Patent Application
20080083701
This invention is described with particularity in the appended claims. The above and further advantages of this invention can be better understood by referring to the following description taken in conjunction with the accompanying drawings, in which:
A plasma system is an apparatus that includes plasma generation components, and can include materials processing components. A plasma system can include one or more vessels, power supply components, metrology components, control components, and other components. Processing can occur in one or more vessels and/or in one or more processing chambers in communication with the one or more vessels. A plasma system can be a source of plasma or reactive gas species generated in a plasma or can be a complete processing tool.
A vessel is a container or portion of a container that contains a gas and/or a plasma, and within which a plasma can be ignited and or/maintained. A toroidal vessel includes at least one dielectric portion, or is formed entirely of dielectric material. A vessel can also be referred to as a plasma body. A vessel is combined with other components, such as power generation and cooling components to form a plasma processing system. A vessel can define channels having a variety of shapes. For example, a channel can have a linear shape, or can have a loop shape (e.g., to support a toroidal plasma).
A channel is the volume defined and enclosed by a vessel. A channel can contain a gas and/or a plasma, and can be in communication with one or more input ports and one or more output ports of the vessel, for receiving and delivering gas and plasma species. A plasma system can include means to apply a DC or oscillating electric field within the channel. The electric field can maintain a plasma in the channel, and can, alone or in cooperation with other means, ignite a plasma in the channel.
A plasma is a state of matter that includes a collection of charged particles that are related to a gas. A plasma is a quasineutral, or approximately neutral collection of positive and negative ions. A plasma can include neutral atoms and/or molecules associated with the ionized species. A plasma can contain a significant fraction of un-ionized gas. The matter in a vessel, after ignition, is herein broadly referred to as a plasma without intending to limit such matter to that consisting solely of species in a plasma state.
A toroidal plasma is a plasma in the form of a closed path and with plasma current circulating in the closed path. A toroidal plasma can reside in a toroidal channel enclosed by a toroidal vessel.
Ignition is the process of causing an initial breakdown in a gas, to form a plasma.
An ignition electrode is an electrode that is capacitively coupled to a vessel, and to which a voltage can be applied for ignition of a gas in the vessel. An ignition voltage can be applied, for example, between an ignition electrode and a reference electrode or between an ignition electrode and a conductive portion of a vessel. One or more ignition electrodes can be adjacent to an inner or outer surface of a vessel (the illustrative embodiments described herein include ignition electrodes adjacent to an outer surface). An ignition electrode can be insulated from the plasma by a dielectric material (e.g., quartz, sapphire, and/or aluminum). In some embodiments, plasmas can be ignited by a UV light source.
Reference electrode refers to one or more electrodes and/or one or more conductive portions of a vessel that act in cooperation with one or more ignition electrodes.
Inert gases are gases that in many circumstances are non-reactive or have low reaction rates, including argon and the other noble gases.
Noble gases are a group of rare gases that include helium, neon, argon, krypton, xenon, and sometimes radon, and that exhibit chemical stability and low reaction rates.
A reactive gas is a gas containing some species that are prone to engage in one or more chemical reactions. Reactive gases include gases that are not inert gases.
An activated gas includes any of ions, free radicals, neutral reactive atoms and molecules.
A heat sink is a structure including one or more portions and/or components for absorption, dissipation and/or removal of heat. A heat sink can also be an electrode, for example, an ignition electrode and a reference electrode.
The vessel 110 can be formed entirely from one or more dielectric materials, or can be formed from both conductive and dielectric materials. Appropriate conductive materials include metals such as aluminum, copper, nickel and steel. The vessel 100 can also be formed from a coated metal such as anodized aluminum or nickel plated aluminum. The vessel 100 can also be formed from a metal coated with a dielectric material. In some embodiments of the invention the vessel 110 is formed from a dielectric material, and is surrounded by heat sink materials to assist cooling of the dielectric material.
The vessel 110 includes at least one dielectric region, for example, at the mating surface 116, which electrically isolates a portion of the vessel 110 so that electrical continuity around the vessel 110 is broken. If the vessel is formed entirely of dielectric material, the vessel 110 can be formed of a single piece of material, having no joined surfaces, and thus not including the mating surface 116.
Joined surfaces of the vessel 110 can provide a high vacuum seal. The seal can include an elastomer seal or can be a permanent seal such as a brazed joint. A seal can include metal.
As shown, magnetic cores 102, 104, 106, 108 surround portions of the vessel 110, i.e., portions of the channel 114. The magnetic cores 102, 104, 106, 108, together with primaries (not shown) of a transformer, induce an electric field and a current aligned with the channel 114, as described, for example, in U.S. Pat. No. 6,150,628 to Smith et al. A plasma in the channel 114 completes a secondary circuit of the transformer.
The transformer can include additional magnetic cores and conductor primary coils that form additional secondary circuits. The primary coils can be powered, for example, by an AC power supply having a frequency, for example, in a range of less than 10 kHz to greater than 20 MHz. The choice of frequency will depend on the desired power and voltage to be applied to the plasma.
The selection of optimal operating frequency can depend on the application, the AC power supply, and the magnetic core materials. Gases such as oxygen and nitrogen, for example, having a pressure in a range of 1 torr to 10 torr can be utilized with particular advantage at a frequency from 50 KHz to 14 MHz.
The magnetic cores 102, 104, 106, 108 can have primary windings that are adjustable. This can permit, for example, the voltage and current applied to the plasma to be optimized for ignition and for a particular process operating condition (for example, for particular pressure, flow rate and gas species conditions).
Electrical components can be in a circuit path between an output of the AC power supply and an input of the primary of the magnetic cores 102, 104, 106, 108. These components can include resistors, capacitors, and/or inductors. For example, a series inductor can be used to smooth a voltage waveform applied to the plasma, and thus improve plasma stability.
The components can be fixed or variable, with variability controlled, for example, via electrical or mechanical means. The components can form an impedance altering circuit or an impedance matching network.
A resonant circuit at the output of or built into the AC power supply can be used to raise an ignition voltage and the loop voltage (i.e., the voltage drop along the channel) for ignition purposes.
A DC power source connected to an input of the AC power supply can be obtained via rectification and filtering of an AC line voltage. The DC power source voltage can be regulated via additional circuitry to stabilize the voltage applied to the plasma and to provide regulation relative to variability in AC line voltage. The DC source voltage and current can also be used to control the power delivered to the plasma.
It can be desirable to monitor various parameters, such as power, current and voltage. Power delivered to the plasma can be estimated, for example, by measuring the power output by the DC power source. Power measurement can be refined by measuring or estimating electrical losses in the electrical elements disposed between the output of the DC power source and the plasma. Power can also be measured, for example, at the output of the AC power supply.
Power delivered to the plasma can be controlled via several means, for example, by varying: the magnitude of the DC power source voltage; the peak current applied to the plasma; the duty cycle of the AC power applied to the plasma; the magnitude of the AC voltage applied to the plasma; and the frequency of the AC power applied to the plasma. The efficiency of the power transfer between the output of the AC power supply and the plasma can be varied to vary the power applied to the plasma.
To reduce cost and complexity of a plasma source and its AC power supply and control system, these components can be integrated into a single enclosure. Alternatively, to increase flexibility, the plasma source can be separated from any of the following: the AC power supply, the DC power source, and the control system. A dielectric plasma vessel and related cooling and mounting components can be separated from other components to assist component replacement in the field.
The shape of the vessel 110 can take on a variety of forms. For example, the vessel 110 can be a square donut shape (as shown), a rectangular donut shape, a round donut shape, etc.
In operation, a feed gas flows into the gas inlet 118. A gas can be fed into the channel 114 until a pressure between, for example, 0.001 torr and 1000 torr is reached. The gas can include an inert gas, a reactive gas or a mixture of at least one inert gas and at least one reactive gas. The gas composition can be varied, for example, by providing one composition for ignition and a second composition for process operating conditions. Portions of the plasma can be delivered from the channel 114 via the outlet 119.
In some embodiments, a plasma system is configured so that little or none of the ionized species leaves a plasma vessel. In other embodiments, some ionized species are delivered from a vessel, for example, to assist processing in a chamber in communication with the vessel. In still other embodiments, the vessel is integrated with a process chamber, so that plasma is generated within the chamber.
Once the gas is ionized, a plasma forms and completes a secondary circuit of the transformer. The electric field in the plasma can be in a range of less than 1 to greater than 100 volt/cm. If only noble gases are present in the vessel 110, the electric fields in the plasma can be as low as 1 volt/cm or less. If, however, electronegative gases are present in the chamber, the electric fields in the plasma can be considerably greater than 1 volt/cm.
Operating the vessel 110 with low electric fields in the channel 114 can be beneficial because a low potential difference between the plasma and the chamber can reduce erosion of the chamber by energetic ions and related contamination of a material being processed.
The vessel 110 can include means for generating free charges that provides an initial ionization event that ignites a plasma in the vessel 110. The initial ionization event can be a short, high voltage pulse that is applied to the plasma chamber. The pulse can have a voltage of approximately 500-20,000 volts, and can be approximately 0.1 to 10 microseconds long. The initial ionization event can also be generated by use of a high voltage pulse of longer duration, approximately 10 microseconds to 3 seconds, which can be an RF pulse. An inert gas, such as argon, can be inserted into the channel to reduce the voltage required to ignite a plasma. Ultraviolet radiation can also be used to generate the free charges in the vessel 110 that provide the initial ionization event that ignites the plasma in the vessel 110.
In one implementation, the short, high voltage electric pulse is applied to the primary of the magnetic cores to provide the initial ionization event. In another implementation, the short, high voltage electric pulse is applied to an electrode or electrodes positioned in or on the vessel 110. In yet another implementation, ignition can include one or more pulses to the primary of the magnetic core(s) and/or one or more pulses to the ignition electrodes. Ignition is described in more detail below, with respect to other illustrative embodiments of the invention.
Now referring to
The vessel 210 encloses a channel 215, which has a square cross-section shape and within which a plasma can be maintained. A vessel can have a non-square cross section. The vessel 210 is formed from a single piece of dielectric material. The dielectric material can be, for example, quartz, sapphire, alumina, aluminum, aluminum nitride, a yttrium oxide, a zirconium oxide, and/or ceramic materials. The vessel 210 can include a metal vessel coated with dielectric material. The material used to form the vessel 210 can be chosen based on planned applications for the system 200. For example, the material can be chosen based on a planned power of operation, plasma species and/or required purity level.
The vessel 210 supports a toroidal plasma, and has a circular donut shape with a square cross section. Other vessels that support a toroidal plasma can have a variety of shapes. Such shapes can include, for example, any of the following overall shapes: an elliptical donut shape; a square donut shape; a rectangular donut shape; and a polygonal donut shape, and can have, for example, a circular cross section or an elliptical cross section.
The vessel 210 can include one or more gas inlet ports and one or more outlet ports. Multiple ports can be included to provide additional control over the plasma in the vessel 210. Control of gas flow, in particular during ignition, is discussed below in more detail.
As illustrated, the ignition electrode 890 can be located by a surface of the vessel 810 or by a surface of the upstream portion 880. The upstream portion 880 can be, for example, a flange for mating with a gas delivery pipeline. The upstream portion 880 and the vessel 810 can be formed from a single piece of material, for example, a single piece of fused quartz.
One or more ignition electrodes 890 can be upstream or downstream of the input port 841, or can overlap the input port 841. Methods according to the technology can be implemented, for example, with the system 800, can provide improved ignition. The ignition electrode 890 adjacent to the gas input port 841 can ignite a flowing gas in the vicinity of the site of gas entry into the vessel 810. The site of ignition, in cooperation with the flow of ionized components, can help to seed a plasma along the full channel.
The system 900 has features similar to that of the system 800, however, with the linear vessel 810 replaced with the toroidal-shaped vessel 910. The system 900 can implement methods according to the technology, and provide the benefits described with respect to
As indicated above, an upstream ignition site can seed electrons into an incoming gas stream. The electrons can then flow with the gas along the channel and assist, for example, inductive ignition of a plasma. The method 700 and systems 800, 900 can provide reduction of plasma system manufacturing costs, easier field service, and provide reduced erosion of an inner surface of a vessel 810, 910.
The one or more magnetic cores 1520 have windings that act as primaries of a transformer to induce an electric field and a plasma current aligned with the channel defined by the dielectric vessel 1510. A plasma in the channel completes a secondary circuit of the transformer. Some implementations of magnetic cores and associated AC power supplies that can support a toroidal plasma are described in U.S. Pat. No. 6,150,628 to Smith et al.
The vessel 1510 has a square cross section, and four of the heat-sink segments 1530 are adjacent to each of four surfaces defined by the vessel 1510 (i.e., upper, lower, inner, and outer surfaces). The segmentation of the heat sink aids assembly and accommodates thermally induced dimensional changes.
The system 1500 also includes a gas input pipeline 1551 in communication with the input port 1541, a bypass gas pipeline 1552, a bypass valve 1571, and a process vessel 1590 defining a process chamber in communication with the output port 1542 of the dielectric vessel 1510. To implement the method 1000, the bypass valve 1571 can direct a portion or all of a gas flow from the input pipeline 1551 to the bypass gas pipeline 1552 during plasma ignition. The system 1500 can include a gas showerhead 1551 in or near the input port 1541 to mediate flow of gas from the pipeline 1151 into the input port 1541.
The inclusion of the gas showerhead 1551 can improve stability of a plasma and the uniformity of heat distribution onto the inside surface of the vessel. The gas showerhead 1551 can improve the distribution of gas directed through input port 1541 into the toroidal channel.
The technology can include, and/or be used in conjunction with, related methods and apparatus (e.g., U.S. Patent Application Publication No. US 2006/0118240 by Holber et al. and U.S. Pat. No. 6,872,909 by Holber et al., which disclose methods and apparatus for downstream dissociation of gases and a toroidal low-field reactive gas and plasma source having a dielectric vacuum vessel, and which are incorporated herein by reference).
In various embodiments, the technology features a method for operating a plasma. An oxygen containing plasma is generated. The plasma is provided to a plasma vessel including quartz, sapphire, aluminum and/or a dielectric material to clean and/or condition the vessel.
In some embodiments, the technology features a method for operating a plasma. An oxygen containing gas is received in a plasma vessel including quartz, sapphire, and/or aluminum. An oxygen containing plasma is formed. The plasma cleans and/or conditions the vessel.
In certain embodiments, the technology features a method including receiving an oxygen containing plasma in a vessel, including quartz, sapphire, and/or aluminum, to clean and/or condition the vessel.
In various embodiments, the technology features a method for operating a plasma. An oxygen containing plasma is provided to a vessel including quartz, sapphire, and/or aluminum. The plasma chemically and/or thermally interacts with the vessel to add oxygen to a surface of the quartz, sapphire, and/or aluminum.
In some embodiments, the technology features a method including providing an oxygen containing plasma to a vessel including quartz, sapphire, and/or aluminum. The plasma chemically and/or thermally interacts with a contaminant in the vessel to remove the contaminant from a surface of the quartz, sapphire, and/or aluminum.
In various embodiments, the degree of cleaning and/or conditioning of the quartz, sapphire, and/or aluminum vessel can depend upon parameters of the oxygen containing plasma including a pressure, flow rate, power, and/or time. In one embodiment, the oxygen containing plasma conditions the vessel. Conditioning can include the plasma chemically and/or thermally interacting with the vessel to add oxygen to a surface of the quartz, sapphire, and/or aluminum. In another embodiment, the oxygen containing plasma cleans the vessel. Cleaning can include removing atoms from a surface of the vessel, which can remove undesired molecules from a surface of the vessel. Undesired molecules can include organic compounds. In yet another embodiment, cleaning can include removing contamination from the vessel by removing atoms from a surface of the vessel. In still another embodiment, cleaning can include removing contamination from the vessel by chemically and/or thermally interacting with contamination on a surface of the vessel.
In some embodiments, an oxygen containing plasma can chemically reduce undesired hydrogen products on the surface of the SiO2 or Al2O3 vessel, restoring the SiO2 or Al2O3 surface. In certain embodiments, an oxygen containing plasma can remove or “burn off” hydrogenated or hydrated surface molecules (e.g., Si(OH)4) before they build up, and/or accumulate and break off and form particles.
In various embodiments, the technology includes methods that can be used in conditioning/cleaning newly manufactured quartz and/or sapphire vessels. A new vessel can produce an unacceptable amount of particles upon turn on if it is not conditioned/cleaned before use. A new vessel can produce an unacceptable amount of particles within about the first one to about ten hours of operation. Conditioning/cleaning a new vessel according to methods of the technology can reduce particle counts to an acceptable operating level.
In some embodiments, the technology includes methods that can be used in situ to clean and/or condition quartz and/or sapphire vessels. A vessel can become contaminated from environmental sources (e.g., sources other than the gas or plasma deliberately flowed into the vessel) including environmental dust and/or dirt.
In certain embodiments, the technology includes methods where one vessel can be used to clean and/or condition another vessel. A vessel can be remanufactured and/or reconditioned.
The surface of the quartz, sapphire, and/or aluminum vessel can be damaged by a plasma that can react with SiO2 or Al2O3, to remove and/or replace oxygen atoms on the surface of the quartz, sapphire, and/or aluminum. However, operating an oxygen containing plasma can form oxygen radicals and/or ions, which can react with SiO2 or Al2O3, to refill, repair and/or replace oxygen atoms on the surface of the quartz, sapphire, and/or aluminum.
Hydrogen or hydrogen containing plasmas (e.g., H2/N2, NH3, and/or H2O) can react with a surface of a vessel. This reaction can damage and/or form particles on the surface of the vessel. The particles can include silicon, silicon nitrides such as SiXNY, and/or silanols such as Si(OH)4.
Water vapor plasma can react with a surface of a vessel. This reaction can form particles on the surface. The particles can include silicon hydroxides and silicon oxides such as Si(OH)4 and SiO2. The formation of particles can degrade the surface and/or form deposits. Deposits can come off of the surface and exit the vessel as undesired particles, which can affect semiconductor processing rates.
Hydrogen containing plasmas (e.g., H2/He, Ar/H2, H2, NH3, and/or H2O) can react with a surface of a sapphire vessel. This reaction can form particles on the surface. For example, the hydrogen containing plasma can remove oxygen from Al2O3 and can form aluminum particles and/or a layer of metallic aluminum on the surface. The formation of particles can degrade the surface and/or form deposits. Deposits can come off of the surface and exit the vessel as undesired particles, which can affect semiconductor processing rates.
Operating an oxygen containing plasma in the quartz, sapphire, and/or aluminum vessel can re-oxidize the damaged vessel surface. In various preferred embodiments, an oxygen containing plasma is operated to clean, condition, and/or repair a quartz, sapphire, and/or aluminum vessel immediately after exposure to the damaging plasma. In other embodiments, an oxygen containing plasma is operated to clean, condition, and/or repair a quartz, sapphire, and/or aluminum vessel during or after exposure to the damaging plasma.
In various embodiments, the method includes a recipe for operating a plasma in the quartz, sapphire, and/or aluminum vessel with one or more steps.
In certain embodiments, operating oxygen containing plasmas in quartz, sapphire, and/or aluminum vessels can increase the operating life of the vessel. In one embodiment, an oxygen plasma process can increase the lifetime of a quartz tube with water vapor plasma from about tens to at least about 1,000 hours. Oxygen containing plasma conditioning can increase the lifetime of a quartz, sapphire, and/or aluminum vessel to more than about 1,000 hours.
In various embodiments, cooling of the quartz, sapphire, and/or aluminum vessel, in addition to operating an oxygen containing plasma, can further reduce particle count during operation of a plasma.
In some embodiments, decreasing an operating power of the plasma, in addition to operating an oxygen containing plasma, can further reduce particle count during operation of a plasma. For example, decreasing power from about 5-6 kW (high power) to about 3.5 kW (moderate power) can reduce the incidence of particles in water vapor plasmas.
In certain embodiments, operating an oxygen containing plasma can have advantages in addition to reducing particle count during operation of a plasma. For example, operating an O2/N2 plasma can be useful in applications including etching.
While the invention has been particularly shown and described with reference to specific preferred embodiments, it should be understood by those skilled in the art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
