WO2007118376A1

WO2007118376A1 - Dual stage switching positioning system for step and scan lithography machine

Info

Publication number: WO2007118376A1
Application number: PCT/CN2006/002862
Authority: WO
Inventors: Yingsheng Li; Xiaoping Li
Original assignee: Shanghai Micro Electronics Equipment Co., Ltd.
Priority date: 2006-04-14
Filing date: 2006-10-26
Publication date: 2007-10-25
Also published as: CN100504614C; CN1828427A

Abstract

A dual stage switching positioning system for a step and scan lithography machine comprises a base, and first and second positioning units disposed on the base respectively for a pre-processing workstation and an exposure workstation. Each of the positioning units comprises two y-direction guide bars; at least one x-direction guide bar positioned on and movable along the y-direction guide bars; a wafer stage positioned on and movable along the at least one x-direction guide bar; and a motion positioning detector for measuring and feeding back position data. The first positioning unit has one x-direction guide bar, and the second positioning unit has two x-direction guide bars. The x-direction guide bars of the two positioning units can be connected each other.

Description

A DUAL STAGE SWITCHING POSITIONING SYSTEM FOR A STEP AND SCAN LITHOGRAPHY MACHINE

Technical Field

The present invention relates to the field of precise positioning techniques, particularly to a wafer motion positioning apparatus used in the semiconductor industry.

Background Art

Lithograph 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 IC chip manufacturing. A lithograph process comprises several sub-processes: wafer loading/unloading, pre-alignment, alignment, exposure, etc. The throughput of the system is determined by the time durations of the sub-processes.

A typical lithography machine adopts a wafer stage structure. As shown in FIG. 1, a lithography machine mainly comprises an illumination system 16, a reticle stage positioning system 15, a projection object lens system 14, a wafer stage motion positioning system 2, a focus and level adjustment measuring system 13, an alignment system 12, etc. In the figure, 200 refers to a wafer; 500 refers to a mask. The illumination system 16 is composed of a radiation source and an illumination object lens system. Light beam passes through the mask unit and transfers the image on the mask 500 onto the wafer 200 via a projection object lens. The main function of the wafer stage motion positioning system 2 is to support the wafer 200 and carry out the operations of alignment, exposure, wafer loading/unloading and so on. All the operations are done on a single wafer stage.

FIG. 2 shows the exposure cycle of a single wafer. From wafer loading, measuring and aligning, exposing, to wafer unloading, all the steps are serially carried out. The duration of this cycle influences the throughput of the system. In order to raise the efficiency, every step of the cycle must be shortened.

As the critical dimension (CD) of the wafer is becoming much thinner, the precision of the alignment technique is increasingly required. It is rather difficult to reduce the time of alignment under such requirement that the wafer stage scan with a high precision and a low speed. One way to reduce the time is to raise the step and scan speed of the wafer stage. However, raising the speed may cause the deterioration of the dynamic performance of the system, or need to adopt some protection devices and operation precision control techniques, either sacrificing the performance or increasing the cost.

In order to solve the abovementioned problem, present lithography machines have adopted the dual wafer stage structure, which has one more wafer stage than a single stage structure does. Referring to FIG. 3, a dual stage system comprises an illumination system 16, a reticle stage positioning system 15, a projection object lens system 14, two wafer stage positioning systems 2a, 2b, a focus and level adjustment measuring system 13, and an alignment system 12. During operation, the alignment and wafer loading/unloading steps are carried out on stage 2a, while simultaneously the exposure process is carried out on stage 2b. In this way, as shown in FIG. 4, the time duration of the exposure cycle of a single wafer is greatly shortened, and the throughput is raised without increasing the step and scan speed of the wafer stage.

A dual wafer stage structure is described in PCT patent application WO 98/40791, 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. This method enables the reduction of exposure time of every wafer and the improvement of the throughput of the system without increasing the running speed of the wafer stages. However, there remains a problem of this structure: since each wafer stage couples to the guide bars, during the exchange process, the object holder and the wafer stage need to be separated for a short period of time, during which the wafer stages are under an unrestricted status, so that the positioning accuracy of the system is influenced. One improvement of the above structure is described in patent application US 2001/0004105, in which, many protection and detection devices are added to the system to ensure the positioning accuracy. However, these extra devices make the structure of the system much more complicated and increase the manufacturing cost. Besides, due to the overlapped moving area and high running speed of the two stages, there exists a risk of collision of the two stages during the exchange process. Any collision will lead to a serious result. So, the system adopts some extra mechanical protection devices and hardware/software control methods for preventing such kind of collision. However, this is not the best way to solve the problems of the structure.

Another dual stage structure is disclosed in PCT patent application WO 01/40875. The system has two data collection stations and an exposure station located there between. Each wafer stage has its own data collection station, and is movable only between its own data collection station and the exposure station. During operation, one wafer stage carries out the exposure process at the exposure station, while another loads a new wafer and carries out the data collection process at its data collection station. After that, the first stage moves back to its data collection station; unloading the wafer; loading a new wafer; and carries out the data collection process, while the second stage moves to the exposure station, and carries out the exposure process. The two stages repeat the above steps, alternately moving to and from the exposure station. The movements of the two stages do not interfere. The moving paths are short, and the moving speeds are high. This structure has an advantage of easy operation and high reliability. But compared with the former structures, this structure adopts one more alignment apparatus for data collection and one more wafer loading/unloading apparatus, greatly increasing the cost. Furthermore, since this structure has one more station than the former structures, the whole size of the wafer base will also be increased.

Summary of Invention

It is an object of the present invention to provide a dual stage switching positioning system for a step and scan lithography machine to simplify the structure while reducing the exposure cycle of a wafer.

In order to achieve the aforementioned object, the present invention is set forth as follows: the system comprises a base, first and second positioning units disposed on the base respectively for a pre-processing workstation and an exposure workstation, each of the positioning units further comprises: two y-direction guide bars; at least one x-direction guide bar positioned on and movable along the y-direction guide bars; a wafer stage positioned on and movable along the at least one x-direction guide bar; and a motion positioning detector for measuring and feeding back position data; characterized in that, the first positioning unit has one x-direction guide bar, and the second positioning unit has two x-direction guide bars, x-direction guide bars of the two positioning units can be connected to each other.

In one embodiment of the present invention, a cable stage is connected to each of the wafer stages, the cable stages moving on opposite sides of the base via cable stage guide bars. The cable stage comprises an x-direction driver and a y-direction driver for driving the cable stage in both directions.

In one embodiment of the present invention, each of the wafer stages connects to the guide bars via hydrostatic gas bearings or hydrostatic magnetic bearings to achieve frictionless movement between the stages and the guide bars.

In one embodiment of the present invention, the motion positioning detector comprises laser interferometers and linear gratings. The interferometers are positioned on adjacent sides of each positioning unit. The linear gratings are positioned on each of the x-direction guide bars and on the y-direction guide bars of one of the positioning units.

In one embodiment of the present invention, each wafer stage steps along the x-direction guide bar without friction. The x-direction guide bar and the y-direction guide bars of each positioning unit form an "H" shaped structure. The x-direction guide bar steps along the y-direction guide bars without friction. The frictionless stepping is achieved by using hydrostatic gas bearings or hydrostatic magnetic bearings.

Compared with the known art, the present invention has the following advantages: since one guide bar is added to the exposure workstation, it not only enables the exchange of the two stages, but also greatly reduces the time needed for the exchange of the stages at the exposure workstation. The exchange process is simplified, thus effectively controlling the cost. In addition, adopting two workstations, the exposure workstation and the pre-processing workstation, enables the simultaneous work of the two workstations, reducing the exposure time of a single wafer, so that the throughput of the system can be improved while remaining the same running speed and acceleration as a single stage apparatus. Furthermore, the simplified structure of the present invention eliminates the overlapped area of the work spaces, so that the two workstations no longer interfere with each other. No additional apparatus for preventing collision is needed, thereby simplifying the system, reducing the cost, and effectively improving the reliability.

Brief Description of Drawings

Fig. 1 is a schematic view of the structure of a single positioning system of a lithography machine.

Fig. 2 is a schematic view of the exposure cycle of a single wafer stage.

Fig. 3 is a schematic view of the structure of a known dual positioning system of a lithography machine.

Fig. 4 is a schematic view of the exposure cycle of the dual wafer stage of Fig. 3.

Fig. 5 is a schematic view of the structure of the dual positioning system of the present invention.

Fig. 6 is a flow chart of the dual wafer stage switching process of the present invention.

Figs. 7 to 12 are schematic views of the dynamic operations of a work flow.

Detailed Description of Preferred Embodiments

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

Fig. 5 shows the operation status of the dual positioning system of the present invention, the structure of which comprises a base 1 and two positioning units disposed on the base 1 respectively working for an exposure workstation and a pre-processing workstation. Each of the positioning units comprises a wafer stage 2a (for the pre-processing workstation) or 2b (for the exposure workstation); motion positioning detectors 50a, 51a or 50b, 51b; x-direction guide bars 10a or 10b, lib; y-direction guide bars 20a, 21a or 20b, 21b, wherein, each wafer stage is positioned on and movable along the x-direction guide bar; x-direction guide bars are positioned on and movable along y-direction guide bars; x-direction guide bars of the two workstations can be connected to each other. All the guide bars have linear gratings 40a, 49a or 40b, 41b, 49b disposed thereon. Motion positioning detectors are used for measuring and feeding back the wafer exposure position at the exposure workstation and the wafer alignment position at the pre-processing workstation.

Referring to Figs. 7 to 13 of the drawings, 10a is the x-direction guide bar set for the pre-processing workstation. 10b and lib are the two x-direction guide bars of the exposure workstation. The system further comprises cable stages 30a, 30b, which move on both sides of the base 1 via cable stage guide bars 39a, 39b.

Referring to Fig. 5, the predetermined operations at the pre-processing workstation are earned out on wafer stage 2a supported by x-direction guide bar 10a. The predetermined exposure operation at the exposure workstation is carried out on another wafer stage 2b supported by x-direction guide bar 10b. X-direction guide bar lib is positioned at the edge of wafer stage 2b, temporarily under an idle status. Cable stages 30a, 30b are driven by the motors set inside to keep the cables on the wafer stages moving synchronously with wafer stages 2a, 2b.

The present invention has adopted non-friction hydrostatic gas bearings between wafer stages 2a, 2b and x-direction guide bars 10a, 10b, lib; x-direction guide bars 10a, 10b, lib and y-direction guide bars 20a, 21a, 20b, 21b. Some parts have adopted vacuum preload hydrostatic gas bearings. If necessary, permanent magnetic preload hydrostatic gas bearings can also be used.

All the guide bars of the present invention respectively have a linear grating 40a, 49a, 40b, 41b, 49b disposed thereon, wherein, gratings 40a, 40b, 41b can be used as the position feedback devices when wafer stages 2a, 2b are moving in the x-direction; gratings 49a, 49b can be used as the position feedback devices when wafer stages 2a, 2b are moving in the y-direction. Laser interferometer measuring systems 50a, 51a, 50b, 51b are used as the feedback devices for position measuring. Additionally, assistant sensors are used to control the positions of the two stages during the switching process.

Fig. 6 is a flow chart of the operations of the two wafer stages. During the lithograph process, according to practice, the steps of wafer loading/unloading, alignment, and measuring the exposure area conditions require less time than the step of exposing the whole wafer does. Therefore, the flow of the dual stage operation can be optimized into the steps shown in the flow chart.

Please refer to Figs. 7 to 12 for detailed structure layouts. In the figures, the stage at the pre-processing workstation is 2a; the stage at the exposure workstation is 2b. At the beginning of the process, referring to step 200, both stages have no wafer, at which time stage 2b is under an idle status, while stage 2a moves to the wafer loading/unloading position to load a wafer, and then carries out the data collection of alignment and focus and level adjustment. Position measurements are fed back by linear gratings 40a, 49a and laser interferometers 50a, 51a.

Step 210, referring to Fig. 8, after wafer stage 2a finished the pre-processing steps, stage 2a moves to the switching position, during which time, the two guide bars and wafer stage 2b also move to the switching position, enabling the interconnection of guide bar 10a and guide bar lib. The positions of the guide bars are measured and controlled by the linear gratings and the sensors.

Step 220, referring to Fig. 9, the linear motor drives wafer stage 2a to move from the pre-processing workstation to the exposure workstation, finishing the switch of wafer stage 2a.

Step 230, referring to Fig. 10, the guide bar of the pre-processing workstation quickly moves to the position of wafer stage 2b, which has finished the exposure process at the exposure workstation, enabling the interconnection of guide bar 10a and guide bar 10b, guiding wafer stage 2b to move from the exposure position to the pre-processing workstation.

Step 240, referring to Fig. 11 , wafer stage 2b is driven by the linear motor to move from the exposure workstation to the pre-processing workstation.

Step 250, referring to Fig. 12, wafer stage 2b moves to the wafer loading/unloading position of the pre-alignment workstation to unload the wafer after exposure, and load a new wafer. Then, wafer stage 2b moves to the alignment position to carry out a series of predetermined operations. Simultaneously, wafer stage 2a is driven by guide bar lib to carry out the exposure operation at the exposure workstation. Guide bar 10b moves to the edge position, temporarily under an idle status.

Step 260, after exposing the wafer on wafer stage 2a, the stage moves to the switching position. At the same time, wafer stage 2b which has finished the pre-processing steps also moves to the switching position, enabling the interconnection of guide bar 10a and guide bar 10b. Driven by the linear motor, stage 2b moves from the pre-processing workstation to the exposure workstation. Detailed description of the figure is similar to that of Figs. 8 and 9.

Step 270, after guide bar 10a of the pre-processing workstation guides wafer stage 2b to move to the exposure workstation, guide bar 10a quickly moves to the other portion of the base and couples to guide bar lib, while wafer stage 2b is waiting for the exposure process. Detailed description of the figure is similar to that of Fig. 10.

Step 280, after the linear motor drives wafer stage 2a to move from the exposure workstation to the pre-processing workstation, a series of predetermined operations such as wafer loading/unloading, alignment, focus and level adjustment measuring, etc. are carried out on stage 2a, while wafer stage 2b, driven by guide bar 10b, carries out the exposure process. Detailed description of the figure is similar to that of Figs. 11 and 12.

Step 290, stage 2a waits for the exposure process of stage 2b after finishing the pre-process operations. When the exposure process of stage 2b is finished, these two stages respectively move to the switching position. Guide bar 10a of the pre-processing workstation and the temporarily idle guide bar lib of the exposure workstation couple to each other, carrying out the moving and switching process of the stages. Repeat step 220 and follow the cycle to accomplish continuous exposure operations of wafers.

The foregoing description has disclosed some embodiments of the present invention. But the present invention should not be restricted to the field of wafer 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.

Claims

What is claimed is:

1. A dual stage switching positioning system for a step and scan lithography machine, which comprises a base, first and second positioning units disposed on the base respectively for a pre-processing workstation and an exposure workstation, each of the positioning units further comprises: two y-direction guide bars; at least one x-direction guide bar positioned on and movable along the y-direction guide bars; a wafer stage positioned on and movable along the at least one x-direction guide bar; and a motion positioning detector for measuring and feeding back position data; characterized in that, the first positioning unit has one x-direction guide bar, and the second positioning unit has two x-direction guide bars, x-direction guide bars of the two positioning units can be connected to each other.

2. A dual stage switching positioning system as claimed in claim 1, characterized in that a cable stage is connected to each of the wafer stages, the cable stages moving on opposite sides of the base via cable stage guide bars.

3. A dual stage switching positioning system as claimed in claim 2, characterized in that each cable stage comprises an x-direction driver and a y-direction driver for driving the cable stage in both directions.

4. A dual stage switching positioning system as claimed in claim 1, characterized in that each wafer stage connects to and steps along the x-direction guide bars without friction; the x-direction guide bars connect to and step along y-direction guide bars without friction.

5. A dual stage switching positioning system as claimed in claim 4, characterized in that the frictionless stepping is achieved by using bearings selected from the group consisting of hydrostatic gas bearings and hydrostatic magnetic bearings.

6. A dual stage switching positioning system as claimed in claim 1, characterized in that the motion positioning detector comprises laser interferometers and linear gratings, the interferometers are positioned on adjacent sides of each positioning unit; the linear gratings are positioned on each of the x-direction guide bars and on the y-direction guide bars of one of the positioning units.

7. A dual stage switching positioning system as claimed in claim 1, characterized in that the x-direction guide bar and the y-direction guide bars of each positioning unit form an "H" shaped structure.