CHUCK TABLE FOR SEMICONDUCTOR WAFER
TECHNICAL FIELD OF THE INVENTION
This invention relates to an improved method and assembly useful in the manufacture of semiconductor devices. More particularly, the present invention relates to a new and improved method and apparatus for applying a backing tape to a semiconductor wafer prior to cutting or separating the wafer into individual die.
BACKGROUND OF THE INVENTION
The manufacture of modern electronic semiconductor devices usually involves the use of silicon (Si) or gallium arsenide (GaAs) interval. These materials are often manufactured in the form of circular discs known as wafers. While the majority of semiconductor applications to date have employed silicon wafers having a typical thickness of 500-680 micrometers (μm), increasing emphasis is being placed on the use of gallium arsenide semiconductors formed from wafers having a typical thickness of only 300 μm. The wafers have diameters of 2 to 12 inches, with a trend toward the latter size. The wafers are cut or diced along straight lines- into separate chips or die having lengths and widths which that may be in some cases no more than 0.1 inches. Each of these chips will be placed in its own integrated circuit (IC) package.
During the dicing process, the wafer must be maintained in a fixed position relative to the cutting device. Each of the cut chips must be maintained in a fixed position after cutting to provide for easier sorting. Maintaining the wafer in a fixed position is often accomplished by the use of a backing tape attached to the wafer. The dicing process cuts only through the wafer and not through the tape, thereby leaving an assortment of chips attached to the tape after dicing. Previous methods of attaching a backing tape to a wafer usually involved a mechanism known as a chuck table. The wafer is placed face-down on the chuck table,
and the backing tape is placed across the back of the wafer. The tape and wafer combination is removed from the chuck table to a dicing station. The portion of the tape that is located radially to the outside of the wafer will often come in contact with the surface of the chuck table and will adhere to this surface during the removal stage. The adhesive tension between the tape and the chuck table requires an additional force to remove the tape and wafer combination from the chuck table. This force, if applied by simply peeling the tape away, often results in the bending of the wafer. The wafers are very thin and relatively brittle, breaking rather easily. For this reason, an opening is placed in the very center of the chuck table for air pressure to be applied to force or blow-off the tape and wafer combination. This opening is supplied with air pressure through a purge hole. Because there is a single opening in the center of the chuck table, all of the pressure to cause the tape and wafer combination to lift off the chuck table is directed at the very center of the wafer. The wafer will thus bow upward in a parabolic disk shape until it begins to pull the tape away from the chuck table. Because the tape adheres strongly to the chuck table, the wafer is bent rather severely and often fractures.
When a wafer fractures, the entire wafer is not usable. Such product loss is undesirable in the semiconductor industry.
Another historic problem in the manufacture of semiconductor devices is contamination of the wafer with particulate matter. Because the wafer has to be placed face down, its is typical to have a lowered section or opening in the center of the chuck table that is just smaller than the outer diameter of the wafer. The lowered center section allows for the mounting of the tape to the back of the wafer while reducing the surface area of the face-down wafer that comes into contact with the chuck table. However, there are two drawbacks to this approach. First, because there is no support underneath the wafer, the wafer can fracture when force is applied during the application of the backing tape. Second, chuck tables are designed to accommodate wafers having a predetermined diameter. In the industry, wafers of varying sizes are often used and it is therefore desirable to have a universal chuck table that can be used with wafers that may vary in size from 2 to 12 inches in diameter.
SUMMARY OF THE INVENTION
The present invention features a chuck table assembly with a top surface that provides support for the wafer in the center of the chuck table while reducing the effective surface area at the outer radial area of the chuck table with the use of concentric grooves. Pure Teflon provides a non-stick surface for both the center and grooved regions. In accordance with a significant aspect of the invention, an apparatus and a method for applying a backing tape to a wafer with a chuck table involves removing the tape and wafer combination from the chuck table in a nondestructive fashion. Air pressure is directed to the tape portion of the tape and wafer combination by an internal manifolding system involving internal passageways, a concentric channel, and radial channels.
In accordance with another significant aspect of the present invention, the apparatus for applying a backing tape to a wafer with a chuck table accommodates wafers as small as 2 inches in diameter and as large as 12 inches in diameter without any modification to the apparatus or the set-up. A significant advantage of the present invention is that, as compared to prior art devices, very little air pressure is needed to remove the tape and wafer combination from the chuck table. A more complete understanding of the present invention can be obtained by reference to the accompanying drawings, which are briefly described below, the following detailed description of a presently preferred embodiment, and the appended claims.
DESCRIPTION OF THE DRAWINGS
Figure 1 is an exploded perspective view of the chuck table design of the present invention with the wafer and tape frame shown;
Figure 2 is a top view of the chuck table of the present invention as shown from Figure 1 ;
Figure 3 is a side section view along line A-A in Figure 2;
Figure 4 is a bottom view of the table top portion of the chuck table design shown in Figure 3;
Figure 5 is a bottom view of the manifold plate portion of the chuck table shown in Figure 3; and
Figure 6 is a side section view along line B-B in Figure 2.
DETAILED DESCRIPTION OF THE INVENTION
A presently preferred embodiment of an improved chuck table 10 is shown in a condition of actual use in Figure 1. Chuck table 10 includes a table top 11a and a manifold plate l ib, which are connected together. Figure 1 also shows a wafer 12 in a face-down orientation, a backing tape 14 to be attached to wafer 12 in order to hold the individual die in place after the die are cut, and a frame 16 to which the backing tape 14 and wafer 12 will be attached.
Figure 2 shows further detail of chuck table 10. A region of grooves 22 is located in the form of concentric rings at the outer radial area of chuck table 10. Located in the region of concentric grooves 22 is a concentric channel 24 and eight radial channels 26. The center of the chuck table 10 has a relatively flat upper surface 28. Each of these elements, including the concentric grooves 22, the concentric channel
24, the radial channels 26, and the relatively flat surface 28 are composed of pure Teflon. Pure Teflon is used to greatly reduce the sticking of the backing tape 14 to any surface of the chuck table 10 upon removal of the backing tape 14 and wafer 12 combination. The pure Teflon surface is also desirable because particulate contaminant matter is relatively less likely to stick to a pure Teflon surface than to a non-Teflon surface. Pure
Teflon is desirable as opposed to a surface of partial Teflon for its greater non-stick properties. It should be recognized that other sufficiently non-adhesive surfaces may be suitable for the purposes of this invention. These surfaces include nylon, ceramic, engineering resins, or, if sufficiently non-adhesive, partial Teflon surfaces. Eight screw holes 29 allow the table top 1 la to be connected to the manifold plate 1 lb.
The cross-sectional view of Figure 3 illustrates the shape of the V-shaped grooves in grooved region 22. The width of the concentric channel 24 is approximately the width of two concentric grooves in the grooved region 22. Wafer 12 shown in Figure 3 covers the entire relatively flat surface 28 as well as some portion of grooved
region 22, depending on the diameter of the wafer. Wafer 12 contacts only the top portion of each groove in grooved region 22, as shown in Figure 3. Backing tape 14 in this example only comes in contact with the top portion of the relatively flat center portion 28. Therefore, the surface area of backing tape 14 that comes into contact with chuck table 10 is small. Frame 16 is attached to backing tape 14.
Figure 4 shows the bottom of the table top portion 11a of chuck table 10. The screw holes 29 that allow table top 1 la to be connected to manifold plate 1 lb can be seen. Four slots are cut into the bottom of table top 11a. When manifold plate lib is connected flush against the bottom of table top 11a, these slots form four internal passageways 32. Four ports 34 connect the internal passageways 32 to the concentric channel 24 shown in Figure 2 and Figure 4.
Figure 5 shows the bottom of manifold plate 1 lb. The top of manifold plate 1 lb (not shown) is identical to the bottom of manifold plate 1 lb. The threaded screw holes 39 show where the screws 74 connect the table top 1 la to the manifold plate l ib. An inlet hole 40 in the radial center of the chuck table is the hole through which purge air is admitted. The inlet hole 40 is connected to the internal passageways 32.
The internal manifolding, comprising the connection of passageways, ports, channels, and grooves of the chuck design, are shown in the cross-sectional view of Figure 6. Figure 6 shows two of the four internal passageways 32 formed between the table top 11a and the manifold plate 1 lb. The air passageways 32 distribute air pressure to concentric channel 24 and the radial channels 26. Each of internal passageways 32 connect to a port 34 that allows air to pass from internal passageway 32 to concentric channel 24. Air can flow from concentric channel 24 to each of the eight radial channels 26 that in turn can distribute air to each groove in grooved region 22 (Figure 2). Figure 6 also shows how table top 1 la is held against the manifold plate 1 lb by eight screws 74. Each of the screws 74 fits through a screw hold 29 in table top 1 la and screws into a threaded screw hole 39.
Referring to Figure 6, when the wafer 12, backing tape 14, and frame 16 are placed on top of chuck table 10, purge air admitted through the inlet hole 40 is distributed to concentric grooved region 22. This air flowing to the concentric grooved region 22 creates a pressure that forces the backing tape 14 off the chuck 10, thus pulling
the entire wafer 12, backing tape 14, and frame 16 off the chuck table. Despite the pressure exerted on wafer 12, backing tape 14, and frame 16, there is not extreme deformation or bowing of the combination. The lack of deformation or bowing of the wafer 12 contrasts with prior art devices, where the pressure exerted to remove the tape and wafer combination from the chuck table often deformed or bowed the wafer.
The present invention also allows the use of a wafer that nearly covers the entire chuck table, such as a wafer of twelve inches in diameter, as well as a wafer that has a diameter smaller than the relatively flat area at the radial center of the chuck table, such as a wafer of two inches in diameter. The chuck table assembly of the present invention achieves substantial advantages and improvements that result in a reduction in the number of wafers damaged by the manufacturing process of applying a backing tape. The wafer of the present invention is supported directly from underneath. Pure Teflon, or another appropriately non-adhesive substance, provides for a less sticky surface on the chuck table. Grooves along the outer radial portion of the chuck table allow for a reduced surface area for the backing tape, thereby reducing the surface area to which the backing tape could stick. The internal manifold system air pressure directly to the backing tape and not to the wafer as a means of removing the wafer and tape assembly from the chuck table. Other modifications of the invention described above will be obvious to those skilled in the art, and it is intended that the scope of the invention be limited only as set forth in the appended claims.