Precise positioning system for dual stage switching exposure

The present invention relates to the field of motion positioning techniques, particularly to a precise positioning system for dual stage switching exposure.

Exposure refers to a process of exposing and transferring the chip pattern on a mask onto a silicon wafer, which is one of the important processes during semiconductor manufacturing. An exposure process comprises several sub-processes, such as wafer loading/unloading, pre-alignment, alignment, level adjustment detection, exposure, etc. The apparatus for exposure process is called a lithography machine. A main part of a lithography machine is the wafer stage motion positioning system, whose operation efficiency greatly influences the throughput of the lithography machine.

Present high-resolution lithography machines are prone to adopt a dual wafer stage structure. As shown in FIG. 1 , a lithography machine adopting dual stage structure comprises from the top down an illumination system 4 , a reticle stage positioning system 3 , a projection object lens system 2 , a focus and level adjustment detecting system 5 , an alignment system 6 , two wafer stage positioning units 100 a , 100 b , a base 1 , etc. Wafer loading/unloading, pre-alignment, alignment, level adjustment detection and other pre-processing steps are carried out on the wafer stage unit 100 a , which can work simultaneously with the wafer stage unit 100 b responsible for the exposure process.

A dual wafer stage structure is described in PCT patent application WO98/40791, in which, each wafer stage has two exchangeable displacement units and an object holder. The object holders are connected to the guide bars. During operation, several pre-processing steps before exposure process are carried out on a wafer at the pre-processing workstation, while the exposure process is carried out on another wafer at the exposure workstation. After finishing these two series of steps, the two wafer stages move to an intermediate position to exchange the two object holders, so that either object holder moves from its displacement unit to the other holder's displacement unit, thereby accomplishing the exchange of two wafer stages.

The above mentioned structure enables the simultaneous operation and the exchange of two wafer stages, however, it has the following disadvantages: when the two wafer stages are exchanging, during a short period of time, the wafer stages are under an unrestricted status, so that the positioning accuracy of the system is influenced; besides, there exists a risk of collision of the two wafer stages during the exchange process due to the overlapped moving area and the high running speed of the two stages. Any collision will lead to a serious result. Although software can be used to control and protect the wafer stages, collision will still be possible if the software goes wrong or the power is suddenly cut off.

It is an object of the present invention to provide a precise positioning system for dual stage switching exposure to improve the operation accuracy and the throughput of lithography machines.

In order to achieve the aforementioned object, the present invention is set forth as follows: the system comprises at least a base, a first wafer stage positioning unit disposed on the base for a pre-processing workstation, and a second wafer stage positioning unit for an exposure workstation, each of the wafer stage positioning units further comprising at least a wafer stage, a motion positioning detector, an X-direction guide bar, and a Y-direction guide bar, characterized in that each workstation has two X-direction guide bars positioned on and movable along the Y-direction guide bars, the X-direction guide bars of adjacent workstations can be connected to each other. The X-direction guide bars are used to support the wafer stages. The linear gratings positioned on the guide bars cooperate with the motion positioning detectors to measure and feedback the position data of the stages during the wafer alignment process at the pre-processing workstation and the wafer exposure process at the exposure workstation.

A cable stage is connected to each of the wafer stages. The cable stages move on opposite sides of the base via cable stage guide bars of the system.

The wafer stage is disposed in noncontact association with the X-direction guide bars. The X-direction guide bars are disposed in noncontact association with the Y-direction guide bars. The noncontact association can be achieved through gas levitation bearing or magnetic levitation bearing, for reducing the friction during stepping motions.

The wafer stage is positioned on either of the X-direction guide bars, and can step along the X-direction guide bar. Each of the workstations has two Y-direction guide bars, the Y-direction guide bars and either of the X-direction guide bars of the corresponding workstation forming an “H” shaped structure. Linear motors are installed into the X-direction guide bars for driving the X-direction guide bars to step along the Y-direction guide bars.

The motion positioning detectors are laser interferometers and linear gratings. Laser interferometers are used for level adjustment detection and alignment at the pre-processing workstation and for exposure position measurement at the exposure workstation. The linear gratings are positioned on both of the X-direction guide bars and at least one of the Y-direction guide bars of each workstation to cooperate with the laser interferometers in measuring and feeding back the positions of the wafers.

Compared with the known art, the present invention has the following advantages: since each of the workstations has two X-direction guide bars, when switching wafer stages, the switching paths are short, greatly raising the speed of wafer stage exchange, therefore, improving the throughput of the lithography machine. In addition, the wafer stages are symmetrically positioned according to the central axis of the guide bars, and are connected to the guide bars both during the processes at the two workstations and during the switching process, thereby assuring the operation accuracy of the system. Moreover, the dual stage structure eliminates the overlapped moving area of the two stages, preventing the collision between the stages, so that no extra protection devices are needed, and the structure of the system can be simplified. Furthermore, there is no specific limitation on the size of the wafer stages, and therefore, the system can be used in exposure processes involving wafers of different sizes. Due to the similarity of the wafer stage positioning units of the two workstations, the system can be easily extended into a multiple stage positioning system.

FIG. 1 is a schematic view of the structure of a dual wafer stage switching step-and-scan projection lithography machine.

FIG. 2 is a layout of the structure of the dual stage positioning system of the present invention.

FIG. 3 is a top plan view of the two wafer stages under the operation status.

FIG. 4 is a top plan view of the two wafer stages at the switching position.

FIG. 5 is a top plan view of the two wafer stages during the switching process.

FIG. 6 is a top plan view of the two wafer stages after the switching process.

FIG. 7 is a schematic view of a multiple stage system.

The present invention will be described in detail by reference to the drawings and the preferred embodiments.

FIG. 2 shows the operation status of the dual wafer stage positioning system of the present invention, which comprises a base 1 , a first wafer stage positioning unit disposed on the base 1 for a pre-processing workstation, and a second wafer stage positioning unit disposed on the base 1 for an exposure workstation. Each of the wafer stage positioning units comprises a wafer stage 100 a (for pre-processing workstation) or 100 b (for exposure workstation); motion positioning detectors (laser interferometers) 50 a , 51 a , 50 b , 51 b ; two X-direction guide bars 10 a , 11 a or 10 b , 11 b , wherein, X-direction guide bars 10 a , ha belong to the wafer stage positioning unit of the pre-processing workstation, while X-direction guide bars 10 b , 11 b belong to the wafer stage positioning unit of the exposure workstation; two Y-direction guide bars 20 a , 21 a or 20 b , 21 b , wherein, Y-direction guide bars 20 a , 21 a belong to the wafer stage positioning unit of the pre-processing workstation, while Y-direction guide bars 20 b , 21 b belong to the wafer stage positioning unit of the exposure workstation.

The wafer stages are positioned on and movable along the X-direction guide bars. The X-direction guide bars are positioned on the Y-direction guide bars and move along the Y-direction guide bars driven by linear motors. The X-direction guide bars of adjacent workstations can be connected to each other. The guide bars have linear gratings 40 a , 41 a , 42 a , 40 b , 41 b , 42 b disposed thereon, wherein, 40 a is disposed on X-direction guide bar 11 a ; 41 a is disposed on X-direction guide bar 10 a ; 42 a is disposed on Y-direction guide bar 20 a ; 40 b is disposed on X-direction guide bar 11 b ; 41 b is disposed on X-direction guide bar 10 b ; 42 b is disposed on Y-direction guide bar 20 b . Wafer stage 100 a is connected to a cable stage 30 a moving along cable stage guide bar 39 a . Wafer stage 100 b is connected to a cable stage 30 b moving along cable stage guide bar 39 b.

Referring to FIG. 2 , wafer stage 100 a is supported by X-direction guide bar 10 a . A series of pre-processing steps before exposure are carried out on wafer stage 100 a at the pre-processing workstation. Wafer stage 100 b is supported by X-direction guide bar 11 b . The exposure process is carried out on wafer stage 100 b at the exposure workstation. X-direction guide bars 11 a , 10 b are temporarily under an idle status, respectively positioned at the edge of their own workstations without interfering with the wafer stages under operation. Cable stages 30 a , 30 b are driven by the motors set inside to keep the cables moving synchronously with wafer stages 100 a , 100 b.

The present invention has adopted non-friction vacuum preload hydrostatic gas bearings between: wafer stage 100 a and X-direction guide bars 10 a , 11 a ; wafer stage 100 b and X-direction guide bars 10 b , 11 b ; X-direction guide bars 10 a , 11 a and Y-direction guide bars 20 a , 21 a ; X-direction guide bars 10 b , 11 b and Y-direction guide bars 20 b , 21 b . If necessary, permanent magnetic hydrostatic gas bearings can be used instead.

Each guide bar of the present invention has a linear grating disposed thereon. Gratings 40 a , 41 a are used as position feedback devices when wafer stage 100 a is moving in the X-direction. Gratings 40 b , 41 b are used as position feedback devices when wafer stage 100 b is moving in the X-direction. Grating 42 a is used as position feedback device when X-direction guide bars 10 a , 11 a are moving in the Y-direction. Grating 42 b is used as position feedback device when X-direction guide bars 10 b , 11 b are moving in the Y-direction. Motion positioning detectors 50 a , 51 a are used for real-time detection and control in alignment, level adjustment detection at the pre-processing workstation. Motion positioning detectors 50 b , 51 b are used for real-time detection and control in exposure position determination at the exposure workstation.

FIGS. 3 to 6 are schematic views of the dual stage switching process.

FIG. 3 is a top plan view of the two wafer stages under the operation status. X-direction guide bars 11 a , 10 b under idle status are respectively positioned at the edge of their own workstations to make sure that the movements of wafer stages 100 a , 100 b are not interfered.

FIG. 4 is a top plan view of the two wafer stages 100 a , 100 b under the switching position. When wafer stages 100 a , 100 b finish the work at their respective workstation, the original idle X-direction guide bars 11 a ; 10 b are driven by linear motors to move along Y-direction guide bars 20 a , 21 a ; 20 b , 21 b from the edges to the switching position. X-direction guide bars 10 a , 11 b also move to the switching position, so that X-direction guide bars 11 a and 11 b ; 10 a and 10 b can be accurately connected to each other. Then, wafer stage 100 a is driven by the linear motor to move from the pre-processing workstation to the exposure workstation along the X-direction. Wafer stage 100 b is driven by the linear motor to move from the exposure workstation to the pre-processing workstation.

FIG. 5 is a top plan view of the two wafer stages during the switching process.

When the two stages are switched and arrive at the corresponding workstation, the pre-processing steps and the exposure process are carried out at the corresponding workstation. FIG. 6 is a top plan view of the two wafer stages after the switching process. X-direction guide bars 10 a , 11 b move to the edge of their own workstations, staying under an idle status. Wafer stages 100 a , 100 b are respectively supported by X-direction guide bars 10 b , 11 a . The exposure process is carried out on stage 100 a at the exposure workstation. Pre-processing steps before exposure are carried out on stage 100 b at the pre-processing workstation. When the exposure process and the pre-processing steps of the two stages are finished, the four X-direction guide bars move to the switching position again in the same way as described above to repeat the switching process as shown in FIGS. 4 to 6 , thereby finishing the continuous and complete process of wafer exposure.

FIG. 7 is a top plan view of a three stage system derived from the system described above to explain the flexibility of the present invention. Since the structures of the two workstations of the system are quite similar, when more workstations are needed under other technical requirements, the system can be easily extended to a multiple stage structure. Referring to FIG. 7 , a wafer stage positioning unit c having two X-direction guide bars 10 c , 11 c is added to the original system. The operation and detection methods are the same as the two positioning units mentioned above. When wafer stage 100 a or 100 b needs to move to workstation c, just connect the X-direction guide bars 10 c , 11 c to 10 a , ha and drive the wafer stages to move in the X-direction, so that the three wafer stages can be switched. Similarly, the present system can be further extended into a multiple stage system having more than three workstations.

The foregoing description has disclosed some embodiments of the present invention. But the present invention should not be restricted to the field of motion positioning of the semiconductor lithography process. The present invention can be used in any apparatus or system involving precise positioning techniques and requiring the exchange and simultaneous operation of two stages. Although the preferred embodiments of the present invention are disclosed as above, technicians of this field should aware that any modification, interpolation or variation within the principle of the present invention falls in the scope of the present invention.