Wafer stage and related method

There are provided a wafer stage and methods for chucking a wafer using the same. The wafer stage includes a wafer chuck adapted to hold a wafer; lift pins adapted to pass through the wafer chuck, move vertically, and support the wafer; and an air expulsion unit adapted to expel air towards an edge of the wafer. The method for attaching a wafer to a wafer chuck comprises lowering lift pins supporting the wafer; and expelling air towards an edge of the wafer using an air expulsion unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention relate to a wafer stage. In particular, embodiments of the invention relate to a wafer stage adapted to hold a wafer, and a method for attaching a wafer to a wafer stage.

This application claims priority to Korean Patent Application No. 10-2006-0000652, filed on Jan. 3, 2006, the subject matter of which is hereby incorporated by reference in its entirety.

2. Description of Related Art

In general, semiconductor devices are fabricated by application of a complex sequence of fabrication processes (e.g., material deposition, etching, ashing, diffusion, photolithography, etc.) to a wafer. By means of these selectively and repeatedly applied fabrication processes, various material layers (e.g., conductive and insulating layers) are formed and patterned on the wafer.

Among the fabrication processes commonly used to manufacture semiconductor devices, photolithography processes generally comprise a coating process wherein a wafer is coated with a photoresist; an exposure process during which the coated wafer is selectively exposed to light through a reticle defining a circuit-pattern; and, a developing process during which a developing solution is applied to remove the portions of the photoresist from the wafer.

Conventional photolithography equipment adapted for use in photolithography processes may be generally divided into coating/developing equipment (e.g., a spinner) and exposure equipment (e.g., a scanner or stepper). Spinners and scanners are typically associated with one another in a fabrication line to perform photolithography processes.

Conventional exposure equipment includes a wafer stage adapted to hold a wafer. The wafer stage typically includes a wafer chuck adapted to directly hold the wafer, and a driver adapted to move (i.e., transfer) the wafer chuck.

The wafer chuck includes lift pins on a central portion of the wafer chuck, and the lift pins may be raised and lowered so that the wafer may be placed on the wafer chuck. The wafer chuck also includes a plurality of vacuum holes adapted to draw the wafer onto the wafer chuck once the wafer is positioned by operation of the lift pins.

That is, to expose a wafer coated with photoresist, for example, the wafer is first positioned over the wafer chuck by a transfer robot. The lift pins of the wafer chuck are raised to support a bottom surface of the wafer. The wafer, which is supported by the lift pins, is then positioned on a top surface of the wafer chuck as the lift pins are lowered. As soon as the lift pins have been completely lowered, the wafer is held to the wafer chuck by a vacuum suction force provided through the vacuum holes of the wafer chuck. The wafer, which is held to the wafer chuck by the vacuum suction force, is held (i.e., fixed) to the wafer chuck with a predetermined amount of pressure so that the wafer will not shake during the exposure process for forming a predetermined pattern on the wafer.

However, as illustrated in figures (FIGS.)1A and1B, a conventional wafer stage10comprises lift pins30disposed in a central portion of a wafer chuck20, as described above. Thus, a wafer W, and in particular wafer W having a diameter of 300 mm, which is placed on wafer chuck20by lift pins30and held to wafer chuck20using vacuum holes (not shown), sags at its edge of when it is placed on wafer chuck20to be held by wafer chuck20. As illustrated inFIG. 1B, wafer chuck20collides with the edge of wafer W when wafer W is placed on wafer chuck20. Thus, placing wafer W on and attaching wafer W to conventional wafer stage10may damage the edge of wafer W. Further, when the exposure process is performed for a relatively long amount of time, a portion of wafer chuck20may be worn down by periodic collisions between wafer W and wafer chuck20.

SUMMARY OF THE INVENTION

Embodiments of the invention provide a wafer stage, wherein a wafer may be attached to the wafer stage for an exposure process without substantially damaging the wafer. Embodiments of the invention also provide a method for attaching a wafer to a wafer stage for an exposure process without substantially damaging the wafer.

In one embodiment, the invention provides a wafer stage comprising a wafer chuck adapted to hold a wafer; lift pins adapted to pass through the wafer chuck, move vertically, and support the wafer; and an air expulsion unit adapted to expel air towards an edge of the wafer.

In another embodiment, the invention provides a wafer stage comprising a wafer chuck; lift pins adapted to pass through the wafer chuck, move vertically, and support the wafer; an air expulsion unit adapted to expel air towards an edge of the wafer; and a controller adapted to control when the air expulsion unit expels air towards the edge of the wafer. The wafer chuck comprises a body, a plurality of chucking protrusions disposed on an upper surface of the body and adapted to contact the wafer when the wafer is attached to the wafer chuck, and an edge ring disposed on an edge of the upper surface of the body and adapted to contact the edge of the wafer.

In yet another embodiment, the invention provides a method for attaching a wafer to a wafer chuck comprising lowering lift pins supporting the wafer, and expelling air towards an edge of the wafer using an air expulsion unit.

DESCRIPTION OF EMBODIMENTS

FIG. 2is a schematic view illustrating exposure equipment comprising a wafer stage in accordance with an embodiment of the invention.

Referring toFIG. 2, exposure equipment100generally comprises a light source110, a reticle R defining a circuit pattern, an optical system adapted to convey light emitted from light source110onto a wafer W, and a wafer stage200on which wafer W is attached (i.e., chucked) and which moves wafer W during the exposure process.

Light source110emits light having a predetermined wavelength. For example, light source110may emit ultraviolet light or extreme ultraviolet light.

The optical system is adapted to guide the light emitted from light source110towards wafer W to irradiate light onto wafer W, which is attached to wafer stage200. In addition, the optical system is subdivided into an illumination optical system130, which is interposed between light source110and reticle R, and a projection optical system140, which is interposed between reticle R and wafer stage200.

Illumination optical system130comprises a filter (not shown) that allows only a predetermined band of light emitted from light source110to pass through. Illumination optical system130also comprises a condenser lens (not shown) that condenses and irradiates onto reticle R the light filtered by the filter. Projection optical system140comprises a plurality of reduction projection lenses (not shown) adapted to focus light received through reticle R via illumination optical system130onto a predetermined portion of the wafer W.

In addition, while not shown, the optical system may be used as a reflective optical system comprising multipurpose optical lenses and reflectors.

FIG. 3is a perspective view illustrating a wafer stage in accordance with an embodiment of the invention,FIG. 4is a top plan view illustrating a wafer stage in accordance with an embodiment of the invention,FIG. 5shows a wafer stage in accordance with an embodiment of the invention, andFIG. 6is a magnified view of a circle A ofFIG. 5.

An embodiment of a wafer stage in accordance with the invention will be described below with reference toFIGS. 3 through 6.

Wafer stage200comprises a wafer chuck210to which wafer W (of FIG.2) is attached, and a drive unit260adapted to move wafer W during the exposure process. Wafer stage200further comprises a lift pin unit220disposed at a central portion of wafer chuck210, a vacuum unit230adapted to pull wafer W towards wafer chuck210when wafer W as wafer W is placed on wafer chuck210and when wafer W is attached to wafer chuck210, and an air expulsion unit240adapted to expel air towards wafer W, and particularly towards an edge of wafer W, when wafer W is placed on and attached to wafer chuck210by lift pin unit220and vacuum unit230.

Additionally, wafer chuck210comprises a body212, a plurality of chucking protrusions214disposed on an upper surface of body212and adapted to make contact with a bottom surface of wafer W when wafer W is placed on and attached to wafer chuck210, and an edge ring216disposed along an edge of the upper surface of body212and adapted to make contact with an edge of the bottom surface of wafer W.

In the embodiment illustrated inFIGS. 3 through 6, body212has a circular disc shape, and lift pin holes215are disposed in a central portion of body212and formed such that lift pins222of lift pin unit220will fit into lift pin holes215, respectively.

As mentioned previously, the plurality of chucking protrusions214are disposed on the upper surface of body212and are adapted to make contact with the bottom surface of wafer W when wafer W is placed on and attached to wafer chuck210. In the embodiment illustrated inFIGS. 3 through 6, chucking protrusions214protrude from body212to a predetermined height and are integrally formed with body212.

In addition, edge ring216is disposed on the edge of the upper surface of body212and is adapted to make contact with the edge of the bottom surface of wafer W when wafer W is placed on and attached to wafer chuck210. In embodiment illustrated inFIGS. 3 through 6, edge ring216comprises of a first edge ring218and a second edge ring217.

Drive unit260comprises a base261disposed beneath body212, and also comprises drive blocks263and265adapted to move body212, which is disposed over261, along a two-dimensional plane (e.g., an X-Y plane). In the illustrated embodiment ofFIGS. 3 through 6, a bottom side of body212is disposed on a mirror block262adapted to sense a position of body212disposed over base261. Drive blocks263and265are each disposed on a respective side of body212. Driver263is adapted to function as a Y-axis driver263adapted to move wafer W, which is attached to body212, along a first axis (e.g., a Y-axis), and driver265is adapted to function as an X-axis driver265that is connected to Y-axial driver263and is adapted to move wafer W along a second axis orthogonal to the first axis (e.g., an X-axis).

Although it is not shown, coils are disposed on both sides of Y-axis driver263, and magnets adapted to react with the coils disposed on Y-axis driver263are disposed on body212and X-axis driver265. Accordingly, wafer W, which is attached to body212, may be moved over base261in accordance with reactions between the coils and the magnets.

Lift pin unit220is adapted to guide wafer W onto body212, to which wafer W will be attached. In the embodiment illustrated inFIGS. 3 through 6, lift pin unit220comprises lift pins222adapted to fit into lift pin holes215formed in a central region of body212, and a lifting mechanism224adapted to move lift pins222up and down (i.e., vertically). Lifting mechanism224may be implemented using a hydraulic or pneumatic cylinder, or a mechanical assembly, such as a ball screw driven by a separate motor. In any practical form, lifting mechanism224is adapted to move wafer W up and down.

Vacuum unit230is adapted to pull wafer W, which is guided to body212by lift pins222, using the suction generated by the vacuum (i.e., vacuum suction). Vacuum unit230comprises a vacuum channel231formed in body212and a plurality of vacuum holes232adapted to communicate with vacuum channel231and exposed through top surfaces of chucking protrusions214.

In the illustrated embodiment ofFIGS. 3 through 6, each of the plurality of vacuum holes232is exposed through the top surface of a respective chucking protrusion214, as mentioned above, or through a top surface of first edge ring218, which is an outer ring of edge ring216.

Vacuum unit230further comprises a vacuum line233, which is disposed partially outside of body212and is connected to vacuum channel231, and a vacuum pump235that is connected to vacuum line233.

The edge of wafer W, particularly when wafer W has a diameter of 300 mm, may sag when wafer W is lowered and pulled onto body212by lift pins222and vacuum unit230. Air expulsion unit240is adapted to prevent the edge of wafer W from colliding with body212when the edge of wafer W sags.

Air expulsion unit240comprises an air expulsion channel241formed in body212, a plurality of air expulsion holes242adapted to communicate with air expulsion channel241and exposed through an upper surface of second edge ring217, which is the inner edge ring of edge ring216, and an air expulsion line243, which is disposed partially outside of body212and is connected to air expulsion channel241. Air expulsion unit240further comprises an air expulsion pump245connected to air expulsion line243.

In another embodiment, vacuum holes232may be disposed in second edge ring217rather than first edge ring218, and air expulsion holes242may be disposed in first edge ring218rather than second edge ring217.

Vacuum unit230further comprises a vacuum sensor237adapted to sense a vacuum suction force applied to wafer W when wafer W is being pulled towards body212(i.e., the force applied to wafer W by body212).

In addition, air expulsion unit240further comprises a pressure sensor247adapted to measure an amount of air pressure applied to the edge of wafer W by air expulsion unit240.

Wafer stage200further comprises a controller250adapted to control the process of attaching wafer W to wafer chuck210. Controller250is electrically connected to vacuum pump235, air expulsion pump245, vacuum sensor237, and pressure sensor247. Controller250operates vacuum pump235to pull wafer W towards wafer chuck210when wafer W is being placed on wafer chuck210. Further, controller250operates air expulsion pump245to prevent the edge of the wafer W from colliding with body212of wafer chuck210when wafer W is being placed on wafer chuck210.

Controller250receives a measurement value from pressure sensor247, which is adapted to measure the amount of air pressure applied through air expulsion holes242, air expulsion channel241, and air expulsion line243, so that controller250can determine whether or not the air pressure is equivalent to a preset air pressure. If the measured value received from pressure sensor247is greater than (i.e., beyond) a preset value, controller250can generate an interlock to stop the process of attaching wafer W to wafer chuck210.

FIG. 7illustrates another embodiment of a wafer stage in accordance with the invention. Referring toFIG. 7, a position sensor280is disposed at an upper portion of wafer chuck210and is adapted to sense when wafer W has reached wafer chuck210. In the embodiment illustrated inFIG. 7, the upper surface of position sensor280is preferably lower than the upper surfaces of chucking protrusions214and lower than the upper portion of edge ring216so that position sensor280does not hinder wafer W from being attached to wafer chuck210. Although it is not shown, a plurality of position sensors280may be disposed on one side of the upper portion of wafer chuck210.

Position sensor280may be an optical sensor comprising a light emitting element adapted to emit light towards wafer W, which is lowered by lift pins222, and a light receiving element adapted to receive light reflected by wafer W. Alternatively, position sensor280may be a proximity sensor.

In addition, position sensor280is electrically connected to controller250. Thus, controller250can determine when air should be expelled towards the edge of wafer W in accordance with the position of wafer W as sensed by position sensor280.

A method for attaching a wafer to a wafer stage, in accordance with an embodiment of the invention, wherein the method uses a wafer stage in accordance with an embodiment of the invention, will now be described with reference to the accompanying drawings.

Referring toFIG. 8, to attach wafer W to wafer stage200for the exposure process, wafer W, which is coated with a photoresist layer, is first positioned (i.e., transferred) over body212by a transfer robot (not shown). When the positioning of wafer W is completed (i.e., when wafer W has been moved over body212), lift pins222are raised to support the bottom surface of wafer W. Then, lift pins222are lowered to guide wafer W to body212(S10).

When lifting mechanism224begins to lower lift pins222, controller250operates vacuum unit230. Specifically, controller250operates vacuum pump235to generate a vacuum suction force and exert the vacuum suction force on wafer W through body212, and more specifically, through vacuum line233, vacuum channel231, and vacuum holes232. Thus, wafer W, which is guided to body212by lift pins222, is pulled towards the upper surface of body212in accordance with the vacuum suction force exerted by vacuum unit230(S20).

Controller250then continues to sense the vacuum suction force, which is exerted on wafer W by vacuum unit230, using vacuum sensor237(S30).

Vacuum sensor237then checks whether or not the vacuum suction force by which wafer W is being pulled towards body212has reached a first preset value, that is, whether or not wafer W has reached a first preset position (S40). The first preset position is a position at which the vacuum suction force generated by vacuum unit230and applied to wafer W has a first preset value.

If the vacuum suction force by which wafer W is being pulled towards body212by vacuum unit230has reached the first preset value, air expulsion unit240expels air towards the edge of wafer W (S50). That is, if wafer W has reached the first preset position, vacuum sensor237sends a signal to controller250, and controller250then operates air expulsion pump245to expel air towards the edge of wafer W. In contrast, when wafer W has not reached the first preset position, controller250continuously checks whether wafer W has reached the first preset position. By expelling air towards the edge of wafer W as described above, wafer W is substantially prevented from sagging when wafer W is guided by lift pins222.

Then, controller250checks whether or not the vacuum suction force by which wafer W is being pulled by vacuum unit230has reached a second preset value, that is, whether or not wafer W has reached a second preset position (S60). The second preset position is a position at which the vacuum suction force generated by vacuum unit230and applied to wafer W has a second preset value.

If the vacuum suction force has reached the second preset value, air expulsion unit240stops expelling air towards the edge of wafer W (S70). In other words, if wafer W has reached the second preset position, vacuum sensor237sends a signal to controller250, and controller250then stops operating air expulsion pump245. In contrast, if the vacuum suction force by which wafer W is pulled has not reached the second preset value, air expulsion unit240continues to expel towards the edge of wafer W. Air expulsion unit240stops expelling air towards the edge of wafer W when the vacuum suction force has reached the second preset value because expelling air towards wafer W has no effect on wafer W as wafer W comes near to body212.

Thereafter, wafer W is placed on and attached to body212by continuously lowering lift pins222(S80).

As shown inFIG. 9, the expulsion of air towards the edge of wafer W can alternatively be controlled in accordance with the output of position sensor280, i.e., the position of wafer W.

FIG. 9is a flowchart illustrating a method for attaching a wafer to a wafer stage in accordance with another embodiment of the invention.

Referring toFIG. 9, to attach wafer W to wafer stage200to perform the exposure process, wafer W, which is coated with a photoresist layer, is first positioned (i.e., transferred) over body212by a transfer robot (not shown). When the positioning of wafer W is completed, lift pins222are raised to support the bottom surface of wafer W. Then, lift pins222are lowered to guide wafer W to body212(S110).

When lifting mechanism224begins to lower lift pins222, controller250operates vacuum unit230. Specifically, controller250operates vacuum pump235to generate a vacuum suction force and exert the vacuum suction force on wafer W through body212, and more specifically, through vacuum line233, vacuum channel231, and vacuum holes232. Thus, wafer W, which is guided to body212by lift pins222, is pulled towards the upper surface of body212in accordance with the vacuum suction force exerted by vacuum unit230(S120).

Then, while wafer W is lowered by lift pins222, position sensor280continually senses a position of wafer W (S130). Position sensor280continues to sense the position of wafer W until wafer W is placed on and attached to body212.

Position sensor280senses whether or not wafer W, which is being lowered, has reached a preset position (S140). If wafer W has reached the preset position, position sensor280sends an electrical signal to controller250. In response, controller250operates air expulsion pump245such that it begins expelling air towards the edge of wafer W (S150).

While wafer W is being lowered by lift pins222as air is being expelled towards the edge of wafer W, controller250gradually decreases the pressure with which air is expelled towards the edge of wafer W in accordance with the position of wafer W, which is measured by position sensor280(S160).

Thereafter, wafer W is placed on and attached to body212by continuously lowering lift pins222(S170). The pressure with which the air is expelled by air expulsion unit240decreases in accordance with the position of wafer W, which is measured by position sensor280, and air expulsion unit240is adapted to stop expelling air once wafer W is disposed on body212.

As stated above, the wafer stage, in accordance with embodiments of the invention, is adapted to expel air towards the edge of a wafer during the process of attaching the wafer to the wafer stage in order to prevent the wafer from being damaged by a collision between the edge of the wafer and the wafer chuck. In addition, the method for attaching the wafer to the wafer stage, in accordance with embodiments of the invention, comprises expelling air towards the edge of a wafer during the process of attaching the wafer to the wafer stage in order to prevent the wafer from being damaged by a collision between the edge of the wafer and the wafer chuck.

While embodiments of the invention have been shown and described herein, it will be understood by those of ordinary skill in the art that various changes in form and detail may be made to the embodiments without departing from the scope of the invention as defined by the accompanying claims.