The present invention relates generally to an exposure method and apparatus that exposes a pattern of a reticle (mask) onto a plate to be exposed, such as a wafer, and more particularly to a detection of a surface form of the reticle. The present invention is suitable, for example, for a scanning type projection exposure apparatus that synchronously scans the reticle and the wafer to a projection optical system.
The photolithography technology for manufacturing fine semiconductor devices, such as semiconductor memory and logic circuits, has conventionally employed a reduction projection exposure apparatus that uses a projection optical system to project and transfer a reticle pattern onto a plate to be exposed. A numerical aperture (NA) of the projection optical system has recently been further higher. As a result, a focal depth has been further smaller. Then, an imaging error (a defocus or a distortion error) cannot be disregarded, and it is necessary to detect a surface form (a surface position or a deformation) of the reticle and corrects a focus based on a detection result. Especially, an exposure apparatus in a step-and-scan manner (hereafter, “a scanner”) that exposures the reticle pattern onto the plate while synchronously scanning the reticle and the plate needs a focus correction during scanning exposure.
It is necessary to measure the surface form of the reticle actually mounted in the exposure apparatus to correctly measure a deformation amount of the reticle. Therefore, a conventional detecting system irradiates a detection light to a pattern surface of the reticle (a grazing incidence method), receives a reflected light from the pattern surface, and measures the surface form of the reticle. The detecting system measures the surface form of the reticle at a predetermined timing (for example, a predetermined time interval, one or plural shots, wafer or lot).
As conventional technology, for example, there are Japanese Patent Application, Publication No. 6-36987, Japanese Patent Application, Publication No. 10-214780, Japanese Patent Application, Publication No. 11-26345, and Japanese Patent Application, Publication No. 2003-264136. Moreover, as conventional technology, for example, there are Japanese Patent Application, Publication No. 2003-297726, Japanese Patent Application, Publication No. 2005-085991, and Japanese Patent Application, Publication No. 2003-273008.
However, an influence of the reticle pattern cannot be disregarded according to a demand of further highly precision for the detecting system. For example, when the reticle is made of a glass substrate and the pattern is formed by chromium, a reflectivity in a pattern area (chromium) for the detection light is different from a reflectivity in a non-pattern area (glass substrate) for the detection light. When the detection light is irradiated a boundary between the pattern area and the non-pattern area as shown in
It is difficult to increase the number of measurement points in a scanning direction, maintaining a scan speed and a processing speed of a measurement result. On the other hand, if the scan speed and the processing speed of a measurement result are delayed and the number of measurement points in the scanning direction is increased, a throughput decreases. If the reticle is moved in the scanning direction at a specific pitch and a still measurement is executed to the entire reticle pattern in the position, the error measurement position is manifested. However, this method causes the decrease of throughput similarly.
Accordingly, the present invention is directed to an exposure method and apparatus that correctly detect a surface form of a reticle without causing a decrease of throughput.
An exposure method of one aspect of the present invention for exposing a pattern of a reticle onto a plate, via a projection optical system, while synchronously scanning the reticle and the plate, said exposure method includes the steps of obtaining surface form data that shows a surface form of the reticle, and controlling synchronous scanning of the reticle and the plate based on the surface form data, wherein said surface form obtaining step includes the steps of detecting a measurement position having an abnormal measurement result as an error measurement position among measurement positions to measure the surface form of the reticle, and measuring the surface form of the reticle at a scan speed used for exposure, and wherein said controlling step uses, as the surface form data, a measurement result of the measuring step that excludes a measurement result with the error measurement position.
An exposure apparatus according to another aspect of the present invention for exposing a pattern of a reticle onto a plate, via a projection optical system, while synchronously scanning the reticle and the plate, said exposure apparatus includes a detecting system for detecting a position of the reticle in an optical axis of the projection optical system, and a controller for controlling synchronous scanning of the reticle and the plate based on a detection result of the detecting system, wherein said detecting system includes a first mode for detecting plural measurement positions of the reticle at a scan speed used for exposure, and a second mode for measuring a surface form of the reticle more fully than the first mode.
Other objects and further features of the present invention will become readily apparent from the following description of the preferred embodiments with reference to the accompanying drawings.
Hereafter, referring to
The light source section 12 uses, for example, ArF excimer laser with a wavelength of approximately 193 [nm], KrF excimer laser with a wavelength of approximately 248 [nm], and F2 laser with a wavelength of approximately 157 [nm]. The kind and the number of laser are not limited.
The illumination optical system 20 is an optical system that illuminates the reticle 30, and includes a lens, a mirror, an optical integrator, a stop, and the like, for example, a condenser lens, an optical integrator (a fly-eye lens), an aperture stop, a condenser lens, a slit, and an image-forming optical system in this order. The optical integrator may include a fly-eye lens or an integrator formed by stacking two sets of cylindrical lens array plates (or lenticular lenses), and can be replaced with an optical rod or a diffractive element.
The reticle 30 forms a circuit pattern (or an image) to be transferred. Diffracted light emitted from the reticle 30 passes through the projection optical system 50 and is then projected onto a wafer 60. The reticle 30 and the wafer 60 are located in an optically conjugate relationship. Since the exposure apparatus 100 is a scanner, the reticle 30 and the wafer 60 are synchronously scanned at the speed ratio of the reduction ratio of the projection optical system 50, thus transferring the pattern from the reticle 30 to the wafer 60.
The reticle 30 is mounted on a moving part of the reticle stage 36. The reticle stage 36 supports the reticle 30 via a reticle holder (not shown) and drives the reticle 30. The reticle stage 36 is scanned by a liner motor (not shown). A pellicle 32 is provided in a bottom surface via a metal frame 34.
In
The detecting system 40 detects a surface form of the reticle 30 and is included in a fixing part of the reticle stage 36. The detecting system 40 has the same structure and the same function as a focus sensor in grazing incident method that accord a target exposed plane of the wafer 30 with an imaging plane of the projection optical system 50, and includes a light irradiating part and a light detector. The light irradiating part includes, as main elements, a light source for detection 41 such as a light emitting diode, a slit for a projection mark 42, and a projection lens 43. The light detector includes, as main elements, a receiver lens 44 and a detector 45 such as a CCD sensor. Each member that constitutes the detecting part 40 may use any structure known in the air, thus, a detailed description is omitted.
The detecting part 40 has two modes. A first mode is a mode that detects plural measurement positions of the reticle 30 at a scan speed used for exposure. A second mode measures the surface form of the reticle 30 more fully than the first mode, and is a preliminary mode to the first mode. The detecting system 40 executes the second mode and, next, executes the first mode described later.
When the detecting system 40 detects surface positions of the entire pattern surface of the reticle 30, the moving part of the reticle stage 36 is scanned similar to scan projection exposure. Moreover, the detecting system 40 can irradiate three or more detection lights 41a to 41c in the orthogonal direction to the paper surface and detects surface positions using those detection lights. An inclination and surface position precision of the reticle 30 can be improved by using three or more detection lights. Sihce the detecting system 40 is included in the fixing part of the reticle stage 36, it can easily adjust a correlation at a unit assembly, can reduce timely change, and can detect the surface position of the reticle 30 with high precision.
The pattern surface detection position of the reticle 30 detected by the detecting system 40 preferably provide a position that almost accord with a projected position by the projection optical system 50. In other words, an optical axis of the projection optical system 50 and the detection light from the detecting system 40 preferably intersect on the pattern surface of the reticle 30 in
The projection optical system 50 exposes the reticle pattern illuminated by the exposure light from the illumination optical system 20 onto the wafer 60 at a predetermined magnification (for example, ¼ or ⅕). The projection optical system 50 may use a dioptric system comprising solely of a plurality of lens elements, a catadioptic optical system including a plurality of lens elements and at least one concave mirror, and a catoptric system comprising solely of a plurality of mirror elements.
The wafer 60 is a plate to be exposed. The plate is a liquid crystal substrate in another embodiment. Photoresist is applied to the wafer 60. The wafer 60 is mounted on the wafer stage 62 that can drive the wafer 60 in the XYZ and inclination directions so that exposure of the entire wafer, scan exposure and focus correction may be possible. The wafer stage 62 may use any structure known in the art, thus, a detailed description of its structure and operation is omitted. The wafer stage 62 may use, for example, a linear motor to move the wafer 60. The reticle 30 and wafer 60 are, for example, synchronously scanned, and the positions of the reticle stage 36 and the wafer stage 62 are monitored, for example, by a laser interferometer and the like, so that both are driven at a constant speed ratio. The wafer stage 62 is installed on a stage stool supported on the floor and the like, for example, via a dampener.
The controller 70 controls each part and executes an exposure method shown in
First, a detection result of an error measurement position is obtained from the detecting system 40 (step 1002). This step corresponds to the second mode of the detecting system 40 described later. Concretely, the step 1002 includes the steps of obtaining detail data of the reticle surface form and discriminating the error measurement position based on the data. The obtaining method of detail data of the reticle surface form is described later with reference to
Next, the detection result of the reticle surface form is obtained from the detecting system 40 (step 1004). This step corresponds to the first mode of the detecting system 40 described later. The step 1004 is a conventional detection operation of the reticle surface form by the detecting system 40. The number of measurement point must be maintained to a predetermined number to maintain the scan speed and the processing speed of the measurement result.
Finally, synchronous scanning of the reticle 30 and wafer 60 is controlled based on the detection result of the reticle surface form that excludes the detection result of the error measurement position (step 1006). The detection result of the reticle surface form that excludes the detection result of the error measurement position (surface form data) may be the same time with the step 1004 or between the step 1004 and the step 1006. In other words, if the error measurement position detected by the step 1002 is removed from measurement positions before the step 1004, the detection result of the step 1004 becomes the surface form data. On the other hand, if the error measurement position detected by the step 1002 is not removed from measurement positions before the step 1004, a result removed the detection result of the step 1002 from the detection result of the step 1004 becomes the surface form data.
In the step 1006, a main correcting part that controls synchronous scanning corrects the scan position of the wafer stage 62, in other words, a position in a height direction or inclination according to the surface form. Moreover, the correcting part may corrects the imaging plane form to a form corresponding to the surface form of the reticle pattern surface by driving the optical element in the projection optical system 50, or may corrects the reticle surface form itself.
A description will be given of the obtaining method of detail data of the reticle surface form in the step 1002. The second mode of the detecting system 40 is a mode that detects, as the error measurement position, the measurement position including an abnormal measurement result. In the detecting system 40, the detection light from the light source 41 is grazing incident upon the reticle surface shown with a broken line, and the reflected light is incident upon the detector 45 as shown in
However, as shown in
Here, the second mode in the instant embodiment moves the reticle stage 36 at regular step intervals along the scanning direction, and executes the still measurement at the position. This operation is executed to the entire reticle surface position measurement area, and the error measurement position is manifested. In this case, the controller 70 controls the reticle stage 36 so that the reticle 30 is still whenever stepping the reticle 30 in the scanning direction.
The controller 70 generates the surface form data from the detection result by the detecting system 40 of the first mode that excludes the measurement result of the error measurement position (in other words, the detection result of the second mode) by storing the error measurement position in the memory 72. Moreover, the controller 70 controls synchronous scanning of the reticle 30 and wafer 60 based on the surface form data. When the surface form data is generated, the detection result of the second mode is removed from the detection result of the first mode or the measurement point of the error measurement position is not used as the measurement point of the first mode.
Referring to
Next, a description will be given of the discriminating method of the error measurement position by the controller 70 in the step 1002.
A first method averages, as shown in
A second method obtains, as shown in
In the first mode, the detecting system 40 measures the surface form of the entire reticle 30 by scanning the reticle 30 before exposure. At this time, the error measurement position detected in the second mode is not measured in the first mode, or even if the error measurement position detected in the second mode is measured, a measurement value is removed. The reticle stage 36 has a function that scans the reticle 30 at scan exposure and a function that scans the reticle 30 at detection of the reticle-surface position, and achieves the miniaturization of the apparatus and the simplification of structure. Since the detecting system 40 is a part of the reticle stage 36, the detecting system 40 is stabilized to the reticle scan and highly precision reticle surface position detection is achieved.
Moreover, the reticle pattern surface detection position detected by the detecting system 40 is arranged to approximately accord a position projected by the projection optical system 50. Thereby, the scan range of the reticle stage 36 can be the minimum, the simplification of the structure of the reticle stage 36 and the miniaturization of the apparatus are achieved, and the highly precision reticle surface position detection and highly precision scan projection exposure according to the reticle surface position detection are achieved.
The surface form detected by the detecting system 40 in the first and second mode is stored in the memory 72, and the operation part 74 calculates the approximate surface of the entire reticle 30. The deformation information in the scanning direction is sent to the wafer stage 62, and the wafer stage 62 is corrected so that the focus drive amount in scan exposure becomes the optimal. When it is judged that there is a trouble in the imaging performance of exposure based on the measurement result of the surface form of the reticle, the detecting system 40 send a signal to the reticle stage 36 through the controller 70 and has a function as a caution part that recommends an exchange and re-installation of the reticle.
In exposure, the light emitted from the light source section 10 is incident upon the illumination optical system 20 and uniformly illuminates the reticle 30. The image of the pattern formed on the reticle 30 is projected onto the wafer 60 through the projection optical system 50. One shot is exposed by relatively scanning the reticle 30 and the wafer 60 in the orthogonal direction to the paper surface. In other words, the surface position of the reticle 30 is detected by irradiating the detection light to the pattern surface of the reticle 30 from the light irradiation part and detecting the reflected light at the light detector. The controller 70 controls synchronous scanning for the deformation of the reticle 30 based on the surface form of the reticle 30. Therefore, the exposure apparatus 100 transfers the pattern onto the resist with high precision and provide high-quality devices (such as semiconductor devices, LCD devices, photographing devices (such as CCDs, etc.), thin film magnetic heads, and the like).
Referring now to
Furthermore, the present invention is not limited to these preferred embodiments and various variations and modifications may be made without departing from the scope of the present invention.
This application claims a foreign priority benefit based on Japanese Patent Application No. 2005-162718, filed on Jun. 2, 2005, which is hereby incorporated by reference herein in its entirety as if fully set forth herein.
Number | Date | Country | Kind |
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2005-162718 | Jun 2005 | JP | national |