Wafer handling apparatus

Disclosed is an end effector apparatus including a base including a wrist coupling component. The base may be substantially triangular in shape. A plurality of fingers extends from the base. Each finger includes a plurality of wafer support pads for supporting wafers being processed. Each finger has a width dimension, a height dimension and a length dimension, wherein the height dimension tapers smaller along at least a tip portion of the finger.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention relate to the field of device fabrication. More particularly, the present invention relates to a wafer handling end effector apparatus used to transport wafer materials among devices.

2. Discussion of Related Art

Silicon wafers are used in semiconductor and/or solar cell fabrication. The wafers are subjected to a multi-step manufacturing process that may involve a plurality of machines and a plurality of stations. Thus, the wafers need to be transported from one machine/station to another machine/station one or more times.

When transporting wafers from station to station or machine to machine in a manufacturing process, apparatuses called end effectors are typically employed. A typical end effector apparatus may be hand-like in appearance. A base unit may attach to a plurality of finger-like extensions. On each of the finger-like extensions, a plurality of wafers may be seated atop wafer pads at spaced apart intervals. The end result may be a matrix of wafers supported by the plurality of end effector fingers. The end effector may typically be moved linearly (e.g., forward and backward) as well as rotationally all in the same plane (e.g., x-y axis). The end effector may also be moved in a third direction along a z-axis to provide a full range of motion.

There are several styles of wafer interface features used in semiconductor wafer handling equipment. Sometimes silicone pads are used to isolate the silicon wafer from the metallic robot end effector fingers to prevent contamination of the wafer by the metallic arm. Sometimes wafers sit on hard slippery pads affixed at periodic intervals along the end effector fingers. The hard slippery pads are typically made of a polyetheretherketone (PEEK) plastic. PEEK is a high performance thermoplastic material comprised of a polymer that is semi-crystalline. PEEK polymer is advantageous in that retains its mechanical properties at extremely high temperatures, is weldable, machinable, and can be bonded with epoxies cyanoacrylates, polyurethanes, or silicones.

One of the characteristics of an end effector apparatus is its rigidity. An end effector apparatus should be rigid enough to withstand the forces that are applied to it during normal operation. An end effector apparatus should be rigid enough to operate at higher speeds. Higher speeds translate to greater product workflow as measured by the number of wafers that can be handled per hour (WPH) by a wafer handling robot. Increasing the WPH allows the wafer handling robot to process more wafers leading to a more productive and efficient process.

End effector apparatus stiffness or rigidity can impact the speed at which the wafer handling robot can operate and consequently, impact the number of wafers that can be processed (e.g., WPH). One measurement or characteristic of an end effector apparatus is its natural frequency. Natural frequency is the frequency at which a system naturally vibrates once it has been set into motion. In other words, natural frequency is the number of times a system will oscillate (move back and forth) between its original position and its displaced position, if there is no outside interference. Resonance is the buildup of large vibration amplitude that occurs when an object is excited at its natural frequency. Undesirable mechanical resonance can cause bridges to collapse, aircraft wings to break, and machinery to break or malfunction.

The natural frequency of the end effector apparatus is one factor that contributes to the overall stiffness and system stability. The higher the natural frequency, the stiffer the end effector apparatus, thus the more stable the wafer handling system. For example, typical end effector apparatuses exhibit a natural frequency of approximately 20 to 27 Hz and systems using such an end effector apparatus can process approximately 1700 wafers per hour (WPH). Another factor affecting WPH may be the mass of an end effector apparatus. Minimizing mass while maximizing the natural frequency leads to an optimized end effector apparatus for throughput and stability purposes as measured by WPH.

SUMMARY OF THE INVENTION

In view of the foregoing, there's a need to minimize mass while maximizing the natural frequency of an end effector apparatus to increase the throughput of a wafer handling robot tasked with moving wafers from station to station in a manufacturing process. In one embodiment there is disclosed an end effector apparatus including a base including a wrist coupling component. The base may be substantially triangular in shape. A plurality of fingers extends from the base. Each finger includes a plurality of wafer support pads for supporting wafers being processed. Each finger has a width dimension, a height dimension and a length dimension, wherein the height dimension tapers smaller along at least a latter portion of the length of the finger.

In another embodiment, the base further comprises a base floor portion and a base frame portion extending upward from the base floor portion, the base frame portion comprised of a perimeter wall and a plurality of ribs spaced apart at angular intervals.

In another embodiment, each of the plurality of fingers further comprises a pair of opposing side walls connected by a top wall. Each finger further includes a plurality of holes dispersed along the length of the top wall where the plurality of circular holes may have a diameter between 30% to 80% of the width of the top wall.

DESCRIPTION OF EMBODIMENTS

The embodiments described herein present materials and geometries that maximize the natural frequency and minimize the mass of an end effector apparatus. An end effector apparatus may be characterized as a hand-like apparatus comprising a base and fingers. The fingers and base of the embodiments describe features that have been optimized to maximize the natural frequency and minimize the mass of the end effector apparatus. For example, the fingers may include a tapered design. The fingers and base may include a plurality of holes to minimize mass. The base may include a plurality of radial ribs separated by partially or fully cutout areas of the base. The thickness and angular spacing of the radial ribs may also affect the mass and natural frequency of an end effector apparatus. The thickness of the fingers and base may be manipulated as well. These and other features are more fully described in the description that follows.

FIG. 1is a bottom perspective view illustration of one embodiment of an end effector apparatus100generally comprised of a substantially triangular shaped base105and a plurality of fingers120extending therefrom. The base105includes a wrist coupling component115adapted to attach the end effector apparatus100to a larger transporting device such as, for instance, a robotic arm (not shown). The robotic arm is movable in a variety of directions (e.g., up, down, forward, backward, left, right) and can even rotate the end effector apparatus100via the wrist coupling component115.

The base105may be further comprised of a frame having a perimeter wall110and a plurality of radial ribs130. Between each of the radial ribs130may be cutout area135. The cutout areas135remove mass from the end effector apparatus100while the radial ribs130maintain a structural integrity and stiffness. In another embodiment, the cutout area135may be replaced by a floor portion that is substantially thinner than and integrated with the frame.

The base105may further be comprised of a plurality of paired sets of base ribs125. Each paired set of base ribs125extends from the edge opposite the wrist coupling115of the substantially triangular shaped base105. The paired sets of base ribs125are tapered such that the opposing base ribs125converge toward one another as they get further from the base105. The opposing base ribs125are also configured to surround a portion of a finger120. In this configuration, an additional measure of stability or stiffness may be achieved. The fingers120include a plurality of wafer supports140adapted to receive and seat a plurality of wafers. Other features and characteristics of the fingers120are described in more detail with reference toFIGS. 2-4.

FIG. 1Ais a bottom perspective view illustration of one embodiment of an end effector apparatus100with a plurality of wafers175seated thereon. The wafers175(shown upside down) are seated upon the wafer supports140and may be delivered from station to station in a manufacturing process by way of, for instance, a robotic arm coupled to the wrist coupling component115of the end effector apparatus100. This illustration also shows the substantially triangular shaped base105and the plurality of fingers120extending therefrom. The base105includes the wrist coupling component115adapted to attach the end effector apparatus100to a larger transporting device such as, for instance, a robotic arm (not shown).

The wafer supports140provide multiple points of contact upon which a wafer175may be seated. In this embodiment, each wafer support140presents four points of contact upon which a wafer175may rest. Each wafer support140may be removably attachable to the end effector apparatus100—specifically to an end effector finger120. The fingers120are typically made from metal (e.g., aluminum) for strength, rigidity, and resonance so as to perform satisfactorily during its operation of delivering wafers175from station to station in a manufacturing process. The metal, however, needs to be shielded from the wafers175it is tasked with delivering because the metal may contaminate the wafer175and change the desired properties of the wafer175. Thus, the wafer support140is comprised of a polymer material, such as, for instance, polyetheretherketone (PEEK).

The wafer support140may be removably attachable using a snap-fit coupling in which the wafer support140fits snugly about a portion of a finger120but may still be removed and replaced if necessary. Threaded fasteners may also be used to attach the wafer support140to the finger120. Other fastening methods likewise can be used to attach the wafer support140to the finger120.

In this bottom view, a plurality of wafers175is shown seated on a plurality of wafer supports140. In this example, each wafer175is associated with a single end effector finger120. A plurality of wafers175are spaced apart and positioned along the length of each end effector finger120to form a row. Each wafer175rests upon two opposing or adjacent wafer supports140. In addition, each wafer support140includes four flat portions and four alignment lip portions operatively arranged in pairs: a front facing side by side pair and a rear facing side by side pair. The flat portions141and alignment lips142are shown in more detail with respect toFIG. 3. The side by side front and rear facing pairs each straddle the end effector finger120. Each wafer175may rest upon a rear facing pair of one wafer support140and a front facing pair of the next wafer support140along the end effector finger120. The wafers175may be aligned to either the front or rear sets of alignment lip portions, but not both. The wafers175are positioned against one set of lip portion alignment features. This works because there is a small gap on the other side. In this arrangement, a wafer175may contact four surfaces operative to keep the wafers in place during motion of the end effector apparatus300. This arrangement is repeated for each of the end effector fingers120to produce a matrix of wafers175that can be reliably and efficiently moved with less chance of a wafer175slipping out of alignment.

FIG. 2is a side view illustration of one embodiment of a finger120of an end effector apparatus100. In this illustration, the finger120shows a tapered tip portion145. Each finger120has a height, width and length dimension. The tapered tip portion145tapers along the length dimension of the finger such that the height dimension decreases in magnitude as the tip of the finger120approaches its terminus. In one embodiment, the tapered tip portion145may extend 40% of the length of the finger140from the tip of the finger120toward the base105(shown inFIG. 1). In another embodiment, the tapered tip portion145may range from 20% to 40% of the length of the finger140from the tip of the finger120toward the base105.

FIG. 3is a top perspective view illustration of one embodiment of a finger120of an end effector apparatus100. In this illustration, the finger120is comprised of a pair of opposing side walls155with a top wall160interposed and coupled therebetween. The wafer supports140are periodically attached along the length of the finger120. One of the base side ribs125is also shown at one end of finger120. Finger120further includes a plurality of holes150dispersed along the length of the top wall160for at least a portion of finger120. The holes150provide negative space meaning that the overall mass of the finger120is reduced due to removal of material to form the holes150. The holes150are presented as circular in this illustration, but may be oblong or other shaped sufficient to remove material to reduce the mass of the finger120. In one embodiment, the holes150may extend up to 50% of the length of the finger120from the finger tip toward the base105(shown inFIG. 1). For circular holes150, the center spacing may be, for instance, 1.2 times the diameter of the hole and the hole diameter may be between 30% to 80% of the width of the top wall160. In one embodiment, the thickness of the top wall160may range from 10% to 50% of the height of the side walls155. The thickness of the side walls155range from 3% to 10% of the width of the finger160.

Each wafer support140may include a flat portion141upon which a wafer175(or portion thereof) may be seated and an alignment lip portion142that protrudes or extends upward normal to the flat portion141. The alignment lip portion142may be operative to provide a stop for a seated wafer175especially when the entire end effector apparatus100is in motion. The alignment lip portion142may have a slight curvature to assist in wafer175placement in which the peak or apex point of the curvature may be characterized as the alignment point when used in conjunction with other wafer support(s)140. In addition, the alignment lip portion142may be operative to align the wafers175supported by the wafer support140by working in conjunction with other wafer support(s)140. The alignment lip portion(s)142of other wafer support(s)140are all aligned such that the wafers175align themselves when in contact with the respective alignment lip portion(s)142.

FIG. 4is a top view illustration of one embodiment of a finger120of an end effector apparatus100. In this illustration, the finger120is partially pictured from left to right as extending from the base105(shown inFIG. 1) toward the finger tip. A paired set of opposing base ribs125extend from the base105toward the finger tip. The opposing base ribs125may extend from the base105toward the finger tip up to 10% to 50% of the finger length with one embodiment at 25% the length of the finger120. The wafer supports140are again show periodically spaced along the length of finger120. At the right side ofFIG. 4, holes150begin to appear through the top wall160of finger120.

FIG. 5is a bottom perspective view illustration of one embodiment of a base105of an end effector apparatus100. In this illustration, the perimeter wall110substantially forms a triangle with the wrist coupling115at one vertex of the triangle. The paired sets of base ribs and fingers120extend outward from the edge of the base105opposite the wrist coupling115. A plurality of cutout areas135are defined by a base frame. The base frame includes the perimeter wall110and a plurality of radial ribs130that generally extend outward in a radial pattern from a region near the wrist coupling component115toward the edge of the base105opposite the wrist coupling component115. The intersections of the radial ribs130and the perimeter wall110define the cutout areas135.

In one embodiment, the radial ribs may be more concentrated in the center area of the base105and less concentrated as the pattern extends out radially. The radial ribs130and perimeter wall110that make up the frame of the base105provide stability and stiffness for the overall end effector apparatus100. In another embodiment, a floor portion (not shown) replaces the cutout areas135. In this case, the cutout areas become the floor portion. The floor portion is substantially thinner height-wise than the perimeter wall110. In one embodiment, for instance, the floor portion may be 3% of the height of the perimeter wall110. The floor portion may range from 1% to 25% of the perimeter wall height. In addition, the width of the perimeter walls110may range from 50% to 250% of the height of the perimeter walls110. Similarly, the width of the radial ribs130may range from 25% to 50% of the height of the radial ribs130. The height of the radial ribs130and the perimeter wall110is substantially the same.

The end effector apparatus100including the base105and fingers120may be comprised of aluminum in one embodiment. In another embodiment, the end effector apparatus100including the base105and fingers120may be comprised of magnesium or titanium.

The embodiments described above have been implemented for an end effector apparatus designed to carry a 4×4 array of 164 mm solar cells (wafers). The techniques described led to an optimized base and finger geometry for the end effector apparatus to achieve a maximized natural frequency and a minimized mass. The end effector apparatus exhibited a natural frequency of approximately 45 Hz where predecessor end effector apparatuses exhibited a natural frequency of approximately 27 Hz. Coupled with the reduced mass of the end effector apparatus resulting from the various tapered portions, the holes in the top wall of the fingers, and the cutout areas in the base, the end effector apparatus was able to improve throughput of wafer handling by approximately 20%.