Patent Application
20060278339
The present invention relates to semiconductor fabrication. More particularly, the present invention relates to a plasma etching apparatus.
A typical plasma etching apparatus comprises a reactor in which there is a chamber through which reactive gas or gases flow. Within the chamber, the gases are ionized into a plasma, typically by radio frequency energy. The highly reactive ions of the plasma are able to react with material, such as the dielectric between interconnects or a polymer mask on a surface of a semiconductor wafer during it being processed into Integrated Circuits (IC's). Prior to etching, the wafer is placed in the chamber and held in proper position by a chuck or holder which exposes a top surface of the wafer to the plasma.
In semiconductor processing, the etch or deposition rate uniformity across the wafer during each process directly affects the device yield. This has become one of the main qualifying requirements for a process reactor and hence is considered a very important parameter during its design and development. With each increase in the size of wafer diameter, the problem of ensuring uniformity of each batch of integrated circuits becomes more difficult. For instance, with the increase from 200 mm to 300 mm in wafer size and smaller circuit size per wafer, the edge exclusion shrinks to, for example, 2 mm. Thus maintaining a uniform etch rate, profile, and critical dimensions all the way out to 2 mm from the edge of the wafer has become very important.
In a plasma etch reactor, the uniformity of etch parameters' (etch rate, profile, CD, etc.) is affected by several parameters. Maintaining uniform plasma discharge and hence plasma chemistry above the wafer has become very critical to improve the uniformity. Many attempts have been-conceived to improve the uniformity of the wafer by manipulating the gas flow injection through a showerhead, modifying the design of the showerhead, and placing edge rings around the wafer.
One problem in a capacitively-coupled etching reactor is the lack of uniform RF coupling especially around the edge of a wafer.
Center bottom electrode 108 is connected to RF power supply 118 while top electrode 106 and edge bottom electrode 110 are grounded for draining charge from plasma 116 produced between top electrode 106 and bottom electrode 104. As illustrated in
During plasma processing, the positive ions accelerate across the equipotential field lines to impinge on the surface of the substrate, thereby providing the desired etch effect, such as improving etch directionality. Due to the geometry of the upper electrode 106 and the bottom electrode 104, the field lines may not be uniform across the wafer surface and may vary significantly at the edge of the wafer 104. Accordingly, grounded ring 110 is typically provided to improve process uniformity across the entire wafer surface.
Because the parts in top electrode 106 are static, the etch rate cannot be separately controlled at the center and at the edge of the wafer. The non-uniformity during the etching process can lead to different dimensions between the center and the edge lowering the yield of reliable devices per wafer.
Accordingly, a need exists for a method and apparatus for independently controlling the etch rate at the center and the edge of a wafer. A primary purpose of the present invention is to solve these needs and provide further, related advantages.
A plasma reactor comprises a chamber, a bottom electrode, a top electrode, a bottom grounded extension adjacent to and substantially encircling the bottom electrode. The top grounded extension adjacent to and substantially parallel to the top electrode. The top electrode is also grounded. The top grounded extension is capable of being independently raised or lowered to extend into a region above the bottom grounded extension.
The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more embodiments of the present invention and, together with the detailed description, serve to explain the principles and implementations of the invention.
In the drawings:
Embodiments of the present invention are described herein in the context of plasma reactor. Those of ordinary skill in the art will realize that the following detailed description of the present invention is illustrative only and is not intended to be in any way limiting. Other embodiments of the present invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to implementations of the present invention as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts.
In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer's specific goals, such as compliance with application- and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure.
Bottom electrode 208 is connected to RF power supply 218 while top electrode 212, top electrode extension 214, and bottom electrode extension 210 are grounded for draining charge from plasma 216 produced between top electrode 212 and bottom electrode 208. By way of example, bottom electrode extension 210 and top electrode extension 212 may be made of a conductive material such as aluminum. As illustrated in
Bottom electrode 208 is configured to receive a workpiece and includes an associated bottom electrode area that is adapted to receive the workpiece. Bottom electrode 208 is coupled to at least one power supply 218. Power supply 218 is configured to generate RF power that is communicated to bottom electrode 208. For illustrative purposes only, a dual frequency power supply 218 may be used to generate the high electric potential that is applied to a gas to produce plasma 216. More particularly, the illustrated power supply 218 is a dual power frequency power supply operating at 2 MHz and 27 MHz that is included in etching systems manufactured by Lam Research. It shall be appreciated by those skilled in the art that other power supplies capable of generating plasma in the processing chamber 202 may also be employed. It shall be appreciated by those skilled in the art that the invention is not limited to RF frequencies of 2 MHz and 27 MHz but may be applicable to a wide range of frequencies. The invention is also not limited to dual frequency power supplies but is also applicable to systems that have three or more RF power sources with a wide variety of frequencies.
Top electrode 212 is disposed at a predetermined distance above from bottom electrode 208. Top electrode 212, top electrode extension 214, together with ground extension 210 are configured to provide a complete electrical circuit for RF power communicated from bottom electrode 208. Top electrode extension 214 can move up or down independently from top electrode 212 to manipulate plasma density at the edge of bottom electrode 208—plasma region 222. With the plasma density varied at the edge of bottom electrode 208, the etch rate at that region can be independently controlled (either faster rate or slower rate) from the etch rate in the plasma region 220. Those of ordinary skills in the art will appreciate that there are many ways to lower and raise the top electrode extension 214. For example, a mechanical or motorized knob may be used to raise or lower top electrode extension 214 without having to open and access the interior of chamber 202.
During plasma processing, the positive ions accelerate across the equipotential field lines to impinge on the surface of the substrate, thereby providing the desired etch effect, such as improving etch directionality. Due to the geometry of top electrode 212 and bottom electrode 208, the field lines may not be uniform across the wafer surface and may vary significantly at the edge of the wafer. Accordingly, top and bottom electrodes extensions 214 and 210 are provided to improve process uniformity across the entire wafer surface.
Plasma reactor 200 is configured to receive a gas (not shown) that is converted into plasma 216 by plasma reactor 200. By way of example and not of limitation, the relatively high gas flow rate that is pumped into chamber is 1500 sccm. Gas flow rates less than 1500 sccm as well as more than 1500 sccm may also be applied.
To generate plasma 216 within chamber 202, power supply 218 is engaged and RF power is communicated between bottom electrode 208 and top electrode 212. Gas is then converted to plasma 216 that is used for processing workpiece or a semiconductor substrate. By way of example and not of limitation, RF power levels of 2 W per cm3 of plasma volume may be applied. RF power levels of less than 2 W per cm3 of plasma volume may also be applied.
For illustrative purposes, plasma reactor 200 described in
Those of ordinary skill in the art will appreciate that the above configurations shown in
While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art having the benefit of this disclosure that many more modifications than mentioned above are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims.
