Patent Publication Number: US-2003234079-A1

Title: Plasma ashing/etching using solid sapphire disk

Description:
FIELD OF THE INVENTION  
       [0001] The invention relates generally to plasma ashing and etching of photoresist and dry film resist from semiconductor wafers, and more particularly to such plasma ashing and etching in which a sapphire disk is utilized.  
       BACKGROUND OF THE INVENTION  
       [0002] Dry film resist (DFR) and photoresist are commonly used types of resist for the photolithography and other processing of semiconductor wafers into semiconductor devices fabricated from the wafers. More generally, DFR and photoresist are types of resist. At times during the processing of semiconductor wafers, the resist must be removed from the wafers. This process can be accomplished by ashing or etching, among other types of processes.  
       [0003] Ashing is the operation of removing the resist by oxidation, in which a reaction between a chemical and the resist removes the resist. Wet etching refers to the use of wet chemical processing to remove the resist. The chemicals are placed on the surface of the wafer, or the wafer itself is submerged in the chemicals. Dry etching refers to the use of plasma stripping, using a gas such as oxygen (O 2 ), C 2 F 6  and O 2 , or another gas. Whereas wet etching is a low-temperature process, dry etching is typically a high-temperature process. The removal of resist is also known as resist stripping.  
       [0004] Ashing and dry etching may be able to be performed using the same type of device, a plasma etcher or asher. Downstream plasma reactors generate plasmas using microwave sources at low or high pressures. Other types of sources, such as radio frequency (RF) sources, may alternatively be used. Plasma ashers and etchers are available from Matrix Integrated Systems, of Richmond, Calif., among other suppliers and manufacturers.  
       [0005] A difficulty with plasma ashing and etching is that the processes may not be uniform. For instance, in ashers and etchers from Matrix Integrated Systems, more resist may be removed towards the center of the wafer than from the edges of the semiconductor wafer. This can be problematic, because semiconductor foundries and their customers have tight tolerances and expected specifications of semiconductor wafer uniformity. If the thickness of the wafer varies too much over the wafer, it may have to be relegated to scrap, which can be costly.  
       [0006] Semiconductor wafer uniformity can be defined as the thickness of the wafer at its thickest minus the thickness of the wafer at its thinnest, divided by two times the average thickness of the wafer. Desirably, the uniformity should be less than ten percent, but in actuality may be as high as eleven to thirteen percent, which is problematic. That is, in ashers and etchers such as those from Matrix Integrated Systems, the uniformity may be as high as eleven to thirteen percent, but some foundries and their customers may desire a uniformity of no greater than ten percent.  
       [0007]FIG. 1 shows a cross-sectional side view of a plasma asher or etcher chamber  100  according to the prior art that exhibits these problems. A semiconductor wafer  120  is positioned on a chuck  108  of the chamber  100 . The chuck  108  has an associated cooling jacket  106 . The chamber  100  has a primary chamber body  104  covered by a chamber dome  114 , in which there is a process gas inlet port  116  to inlet the gas. A pump port  102  on the bottom end of the chamber  100  pumps in the gas through the chamber  100 . There are upper and lower baffles  112  and  110 , respectively, to evenly distribute the gas on the semiconductor wafer  120 . In particular, the upper baffle  112  has a holed sapphire disk  118  inserted therein. Sapphire is the mono-crystalline form of aluminum oxide.  
       [0008] The gas flows onto the semiconductor wafer  120  as indicated by the gas flow  122 . In particular, the gas flows through the holed sapphire disk  118  of the upper baffle  112 , and then through the lower baffle  110 , before reaching the wafer  120 . As indicated by the gas flow  122 , significantly more gas reaches the center of the wafer  120  than the edges of the wafer  120 . As a result, more resist is removed from the center of the semiconductor wafer  120  than from the edges of the semiconductor wafer  120 , causing the problems that have been described.  
       [0009]FIGS. 2, 3, and  4  show the sapphire disk  118 , the upper baffle  112 , and the lower baffle  110 , respectively, in more detail. Thus, each of the sapphire disk  118 , the upper baffle  112 , and the lower baffle  110  has a number of holes therein. Another problem with the prior art is that the etching or ashing that occurs within the chamber  100  of FIG. 1 also tends to etch the baffles  112  and  110 , as well as the sapphire disk  118 . More particularly, the holes of the sapphire disk  118  and the baffles  112  and  110  are etched by the plasma. This reduces their longevity, requiring more frequent replacement.  
       [0010] Therefore, there is a need to overcome these disadvantages. More specifically, there is a need for a plasma asher or etcher that more uniformly removes resist from semiconductor wafers, so that the thickness of such a wafer is more uniform. Furthermore, there is a need for a plasma asher or etcher that does not reduce the longevity of the sapphire disk, the upper baffle, and/or the lower baffle. For these and other reasons, there is a need for the present invention.  
       SUMMARY OF THE INVENTION  
       [0011] The invention relates to plasma ashing and/or etching using a solid sapphire disk. A plasma etcher/asher of one embodiment of the invention includes at least a chamber body, upper and lower baffles, and a solid sapphire disk. The chamber body defines an interior chamber in which a semiconductor wafer is positionable for etching or ashing. The baffles are positioned over the semiconductor wafer, and distribute gas onto the semiconductor wafer. The solid sapphire disk has no holes, and is positioned over one of the baffles to affect distribution of the gas onto the semiconductor wafer.  
       [0012] Embodiments of the invention provide for advantages over the prior art. The solid sapphire disk of the invention, unlike the holed sapphire disk of the prior art, provides for more uniform distribution of the gas onto the semiconductor wafer. As a result, etching or ashing of the semiconductor wafers occurs more uniformly, providing for a more uniform thickness of the wafers. That is, the uniformity of the semiconductor wafers is more likely to be at or under ten percent by using an embodiment of the invention as compared to the prior art. In addition, etching of the sapphire disk is reduced as a result of the elimination of its holes, prolonging the longevity of the disk and reducing the need for its replacement.  
       [0013] It has also been determined that etching and ashing occur at a faster rate using the solid sapphire disk of the invention, as compared to using the holed sapphire disk of the prior art. Still other advantages, aspects, and embodiments of the invention will become apparent by reading the detailed description that follows, and by referring to the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014]FIG. 1 is a diagram of a cross-sectional side view of a plasma asher/etcher chamber according to the prior art. The chamber of FIG. 1 specifically utilizes a sapphire disk that has holes. Etching and ashing performed in the chamber of FIG. 1 result in non-uniformly thick semiconductor wafers, which can be problematic.  
     [0015]FIG. 2 is a diagram of a perspective view of the sapphire disk of FIG. 1 in more detail, according to the prior art. The disk has a number of holes.  
     [0016]FIG. 3 is a diagram of a perspective view of an upper baffle of the chamber of FIG. 1 in more detail, according to the prior art. The upper baffle also has a number of holes.  
     [0017]FIG. 4 is a diagram of a perspective view of a lower baffle of the chamber of FIG. 1 in more detail, according to the prior art. The lower baffle, like the upper baffle and the holed sapphire disk of the prior art, has a number of holes.  
     [0018]FIG. 5 is a diagram of a cross-sectional side view of a plasma asher/etcher chamber according to an embodiment of the invention. The chamber of FIG. 5 specifically utilizes a solid sapphire disk without holes. Etching and ashing performed in the chamber of FIG. 5 result in more uniformly thick semiconductor wafers as compared to the prior art.  
     [0019]FIG. 6 is a diagram of a perspective view of the solid sapphire disk of FIG. 5 in more detail, according to an embodiment of the invention. Unlike the sapphire disk of the prior art, the solid sapphire disk of FIG. 6 does not have any holes. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0020] In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized, and logical, mechanical, and other changes may be made without departing from the spirit or scope of the present invention. For instance, whereas the invention is substantially described in relation to a solid sapphire disk, other types of metallic disks may be able to used as well. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.  
     [0021]FIG. 5 shows a cross-sectional side view of a plasma asher and/or etcher chamber  500  according to an embodiment of the invention. The chamber  500  may in one embodiment specifically be only an asher chamber, whereas in another embodiment specifically be only an etcher chamber. The chamber body  504  defines an interior cavity or chamber in which the semiconductor wafer  520  is positioned or situated. The semiconductor wafer  520  specifically rests on the chuck  508 , which has a cooling jacket  506 . A chamber dome  514  covers the chamber  504  and its interior cavity, and also has a process gas inlet port  516  disposed therein. The process gas used is preferably oxygen, but may be another gas as well. A pump port  502  is disposed within the bottom of the chamber body  504 .  
     [0022] The upper baffle  512  and the lower baffle  510  are positioned over the semiconductor wafer  520  and under the process gas inlet port  516 . A solid sapphire disk  518  is positioned over the baffles  512  and  510 , and preferably is positioned substantially on the upper baffle  512 . Gas is received through the process gas inlet port  516 . The upper and lower baffles  510  and  512  distribute the gas over the top surface of the semiconductor wafer  520 . The solid sapphire disk  518  specifically affects this distribution of the gas, so that ashing or etching occurs more uniformly as compared to using a holed sapphire disk as in the prior art.  
     [0023] The gas flow  522  specifically shows the pattern of the distribution of the gas by the baffles  510  and  512  as affected by the solid sapphire disk  518 . It is noted that the gas flow  522  is more directed towards the edges of the semiconductor wafer  520  as compared to the gas flow of the prior art. As a result, ashing or etching occurs more uniformity at the edges and the center of the semiconductor wafer  520 . As indicated, this preferably allows for a uniformity no greater than ten percent, which is desirable and an advantage of the invention.  
     [0024] Finally, FIG. 6 shows a perspective view of the solid sapphire disk  518  of FIG. 5 in more detail. By comparison, the upper and lower baffles  512  and  510  of FIG. 5 may be implemented as has been described in relation to FIGS. 3 and 4. The solid sapphire disk  518  is solid in that it has no holes. Furthermore, whereas in the preferred embodiment the disk  518  is in fact sapphire, or mono-crystalline aluminum oxide, it may be another metal as well. For instance, such an alternative metal may be another type of aluminum oxide, or another type of metal besides aluminum oxide, as can be appreciated by those of ordinary skill within the art.  
     [0025] It is noted that, although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement is calculated to achieve the same purpose may be substituted for the specific embodiments shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the claims and equivalents thereof.