Emissivity-change-free pumping plate kit in a single wafer chamber

[0002] This non-provisional patent application claims benefit of provisional patent application U.S. Ser. No. 60/220,039, filed Jul. 21, 2000, now abandoned.

[0003] 1. Field of the Invention

[0004] The present invention relates generally to the field of semiconductor manufacturing. More specifically, the present invention relates to an emissivity-change-free pumping plate kit in a single wafer chamber.

[0005] 2. Description of the Related Art

[0006] Chemical vapor deposition, commonly referred to as “CVD” is one of a number of processes used to deposit thin layers of material on a semiconductor wafer, and may be based on thermal, plasma, or optically assisted decomposition, or reaction of chemicals. To process wafers in, for example, a thermal CVD process, a chamber is provided with a susceptor configured to receive a wafer. The wafer is typically placed onto and removed from the susceptor by a robot blade and supported by the susceptor during processing. In these typical prior art systems, the susceptor and the wafer are heated to a temperature of between 200-650° C. prior to processing. Once the wafer is heated to an appropriate temperature, a processing fluid, typically a gas, is introduced into the chamber through a gas manifold often situated above the wafer. The processing gas thermally decomposes upon contact with the heated wafer surface to deposit a thin material layer thereon.

[0007] A primary goal of wafer processing is to obtain as many useful dies as possible from each wafer. Many factors affect the ultimate yield of die from each wafer processed. These factors include processing variables, which affect the uniformity and thickness of the material layer deposited on the wafer, and particulate contaminants that can attach to a wafer and contaminate one or more die. Both of these factors must be controlled in CVD and other processes to maximize the die yield from each wafer.

[0008] During the deposition, yellow or black powders tend to accumulate inside the chamber (e.g., on the pumping and face plates), which would cause emissivity change in the chamber and further temperature change. After processing certain number of wafers, emissivity change would render the process inconsistent from one wafer to another. Therefore, the prior art is deficient in the lack of effective means or process system that would prevent emissivity change, thereby improve the uniformity of process. Additionally, the prior art is deficient in the lack of an effective means of providing a uniform thermal boundary condition around the wafer heater so as to enhance optimal film thickness uniformity. The present invention fulfills these long-standing needs and desires in the art.

[0009] Provided herein in one aspect of the present invention is an emissivity-change-free pumping plate kit used in a single wafer chamber. This kit comprises a top open pumping plate, wherein there is no restriction to the flow. This kit may further comprise a skirt and/or a second stage choking plate. The skirt may be installed around the wafer heater, underneath the wafer heater, or along the chamber body inside the chamber, while the choking plate is installed downstream of the top open pumping plate along the purge gas flow.

[0010] The emissivity-change-free pumping plate kit disclosed herein may be used for preventing emissivity change during wafer processing by providing, in part, a gas purge to the chamber to prevent residual or powder formation on the pumping and face plates, thereby preventing an emissivity change in the chamber. More specifically, the gas purge may flow from the bottom purge or from the showerhead. Furthermore, even with a gas purge, powder formation may occur. Therefore, to reduce powder formation on the pumping and face plates, minimization of exposure to the gas is desirable, i.e., one can facilitate gas exiting between the pumping plate and face plate by using this top open pumping plate kit. The kit may also be used for providing optimal film thickness uniformity during wafer processing.

[0011] Other and further aspects, features, and advantages of the present invention will be apparent from the following description of the embodiments of the invention given for the purpose of disclosure.

[0012] So that the matter in which the above-recited features, advantages and objects of the invention, as well as others which will become clear, are attained and can be understood in detail, more particular descriptions of the invention briefly summarized above may be had by reference to certain embodiments thereof which are illustrated in the appended drawings. These drawings form a part of the specification. It is to be noted, however, that the appended drawings illustrate embodiments of the invention and therefore are not to be considered limiting in their scope.

[0013] FIG. 1 shows 30 micron doped poly cycling using a standard pumping plate illustrating that cleaning was postponed until about 10 microns.

[0014] FIG. 2 shows that the uniformity is 1.37% using a standard pumping plate. This standard pumping plate of the prior-art does not have a top opening but holes. During the pumping, the purge gas goes through the holes.

[0015] FIG. 3 shows that with a top open pumping plate, the thickness uniformity is 0.79%. It is indicated that opening the pumping plate improves the uniformity.

[0016] FIG. 4 is a cross-sectional view of POLYGen chamber 100, comprising pumping plate channel ring 101, face plate 102, blocker plate 103, chamber lid 104, chamber body 105, and pumping plate with top open 106. The pumping plate channel ring serves as a second stage choking plate. The purge gas enters the pumping plate from the bottom or the top of the chamber. With the top open, the gas flows freely out of the chamber.

[0017] FIG. 5 is a 3-dimensional view of the top open pumping plate 106.

[0018] FIG. 6 is a 3-dimensional view of a uniform choking plate, wherein the holes are evenly spaced 101.

[0019] FIG. 7 is a plot of the data contained in Table 1, illustrating that the uniformity and thickness stayed the same as the total deposition of silicon approached 21 μm using the presently disclosed pumping plate kit during wafer processing.

[0020] Disclosed herein is an emissivity-change-free pumping plate kit used for preventing the emissivity change during wafer processing which leads to process drift and particles. Problems such as powder formation in the inner chamber and blockage of pumping holes by powder are also addressed herein.

[0021] In the prior art for silicon (Si) deposition, a standard pumping plate is used, which has pumping holes for gas to flow through. FIG. 2 shows that with the standard pumping plate, the uniformity is 1.37%. During the deposition, yellow or black powders tend to accumulate on the pumping and face plates, which would cause emissivity change in the chamber and further temperature change. In order to improve the uniformity and meanwhile prevent emissivity change, a top open pumping plate is used in the present invention (see FIG. 5). With the top of the pumping plate fully open, purge gas can easily flow into the pumping channel and further eliminate the powder from the chamber. FIG. 3 shows that with a top open pumping plate, the thickness uniformity is 0.79%. It is indicated that opening the pumping plate improves the uniformity.

[0022] Additionally, during the deposition, the wafer heater tends to interact with the chamber body, which causes heat loss. In order to reduce the heat loss thereby improve the reliability and lifetime of the heater, a skirt is installed around the heater, underneath the heater, or along the chamber body inside the chamber. The skirt prevents the heater from interacting with the chamber body directly and makes the process condition more consistent from one chamber to another, therefore provides the same thermal boundary condition around the wafer heater and leads to optimal film thickness uniformity.

[0023] Another problem with the prior-art methodology for depositing silicon is that due to high deposition temperature, the chamber is constantly under high pressure, which makes it hard to control the exit gas flow uniformity. To solve this problem, a second pumping plate with reduced opening is hereby utilized in the present invention, which is installed downstream of the top open pumping plate along the purge gas flow (see pumping plate channel ring in FIG. 4). This second pumping plate provides choking effect for uniform exit gas pumping to ensure optimal thickness uniformity on the wafer. The choking plate can be uniform (see FIG. 6) or non-uniform. Uniform choking plate has evenly spaced holes, while non-uniform plate has more holes in one area and fewer in others.

[0024] As a specific example, a process chamber incorporating the above-described emissivity-change-free pumping plate kit is disclosed in one aspect of the present invention. The chamber is called POLYGen chamber 100, comprising a chamber body 105, a chamber lid 104, a top open pumping plate 106, pumping plate channel ring(s) 101 (i.e., second stage choking plate), a face plate 102, and a blocker plate 103 (see FIG. 4). A skirt (not shown) may be installed around the wafer heater (not shown), underneath the wafer heater, or along the chamber body 105 inside the chamber 100 and underneath the pumping plate 106. The emissivity-change-free pumping plate kit allows for two-stage pumping: at the first stage, the top open pumping plate 106 makes the pumping process freer and quicker as compared to a standard pumping plate. With purge gas being flown into the top open pumping plate 106 from the bottom of the chamber 100, powder formation is reduced on the pumping plate 106 and on the face plate 102. At the second stage, a choking effect is provided for uniform exit gas pumping to ensure optimal thickness uniformity on the wafer via a second pumping plate, which has reduced openings on the top. Standard purge gas may be used, such as N₂, Ar, and He.

[0025] In addition, the pumping channel designed provides a larger area for trapping the powders which thus significantly reduces the possibility of blocking the pumping holes by powders. Furthermore, the emissivity-change-free pumping plate kit provides a uniform thermal boundary condition around the wafer heater (especially with the skirt), thus making the condition between the heater and the surrounding area consistent. This leads to optimal film thickness uniformity.

[0026] Table 1 shows the test results from an emissivity change free pumping plate with top open and second stage choking plate. The smaller is the percentage of uniformity of thickness, the better is the uniformity (0=completely uniform). FIG. 7 is a plot of the data contained in Table 1.

[0027] This shows that as the total deposition of silicon (Si) approached 21 μm, the uniformity and the thickness stayed the same. Using the presently disclosed pumping plate kit during wafer processing, the productivity is significantly improved for a P-doped polysilicon process from 5 μm total deposition per chamber dry clean (90 min each time for chamber clean) to more than 25 μm of total deposition per chamber clean (see FIGS. 1 and 7 for comparison). With reduced frequency of cleaning, the system throughput is increased. The pumping plate kit disclosed herein prevents the emissivity change which leads to process drift. When there is no process drift, cleaning is not necessary.

[0028] As described above, provided herein in one aspect of the present invention is an emissivity-change-free pumping plate kit used in a single wafer chamber. This kit comprises a top open pumping plate, wherein there is no restriction to the flow. This kit may further comprise a skirt and/or a second stage choking plate. The skirt may be installed around the wafer heater, underneath the wafer heater, or along the chamber body inside the chamber, while the choking plate is installed downstream of the top open pumping plate along the purge gas flow. The choking plate may have uniform or non-uniform holes.

[0029] The emissivity-change-free pumping plate kit disclosed herein may be used for preventing an emissivity change during wafer processing by providing a gas purge to the chamber so as to prevent residual or powder formation on the pumping and face plates, thereby preventing an emissivity change in the chamber. The kit may also be used for providing optimal film thickness uniformity during wafer processing, wherein uniform exit gas pumping is provided, thereby a uniform thermal boundary condition is provided around the wafer heater which leads to optimal film thickness uniformity.

[0030] One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objects and obtain the ends and advantages mentioned, as well as those inherent therein. It will be apparent to those skilled in the art that various modifications and variations can be made in practicing the present invention without departing from the spirit or scope of the invention. Changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention as defined by the scope of the claims.