Patent Application
20090153832
The current invention is generally related to vibration isolation techniques in a lithographic imaging system, and more particularly related to the isolating apparatus and method of isolating vibrations based upon at least two active control units during an imaging transforming operation of the lithographic system.
Lithography systems are commonly used to transfer images from a reticle onto a semiconductor wafer during semiconductor manufacturing processing. Lithography apparatuses are also used for manufacturing liquid crystal devices, imaging devices such as CCDs, thin film magnetic heads on a glass plate or the like. In general, a typical lithography projection system includes an optical assembly, a reticle stage for positioning a reticle or a mask defining a predetermined pattern, a wafer stage assembly for positioning a semiconductor wafer or a substrate and a measurement sub-system for monitoring the precise position of the reticle and the wafer.
During operation, the optical assembly projects an image pattern on the mask onto the wafer, and the projected image is exposed on one or more die on the wafer. A single wafer usually contains a plurality of die or fields to be successively irradiated to form multiple semiconductor devices. During each exposure of the so-called “step and scan” process, the mask stage and the wafer stage move in a synchronized manner to transfer the image pattern from the mask to a particular field of the wafer. After each exposure, the wafer stage assembly moves the wafer so as to expose every die of the wafer. Subsequently, the wafer is replaced by a new wafer. In the above described semiconductor manufacturing process, a lithographic apparatus must accurately image the pattern from the mask onto the substrate with typical dimensions in the micron or submicron range.
Accordingly, disturbances or vibrations need to be avoided since they can significantly alter the position of the pattern with respect to the wafer to affect the above required accuracy. The disturbances originate from external sources such as floor vibrations and air pressure waves. In general, the external vibration sources are not directly a part of the lithography apparatus. The disturbances also originate from internal sources within the lithography apparatus such as reaction forces of a positioning device of the substrate holder, the mask holder and other mechanically moving parts. Consequently, it is necessary that the lithographic apparatus is configured to substantially suppress or circum-vent these external and internal vibrations from affecting its precise operation.
As disclosed in U.S. Pat. No. 7,084,956, a lithographic apparatus is supported by a base via supporting devices for preventing the transmission of vibrations from the base to the frame. As shown in
In the above prior art technique and many others, the vibrations are isolated based upon a combination of the active control unit and the passive control unit. Although the passive unit can be adjusted depending upon its application prior to its use, the effectiveness for reducing vibrations is not adjusted during operation. Thus, it still remains desirable to improve the isolation of vibrations.
An apparatus and method effectively isolate vibrations in a lithography machine. The apparatus and method include a first control for actively reducing the vibrations in a first frequency range and a second control for actively reducing the vibrations in a second frequency range. The first control further includes a first actuator and a static reference object with which the vibrations are measured. The second control further includes a second actuator and an air spring in which the vibrations are measured. The apparatus and method are applied to substantially prevent the vibrations on the floor from traveling to the mask stage in one embodiment.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a embodiment of the invention.
The invention will be described in conjunction with the following drawings of exemplary embodiments in which like reference numerals designate like elements, and in which:
Referring now to the drawings, wherein like reference numerals designate corresponding structures throughout the views, and referring in particular to
Still referring to
Now referring to
The reference body subsystem 1500 of the anti-vibration system includes a base support structure or base 275, a plurality of reference body isolators 700, a reference body position sensor 500 and a reference body 285. In general, the base 275 is placed directly over the floor such as concrete and is made of rather rigid material such as cast iron. A plurality of the reference body isolators 700 is placed on the base 275 to mount the reference body 285 at a certain predetermined height from the base 275. Although the diagram illustrates only two reference body isolators 700 due to its side view, a set of three reference isolators 700 is usually used in a embodiment.
The reference body subsystem 1500 provides an extremely static reference object. To effectively maintain the static state, the reference body 285 is a huge mass, weighing approximately six metric tons that is at least one half of the total lithographic apparatus weight. The physical dimension of the reference body 285 is in the order of several feet in width, length and height. The reference body 285 has no moving parts to cause internal vibrations and is substantially isolated from external vibrations by the reference body isolators 700. Since the base 275 is placed directly over the floor and made of rather rigid material such as cast iron, it lacks vibration-attenuating function on the vibrations existing on the floor. Although the reference body 285 is placed over the floor, it is supported by a plurality of the reference body isolators 700 to prevent the transmission of the vibrations from the floor via the base 275.
The reference body isolators 700 isolate the vibrations which are both internally and externally originated. The internally originated vibrations are primarily caused by the reaction force in response to the movement initiated by the wafer stage 90. The externally originated vibrations primarily travel through the base 275 from the floor. In one embodiment, a set of three reference body isolators 700 is kinematically placed on the base 275 to mount the reference body 285 so as not to over-constrain the reference body 285 (only two reference body isolators 700 are shown in
In one embodiment, the reference body subsystem 1500 also includes the lens body 85 that houses an optical assembly 290 for forming an image pattern from the mask onto the wafer. As described above, since the reference body 285 is extremely static due to its mass and the reference body isolators 700, the optical assembly 290 firmly fixed inside the lens body 85 that is attached to the massive reference body 285 are also extremely stable to accurately form an image on the mask without being disturbed by vibrations. As shown in dotted lines, the optical assembly 290 is placed in a cylindrical lens body 85 in the center of the reference body 285, and the light transmitted through the mask or reticle passes through the optical assembly to reach the wafer or substrate.
In addition, the reference body subsystem 1500 includes the position sensor 500. In one embodiment as illustrated in
For the reference body subsystem 1500, the external disturbances also include air waves such as sounds that do not necessarily travel through the floor. In general, since the static reference body subsystem 1500 is generally located in a certain protected area usually isolated from major sources of external vibrations, the above described other external disturbances are minimized. However, when the minimal disturbances are introduced in the environment, the reference body 285 is so massive that no significant effect is realized for the lithography apparatus by the minimal air disturbances.
As illustrated in the left hand side of
To accomplish this goal, the position of the isolated body 200 is constantly monitored and continually adjusted relative to that of the static reference body 285 in order to substantially eliminate the effect of vibrations during the image transferring operation in the lithography apparatus. In general, two independent control mechanisms provide the above functions to make the isolated body 200 substantially free from vibrations. One vibration control mechanism involves a first control loop based upon the reference body position sensor 600, the position sensor 500, a force actuator controller 305 and the force actuator 300. The reference body position sensor 600 and the position sensor 500 continuously measure a relative distance between the reference body 285 and the isolated body 200 in real time. Based upon a signal indicative of the relative measured distance, the force actuator controller 305 controls the force actuator 300 to adjust the position of isolated body 200 with respect to the reference body 285. The vibrations on the isolated body 200 are substantially reduced by the physical movement of the isolated body 200 in an opposite direction over the measured change in distance. For example, the force actuator 300 is a Lorentz actuator, and the response characteristic of the force actuator 300 is less than approximately 20 Hz. In order to detect vibrations in various degrees of freedom, at least one pair of the position sensors 500 and 600 is used. One embodiment includes six pairs of the sensors for detecting vibrations respectively in the x, y and z translational and rotational directions for controlling the physical movement in six degrees of freedom. The details for implementing the vibration detection mechanism is known to one of ordinary skill, and one example of such disclosure is seen in U.S. Pat. No. 7,084,956.
Still referring to
The piezo actuator unit 400 is controlled by the Piezo actuator controller 405 and at least a pair of relative position sensors 550 and 650. The position sensors 550 and 650 are respectively mounted on the bottom and top walls of the gas chamber 455. The top wall of the gas chamber 455 is mounted on the isolated body 200. The position sensors 550 and 650 continuously measure in real time a relative distance between them that reflects the relative displacement of the gas chamber 455 with respect to the isolated body 200. Based upon a signal indicative of the relative measured distance, the Piezo actuator controller 405 controls the position of isolated body 200 with respect to the frame structure 100 by controlling the Piezo actuator 450. The vibrations on the isolated body 200 are substantially reduced by the physical movement of the isolated body 200 in an opposite direction over the measured change in distance. In general, the response characteristic of the Piezo actuator 450 ranges less than approximately 200 Hz or approximately 300 Hz. In particular, the response characteristic of the Piezo actuator 450 ranges from 1-2 Hz to 50-80 Hz, especially from 20 to 30 Hz. In order to detect vibrations in directions of various degrees of freedom, at least one pair of the position sensors 550 and 650 is used.
The Piezo actuator unit 400 includes an additional mechanism for protecting a Piezo actuator during its operation. The protection mechanism includes the ball joint 475, the air-bearing pad 480 and the air-bearing layer 485 to support the Piezo actuator as it expands and constricts. These elements 475, 480 and 485 are located below the Piezo actuator 450 to allow some degree of lateral movement for the Piezo actuator 450 so that they do not impose undesirable lateral constraint during the operation.
The force actuator 300 and the Piezo actuator unit 400 are illustrated to be located on the opposite sides of the isolator body 200 in the schematic diagram in
In addition, the Piezo actuator unit 400 in the embodiment utilizes a gas spring as illustrated in
The above described anti-vibration system is used to isolate vibrations in the lithography apparatus. That is, the anti-vibration system prevents the vibrations from the floor from traveling to the mask stage 80. Furthermore, the anti-vibration system also prevents the vibrations caused by the reaction force of the mask stage 80 from travelling through the isolated body 200 and the frame structure 100 to the lens body 85. The substantially eliminated vibrations primarily from the floor and secondarily from the mask stage 80 secure a static state in the lens body so that the optical assembly projects a predetermined pattern on the wafer without movement disturbances. Although the embodiment of the anti-vibration system is applied to substantially reduce the vibrations from the floor, the anti-vibration system is optionally applicable to different parts of the lithography apparatus for other sources of internal vibrations such as a wafer stage.
Now referring to
As also described, the first control loop involves the reference body 285, whose position 285A is substantially free from movement due to vibrations and force exerted by the force actuator 300. Lastly, the first control loop involves the isolated body 200, whose position 200A is affected by movement due to vibrations and force exerted by the force actuator 300. The reference body position sensor 600 and the position sensor 500 continuously measure a relative distance between the substantially static reference body position 285A and the isolated body position 200A in real time and send the signals indicative of the measured distance to the force actuator controller 305. Based upon the continuously received signal from the sensors 500 and 600, the force actuator controller 305 generates in real time a control signal indicative of an amount and a direction of the movement for controlling the position of isolated body 200 with respect to the frame structure 100 so that the undesirable vibrations with respect to the static reference body 285 are substantially reduced. In other words, the force actuator controller 305 determines the amount of physical movement of the isolated body 200 in an opposite direction over the measured relative distance change. Thus, the force actuator controller 305 continuously sends the generated control signal to the force actuator 300 so as to cancel the measured vibrations. For example, the response characteristic of the force actuator 300 is approximately 20 Hz. The above described feedback loop is continuously repeated in real time to maintain the desirably isolated body position 200A with respect to the reference body position 285A.
Now referring to
Still referring to
Furthermore, the second feed-back loop optionally includes a scale modifier gain 405C and a low-pass filter 405A for further reducing low frequency vibration. The scale modifier gain 405C receives an output control command signal from the Piezo actuator controller 405 and detects a low frequency component indicative of low frequency vibrations in the Piezo control command signal. Some low frequency vibrations are leaked through or not completely filtered by the high-pass filter 405B. Upon detection of the low frequency component, the scale modifier gain 405C generates a low frequency vibration signal indicative of the same frequency but in a reverse direction to effectively cancel the detected low frequency signal when the detected low frequency vibration and the generated signal are combined. The low-pass filter 405A is connected to the scale modifier gain 405C to ascertain that only the generated low frequency signal is passed back to the Piezo actuator unit 400, which in turn incorporates the reverse low frequency signal into the Piezo control command signal. Ultimately, at the Piezo actuator 450, the still existing low frequency vibrations are now substantially reduced.
The first and second feed-back control loops of
Now referring to
Still referring to
The reference body subsystem of the anti-vibration system includes a base support structure or base 275, a plurality of reference body isolators 700, a lens body position sensor 500A and a reference body 285. In general, the base 275 is placed directly over the floor such as concrete and is made of rather rigid material such as cast iron. A plurality of the reference body isolators 700 is placed on the base 275 to mount the reference body 285 at a certain predetermined height from the base 275. Although the diagram illustrates only two reference body isolators 700 due to its cross-sectional view, a set of three reference isolators 700 is usually used in a second embodiment.
The reference body subsystem provides an extremely static reference object. To accomplish this goal, the reference body 285 is a huge mass, weighing approximately six metric tons that is at least one half of the total lithographic apparatus weight. The physical dimension of the reference body 285 is in the order of several feet in width, length and height. The reference body 285 has no moving parts to cause internal vibrations and is substantially isolated from external vibrations by the reference body isolators 700. Since the base 275 is placed directly over the floor and made of rather rigid material such as cast iron, it lacks vibration-attenuating function on the vibrations existing on the floor. Although the reference body 285 is placed over the floor, it is supported by a plurality of the reference body isolators 700 to prevent the transmission of the vibrations from the floor via the base 275.
The reference body isolators 700 isolate the vibrations which are externally originated. It should be made certain that no internal vibration source or components are contained within the body that the reference body isolator 700 supports. The externally originated vibrations primarily travel through the base 275 from the floor. In one embodiment, a set of three reference body isolators 700 is kinematically placed on the base 275 to mount the reference body 285 so as not to over-constrain the reference body 285 (only two reference body isolators 700 are shown in
In the second embodiment, the reference body subsystem 1500 also includes the lens body 85 that houses an optical assembly for forming an image pattern from the mask onto the wafer. As described above, since the reference body 285 is extremely static due to its mass and the reference body isolators 700, the optical lenses firmly fixed inside the lens body 85 are also extremely static to accurately form an image on the mask without being disturbed by vibrations.
In addition, the extremely static reference body subsystem includes the position sensor 500A. In the second embodiment as illustrated in
As illustrated in the drawing, the reference body subsystem containing the lens body 85 and the reference body 285 is effectively separated from the isolated body subsystem containing the isolated body 200. Although the base 275 and the frame 100 are mechanically continuous, the lens body 85 and the reference body 285 are vibrationally-isolated with the frame structure 100 so that the vibrations experienced at the frame structure 100 is not traveling to the reference body 285.
For the reference body subsystem 1500, the external disturbances also include air waves such as sounds that do not necessarily travel through the floor. In general, since the static reference body subsystem is generally located in a certain protected area usually isolated from major sources of external vibrations, the above described other external disturbances are minimized. However, when the minimal disturbances are introduced in the environment, the reference body 285 is so massive that no significant effect is realized for the lithography apparatus by the minimal air disturbances.
Now referring to
To accomplish this goal, the position of the isolated body 200 is constantly monitored and continually adjusted relative to that of the lens body 85 in order to substantially eliminate the effect of vibrations during the image transferring operation in the lithography apparatus. In general, two independent active control mechanisms provide the above functions to make the isolated body 200 substantially free from vibrations. One vibration control mechanism involves a first control loop based upon the lens body position sensor 500A of
Based upon a signal indicative of the relative measured distance, the force actuator controller 305 controls the force actuator 300 in order to adjust the position of isolated body 200 with respect to the lens body 85 and the reference body 285. The vibrations in a predetermined low frequency range on the isolated body 200 are substantially reduced by the physical movement of the isolated body 200 in an opposite direction over the measured change in distance. For example, the force actuator 300 is a Lorentz actuator, and the response characteristic of the force actuator 300 is less than approximately 20 Hz. The force actuator 300 further includes an actuator reaction force channeling structure 310, which absorbs the reaction force and channels it to the frame structure 100 or the floor.
Still referring to
The piezo actuator unit 400 is controlled by the Piezo actuator controller 405 (not shown) based upon a signal from a pair of relative position sensors 550 and 650. The position sensors 550 and 650 are respectively mounted on the air spring piston 455A and the bottom frame of the gas chamber 455. The position sensors 550 and 650 continuously measure in real time a relative distance between them. Based upon a signal indicative of the relative measured distance, the Piezo actuator controller 405 controls the Piezo actuator 450 to adjust such that the distance between the position sensors 550 and 650 is always kept constant. The vibrations transmitted to the isolated body 200 are substantially reduced by the physical movement of the Piezo material 450 in an opposite direction over the measured change in distance. For example, the response characteristic of the Piezo actuator 450 ranges less than approximately 200 Hz or approximately 300 Hz. In particular, the response characteristic of the Piezo actuator 450 ranges from 1-2 Hz to 50-80 Hz, especially from 20 to 30 Hz. Only one pair of the position sensors 550 and 650 is used for each of the Piezo unit.
The Piezo actuator unit 400 includes an additional mechanism for protecting a Piezo actuator 450 during its operation. Although it is not shown in the drawing, the protection mechanism protects the Piezo actuator as it expands and constricts. The protection mechanism is placed below the Piezo actuator 450 to allow some degree of lateral movement for the Piezo actuator 450 so that the surrounding structures do not impose undesirable lateral constraint during the operation.
The force actuator 300 and the Piezo actuator unit 400 are illustrated on the same side of the isolator body 200 in the schematic diagram in
In addition, the Piezo actuator unit 400 in the second embodiment utilizes a gas spring as illustrated in
The above described anti-vibration system is used to isolate vibrations in the lithography apparatus. That is, the anti-vibration system is located near the isolated 200 body so that the vibrations caused by the floor are prevented from traveling through the isolated body and the frame structure 100 to support the mask stage 80. Furthermore, the anti-vibration system is also located near the isolated body 200 where the mask stage 80 is mounted so that the vibrations caused by the reaction force of the mask stage 80 are prevented from traveling through the isolated body 200 and the frame structure 100 to the lens body 85. Thus, the lack of vibrations primarily from the floor and secondarily from the mask stage 80 secures a static state in the lens body 85 so that the optical assembly 290 projects a predetermined pattern on the wafer without disturbance. Although the embodiment of the anti-vibration control system is applied to substantially reduce the vibrations from the floor, the anti-vibration system is optionally applicable to different parts of the lithography apparatus for other sources of internal vibrations such as a wafer stage.
It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and that although changes may be made in detail, especially in matters of shape, size and arrangement of parts, as well as implementation in software, hardware, or a combination of both, the changes are within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
