# Patent

## Title
Exposure apparatus and exposure method thereof

## Abstract

An exposure apparatus is provided for performing an unidirectional scan-exposure. The exposure apparatus includes a base and a wafer stage group having a plurality of wafer stages on the base for holding wafers and successively moving from a first position to a second position of the base cyclically. The exposure apparatus also includes an alignment detection unit above the first position for detecting wafer stage fiducials at the first position and alignment marks on a wafer on the wafer stage to align the wafer. Further, the exposure apparatus includes a reticle stage on the second position for loading a cylindrical reticle and causing the cylindrical reticle to rotate around the center axis of the reticle stage and an optical projection unit between the reticle stage and the base for projecting light passing through the cylindrical reticle onto exposure regions on a wafer on the wafer stage.

## Background
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the priority of Chinese patent application No. 201310069610.2, filed on Mar. 5, 2013, the entirety of which is incorporated herein by reference.
FIELD OF THE INVENTION
The present invention generally relates to the field of semiconductor manufacturing technology and, more particularly, relates to exposure apparatuses and exposure methods thereof.
BACKGROUND
Photolithography process is a very important process of the semiconductor manufacturing technology, which transfers patterns on a mask to a substrate by an exposure process. The photolithography process is a core step of the manufacturing of large scale integrations (LSIs). The complex and time-consuming photolithography process of the semiconductor manufacturing technology is mainly performed by corresponding exposure apparatus. Further, the development of the photolithography technology or the improvement of the exposure apparatus are mainly focused on three specifications including feature size, overlay resolution, and yield.
In the manufacturing of a semiconductor device, the photolithography process may include three main steps: changing wafers on the wafer stages; aligning the wafers on the wafer stages; and transferring patterns on the mask to the wafers. These three steps may be sequentially repeated on the same wafer stage.
Since the photolithography process is a key step of the semiconductor manufacturing process, how to improve the yield of an exposure apparatus in the practical manufacturing process have become a very important topic. Various exposure apparatuses with twin-stages have been developed in past a few years in order to further increase the yield of the exposure apparatuses.
FIG. 1 illustrates an existing exposure apparatus with twin-stages. The exposure apparatus includes a first stage 101 and a second stage 102 for holding wafers; an alignment detection unit 103 for detecting align marks on wafers and aligning wafers; a mask stage 107 for holding a mask 108; an optical projection unit 104 under the mask stage 107 for projecting light through the mask 108 on the wafers on the first stage 101 or the second stage 102 and performing an exposure on the wafers; and an illuminator 109 above the mask stage 107 for providing an exposure light.
An exposure process using the existing tool may include sequentially: aligning the first wafer 106; moving the first stage 101 under the optical projection unit 104; and performing an exposure on the first wafer 106 using the optical projection unit 104 which projects light through the mask 108 on the first wafer 106. At the same time, a second wafer 105 may be installed on the second stage 102, and moved under the alignment detection unit 103. The alignment detection unit 103 may detect the alignment mark on the second wafer 105 on the second stage; and the second wafer 105 may be aligned. After the first wafer 106 is exposed, a new wafer may be installed on the first stage 101, and the first stage 101 with the new wafer may be moved under the alignment detection unit 103. The alignment detection unit 103 may align the new wafer. At the same time, the second stage 102 may be moved under the optical projection unit 104, and the second wafer 105 may be exposed by the optical projection unit 104.
However, even with such improvements, the exposure efficiency and the yield of the existing exposure apparatuses may still be relatively low. The disclosed methods and systems are directed to solve one or more problems set forth above and other problems.
BRIEF SUMMARY OF THE DISCLOSURE
One aspect of the present disclosure includes an exposure apparatus for performing an unidirectional scan-exposure. The exposure apparatus includes a base and a wafer stage group having a plurality of wafer stages on the base for holding wafers and successively moving from a first position to a second position of the base cyclically. The exposure apparatus also includes an alignment detection unit above the first position for detecting wafer stage fiducials at the first position and alignment marks on a wafer on the wafer stage to align the wafer. Further, the exposure apparatus includes a reticle stage on the second position for loading a cylindrical reticle and causing the cylindrical reticle to rotate around the center axis of the reticle stage and an optical projection unit between the reticle stage and the base for projecting light passing through the cylindrical reticle onto exposure regions on a wafer on the wafer stage.
Another aspect of the present disclosure includes an exposure method. The exposure method includes a Step 1 for installing wafers successively on a plurality of wafer stages and a Step 2 for moving the wafer stages holding wafers to a first position successively, detecting stage fiducials on the wafer stages and alignment marks on the wafers to align the wafers. The exposure method also includes a Step 3 for moving the wafer stage having the aligned wafer from the first position to a second position and performing an unidirectional scanning along a scan direction; rotating a cylindrical reticle around the center axis of a reticle stage; projecting light passing through the cylindrical reticle onto the wafer on the wafer stage; and exposing a first column of exposure regions along the scanning direction. Further, the exposure method includes a Step 4 for moving the wafer stage holding the partially exposed wafer from the second position to the first position after exposing the first column of exposure regions and a Step 5 for repeating the Step 2 to the Step 4 until a predetermined number of columns of exposure regions of the wafer on the wafer stage are exposed
Other aspects of the present disclosure can be understood by those skilled in the art in light of the description, the claims, and the drawings of the present disclosure.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates an existing exposure apparatus and exposure process;
FIG. 2 illustrates scanning directions for each exposure regions of the existing exposure apparatus;
FIGS. 3-6 illustrate certain structures of an exemplary wafer stage consistent with the disclosed embodiments; and
FIGS. 7-14 illustrate certain steps of an exemplary wafer scanning process consistent with the disclosed embodiments.



DETAILED DESCRIPTION
Reference will now be made in detail to exemplary embodiments of the invention, which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
FIG. 2 illustrates scanning directions of the existing exposure apparatus for each exposure regions of a wafer, i.e., the direction of an arrow may refer to the scanning direction. For example, referring to FIG. 1, for each scanning, the stage (the first stage 101 or the second stage 102) may move along the scanning direction, and the mask stage 107 with the mask 108 may move along an opposite direction, and a first exposure region may be exposed. After exposing the first exposure region, a second exposure region may be exposed.
As shown in FIG. 2, the first wafer 106 may have a plurality of exposure regions. Referring FIGS. 1-2, the first stage 101 may move along a first direction to scan and expose a first exposure region 11. Wherein the first direction is the direction of the arrow shown in first exposed region 11. After exposing the first exposure region 11, a second exposure region 12 adjacent to the first exposure region 11 may be exposed by moving the first stage 101 with a direction opposite to the first direction which may be referred as a second direction as shown in the second exposure region 12. Scanning (or exposures) along the first direction and the second direction may be sequentially repeated until all the exposure regions of the first wafer 106 are exposed.
An accelerating process, a scanning and exposing process and a decelerating process may thus exist in every scanning (or exposure) when the existing exposure apparatus (or method) is used. The accelerating process and the decelerating process may be used to improve the accuracy and efficiency of changing exposure regions, they may be unable to aid the actual exposure of wafers although occupying a portion of the total time of the exposure process. Thus, the accelerating process and the decelerating process may waste time, and may cause a relatively low yield in per unit time.
FIGS. 3-6 illustrate certain structures of an exemplary exposure apparatus consistent with the disclosed embodiments.
FIG. 3 illustrates an exemplary exposure apparatus. As shown in FIG. 3, the exposure apparatus includes a base (not shown). The base may provide a moving region for wafer stages. The base may be designed with any appropriate size and geometry. Certain damping system may also be included in the base to reduce vibration, or other kind of noises. Other necessary components may also be installed in the base to make it have desired functionalities.
The exposure apparatus also includes a stage group on the base which is used to hold, load and unload wafers. The stage group may have a plurality of wafer stages 301. The plurality of wafer stages 301 may sequentially circularly move between a first position (pre-align position) and a second position (pre-exposure position). The stage group may be controlled by a close-loop control system, or an open-loop control system, etc.
Further, the exposure apparatus includes an alignment detection unit 302 above the first position 311 of the base. The alignment detection unit 302 may be used to detect stage fiducials on the wafer stages 301 at the first position. The alignment detection unit 302 may also be used to detect alignment marks on wafers on the wafer stages 301, and align the wafers. Various sensors may be used in the alignment detection unit 302, such as a laser sensor, an infrared sensor, or an position sensor, etc.
Further, the exposure apparatus also includes a cylindrical reticle stage 305 above the second position of the base. The cylindrical reticle stage 305 may be used to hold a cylindrical reticle 303 through a first bearing 304a and a second bearing 304b, and to cause the cylindrical reticle 303 to rotate along the center axis of the cylindrical reticle stage 305.
Further, the exposure system also includes an optical projection unit 309 between the cylindrical reticle stage 305 and the base. The optical projection unit 309 may project light onto exposure regions of the wafers on the wafer stages 301, and perform exposure. After the wafer stages 301 move from the first position 311 to the second position 312, an unidirectional scan may be performed along a scanning direction. The cylindrical reticle 303 may rotate along the center axis of the cylindrical reticle stage 305, the light through the cylindrical reticle 303 may be projected on the wafer on the wafer stage 301. Thus, a column of exposure regions on the wafer along the scanning direction may be exposed.
Further, the exposure apparatus may also include a main control unit 300. The main control unit 300 may communicate with the wafer stages 301, the alignment detection unit 302, the cylindrical reticle system 305, and the optical projection unit 309, etc. The main control unit 300 may be used to manage wafer alignment and exposure processes. The main control unit 300 may also be used to send out various kinds of commands, receive feedback information from various units, manage position information, and calculate lateral movement constants, rotation constants, and amplification constants of the wafer stages 301 and the cylindrical reticle 303.
Further, the exposure apparatus may also include an encoder plate 306 having a first opening 311 and a second opening 312. The encoder plate 306 may be used to align wafers, wafer stages 301 and cylindrical reticle 303, etc.
Further, the exposure apparatus may also include a plurality of cables and connectors, such as charging cables 307 and charging ports 308 for charging a power source of the wafer stages 302. Other cables may also be used for communications of different components.
Further, the exposure apparatus may also include an illuminator box 308. The illuminator box 308 may have a light source inside. The light source may be used to expose the wafers.
Further, the exposure apparatus may also include a time fiducial unit (not shown). The time fiducial unit may be used to provide a fiducial time unit signal, and cause the collection of all signals of the wafer alignment and exposure processes to be related with time.
The detailed structures of the exposure apparatus are described below together with various illustrative drawings.
Referring to FIG. 3, the wafer stages 301 may be driven by a magnetic suspension system to move along a scanning direction (the arrow direction) in the xy-plane. The wafer stages 301 may also move from a first position to a second position by the magnetic suspension system. The wafer stages 301 may move along the positive direction of the y-axis (the scanning direction), the negative direction of the y-axis, the positive direction of the x-axis, the negative direction of the x-axis, the positive direction of the z-axis, and the negative direction of the z-axis.
The magnetic suspension system may be a maglev planar motor. The stator of the maglev planar motor may be fixed on the top surface of the base. The rotor of the maglev planar motor may be fixed on the bottom surface of the wafer stages 301. The maglev planar motor may be a permanent magnet dynamic maglev planar motor, a permanent magnet moving-iron maglev planar motor, or a maglev induction planar motor, etc.
The wafer stages 301 may sequentially move on the base. As shown in FIG. 3, when a plurality of wafer stages 301 carrying wafers are sequentially aligned at the first position, they may sequentially move to the second position. At the same time, the cylindrical reticle 303 may rotate around the center axis of the cylindrical reticle stage 305. The light penetrating through the cylindrical reticle 303 may be projected on the wafer on one wafer stage 301, thus a column of exposure regions along the scanning direction may be exposed. After exposing the column of the exposure regions, the wafer stage 301 may sequentially move from the second position to the first position to perform an alignment. The alignment and exposure processes may be repeated until the entire wafer are exposed.
When the wafer is exposed, it may unnecessarily need to change the scanning direction the wafer stages 301. At the same time, it may unnecessarily need to change the rotation direction of the cylindrical reticle 303 as well. Thus, it may unnecessarily need to have a deceleration and an acceleration process during the process for exposing each exposure area, a total exposure time of each exposure region may be significantly reduced. The yield in per unit time of the exposure apparatus may be significantly increased.
The wafer stages 301 may have corresponding sub control units (not shown). The sub control units may be inside of the wafer stages 301. The sub control units may be used to control the position of the wafer stages 301, the movement of the wafer stages 301, and the alignment of the wafers. The sub control units may communicate with the main control unit 300, the magnetic suspension system, the alignment detection unit 302, and the cylindrical reticle stage 305.
In one embodiment, when performing an exposure process, the wafer stages 301 may scan along one direction of the y-axis with a pipeline mode. The cylindrical reticle 303 may rotate around the center axis of the cylindrical reticle system 305, the light passing through the cylindrical reticle 303 may be projected on the wafer on the wafer stages 301, thus a column of exposure areas on the wafer may be exposed.
Therefore, a number of the wafer stages 301 may be greater than, or equal to two, which may increase the number of wafers carried by the wafer stages 301, and improve the efficiency of the exposure. In one embodiment, the number of the wafer stages 301 may be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25, etc.
If the number of the wafer stages 301 is two, the sub control units on the wafer stages 301 may communicate with the main control unit 300, the alignment detection unit 302 and the cylindrical reticle stage 305, etc., with a wired connection. In certain other embodiments, when the number of the wafer stages 301 is two, the sub control units on the wafer stages 301 may communicate with the main control unit 300, the alignment detection unit 302 and the cylindrical reticle stage 305 etc., with a wireless communication method.
In certain other embodiments, when the number of the wafer stages 301 is greater than two, the sub control units on the wafer stages 301 may communicate with the main control unit 300, the alignment detection unit 302 and the cylindrical reticle system, etc., with a wireless communication method. Since the wafer stages 301 may move circularly on the base, the wireless communication method may avoid the difficulties of placing wires and the movement of the wafer stages 301 which may be required for the wired communication method.
The wireless communication method may include a bluetooth technology, a infrared data association technology, a wireless fidelity (Wi-Fi) technology, a wireless application protocol (WAP), an ultra wideband technology, or a near field communication (NFC) technology, etc.
In one embodiment, if a wireless communication technology is used for the wafer stages 301 to communicate with peripheral circuits, each of the wafer stage may have a power storage unit (not shown) used to store the power for operating the wafer stages 301. The power for operating the wafer stages 301 may include the power for moving the wafer stages 301, the power for operating the sub control units, and the power for the communication between the wafer stages 301 and the peripheral circuits. The power storage unit may be fast charging battery packs, or super capacitors, which may be able to store a relatively large amount of power, and may be charged in a relative fast speed.
As shown in FIG. 3, in order to charge the power storage unit of the wafer stage 301, the exposure apparatus may have the charging cable 307 and the charging port 310. When the charging cable 307 is connected with the charging port 307, the charging cable may charge the power storage unit of the wafer stage 301.
If the number of the wafer stages 301 is 2, the charging cable 307 and the charging port 310 may be connected with an immovable method.
If the number of the wafer stages 301 is equal to, or greater than two, the exposure apparatus may have a cable connection unit (not shown). The cable connection unit may be used to form a detachable connection between the charging cable 307 and the power storage unit on the wafer stages 301. When the wafer stages 301 move to a certain position (such as the first position), a connection may be formed between the charging cable 307 and the charging port 310 by the cable connection unit, the charging cable 307 may charge the power storage unit.
When the charging cable 307 moves to a next position (such as the second position) with the wafer stages 301, the charging cable 307 may disconnect with the charging port 310 by the cable connection unit, a charging process may be finished. When a plurality of wafer stages 301 moves cyclically, the difficulties for arranging wires may be effectively solved. The charging process may be performed during an exposure process.
In certain other embodiments, the charging process may be performed when the exposure apparatus is at a standby status. Specifically, when the wafer stages 301 are moving to a certain position, a connection may be formed between the charging cable 307 and the power storage unit on the wafer stage 301 by the cable connection unit, the power storage unit may be charged by the charging cable 307, and the wafer stages 301 and the charging cable 307 may be kept static. After a certain period of time, the charging cable 307 may disconnect with the wafer stage 301 by the cable connection unit.
The cable connection unit may include a clamping unit (not shown) and a drive unit (not shown). The clamping unit may be used to clamp the charging cable 307, and move the charging cable 307 in a micrometer scale. The drive unit may be used to cause the clamping unit to move along the x-axis, the y-axis and the z-axis, and to rotate around the x-axis, the y-axis and the z-axis.
In order to achieve an accuracy position of multiple wafer stages 301, the exposure apparatus may have position detection units. Referring to FIG. 3 and FIG. 4, the position detection unit may include the alignment detection system 302, the encoder plate 306 between the optical projection unit 309 and the wafer staged 301, and encoder plate readers 313 on the top surface of the wafer stages 301.
As shown in FIG. 4, the top surface of the wafer stage 301 may have a wafer loading region 314 and a peripheral region 315 surrounding the wafer loading region 314. The encoder plate readers 313 may be at the peripheral region 315 of the top surface of the wafer stage 301. Each of the encoder plate readers 315 may have two encoder detector units 318. Each of the encoder detector units 318 may have optical emission units (not shown), optical receiver units (not shown), and sub recognition units (not shown), etc.
The optical emission units may be used to emit a detection light. The optical receiver units may be used to receive the light reflected by the encoder plate 306, and covert the light signal to an electric signal varying with time. The sub recognition units may be used to perform a signal amplification process, a signal filtering process, a direction sensing process, a pulse width calculation process, and/or a data counting process, etc, thus the displacement of the wafer stage 310 may be found after a signal processing.
When a number of the encoder plate readers 315 is greater than one, each of the sub recognition units may send signals processed by amplifying or filtering, etc., to a main recognition unit (not shown). The main recognition unit may perform a direction sensing process, a pulse width calculation process, and/or a data counting process, etc., thus the displacement of the wafer stage 301 may be found. A direction of the light emitted from the optical emission unit may be inclined to the encoder plate 306, that is, the irradiating direction of the emission light may have a certain angle with the normal of the encoder plate 306, which may cause the reflected optical signal from the encoder plate 306 to have a relatively large amplitude. Further, the emission light on the two encoder detector units 318 may be both inclined to a direction opposite to the two encoder detector units 318, which may cause the two encoder detector units 318 to have different phases when the wafer stage 301 moves along the z-axis. Thus, the displacement of the wafer stage 301 along the z-axis direction may be determined.
The number of the encoder plate readers 313 may be at least three. The three encoder plate readers 313 may be distributed at different positions of the peripheral region 315 of the wafer stage 301. In one embodiment, the number of the encoder plate readers 313 is four. The four encoder plate readers 313 are at the four corners of the peripheral region 315 of the wafer stage 301. A distance between each of the encoder plate readers 313 and the center of the wafer stage 301 may be equal or different.
Referring to FIG. 4, each of the encoder plate readers 313 may have a zeroing mark detection unit 317. The zeroing mark detection unit 317 may be used to detect a zeroing mark on the encoder plate 306. In one embodiment, the zeroing mark detection unit 317 may be an imaging alignment sensor. The zeroing mark detection unit 317 may include a light source (such as a halogen light), an optical imaging system, and a camera (such as a CCD camera), etc.
The zeroing mark detection unit 317 may irritate the zeroing mark on the encoder plate 306 using a wide band light from the light source, the camera may receive the reflected signal from the zeroing mark using the optical imaging system. Thus, the zeroing mark may be imaged on the viewing filed of the camera. After a signal processing of the image of the zeroing mark on the viewing field of the camera, a position relationship between the zeroing marks and the center of the viewing field may be obtained.
The zeroing mark detection unit 317 may return the position relationship information to the sub-control unit on the wafer stage 301, the wafer stage 301 may be driven to adjust until the zeroing mark appear at the center of the viewing field. A coarse position information (information obtained by the encoder plate readers 313) of the wafer stages 301 may be obtained, and a coarse alignment of the wafer stage 301 may be finished.
A pull-in range of the camera of the zeroing mark detection unit 317 may be approximately 100 μm ̃300 μm. After the coarse alignment of the wafer stage 301, a position accuracy of the wafer stage 301 may be in a range of approximately ±2 μm. The position accuracy may be sufficient for subsequent wafer alignments and cylindrical reticle alignments.
Further, as shown in FIG. 4, the peripheral region 315 of the wafer stage 301 may also have wafer stage fiducials 316. When the zeroing mark detection unit 317 is at a position of the zeroing detection mark, and the coarse alignment is finished, the wafer stage 301 may move to cause the alignment detection unit 302 to detect the wafer stage fiducials 316 of the wafer stage 301, a precise position information (information detected by the encoder plate readers 313) of the wafer stage 301 (or the wafer stage fiducials 316) may be obtained. The precise position information of the wafer stage 301 may be used as the zero position (origin) of the coordinate of the wafer stage 301, thus a fine alignment of the wafer stage 301 may be achieved. In certain other embodiments, after the fine alignment of the wafer stage 301, the information detected by the encoder detector units 318 (as shown in FIG. 6) may be correspondingly reset, the information after the resetting process may be used as the zero position (origin) of the coordinate of the wafer stage 301.
Since the wafer installed on the wafer stage 301 and the reticle alignment sensors 338 may be all on the surface of the wafer stage 301, the relative position of the wafer stage 301 and the wafer stage fiducials 316 may be fixed, and the relative position of the reticle alignment sensors 338 and the wafer stage fiducials 316 may also be fixed, after the fine alignment of the wafer stage 301, the alignment detection units 302 (shown in FIG. 3) may detect the alignment marks on the wafer, the position relationship between the alignment marks on the wafer and the wafer stage fiducials 316 may be obtained, and the wafer may be aligned. Further, the wafer stage 301 may move, alignment marks on the cylindrical reticle 303 may be detected by a reticle alignment detection unit, the position relationship between the alignment marks on the cylindrical reticle 303 and the wafer stage fiducials 316 may be obtained, thus the cylindrical reticle 303 may aligned. After aligning the wafer and the cylindrical reticle 303, a position relationship between the cylindrical reticle 303 and the wafer may be formed, thus a precise exposure may be achieved on the exposure areas of the wafer.
When the alignment detection unit 302 detects the wafer stage fiducials 316, an optical system of the alignment detection unit 302 may irradiate the wafer stage fiducials 316, a reflected light from the wafer stage fiducials 316 may form an image on the viewing area of the camera of the alignment detection unit 302. After an imaging processing process of the imaging signal from the camera, the position relationship between the wafer stage fiducials 316 and the center of the viewing area of the camera may be obtained. Then the position relationship information may be sent back to the sub control units of the wafer stage 301. The sub control unit may drive the wafer stage 301 to adjust its position until the wafer stage fiducials 316 appears at the center of the viewing area of the camera.
The wafer stage fiducials 316 may be formed by a plurality of gratings distributed along different directions. In one embodiment, the wafer stage fiducials 316 are formed by first gratings along the x-direction and second gratings along the y-direction.
Further, referring to FIG. 3, the encoder plate 306 may fixed on the base (not shown) of the exposure apparatus, a width of the encoder plate 306 may be greater than a width of the wafer stage 301; and a length of the encoder plate 306 may be greater than a line distance between the alignment detection unit 302 and the optical exposure unit 309. Thus, when the wafer stage 301 is at the first position, the second position, and or moves from the first position to the second position, an accurate position information may always be obtained by a position detection unit consisting of the alignment detection unit 302 and the encoder plate 306. The accurate position information may be obtained during an alignment process and an exposure process, the exposure precision may be improved. When the wafer stage 301 moves on other positions of the base, other appropriate methods may be used to detect the position, such as guide rails, photoelectrical sensors, or interferometers, etc.
As shown in FIG. 3, the encoder plate 306 may have the first opening 311 (may refer as a metrology window) and the second opening 312 (may refer as an exposure window). A position of the first opening 311 may correspond to a position of the alignment detection unit 302, i.e., the first opening 311 may be underneath the alignment detection unit 302. The first opening 311 may be used as an optical pass between the alignment detection unit 302 and the wafer stage 301. A position of the second opening 312 may correspond to a position of the optical projection unit 309, i.e., the second opening 312 may be underneath the optical projection unit 309. The second opening may be used as an optical pass between the optical projection unit 309 and the wafer stage 301.
A detail structure of the encoder plate 306 is illustrated in FIG. 5. As shown in FIG. 5, the encoder plate 306 may have a plurality of parallel equal groves 326 and heaves 325. The groves 326 and the heaves 325 may form a reflective grating. The surface of the encoder plate 306 having the groves 326 and the heaves 325 may face the top surface of the wafer stage 301. A distance between adjacent groves 326 and a distance between adjacent heaves 325 may be equal.
The encoder plate 306 may be made of glass, the groves 326 and the heaves 325 may be formed by etching the glass. In certain other embodiments, opaque strips may be formed on the transparent glass encoder plate 306 to form the groves 326 and the heaves 325, that is the reflective grating. The opaque stripes may be made of any appropriate material, such as metal thin film, etc.
As shown in FIG. 5, in one embodiment, the encoder plate 306 may have a first sub encoder plate 320 and a second sub encoder plate 321. The first sub encoder plate 320 and the second sub encoder plate 321 may be dissymmetrical. A symmetrical center line AB of the first sub encoder plate 320 and the second sub encoder plate 321 and the connecting line between the alignment detection unit 302 and the center of the optical projection unit 309 may be on a same plane perpendicular to the base of the exposure apparatus. The symmetrical center line AB of the first sub encoder plate 320 and the second sub encoder plate 321 and a connecting line between the center of the first opening 311 and the second opening 312 may be coincide.
In one embodiment, the groves 326 and the heaves 325 of the first sub encoder plate 320 and the groves 326 and the heaves 325 of the second sub encoder plate 321 may be dissymmetrical. The heaves 325 (groves 326) of the first sub encoder plate 320 may connect with the symmetrical center line AB, and have a first angle 32. The heaves 325 (groves 326) of the second sub encoder plate 321 may connect with the symmetrical center line AB, and have a second angle 31. The angle of the second angle 31 may be equal to the angle of the first angle 32. Thus, the accuracy of the first sub encoder plate 320 may be identical to the accuracy of the second sub encoder plate 321, a high accuracy of the position coordinate of the wafer stage 301 detected by the encoder plate readers 313 may be obtained. A moving direction and displacement of the wafer stage 301 may be obtained by the phase change, interval change, and pulse number of signals detected by the encoder plate readers 313.
Angles of the first angle 32 and the second angle 31 may be in a range of approximately 5° ̃85°. Specifically, the angle of the first angle 32 and the second angle 31 may be 10°, 20°, 30°, 40°, 45°, 50°, 60°, 70°, or 80°, etc. When the wafer stage 301 moves under the first sub encoder plate 320 and the second sub encoder plate 321 along the x-axis, the y-axis or the z-axis, phase and interval changes between two electrical signals may be obtained by a single encoder detector unit 318. In certain other embodiments, the phase and interval changes between a plurality signals may be obtained from a plurality of the encoder detector units 318. The moving direction and displacement of the wafer stage 301 may be determined and calculated by the obtained phase/interval changes.
In one embodiment, the number of the encoder plate readers 313 may be at least three; and each of the encoder plate readers 313 may include two encoder detector units 318. The encoder plate readers 313, the first sub encoder plate 320 and the second sub encoder plate 321 may form a detection system. Each of the encoder plate readers 313 may detect two degrees of freedom of the wafer stage 301, including the x-direction (or the y-direction) and the z-direction. A detection of six degrees of freedom may be achieved using at least three encoder plate readers 313. The six degrees of freedom may include the x-direction, the y-direction, the z-direction, the rotation x-direction, the rotation y-direction, and the rotation z-direction. The detection of these directions may be simple with a high accuracy, and the data processing may also be simple.
FIG. 6 illustrates an exemplary embodiment using a detection system consisting of four encoder plate readers 313, the first sub encoder plate 320 and the second sub encoder plate 321 to detect a position of the wafer stage 301. As shown in FIG. 6, the four encoder plate readers 313 may include a first encoder plate reader 313a, a second encoder plate reader 313b, a third encoder plate reader 313c, and a fourth encoder plate reader 313d. Distances between the center of the surface of the wafer stage 301 and the first encoder plate reader 313a, the second encoder plate reader 313b, the third encoder plate reader 313c, and the fourth encoder plate reader 313d may be equal. The distance may refer as a “r”. Connecting lines of the centers of the four encoder plate readers may form a rectangle.
The x-axis coordinate of the wafer stage 301 obtained by the detection system may refer as a Cx. The y-axis coordinate of the wafer stage 301 obtained by the detection system may refer as a Cy. The z-axis coordinate of the wafer stage 301 obtained by the detection system may refer as a Cz. The x-axis rotation constant obtained by the detection system may refer as a Rx. The y-axis rotation constant obtained by the detection system may refer as a Ry. The z-axis rotation constant obtained by the detection system may refer as a Rz. Wherein:



  
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The above equations may be correct when the 2 encoder plates are angled at 45 degrees to the symmetry axis and orthogonal to each other. Wherein: E1, E2, E3, and E4 may refer to detected values obtained by the first encoder plate reader 313a, the second encoder plate reader 313b, the third encoder plate reader 313c, and the fourth encoder plate reader 313d when the wafer stage 301 moves along the x-direction and/or the y-direction, respectively. E1z, E2z, E3z, and E4z may refer to detected values obtained by the first encoder plate reader 313a, the second encoder plate reader 313b, the third encoder plate reader 313c, and the fourth encoder plate reader 313d when the wafer stage 301 moves along the z-direction, respectively. Sy may refer to a vertical distance between the connecting line of the centers of the first encoder plate reader 313a and the second encoder plate reader 313b and the center of the surface of the wafer stage 301. Sx may refer to a vertical distance between the connecting line of the centers of the first encoder plate reader 313a and the second encoder plate reader 313d and the center of the surface of the wafer stage 301.
Referring to FIG. 5, when the encoder plate 306 and the encoder detector units 318 are used to form a position detection unit, a detection accuracy the position detection unit may be in a range of approximately 1 nm ̃10 nm. When the wafer stage 301 moves within the regime of the encoder plate 306, the position error of the wafer stage 301 may be smaller than a range of approximately 1 nm ̃10 nm. A precise position relationship between the wafer stage 301, the wafer on the wafer stage 301, and the cylindrical reticle 303 may be achieved, thus the exposure apparatus may have a relatively high accuracy.
Further, as shown in FIG. 5, the encoder plate 306 in the peripheral region of the first opening 311 may have zeroing marks 322. The zeroing marks 322 may be used for a quick alignment and leveling capture. A number of the zeroing marks 322 may be equal to the number of the zeroing mark detection units 317. A distribution of the zeroing marks 322 may be same as a distribution of the zeroing mark detection units 317 on the wafer stage 301. That is, a pattern formed by center connecting lines of the zeroing marks 322 on the encoder plate 306 may coincide with a pattern formed by center connecting lines of the zeroing detection units 317 on the wafer stage 301. Thus, an accurate positioning of the wafer stage 301 may be achieved.
In one embodiment, the number of the zeroing marks 322 is corresponding to the number of the zeroing mark detection units 317. The number of the zeroing marks 322 may be four. As shown in FIG. 5, each of the zeroing marks 322 may have a plurality of first grating 323 distributed along the y-axis direction and a plurality of the second grating 324 distributed along the y-axis direction.
Further, referring to FIG. 3, the reticle stage 305 may include a reticle stage frame (not shown) and a center shaft extension tube (not shown) fixed at one side of the reticle stage frame. The first bearing 304a may be fixed on one end of the center shaft extension tube near the reticle stage frame. The second bearing 304b may be fixed on the other end of the center shaft extension tube. In certain other embodiment, the second bearing 304b may be a removable bearing, i.e., may be installed on installed on the center shaft extension tube by certain control units. Two side faces of the first bearing 304a and the second bearing 304 facing each other may have slots. The cylindrical reticle 303 may be clamped in the slots of the side faces of the first bearing 304a and the second bearing 304b. When the first bearing 304a and the second bearing 304b rotate around the center shaft extension tube, the cylindrical reticle 303 may also rotate around the center shaft extension tube. Wherein, the center axis of the center shaft extension tube may be equivalent to the center axis of the cylindrical reticle 303. Certain drive units may be connected with the first bearing 304a and the second bearing 304b to drive them to rotate around the center shaft extension tube.
The cylindrical reticle 303 may be a hollow cylinder. Designed patterns may be formed on the inner surface and/or outer surface of the cylindrical reticle 303
Referring to FIG. 3, the center shaft extension tube may have an illumination slit (not shown) penetrating through the bottom, and the illuminator box 308 may be installed in the center shaft extension tube. Light illuminating from the illuminator box 308 may reach on the cylindrical reticle 303 through the illumination slit. Then light illuminating through the reticle 303 may be projected on the exposure areas of the wafer on the wafer stage 301 by the optical projection unit 309, and the wafer may be exposed.
Various light sources may be used as the illumination box 308. In one embodiment, the illumination box 308 may be a KrF excimer laser (wavelength may be approximately 248 nm) or an ArF excimer laser (wavelength may be approximately 193 nm). The illumination box 308 may also be an F2 laser (wavelength may be approximately 157 nm), or an ultraviolet light source (wavelength is approximately 13.5 nm), etc. The light of the illumination box 308 may also be a glow discharge in the ultraviolet region generated from a high pressure mercury light source (i line, or g line, etc).
A projected length of the perimeter of the outer surface of the cylindrical reticle 303 projected by the optical projection unit 309 may be equal to a length of an exposure area on a wafer (along a scanning direction). That is, referring to FIG. 3, when the cylindrical reticle 303 rotates around the center shaft extension tube 329 for one cycle, at the same time, the wafer stage 301 scans one exposure region along the scanning direction (the arrow direction shown in FIG. 3), patterns on the cylindrical reticle 303 may be completely transferred to an exposure region on the wafer. The cylindrical reticle 303 may continue rotating, and the wafer stage 301 keeps scanning along the scanning direction, the patterns on the cylindrical reticle 303 may be completely transferred to a next exposure region on the wafer.
The rotating and scanning process may be repeated, a column of exposure areas distributed along the scanning direction may be all exposed. During the exposure process of the exposure areas, it may be unnecessary for the cylindrical reticle 303 to change the rotation direction, and it may be unnecessary for the wafer stages to change the scanning direction as well. Thus, when the exposure area is changed, it may be unnecessary to have an accelerating process or a decelerating process. When a series of exposure areas along the scanning direction are exposed continuously, the wafer stages may keep a constant scanning speed. Therefore, the time for exposure processes may be significantly reduced, and the exposure efficiency of the exposure apparatus may be increased.
In certain other embodiments, the projected length of the perimeter of the outer surface of the cylindrical reticle 303 projected by the optical projection unit 309 may be equal to a length of a plurality of exposure regions on a wafer (along a scanning direction). That is, when the cylindrical reticle 303 rotates around the center shaft extension tube for one cycle, the wafer stage 301 scans on the plurality of exposure regions (an entire column of exposure regions) along the scanning direction at the same time. A plurality of exposure regions may be exposed at same time. The exposure efficiency may be further increased.
The cylindrical reticle 303 may have a plurality of the reticle alignment marks (not shown). The peripheral region 315 of the wafer stage 301 may have a plurality of reticle detection units. The reticle detection units may be used to detect the reticle alignment marks, a position relationship between the reticle alignment 303 and the wafer stage 301 may be formed, thus the cylindrical reticle 303 may be aligned.
The optical projection unit 309 may be used to project the light passing through the cylindrical reticle 303 on the exposure areas of the wafer on the wafer stage 301. When a KrF excimer laser or an ArF excimer laser is used as the light source in the illuminator box 308, the optical projection unit 309 may be a refraction system, only made of optical refraction devices (such as lenses). When an F2 laser is used as the light source in the illuminator box 308, the optical projection unit 309 may be a deflection/refraction system, made of optical refraction devices, optical reflection devices, or a combination thereof.
FIGS. 7-14 illustrate certain steps of an exemplary exposure process using the above disclosed exposure apparatus. For illustrative purposes, an exposure apparatus with four wafer stages may be used to describe the exposure process in details.
As shown in FIG. 7, the exposure apparatus has four wafer stages including a first wafer stage 3011, a second wafer stage 3012, a third wafer stage 3013, and a fourth wafer stage 3014. A first wafer 1, a second wafer 2, a third wafer 3 and a fourth wafer 4 may be successively loaded on the first wafer stage 3011, the second wafer stage 3012, the third wafer stage 3013, and the fourth wafer stage 3014.
Before the exposure apparatus starts working, the first wafer stage 3011, the second wafer stage 3012, the third wafer stage 3013, and the fourth wafer stage 3014 may distribute in queue on the base of the exposure apparatus. When the exposure process is started, exposure programs may be firstly installed in the exposure apparatus. Then four wafers may be loaded on the four wafer stages successively. The wafer stages loaded with wafers may successively move toward a first position to align the wafers at the first position.
When the first wafer stage 3011, the second wafer stage 3012, the third wafer stage 3013, and the fourth wafer stage 3014 move in regions outside the encoder plate 306, tracks, interferometers, or grating plates may be used to detect their positions. The accumulated position errors may be less than 100 μm.
Further, as shown in FIG. 8, the first wafer stage 3011 moves to the first position of the base, i.e., a pre-alignment position underneath the first opening 311 of the encoder plate 306, the zeroing mark detection units 317 (shown in FIG. 5) on the first wafer stage 3011 may detect the zeroing marks 322 on the encoder plate 306, a coarse position information of the first wafer stage 3011 may be obtained, and a coarse alignment of the first wafer stage 3011 may be finished.
In one embodiment, if at least three zeroing mark detection units 317 have detected the corresponding zeroing marks 322, the coarse alignment of the wafer stage 3011 may be finished. If less than three zero mark detection units 317 have detected the corresponding zeroing marks 322, the coarse alignment may need to repeat.
After the coarse alignment of the wafer stage 3011 is finished, the wafer stage 3011 may quickly to move under the alignment detection unit 302 (referring to FIG. 3), the alignment detection unit 302 may detect the wafer stage fiducials 316 on the first wafer stage 3011, an accurate position information of the wafer stage 3011 (or wafer stage fiducials 316) may be obtained. At the same time, the accurate position information of the wafer stage 3011 may be used as a zero point (origin) of a position coordinate of the wafer stage 3011, and a fine alignment of the wafer stage 3011 may be finished.
In certain other embodiments, after finishing the fine alignment of the wafer stage 3011, the detected information of the encoder plate readers 313 on the wafer stage 3011 may be reset correspondingly, the reset zero information may be used as the zero (origin) of the position coordinate of the wafer stage 3011. The main control unit 300 may save and calculate the displacement bias of the wafer stage 3011 between the fine alignment and the coarse alignment.
After the alignment detection units 302 detect the wafer stage fiducials 316 on the first wafer stage 3011, the first wafer stage 3011 may move, the alignment detection unit 302 may detect alignment marks on the first wafer 1 loaded on the first wafer stage 3011, the position information of the alignment marks on the first wafer 1 may be obtained. The main control unit 300 may convert the position information of the alignment marks on the first wafer 1 to a position coordinate using the position information of the wafer stage fiducials 316 as an origin, a position management of exposure regions on the wafer 1 may be achieved. The related position information and position coordinate may be saved in the main control unit 300, and an alignment of the first wafer 1 may be finished. The main control unit 300 may save and calculate the displacement bias of the wafer stage 3011 between the fine alignment and the detection of the alignment marks on the first wafer 1.
As shown in FIG. 9, after the alignment of the wafer 1, the first wafer stage 3011 may move from the first position to the second position, i.e., a pre-exposure position underneath the second opening 312 of the encoder plate 306. Then, the wafer stage 3011 may perform a unidirectional scan along a scanning direction, i.e., the positive direction of the y-axis. At the same time, the cylindrical reticle 303 may rotate around the center axis of the cylindrical reticle stage 305. Light passing through the cylindrical reticle 303 may be projected on the first wafer 1 on the first wafer stage 3011 by the optical projection unit 309 (shown in FIG. 3), thus a first column of exposure regions along the scanning direction may be exposed. At the same time, the second wafer stage 3012 may move to the first position of the base, and the second wafer 2 on the second wafer stage 3012 may be aligned.
Before exposing the first wafer 1, the reticle alignment detection unit on the first wafer stage 3011 may detect the reticle alignment marks on the cylindrical reticle 303, a position information of the reticle alignment marks may be obtained. Thus, a position relationship between the cylindrical reticle 303 and the first wafer 1 may be formed as well, and an alignment of the cylindrical reticle 303 may be finished. The related position information and position coordinate may be saved in the main control unit 300.
When the first column of exposure regions of the first wafer 1 are exposed, the wafer stage 3011 may keep the positive scanning direction of the y-axis, the rotation direction of the cylindrical reticle 303 around the center axis of the cylindrical reticle stage 305 may also keep same, thus after exposing the first exposure region of the first column of exposure regions, it may unnecessarily change the scanning direction of the first wafer stage 3011 and the rotation direction of the cylindrical reticle 303, a second exposure region of the first column of exposure regions may be exposed. Similarly, all the exposure regions of the first column may be exposed without changing the scanning direction of the first wafer stage 3011 and the rotation direction of the cylindrical reticle 303. Thus, when the first column of exposure regions of the first wafer 1 are exposed, it may be unnecessary for the first wafer stage 3011 to accelerate or decelerate, the time for the exposure process may be significantly reduced.
Before exposing the first exposure region of the first column of exposure regions of the first wafer 1, the first wafer stage 3011 may need an acceleration process. After exposing the last exposure region of the first column of exposure region, the first wafer stage 3011 may need a deceleration process.
In one embodiment, since the scanning direction of the first wafer stage 3011 may keep constant, on the basis providing a relatively high exposure resolution, the scanning speed may be increased. The scanning speed of the first wafer stage 3011 may be in a range of approximately 100 mm/s ̃10 m/s, or higher. Physically, the scanning speed may have no limitation except the position detections and the feedback time.
The time for the cylindrical reticle 303 to rotate around the center axis of the cylindrical reticle stage 305 for one circle may be equal to the time for the first wafer stage 3011 to move one exposure region along the scanning direction. Thus, patterns of the cylindrical reticle 303 may be completely transferred onto the exposure regions on the first wafer 1, and an unidirectional step scanning exposure of the exposure regions on the first wafer 1 may be achieved.
In certain other embodiments, the time for the cylindrical reticle 303 to rotate around the center axis of the cylindrical reticle stage 305 for one circle may be equal to the total time for the first wafer stage 3011 to move a plurality of exposure regions along the scanning direction. When the cylindrical reticle 303 rotates for one circle, a plurality of exposure regions of the first column of exposure regions along the scanning direction may be exposed.
When the first column of exposure regions of the first wafer 1 on the first wafer stage 3011 are partially exposed, after finishing the alignment the second wafer 2, the second wafer stage 3012 may move from the first position toward the second position, or a nearby position on the base to wait for an exposure. The third wafer stage 3013 may move to the first position to align the third wafer 3. Then, the fourth wafer stage 3014 may move toward the first position after loading the fourth wafer 4. The alignment of the second wafer 2 is similar as the alignment of the first wafer 1.
As shown in FIG. 10, when the exposure of the first column of exposure regions of the first wafer 1 on the first wafer stage 3011 is completed, the first wafer stage 3011 may continue to move along the positive direction of the y-axis, the second wafer stage 3012 may move to the second position. Then, the second wafer stage 3012 may perform an unidirectional scan along the scanning direction, i.e., the positive direction of the y-axis. At the same time, the cylindrical reticle 303 may rotate around the center axis of the cylindrical reticle stage 305, the light passing through the cylindrical reticle 303 may be projected on the second wafer 2 loaded on the second wafer stage 3012 by the optical projection unit 309. A first column of exposure regions of the second wafer 2 along the scanning direction may be exposed. At the same time, after aligning the third wafer 3, the third wafer stage 3013 may move from the first position toward the second position. The fourth wafer stage 3014 move to the first position, and the fourth wafer 4 may be aligned.
Before exposing the second wafer 2, the reticle alignment detection unit on the first wafer stage 3012 may detect the reticle alignment marks on the cylindrical reticle 303, a position information of the reticle alignment marks may be obtained, and a position relationship between the cylindrical reticle 303 and the second wafer stage 3012 may be formed. Thus, a position relationship between the cylindrical reticle 303 and the second wafer 2 may be formed, and an alignment of the cylindrical reticle 303 may be finished. The related position information and position coordinate may be saved in the main control unit 300.
As shown in FIG. 11, the first wafer stage 3011 may move toward the first position. After the first column of exposure regions of the second wafer 2 are exposed along the scanning direction, the second wafer stage 3012 may move away from the second position, and the third wafer stage 3013 may move to the second position. Then, the third wafer stage 3013 may perform a unidirectional scan along the scanning direction, i.e., the positive direction of the y-axis. At the same time, the cylindrical reticle 303 may rotate around the center axis of the cylindrical reticle stage 305, and the light passing through the cylindrical reticle 303 may be projected on the third wafer 3 loaded on the third wafer stage 3013 by the optical projection unit 309. A first column of exposure regions of the third wafer 3 along the scanning direction may be exposed. At the same time, after aligning the fourth wafer 4, the fourth wafer stage 3014 may move from the first position toward the second position.
Before exposing the third wafer 3, the reticle alignment detection unit on the first wafer stage 3013 may detect the reticle alignment marks on the cylindrical reticle 303, a position information of the reticle alignment marks may be obtained, and a position relationship between the cylindrical reticle 303 and the third wafer stage 3013 may be formed. Thus, a position relationship between the cylindrical reticle 303 and the third wafer 3 may be formed, and an alignment of the cylindrical reticle 303 may be finished. The related position information and position coordinate may be saved in the main control unit 300.
As shown in FIG. 12, after the first column of exposure regions of the third wafer 3 are exposed, the first wafer stage 3011 may move to the first position. The first wafer 1 on the first wafer stage 3011 may be aligned. The fourth wafer stage 3014 may move to the second position. Then, the fourth wafer stage 3014 may perform a unidirectional scan along the scanning direction, i.e., the positive direction of the y-axis. At the same time, the cylindrical reticle 303 may rotate around the center axis of the cylindrical reticle stage 305, and the light passing through the cylindrical reticle 303 may be projected on the fourth wafer 4 loaded on the fourth wafer stage 3014 by the optical projection unit 309. A first column of exposure regions of the fourth wafer 4 along the scanning direction may be exposed.
Since the main control unit 300 may be used to save and calculate the displacement bias of the wafer stage 3011 between the fine alignment and the coarse alignment and the displacement bias of the wafer stage 3011 between the fine alignment and the detection of the alignment marks on the first wafer 1, when the first wafer 1 on the first wafer stage 3011 is realigned, it may only need the zeroing mark detection unit 317 to detect the zeroing marks 322 on the encoder plate 306, the position coordinate of the wafer stage 3011 may be obtained by the main control unit 300 using the coarse position information of the first wafer stage 3011 and certain types of calculation. Thus, a position management of the first wafer 1 may be achieved, and the time for a realignment of the first wafer 1 may be reduced.
In certain other embodiments, when the first wafer 1 is realigned, the alignment detection unit 302 may detect the wafer stage fiducials on the first wafer stage 1 and the alignment marks on the first wafer 1.
Further, as shown in FIG. 13, the first wafer stage 3011 may move from the first position to the second position, then the first wafer stage 3011 may perform a unidirectional scan along the scanning direction, i.e., the positive direction of the y-axis. At the same time, the cylindrical reticle 303 may rotate around the center axis of the cylindrical reticle stage 305, and the light passing through the cylindrical reticle 303 may be projected on the first wafer 1 on the first wafer stage 3011 by the optical projection unit 309. A second column of exposure regions of the first wafer 1 along the scanning direction may be exposed. At the same time, the second wafer stage 3012 may move to the second position of the base, the second wafer 2 on the second wafer stage 3012 may be aligned.
In one embodiment, since the position relationship between the cylindrical reticle 303 and the first wafer stage 3011 may be already formed when the first column of exposure regions of the first wafer 1 are exposed, it may unnecessarily detect the reticle alignment marks, a position relationship between the cylindrical reticle 303 and the first wafer stage 3011 for exposing the second column of exposure regions may be obtained by the main control unit 300 using the saved position relationship between the cylindrical reticle 303 and the first wafer stage 3011, and the displacement of the first wafer stage 3011 moving along the x direction, i.e., a distance along the x-direction for the wafer stage 3011 to move one exposure region comparing with the first column of exposed regions after aligning the first wafer 1 and before exposing the second column of exposure regions, the exposure time may be effectively reduced.
In certain other embodiments, before exposing the second column of exposure regions of the first wafer 1, the reticle alignment detection unit may detect the reticle alignment marks on the cylindrical reticle 303, the position relationship between the cylindrical reticle 303 and the first wafer stage 3011 may be obtained.
Further, as shown in FIG. 14, after the second column of exposure regions of the first wafer 1 are exposed, the first wafer stage 3011 may continue to move toward the first position of the base along the positive direction of the y-axis, and the second wafer stage 3012 may move to the second position. Then the second wafer stage 3012 may perform an unidirectional scan along the scanning direction, i.e., the positive direction of the y-axis. At the same time, the cylindrical reticle 303 may rotate around the center axis of the cylindrical reticle stage 305, and the light passing through the cylindrical reticle 303 may be projected on the second wafer 2 on the second wafer stage 3012 by the optical projection unit 309. A second column of exposure regions of the second wafer 2 along the scanning direction may be exposed. At the same time, after the third wafer 3 is aligned, the third wafer stage 3013 may move from the first position toward the second position of the base. The fourth wafer stage 3014 may move to the first position 311, and the fourth wafer 4 on the fourth wafer stage 3014 may be aligned.
The first wafer stage 3011, the second wafer stage 3012, the third wafer stage 3013, and the fourth wafer stage 3014 may cyclically move on the base in a pipelined mode. The alignment and exposure processes may be repeated until all the exposure regions of the first wafer 1, the second wafer 2, the third wafer 3 and the fourth wafer 4 are exposed. When a certain wafer on one of the four wafer stages are completely exposed, a new wafer may be loaded.
The present exposure apparatus may have the cylindrical reticle 303 and a plurality of wafer stages 301. The cylindrical reticle 303 may rotate around the center axis of the cylindrical reticle stage 305, one wafer stage 301 may perform an unidirectional scan along the scanning direction, the light passing through the cylindrical reticle 303 may be projected on a certain column of exposure regions on the wafers on the wafer stage 301, thus the certain column of exposure regions may be exposed along the scanning direction. When the certain column of exposure regions are exposed, since the cylindrical reticle 303 may return to the origin after rotating one circle, after exposing the certain column of the exposed areas, it may unnecessarily change the rotation direction of the reticle 303 and the scanning direction of the wafer stage 301 an exposure of a next exposure region in the same column may be achieved. Therefore, it may unnecessarily need an accelerating process and a decelerating process when exposure regions in a same column are exposed, the total time for an exposure process may significantly reduced, and the yield in per unit time of the exposure apparatus may be increased.
In one embodiment, using the cylindrical reticle 303 may have a similar reticle alignment process as other exposure apparatuses. However the wafer exposure map may be changed. Each column of exposure regions is unidirectional scan-exposed during one scan instead of one exposure shot. The only time loss may be to scan back the wafer for next column exposure. The throughput gain may be still substantial: For example: for a two-wafer stage configuration (alignment and leveling may be done in parallel, and may unnecessarily be counted as a throughput overhead), currently, each exposure area may need 0.26 seconds for entire scan, including acceleration (0.10 sec), scan-exposure (0.06 sec), de-acceleration (0.10 sec). For a scan speed of 600 mm/s and 300 mm wafer, each column may only need about 2 times (back scan to prepare for next column exposure) of (0.1 sec+0.5+0.1 sec), but it may include the exposure of up to 9 shots (average of 7 shots), the time gain is: 0.26×7−0.7×2=1.82−1.4=0.42 sec, or 30% throughput gain. If the scan speed may be further increased, for example, 2 msec, assuming the acceleration and de-acceleration may use the same time, the gain will be more: 0.22×7−0.36×2=1.54−0.72=0.82 sec, i.e., a 114% yield gain.
For a plurality of wafer stages, the gain in yield may be more since when one exposed wafer is going back to the first position, other wafers may be exposed. For example, in case of a 25 wafer stage systems, if one wafer has 12 columns of exposure regions, the total processing time for 25 wafers may be estimated as: [(0.1+0.54+0.1+0.06×2 (time lag between wafer stage to wafer stage))×12 (column)+2 (first column reticle alignment)]×25=308 seconds, i.e., the yield will be 3600/308×25=292 wph which may be significantly higher than the yield of current methods, which may be about 3600/[(0.1+0.06+0.1)×110]=126 wph. Wherein, “wph” may refer to wafer per hour.
In certain other embodiments, the exposure system may have one wafer stage 301, the wafer stage 301 may unnecessarily go back the first position after the first column of the wafer is exposed. The wafer stage 301 may only need move to a next exposure region, and perform an unidirectional scan. At the same time, the cylindrical reticle 303 may rotate for one cycle, the next exposure region may be exposed. The exposure process may be repeated until the entire wafer is exposed.
The above detailed descriptions only illustrate certain exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention. Those skilled in the art can understand the specification as whole and technical features in the various embodiments can be combined into other embodiments understandable to those persons of ordinary skill in the art. Any equivalent or modification thereof, without departing from the spirit and principle of the present invention, falls within the true scope of the present invention.

## Claims

1. An exposure apparatus, comprising:
a base;
a wafer stage group having a plurality of wafer stages on the base for holding wafers and successively moving from a first position to a second position of the base cyclically;
an alignment detection unit above the first position for detecting wafer stage fiducials on the wafer stage at the first position and alignment marks on a wafer on the wafer stage at the first position to align the wafer;
a reticle stage on the second position for loading a cylindrical reticle and causing the cylindrical reticle to rotate around a center axis of the reticle stage; and
an optical projection unit between the reticle stage and the base for projecting light passing through the cylindrical reticle on exposure regions of a wafer on the wafer stage,
wherein a control system is configured to control the wafer stage group such that:
when the wafer stage moves from the first position to the second position, the wafer stage performs a unidirectional scan along an scanning direction, the cylindrical reticle rotates around the center axis of the reticle stage, the light passing through the cylindrical reticle is projected onto the wafer on the wafer stage, and a column of exposure regions on the wafer along the scanning direction are exposed, and
a first column of exposure regions on a first wafer and a corresponding column of exposure regions on a second wafer are each exposed prior to exposing a second column of the exposure regions on the first wafer.

2. The exposure apparatus according to claim 1, wherein:
the wafer stages are driven by a magnetic suspension system.

3. The exposure apparatus according to claim 2, wherein:
each of the wafer stages has a corresponding sub control unit for controlling positioning, moving and alignment of the wafer stage, and for communicating with the magnetic suspension system and the alignment detection unit.

4. The exposure apparatus according to claim 3, further including:
a main control unit communicating with the wafer stage, the alignment detection unit, the optical projection unit, and the sub control unit, and managing alignment and exposure of the wafer.

5. The exposure apparatus according to claim 4, wherein:
the sub control unit of the wafer stage communicates with the main control unit by a wireless communication technology.

6. The exposure apparatus according to claim 5, wherein:
each of the wafer stages has a power storage unit storing power for operating the wafer stage.

7. The exposure apparatus according to claim 6, wherein the exposure apparatus further includes:
a cable connection unit for forming a detachable connection between a charging cable and the power storage unit for charging the power storage unit when the charging cable and the power storage unit are connected.

8. The exposure apparatus according to claim 7, wherein:
a fixed or detachable connection is used between the charging cable and the wafer stage when the number of the wafer stage is two; and
the detachable connection is used between the charging cable and the wafer stage when a number of the wafer stages is greater than two.

9. The exposure apparatus according to claim 1, further including:
a position detection system for detecting the position information of the wafer stage,
wherein:
the position detection system includes the alignment detection unit, an encoder plate between the optical projection unit and the wafer stage, and encoder plate readers on the top surface of the wafer stage.

10. The exposure apparatus according to claim 9, wherein:
the encoder plate has a plurality of groves and heaves;
a reflection grating is formed by the groves and the heaves with an alternative distribution; and
a surface of the encoder plate having the groves and the heaves faces the top surface of the wafer stage.

11. The exposure apparatus according claim 9, wherein:
the encoder plate includes a first sub encoder plate and a second sub encoder plate;
the first sub encoder plate and the second sub encoder plate are dissymmetrical; and
a symmetrical line between the first sub encoder plate and the second sub encoder plate and a connecting line between the alignment detection unit and the center of the optical projection unit are in a same plane perpendicular to the base.

12. The exposure apparatus according to claim 9, wherein:
a width of the encoder plate is greater than a width of the wafer stage;
a length of the encoder plate is greater than a line distance between the alignment detection unit and the center of the optical projection unit;
the encoder plate has a first opening and a second opening;
the first opening is at a position corresponding to the alignment detection unit; and
the second opening is at a position corresponding to the optical projection unit.

13. The exposure apparatus according to claim 9, wherein:
a surface of the wafer stage has a wafer holding region and a peripheral region surrounding the wafer holding region;
the encoder plate readers are in the peripheral region of the top surface of the wafer stage;
each of the encoder plate readers has two encoder plate readers; and
each of the encoder plate readers has an optical emission unit for emitting light, an optical receiver unit for receiving reflected light from the encoder plate and converting the reflected light to electrical signals, and a recognition unit for obtaining the displacement of the wafer stage by orienting and counting the electrical signals.

14. The exposure apparatus according to claim 13, wherein:
a number of the encoder plate readers is at least three locating at different positions of the peripheral region of the wafer stage.

15. The exposure apparatus according to claim 13, wherein:
the encoder plate at a surrounding region of a first opening has zeroing marks;
each of the encoder plate readers has zeroing mark detection units for detecting the zeroing marks;
a number of the zeroing marks is equal to a number of the zeroing mark detection units; and
a distribution of the zeroing marks on the encode plate is same as a distribution of the zeroing mark detection units.

16. The exposure apparatus according to claim 1, wherein:
the cylindrical reticle is a hollow cylinder;
the surface of the cylindrical reticle has patterns; and
a projected length of the perimeter of the outer surface of the cylindrical reticle projected by the optical projection unit is equal to a length of an exposure area on a wafer, or a total length of a plurality of the exposure regions.

17. The exposure apparatus according to claim 16, wherein:
the cylindrical reticle has reticle alignment marks;
the wafer stage has reticle alignment sensors; and
the reticle alignment sensors are used to detect the reticle alignment marks to align the cylindrical reticle.

18. An exposure method, comprising:
Step 1, installing wafers successively on a plurality of wafer stages;
Step 2, moving the wafer stages holding the wafers to a first position successively, detecting stage fiducials on the wafer stages and alignment marks on the wafers to align the wafers;
Step 3, moving the wafer stage having the aligned wafer from the first position to a second position and performing an unidirectional scanning along a scanning direction; rotating a cylindrical reticle around a center axis of a reticle stage; projecting light passing through the cylindrical reticle onto the wafers on the wafer stages; and exposing a first column of exposure regions on a first wafer and a corresponding column of exposure regions on a second wafer along the scanning direction;
Step 4, moving the wafer stage holding the partially exposed wafer from the second position to the first position after exposing the first column of the exposure regions on a first wafer and the corresponding column of the exposure regions on the second wafer; and
Step 5, repeating the Step 2 to the Step 4 including exposing a second column on the first wafer, until a predetermined number of columns of exposure regions on each wafer on the wafer stage are exposed.

19. The exposure method according to claim 18, before detecting the stage fiducials, further including:
detecting zeroing marks on an encoder plate using the zeroing mark detection units to obtain fiducial position information of the wafer stage.

20. The exposure method according to claim 18, wherein:
a time length for the cylindrical reticle to rotate around the center axis of the reticle stage for one cycle is equal to a time length for the wafer stage to move one exposure region along the scanning direction.