Apparatus for monitoring a semiconductor wafer during a spin drying operation

An apparatus for spin drying a semiconductor wafer includes a hollow core spindle and a chuck assembly having grippers for supporting a wafer at an edge thereof. A sleeve is disposed in the central opening of the spindle and a manifold is disposed in the upper end of the sleeve. A capacitance sensor is affixed to the manifold. In another apparatus, an arm having a capacitance sensor mounted thereon is positioned such that the capacitance sensor is disposed above a space to be occupied by a wafer that is supported by the grippers. An additional apparatus includes an arm having a light source and a detector mounted thereon. The light source directs light toward a surface of a wafer such that light that reflects off of the surface is substantially perpendicular to that surface. The detector is positioned to measure the intensity of the reflected light.

BACKGROUND OF THE INVENTION

The present invention relates generally to semiconductor fabrication and, more particularly, to a method for monitoring a semiconductor wafer during a spin drying operation, a method for spin drying a semiconductor wafer, and an apparatus for spin drying a semiconductor wafer.

In the fabrication of semiconductor devices, a variety of wafer preparation operations are performed. In conventional wafer cleaning systems, the wafers are scrubbed in a brush station, which typically includes a first brush box and a second brush box. A wafer is first scrubbed in the first brush box in a solution containing specified chemicals and deionized (DI) water. After being moved into the second brush box, the wafer is again scrubbed in a solution containing specified chemicals and DI water. The wafer is then moved into a spin, rinse, and dry (SRD) station where DI water is sprayed onto the top and bottom surfaces of the wafer as the wafer is spun. Once the wafer has been thoroughly rinsed, a spin drying operation is performed to dry the top and bottom surfaces of the wafer.

The spin drying operation must thoroughly dry the top and bottom surfaces of the wafer. If the spin drying operation is stopped prematurely, i.e., before the surfaces of the wafer are thoroughly dry, then the fluid remaining on the surfaces of the wafer may adversely affect subsequent fabrication operations. On the other hand, if the spin drying operation lasts longer than necessary to dry the surfaces of the wafer thoroughly, then the throughput productivity of the wafer cleaning system suffers. In conventional wafer cleaning systems, spin drying operations are not monitored to determine precisely when the surfaces of the wafer are thoroughly dry. Consequently, these wafer cleaning systems run the risk of either stopping the spin drying operation prematurely or unnecessarily extending the length of the spin drying operation.

In view of the foregoing, there is a need for a method for determining precisely when the surfaces of the wafer are thoroughly dry in a spin drying operation. In addition, there is a need for a method and apparatus for spin drying a semiconductor wafer that enables the spin drying operation to be stopped precisely when the surfaces of the wafer are thoroughly dry.

SUMMARY OF THE INVENTION

Broadly speaking, the present invention fills these needs by providing methods for monitoring a semiconductor wafer during a spin drying operation to determine precisely when the surface (or surfaces) of the wafer are dry. The present invention also provides methods and apparatus for spin drying a semiconductor wafer that enable the spin drying operation to be stopped precisely at the “endpoint” of the operation, i.e., the point at which the surface (or surfaces) of the wafer are dry.

In accordance with one aspect of the present invention, a first method for monitoring a semiconductor wafer during a spin drying operation is provided. In this method, a capacitance value between a capacitance sensor and the wafer is measured as the wafer is being spun to dry a surface thereof. When it is determined that the measured capacitance value has reached a substantially constant level, a signal is generated indicating that the surface of the wafer is dry. In one embodiment, spinning of the wafer is stopped in response to the signal.

In accordance with another aspect of the present invention, a first method for spin drying a semiconductor wafer is provided. This method includes spinning the wafer to dry a surface thereof. As the wafer is spinning, the capacitance value between a capacitance sensor and the wafer is measured. When it is determined that the measured capacitance value has reached a substantially constant level, a signal is generated. In response to the signal, spinning of the wafer is stopped.

In accordance with a further aspect of the present invention, a second method for monitoring a semiconductor wafer during a spin drying operation is provided. In this method, light is directed toward a surface of the wafer as the wafer is being spun to dry a surface thereof. The light is directed such that the light that reflects off of the surface of the wafer is substantially perpendicular to the surface of the wafer. The intensity of the light reflected off of the surface of the wafer is measured. A signal indicating that the surface of the wafer is dry is generated when the measured intensity of the light reflected off of the surface of the wafer reaches an intensity level that corresponds to a measured intensity of light reflected off of the surface of the wafer when the surface is dry.

In one embodiment, spinning of the semiconductor wafer is stopped in response to the signal. In one embodiment, the measured intensity of light reflected off of the surface of the wafer when the surface is dry is determined in a calibration operation.

In accordance with a still further aspect of the present invention, a second method for spin drying a semiconductor wafer is provided. This method includes spinning the wafer to dry a surface thereof. As the wafer is spinning, light is directed toward a surface of the wafer such that the light that reflects off of the surface of the wafer is substantially perpendicular to the surface of the wafer. The intensity of the light reflected off of the surface of the wafer is measured. A signal indicating that the surface of the wafer is dry is generated when the measured intensity of the light reflected off of the surface of the wafer reaches an intensity level that corresponds to a measured intensity of light reflected off of the surface of the wafer when the surface is dry. In response to the signal, spinning of the wafer is stopped. In one embodiment, the measured intensity of light reflected off of the surface of the wafer when the surface is dry is determined in a calibration operation.

In accordance with yet another aspect of the present invention, a first apparatus for spin drying a semiconductor wafer is provided. The apparatus includes a hollow core spindle having a central opening therethrough. A chuck assembly is mounted on the spindle. The chuck assembly has a central opening therethrough and includes grippers for supporting a wafer at an edge thereof. A sleeve is disposed in the central opening of the hollow core spindle such that an upper end thereof extends through the central opening of the chuck assembly. A manifold is disposed in the upper end of the sleeve. A capacitance sensor configured to measure a capacitance value between the wafer and the capacitance sensor is affixed to the manifold. In one embodiment, the apparatus further includes a processor for determining when the capacitance value measured by the capacitance sensor reaches a substantially constant level.

In accordance with a still further aspect of the present invention, a second apparatus for spin drying a semiconductor wafer is provided. This apparatus includes a spindle and a chuck assembly mounted on the spindle. The chuck assembly includes grippers for supporting a wafer at an edge thereof. An arm having a capacitance sensor mounted thereon is positioned such that the capacitance sensor is disposed above a space to be occupied by a wafer that is supported by the grippers. The capacitance sensor is configured to measure a capacitance value between a wafer supported by the grippers and the capacitance sensor.

In one embodiment, the apparatus further includes a processor for determining when the capacitance value measured by the capacitance sensor reaches a substantially constant level. In one embodiment, the arm is movable so that the position of the capacitance sensor relative to the space to be occupied by a wafer that is supported by the grippers can be varied. In one embodiment, the arm has a plurality of capacitance sensors mounted thereon. Each of the capacitance sensors is disposed above a space to be occupied by a wafer that is supported by the grippers, and each of the capacitance sensors is configured to measure a capacitance value between a wafer supported by the grippers and the capacitance sensor.

In accordance with yet another aspect of the present invention, a third apparatus for spin drying a semiconductor wafer is provided. This apparatus includes a spindle and a chuck assembly mounted on the spindle. The chuck assembly includes grippers for supporting a wafer at an edge thereof. The apparatus further includes an arm having a light source and a detector mounted thereon. The light source is positioned to direct light toward a surface of a wafer being supported by the grippers such that light that reflects off of the surface of the wafer is substantially perpendicular to the surface of the wafer. The detector is positioned to measure an intensity of the light reflected off of the surface of the wafer.

In one embodiment, the apparatus further includes a processor for determining when the measured intensity of the light reflected off of the surface of the wafer reaches an intensity level that corresponds to a measured intensity of light reflected off of the surface of the wafer when the surface is dry. In one embodiment, the arm is movable so that the position of the light source and the detector relative to the surface of the wafer can be varied. In one embodiment, the arm has a plurality of light sources and a corresponding number of detectors mounted thereon. Each of the light sources is positioned to direct light toward a surface of a wafer being supported by the grippers such that light that reflects off of the surface of the wafer is substantially perpendicular to the surface of the semiconductor wafer. Each of the detectors is positioned to measure an intensity of the light from a corresponding light source that has reflected off of the surface of the wafer.

The methods and apparatus of the present invention minimize the risk of either stopping a spin drying operation prematurely or unnecessarily extending the length of a spin drying operation. Thus, the methods and apparatus of the present invention advantageously improve the yield and throughput productivity in the manufacturing of semiconductor devices.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Several exemplary embodiments of the invention will now be described in detail with reference to the accompanying drawings.

FIG. 1is a side view, which shows some components in cross-section and other components in perspective view, of an exemplary chuck assembly and hollow core spindle that includes a capacitance sensor in accordance with one embodiment of the invention. As shown therein, chuck assembly100is mounted on hollow core spindle102. Chuck assembly100includes chuck body104, which includes a plurality of spokes, and link arms106, which are situated in the spokes of the chuck body. The inner end of each link arm106is configured to slide along the sidewall of wedge108, which is slidably mounted on sleeve110, as explained in more detail below. Chuck top plate112sits on top of chuck body104and covers the moving parts of link arms106. Wafer backside plate114is attached to chuck top plate112and sits just below the surface of semiconductor wafer116. Grippers118, which are pivotably mounted on chuck body104, support wafer116at an edge thereof. To release wafer116, grippers118are pivoted into an open position by sliding wedge108upwardly along sleeve110. As wedge108moves upwardly, link arms106slide inwardly along the sidewall of the wedge and thereby cause grippers118to pivot into the open position. Additional details regarding the structure and operation of chuck assembly100are set forth in U.S. application Ser. No. 09/747,665, filed on Dec. 22, 2000, and entitled “Chuck Assembly for use in a Spin, Rinse, and Dry Module and Methods for Making and Implementing the Same”. The disclosure of this application, which is assigned to Lam Research Corporation, the assignee of the subject application, is incorporated herein by reference.

Hollow core spindle102includes rotary shaft102aand linear shaft102b, which is coaxially disposed within rotary shaft102a. As is well known to those skilled in the art, hollow core spindle102is coupled to a motor (not shown) that provides rotational power to rotary shaft102a. In operation, both rotary shaft102aand linear shaft102brotate, with the rotational power provided to rotary shaft102abeing transferred to linear shaft102bby pins120. Linear shaft102b, which is coupled to wedge108, also moves up and down to adjust the position of the wedge and thereby cause the grippers to pivot between open and closed positions, as described above. Additional details regarding the structure and operation of a hollow core spindle are set forth in U.S. application Ser. No. 09/470,690, filed on Dec. 23, 1999, and entitled “Hollow Core Spindle and Spin, Rinse, And Dry Module Including the Same”. The disclosure of this application, which is assigned to Lam Research Corporation, the assignee of the subject application, is incorporated herein by reference.

With continuing reference toFIG. 1, sleeve110is disposed in the central opening of hollow core spindle102. The upper portion of sleeve110extends beyond hollow core spindle102and through the central opening of wedge108such that the upper end of sleeve10is flush with the top surface of wafer backside plate114. Manifold120is disposed in the upper end of sleeve110. Manifold120includes ports120athat may be used to deliver fluids, e.g., air and chemistries, to the backside of wafer116. These fluids may be supplied to manifold120through supply lines (not shown) housed in sleeve110. Capacitance sensor124is provided on manifold120, as described in more detail later. If desired, wafer presence sensor122(seeFIG. 2) also may be affixed to manifold120.

In accordance with one embodiment of the invention, capacitance sensor124is provided on manifold120to monitor the semiconductor wafer during a spin drying operation.FIG. 2is a simplified top plan view of manifold120shown in FIG.1. As shown inFIG. 2, capacitance sensor124is affixed to the central portion of manifold120. Capacitance sensor124may be affixed to manifold120using any suitable technique. In one embodiment, capacitance sensor124is affixed to manifold120by embedding the capacitance sensor in the material from which the manifold is formed. Those skilled in the art will appreciate that the capacitance sensor may be either fully embedded or partially embedded in the manifold. Suitable capacitance sensors are commercially available from, e.g., Banner Engineering Corporation of Minneapolis, Minn. and Omron Corporation of Tokyo, Japan.

FIG. 3is a simplified schematic diagram that illustrates an exemplary manner in which a semiconductor wafer may be monitored during a spin drying operation in accordance with one embodiment of the invention. As shown therein, capacitance sensor124transmits an analog energy signal toward the backside of wafer116and detects the energy concentrated between the capacitance sensor and the backside of the wafer. Based on the detected energy level, capacitance sensor124determines a capacitance value between wafer116and the capacitance sensor. The dielectric constant, εo, is defined by the space between the backside of wafer116and the top surface of capacitance sensor124. During a spin drying operation, the dielectric constant, εo, changes as fluid film126is removed from the top surface of wafer116. As shown inFIG. 3, wafer116has a fluid film on only the top surface thereof. In other spin drying operations, the wafer may have a fluid film on both the top and bottom surfaces of the wafer. The capacitance values determined by capacitance sensor124are continuously fed to signal processor128, which is configured to generate signal130when the surface of the wafer is dry, as explained in more detail later. Signal130may be in any suitable form. In one embodiment, signal130is in the form of a flag that causes the motor to be stopped and thereby ends the spin drying operation.

FIGS. 4A and 4Billustrate how the capacitance values provided by the capacitance sensor may be used to determine when the surface of the wafer is dry in accordance with one embodiment of the invention.FIG. 4Ais a graph of capacitance versus time for an exemplary spin drying operation.FIG. 4Bis a table that sets forth the status of the fluid film during stages A, B, and C shown in FIG.4A. As shown inFIG. 4A, in stage A, which is the period of time just before spinning of the wafer begins, the capacitance between the wafer and the capacitance sensor has a relatively high value due to the presence of the fluid film on the surface of the wafer. During stage B, which is the period of time during which the wafer is spinning, the capacitance decreases as the fluid film is removed from the surface of the wafer. In stage C, the capacitance remains at a substantially constant level because the fluid film has been removed from the surface of the wafer. Thus, the region near the onset of stage C, i.e., the region near the point at which the capacitance reaches a constant level, is a reliable indicator that the surface of the wafer is dry. Accordingly, in one embodiment of the invention, signal processor128(seeFIG. 3) is configured to generate a signal when the measured capacitance value reaches a substantially constant level.

As used in connection with the description of the invention, the phrase “the measured capacitance value reaches a substantially constant level” means the point at which the measured capacitance value is no longer changing significantly with time. It will be apparent that the point at which the measured capacitance value is no longer considered to be changing significantly with time can be varied to suit the needs of particular situations. For example, this point can be defined as point E1, which is the point at which the “flat” portion of the curve shown inFIG. 4Astarts. At point E1and all points on the curve to the right of this point, the difference between successive measured capacitance values is essentially zero. Alternatively, the point at which the measured capacitance value is no longer considered to be changing significantly with time can be defined as point E2, which occurs before point E1on the curve shown in FIG.4A. At point E2, the difference between successive measured capacitance values is slightly more than zero.

FIG. 5Ais a side view, which shows some components in cross-section and other components in perspective view, of an arm having a capacitance sensor mounted thereon disposed above an exemplary chuck assembly in accordance with one embodiment of the invention. As shown therein, arm132having capacitance sensor124′ mounted thereon is disposed above wafer116, which is held by grippers118of chuck assembly100. The components of chuck assembly100are described above with reference to FIG.1. Those skilled in the art will appreciate that spindle102shown inFIG. 1has been omitted from FIG.5. Arm132may be anchored to any suitable support member, e.g., a frame piece or wall of a spin, rinse, and dry module. In one embodiment, arm132is supported by a positioner, as described below with reference to FIG.5B. Capacitance sensor124′ transmits an analog energy signal toward the top surface of wafer116and detects the energy concentrated between the capacitance sensor and the top surface of the wafer. Based on the detected energy level, capacitance sensor124′ determines a capacitance value between wafer116and the capacitance sensor. The capacitance values determined by capacitance sensor124′ are continuously fed to signal processor128, which, as described above, generates signal130when the surface of the wafer is dry (signal processor128and signal130are shown in FIG.3).

FIG. 5Bis a simplified top view of an arm having a capacitance sensor mounted thereon coupled to a positioning device in accordance with one embodiment of the invention. As shown therein, arm132is pivotably coupled to positioner134, which pivots arm132in the direction of the arrow so that capacitance sensor124′ mounted thereon “scans” the surface of wafer116. The dashed lines inFIG. 5Bdenote the “scan” path followed by capacitance sensor124′. It will be apparent to those skilled in the art that arm132may be moved relative to wafer116in other ways. For example, arm132may be rigidly coupled to positioner134and the positioner may be moved relative to wafer116. In the case where positioner134pivots arm132, the positioner may be mounted on any suitable support member, e.g., a frame piece or wall of a spin, rinse, and dry module. In the case where positioner134moves relative to wafer116, the positioner may be mounted on a suitable drive track.

FIG. 6Ais a side view, which shows some components in cross-section and other components in perspective view, of an arm having a plurality of capacitance sensors mounted thereon disposed above an exemplary chuck assembly in accordance with one embodiment of the invention. As shown therein, arm132having a plurality of capacitance sensors124′ mounted thereon is disposed above wafer116, which is held by grippers118of chuck assembly100. The use of multiple capacitance sensors124′ enables more of the surface of wafer116to be monitored. The capacitance values determined by each of capacitance sensors124′ are continuously fed to signal processor128, which generates signal130when each of the capacitance sensors indicates that the surface of the wafer is dry (signal processor128and signal130are shown in FIG.3).

FIG. 6Bis a simplified top view of an arm having a plurality of capacitance sensors mounted thereon coupled to a positioning device in accordance with one embodiment of the invention. As shown therein, arm132is pivotably coupled to positioner134, which pivots arm132in the direction of the arrow so that each of capacitance sensors124′ mounted thereon “scans” the surface of wafer116. The combination of the scanning movement of each of the multiple capacitance sensors and the rotation of the wafer makes it possible to monitor essentially the entire top surface of the wafer during a spin drying operation.

FIG. 7is a simplified schematic diagram of an arm having an interferometric sensor mounted thereon in accordance with one embodiment of the invention. As shown therein, interferometric sensor136, which includes a light source and a detector, is mounted on arm132. The light source directs light toward the top surface of wafer116such that the light that reflects off of the top surface is substantially perpendicular to the top surface. This orientation minimizes the effects of light scattering. The detector measures the intensity of the light that reflects off of the top surface of wafer116.

It will be apparent to those skilled in the art that any suitable light source may be used in the interferometric sensor, e.g., a fiber optic transmitter, a laser, or a light emitting diode (LED). The light directed toward the surface of the wafer preferably has a wavelength in the range from about 100 nanometers (nm) to about 1,000 nm, and more preferably in the range from about 500 nm to about 850 nm. In one embodiment, the light has a wavelength of about 680 nm. The use of ultraviolet light is not preferred because it may lead to photoassisted corrosion of copper on wafer116. Those skilled in the art are familiar with suitable detectors for measuring the intensity of the light that reflects off of the surface of wafer116.

The intensity levels measured by interferometric sensor136are continuously fed to signal processor128′, which is configured to generate signal130′ when the surface of the wafer is dry. In one embodiment, signal processor128′ generates signal130′ when the measured intensity of the light reflected off of the surface of wafer116reaches an intensity level that corresponds to a measured intensity of light reflected off of the surface of the wafer when the surface is dry. The measured intensity of light reflected off of the surface of the wafer when the surface is dry may be determined in a calibration operation. The environmental conditions, e.g., humidity, under which this calibration operation is conducted should be the same as the environmental conditions under which the spin drying operation is to be performed. Otherwise, the measured intensity of light determined in the calibration operation may not be indicative of a thoroughly dry surface.

Those skilled in the art will recognize that arm132having interferometric sensor136mounted thereon may be pivoted so that the interferometric sensor “scans” the surface of wafer116, as described above with reference toFIG. 5Bfor the capacitance sensors. In addition, a plurality of interferometric sensors136may be mounted on arm132, as described above with reference toFIGS. 6A and 6Bfor the capacitance sensors.

In summary, the present invention provides methods for monitoring a semiconductor wafer during a spin drying operation, and methods and apparatus for spin drying a semiconductor wafer. The invention has been described herein in terms of several exemplary embodiments. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention. For example, those skilled in the art will recognize that the capacitance sensor may be used with a chuck assembly and spindle having a structure that is different than that of the exemplary chuck assembly and hollow core spindle described herein. In addition, it will be apparent to those skilled in the art that the interferometric sensor shown and described herein may be modified to detect the “endpoint” of a spin drying operation using ellipsometry, which involves the use of polarized light, or other suitable interferometric technique, instead of reflectometry. The embodiments and preferred features described above should be considered exemplary, with the scope of the invention being defined by the appended claims and their equivalents.