Hybrid plasma source

Systems and methods for generating plasma are disclosed. A system for generating a plasma includes a helicon plasma source and an electron cyclotron resonance (ECR) plasma source structured and arranged together to generate a plasma in a tube.

FIELD OF THE INVENTION

The invention relates to plasma generation and, more particularly, to a hybrid plasma source.

BACKGROUND OF THE INVENTION

Plasmas that are used in industry are commonly generated by ionizing a gas in a vacuum chamber. For example, a gas can be introduced into an evacuated plasma chamber where the work-piece is located. A strong electric field can be applied to the plasma chamber. The gas can form a plasma in an excitation region by undergoing an electrical breakdown under the influence of the strong electric field.

The electric field in such chambers is typically either capacitively or inductively coupled to the gas to remove electrons therefrom. In capacitively coupled plasma generators, the electric field can be applied between electrodes on opposing sides of the chamber. In inductively coupled plasma generators, the electric field can be applied to a coil surrounding the chamber, as but one example.

Plasma tools are commonly used in the fabrication of semiconductor devices. For example, plasmas are used to deposit materials on and etch materials from work-pieces to form specific electronic components on the work-piece substrate. However, many plasma tools in the semiconductor industry suffer from relative low density and unstable working conditions.

SUMMARY OF THE INVENTION

In a first aspect of the invention, there is a system for generating a plasma including a helicon plasma source and an electron cyclotron resonance (ECR) plasma source structured and arranged together to generate a plasma in a tube.

In another aspect of the invention, there is a system for generating a plasma. The system includes a helicon plasma source comprising an RF antenna wrapped around a tube and an RF source that provides energy to the RF antenna. The system also includes an electron cyclotron resonance (ECR) plasma source comprising a microwave power source, a circulator, a load, a stub tuner, and a horn arranged at a first end of the tube. The system further includes a gas inlet and a vacuum port at a second end of the tube. The system additionally includes a magnet array that generates a magnetic field inside the tube. The RF antenna is wrapped around a first middle portion of the tube between the first end and the second end. The magnet array is at a second middle portion of the tube between the first end and the second end. The gas inlet is fluidically connected to a gas source that provides a neutral gas to an interior of the tube. The vacuum port is connected to a vacuum source that provides a vacuum to the interior of the tube. Plasma is generated from the neutral gas in the tube using energy from both the RF antenna and the microwave power source.

In yet another aspect of the invention, there is a method of generating a plasma comprising: providing a helicon plasma source comprising RF antenna wrapped around a tube and an RF source that provides energy to the RF antenna; providing an electron cyclotron resonance (ECR) plasma source comprising a microwave power source, a circulator, a load, a stub tuner, and a horn arranged at a first end of the tube; providing a magnet array that generates a magnetic field inside the tube; and generating a plasma in the tube using energy from both the RF antenna and the microwave power source.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to plasma generation and, more particularly, to a hybrid plasma source. Many plasma tools in the semiconductor industry suffer from relative low density and unstable working conditions. Aspects of the invention involve combining two plasma source generation techniques to give a higher density, more stable plasma source than is provided from a single source alone. In embodiments, a hybrid plasma source includes a helicon source system combined with an Electron Cyclotron Resonance (ECR). In this manner, implementations of the invention provide a system that generates plasma with a very high density at a relatively high pressure and low electron temperature.

Electron Cyclotron Resonance (ECR) is a phenomenon observed in plasma physics. An ionized plasma may be efficiently produced or heated by superimposing a static magnetic field and a high-frequency electromagnetic field at the electron cyclotron resonance frequency. A helicon discharge is an excitation of plasma by helicon waves induced through radio frequency heating. Implementations described herein utilize both a ECR component and a helicon component together to generate a plasma.

FIG. 1shows a schematic diagram of an exemplary plasma source hybrid plasma source10in accordance with aspects of the invention. The hybrid plasma source10includes a tube15defining an interior volume17in which a plasma discharge is produced using a combination of a helicon system and an ECR system. In embodiments, a helicon discharge is produced by an antenna20that is wound around the tube to transmit radio-frequency (RF) power into the plasma gas. At one end of the tube15, a microwave source25is fixed to transmit microwave power into the tube end. In this manner, two types of power transmission are combined to produce a plasma in the tube15. Specifically, radio frequency radiation emitted by the RF antenna20and microwave energy emitted by the microwave source25combine to excite a gas in the tube15to produce a plasma.

The RF antenna20includes electrodes30on or in proximity to the tube15. In proximity to the tube15means that the electrodes30are located such that radio frequency radiation emitted by the electrodes30affects the gas inside the tube15to form a plasma. The electrodes30may be on (physically contacting the interior or exterior) of the tube, or may be spaced apart from the tube15. In preferred embodiments, the electrodes30are arranged on the exterior surface of the tube15. The electrodes30may comprise one or more windings of electrically conductive material that encircle a portion of the tube15. As but one example, the electrodes30may comprise windings of hollow copper tubing that are wrapped tightly around the exterior surface of the tube15, although the invention is not limited to this particular type of antenna and other types and configurations of radio frequency antennas may be used. The antenna20may include a connection to ground33.

An RF source35is operatively connected to supply power to the electrodes30of the RF antenna20. In embodiments, the RF source35is a 13.56 MHz radio frequency source with a power of about 200 W to 3000 W. Implementations are not limited to this particular type of RF source and other types and configurations of RF source, including different frequency and/or power, may be used.

With continued reference toFIG. 1, a microwave source25is arranged at one end of the tube15to transmit microwave energy into the tube15to produce plasma. In embodiments, the microwave source25includes a microwave power source40, such as a magnetron, which generates a microwave. The microwave source25may include a circulator45and a load50connected to the microwave power source40. The circulator45and load50protect the microwave power source40from reflected power by the circulator45separating a reflected microwave and directing the reflected microwave to the load50which absorbs the reflected microwave. The microwave source25may include a stub tuner55and a horn60. The horn60is between the microwave power source40and the tube15and functions as a waveguide or antenna that shapes and directs a beam of microwave energy from the microwave power source40into the interior cavity of the tube15. The horn60may be a conical horn, pyramidal horn, or any other suitable shape. The stub tuner55is structured and arranged to match the impedance of the microwave power source40to the plasma (load) inside the tube15. The stub tuner55may include any desired number of stubs65, such as three, which may be adjusted as is understood in the art for impedance matching.

In embodiments, the microwave power source40is a 2.45 GHz magnetron with a 2000 W peak power. However, other configurations may be used for the microwave power source40.

Still referring toFIG. 1, a magnet array70is positioned on or in proximity to the tube15. The magnet array70includes one or more magnets75located in spatial relation to the tube15such that a magnetic field generated by the one or more magnets75extends into the interior17of the tube15and affects the plasma therein. In embodiments, the magnets75are permanent magnets, rather than electromagnets which can require a larger power supply and active cooling. The permanent magnets75may be composed of any suitable materials, including but not limited to: ceramic magnets, Neodymium Iron Boron (NdFeB), samarium-cobalt (SamCo), alnico, barium ferrite, strontium ferrite, etc.

In accordance with aspects of the invention, the magnets75are structured and arranged around the tube15to create a magnetic field near the interior walls of the tube15to repel ions away from the interior walls of the tube15. In this manner, the magnetic field directs ions toward the center of the chamber defined by the tube15and minimizes the number of ions that impinge upon the interior walls of the tube15, i.e., urges the plasma generated inside the tube15away from the interior walls of the tube15. The magnetic field may be used to generate constructive resonant field inside the tube15, e.g., for electron cyclotron resonance. In embodiments, the magnet array70is structured and arranged to produce a magnetic field of between 875 Gauss and 1000 Gauss, although other field strengths may be used. In a particular exemplary embodiment shown inFIG. 2, the magnet array70includes two rings77a,77b. Each ring77a,77bincludes eight permanent magnets75outside the tube15and radially spaced around a central longitudinal axis defined by the tube15.

Still referring toFIG. 1, the tube15may comprise any material suitable for plasma generation. For example, the tube15may be a quartz tube or other suitable material.

As depicted inFIG. 1, the hybrid plasma source10may also include a gas inlet80and a vacuum port85at an end of the tube15opposite the microwave source25. In embodiments, the gas inlet80is fluidicially connected to a process gas source90and communicates process gas from the source90to the interior17of the tube15. The process gas may be any desired neutral gas that is suitable for forming a plasma, including but not limited to: argon, chlorine, fluorine, oxygen, sulfur hexafluoride, or any other suitable gas or any suitable mixture of gases.

In embodiments, the vacuum port85is fluidicially connected to a vacuum source95for providing and maintaining a vacuum at the interior17of the tube15. The vacuum source95may comprise any suitable system that provides a vacuum, such as a turbo pump. A valve100, such as a gate valve or the like, may be connected inline between the vacuum port85and the vacuum source95to control the vacuum at the interior17of the tube15.

The hybrid plasma source10described herein combines two plasma generation methods, i.e., Electron Cyclotron Resonance (ECR) and helicon wave technique, to generate plasma with very high density at relatively high pressure and low electron temperature. In a particular exemplary implementation, the hybrid plasma source10includes a 2.45 GHz and 2000 W peak microwave power source40, a 13.56 MHz RF source35with a power of about 200 to 3000 W, and a magnetic field of between 875 Gauss and 1000 Gauss, and generates a plasma with a density on the order of 1013cm−3, at a pressure on the order of 100 mTorr, and an electron temperature on the order of 1 eV. In empirical testing, a highest plasma density was achieved by combining the ECR and helicon plasma sources together, i.e., higher plasma densities than are obtained using any single source (ECR or helicon) were achieved by combining two sources (ECR and helicon) to ionize the neutral gas.

In embodiments, the hybrid plasma source10includes a measurement system110that is configured to measure parameters of the plasma generated in the tube15. The measured parameters may include, for example, plasma density and electron temperature. The measurement system110may include any suitable components for measuring these parameters and/or other parameters associated with the plasma. For example, the measurement system110may include a camera115, such as a CCD (charge-coupled device) or ICCD (intensified CCD) camera that is directed at the tube15and receives light emitted by the plasma. The camera115may be tuned to receive UV, IR, and/or visible light bands. In a particular embodiment, the camera115is configured to receive light coming from a predefined observation plane in the plasma, wherein the observation plane is defined in accordance with the focal length of a lens unit of the camera115.

The measurement system110may also include a light source120that is configured to excite the plasma in the tube15as part of the measurement process. For example, the light source120may comprise a laser beam that is shone into the plasma by a fiber optic cable. The laser beam may be configured at a particular wavelength to excite particular atoms in the plasma. In embodiments, the laser beam is aimed to intersect the predefined observation plane to which the camera115is focused. In this manner, light that is emitted as a result of the excitation by the laser beam is detected by the camera115.

In embodiments, the camera115transmits detected data (e.g., intensity and/or spectral information of the plasma) to a computer125. In embodiments, the computer125is a computer device that includes a memory, a processor, and program instructions stored in the memory that, when executed by the processor, cause the computer device to perform one or more measurement functions (i.e., determine plasma density and/or electron temperature based on the data transmitted by the camera115).

FIG. 2shows an implementation of a hybrid plasma source10in accordance with aspects of the invention.FIG. 2shows the tube15, stubs65, and rings77aand77bincluding permanent magnets75.FIG. 2also shows a plasma200generated inside the tube15.

The hybrid plasma source10as described herein may be used as a plasma source in semiconductor wafer fabrication, as it provides high density fully ionized plasma at a relatively high pressure. The hybrid plasma source10may also be used in other plasma applications, such as focused ion applications, physics studies, etc. For example, the hybrid plasma source10may be used to generate laboratory plasma with very high density (e.g., on the order of 1015cm−3)

Aspects of the invention also include a method of manufacturing the hybrid plasma source10. For example, aspects of the invention include manufacturing and/or assembling some or all of the components of the hybrid plasma source10as described herein. Further aspects of the invention include a method of generating a plasma using the hybrid plasma source10. For example, aspects of the invention include using some or all of the components of the hybrid plasma source10to generate a plasma.

The foregoing examples have been provided for the purpose of explanation and should not be construed as limiting the present invention. While the present invention has been described with reference to an exemplary embodiment, changes may be made, within the purview of the appended claims, without departing from the scope and spirit of the present invention in its aspects. Also, although the present invention has been described herein with reference to particular materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.