Patent Application
20060021703
1. Field of the Invention
The present invention relates to semiconductor wafer processing systems and, more particularly, to a gas distribution showerhead for supplying at least two process gases to a reaction chamber of a semiconductor wafer processing system.
2. Description of the Related Art
Semiconductor wafer processing systems generally contain a process chamber having a pedestal for supporting a semiconductor wafer within the chamber proximate a processing region. The chamber forms a vacuum enclosure defining, in part, the process region. A gas distribution assembly or showerhead provides one or more process gases to the process region. The gases are then heated and/or supplied energy to form a plasma which performs certain processes upon the wafer. These processes may include chemical vapor deposition (CVD) to deposit a film upon the wafer or an etch reaction to remove material from the wafer.
In processes that require multiple gases, generally the gases are combined within a mixing chamber that is then coupled to the showerhead via a conduit. For example, in titanium nitride deposition using titanium tetrachloride (TiCl4) and ammonia (NH3) as process gases, the two process gases are supplied to a mixing chamber along with respective carrier gases of helium and hydrogen where they are combined to form a gaseous mixture. The gaseous mixture is then coupled through a conduit to a distribution plate, where the plate contains a plurality of holes such that the gaseous mixture is evenly distributed into the process region. As the gaseous mixture enters the process region and is infused with energy, a chemical reaction occurs between the titanium tetrachloride and the ammonia such that the titanium tetrachloride chemically reacts with the ammonia (i.e., the TiCl4 is reduced by the NH3) to produce titanium nitride. The titanium nitride is deposited on the wafer in a chemical vapor deposition reaction.
Other two gas chemical vapor deposition reactions include the thermal decomposition of tetradiethylaminotitanium (TDEAT) in combination with ammonia to produce titanium nitride, the thermal decomposition of tetradimethylaminotitanium (TDMAT) in combination with ammonia or a nitrogen-hydrogen mixture to produce titanium nitride, or a reduction of tungsten hexafluoride (WF6) using hydrogen (H2) to produce tungsten. In any of these cases and any others that require two or more gases to process a wafer, multiple gases need be uniformly supplied to the process region.
Although it is generally advantageous to mix the gases prior to release into the process region to ensure that the gases are uniformly distributed into the process region, the gases tend to begin reduction, or otherwise react, within the mixing chamber. Consequently, deposition or etching of the mixing chamber, conduits and other chamber components may result prior to the gaseous mixture reaching the process region. Additionally, reaction by products may accumulate in the chamber gas delivery components.
In an effort to maintain the gases in separate passageways until they exit the distribution plate into the process region, U.S. Pat. No. 5,595,606 issued Jan. 21, 1997 (the “'606 patent”) discloses a multiple block stack that forms a showerhead that ostensibly maintains two gases in separate passageways until they exit the distribution plate into the process region. As such, the gases do not mix or react with one another until they reach the process region near the wafer.
A coolant channel 84 is provided in the lower block 62 near the gas outlets 78 for cooling the gas outlets 78. In this way, the showerhead 50 is maintained at a temperature below the liquefaction temperature of a process gas, e.g., below 40° C. for TDEAT.
The blocks 58, 60 and 62 are stacked upon one another, with O-rings 90 being placed between the blocks 58, 60, and 62 in an attempt to seal the gases within the showerhead 50. While such O-rings 90 are effective for ensuring that the gases do not leak out of the showerhead, they are less effective in ensuring that the gases do not commingle within the showerhead by leaking between the gas passageways 52 and 54 at the interfaces of the various blocks. Such commingling defeats the purpose of the dual gas passageway assembly, i.e., the gases are not completely separated until they exit the lower block 62 into the process region. Additionally, the existence of O-rings within a process chamber leads to the possibility that the O-ring material will breakdown and contaminate the chamber and even the wafer surface.
Therefore, there is a need in the art for a showerhead that conveys at least two gases into a process region without commingling the gases prior to reaching the process region. In addition, there is a need for a showerhead arrangement that does not require elastomeric or soft O-rings to seal the gases within a showerhead. Still further, there is a need for a dual gas faceplate for a showerhead fabricated from a solid Nickel material.
Certain disadvantages associated with the prior art are overcome by the present invention, which provides a faceplate for a showerhead of a semiconductor wafer processing system. The wafer processing system has a reaction chamber therein for depositing materials onto a wafer surface, or for etching materials therefrom. The faceplate includes a plurality of gas passageways to feed a plurality of gases into a process region without commingling those gases before they reach the process region.
The inventive showerhead contains a unitary faceplate, and a gas distribution manifold assembly. The faceplate is fabricated from separate upper and lower gas distribution plates. Each of the plates is preferably fabricated from a solid nickel material, with the plates being brazed or fused together to form the unitary element. Processing gases are separately carried to the various channels in the faceplate by a gas distribution manifold assembly. The gas distribution manifold assembly is bolted to the back or top surface of the upper gas distribution plate. Optionally, a cold plate can be bolted to the gas distribution manifold assembly to maintain the showerhead at a predefined temperature.
Each of the upper and lower gas distribution plates comprises a plurality of first gas holes that extend in aligned fashion through both the lower plate and the upper plate. The upper gas distribution plate of the faceplate contains a chamber that feeds gas into the plurality of first gas holes. A first process gas is fed through the plurality of holes in the upper chamber. The first gas holes distribute a first gas into the processing region. As noted, the lower gas distribution plate likewise contains a plurality of holes that align with the holes in the upper gas distribution plate. The lower gas distribution plate is disposed below the upper plate. In this manner, the first processing gas is distributed into the processing region in a pure form. In one arrangement, the lower gas distribution plate has a circular plan form, with the gas distribution holes evenly distributed about the surface of the plate for more uniform distribution of gases into the processing region.
In addition, a plurality of second gas holes is provided that extend through the lower gas distribution plate, and are connected by a plurality of interconnecting channels. The interconnecting channels are coupled to a circumferential plenum that receives a second process gas. The second gas holes are in fluid communication for the second processing gas by the circumferential plenum. The plurality of second gas holes and their interconnecting channels are sealed relative to each of the plurality of first gas holes. In this manner, fluid communication for the separate gases is precluded within the faceplate.
The bottom surface of the upper gas distribution plate is coupled and fused to the top surface of the lower gas distribution plate. In this respect, the flat surfaces of the bottom of the upper gas distribution plate form a top surface of the manifold channels that carry the second gas. The manifold channels are all coupled to one another by the circumferential plenum that is located near the outer edge of the lower gas distribution plate. A plurality of holes are drilled proximate the edge of the upper gas distribution plate into the circumferential plenum to provide gas to the circumferential plenum. The gas is coupled to the manifold channels that supply gas to the second gas holes in the lower gas distribution plate.
To avoid the use of O-rings within the faceplate, the lower and upper gas distribution plates are fused. In one arrangement, fusing is performed by first applying to the contacting surfaces a silicon-rich aluminum film or foil of 3 to 5 mils thickness. Next, the two gas distribution plates are clamped to one another. The faceplate is then heated to inside a vacuum chamber at a temperature of approximately 550° C. In this way, the gas distribution plates are melded at locations where the plates contact one another. In another arrangement, each of the gas distribution plates is fabricated from a solid Ni 200 series material. The brazed surfaces preferably have a flatness of 1 to 3 mils to form an appropriate seal that maintains the separation of the gases as they transition from the upper gas distribution plate into the lower gas distribution plate. The solid nickel plates are brazed to provide the desired contact seal.
The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.
The showerhead 114 has two main components—a faceplate 130 and a gas distribution manifold 132. The gas distribution manifold 132 has two conduits 134 and 136 that respectively couple to the conduits 124 and 126 that carry the gases through the chamber wall 128. The conduits at the interface 138 between the showerhead 114 and the wall 128 of the process chamber 102 are effectively sealed using O-rings 140 and 142 that circumscribe each conduit 124 and 126. The first process gas is provided via the conduit 134 to a cylindrical chamber 144 that distributes the first process gas to the faceplate 130. The second process gas is provided via conduit 136 to an annular chamber 146 that distributes the second process gas to the faceplate 130.
The faceplate 130 also contains two components—a lower gas distribution plate 148 and an upper gas distribution plate 150. These two plates 148, 150 contain various channels and holes that define two distinct passageways for the two process gases to enter the process region 104. The specific arrangement of channels and holes are described in detail with respect to
Referring to the lower gas distribution plate 148, the plate 148 is circular or disc-like in plan form. The lower plate 148 has a central portal region 200, and a circumferential flange 202. Preferably, the flange 202 has a thickness of approximately 2.5 mm, while the central portal region 200 has a thickness of approximately 1.21 cm. The central region 200 is defined by the width of the flange 202, which is approximately 2.54 cm. The central portal region 200 contains two sets of holes 204 and 206, where each hole has a center-to-center spacing of approximately 6.35 mm from a neighboring hole. Generally, holes 206 for the first gas (e.g. holes for TiCl4 are 0.025 inches) are approximately the same size as the holes 204 for the second gas (e.g., holes for NH3). However, the choice of hole size for each gas is a matter of designer's choice based upon the process condition. In this respect, hole size will vary depending upon gas flow rate, gas pressure, gas type, chamber pressure and the like. The hole size may also vary across the faceplate surface such that gas flow rates through the holes are correlated with the location of the hole in the faceplate 130.
The central portal region 200 is cut with grooves or channels 208 having a width of 3.173 mm and a depth of 9.525 mm. The grooves are cut at an angle of 45° from the horizontal (as shown by lines 201). As such, a plurality of interconnecting channels 208 are formed over the holes 204 for the second gas. The holes 206 for the first gas extend through the portal region 200 and are counterbored with bores 210. Alternatively, the holes 604 and 210 may be drilled at the same time after the two plates 148, 150 are brazed together. The junction of the bores 210 and the corresponding holes 206 is angled at, for example, 120 degrees. The channels 208 interconnect in a “crisscross” pattern and, when enclosed at the open top thereof, form a gas manifold for the second gas. There are approximately 700 holes 204 and 206 for each of the gases to exit the lower gas distribution plate 148.
The bottom 148 and top 150 plates are fused at the junction of the flange 202 and flange support 600. In addition, the plates 148 and 150 join at the surfaces 608 adjacent the tops of holes 204 and 206. Specifically, the flange 202 and the flange support 600 fuse at the outer edge 902 forming a sufficient seal to maintain all of the gases inside the faceplate. Additionally, the upper gas distribution plate 150 and the flange 202 of the lower gas distribution plate 148 form a circumferential plenum 900 that provides gas to the gas channels 208 formed in the lower gas distribution plate 148. The holes 606 provide gas to this circumferential plenum 900. The upper gas distribution plate 150 forms the tops of the channels 208 such that uniform rectangular cross section channels 208 are formed to distribute the second process gas to the holes 204 in the lower gas distribution plate 148. The holes 604 in the upper gas distribution plate 150 are aligned with the holes 210 in the lower gas distribution plate 148 (seen in
To facilitate flow of the first gas from holes 604 and then through corresponding holes 210 and holes 206, square-shaped islands 212 are provided around holes the 206. The square hole pattern is easier to machine than the earlier-known diamond-shaped island pattern. The square hole pattern, makes machining of the faceplate 130 more economical. Moreover, the novel square cuts leave fewer burrs than do diamond-shaped islands.
It is desirable that the faceplate be fabricated from a material that is non-reactive with chamber process gases. Preferably, the faceplate is fabricated from solid nickel, such as a solid Ni 200 series material. U.S. Pat. No. 6,086,677, issued to Umotoy, et al. in 2000, provided a faceplate that was fabricated from aluminum, and then plated with nickel to a depth of 0.2 to 0.4 mils. However, it was found that the process of nickel plating inside the various cavities and channels of the faceplate was expensive. In addition, the nickel plating composition was subject to degradation at higher process temperatures. In this respect, the nickel plating would begin to experience degradation at processing temperatures greater than about 650° F. In some chemical vapor deposition processing steps, the processing region is brought to a temperature of up to about 710° F. It has been determined that a solid Ni 200 material faceplate is able to withstand this higher temperature with less degradation.
It has also been discovered that technology for brazing materials has advanced. It is now possible to braze solid Ni 200 material, where such was not feasible (or at least not economically feasible) in 1998 when the '677 patent was filed.
To couple the second process gas from the conduit 126 and the wall of the chamber to the faceplate, an annular channel 146 is defined in the manifold 132. The annular chamber is formed by milling an annular channel 146 in the top surface of the lower plate 1000. Radially directed channels 1012 connect the annular channel 146 to a bore 1014 at the distal end of each channel 1012. Additionally, a channel that forms conduit 136 is formed in the lower plate 1000 extending from the annular channel 146 to the conduit coupling location at interface 138. The top of the annular channel 146 is closed by middle plate 1002 such that a closed annular channel 146 is formed with radially extending channels 1012 and bores 1014 that couple the second process gas to the distribution plenum 900 in the faceplate 130.
To fabricate the gas distribution manifold assembly 132 the lower, middle and upper plates 1000, 1002, and 1004 may have their mating surfaces coated with a silicon-rich aluminum film. Alternatively, each of the lower 1000, middle 1002, and upper 1004 plates is fabricated from a solid Ni 200 series material. The entire manifold assembly 132 is then clamped and placed in a furnace at a temperature of approximately 550° C. to fuse the contacting surfaces to one another and form a unitary manifold assembly 132. As such, no O-rings are necessary to maintain a separation between the process gases.
The manifold assembly 132 and faceplate 130 that form the showerhead are fabricated from solid nickel. Nickel is a thermally conductive material. As such the showerhead can be coupled to a cold plate or other cooling apparatus that will maintain the entire showerhead at a uniform and constant temperature. Such a cold plate may be formed using a body having cooling channels cut or otherwise formed therein such that a coolant is circulated through the cooling plate while the cooling plate is mounted to a top of the manifold 132. An illustrative placement of a cold plate 1100 mounted to the top of the manifold assembly 132 is shown in
The showerhead of the foregoing embodiment of the invention has been tested in a 10−5 torr vacuum test and no cross talk has been experienced between the gases provided to each of the gas input conduits 134 and 136.
Each of the tubes 1312 defines a gas passage for the second gas to reach the gas distribution holes 1308. The lower surface 1314 of the upper gas distribution plate 1302 and the upper surface 1310 of the lower gas distribution plate 1304 define a cavity 1316 that distributes the first gas to the gas distribution holes 1306. The first gas is supplied to the cavity 1316 via one or more portals 1318. A gas manifold (not shown, but identical to the manifold assembly 132 of
An alternative manufacturing process for either embodiment of the invention involves stacking die-cut layers (each layer being approximately 5 mils thick) to “build up” the faceplate structure. The stack or laminate of layers is then placed in a furnace and fused into a unitary faceplate. The material of the faceplate is solid nickel. Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
