1. Field
Embodiments of the present invention relate to the field of semiconductor substrate processing system. More specifically, the invention relates to a focus ring assembly suitable for use in a substrate process chamber.
2. Description of the Related Art
For more than half a century, the semiconductor industry has followed Moore's Law, which states that the density of transistors on an integrated circuit doubles about every two years. Continued evolution of the industry along this path will require smaller features patterned onto substrates. As feature size shrinks, manufacturers are challenged to maintain control of device properties and performance. Maintaining control of critical dimensions of features on a semiconductor substrate is a fundamental requirement of etching processes used to form those features. During a plasma etch process, for example, the critical dimension (CD) could be the width of a gate structure, trench or via and the like.
As technology nodes advance and critical dimensions shrink, increasing emphasis is placed on reducing the amount of edge-exclusion on a substrate. Edge-exclusion refers to the area near the edge of a substrate in which no features or devices are formed. Reducing edge-exclusion provides space for forming additional devices nearer the edge of a substrate. As structures are formed closer to the edge, maintaining CD uniformity across the substrate during etching processes becomes more difficult. A common form of CD non-uniformity is known as “edge roll-off”, which features a dramatic reduction in CD control close to the edge of the substrate. Additionally, CD bias—the change in CD as successive layers are etched—declines near the edge.
Current plasma etch processes attempt to address this problem by providing a “focus ring” near the edge of the substrate that has similar composition to the substrate. It is thought that the focus ring behaves as an “extension” of the film being etched and promotes a uniform concentration of etch by-product species across the substrate. This, in turn, promotes a more uniform etch rate. In etch chambers that etch silicon, for example, it is common to use a quartz focus ring due to the low etch rate of quartz relative to the substrate material and its lack of contaminants. Quartz, however, allows residual non-uniformity that becomes increasingly important as devices, and edge-exclusion, become smaller.
Thus, there is a need for an apparatus that enhances etch performance at the edge of a substrate.
Embodiments of the invention include a processing chamber for etching a substrate. In one embodiment, the processing chamber includes a chamber body having a substrate support disposed on a cathode. An electrode is disposed in the cathode and has a diameter greater than the substrate support. A focus ring is disposed on an upper surface of the substrate support. The focus ring is comprised of a material selected from the group consisting of silicon, monocrystalline silicon, silicon carbide, silicon nitride, silicon oxycarbide, and combinations thereof. A quartz ring is disposed on the upper surface of the substrate support and circumscribes the focus ring.
In one embodiment of a processing chamber, the focus ring includes a substantially vertical inner wall at an inner radius, a first surface extending from the inner wall in an orientation substantially perpendicular thereto. A first step extends from the first surface and is substantially perpendicular thereto. A second surface extends from the first step and is substantially perpendicular thereto. A bevel extends from the second surface and forms an angle less than about 80° with the second surface. The second surface extends from the first step to the bevel a distance between about 0.08 inches and about 0.14 inches. An upper surface of the focus ring extends from the bevel and is substantially parallel to the second surface.
Other embodiments of the invention provide methods for etching a substrate. In one embodiment, a method for etching a substrate includes providing one or more etchants to a process chamber; establishing an electric field in the chamber using RF power; and focusing the electric field using a focus ring assembly comprising a first ring and a second ring, wherein the first ring comprises quartz, the second ring comprises silicon, and the second ring is conductive.
So that the manner in which the above-recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.
Embodiments of the invention generally provide a chamber for etching a substrate in a semiconductor manufacturing process.
One or more antennas or coils 164 are provided proximate the lid 112 of the process chamber 100. In the embodiment depicted in
One or more bias power sources 172 are coupled to the substrate support assembly 114 to bias the substrate during processing and/or the substrate support assembly 114 during chamber cleaning. In the embodiment depicted in
The controller 130 generally includes a memory 132, a CPU 134 and support circuits 136. The CPU 134 may be one of any form of computer processor that can be used in an industrial setting for controlling various chambers and subprocessors. The support circuits 136 are coupled to the CPU 134 for supporting the processor in a conventional manner. These circuits include cache, power supplies, clock circuits, input/output circuitry, subsystems, and the like. The memory 132 is coupled to the CPU 134. The memory 132, or computer-readable medium, may be one or more of readily available memory such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. Instructions for performing processes may be stored on the memory 132. The instructions, when executed by the controller, cause the processing system to perform a process, such as an etch process described further below.
Isolators 208 and 202 are disposed between the cathode shell 204 and the cathode 200. The isolators 208 and 202 generally comprise an electrically insulating material, such as quartz, and function to isolate the cathode 200 from the cathode shell 204.
A focus ring assembly 120 is shown engaging the edge of the substrate support 116. The focus ring assembly 120 includes a first ring 212, which may be an annular base ring, and a second ring 214, which may be an annular focus ring.
The first and second rings 302 and 304 are generally disposed above an upper surface of the substrate support assembly 322. In some embodiments, the first and second rings 302 and 304 are disposed above an upper surface of the cathode 308. In one aspect, the first ring 302 may contact the upper surface of the cathode 308. In another aspect, the second ring 304 may contact the upper surface of the cathode 308. In another aspect, both rings may contact the upper surface of the cathode 308.
The first ring 302 of
The second ring 304 of
The recess 324 and extension 326 of
Wishing not to be bound by theory, it is believed that the second ring provides a passivating function for an etch process. Felicitous choice of materials for the second ring influences electric field lines and plasma density near the edge of a substrate disposed on the substrate support. Materials similar to the material of the substrate being etched provide a substantially continuous electrical and chemical environment for maintaining the plasma, promoting uniform plasma composition and uniform etch rates. The location of the second ring also influences etch rate near the edge of the substrate, with distance between the second ring and the substrate providing a way to influence plasma behavior near the substrate edge. Depending on the etch conditions and chamber geometry, a larger or smaller distance may provide suitable results.
Other embodiments of the present invention provide a method of etching a substrate, comprising providing one or more etchants to a process chamber establishing an electric field in the chamber using RF power, inductively coupling the RF power to form a plasma from the etchants and focusing the electric field using a focus ring assembly disposed on a substrate support assembly, the focus ring assembly comprising a first ring and a second ring, wherein the first ring comprises quartz, the second ring is conductive and comprises silicon. A substrate may be provided to a process chamber having a substrate support, a gas distribution assembly, a means for generating RF power such as electrodes coupled to an RF generator, and a focus ring assembly. The focus ring assembly acts to smooth the electric field lines and normalize the composition of the gas phase above the edge of the substrate.
In one embodiment, a substrate is disposed on a substrate support in an etch chamber. A first etchant selected to etch a silicon nitride hard mask layer is provided to the chamber. The first etchant may be a halogenated hydrocarbon or mixture thereof, such as a C1-C4 linear or cyclic fluorocarbon. Examples of such etchants are CF4 and CHF3. RF power is applied to coils to generate an electric field in the chamber to inductively activate the etchant. The activated etchant reacts with a silicon nitride hard mask layer disposed on the substrate, exposing a layer beneath. The etchant also reacts with the material of the second ring to generate vapor species similar to that generated above the substrate. Because the vapor chemistry above the second ring is similar to that above the edge of the substrate, activated species in the vapor phase are not concentrated or diluted above the edge of the substrate, relative to other portions of the substrate. Thus, etch rate and critical dimension uniformity are enhanced. Additionally, because the second ring is conductive and has a beneficial geometry, electric field lines are not distorted near the edge of the substrate by a difference in conductivity between the second ring and the substrate. Activated species in the vapor thus respond to the uniform electric field lines by etching the edge of the substrate surface at substantially the same rate as the center of the substrate.
In some embodiments, it may be advantageous to perform a reconditioning process on the second ring. During substrate processing, the second ring may develop impurities on its surface that are deposited from the vapor phase. These impurities may result in “micromasking” on the surface of the ring, leading to formation of a porous or grass-like structure that can generate particles in the chamber. Such impurities may be removed by using a cleaning process in which the second ring is etched under a high bias power. In one embodiment, a silicon ring may be etched with a sacrificial substrate disposed in the chamber using a fluorocarbon etchant such as CF4 or CHF3 under an electrical bias of between 100 watts and 3000 watts combined power for the dual frequency bias, such as about 500 watts at 13 MHz or about 1000 watts at 60 MHz, to remove the impurities.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention thus may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
This application claims benefit of U.S. provisional patent application Ser. No. 61/032,920, filed Feb. 29, 2008, which is herein incorporated by reference.
Number | Date | Country | |
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61032920 | Feb 2008 | US |