Patent Application
20060011583
The present invention relates to apparatus and methods for processing substrates such as semiconductor substrates for use in IC fabrication or panels (e.g., glass, plastic, or the like) for use in flat panel display applications. More particularly, the present invention relates to improved plasma processing systems that are capable of processing substrates with a high degree of processing uniformity across the substrate surface.
Plasma processing systems have been around for some time. Over the years, plasma processing systems utilizing inductively coupled plasma sources, electron cyclotron resonance (ECR) sources, capacitive sources, and the like, have been introduced and employed to various degrees to process semiconductor substrates and display panels.
In a typical plasma processing application, the processing source gases (such as the etchant gases or the deposition source gases) are introduced into the chamber. Energy is then provided to ignite a plasma in the processing source gases. After the plasma is ignited, it is sustained with additional energy, which may be coupled to the plasma in various well-known ways, e.g., capacitively, inductively, through microwave, and the like. The plasma is then employed in the processing task, e.g., to selectively etch or deposit a film on the substrate. Plasma processing systems in general are well known in the art and the reference literature is replete with details pertaining to various commercially available systems. Thus general principles pertaining to plasma processing will not be discussed in great detail here for brevity's sake.
In processing the substrates, one of the important parameters that process engineers strive to improve is processing uniformity. In the etch environment, for example, etch uniformity is an important determinant of yield, i.e., a high level of etch uniformity tends to improve the percentage of defect-free processed substrates, which translates into lower cost for the manufacturer. As the term is employed herein, etch uniformity refers to the uniformity of the entire etch process across the substrate surface including etch rate, microloading, mask selectivity, underlayer selectivity, critical dimension control, and profile characteristics like sidewall angle and roughness. If the etch is highly uniform, for example, it is expected that the etch rates at different points on the substrate tend to be substantially equal. In this case, it is less likely that one area of the substrate will be unduly over-etched while other areas remain inadequately etched. In addition, in many applications these stringent processing requirements may be contradictory at different stages during the substrate processing. Often this is due to the presence of multiple films that must be processed with dramatically different plasma processing requirements. For example, the gas pressure, plasma density and chemistry may be required to dramatically change while processing a single substrate to achieve the desired processing performance.
In addition to processing uniformity, there also exist other issues of concern to the process engineers. Among the important issues to manufacturers is the cost of ownership of the processing tool, which includes, for example, the cost of acquiring and maintaining the system, the frequency of chamber cleaning required to maintain an acceptable level of processing performance, the longevity of the system components, and the like. Thus a desirable etch process is often one that strikes the right balance between the different cost-of-ownership and process parameters in such a way that results in a higher quality process at a lower cost. Further, as the features on the substrate become smaller and the process becomes more demanding (e.g., smaller critical dimensions, higher aspect ratios, faster throughput, and the like), process engineers are constantly searching for new methods and apparatuses to achieve higher quality processing results at lower costs.
The invention relates, in one embodiment, to a plasma processing system for processing a substrate which includes a single chamber, substantially azimuthally symmetric plasma processing chamber within which a plasma is both ignited and sustained for the processing. The plasma processing chamber has no separate plasma generation chamber. The plasma processing chamber has an upper end and a lower end. The plasma processing chamber includes a material that does not substantially react with the reactive gas chemistries that are delivered into the plasma processing chamber. In addition, the reactant gases that are flown into the plasma processing chamber are disclosed.
The plasma processing system includes a coupling window disposed at an upper end of the plasma processing chamber and an RF antenna arrangement disposed above a plane defined by the substrate when the substrate is disposed within the plasma processing chamber for the processing. The plasma processing system also includes an electromagnet arrangement disposed above the plane defined by the substrate. The electromagnet arrangement is configured so as to result in a radial variation in the controllable magnetic field within the plasma processing chamber in the region proximate the coupling window and antenna when at least one direct current is supplied to the electromagnet arrangement. The radial variation is effective to affect processing uniformity across the substrate.
The plasma processing system additionally includes a dc power supply coupled to the electromagnet arrangement. The dc power supply has a controller to vary a magnitude of at least one direct current, thereby changing the radial variation in the controllable magnetic field within the plasma processing chamber in the region proximate the antenna to improve the processing uniformity across the substrate.
In another embodiment, the invention relates to a method for controlling processing uniformity while processing a substrate using a plasma-enhanced process. The method includes providing a plasma processing chamber having a single chamber, substantially azimuthally symmetric configuration within which a plasma is both ignited and sustained during the processing of the substrate, the plasma processing chamber having no separate plasma generation chamber. The plasma processing chamber includes a material that does not substantially react with the reactive gas chemistries that are delivered into the plasma processing chamber. In addition, the reactant gases that are flown into the plasma processing chamber are disclosed.
The method also includes providing a coupling window disposed at an upper end of the plasma processing system and providing an RF antenna arrangement disposed above a plane defined by the substrate when the substrate is disposed within the plasma processing chamber for the processing. The method additionally includes providing an electromagnet arrangement disposed above the plane defined by the substrate. The electromagnet arrangement is configured so as to result in a radial variation in the controllable magnetic field within the plasma processing chamber in the region proximate the coupling window and antenna when at least one direct current is supplied to the electromagnet arrangement. The radial variation is effective to affect processing uniformity across the substrate.
Additionally, there is included providing a dc power supply coupled to the electromagnet arrangement, placing the substrate into the plasma processing chamber, flowing reactant gases into the plasma processing chamber, striking the plasma out of the reactant gases, and changing the radial variation in the controllable magnetic field within the plasma processing chamber in the region proximate the antenna to improve the process uniformity across the substrate.
In yet another embodiment, the invention relates to a plasma processing system for processing a substrate, which includes a single chamber, substantially azimuthally symmetric plasma processing chamber within which a plasma is both ignited and sustained for the processing. The plasma processing chamber has no separate plasma generation chamber. The plasma processing chamber has an upper end and a lower end.
The plasma processing system includes a coupling window disposed at an upper end of the plasma processing chamber, and an RF antenna arrangement disposed above a plane defined by the substrate when the substrate is disposed within the plasma processing chamber for the processing.
There is further included a first RF power supply coupled to the RF antenna, and a first magnet arrangement disposed above the plane defined by the substrate. The magnet arrangement is configured so as to result in a radial variation in the controllable magnetic field within the plasma processing chamber in the region proximate the coupling window and antenna due to magnetic field lines emanating from the magnet arrangement. The radial variation is effective to affect processing uniformity across the substrate.
Additionally, there is included a substrate support arrangement configured to support the substrate within the plasma processing chamber during the processing, and a second RF power supply coupled to the substrate support arrangement. The second RF power supply is controllable independently from the first RF power supply. Further, there is included means to vary the radial variation in the controllable magnetic field within the plasma processing chamber in the region proximate the antenna to improve the processing uniformity across the substrate.
These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures.
The present invention is illustrated by way of example, and not by way of limitation, in which:
The present invention will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention.
The invention relates, in one embodiment, to an improved plasma processing system that is capable of a high degree of processing uniformity control. The exemplary improved plasma processing system includes a single chamber, substantially azimuthally symmetric, i.e., each cross section parallel to the wafer plane has a nearly circular shape, plasma processing chamber that is employed to both generate the plasma and to contain the plasma for the processing task. The improved plasma processing system further includes an upper magnet arrangement and an RF antenna arrangement disposed above the plane of the substrate during processing.
The RF antenna arrangement and the upper magnet arrangement are arranged such that there would be a nontrivial amount of radial variation in the controllable magnetic field strength and topology within the plasma processing chamber sufficiently far above the substrate that the induced variation in processing uniformity is achieved while simultaneously ensuring the magnetic field strength at the substrate is low. In the preferred embodiment, this radial variation in the controllable magnetic field strength and topology is primarily in the vicinity of the region of power coupling near the RF antennae/vacuum interface. The radial variation in the controllable magnetic field strength and topology is such that it affects the processing uniformity in a nontrivial way. By purposefully designing a plasma processing system to create a pattern of radial variation in the controllable magnetic field strength and topology that is capable of affecting processing uniformity, and then providing a way to vary that radial variation, a uniformity dial is provided to allow process engineers to tune the process so as to improve uniformity.
In one example, the aforementioned radial variation in the controllable magnetic field strength and topology is created by making the RF antenna arrangement non-coplanar with the upper magnet arrangement. Alternatively or additionally, the radial variation in the controllable magnetic field strength and topology may be created by providing an upper magnet arrangement that includes two or more electromagnet coils, which may be coplanar or non-coplanar relative to each other. The multiple electromagnet coils may be (but not required to be) furnished with dc currents having opposite directions to induce the aforementioned radial variation in the controllable magnetic field strength and topology.
For ease of manufacturing and simplicity of operation, the plasma processing chamber is preferably configured (though not restricted to) to be a single chamber, substantially azithmuthally symmetric plasma processing chamber: In other words, the plasma processing chamber of the present invention preferably consists of a single chamber that both generates and contains the plasma for substrate processing (and therefore eliminates the need for a separate chamber for plasma generation), and also is substantially azithmuthally symmetric to promote uniformity. By way of example and not by way of limitation, the chamber may assume the shape of single cylindrical or dome-shaped chamber.
In a preferred embodiment, the chamber assumes the shape of a single cylindrical chamber wherein the plasma is both ignited and contained for the processing task without the requiring the use of a separate chamber for plasma generation and a separate chamber for processing.
In one exemplary improved plasma processing system, there is further provided a magnetic bucket arrangement that is configured to force a substantial number of the plasma density gradients to occur away from the substrate. In one preferred embodiment, the magnetic bucket arrangement is disposed about the periphery of the plasma processing chamber. Preferably but not necessarily, the magnetic bucket arrangement includes a plurality of permanent magnets that are axially oriented about the periphery of the plasma processing chamber, either inside or outside of the chamber walls. Irrespective of the specific implementation, the magnetic bucket arrangement is configured to force the plasma density gradients to concentrate near the chamber walls away from the substrate. In this manner, uniformity is further enhanced as the plasma density gradient change across the substrate is minimized or substantially reduced. In combination with the aforementioned controllable radial variation of magnetic field strength and topology, process uniformity is improved to a much greater degree in the improved plasma processing system than is possible in many existing plasma processing systems.
The magnetic bucket tends to reduce the plasma losses to the wall, hence the exemplary improved plasma processing system may more efficiently use the plasma created by the source. Accordingly, for a given source power, more density can generally be achieved than in typical processing systems, which in turn offers a wider processing window. In many cases the desired processing density may be easily achieved, yet in the exemplary improved system, less source power is typically required to generate the density. As can be appreciated by those skilled in the art, the lower setting of the source power tends to reduce possible wafer damage mechanisms and further widens the allowed processing window of the system.
Plasma analyses of reactors (such as those based on volume ionization balanced by Bohm losses to the walls) also predict that the electron temperature for a given power deposition will be reduced by reducing the plasma loss area. This is accomplished, in one embodiment, by incorporating the magnetic bucket. Such a reduction in electron temperature generally leads to lower potentials on and across the wafer that could cause damage to the electronic circuits being processed. Eliminating this root cause of plasma induced damage tends to significantly enhance the operating window of the tool.
It has also been observed that in some depositing plasma chemistries, the bucket fields tend to reduce the total polymer deposition on the walls thereby reducing the chamber clean times expected from the increased surface areas required in chambers suitable for increasingly large wafers.
The average density across the wafer also may play a large role in determining the resulting process result. By reducing the plasma loss to the walls using the magnetic bucket, the uniformity control mechanism disclosed here is substantially independent of the average density.
In addition, the disclosed uniformity control invention is facilitated by a very low magnetic field at the wafer, which is preferentially achieved by locating the higher magnetic field regions away from the wafer. Using the magnetic bucket to efficiently use the density created by the source is thus very beneficial.
The features and advantages of the present invention may be better understood with reference to the figures and discussions that follow.
RF antenna arrangement 102 is shown coupled to an RF power supply 112, which may supply RF antenna arrangement 102 with RF energy having a frequency in the range of about 0.4 MHz to about 50 MHz. More preferably, the frequency range is about 1 MHz to about 30 MHz. In the preferred embodiment for etching, the RF frequency supplied to RF antenna arrangement 102 is preferably about 4 MHz.
Upper magnet arrangement 104 of the embodiment of
A substrate 122 is shown disposed above a substrate support arrangement 124, which is coupled to a bias RF power supply system 128 to independently control the energies of the charged particles impinging on the wafer. Bias RF power supply 128 may supply RF energy having a periodic, but not necessarily sinusoidal, frequency range of about 0.3 MHz to about 50 MHz, more preferably about 2 MHz to about 30 MHz, and preferably at about 13.5 MHz. Substrate 122 represents the workpiece to be processed, which may represent, for example, a semiconductor substrate to be etched, deposited, or otherwise processed or a display panel to be processed into a flat panel display. Preferably in one embodiment utilizing the magnetic bucket, but not absolutely necessary, the substrate should be supported well inside the lowest portion of the magnetic bucket to avoid any axial gradients in the plasma processing mixture that may occur to the proximity of the changing level of confinement provided at the transition from the magnetic bucket portion to a non-magnetic portion. Manufacturing and cost aspects may determine the actual extent of the magnetic bucket and relative location of the substrate during processing.
As shown in
In the drawing of
Advantageously, there is now a nontrivial radial variation in the controllable magnetic field strength and topology, which is purposefully created in the improved plasma processing system and purposefully configured to be capable of having a nontrivial effect on the processing uniformity at the substrate surface. For example the field lines 140 in
There is also shown in
In general, the number of cusps should be sufficiently high to ensure that there is a strong plasma density gradient away from the substrate. However as the losses are, relative to the rest of the chamber bucket, highest at the cusp, too many cusps may degrade the density enhancement. By way of example, a magnetic field strength of about 15-1,500 Gauss at the vacuum-wall interface may be suitable for some processes. More preferably, the magnetic field strength at the vacuum-wall interface may be between about 100 Gauss and about 1,000 Gauss. Preferably, the magnetic field strength at the vacuum-wall interface may be about 800 Gauss. It should be understood that the use of magnetic bucket arrangement 102 enhances the plasma uniformity across the wafer surface and may not be required for all processes. However, if a high degree of uniformity is critical, the inclusion of a magnetic bucket arrangement can be quite beneficial.
In the preferred embodiments, the RF antenna arrangement is preferably disposed above the RF coupling window to advantageously simplify the design and construction of the chamber and/or the RF coupling window and/or the magnetic bucket arrangement. However, it is contemplated that the desired controllable radial variation in magnetic field strength and topology may also be achieved by placing the RF antenna arrangement in other positions on the chamber. By way of example,
In the exemplary embodiment of
With respect to the RF frequency employed, as a general guideline, a lower RF frequency, e.g., <13 MHz with typical dielectric constants and physical dimensions found on these tools, tends to make any inherent azimuthally asymmetric coupling characteristic of an antenna less pronounced. Accordingly, a wider array of antenna configurations may be employed at a lower RF frequency. By way of example, a planar spiral antenna may be employed to achieve high quality etches in the improved plasma processing chamber when the RF frequency is low, e.g., 4 MHz. At a relatively high RF frequency, e.g., 13 MHz and above, the inherent azithmuthally asymmetric coupling characteristic of an antenna can become more pronounced and can affect the process uniformity in a negative way. Accordingly, antennas that are inherently azithmuthally asymmetric in their coupling characteristics (e.g., simple spiral antennas) may be unsuitable for some processes that require a high level of process uniformity. In these cases, the use of antennas that have inherent azithmuthally symmetric coupling characteristics may be warranted.
In the preferred embodiment, the RF antenna arrangement is preferably co-axial with both the electromagnetic coils, the plasma processing chamber, and the substrate. However, such is not an absolute requirement. For some processes that may not need a high degree of process uniformity provided by the co-axial RF antenna arrangement or in chambers that employ asymmetric pumping, the RF antenna arrangement may be offset from this co-axial configuration to address the asymmetry in the chamber design. However, the purposeful introduction of the controllable radial variation controllable magnetic field strength and topology and the ability to control such radial variation in controllable magnetic field strength and topology to fine tune process uniformity across the substrate surface is still desirable.
With respect to the size of the RF antenna arrangement, it is generally preferable (but not absolutely necessary) to size the RF antenna arrangement to be smaller than the cross-section of the chamber in order to keep the plasma concentrated in the region above the substrate and to prevent undue plasma diffusion to the chamber walls, which disadvantageously require more power to operate the plasma processing system and increases wall erosion. In the exemplary improved plasma processing system of
In
At a lower RF frequency (e.g., less than about 13 MHz), the capacitive coupling between the antenna and the plasma is reduced, which reduces bombardment of the coupling window 130. With reduced bombardment, it is possible to eliminate the requirement of a semiconductor window or the use of a Faraday shield. In fact, it is contemplated that coupling window 130 may advantageously be formed from either a dielectric material such as SiC or AlxNy or SixNy, which may also be bonded with SiC to render the coupling window more compatible with the plasma environment within the chamber.
In general, the radially divergent magnetic field topology may be varied by changing the magnitude and/or direction of the dc current(s) that is/are supplied to the electromagnet coil(s). If there are multiple electromagnet coils involved, as is the case in the example of
Since uniformity control is facilitated by manipulating the radial variation of the magnetic field strength and topology that is generated primarily in the vicinity of region 110 near RF antenna arrangement 102, the distance between the substrate and the upper magnet arrangement is an important parameter. This is because changes to the radial component of the magnetic field topology also impact the axial component. Preferably, the magnetic field strength while processing the substrate should be fairly weak (e.g., less than about 15 Gauss) at the substrate surface and strong at axial positions near the RF antenna arrangement (e.g., about 15 Gauss to about 200 Gauss near the vacuum-window interface). If the field strength becomes too low in too large a volume adjacent to the wafer, the plasma will nearly approach the diffusion profile obtainable without the uniformity control mechanism in place. Although such a diffusion profile may be sufficiently uniform for some areas within the reactor's designed processing window, the advantages associated with having a controllable radial variation in the magnetic field strength and topology are substantially attenuated.
With these considerations in mind, the distance should be sufficiently small enough to allow processing uniformity to be manipulated when the radially varying magnetic field strength and topology is altered. However, the distance should not be unduly small so as to induce substrate damage due to variations in currents flowing in the wafer or charging of the etched features on the wafer being processed caused or enhanced by excessive the magnetic field at the wafer location during processing. In addition if the source to wafer distance is too small, the axial diffusion begins to dominate the processing uniformity. The radial variation scale length then required to control the uniformity becomes close to the size of the non-uniformity to be controlled. This leads to a less optimal magnetic design because of the increased number and required control precision of local radial variations in the magnetic field strength and topology. In other words if the chamber is too small, its physical boundaries control the processing uniformity to such an extent that the application of the principles of this invention, though still applicable, force over-complication of the design and a less optimal balance between the desired uniformity control and other real life considerations as described earlier, i.e., cost, reliability etc.
In the preferred embodiment, the distance between the substrate and the upper magnet arrangement may be determined, empirically in some cases, by taking into account the strengths of the radially divergent component and the axial component of the controllable magnetic field topology and the need to avoid undue substrate damage when dc current is furnished to the electromagnetic coil arrangement to tune the process uniformity. In one exemplary embodiment, a distance of 20 cm is appropriate for a substrate processing chamber designed for processing semiconductor substrates having a diameter of less than about 470 mm.
In the embodiment of
In the preferred embodiment, the upper magnet arrangement is co-axial with the antenna, the chamber, and the substrate to simplify the alignment of the plasma cloud with the substrate. However, it is contemplated that in some plasma processing chambers, e.g., those employing asymmetric pumping or those that require a more complex magnetic field topology, it may be advantageous to offset the upper magnet arrangement from the chamber axis and/or the substrate axis to improve the process results. One such implementation is shown in
Additionally, there is no requirement that the coils have to directly overlie the antenna. By way of example, in the embodiment of
Furthermore, although the preferred implementation of the upper magnet arrangement is electromagnet coil(s), it is contemplated that a sufficiently powerful permanent magnet arrangement, e.g., one formed from NdFeB or SmCo families of magnetic material may also be employed to purposefully create the aforementioned radial divergence in the magnetic field topology. In the case of a permanent magnet implementation, the resultant radial divergence in the magnetic field topology may be changed by physically moving components of the upper magnet arrangement and/or by providing appropriate structural or magnetic circuit elements, e.g., by interposing a structure with high magnetic permeability as part of the effective magnetic circuit of the upper permanent magnet arrangement and the coupling window, to alter the magnetic field lines appropriately. Similarly, a combination of ferromagnetic elements and electromagnets can be used.
In the embodiment of
Although simplicity and symmetry are demonstrated in the preferred embodiment, it is anticipated similar uniformity controlling variations can also be achieved with magnetic coils which are not circular in cross section (e.g., hexagonal or square or other geometric shapes) or with axes that are not parallel to the primary system axis.
In the exemplary plasma processing system of
Furthermore, there is no requirement that the footprint of the RF antenna has to be larger than the footprint of the upper magnetic arrangement. That is, there is no requirement that the cross-section of the upper magnetic arrangement be smaller than the cross-section of the RF antenna. As long as these two are configured so as to result in a controllable radial variation in the magnetic field strength and topology within the plasma processing chamber in the vicinity of the plasma/window interface, the relative sizes of the RF antenna and the upper magnetic arrangement can be dimensioned as desired.
If a magnetic bucket arrangement is involved, as in the case of the preferred embodiment, for improving processing uniformity for some critical processes, the design of the magnetic bucket is also of importance. In general, the magnetic bucket arrangement should produce a sufficiently strong magnetic field to force most of the plasma density gradient away from the substrate and close to the chamber walls. Preferably, the magnetic field strength at the vacuum/wall interface within the plasma processing chamber should be relatively high, e.g., between 15 Gauss and 1,500 Gauss, more preferably between about 100 Gauss and about 1,000 Gauss and in one embodiment at about 800 Gauss. However, the magnetic field strength at the center of the substrate should be kept low, e.g., less than about 15 Gauss and more preferably less than about 5 Gauss.
Although
Although this implementation is highly advantageous and preferred, it is contemplated that it may be possible, for some processes, to employ a plasma processing system which has chamber magnets (i.e., the magnets of the magnetic bucket arrangement) disposed on only one side of the substrate plane. By way of example, if the process uniformity requirement can tolerate the presence of some axial gradients of the magnetic field lines generated by the magnetic bucket arrangement, it may not be necessary to require that the chamber magnets extend to both sides of the substrate plane. As another example, it may be possible to have two sets of chamber magnets, one on each side of the substrate plane (such as sets 132 and 180 in
Further, although permanent magnets are employed for implementing the magnetic bucket arrangement in the preferred embodiment, it is also possible to implement the magnetic bucket arrangement using electromagnets.
As mentioned, although one important feature of the present invention is the elimination of the plasma generation chamber, it is recognized that while the same chamber can be used to ignite, generate, and contain the plasma for processing, there is no absolute necessity to keep the substrate in the same chamber. As shown in
Further, although the magnets of the buckets are aligned azithmuthally (e.g., along the axis of the chamber) with radial magnetization patterns alternating around the chamber, it is contemplated that the magnetization patterns may be non-alternating. By way of example, the set of magnets may be divided into multiple subsets, each of which may have the same or different number of magnets. This may be appropriate to address any asymmetry issues encountered in a particular chamber. Also, the axes of each magnet may be aligned in a direction other than the radial direction. Again, this implementation may be appropriate to address any asymmetry issues encountered in a particular chamber.
In a particularly advantageous embodiment, some or all of the magnets of the magnetic bucket may be made rotatable on their axes to change the magnetization pattern. One such implementation is shown in
Further, although the embodiment of
As noted above, the etching process needs to be tightly controlled to achieve desirable etch characteristics such as selectivity, etch uniformity, etch rate, etch profile, etc. One important consideration in achieving tight control over the etch process is the material utilized for the plasma processing chamber, e.g., the single chamber provided in step 702. More particularly, although undesired, the material of the plasma processing chamber often participates in the etch process. As examples of reactions which are undesirable if left uncontrolled, inner surfaces of a plasma processing chamber may interact with the reactant gases that are used in the plasma processing chamber, or materials such as polymers may stick to inner surfaces of the processing chamber in ways that vary from wafer to wafer or disadvantageously during a single wafer. Dielectric etching processes are used for many applications; often to form self-aligned contacts, high aspect ratio contacts, borderless contacts, vias, trenches etc. by etching through doped or undoped oxides.
Recently a large number of alternative dielectrics have been proposed aimed at reducing the dielectric constant of the material. These are known collectively in the community as low-k materials, e.g., carbon or fluorine doped oxides or organic based materials. Dielectric etching by its nature depends on a very subtle balance between competing reactions on the evolving surface of the wafer, surfaces of the etched features and surfaces of the chamber. These reactions involve plasma species such as ions and electrons, neutral gasses introduced as feed gas, dissociated by plasma excitation or formed via a multitude of physical and chemical processes within the chamber. Due to the nature of these reactions, the area of material facing the plasma and the proximity of the chamber materials to the wafer, the material of the plasma processing chamber is especially important. In addition, since the materials themselves are changing at an ever increasing rate, the exact nature of the required processes are not know ahead of time. This is especially true of difficult processing metrics such as uniformity of etched critical dimension across the wafer. Such metrics often depend on not only the details of the chamber design, but also on the overall system design. Hence, focussing in particular relating to this invention; it is desirable to minimize the extent to which the material of the plasma processing chamber reacts with the etch process to achieve a processing chamber that can meet the requirements of all the etch applications.
Besides minimization of the reactance, the material utilized for the plasma processing chamber should also desirably have moderate to high thermal and electrical conductivity as well as have strong mechanical properties. During various stages of the etching process it is desirable to control the temperature of a plasma processing chamber within a few degrees Celsius. A material that can provide moderate to high thermal conductivity is beneficial since it can facilitate control of the temperature of the plasma processing chamber. A material that can provide moderate to high electrical conductivity is also beneficial because it is beneficial to the repeatability of the chamber. It is also beneficial to provide sufficient ground area for plasma stability and repeatability. Further, a material that has strong mechanical properties is helpful because the material is subjected to harsh environmental conditions (pressure and temperature and maintenance activities). One material with such desirable characteristics is silicon carbide (SiC). SiC is a material with relatively high thermal conductivity and moderate electrical conductivity. In addition, SiC offers good mechanical properties, such as its strength, needed to hold a vacuum in the chamber.
The plasma processing chamber can be made of SiC to facilitate tighter control over the etching process. As will be understood by those skilled in the art, the entire plasma processing chamber may be made from SiC. Alternatively, only inner surfaces of the plasma processing chamber can be made of SiC, e.g., a coating of SiC may be used as will be discussed later. SiC can be made in a variety of ways. It is desirable to use a pure form SiC so that it does not include significant amounts of metal elements. As is known in the art, material containing metal that is exposed to plasma during an etch process can cause metal contamination which adversely effects the etching process. Such contamination of the etching process makes it difficult to clean the plasma processing chamber and/or maintain a uniform sticking coefficient for the material that sticks to the walls of the plasma processing chamber, e.g., polymers. To achieve tight control over the etching process, contamination should be minimized. Hence, SiC is a well suited material for the plasma processing chamber since it is resistant to etching processes and can be made in a pure form. Several methods can be used to produce SiC in a pure form. For example, Chemical Vapor Deposition (CVD), Slipcast Forming, hot-pressed and sintered, Iso-statically-pressed and Sintered Forming can be used to produce SiC in a pure form.
In accordance with a preferred embodiment of the present invention, the plasma processing chamber (e.g., the single chamber of step 702) is made of CVD deposited SiC. CVD technique is preferred because it can produce SiC in an “ultra pure” form. Pure SiC is also etch resistant with respect to plasma processing reactant gas chemistries that are introduced to facilitate the etching processing. Suitable reactant gas chemistries will be discussed below. Given the relative expense associated with producing CVD deposited SiC, other forms of SiC may be more cost effective for some etch process, e.g., non-dielectric etching and/or etching processes where achieving tight control over etching parameters is not an important factor. Alternatively, the SiC can be provided as a coating on another material. For example, SiC can be applied on another material (e.g., aluminum) using flame sprayed coatings or sputter deposited coatings or even CVD SiC coating on another suitable substrate such as Slipcast SiC, graphite or Aluminum. In addition the SiC or other suitable material may be bonded to either a support that is attached to the cylindrical chamber wall or bonded directly to a cylindrical support. This method may have advantages if the desired material for the inner surface of the chamber does not contain all the desired physical properties or may be more cost effectively implemented for example.
SiC can also be made with higher electrical resistivity. As noted above, SiC often has moderate electrical conductivity. However, electrical conductivity of SiC is manageable so that SiC with higher electrical resistivity can be produced. Advantageously, some parts of the plasma processing chamber may be made of SiC material with higher electrical resistivity. By way of example, in plasma processing systems that utilize a Radio Frequency (RF) powered wafer supporting mechanisms, e.g., an electrostatic chuck (ESC), it is desirable to have a wafer supporting mechanism that can offer higher electrical resistivity in order to minimize RF coupling therefrom. As another example, as noted earlier, it is contemplated that coupling window 130 (shown in
Although SiC has been discussed as a particularly suitable material for the plasma processing chamber (e.g., the single chamber of step 702), other materials may be used for the plasma processing chamber. In addition, other materials besides SiC can be used to produce one or more of the components of a plasma processing system (e.g., ESC or coupling window). By way of example, other suitable materials for the plasma processing chamber or components thereof can include quartz, silicon, silicon dioxide, carbon, boron carbide, boron nitride.
It should also be understood that other material maybe more suitable for some particular etch process. For example, given the relative high cost associated with producing SiC in pure form, other material, e.g., quartz, which is a relatively easy and inexpensive material to produce and thus may be a more suitable alternative for some etching processes where achieving a tight control over the etching parameters has more tolerance. Further, when even greater latitude is available with respect to the tight control the material used within the plasma processing chamber could even use aluminum, or anodized aluminum. Furthermore, as will be apparent to those skilled in the art, configurations that utilize a combination of materials may also be used to make the plasma processing chamber as well as other components of the plasma processing system (e.g., ESC or coupling window).
As noted above, in step 702, a single chamber, substantially azithmuthally symmetric plasma processing chamber is provided. Continuing with the process illustrated in
In step 708, the substrate is placed within the plasma processing chamber for processing. In step 710, reactant gases (e.g., deposition source gases, etchant source gases, dilutant gases, etc.) are flown into the plasma processing chamber and a plasma is ignited therefrom. A wide variety of gas chemistries are available for the reactant gases that are flown into the plasma processing. These gas chemistries can be selected for a particular etching processes and/or in consideration of several other factors. Examples of other factors include the material of the plasma processing chamber, type of etch process, or other components of the plasma processing system. Generally speaking, in accordance with an embodiment of the present invention, a combination of gases of the form Cx Fy Hz Ow (where, x, y, z and w are integers and where z and/or w can be zero or where y and/or w can be zero) can be used in conjunction with one or more of O2, N2, CO, CO2 and SF6, NF3, NH3, Cl2 or HBr gases for dielectric etching processes. In addition, other gases can be added to the chemistries noted above, such as He, Ne, Ar, Kr, Xe may be utilized to serve as dilutants or deposition precursors. By way of example, a combination of gases of the form Cx Fy Hz Ow can include a Florocarbon (CxFy) and/or Hydroflurocarbon (CxHyFz) gas that is combined with a mixture of other gases. Representative combinations of gases that can be used for the reactant gas chemistries are provided in Table 1 below.
As noted earlier, one or more of the O2, N2, CO, CO2 and SF6 gases can also be provided in the combination of gases used for the reactant gas chemistries. Hence, one or more of O2, N2, CO, CO2 and SF6 NF3, NH3, Cl2 or HBr can be added to the reactant gas chemistries listed in Table 1. In addition, one or more other gases can be added to form the desired reactant gas chemistries, e.g., gases such as He, Ne, Ar, Kr and Xe may be utilized to serve as dilutants or other gases may be added as deposition precursors. Representative combinations of gases which include these other gases can, for example, result from combining one or more of He, Ne, Ar, Kr and Xe with any of the gas chemistries provided in Table 1.
After the reactant gases are delivered into the plasma processing chamber and a plasma is ignited in step 710, next in step 712, the radial variation of the controlled magnetic field strength and/or topology in the vicinity of the RF antenna is adjusted to a setting that improves processing uniformity across the substrate surface. The setting may be done in advance prior to processing to a predefined setting or may be done in real time to tune the processing uniformity during plasma processing either by fixed setting or with a feedback loop to some process sensitive variable.
As can be appreciated by those skilled in the art, the invention may easily be adapted to control process uniformity in an active, time-dependent manner that allows full control of the wafer processing over a wider processing regime than possible without the uniformity control. By way of example, it is expected that a wider range of plasma density may be employed in the inventive plasma processing system (e.g., about 109 to about 1013 ions/cm3) since the magnetic bucket allows the source energy to be utilized very efficiently in the generation and sustaining of the plasma and the upper magnetic arrangement allows process uniformity control to be maintained throughout the plasma density range. Likewise, it is expected that a wider range of pressure (e.g., <1 mT to about 100 mT) may be successfully employed in processing substrates since the magnetic bucket allows the plasma to be sustained at lower pressures. Thus, a single reactor may be employed for different processes having wide process windows, which gives the process engineer a degree of flexibility not available in prior art plasma processing systems.
Furthermore, it is contemplated that an appropriate feedback mechanism may be employed to monitor the process uniformity on a substrate in real time and to modify the radial variation in the controlled magnetic field strength and topology, also in real time, in order to achieve the desired optimum process uniformity result. Alternatively or additionally, the radial variation in the controlled magnetic field strength and topology may be dialed to different settings to achieve the right uniformity control for different etch steps in a given etch process. Note that these settings may be done with or without the benefit of the feedback mechanism, and may be performed either while etching through a single film or as the etch moves from film to film. In the case without the feedback mechanism, the appropriate uniformity settings for the various steps may be ascertained in advance, empirically or otherwise, and employed during etching.
While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. By way of example, although etching is employed throughout the preferred embodiment to simplify the discussion, it should be understood that the uniformity control applies to any semiconductor processing process, e.g., deposition. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.
This application is related to following concurrently filed U.S. Patent Applications: Application Ser. No. ______: entitled “IMPROVED PLASMA PROCESSING SYSTEMS AND METHODS THEREFOR”. (Attorney Docket No.: LAMIP0122/P0527) Application Ser. No. ______: entitled “PLASMA PROCESSING SYSTEM WITH DYNAMIC GAS DISTRIBUTION CONTROL”; (Attorney Docket No.: LAMIP0123/P0557) Application Ser. No. ______: entitled “TEMPERATURE CONTROL SYSTEM FOR PLASMA PROCESSING APPARATUS”; (Attorney Docket No.: LAMIP0124/P0558) Application Ser. No. ______: entitled “METHOD AND APPARATUS FOR PRODUCING UNIFORM PROCESS RATES”, (Attorney Docket No.: LAMIP0125/P0560) Application Ser. No. ______: entitled “METHOD AND APPARATUS FOR CONTROLLING THE VOLUME OF PLASMA”, (Attorney Docket No.: LAMIP0129/P0561-2) Each of the above-identified patent application is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09440794 | Nov 1999 | US |
| Child | 11230689 | Sep 2005 | US |
