of the surface of the substrate.
In this type of exposure apparatus, for example, as disclosed in Japanese Patent Laid-Open No. 10-270303 and corresponding US Pat. No. 6,455,214, focus detection is performed from an oblique direction having an arbitrary angle that is not perpendicular to the wafer. A so-called grazing incidence reflection type focus detection system (position measuring device) is often used, in which the slit-shaped detection light is incident on the wafer and the reflected light from the wafer surface is guided to a detector serving as a light receiving portion. In this focus detection system, the detection light is irradiated onto the wafer through the light-sending slit, that is, a slit image is formed on the wafer surface, and the slit image is reflected on the wafer surface and re-formed on the aperture for light reception (slit shape). An image is formed, but when the position of the wafer surface is displaced in the normal direction, the detection light (re-formed slit image) is laterally displaced on the light receiving slit in a direction orthogonal to the optical axis direction of the focus detection system. It will be. Therefore, the lateral shift amount, that is, the change in the position of the light amount centroid of the slit image (detection light) is detected to measure the position of the wafer surface in the optical axis direction of the projection optical system, that is, the position in the focus direction.
By the way, in recent years, along with the further miniaturization of semiconductor devices, the numerical aperture of the projection optical system has increased and the depth of focus has become smaller and smaller. Therefore, the entire surface of the exposure area (that is, the exposure light irradiation area) where the pattern image of the reticle is projected within the projection field of the projection optical system is adjusted so that the wafer surface falls within the depth of focus of the projection optical system. Various efforts have been made to improve the flatness. For example, by performing a surface planarization process called CMP (Chemical Mechanical Polishing) on the wafer, it is possible to improve the flatness of the wafer surface during resist application. However, in spite of the fact that the surface shape does not change due to the improvement in flatness as described above, an error (hereinafter, referred to as a focus error) may be included in the focus detection value due to various factors.
One factor that causes this focus error is thin film multiple interference. This thin film multiple interference is caused by the reflected light on the resist surface and the reflection from the underlayer due to the film thickness of the resist, the structure of the underlayer which is the device portion, and the optical constants (refractive index, extinction coefficient) between the resist and the underlayer. It interferes with light. Semiconductor devices, Si or a metal wiring portion, are formed from SiO _2, SiN, or the like as an interlayer insulating film, SiO 2, _SiN have substantially same optical constants of the resist, the detection light for focus detection (e.g. , Illumination light generated from a halogen lamp) becomes a dielectric substance at the wavelength of the light, and thus it is likely to cause multiple interference. In particular, if there is a portion with a high reflectance (for example, metal wiring) on the base, the ratio of the reflected light intensity on the base to the reflected light intensity on the wafer, that is, the reflection on the base against the reflected light intensity on the resist surface The light intensity ratio will increase relatively. Therefore, the light amount barycentric position on the light receiving slit of the detection light reflected by the wafer deviates laterally from the light amount barycentric position when almost all the reflected light is from the resist surface, which becomes a focus position detection error. I will end up.
Another cause of the focus error is an adjustment error of the focus detection system. If the focus detection system is adjusted out of the ideal state, the position of the light receiving slit will deviate from the focus position. Therefore, the slit image is a set of point images, but what should be a point image at the position of the light receiving slit has a spread, and if the light rays forming the point image have an intensity distribution depending on the incident angle to the point image, the slit image Also has an intensity distribution in the lateral shift direction, which causes an error in the focus detection value. Furthermore, the detection light of the focus detection system that is incident on the wafer surface has the light rays forming a point image that are incident at different incident angles depending on the numerical aperture of the light-sending lens, and as a result, the reflected light intensity is also reflected/refracted. , Or the above-mentioned thin film multiple interference causes an intensity distribution. Therefore, due to the angular distribution of the reflected light intensity in the entire slit light, a focus error that does not occur when a point image is formed occurs.
Therefore, conventionally, by making the detection light of the focus detection system incident at a large incident angle of 80° or more, the reflectance on the resist surface can be increased and a light source having a wavelength bandwidth (such as a halogen lamp) can be used. Focusing errors due to thin-film multiple interference are minimized by increasing the intensity distribution of the wavelength that does not cause errors due to interference. Regarding the adjustment error, the optical system is strictly adjusted so that the focus error is smaller than the depth of focus of the projection optical system. Regarding the difference in the incident angle, by using a focus optical system in which the numerical aperture of the incident light beam is small (for example, one-hundredth level), the incident angle of the light beam forming the image is hardly changed, and the reflectance of I was trying to make no difference.
However, in addition to the factors causing the above-mentioned focus error, there are the following problems.
On the wafer surface, the reflectance is partially different in the projection area of the slit image by the focus detection system (that is, the irradiation area of the detection light), especially in the focus measurement direction (when the wafer is displaced in the focus direction) in that area. When the reflectance distribution exists in the moving direction of the slit image moving on the wafer surface), the reflected slit image also has an intensity distribution in the lateral deviation detection direction at the light receiving slit position. In this case, as shown in FIG. 15, the position of the center of gravity of the slit image moves from the center in accordance with the image intensity distribution, so that the surface position of the wafer seems to be displaced in the focus direction regardless of the actual shape of the wafer surface. It will be difficult to accurately adjust the focus. Moreover, even if the error that occurs is not so large, and even if the wafer surface is within the depth of focus as a result, unnecessary tilt correction is applied during focus adjustment, so scanning type (synchronous scanning type) exposure is performed in particular. In the case of the device, there is also a problem that the synchronization accuracy deteriorates.
Due to the progress of miniaturization of semiconductor devices, the material forming the devices has changed, and the film pressure of the resist has become thinner, so that the slit image projection area (detection light irradiation area) on the wafer Therefore, the reflectance distribution is likely to occur, that is, the state of thin film multiple interference is greatly different.

The present invention has been made in consideration of the above points, and a position measuring method and a position measuring device capable of performing highly accurate focus detection while eliminating adverse effects caused by a distribution of a wafer surface state such as a reflectance distribution. And an exposure method and an exposure apparatus.
In order to achieve the above-mentioned object, the present invention adopts the following configurations associated with FIGS. 1 to 13 showing an embodiment.
The position measuring method of the present invention is a position measuring method for irradiating a measurement point on a substrate with detection light, receiving reflected light reflected at the measurement point, and measuring position information in the normal direction of the substrate surface. And a step of measuring an error component of position information caused by a reflectance distribution of detection light at a measurement position on the substrate, and a step of correcting position information in a normal direction based on the measured error component. It is what
Further, the position measuring device of the present invention is a position measuring device that irradiates a measurement point on a substrate with detection light, receives reflected light reflected at the measurement point, and measures position information in the normal direction of the substrate surface. And a storage device that stores an error component of position information generated by the reflectance distribution of the detection light at the measurement location on the substrate, and a correction device that corrects the position information in the normal direction based on the stored error component. It is characterized by having.
Therefore, in the position measuring method and the position measuring device of the present invention, since the error component of the position information generated by the reflectance distribution of the detection light at the measurement location on the substrate is known in advance, the substrate surface measured using the detection light The error component can be eliminated from the position information in the normal direction, and the substrate can be positioned at a predetermined position without being adversely affected by the reflectance distribution. As a method of obtaining the error component, a method of calculating based on the intensity of the detection signal obtained when the detection light is received, or a surface shape of the substrate is actually measured (for example, by a separate measuring device) and measured. A method of obtaining based on the result of comparison between the surface shape and the designed surface shape (for example, the difference between the two surface shapes), and further, when the substrate surface is flattened by CMP or the like, the measured position information of the substrate surface is obtained. A method of setting the error component as it is can be adopted.
Then, the exposure method of the present invention is an exposure method for exposing a pattern of a mask onto a substrate by exposure light, wherein the position information is measured by the position measuring method described above, and the surface position of the substrate is adjusted based on the measurement result. It is characterized by doing.
Further, the exposure apparatus of the present invention is characterized in that the position measurement apparatus (21) is used as an apparatus for measuring the surface position information of the substrate in the exposure apparatus that exposes the mask pattern on the substrate with the exposure light. To do.
Therefore, in the exposure method and the exposure apparatus of the present invention, the surface position information of the substrate can be measured with high accuracy without being adversely affected by the reflectance distribution of the substrate surface with respect to the detection light, and the substrate surface can be exposed to the light of the exposure light. It becomes possible to perform accurate positioning in the axial direction. Therefore, for example, even when a projection optical system having a shallow depth of focus is used, the substrate surface can be adjusted within the depth of focus, and the necessary contrast (resolution) can be easily obtained. Further, even if the resulting focus error is such that the surface of the substrate falls within the depth of focus, in the case of the scan type (synchronous scanning type) exposure apparatus, since unnecessary tilt correction is not performed, the synchronization accuracy is improved. The exposure can be done without deterioration.
Further, the exposure apparatus of the present invention irradiates detection light onto the substrate in the exposure apparatus which projects the pattern of the mask onto a plurality of partitioned areas on the substrate by moving the mask and the substrate in synchronization, and the reflected light A surface position detecting device for detecting the surface position of the substrate during the synchronous movement by detecting the surface position, a storage device for storing the surface state distribution information in the partitioned area on the substrate according to the synchronous movement direction, and the surface position. A control device for setting the surface position of the substrate based on the detection result of the detection device and the distribution information stored in the storage device.
Therefore, in the exposure apparatus of the present invention, no matter which synchronous movement direction is selected for the divided area on the substrate, the surface position of the substrate is corrected by the distribution information of the surface state in the divided area according to the synchronous movement direction. Can be set by state. Therefore, the surface position of the substrate can be accurately positioned in the optical axis direction of the exposure light (image plane of the projection optical system) without being adversely affected by the surface condition on the substrate or the synchronous movement direction. Therefore, for example, even when a projection optical system having a shallow depth of focus is used, it is possible to adjust the substrate surface within the depth of focus, and even if so-called scanning exposure is performed, unnecessary tilt correction of the wafer surface is performed. Is performed, the exposure can be performed without deteriorating the synchronization accuracy, and the required contrast (resolution) can be easily obtained.

FIG. 1 is a diagram showing a schematic configuration of an exposure apparatus according to an embodiment of the present invention.
FIG. 2 is a perspective view showing an outline of a wafer stage which constitutes the exposure apparatus.
FIG. 3 is a diagram showing a configuration of an oblique incidence type multi-point focus position detection system.
FIG. 4A is a diagram of a focus measurement point and an exposure region projected on the transfer surface of the wafer, and FIG. 4B is a diagram showing a relationship between the shot region and the illumination region.
5A and 5B are diagrams showing a positional relationship between a device pattern and a focus measurement point, respectively.
FIG. 6 is a diagram showing a control system of the wafer stage.
FIG. 7A is a diagram showing a positional relationship between a focus measurement point and regions having different reflectances, and FIGS. 7B and 7C are diagrams showing received light intensity.
8A and 8B are diagrams showing the relationship between the position and the light intensity when the measurement intervals are different.
FIG. 9 is a flowchart of the focus error measurement.
FIG. 10 is a diagram schematically showing a path along which focus measurement is performed and a measurement position.
FIG. 11A is a diagram showing sensor positions during scanning, and FIG. 11B is a diagram showing sensing values at that time.
FIG. 12 is a flowchart showing a focus correction method of another embodiment.
FIG. 13 is a flow chart showing another form of focus correction method.
FIG. 14 is a flow chart when manufacturing a device using the exposure apparatus according to the embodiment of the present invention.
FIG. 15 is a diagram for explaining the relationship between the reflectance distribution and the focus error.

Ａ_０；入射光強度
式（２）から明らかなように、反射光強度Ｉ（ｘ）は反射率分布ｒ（ｘ）に比例しており、有限幅を有する検知光を用いて検出した反射率分布を、無限小幅の検知光で検出した反射率分布としても支障がない。
次に、式（３）のように、フォーカス計測方向に２次で表される反射率分布がウエハＷの表面に存在する場合を考える。
ｒ（ｘ）＝ａｘ^２＋ｂｘ＋ｃ …（３）
この場合の反射光強度Ｉ（ｘ）は、以下のように算出される。

ここで、下地の構造による変動が存在する場合でも、レジスト表面（ウエハ表面）での反射率が大きいということを考慮すると、一定した反射率成分ｃよりも２次の成分の変化率が小さいと見なすことができ、この場合反射光強度Ｉ（ｘ）は以下のように算出される。

式（４）から明らかなように、２次で表される反射率分布の反射光強度Ｉ（ｘ）においても、反射率分布ｒ（ｘ）に比例しており、有限幅を有する検知光を用いて検出した反射率分布を、無限小幅の検知光で検出した反射率分布としても支障がない。これは、３次以上で表される反射率分布でも同様であるため、結果として、フォーカス位置検出系２１の検出信号（光強度）の強度分布を、ウエハＷ上の反射率分布として重心位置の算出に使用することができる。なお、フォーカス位置検出系２１のように、振動板（振動子）を用いる場合には、振動子の振動周波数に対する、倍の周波数成分がフォーカス検出信号となるため、反射光の強度はその振幅を検出することで得ることができる。
上記の方法で反射率分布ｒ（ｘ）が得られると、下記の重心算出の式（５）により、フォーカス計測点ＡＦからの反射光の重心位置ｃ（ｘ）を算出することができる。

重心位置ｃ（ｘ）を算出したら、フォーカス検出原理に基づき、ウエハ表面への入射角 θ において、フォーカス誤差ｅ（ｘ）は次式（６）で求めることができる。
ｅ（ｘ）＝（ｃ（ｘ）×ｔａｎθ）／２ …（６）
そして、主制御系２０は、演算して求めたフォーカス誤差ｅ（ｘ）をフォーカス計測点の座標（ウエハＷ上での反射光強度の計測位置）と対応させて記憶装置４０に記憶させる。
続いて、上記の位置計測方法を用いてウエハＷの転写面のフォーカス調整を行う手順について、図９に示すフローチャートを参照して説明する。
なお、フォーカス誤差計測は、基本的に全てのフォーカス計測点で実施するが、本実施の形態では、同期移動による走査露光時に実際にフォーカス計測が行われる計測点、換言すると、ウエハＷに照射される複数の検知光のうち、実露光時にフォーカス計測に用いられる検知光を使用する。具体的には、フォーカス計測点ＡＦ１１〜ＡＦ１７、ＡＦ２１〜ＡＦ２７、…、ＡＦ７１〜ＡＦ７７に照射される複数の検知光の中、便宜上、図４Ｂに示すように、ショット領域（区画領域）ＳＡ上で露光領域ＥＦの周辺部に配置されるフォーカス計測点ＡＦ５７、ＡＦ５４、ＡＦ５１、ＡＦ３１、ＡＦ３４、ＡＦ３７（以下、符号Ｓ１〜Ｓ６とする）に照射される検知光を用いるものとして説明する。
なお、フォーカス誤差計測を行うタイミングとしては、ロット処理の先頭やロット処理の合間等を選択することができる。ロット先頭で行う場合には、例えばＥＧＡ処理（エンハンスド・グローバル・アライメント；特開昭６１−４４４２９号公報及び対応する米国特許第４，７８０，６１７号参照）後にフォーカス誤差計測を行い、算出されたフォーカス誤差を投影光学系ＰＬの像面に対する補正量（オフセット値）とする。また、フォーカス誤差計測をロット処理の合間に行う場合は、計測対象となるウエハ（例えば、次に露光処理するロット内のウエハ）を取り出して露光装置内にセッティングし、上述と同様にウエハアライメント（ＥＧＡ）を行った後にフォーカス誤差計測を行ってその結果を記憶する。そして、そのロットが露光処理される時に、記憶された情報を読み出して、フォーカス位置を含むウエハの姿勢調整に反映させる。ここでは、ＥＧＡ処理後にフォーカス誤差計測を実施するものとする。
図９に示すように、ステップＳＴ０でロット先頭のウエハに対してＥＧＡ処理が終了すると、まずフォーカス誤差計測を実行するかどうかを判断し（ステップＳＴ１）、実行しない場合はステップＳＴ１０の露光処理に移行する。通常、ウエハＷ上にはレチクルＲのパターンが露光されるショット領域ＳＡが区画された状態で碁盤状に複数配列される。そのため、フォーカス誤差計測を実行する際には、計測対象とするショット領域を選択する（ステップＳＴ２）。
通常、ウエハＷにおける各ショット領域内の構造は同じであり、またプロセスプログラムも同じであることから、あるショット領域で生じるフォーカス誤差は他のショット領域でも生じる。そのため、全領域を計測できるショット領域を選択して計測すれば、計測したフォーカス誤差を他のショット領域に対しても適用することが可能である。ただし、計測精度をより向上させるためには、複数のショット領域に対して反射率分布を計測してもよい。
次に、ステップＳＴ３では上述したように、フォーカス位置検出系２１の検出信号を用いて、ウエハＷの表面状態の分布情報として反射率分布を計測する。
ここで、本実施の形態では、既述のように、図４Ａに示した複数のフォーカス計測点の中、図４Ｂに示すフォーカス計測点Ｓ１〜Ｓ６に照射される検知光を用いて、レチクルＲとウエハＷとの同期移動中にフォーカス計測が行われる経路に対して反射率分布の計測を実施する。より詳細には、本露光装置では、ショットマップデータからウエハＷ上で露光すべきショット領域ＳＡのサイズや位置、及びオートフォーカスアルゴリズムから走査露光時に使用されるフォーカス計測点（露光領域ＥＦの外側に設定される計測点を含んでもよい）が既知であるため、フォーカス計測の信号サンプリング間隔と同期移動速度（スキャン速度）とから、ウエハＷ上の計測位置も判明している。図１０には、走査露光時にフォーカス計測が行われる経路Ｋ及び計測位置Ｐ１１〜Ｐ１４が概略的に示されている。このように、反射率分布の計測は、フォーカス計測が行われる経路Ｋに関してはもちろんのこと、フォーカス計測が行われるウエハＷ上の位置Ｐ１１〜Ｐ１４に対して実施する。なお、図１０中の位置Ｐ１１とＰ１４との間隔は，走査方向（Ｙ方向）に関するウエハ上のショット領域の幅と同程度以下に設定されている。
また、各フォーカス計測点Ｓ１〜Ｓ６の位置は、精密な調整がなされているが、微小な調整誤差が含まれる可能性もある。図４Ｂに示すフォーカス計測経路（矢印が付された点線）の中、例えば左端に示される経路は、フォーカス計測点Ｓ３、Ｓ４のいずれか一方のみで反射率分布を計測することが可能であるが、この計測点の設定位置に誤差が含まれる場合はフォーカス計測を行う位置に対して、正確な反射率分布の計測を実施できない虞がある。そこで、本実施の形態では、全てのフォーカス計測点Ｓ１〜Ｓ６で反射率分布を計測し、各計測点毎にウエハＷの座標位置に対応させた反射率分布を記憶する（ステップＳＴ４）。
続いて、ステップＳＴ５では、設定された平均化回数の計測を実施したか否かを判断し、所定回数の計測が終了するまで上記ステップＳＴ３、ＳＴ４を繰り返す。反射率分布計測においては、計測再現性によるばらつきが生じるため、平均化効果でばらつきを小さくするために、一つのショット領域ＳＡに対して複数回の反射率分布計測を実施することで、補正精度を向上させることができる。次に、ステップＳＴ６では、選択したショット領域に対する計測が全て終了したか否かを判断し、計測が終了するまで上記ステップＳＴ３〜ＳＴ５を繰り返す。
そして、ウエハＷに対する全ての反射率分布計測が終了すると、続いて記憶した反射率分布、及び上記の式（５）、（６）を用いて演算することにより、各フォーカス計測点毎にウエハ（ショット領域）の座標位置に対応させてフォーカス誤差を算出する（ステップＳＴ７）。そして、算出したフォーカス誤差により、走査露光時のオフセットデータをフォーカス計測点の座標位置に対応させたマップを作成し記憶する（ステップＳＴ８）とともに、露光時の像面補正値を作成して（ステップＳＴ）、記憶装置４０に記憶させる。そして、これら一連のフォーカス誤差計測が終了すると露光処理（ステップＳＴ１０）に移行する。
この露光処理では、主制御系２０の制御の下、レチクルＲとウエハＷとを同期移動してレチクルＲに形成されたパターンの像をウエハＷの転写面に転写する際に、多点フォーカス位置検出系２１を用いてフォーカス計測点にて転写面のフォーカス位置を計測しつつ、上記で算出したウエハＷの転写面の形状に応じてウエハＷの姿勢及びＺ位置を制御する。
ここで、同期移動中に、例えばフォーカス計測点Ｓ３（図４Ｂ参照）の計測結果が入力すると、主制御系２０は、記憶装置４０に記憶されているフォーカス誤差の中、フォーカス計測点Ｓ３により計測したフォーカス誤差（のマップ）を選択し、選択したフォーカス誤差を用いて計測結果を補正する。つまり、主制御系２０は、同期移動中に入力した計測値に対して、この計測値が得られたフォーカス計測点でのフォーカス誤差を用いて補正する。これにより、計測結果からフォーカス計測点を設定する際の調整誤差を排除することができる。
すなわち、主制御系２０は補正装置として、多点フォーカス位置検出系２１の計測結果を記憶装置４０に記憶しているフォーカス誤差（オフセットデータ）によってそれぞれ補正し、補正した計測値を用いて上記の演算処理を行うことにより、ウエハ表面の傾斜角及びフォーカス位置を算出する。例えば図１１（ａ）に示すように、フォーカス計測点Ｓ３により、本来一様な面位置を有するウエハを走査した際に、位置ＳＰ１と位置ＳＰ２との間に低反射領域ＬＲが存在する場合、フォーカス計測点Ｓ３における計測結果（センシング値）には、図１１Ｂに示すように、フォーカス誤差が含まれてしまう。そこで、予め記憶したフォーカス誤差を用いて計測結果を補正することで、図中二点鎖線で示すように、実際の面位置（面状態）に即した面位置情報を得ることができる。
そして、主制御系２０は、得られた結果に基づいてアクチュエータ８ａ〜８ｃをそれぞれ個別に駆動することにより、Ｚチルト θ ステージ７を介してウエハＷの面位置を調整することができる。このとき、主制御系２０は、多点フォーカス位置検出系２１の計測結果に対して、この計測点に対応するフォーカス誤差を用いる。このとき、フォーカス計測点にて実際にフォーカス位置が計測されたウエハ上の位置（実計測位置）と、記憶されているフォーカス誤差に対応するウエハ上の位置（誤差計測位置）とが一致している場合は、直接そのフォーカス誤差を用いて補正を行うが、その実計測位置と誤差計測位置とが一致しない場合には実計測位置に最も近い位置のフォーカス誤差を用いるか、もしくは実計測位置近傍２点のフォーカス誤差を用いて補間することにより、当該実計測位置のフォーカス誤差を算出し、得られたフォーカス誤差に基づいて補正を行う。なお、ウエハ表面の傾斜角及びフォーカス位置の詳細な算出方法は、例えば特開２００２−２７０４９８号公報、あるいは特開平９−８２６３６号公報及び対応する米国特許第６０８０５１７号などに開示されているため、ここでは省略する。
そして、１つのショット領域ＳＡの走査露光が終了すると、ウエハＷをステップ移動して次のショット領域の走査露光を開始する。以下、走査露光とステップ移動とを繰り返し実行して、ウエハＷ上の全てのショット領域にレチクルＲのパターンが転写されると、ウエハＷの露光処理が完了する。
以上のように、本実施の形態では、予め走査露光で使用するフォーカス計測点に対応して、走査方向（Ｙ方向）に関するウエハＷ（ショット領域）上の異なる位置でそれぞれ計測される反射率分布からフォーカス誤差を算出しているので、ウエハＷに対するフォーカス位置計測を実施する際には、反射率分布に起因する誤差成分を排除・補正することができ、ウエハＷの表面位置を容易に投影光学系ＰＬの結像面に位置決めすることが可能である。そのため、本実施の形態では、焦点深度の浅い投影光学系を用いた場合でも、正確な合焦調整により高解像度の露光処理を実現することが可能になる。
特に、本実施の形態では、フォーカス計測における検知光受光時の検出信号の強度に基づいてフォーカス誤差を計測しているので、反射率分布計測用の機器を別途設置する必要がなく、装置の小型化及び低価格化に寄与することができる。また、本実施の形態では、レチクルＲとウエハＷとの同期移動中（実露光時）にフォーカス計測を行う経路に対して、予めフォーカス誤差を計測するので、フォーカス誤差計測に要する時間を短縮することができ、生産効率の向上にも寄与できる。さらに、本実施の形態では、複数のフォーカス計測点に対してそれぞれフォーカス誤差を計測するとともに、各計測点毎にマップを作成・記憶させるので、同期移動中にフォーカス計測を実施するフォーカス計測点（フォーカス計測を行う際に用いる検知光）で得られた結果により補正を実施することで、フォーカス計測点の位置設定時の調整誤差による悪影響を排除することができ、より高精度なフォーカス調整を実施できる。
なお、上記実施の形態では、図８Ａに示したように、反射率分布ｒ（ｘ）を計測する際に、フォーカス計測点ＡＦ及びこの計測点ＡＦに間隔をあけた位置の計測点ＡＦＬ、ＡＦＲにおいて反射光の強度を計測する構成としたが、図８Ｂに示すように、フォーカス計測点ＡＦの他に、検知光が互いに重なる（フォーカス計測方向のスリット幅よりも小さいピッチの）複数点において反射光の強度を計測する構成としてもよい。このとき、例えばフォーカス計測点ＡＦに対してウエハＷをフォーカス計測方向に移動することで、図８Ｂの計測点ＡＦを含む複数点でそれぞれ反射光の強度を計測する。この場合、より微視的な反射率分布を得ることができ、例えば最小自乗近似法等により反射光強度分布が２次で変化している成分を算出可能であれば、反射率分布ｒ（ｘ）を２次として上記の光量重心を算出できる。
なお、検知光が互いに重なる複数点で反射光強度分布を計測する場合は、計測間隔が小さいので、式（５）のように積分処理することなく、下式（７）を用いて重心算出を実施してもよい。

ｉ；反射光強度計測点ｘｉにおける反射光強度
また、上記の実施形態では、同期移動方向については特に言及しなかったが、実際には干渉計等により座標位置が得られるタイミングとウエハＷの姿勢及びＺ位置等を制御するタイミングとにギャップが生じる場合がある。このような場合には、同期移動方向に応じて反射率分布の計測結果が異なることがある。そのため、反射率分布及びフォーカス誤差を計測する際には、フォーカス計測点毎にマップを作成したのと同様に、同期移動方向毎に座標位置に対応させた反射率分布及びフォーカス誤差のマップを作成・記憶させ、フォーカス調整時には、同期移動方向に対応したマップを呼び出して、このマップに含まれるオフセット値を用いてフォーカス計測値を補正することが好ましい。なお、本実施形態ではショット領域内で走査方向（Ｙ方向）と平行な経路Ｋ上に離散的に設定される複数位置（本例では４つ）でそれぞれ反射率分布を計測するものとしたが、経路Ｋ上での反射率分布の計測位置の数は任意でよいし、例えば走査方向に関する前述のスリット像ＡＦの幅とほぼ同じピッチでウエハを走査方向に移動することで、走査方向に関するショット領域のほぼ全域に渡って反射率分布を計測してもよい。
続いて、本発明の他の実施形態について説明する。
上記の実施形態では、フォーカス計測に係る検知光の反射光を受光することでウエハ表面の反射率分布を算出・計測する構成としたが、ウエハＷの表面形状を予め実測し、その結果を用いて反射率分布により生じるフォーカス誤差分布を得ることも可能である。なお、以下の計測方法においても、計測精度を向上させるために、単一ショット領域内、複数のショット領域、同期移動方向毎等、複数回計測による平均化を行うことが好ましい。
例えば図１２に示すように、上述のフォーカス位置検出系２１を用いてウエハＷの表面形状を計測し（ステップＳＴ１１）、計測した表面形状と、静電容量センサ等のフォーカス位置検出系２１とは異なる計測器を用いて予め実測した表面形状との差分を反射率分布によるフォーカス誤差としてオフセット値を設定する（ステップＳＴ１２）ことも可能である。この場合、設定したオフセット値を用いてフォーカス計測結果を補正すれば（ステップＳＴ１３）、上記実施形態と同様に、反射率分布に起因する誤差成分を排除することができる。
また、近年のデバイス製造プロセスにおいては、上述したＣＭＰにより平坦化処理が設けられることが多いが、この処理により表面形状が平坦と見なせるウエハに対しては、図１３に示すように、平坦化処理を実施した後に（ステップＳＴ２１）、フォーカス位置検出系２１を用いてフォーカス計測を実施した際に（ステップＳＴ２２）、この計測値（位置情報、面位置情報）をフォーカス誤差として設定することもできる（ステップＳＴ２３）。この場合、ウエハのフラットネスを実測していないので、ウエハが平坦でない場合はフォーカス誤差分布に誤差が含まれることになる。しかし、ウエハホルダの平坦度やウエハ自身のグレード等により、計測時のウエハのフラットネスは概ね把握可能であるので、フラットネスに対応するしきい値を設定し、フォーカス計測結果にしきい値以上の変化が含まれる場合は、反射率分布に起因するフォーカス誤差が存在するとして補正を行うようにしてもよい。なお、例えばウエハのフラットネスを予め実測しておき、この実測されたフラットネスを用いて先に算出したフォーカス誤差分布を補正してもい。また、フォーカス位置検出系２１を用いてフォーカス計測を実施するとき、計測対象となるショット領域が所定の基準面（例えば、投影光学系ＰＬの結像面）に対して傾いていると、先に算出したフォーカス誤差分布にその傾向に起因した誤差が含まれることになる。そこで、例えばフォーカス計測に先立ってショット領域を基準面とほぼ平行に設定しておく、あるいはフォーカス誤差分布からその傾斜に起因した誤差を差し引くことが好ましい。
また、ウエハの姿勢制御に関しても、投影光学系ＰＬの焦点深度を考慮して傾斜の許容値を設定することができる。従って、この許容値をしきい値として設定し、フォーカス位置検出系２１の計測結果からフォーカス調整時のウエハＷの傾斜を算出したときに、しきい値を超える場合には、フォーカス位置検出系２１の計測結果に反射率分布に起因した誤差成分が含まれていると見なし、補正を行う手順とすることもできる。
なお、上述した特開２００２−２７０４９８号公報には、ショット領域ＳＡ内の段差情報を予め計測しておき、その状態に応じて露光処理時のフォーカス調整（合焦動作）モードを複数のモードから選択する技術が開示されている。
本実施の形態においても、上記の技術を適用し、ショット領域内の反射率分布計測時（反射率マップ計測時）に段差状態も併せて計測し、ショット領域内の段差に応じたフォーカス・レベリング補正マップを作成しておいてもよい。このフォーカス・レベリング補正マップも、先に述べた反射率分布により生じるフォーカス誤差に基づくマップ（以下、反射率マップ）と同様に、記憶装置４０に記憶しておけばよい。なお、反射率マップとフォーカス・レベリング補正マップとは、それぞれショット領域を露光するときの同期移動方向（スキャン方向；＋Ｙ方向及び−Ｙ方向）毎に作成し、記憶しておくことが好ましい。尚、フォーカス・レベリング補正マップには反射率分布により生じるフォーカス誤差が混入しているので、各フォーカス計測点において、反射率マップの値をフォーカス・レベリング補正マップの値から差し引くことにより、真のフォーカス・レベリング補正マップが得られることになる。露光時にはこの真の値のマップに基づいて、フォーカス・レベリング補正が行われる。
さらに、ウエハＷ内に存在するショット領域は、通常のショット領域、一部がウエハの周縁部に掛かるエッジショット、各種計測用のダミーショットであるＴＥＧショット等、反射率分布によるフォーカス誤差や段差状態が異なるショット領域が複数種類存在する。従って、これら複数種類のショット領域が存在するウエハではその種類毎に、反射率マップやフォーカス・レベリング補正マップを作成し、記憶しておくことが好ましい。
以上のことから、露光装置が記憶できる反射率マップとフォーカス・レベリング補正マップとのそれぞれの数は、プロセスプログラムに対応して、ショット領域の種類として、例えば８種類、これが同期移動方向（走査方向）に応じてそれぞれ２種類存在するため、合計８対（１６個）となる。この数は、ショット領域の種類に応じてさらに増やすことも可能である。
また、ショット領域に対して露光処理する場合、反射率マップとフォーカス・レベリング補正マップとのそれぞれに応じた補正を行うことになるが、フォーカス・レベリング補正マップに応じた合焦動作の制御モードとしては、例えば段差の中間部分が合焦面に合致するようにウエハホルダ６の高さ位置を制御する第１モード、及び所定の許容値を超えた段差部分についてはフォーカス位置検出系２１を用いた追い込みを行わない第２モードとが考えられる。そして、これらのモードをオペレータが適宜切り換えて設定できるようにしておくことが好ましい。
なお、上記実施の形態では、フォーカス位置検出系２１が振動子を用いる構成として説明したが、これに限定されるものではなく、例えばＣＣＤを用いた画像処理方式や偏光変調素子を用いる方式等、他の検出原理によりフォーカス位置（及び反射率分布）を計測する方式としてもよい。
また、上記各実施形態ではフォーカス調整時にウエハＷを移動して、前述の露光領域ＥＦ内でウエハ表面を投影光学系ＰＬの結像面とほぼ合致させるものとしたが、ウエハの移動の代わりに、あるいはそれと組み合わせて、例えば投影光学系ＰＬの少なくとも１つの光学素子を駆動することで、投影光学系ＰＬの結像面を移動するようにしてもよい。
さらに、上記各実施形態では投影光学系ＰＬを介してレチクルＲのパターンの転写が行われる露光位置に配置される多点フォーカス位置検出系２１を用いて前述のフォーカス誤差を求めるものとしたが、例えば独立に可動な２つのウエハステージを有し、露光位置と、ウエハアライメント系によるマーク検出が行われる計測位置（アライメント位置）とにそれぞれウエハステージを配置して、露光動作と計測動作とをほぼ並行して実行可能な露光装置に本発明を適用し、その計測位置に配置される検出系を用いて前述のフォーカス誤差を求めるようにしてよい。ここで、計測位置に配置される検出系としては、例えば前述の多点フォーカス位置検出系２１と同様の構成のものを用いることができる。
このツインウエハステージ方式の露光装置では、計測位置にてその検出系を用いて前述の反射率分布とフォーカス位置とを計測するとともに、その反射率分布から得られるフォーカス誤差に基づいてその計測されたフォーカス位置を補正し、計測位置から露光位置に移送されるウエハの露光処理ではその補正されたフォーカス位置を用いてフォーカス調整が行われることになる。このとき、露光位置には前述の多点フォーカス位置検出系２１を設けなくてもよく、例えば投影光学系ＰＬ（又はそれを保持する架台）とウエハステージ（例えば、Ｚチルト θ ステージ７）とのＺ軸方向の間隔を計測する干渉計を用いてＺチルト θ ステージ７を駆動してもよい。また、計測位置では反射率分布のみを計測し、露光位置にて計測されるフォーカス位置を、その反射率分布から得られるフォーカス誤差を用いて補正して露光処理を実行するようにしてもよい。さらに、前述の如く平坦化処理が施されたウエハでは、計測位置にてその検出系を用いてフォーカス位置を計測して、この計測結果をそのままフォーカス誤差とし、計測位置から露光位置に移送されるウエハの露光処理ではそのフォーカス誤差を用いてフォーカス調整が行われることになる。なお、ツインウエハステージ方式の露光装置では、露光動作と並行して前述の反射率分布またはフォーカス位置を計測することが可能であるので、露光装置のスループットを低下させることなく、前述の複数回計測を行う、即ちフォーカス調整の精度向上を図ることができる。
なお、このツインウエハステージ方式の露光装置は、例えば特開平１０−２１４７８３号公報及び対応する米国特許第６，３４１，００７号、あるいは国際公開ＷＯ９８／４０７９１号及び対応する米国特許第６，２６２，７９６号などに開示されており、本国際出願で指定した指定国又は選択した選択国の国内法令が許す限りにおいて、その米国特許の開示を援用して本明細書の記載の一部とする。
また、上記実施形態では多点フォーカス位置検出系２１を用いてウエハの反射率分布を計測するものとしたが、多点フォーカス位置検出系と異なるセンサ（検出系）、あるいは露光装置とは別の計測装置などを用いて反射率分布を計測し、この計測した反射率分布に基づいて前述のフォーカス誤差を算出するようにしてもよい。
なお、本実施の形態の基板としては、半導体デバイス製造用の半導体ウエハＷのみならず、ディスプレイデバイス用のガラス基板や、薄膜磁気ヘッド用のセラミックウエハ、あるいは露光装置で用いられるマスクまたはレチクルの原版（合成石英、シリコンウエハ）等が適用される。
露光装置としては、レチクルＲとウエハＷとを同期移動してレチクルＲのパターンを走査露光するステップ・アンド・スキャン方式の走査型露光装置（スキャニング・ステッパー；ＵＳＰ５，４７３，４１０）の他に、レチクルＲとウエハＷとを静止した状態でレチクルＲのパターンを露光し、ウエハＷを順次ステップ移動させるステップ・アンド・リピート方式の投影露光装置（ステッパー）にも適用することができる。また、本発明はウエハＷ上で少なくとも２つのパターンを部分的に重ねて転写するステップ・アンド・スティッチ方式の露光装置にも適用できる。さらに、本発明はミラープロジェクション・アライナー、例えば国際公開ＷＯ９９／４９５０４などに開示される、投影光学系ＰＬとウエハとの間に液体（例えば純水など）が満たされる液浸型露光装置などにも適用できる。
露光装置の種類としては、ウエハＷに半導体素子パターンを露光する半導体素子製造用の露光装置に限られず、液晶表示素子製造用又はディスプレイ製造用の露光装置や、薄膜磁気ヘッド、撮像素子（ＣＣＤ）あるいはレチクル又はマスクなどを製造するための露光装置などにも広く適用できる。
また、露光光の光源として、超高圧水銀ランプから発生する輝線（ｇ線（４３６ｎｍ）、ｈ線（４０４．ｎｍ）、ｉ線（３６５ｎｍ））、ＫｒＦエキシマレーザ（２４８ｎｍ）、ＡｒＦエキシマレーザ（１９３ｎｍ）、Ｆ_２レーザ（１５７ｎｍ）、Ａｒ_２レーザ（１２６ｎｍ）のみならず、Ｘ線、あるいは電子線やイオンビームなどの荷電粒子線を用いることができる。例えば、電子線を用いる場合には電子銃として、熱電子放射型のランタンヘキサボライト（ＬａＢ_６）、タンタル（Ｔａ）を用いることができる。また、ＹＡＧレーザや半導体レーザ等の高調波などを用いてもよい。
例えば、ＤＦＢ半導体レーザ又はファイバーレーザから発振される赤外域又は可視域の単一波長レーザを、例えばエルビウム（又はエルビウムとイットリビウムの両方）がドープされたファイバーアンプで増幅し、かつ非線形光学結晶を用いて紫外光に波長変換した高調波を露光光として用いてもよい。なお、単一波長レーザの発振波長を１．５４４〜１．５５３μｍの範囲内とすると、１９３〜１９４ｎｍの範囲内の８倍高調波、即ちＡｒＦエキシマレーザとほぼ同一波長となる紫外光が得られ、発振波長を１．５７〜１．５８μｍの範囲内とすると、１５７〜１５８ｎｍの範囲内の１０倍高調波、即ちＦ_２レーザとほぼ同一波長となる紫外光が得られる。
また、レーザプラズマ光源、又はＳＯＲから発生する波長５〜５０ｎｍ程度の軟Ｘ線領域、例えば波長１３．４ｎｍ、又は１１．５ｎｍのＥＵＶ（Ｅｘｔｒｅｍｅ Ｕｌｔｒａ Ｖｉｏｌｅｔ）光を露光光として用いてもよく、ＥＵＶ露光装置では反射型レチクルが用いられ、かつ投影光学系が複数枚（例えば３〜６枚程度）の反射光学素子（ミラー）のみからなる縮小系となっている。
投影光学系ＰＬは、縮小系のみならず等倍系および拡大系のいずれでもよい。また、投影光学系ＰＬは屈折系、反射系、及び反射屈折系のいずれであってもよい。なお、露光光の波長が２００ｎｍ程度以下であるときは、露光光が通過する光路を、露光光の吸収が少ない気体（窒素、ヘリウムなどの不活性ガス）でパージすることが望ましい。また電子線を用いる場合には光学系として電子レンズおよび偏向器からなる電子光学系を用いればよい。なお、電子線が通過する光路は、真空状態にすることはいうまでもない。
ウエハステージやレチクルステージにリニアモータ（ＵＳＰ５，６２３，８５３またはＵＳＰ５，５２８，１１８参照）を用いる場合は、エアベアリングを用いたエア浮上型およびローレンツ力またはリアクタンス力を用いた磁気浮上型のどちらを用いてもよい。また、各ステージは、ガイドに沿って移動するタイプでもよく、ガイドを設けないガイドレスタイプであってもよい。
各ステージの駆動機構としては、二次元に磁石を配置した磁石ユニットと、二次元にコイルを配置した電機子ユニットとを対向させ電磁力により各ステージを駆動する平面モータを用いてもよい。この場合、磁石ユニットと電機子ユニットとのいずれか一方をステージに接続し、磁石ユニットと電機子ユニットとの他方をステージの移動面側に設ければよい。
ウエハステージの移動により発生する反力は、投影光学系ＰＬに伝わらないように、特開平８−１６６４７５号公報（ＵＳＰ５，５２８，１１８）に記載されているように、フレーム部材を用いて機械的に床（大地）に逃がしてもよい。
レチクルステージ２の移動により発生する反力は、投影光学系ＰＬに伝わらないように、特開平８−３３０２２４号公報（ＵＳＰ５，８７４，８２０）に記載されているように、フレーム部材を用いて機械的に床（大地）に逃がしてもよい。
以上のように、本願実施形態の露光装置は、本願特許請求の範囲に挙げられた各構成要素を含む各種サブシステムを、所定の機械的精度、電気的精度、光学的精度を保つように、組み立てることで製造される。これら各種精度を確保するために、この組み立ての前後には、各種光学系については光学的精度を達成するための調整、各種機械系については機械的精度を達成するための調整、各種電気系については電気的精度を達成するための調整が行われる。各種サブシステムから露光装置への組み立て工程は、各種サブシステム相互の、機械的接続、電気回路の配線接続、気圧回路の配管接続等が含まれる。この各種サブシステムから露光装置への組み立て工程の前に、各サブシステム個々の組み立て工程があることはいうまでもない。各種サブシステムの露光装置への組み立て工程が終了したら、総合調整が行われ、露光装置全体としての各種精度が確保される。なお、露光装置の製造は温度およびクリーン度等が管理されたクリーンルームで行うことが望ましい。
半導体デバイス等のマイクロデバイスは、図１４に示すように、マイクロデバイスの機能・性能設計を行うステップ２０１、この設計ステップに基づいたマスク（レチクル）を製作するステップ２０２、シリコン材料からウエハを製造するステップ２０３、前述した実施形態の露光装置によりレチクルのパターンをウエハに露光する露光処理ステップ２０４、デバイス組み立てステップ（ダイシング工程、ボンディング工程、パッケージ工程を含む）２０５、検査ステップ２０６等を経て製造される。Embodiments of a position measuring method, a position measuring apparatus, an exposure method, and an exposure apparatus of the present invention will be described below with reference to FIGS. 1 to 14.
FIG. 1 is a diagram showing a schematic configuration of an exposure apparatus according to an embodiment of the present invention. In the following description, the XYZ rectangular coordinate system shown in FIG. 1 is set, and the positional relationship of each member will be described with reference to this XYZ rectangular coordinate system. In the XYZ Cartesian coordinate system shown in FIG. 1, a reticle R as a mask on which a predetermined pattern area is formed and a wafer W as a substrate having a photoresist coated on its upper surface are moved in the scanning movement direction (synchronization). The movement direction) is set to the Y-axis direction, the direction orthogonal to the Y-axis in the plane of the reticle R is set to the X-axis direction, and the normal line direction of the reticle R (wafer surface) is set to the Z-axis direction. In the XYZ orthogonal coordinate system in FIG. 1, the XY plane is actually set to a plane parallel to the horizontal plane, and the Z axis is set to the vertically upward direction.
In the following, a region where the exposure light EL is irradiated on the reticle R by an illumination optical system (not shown) is referred to as an “illumination region”, and the projection optical system PL is conjugate with the illumination region and is transmitted through the projection optical system PL. A region of the wafer W irradiated with the exposure light EL is referred to as an “exposure region”. The exposure apparatus (FIG. 1) of the present embodiment is a scanning exposure apparatus that transfers the pattern of the reticle R to a plurality of shot areas (section areas) on the wafer W by the step-and-scan method. The illumination area of is a rectangular area extending in the X-axis direction on the reticle R around the optical axis of the illumination optical system (which coincides with the optical axis AX of the projection optical system PL).
In FIG. 1, an illumination optical system (not shown) includes a shaping optical system that makes the illumination condition of the reticle R variable, an optical integrator, a blind (variable field stop) that defines an illumination area on the reticle R, and the like. The exposure light EL generated from the illustrated light source (excimer laser or the like) is applied to the above-mentioned illumination area with substantially uniform illuminance. The projection optical system PL generates an image of a part of the pattern of the reticle R arranged on the first surface (object surface) in the illumination area in the exposure area on the second surface (imaging surface). , The image is transferred onto the wafer W, the surface of which is arranged substantially in conformity with the second surface. In the scanning exposure in which the pattern of the reticle R is transferred to each shot area on the wafer W, the relative movement of the reticle R with respect to the illumination area and the relative movement of the wafer W with respect to the exposure area are performed in synchronization, and the entire surface of the pattern is exposed. While being irradiated with the light EL, the exposure light EL is irradiated to each shot area via the projection optical system PL. At this time, the reticle R scans the illumination area at a constant speed V in the positive or negative direction of the Y axis, and the wafer W moves at a constant speed in the negative or positive direction of the Y axis in synchronization with the scanning. Scanning is performed at V/β (1/β is the reduction magnification of the projection optical system PL).
The reticle R is held on the reticle micro-driving stage 1 by a vacuum chuck or the like. The reticle micro-driving stage 1 can be finely moved in the X-axis direction, the Y-axis direction, and the rotation direction (θ direction) in a plane (XY plane) perpendicular to the optical axis AX of the projection optical system PL, with high accuracy. The position of the reticle R is controlled. The reticle micro-driving stage 1 is mounted on a reticle Y driving stage 2 which can be driven in the Y-axis direction, and the reticle Y driving stage 2 is mounted on a reticle support base 3. The movable mirror 4 is arranged on the reticle micro-driving stage 1, and the position of the reticle micro-driving stage 1 in the X-axis direction, the Y-axis direction, and the θ direction is constantly maintained by the interferometer 5 arranged on the reticle support base 3. Is being monitored. The position information S1 obtained by the interferometer 5 is supplied to the main control system 20.
On the other hand, the wafer W is placed on the wafer stage. FIG. 2 is a perspective view showing a schematic configuration of the wafer stage. The wafer W is held on a Z tilt θ stage 7 via a wafer holder 6 that performs vacuum suction, and the Z tilt θ stage 7 has three actuators (eg, voice coil motor, EI core, etc.) that are movable in the Z axis direction. ) 8a to 8c are mounted on the XY stage 9. In this case, the Z tilt θ stage 7 can be moved in the Z-axis direction by making the drive amounts of the three actuators 8a to 8c the same, and the drive amounts of the three actuators 8a to 8c can be set independently. The Z tilt θ can control the tilt angle of the stage 7 around the X axis and the tilt angle around the Y axis. Further, the Z tilt θ stage 7 is configured to be rotatable around the Z axis within a predetermined range by an actuator (not shown) other than the three actuators 8a to 8c. In addition, the XY stage 9 is configured to be able to move the Z tilt θ stage 7 at a constant speed in the Y-axis direction and stepwise move in the X-axis direction and the Y-axis direction by a linear motor, for example. The wafer holder 6, the Z tilt θ stage 7, the actuators 8a to 8c, and the XY stage 9 constitute a wafer stage.
The movable mirror 10 is fixed on the Z tilt θ stage 7, and the position of the Z tilt θ stage 7 in the X axis direction, the Y axis direction, and the θ direction is monitored by an interferometer 11 arranged outside. The position information obtained by the total 11 is also supplied to the main control system 20. Here, as shown in FIG. 2, in order to measure the position information of the Z tilt θ stage 7 in the X-axis direction and the Y-axis direction, a movable mirror 10X and a movable mirror 10Y are arranged on the Z tilt θ stage 7. The interferometer 11X and the interferometer 11Y are arranged at positions facing the movable mirrors 10X and 10Y, respectively. Instead of fixing the movable mirror 10 to the Z tilt θ stage 7, a wafer stage, for example, a reflection surface obtained by mirror-finishing the end surface (side surface) of the Z tilt θ stage 7 may be used. Further, the interferometer 11 may be capable of measuring not only the rotation amount around the Z axis but also the rotation amounts around the X axis and the Y axis.
The main control system 20 controls the positioning operation of the Z tilt θ stage 7 and the XY stage 9 via the wafer driving device 12 and the like, and also controls the operation of the entire device. Further, in order to establish correspondence between the wafer coordinate system defined by the coordinates measured by the interferometer 11 on the wafer W side and the reticle coordinate system defined by the coordinates measured by the interferometer 5 on the reticle R side, Z tilt θ The reference mark plate 13 is fixed on the stage 7 in the vicinity of the wafer W. Various reference marks are formed on the reference mark plate 13.
The exposure apparatus of this embodiment is provided above the reticle R, and has reticle alignment systems 14 and 15 for simultaneously detecting the reference mark on the reference mark plate 13 and the mark on the reticle R. The reticle alignment systems 14 and 15 of the present embodiment are an image processing system in which the images of these two marks are detected by the imaging rod using the above-mentioned exposure light EL as alignment light, and the detection light from the reticle R is detected. Deflection mirrors 16 and 17 for guiding each are movably arranged. When the exposure sequence is started, these deflection mirrors 16 and 17 are retracted to the outside of the optical path of the exposure light EL by the mirror drive devices 18 and 19 under the command from the main control system 20, respectively. Further, on the side of the projection optical system PL, position information of the wafer W in the Z-axis direction (optical axis direction, normal direction) and the inclination angle of the wafer W with respect to the XY plane (image plane of the projection optical system PL), that is, An oblique incidence type multi-point focus detection system 21 is provided as a position measuring device (surface position detecting device) for measuring the surface position of the wafer W.
Next, the oblique incidence multi-point focus position detection system 21 for measuring the tilt angle of the wafer W will be described. FIG. 3 is a diagram showing the configuration of the oblique incidence type multipoint focus position detection system 21. Incidentally, in FIG. 3, a part of the members shown in FIG. 1 is omitted to simplify the illustration. In the oblique incidence type multi-point focus position detection system 21 shown in FIG. 3, the illumination light, which has a wavelength different from that of the exposure light EL and does not expose the photoresist on the wafer W, is emitted from an illumination light source (not shown) from an optical fiber bundle. It is led through 25. The illumination light emitted from the optical fiber bundle 25 passes through a condenser lens 26 and illuminates a pattern forming plate 27 having a plurality of slit-shaped opening patterns formed therein.
The illumination light that has passed through the pattern forming plate 27 is projected onto the transfer surface (photoresist surface) of the wafer W via the lens 28, the mirror 29, and the irradiation objective lens 30, and the pattern W is transferred onto the pattern forming plate 27. The image of the aperture pattern (slit image) is projected and imaged obliquely with respect to the optical axis AX of the projection optical system PL. FIG. 4 is a diagram showing how the aperture pattern formed on the pattern forming plate 27 is imaged on the transfer surface of the wafer W arranged below the projection optical system PL. In FIG. 4A, the rectangular area denoted by reference numeral EF indicates the above-described exposure area. An image of the pattern of the reticle R is irradiated in this exposure area EF.
The pattern forming plate 27 sets the arrangement (number or position) of focus measurement points on the wafer W and the shape and size of the irradiation area (pattern image) of the detection light at the focus measurement points. In the present embodiment, seven focus measurement points are set (49 in total) at predetermined intervals along the Y direction which is the scanning direction (synchronous movement direction) and the X direction which is the non-scanning direction (step movement direction). As shown in FIG. 4A, aperture pattern images (slit images) AF11 to AF17, AF21 to AF27,..., AF71 to AF77 (hereinafter appropriately referred to simply as AF) are projected at 49 focus measurement points. As described above, the opening pattern of the pattern forming plate 27 is formed corresponding to the arrangement of the focus measurement points (FIG. 4A). Further, in the present embodiment, the longitudinal direction of the image (slit image) AF of the aperture pattern projected on the focus measurement point is oblique with respect to the X axis and the Y axis on the transfer surface of the wafer W in FIG. Is set to 45 degrees). Note that, hereinafter, the image (slit image) AF of the aperture pattern may also be referred to as a focus measurement point. ..
Here, the setting of the slit image AF projected on the focus measurement point will be briefly described.
As shown in FIG. 5, the device pattern DP formed in a part of each shot area on the wafer W is usually arranged along the Y direction or the X direction. Therefore, when the slit image AF is arranged along the Y direction (or the X direction), the slit image AF may partially overlap with the device pattern DP formed on the base, as shown in FIG. 5A. In this case, due to the presence of the device pattern DP, in the slit image AF, a large difference occurs in the reflectance of the detection light in the width direction (X direction) over the entire length. Therefore, as shown in FIG. 5B, by tilting the slit image AF so as not to be parallel to the X direction or the Y direction, the portion where the reflectance difference occurs is only around the boundary of the device pattern DP, and the reflectance difference causes the difference. It is possible to minimize the adverse effect that occurs.
Returning to FIG. 3, the illumination light (reflected light) reflected by the wafer W is re-projected on the light receiving surface of the light receiver 34 through the condensing objective lens 31, the rotation direction vibration plate 32, and the imaging lens 33 to receive the light. An image of the pattern on the pattern forming plate 27 is re-imaged on the light receiving surface of the container 34. On the light receiving surface of the light receiver 34, a light shielding plate (not shown) having openings arranged in a similar shape to the pattern forming plate 27 is provided. Here, since the main control system 20 vibrates the rotation direction vibration plate 32 via the vibration exciter 36, the position of the image projected on the light receiver 34 is the longitudinal direction of the opening formed in the light shielding plate. It vibrates in a direction inclined by 45 degrees, that is, in the X direction in FIG. This vibration direction matches the focus measurement direction (X direction) in which the slit image AF moves on the wafer W when the wafer W is displaced in the Z axis direction (the optical axis direction of the projection optical system PL). Detection signals from a large number of light receiving elements of the light receiver 34 are supplied to the signal processing device 35. The signal processing device 35 synchronously detects each supplied detection signal with the drive signal of the vibration device 36 to obtain 49 focus signals corresponding to the focus positions of the focus measurement points AF11 to AF77.
Here, as shown in FIG. 4A, the focus measurement points AF31 to AF37 and AF51 to 57 are arranged in the peripheral portion of the exposure area EF, and the measurement points AF41 to AF47 are arranged inside the exposure area EF. The points AF11 to AF17, AF21 to AF27 and the measurement points AF61 to AF67, AF71 to AF77 are arranged outside the exposure area EF. This is the shape of the area to be exposed (position information in the Z-axis direction) using the measurement results at the measurement points AF61 to AF67 and AF71 to AF77 when the wafer W is scanned in the positive direction of the Y axis. This is to measure (read ahead) in advance. Further, similarly, when the wafer W is scanned in the negative direction of the Y-axis, the shape of the area to be exposed is measured in advance by using the measurement results at the measurement points AF11 to AF17 and AF21 to AF27. .. Then, the attitude control of the wafer W is performed on the portion to be exposed, using the measurement results at the measurement points AF11 to AF17 and AF21 to AF27 or the measurement results at the measurement points AF61 to AF67 and AF71 to AF77.
The signal processing device 35 performs various calculation processes such as least squares approximation on these 49 focus signals (detection signals) to obtain the tilt angle of the transfer surface of the wafer W in the exposure area EF and the focus of the transfer surface. The position is obtained and output to the main control system 20.
Next, the control system of the wafer stage shown in FIGS. 1 and 2 will be described in more detail. FIG. 6 is a diagram showing a control system of the wafer stage, and the same members as those shown in FIGS. 1 and 2 are designated by the same reference numerals. In FIG. 6, the Z tilt θ stage 7 is supported via three actuators 8a to 8c arranged under the Z tilt θ stage 7. The actuators 8a to 8c are mounted on the wafer holder 6 (not shown) provided on the Z tilt θ stage 7 by adjusting the expansion and contraction amounts of the actuators 8a to 8c by the drive units 41a to 41c, respectively. The focus position of the transfer surface of the wafer W, the tilt angle in the scanning direction, and the tilt angle in the non-scanning direction can be set to desired values. Height sensors 38a to 38c capable of measuring the displacement amount of each actuator in the focus direction with a resolution of, for example, about 0.001 μm are attached near the actuators 8a to 8c, respectively. The measurement result is output to the main control system 20. The drive parts 41a to 41c are provided in the wafer drive device 12 shown in FIG.
The main control system 20 of the present embodiment synchronously scans the reticle R and the wafer W when transferring the image of the pattern formed on the reticle R onto the transfer surface of the wafer W via the projection optical system PL. Various calculations are performed according to the shape of the transfer surface and the focus position obtained by the multipoint focus position detection system 21, and the attitude of the wafer W and the position in the Z direction are controlled based on the results. That is, in order to control the attitude/position of the wafer W, the main control system 20 controls the inclination angle of the transfer surface of the wafer W output from the signal processing device 35, the focus position of the transfer surface, and the height sensors 38a to 38c. The focus position and attitude of the wafer W are controlled via the actuators 8a to 8c by controlling the driving of the driving units 41a to 41c according to the displacement amount of the actuators 8a to 8c output from the actuators 8a to 8c. The main control system 20 is also provided with a storage device 40 for storing various calculation results and the like.
Then, prior to transferring the image of the pattern formed on the reticle R onto the transfer surface on the wafer W, the wafer W is moved in the XY plane in advance while the wafer W is moved by using the multipoint focus position detection system 21. A procedure for performing focus adjustment on the transfer surface will be described. Here, when performing the focus adjustment, the multi-point focus position detection system 21 measures the position of the transfer surface in the Z direction at each of a plurality of focus measurement points. The focus error due to the reflectance distribution on the transfer surface may be included as an error component.
As shown in FIG. 7A, when the focus measurement point AF on the wafer W straddles the high-reflectance portion HR and the low-reflectance portion LR, the positions P1 and P4 on both ends of the slit become the high-reflectance portion HR. Since it is located, the reflected light intensity distribution in the focus measurement direction at this portion is larger than the reflected light intensity distribution in the focus measurement direction at position P2 in the low reflectance portion LR, as shown in FIG. 7B. Further, the reflected light intensity distribution in the focus measurement direction at the position P3 extending over both reflectance parts in the focus measurement direction is an intensity distribution according to the reflectance. Since the light receiver 34 of the focus position detection system 21 detects the average reflected light intensity in the slit at the focus measurement point, as shown in FIG. 7C, the detection signal thereof has the above-mentioned positions P1 to P4 (actually, P1 to P4). The reflected light intensity distributions in the entire direction orthogonal to the focus measurement direction are combined (added), and the center of gravity position shifts. The focus detection method of the focus position detection system 21 measures, for example, a detection signal (voltage value V) at the maximum amplitude position of the slit image vibrating with respect to the opening on the light receiver 34. This position is two places when the slit image is located at both ends of the opening. Then, the difference between the two measured detection signals (voltage value V) is used as the focus signal. In this case, if the reflected light of the slit image has an intensity distribution, an error occurs in the voltage value at each maximum amplitude position, and an accurate focus signal cannot be obtained.
Further, when the focus detection method of the focus position detection system 21 uses, for example, the center of gravity position in the slit image as the focus signal, that is, in the case of the line CCD detection method, the displacement of the center of gravity position becomes a focus error as it is. ..
Therefore, in order to perform focus adjustment with high accuracy, this focus error is measured before exposure. In the present embodiment, the focus error is measured based on the intensity of the detection signal obtained when the reflected light of the detection light applied to the focus measurement point is received. In the following, first, a procedure for measuring the focus error caused by the reflectance distribution at each focus measurement point will be described.
As described above, the detection signal at one focus measurement point detected by the focus position detection system 21 is the average reflected light intensity at that focus measurement point, and the reflectance distribution in the focus measurement direction in the slit is Not shown. Further, the reflectance distribution can be obtained by using the detection light of the slit (extremely thin slit) having an infinitesimally small width and measuring the projection area of the slit image AF at the focus measurement point a plurality of times. It is difficult to equip such a detection light. Therefore, in the present embodiment, as shown in FIG. 8A, a predetermined distance is provided on both sides of the focus measurement point AF which is the measurement target and the focus measurement direction (X direction in the present embodiment) sandwiching the measurement point AF. The intensity of the reflected light is measured at each of the position measurement points AFL and AFR. Here, FIG. 8A shows a state in which the slit image is projected onto each of the three focus measurement points and the intensity of the reflected light is measured, but it is not always necessary to project the three slit images. By projecting a slit image only on the focus measurement points of, and moving the wafer W in the X direction, the intensity of the reflected light is measured at each of the three locations on the wafer W corresponding to the three focus measurement points in FIG. 8A. You can Note that the number of measurement points on the wafer at which the reflected light intensity should be detected using at least one slit image AF is not limited to three, and may be two or four or more. From the measurement results of these three points, the reflectance distribution r(x) is obtained by arithmetic processing such as the least square method.
Here, consider a case where a reflectance distribution represented by a primary in the focus measurement direction exists on the surface of the wafer W as in the following expression (1).
r(x)=ax+b (1)
The reflected light intensity I(x) of the slit image having the width Δ in the focus measurement direction at a certain measurement position x is calculated as follows.

A ₀ ;Incoming light intensity
As is clear from the formula (2), the reflected light intensity I(x) is proportional to the reflectance distribution r(x), and the reflectance distribution detected using the detection light having a finite width has an infinite small width. There is no problem with the reflectance distribution detected by the detection light.
Next, let us consider a case where a reflectance distribution represented by a second order in the focus measurement direction exists on the surface of the wafer W as in Expression (3).
r(x)=ax ^Two +bx+c (3)
The reflected light intensity I(x) in this case is calculated as follows.

Considering that the reflectance on the resist surface (wafer surface) is large even if there is a variation due to the structure of the underlying layer, if the rate of change of the secondary component is smaller than the constant reflectance component c. It can be seen that the reflected light intensity I(x) is then calculated as follows:

As is clear from the equation (4), the reflected light intensity I(x) of the reflectance distribution represented by the second order is proportional to the reflectance distribution r(x), and the detected light having a finite width is There is no problem even if the reflectance distribution detected by using it is the reflectance distribution detected by the detection light of infinite small width. This is the same for the reflectance distribution represented by the third order or higher, and as a result, the intensity distribution of the detection signal (light intensity) of the focus position detection system 21 is used as the reflectance distribution on the wafer W for the center of gravity position. It can be used for calculation. When a diaphragm (vibrator) is used as in the focus position detection system 21, the focus detection signal has a frequency component that is twice the vibration frequency of the vibrator. It can be obtained by detecting.
When the reflectance distribution r(x) is obtained by the above method, the gravity center position c(x) of the reflected light from the focus measurement point AF can be calculated by the following gravity center calculation formula (5).

After the gravity center position c(x) is calculated, the focus error e(x) at the incident angle θ 2 on the wafer surface can be calculated by the following equation (6) based on the focus detection principle.
e(x)=(c(x)×tan θ)/2 (6)
Then, the main control system 20 stores the calculated focus error e(x) in the storage device 40 in association with the coordinates of the focus measurement point (measurement position of the reflected light intensity on the wafer W).
Next, a procedure for performing focus adjustment on the transfer surface of the wafer W using the above position measuring method will be described with reference to the flowchart shown in FIG.
Note that the focus error measurement is basically performed at all focus measurement points, but in the present embodiment, the focus measurement is actually performed during scanning exposure by synchronous movement, in other words, the wafer W is irradiated. The detection light used for focus measurement at the time of actual exposure is used among the plurality of detection lights. Specifically, among the plurality of detection lights emitted to the focus measurement points AF11 to AF17, AF21 to AF27,..., AF71 to AF77, as shown in FIG. 4B, for convenience, on a shot area (compartment area) SA. The description will be made assuming that the detection light emitted to the focus measurement points AF57, AF54, AF51, AF31, AF34, and AF37 (hereinafter referred to as S1 to S6) arranged in the peripheral portion of the exposure area EF is used.
As the timing for measuring the focus error, it is possible to select the beginning of the lot process, the interval between lot processes, or the like. In the case of performing the process at the beginning of the lot, for example, focus error measurement was performed after EGA processing (enhanced global alignment; see Japanese Patent Application Laid-Open No. 61-44429 and corresponding US Pat. No. 4,780,617), and calculation was performed. The focus error is the correction amount (offset value) for the image plane of the projection optical system PL. When the focus error measurement is performed between lot processes, the wafer to be measured (for example, the wafer in the lot to be exposed next) is taken out and set in the exposure apparatus, and the wafer alignment ( After performing EGA), focus error measurement is performed and the result is stored. Then, when the lot is exposed, the stored information is read out and reflected in the attitude adjustment of the wafer including the focus position. Here, it is assumed that the focus error measurement is performed after the EGA processing.
As shown in FIG. 9, when the EGA process is completed for the wafer at the top of the lot in step ST0, it is first determined whether or not focus error measurement is to be executed (step ST1). If not, the exposure process of step ST10 is executed. Transition. Usually, a plurality of shot areas SA on which the pattern of the reticle R is exposed are divided on the wafer W and arranged in a checkerboard pattern. Therefore, when executing the focus error measurement, the shot area to be measured is selected (step ST2).
Usually, the structure in each shot area on the wafer W is the same, and the process program is also the same, so that a focus error that occurs in one shot area also occurs in another shot area. Therefore, if a shot area that can measure the entire area is selected and measured, the measured focus error can be applied to other shot areas. However, in order to further improve the measurement accuracy, the reflectance distribution may be measured for a plurality of shot areas.
Next, in step ST3, as described above, the reflectance distribution is measured as the distribution information of the surface state of the wafer W using the detection signal of the focus position detection system 21.
Here, in the present embodiment, as described above, the reticle R is detected using the detection light emitted to the focus measurement points S1 to S6 shown in FIG. 4B among the plurality of focus measurement points shown in FIG. 4A. The reflectance distribution is measured for the path where the focus measurement is performed during the synchronous movement of the wafer W and the wafer W. More specifically, in this exposure apparatus, the size and position of the shot area SA to be exposed on the wafer W from the shot map data, and the focus measurement point (outside the exposure area EF) used during scanning exposure from the autofocus algorithm. Since the set measurement point may be included), the measurement position on the wafer W is also known from the signal sampling interval of the focus measurement and the synchronous movement speed (scan speed). FIG. 10 schematically shows a path K on which focus measurement is performed during scanning exposure and measurement positions P11 to P14. In this way, the reflectance distribution is measured not only for the route K on which the focus measurement is performed, but also on the positions P11 to P14 on the wafer W where the focus measurement is performed. The distance between the positions P11 and P14 in FIG. 10 is set to be equal to or less than the width of the shot area on the wafer in the scanning direction (Y direction).
Further, although the positions of the focus measurement points S1 to S6 are precisely adjusted, there is a possibility that minute adjustment errors are included. Of the focus measurement paths (dotted lines with arrows) shown in FIG. 4B, for example, the path shown at the left end can measure the reflectance distribution at only one of the focus measurement points S3 and S4. If the set position of the measurement point includes an error, there is a possibility that the reflectance distribution cannot be accurately measured at the position where the focus measurement is performed. Therefore, in the present embodiment, the reflectance distribution is measured at all the focus measurement points S1 to S6, and the reflectance distribution corresponding to the coordinate position of the wafer W is stored for each measurement point (step ST4).
Subsequently, in step ST5, it is determined whether or not the set number of times of averaging is measured, and steps ST3 and ST4 are repeated until the measurement of a predetermined number of times is completed. In the reflectance distribution measurement, a variation occurs due to the measurement reproducibility. Therefore, in order to reduce the variation due to the averaging effect, the reflectance distribution measurement is performed a plurality of times for one shot area SA. Can be improved. Next, in step ST6, it is determined whether or not the measurement for the selected shot area is completed, and steps ST3 to ST5 are repeated until the measurement is completed.
Then, when all the reflectance distribution measurements for the wafer W are completed, the wafer is calculated for each focus measurement point by performing calculations using the reflectance distribution that has been stored and the above equations (5) and (6). The focus error is calculated corresponding to the coordinate position of the shot area) (step ST7). Then, based on the calculated focus error, a map in which the offset data at the time of scanning exposure is made to correspond to the coordinate position of the focus measurement point is created and stored (step ST8), and the image plane correction value at the time of exposure is created (step ST8). ST), and stores it in the storage device 40. When the series of focus error measurement is completed, the process proceeds to the exposure process (step ST10).
In this exposure process, under the control of the main control system 20, when the reticle R and the wafer W are synchronously moved to transfer the image of the pattern formed on the reticle R onto the transfer surface of the wafer W, the multi-point focus position is adjusted. While measuring the focus position of the transfer surface at the focus measurement point using the detection system 21, the attitude and Z position of the wafer W are controlled according to the shape of the transfer surface of the wafer W calculated above.
Here, for example, when the measurement result of the focus measurement point S3 (see FIG. 4B) is input during the synchronous movement, the main control system 20 measures the focus measurement point S3 among the focus errors stored in the storage device 40. The (focus map) of the selected focus error is selected, and the measurement result is corrected using the selected focus error. That is, the main control system 20 corrects the measurement value input during the synchronous movement using the focus error at the focus measurement point where the measurement value was obtained. As a result, it is possible to eliminate the adjustment error when setting the focus measurement point from the measurement result.
That is, the main control system 20 as a correction device corrects the measurement result of the multipoint focus position detection system 21 by the focus error (offset data) stored in the storage device 40, and uses the corrected measurement value to perform the above-mentioned operation. By performing the arithmetic processing, the tilt angle and the focus position of the wafer surface are calculated. For example, as shown in FIG. 11A, when a wafer having an originally uniform surface position is scanned by the focus measurement point S3 and a low reflection region LR exists between the positions SP1 and SP2, As shown in FIG. 11B, the measurement result (sensing value) at the focus measurement point S3 includes a focus error. Therefore, by correcting the measurement result using the focus error stored in advance, it is possible to obtain surface position information that matches the actual surface position (surface state), as indicated by the chain double-dashed line in the figure.
Then, the main control system 20 can adjust the surface position of the wafer W via the Z tilt θ stage 7 by individually driving the actuators 8 a to 8 c based on the obtained results. At this time, the main control system 20 uses the focus error corresponding to this measurement point for the measurement result of the multipoint focus position detection system 21. At this time, the position on the wafer at which the focus position is actually measured at the focus measurement point (actual measurement position) matches the position on the wafer corresponding to the stored focus error (error measurement position). If the actual measurement position and the error measurement position do not match, the focus error at the position closest to the actual measurement position is used, or if the actual measurement position is close to the actual measurement position 2 The focus error of the actual measurement position is calculated by interpolation using the focus error of the point, and the correction is performed based on the obtained focus error. A detailed method of calculating the tilt angle and the focus position of the wafer surface is disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-270498, Japanese Patent Application Laid-Open No. 9-82636, and corresponding US Pat. No. 6,080,517. It is omitted here.
When the scanning exposure of one shot area SA is completed, the wafer W is moved in steps to start scanning exposure of the next shot area SA. After that, when the pattern of the reticle R is transferred to all the shot areas on the wafer W by repeatedly performing the scanning exposure and the step movement, the exposure processing of the wafer W is completed.
As described above, in the present embodiment, the reflectance distribution measured at different positions on the wafer W (shot region) in the scanning direction (Y direction) corresponding to the focus measurement points used in the scanning exposure in advance. Since the focus error is calculated from the focus position on the wafer W, the error component resulting from the reflectance distribution can be eliminated/corrected when the focus position is measured on the wafer W, and the surface position of the wafer W can be easily projected by the projection optical system. It is possible to position on the image plane of the system PL. Therefore, in the present embodiment, even when a projection optical system having a shallow depth of focus is used, it is possible to realize high-resolution exposure processing by accurate focus adjustment.
In particular, in the present embodiment, since the focus error is measured based on the intensity of the detection signal when the detection light is received in the focus measurement, it is not necessary to separately install a device for measuring the reflectance distribution, and the size of the device can be reduced. This can contribute to cost reduction and price reduction. Further, in the present embodiment, the focus error is measured in advance for the path where the focus measurement is performed during the synchronous movement of the reticle R and the wafer W (during actual exposure), so the time required for the focus error measurement is shortened. It is possible to contribute to the improvement of production efficiency. Further, in the present embodiment, the focus error is measured for each of the plurality of focus measurement points, and the map is created and stored for each measurement point. Therefore, the focus measurement point for performing the focus measurement during the synchronous movement ( By performing correction based on the results obtained with the detection light used when performing focus measurement, it is possible to eliminate the adverse effects of adjustment errors when setting the position of the focus measurement point, and perform more accurate focus adjustment. it can.
In the above embodiment, as shown in FIG. 8A, when measuring the reflectance distribution r(x), the focus measurement point AF and the measurement points AFL and AFR at positions spaced apart from this measurement point AF are provided. 8B, the intensity of the reflected light is measured. However, as shown in FIG. 8B, in addition to the focus measurement point AF, the detection lights are reflected at a plurality of points (with a pitch smaller than the slit width in the focus measurement direction) overlapping each other. It may be configured to measure the intensity of light. At this time, for example, by moving the wafer W in the focus measurement direction with respect to the focus measurement point AF, the intensity of the reflected light is measured at each of a plurality of points including the measurement point AF in FIG. 8B. In this case, if a more microscopic reflectance distribution can be obtained and, for example, a component in which the reflected light intensity distribution has a quadratic change can be calculated by the least-squares approximation method, the reflectance distribution r(x ) Can be used as a second order to calculate the above-described light amount center of gravity.
In addition, when the reflected light intensity distribution is measured at a plurality of points where the detection lights overlap with each other, the measurement interval is small, and therefore the gravity center is calculated using the following formula (7) without performing the integration process like the formula (5). You may implement.

i; reflected light intensity at the reflected light intensity measurement point xi
Further, in the above-mentioned embodiment, although the synchronous movement direction is not particularly mentioned, there is actually a gap between the timing at which the coordinate position is obtained by the interferometer and the like and the timing at which the attitude and the Z position of the wafer W are controlled. May occur. In such a case, the measurement result of the reflectance distribution may differ depending on the synchronous movement direction. Therefore, when measuring the reflectance distribution and the focus error, a map of the reflectance distribution and the focus error corresponding to the coordinate position for each synchronous movement direction is created in the same way as the map is created for each focus measurement point. It is preferable to store a map and call a map corresponding to the synchronous movement direction at the time of focus adjustment, and correct the focus measurement value using the offset value included in this map. In this embodiment, the reflectance distribution is measured at a plurality of positions (four in this example) discretely set on the path K parallel to the scanning direction (Y direction) in the shot area. The number of measurement positions of the reflectance distribution on the path K may be arbitrary, and for example, by moving the wafer in the scanning direction at substantially the same pitch as the width of the slit image AF in the scanning direction, the shot in the scanning direction is shot. The reflectance distribution may be measured over almost the entire area.
Next, another embodiment of the present invention will be described.
In the above embodiment, the reflectance distribution of the wafer surface is calculated and measured by receiving the reflected light of the detection light related to the focus measurement, but the surface shape of the wafer W is actually measured in advance and the result is used. It is also possible to obtain a focus error distribution caused by the reflectance distribution. Also in the following measurement method, in order to improve the measurement accuracy, it is preferable to perform averaging by a plurality of measurements within a single shot area, a plurality of shot areas, each synchronous movement direction, and the like.
For example, as shown in FIG. 12, the surface shape of the wafer W is measured using the focus position detection system 21 described above (step ST11), and the measured surface shape and the focus position detection system 21 such as the capacitance sensor are It is also possible to set the offset value as the focus error due to the reflectance distribution, which is the difference from the surface shape measured in advance using a different measuring device (step ST12). In this case, if the focus measurement result is corrected using the set offset value (step ST13), the error component caused by the reflectance distribution can be eliminated as in the above embodiment.
Further, in recent device manufacturing processes, a planarization process is often provided by the above-described CMP. For a wafer whose surface shape can be regarded as flat by this process, the planarization process is performed as shown in FIG. After performing (step ST21), when performing focus measurement using the focus position detection system 21 (step ST22), this measurement value (position information, surface position information) can also be set as a focus error ( Step ST23). In this case, since the flatness of the wafer is not actually measured, if the wafer is not flat, the focus error distribution will include an error. However, since the flatness of the wafer at the time of measurement can be roughly understood from the flatness of the wafer holder and the grade of the wafer itself, a threshold value corresponding to the flatness is set and the focus measurement result changes more than the threshold value. If is included, the correction may be performed assuming that a focus error due to the reflectance distribution exists. Note that, for example, the flatness of the wafer may be measured in advance, and the focus error distribution calculated previously may be corrected using the measured flatness. Further, when performing focus measurement using the focus position detection system 21, if the shot area to be measured is inclined with respect to a predetermined reference plane (for example, the image plane of the projection optical system PL), The calculated focus error distribution includes an error caused by the tendency. Therefore, for example, it is preferable to set the shot area substantially parallel to the reference plane prior to focus measurement, or to subtract the error due to the inclination from the focus error distribution.
Also regarding the attitude control of the wafer, the allowable value of the tilt can be set in consideration of the depth of focus of the projection optical system PL. Therefore, when this allowable value is set as a threshold value and the tilt of the wafer W during focus adjustment is calculated from the measurement result of the focus position detection system 21, if the threshold value is exceeded, the focus position detection system 21 It is also possible to consider that the measurement result of 1) includes an error component due to the reflectance distribution and perform a correction procedure.
In the above-mentioned Japanese Patent Laid-Open No. 2002-270498, the step information in the shot area SA is measured in advance, and the focus adjustment (focusing operation) mode at the time of the exposure processing is selected from a plurality of modes according to the state. Techniques for selecting are disclosed.
Also in the present embodiment, by applying the above technique, the step state is also measured at the time of measuring the reflectance distribution in the shot area (at the time of measuring the reflectance map), and the focus/leveling according to the step in the shot area is performed. A correction map may be created. The focus/leveling correction map may be stored in the storage device 40, similarly to the map based on the focus error generated by the reflectance distribution described above (hereinafter, reflectance map). The reflectance map and the focus/leveling correction map are preferably created and stored for each synchronous movement direction (scan direction; +Y direction and −Y direction) when the shot area is exposed. Since the focus/leveling correction map contains a focus error caused by the reflectance distribution, the true focus can be obtained by subtracting the reflectance map value from the focus/leveling correction map value at each focus measurement point.・A leveling correction map will be obtained. At the time of exposure, focus/leveling correction is performed based on the map of this true value.
Further, the shot area existing in the wafer W is a normal shot area, an edge shot that partially covers the peripheral edge of the wafer, a TEG shot that is a dummy shot for various measurements, and the like. There are a plurality of types of shot areas having different values. Therefore, it is preferable to create and store a reflectance map and a focus/leveling correction map for each type of wafer in which a plurality of types of shot areas exist.
From the above, the number of each of the reflectance map and the focus/leveling correction map that can be stored in the exposure apparatus corresponds to the process program, for example, eight types of shot areas, which are synchronous movement directions (scanning directions). ), there are two types each, so that there are a total of 8 pairs (16 pieces). This number can be further increased according to the type of shot area.
In addition, when performing exposure processing on the shot area, correction is performed according to each of the reflectance map and the focus/leveling correction map, but as a control mode of the focusing operation according to the focus/leveling correction map. Is, for example, the first mode in which the height position of the wafer holder 6 is controlled so that the middle part of the step matches the in-focus surface, and the focus position detection system 21 is used for the step part exceeding a predetermined allowable value. It is considered that the second mode is not performed. Then, it is preferable that the operator can switch and set these modes as appropriate.
In the above embodiment, the focus position detection system 21 has been described as a configuration using a vibrator, but the present invention is not limited to this. For example, an image processing method using a CCD, a method using a polarization modulator, etc. A method of measuring the focus position (and reflectance distribution) by another detection principle may be used.
Further, in each of the above-described embodiments, the wafer W is moved at the time of focus adjustment so that the wafer surface substantially coincides with the image plane of the projection optical system PL in the above-described exposure area EF. However, instead of moving the wafer, Alternatively, or in combination therewith, the imaging plane of the projection optical system PL may be moved by driving at least one optical element of the projection optical system PL, for example.
Furthermore, in each of the above-described embodiments, the above-described focus error is obtained using the multipoint focus position detection system 21 arranged at the exposure position where the pattern of the reticle R is transferred via the projection optical system PL. For example, two independently movable wafer stages are provided, and the wafer stage is arranged at each of the exposure position and the measurement position (alignment position) where mark detection is performed by the wafer alignment system, so that the exposure operation and the measurement operation are performed substantially. The present invention may be applied to an exposure apparatus that can be executed in parallel, and the above-mentioned focus error may be obtained using a detection system arranged at the measurement position. Here, as the detection system arranged at the measurement position, for example, a system having the same configuration as the above-mentioned multipoint focus position detection system 21 can be used.
In this twin wafer stage type exposure apparatus, the above-described reflectance distribution and focus position are measured at the measurement position using the detection system, and the measurement is performed based on the focus error obtained from the reflectance distribution. In the exposure process of the wafer which is corrected from the focus position and transferred from the measurement position to the exposure position, focus adjustment is performed using the corrected focus position. At this time, it is not necessary to provide the above-mentioned multi-point focus position detection system 21 at the exposure position. For example, the projection optical system PL (or a pedestal that holds it) and the wafer stage (for example, the Z tilt θ stage 7) The Z tilt θ stage 7 may be driven by using an interferometer that measures the distance in the Z axis direction. It is also possible to measure only the reflectance distribution at the measurement position, correct the focus position measured at the exposure position using the focus error obtained from the reflectance distribution, and execute the exposure process. Further, in the wafer subjected to the flattening process as described above, the focus position is measured at the measurement position by using the detection system, and the measurement result is directly used as the focus error and transferred from the measurement position to the exposure position. In the wafer exposure process, focus adjustment is performed using the focus error. Since the twin wafer stage type exposure apparatus can measure the above-mentioned reflectance distribution or focus position in parallel with the exposure operation, it does not reduce the throughput of the exposure apparatus and can perform the above-mentioned multiple measurements. That is, it is possible to improve the accuracy of focus adjustment.
This twin wafer stage type exposure apparatus is disclosed, for example, in Japanese Patent Application Laid-Open No. 10-214783 and corresponding US Pat. No. 6,341,007, or International Publication WO98/40791 and corresponding US Pat. No. 796, etc., and as long as the domestic laws of the designated country designated in this international application or the selected elected country permit, the disclosure of the U.S. patent is incorporated by reference and made a part of the description of the present specification.
In the above embodiment, the multipoint focus position detection system 21 is used to measure the reflectance distribution of the wafer. However, a sensor (detection system) different from the multipoint focus position detection system or an exposure apparatus is provided. The reflectance distribution may be measured using a measuring device or the like, and the focus error described above may be calculated based on the measured reflectance distribution.
As the substrate of the present embodiment, not only the semiconductor wafer W for manufacturing a semiconductor device but also a glass substrate for a display device, a ceramic wafer for a thin film magnetic head, or an original mask or reticle used in an exposure apparatus. (Synthetic quartz, silicon wafer) or the like is applied.
As the exposure apparatus, in addition to a step-and-scan type scanning exposure apparatus (scanning stepper; USP 5,473,410) for synchronously moving the reticle R and the wafer W to scan and expose the pattern of the reticle R, The present invention can also be applied to a step-and-repeat type projection exposure apparatus (stepper) that exposes the pattern of the reticle R while the reticle R and the wafer W are stationary and sequentially moves the wafer W. The present invention can also be applied to a step-and-stitch type exposure apparatus that transfers at least two patterns on the wafer W by partially overlapping them. Furthermore, the present invention is also applicable to a mirror projection aligner, such as an immersion exposure apparatus disclosed in International Publication WO99/49504, in which a liquid (for example, pure water) is filled between the projection optical system PL and a wafer. Applicable.
The type of exposure apparatus is not limited to an exposure apparatus for manufacturing a semiconductor element that exposes a semiconductor element pattern on a wafer W, and an exposure apparatus for manufacturing a liquid crystal display element or a display, a thin film magnetic head, an image sensor (CCD). Alternatively, it can be widely applied to an exposure apparatus for manufacturing a reticle or a mask.
In addition, as a light source of exposure light, bright lines (g line (436 nm), h line (404.nm), i line (365 nm)) generated from an ultra-high pressure mercury lamp, KrF excimer laser (248 nm), ArF excimer laser (193 nm) ), F _Two Laser (157nm), Ar _Two Not only a laser (126 nm) but also an X-ray, or a charged particle beam such as an electron beam or an ion beam can be used. For example, when an electron beam is used, thermionic emission type lanthanum hexaboride (LaB) is used as an electron gun. ₆ ) And tantalum (Ta) can be used. Further, a harmonic wave of a YAG laser or a semiconductor laser may be used.
For example, a single-wavelength laser in the infrared region or visible region emitted from a DFB semiconductor laser or a fiber laser is amplified by a fiber amplifier doped with erbium (or both erbium and ytterbium), and a nonlinear optical crystal is used. The exposure light may be a harmonic wave whose wavelength is converted to ultraviolet light. When the oscillation wavelength of the single-wavelength laser is within the range of 1.544 to 1.553 μm, an 8th harmonic within the range of 193 to 194 nm, that is, ultraviolet light having substantially the same wavelength as the ArF excimer laser is obtained. , If the oscillation wavelength is within the range of 1.57 to 1.58 μm, the 10th harmonic within the range of 157 to 158 nm, that is, F _Two Ultraviolet light having almost the same wavelength as the laser can be obtained.
Further, EUV (Extreme Ultra Violet) light having a wavelength of about 5 to 50 nm generated from a laser plasma light source or SOR, for example, a wavelength of 13.4 nm or 11.5 nm may be used as the exposure light. The exposure apparatus uses a reflective reticle, and the projection optical system is a reduction system including only a plurality of (for example, about 3 to 6) reflective optical elements (mirrors).
The projection optical system PL may be not only a reduction system but also a unity magnification system or an enlargement system. Moreover, the projection optical system PL may be any of a refraction system, a reflection system, and a catadioptric system. When the wavelength of the exposure light is about 200 nm or less, it is desirable to purge the optical path through which the exposure light passes with a gas (inert gas such as nitrogen or helium) that absorbs the exposure light little. When an electron beam is used, an electron optical system including an electron lens and a deflector may be used as the optical system. Needless to say, the optical path through which the electron beam passes is in a vacuum state.
When a linear motor (see USP 5,623,853 or USP 5,528,118) is used for the wafer stage or reticle stage, either an air levitation type using an air bearing or a magnetic levitation type using Lorentz force or reactance force is used. You may use. Further, each stage may be of a type that moves along a guide, or may be a guideless type that does not have a guide.
As a drive mechanism for each stage, a plane motor may be used in which a magnet unit having a two-dimensionally arranged magnet and an armature unit having a two-dimensionally arranged coil are opposed to each other and each stage is driven by an electromagnetic force. In this case, one of the magnet unit and the armature unit may be connected to the stage, and the other of the magnet unit and the armature unit may be provided on the moving surface side of the stage.
The reaction force generated by the movement of the wafer stage is not transmitted to the projection optical system PL, and mechanically using a frame member as described in JP-A-8-166475 (USP 5,528,118). You may let it escape to the floor (ground).
The reaction force generated by the movement of the reticle stage 2 is prevented from being transmitted to the projection optical system PL, and as described in Japanese Patent Application Laid-Open No. 8-330224 (USP 5,874,820), a machine member using a frame member is used. You may let it escape to the floor (ground).
As described above, the exposure apparatus of the embodiment of the present application, various subsystems including the respective components recited in the claims of the present application, in order to maintain predetermined mechanical accuracy, electrical accuracy, and optical accuracy, Manufactured by assembling. Before and after this assembly, adjustments to achieve optical precision for various optical systems, adjustments to achieve mechanical precision for various mechanical systems, and various electrical systems to ensure these various types of precision are made. Is adjusted to achieve electrical accuracy. The process of assembling the exposure apparatus from various subsystems includes mechanical connection, electrical circuit wiring connection, pneumatic circuit piping connection, and the like between the various subsystems. It goes without saying that there is an individual assembly process for each subsystem before the assembly process for the exposure apparatus from these various subsystems. When the process of assembling the various subsystems into the exposure apparatus is completed, comprehensive adjustments are performed to ensure the various accuracies of the exposure apparatus as a whole. It is desirable that the exposure apparatus be manufactured in a clean room where the temperature and cleanliness are controlled.
For a microdevice such as a semiconductor device, as shown in FIG. 14, step 201 of designing the function/performance of the microdevice, step 202 of manufacturing a mask (reticle) based on this design step, and manufacturing of a wafer from a silicon material. Step 203, exposure processing step 204 for exposing the reticle pattern onto the wafer by the exposure apparatus of the above-described embodiment, device assembly step (including dicing step, bonding step, package step) 205, inspection step 206, etc. .

  As described above, in the present invention, when measuring the position information of the substrate, the error component due to the reflectance distribution can be eliminated and corrected, and the surface position of the substrate can be easily imaged by the projection optical system. It becomes possible to position on the surface. Therefore, according to the present invention, even when a projection optical system having a shallow depth of focus is used, it is possible to realize a high-resolution exposure process through accurate focus adjustment.

Claims (21)

A position measuring method of irradiating a measurement point on a substrate with detection light, receiving reflected light reflected at the measurement point, and measuring position information in a normal direction of the substrate surface,
Measuring an error component of the position information caused by the reflectance distribution of the detection light at the measurement location on the substrate;
Correcting the position information in the normal direction based on the measured error component. The position measuring method according to claim 1,
The position measuring method further comprising calculating the error component based on the intensity of a detection signal obtained when the detection light is received. The position measuring method according to claim 2,
A position measuring method for calculating the error component based on the intensity distribution of the detection signal at a plurality of points along the measurement direction of the detection light on the surface of the substrate. The position measuring method according to claim 3, wherein the detection lights overlap each other at the plurality of points. The position measuring method according to claim 1,
Measuring the surface shape of the substrate,
And a step of obtaining the error component based on a result of comparing the measured surface shape with a designed surface shape. The position measuring method according to claim 1,
Planarizing the surface of the substrate,
Measuring the position information of the substrate surface using the detection light,
And a step of setting the measured position information as the error component. The position measuring method according to claim 6,
Calculating a posture of the substrate based on the measured position information,
And a step of correcting the posture based on a result of comparing the calculated posture with a predetermined threshold value. The position measuring method according to any one of claims 1 to 7,
Irradiate each of the plurality of detection light to a plurality of measurement points on the substrate,
A position measuring method for measuring the error component at each of the plurality of measurement points. In the exposure method of exposing the pattern of the mask to the substrate by the exposure light,
An exposure method for measuring the position information by the position measuring method according to claim 1, and adjusting the surface position of the substrate based on the measurement result. The exposure method according to claim 9,
Storing the error component before the exposure,
Exposing the substrate while synchronously moving the mask and the substrate;
An exposure method comprising: driving the substrate based on the position information detected during the synchronous movement and the stored error component. The exposure method according to claim 10,
An exposure method for setting a measurement position of the error component based on a detection position on the substrate that detects the position information during the synchronous movement. The exposure method according to claim 11,
An exposure method for measuring the error component using a detection light for measuring the position information during the synchronous movement among a plurality of detection lights for measuring the position information. The exposure method according to any one of claims 10 to 12,
An exposure method for storing the error component for each of the plurality of synchronous movement directions. A position measuring device that irradiates a measurement point on a substrate, receives reflected light reflected at the measurement point, and measures position information in the normal direction of the substrate surface,
A storage device that stores an error component of the position information generated by the reflectance distribution of the detection light at the measurement location on the substrate,
A position measurement device having a correction device that corrects position information in the normal direction based on the stored error component. In an exposure apparatus that exposes a mask pattern onto a substrate with exposure light,
An exposure apparatus using the position measuring device according to claim 14 as a device for measuring the surface position information of the substrate. The exposure apparatus according to claim 15,
An exposure apparatus having a control device that drives the substrate based on the corrected position information and simultaneously moves the mask and the substrate to expose the pattern to the substrate. In an exposure apparatus that projects the pattern of the mask onto a plurality of partitioned areas on the substrate by synchronously moving the mask and the substrate,
A surface position detection device that detects the surface position of the substrate during the synchronous movement by irradiating the substrate with detection light and detecting the reflected light thereof,
A storage device that stores distribution information of the surface state in the partitioned area on the substrate according to the synchronous movement direction,
An exposure apparatus comprising: a control device that sets a surface position of the substrate based on a detection result of the surface position detection device and distribution information stored in the storage device. The exposure apparatus according to claim 17,
The exposure apparatus, wherein the surface condition in the partitioned area is one of a reflectance of the detection light in the partitioned area and a step existing in the partitioned area. The exposure apparatus according to claim 17 or 18,
The said memory|storage device is an exposure apparatus which memorize|stores the distribution information of the said surface state in each of several types of division area which exists in several board|substrates which have the same process program. An exposure method for synchronously moving a mask and a substrate to transfer the pattern of the mask onto the substrate through a projection optical system,
Measuring the error component caused by the reflectance distribution of the substrate when receiving the reflected light of the detection light irradiated on the substrate and measuring the position information in the normal direction of the substrate; ,
An exposure method comprising the step of adjusting the positional relationship between the image plane of the projection optical system and the substrate using the measured error component during the synchronous movement. An exposure apparatus for synchronously moving a mask and a substrate to transfer a mask pattern onto a substrate via a projection optical system,
A position detection system that receives reflected light of detection light irradiated on the substrate and measures position information in the normal direction of the substrate,
An adjusting device that adjusts the positional relationship between the image plane of the projection optical system and the substrate by using an error component caused by the reflectance distribution of the substrate when the position detection system measures the position information. Exposure equipment.

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