Patent Application
20090206275
The present invention relates generally to technique including a method and a structure for forming substrates using a layer transfer technique. More particularly, the present invention provides a method and system using a linear accelerator particle beam or a particle beam from another type of accelerator such as a cyclotron or the like, with low contaminate process for the manufacture of thick free-standing semiconductor films for a variety of applications including photovoltaic cells. But it will be recognized that the invention has a wider range of applicability; it can also be applied to other types of applications such as for three-dimensional packaging of integrated semiconductor devices, photonic or optoelectronic devices, piezoelectronic devices, flat panel displays, microelectromechanical systems (“MEMS”), nano-technology structures, sensors, actuators, integrated circuits, biological and biomedical devices, and the like.
From the beginning of time, human beings have relied upon the “sun” to derive almost all useful forms of energy. Such energy comes from petroleum, radiant, wood, and various forms of thermal energy. As merely an example, human being have relied heavily upon petroleum sources such as coal and gas for much of their needs. Unfortunately, such petroleum sources have become depleted and have lead to other problems. As a replacement, in part, solar energy has been proposed to reduce our reliance on petroleum sources. As merely an example, solar energy can be derived from “solar cells” commonly made of silicon.
The silicon solar cell generates electrical power when exposed to solar radiation from the sun. The radiation interacts with atoms of the silicon and forms electrons and holes that migrate to p-doped and n-doped regions in the silicon body and create voltage differentials and an electric current between the doped regions. Depending upon the application, solar cells have been integrated with concentrating elements to improve efficiency. As an example, solar radiation accumulates and focuses using concentrating elements that direct such radiation to one or more portions of active photovoltaic materials. Although effective, these solar cells still have many limitations.
As merely an example, solar cells rely upon starting materials such as silicon. Such silicon is often made using either polysilicon (i.e. polycrystalline silicon) and/or single crystal silicon materials. These materials are often difficult to manufacture. Polysilicon cells are often formed by manufacturing polysilicon plates. Although these plates may be formed effectively, they do not possess optimum properties for highly effective solar cells. Single crystal silicon has suitable properties for high grade solar cells. Such single crystal silicon is, however, expensive and is also difficult to use for solar applications in an efficient and cost effective manner. Additionally, both polysilicon and single-crystal silicon materials suffer from material losses during conventional manufacturing called “kerf loss”, where the sawing process eliminates as much as 40% and even up to 60% of the starting material from a cast or grown boule and singulate the material into a wafer form factor. This is a highly inefficient method of preparing thin polysilicon or single-crystal silicon plates for solar cell use.
Generally, thin-film solar cells are less expensive by using less silicon material but their amorphous or polycrystalline structure are less efficient than the more expensive bulk silicon cells made from single-crystal silicon substrates. These and other limitations can be found throughout the present specification and more particularly below.
From the above, it is seen that techniques for forming suitable substrate materials of high quality and low cost are highly desired.
The present invention relates generally to technique including a method and a structure for forming substrates using a layer transfer technique. More particularly, the present invention provides a method and system using a linear accelerator particle beam or a particle beam from another type of particle accelerator such as a cyclotron of the like, with low contaminate process for the manufacture of thick free-standing semiconductor films for a variety of applications including photovoltaic cells. But it will be recognized that the invention has a wider range of applicability; it can also be applied to other types of applications such as for three-dimensional packaging of integrated semiconductor devices, photonic or optoelectronic devices, piezoelectronic devices, flat panel displays, microelectromechanical systems (“MEMS”), nano-technology structures, sensors, actuators, integrated circuits, biological and biomedical devices, and the like.
In a specific embodiment, the present invention provides a system of introducing a particle beam for low contaminate processing. The system includes a particle accelerator with at least an ion source for generating a plurality of charged particles and an apparatus for accelerating and confining the plurality of charged particles in a first particle beam. The first particle beam includes at least a first ion specie and is outputted to a first exit aperture in a first spatial direction. Additionally, the system includes a beam filter apparatus coupled to the first exit aperture to receive the first particle beam. The beam filter apparatus includes a first chamber of a first mass-selection device to process the first particle beam and generate a second particle beam. The second particle beam includes substantially the first ionic specie and being outputted to a second exit aperture in a second spatial direction different from the first spatial direction. Moreover, the system includes an end-station with a second chamber coupled to the beam filter apparatus to receive the second particle beam. The second chamber is configured to house a workpiece having a planar surface configured to receive the second particle beam for implanting the first ionic specie.
In an alternative specific embodiment, the invention provides a system of introducing a particle beam for low contaminate processing. The system includes a particle accelerator apparatus configured to generate a first particle beam. The system further includes a beam filter coupled to the linear accelerator apparatus to receive the first particle beam. The beam filter is in a first chamber and is configured to generate a second particle beam with substantially a first ionic specie. Moreover, the system includes an end-station with a second chamber coupled to the first chamber for extracting the second particle beam. The second particle beam is irradiated onto a planar surface of a workpiece loaded in the second chamber for implanting the first ionic specie.
In yet another specific embodiment, the present invention provides a method of introducing an accelerator particle beam for low contaminate processing. The method includes generating a plurality of ionic particles by an ion source. The plurality of ionic particles contain multiple species including a first ion specie. Additionally, the method includes accelerating and confining the plurality of ionic particles to a first particle beam with energy level of the first specie at least in a range of about 0.5 MeV to 5 MeV and greater, for example 10 MeV using a particle accelerator. The method further includes extracting the first particle beam through a first exit aperture to a first chamber. Moreover, the method includes processing the first particle beam in the first chamber to separate the first ion specie out of the multiple species and extracting a second particle beam through a second exit aperture into a second chamber. The second particle beam includes substantially the first ion specie only. Furthermore, the method includes irradiating the second particle beam to one or more planar surfaces of one or more workpieces loaded in the second chamber to implant the first ion specie. In one embodiment, the first chamber is associated with a first pressure and the second chamber is associated with a second pressure that is higher than the first pressure.
Numerous benefits are achieved using embodiments of the present invention. In particular, certain embodiments of the present invention may use a linear accelerator based on RFQ-linac and/or RFI technology that has been proven to be a cost effective way to obtain high-energy proton beam in 1 MeV to 5 MeV or higher. Alternative embodiments may employ a cyclotron particle accelerator. Alternative embodiments may employ other types of particle accelerators such as a DC electrostatic accelerator, an example of which is the DYNAMITRON proton accelerator available from Ion Beam Applications SA, Belgium) can also be used. Other DC electrostatic accelerators which may be used include Van de Graaff or Tandem Van de Graaff types. According to certain embodiments of the invention with proper dosage and temperature controls these high-energy H+ ions can be utilized for deep implantation down to 200 μm beneath a surface of a selected bulk semiconductor with minimum surface damage to form a desired cleave region thereof. Subsequently, through various controlled cleaving processes or direct layer transfer processes a free-standing thick film (with thickness about 200 μm or less) can be produced. Some embodiments of the invention can be used to produce free-standing single crystalline silicon or polycrystalline silicon thick films for manufacture photovoltaic cells. For example, implanting H+ ions at 5 MeV into silicon, would generate an approximate cleave depth of 220 μm. Some other embodiments of the present invention provide a method of introducing high energy particles for ion implantation with a less contaminate process. The method utilizes a beam filter to separate a desired ionic specie, for example, the H+ ion, from other contaminate species with different mass or charge which may be originated from the ion source and generated during propagation through the particle accelerator. Therefore, less contaminate ions remain in the particle beams the subsequent implantation. Those contaminates, if being implanted, otherwise may generate recombination centers in the target material and wide-spreading defects, instead of forming the cleave region as a predominant 2-D defect network. The contamination-induced recombination centers are of particular concern since these can severely degrade solar cell conversion efficiency. Additionally, the beam filter according to certain embodiments of the invention can bend the beam angle, either horizontally or vertically, providing a geometric flexibility for system arrangement. Particularly, the end-station is such a system can be easily incorporated into a cluster processing tool. Some specific embodiments of the present invention also provide method of performing ion implantation with a less contaminate process by setting a pressure difference between the end-station chamber and the beam filter chamber so that any impurity atoms or molecules sputtered by the particle beam can be prevented from re-depositing onto the implanting surface. Depending upon the embodiment, one or more of these benefits may be achieved. These and other benefits may be described throughout the present specification and more particularly below.
Embodiments in accordance with the present invention achieve these benefits and others in the context of known process technology. However, a further understanding of the nature and advantages of the present invention may be realized by reference to the latter portions of the specification and attached drawings.
Embodiments in accordance with the present invention relate generally to techniques including a method and a structure for forming substrates using layer transfer. More particularly, the present invention provides a method and system using a linear accelerator particle beam with low contaminate process for the manufacture of thick free-standing semiconductor films for a variety of applications including photovoltaic cells. But it will be recognized that the invention has a wider range of applicability; it can also be applied to other types of applications such as for three-dimensional packaging of integrated semiconductor devices, photonic or optoelectronic devices, piezoelectronic devices, flat panel displays, microelectromechanical systems (“MEMS”), nano-technology structures, sensors, actuators, integrated circuits, biological and biomedical devices, and the like.
Using hydrogen as the implanted species into the silicon wafer for photovoltaic application as an example, the desired implantation dose ranges from about 1×1015 to about 1×1016 atoms/cm2, and preferably the dose is less than about 5×1016 atoms/cm2. Using a suitable hydrogen plasma source such as an electron cyclotron resonance (ECR) ion source and acceleration extractor voltage, the hydrogen gas is ionized in a microwave plasma and a beam of H+ ions is formed by using a low-voltage particle extractor (<100 kV) and then shaped by suitable beam optics such as an Einzel lens or solenoid. Eventually, the linear accelerator apparatus can accelerate the H+ ion beam to an energy level ranging from about 0.5 MeV and greater to about 5 MeV and greater. The H+ ion beam is guided into the end-station where one or more silicon ingots may be ready for the implantation process. Depending on certain embodiments, implantation temperature ranges from about −50 to about 550 Degrees Celsius is selected, and is preferably less than about 400 Degrees Celsius to prevent a possibility of H+ ions from diffusing out of the implanted silicon ingot. According to certain preferred embodiments, the H+ ions in an energy level ranging from 1 MeV to 5 MeV or greater are implanted with about 1×1016 atoms/cm2 dose. The implantation process can have multiple steps with various dosage for each step. The implanted H+ ions causes the formation of a cleavable region at a depth ranging from approximately 10 μm (corresponding to an implant energy of about 750 keV) to over 120 μm or even 150 μm (corresponding to implant energies of 3.5 MeV and 4 MeV respectively) beneath the silicon surface. After that, further processes can be performed including a controlled cleaving process to produce a thick silicon free-standing film with a thickness μm to over 120 μm, which further can be used for the manufacture of photovoltaic cell.
In a specific embodiment, the present method uses a linear accelerator apparatus based on Radio-Frequency Quadrupole linear accelerator (RFQ-Linac) or Drift-Tube Linac (DTL), Quadrupole-Focused Interditigated Linac (QFI), or RF-Focused Interdigitated (RFI) technology. Some or all of the above technologies are available from companies such as Accsys Technology Inc. of Pleasanton, Calif.; Linac Systems, LLC of Albuquerque, N. Mex. 87109, and others. Alternatively, a type of accelerator apparatus which may be utilized is a DC electrostatic accelerator such as the DYNAMITRON mentioned above.
And while the particular embodiment described above utilizes a linear accelerator apparatus, this is not required by the present invention. In alternative embodiments, other types of particle accelerators, such as cyclotron or the like, can be used. An example of such a cyclotron particle accelerator which may be used is the CYCLONE 10/5 or 18/9 also available from Ion Beam Applications SA.
In another specific embodiment, these approaches use RF acceleration of an ion beam extracted from an ion source (such as an ECR ion source), to increase the total energy of the H+ ion beam from a range of approximately 20-100 keV to 0.5 to 7 MeV or more. The H+ ion current available with these technologies can be up to 100 mA or more. As a specific example, assuming 100 kW of beam power, a 3.5 MeV RFQ/RFI-Linac would yield a proton beam current of about 29 mA. Using a dose of approximately 1×1016 ion/cm2 and an expanded beam of about 500 mm×500 mm, the area per hour is about 6.5 square meters while the power flux is kept to about 40 Watts/cm2.
Alternatively, the beam can be spatially averaged using a fast scanning method such as using a electro-magnetic beam scanning system, to take a smaller, non-expanded beam quickly “paint” the target area. This approach effectively averages the high-power beam flux.
Such a configuration may offer concurrent advantages and further system flexibility. For example, electro-magnetic beam scanning can lower the throughput losses and decrease the overall system size, by keeping the beam overscan to a smaller percentage. Specifically, since overscan is a function of the beam diameter, an expanded beam would need a larger overscan which lowers throughput and causes more X-Y scan travel. This configuration also reduces system size and allows the possibility of implant dose patterning under scan control.
While certain embodiments have been described in connection with an ECR ion source, the present invention is not limited to this particular example. In accordance with alternative embodiments, ions can be extracted from other sources, including but not limited to magnetized or non-magnetized microwave sources, and hot cathode ion sources.
Of course, there can be other variations, alternatives, and modifications. For example, the high-energy H+ ion beam based on the above combination of parameters may be applied in a Direct Film Transfer (DFT) process for producing free-standing thick silicon films out of the bulk silicon ingot, making it a particularly cost-effective way to manufacture solar cells.
However, due to the imperfection of the ion source, in one embodiment, other contaminate species in addition to the desired ionic specie (e.g., H+ ion) may be included. All these ionic species will be accelerated by the linear accelerator into the ionic particle beam such as the beam 110. In another embodiment, many unavoidable contaminants may be generated during the acceleration process along the path while all particles propagate through the linear accelerator into the end-station. For example, ionic or neutral species like Hydrogen isotope species, Helium species, Oxygen species, Nitrogen species, or Carbon species, sputtered metals such as Aluminum, Iron, Manganese, Magnesium, Copper and Tungsten, etc may be included into the beam 110 as contaminates. Some of these contaminate ion species may degrade the formation of a clean two dimensional EOR region and its overlying film for cleaving in the Direct Film Transfer process mentioned above. The desired H+ ion beam is required to be separated out of other contaminate species for a desired low contaminate implantation process. According to certain embodiments of the present invention, a beam filtering mechanism is used to reduce the impurity levels of the high-energy particle beam produced by the linear accelerator and implement for a low contaminate Direct Film Transfer process for solar cell production. Of course, the filtered ionic particle beam with substantially the desired ion specie may have much wider ranges of applications.
As shown in
In one embodiment, the beam filter 210 is configured to process all the ionic species contained in the first particle beam 215. In one specific embodiment, the beam filter 210 includes a mass-selection device based on a mechanism of generating separate trajectories with different radius of curvature for particles with different charge-to-mass ratio. For example, as a high-energy ionic particle with mass heavier than the desired first ionic specie is received by the beam filter, its trajectory may be curved with a larger radius than that of the first ion specie. The mass-selection device includes an internal passage channel to match with the curved trajectory of the first ion specie. The mass-selection device also includes one or more ion traps set in the trajectories of unwanted ion species. Therefore, the desired first ionic specie can be separated out and be extracted as the second particle beam while the rest of un-desired ionic species may be dumped. For example, the beam filter 210 outputs a second particle beam 216 with nearly pure H+ ions while dumps all other heavier ions and neutral species elsewhere. Then the filtered second particle beam can be utilized for various material processing applications with a low contaminate process.
In one embodiment, an electric sector may be used for fulfilling the above mass-selection for the charged particles. In another embodiment, the beam filter may include a magnetic sector for performing the mass-selection. In yet another embodiment, various types of combination of one or more electric sectors, one or more magnetic sectors, and one or more drift channels can be assembled to build the beam filter.
As a result of the above mass-selection process based on a mechanism for differentiating charge-to-mass ratio, the spatial direction of the second particle beam is different from that of the first particle beam received by the mass-selection device, forming an effective beam-bending angle from a first direction to a second direction. For example, the beam filter is designed to allow the second particle beam including the desired H+ ions being extracted in a direction forming an angle of 90 degree relative to original beam direction. Other heavier ionic specie cannot reach the exit aperture due to their different trajectories and are dumped to certain ion traps set aside.
Depending on the applications, the beam filter can be designed to have different effective beam-bending angles for different desired ion species. For example, the beam filter may have a first passage channel for H+ ions for one application/process and a second passage channel for H2+ ions for another application/process. Of course, there can be other variations, alternatives, and modifications. For example, the charge-to-mass ratio mechanism may be utilized for the separation of like charged particles of different energies.
As mentioned above, certain embodiments in accordance with the present invention may employ a scanning mode for implantation. An example of such an embodiment is shown in the simplified schematic views of
Apparatus 500 comprises ion source 502 in vacuum communication with Low Energy Beam Transport (LEBT) section 504. The LEBT section 504 performs at least the following functions.
Referring to
Examples of ion sources include ECR ion sources, magnetron ion sources, and Penning sources. Examples of ionization methods include the use of e-beams, lasers, glow discharge, and thermal techniques.
The LEBT 504 also typically functions to shape the ion beam for optimum acceptance into the first, RFP stage 522 of the linac section 520. In this particular embodiment, the beam shaping element is an Einzel lens 506.
The LEBT 504 also include an electron suppressor element 508. This element 508 serves to suppress secondary electrons generated by errant ions interacting with exposed surfaces of the LEBT.
Upon entry into the linac section 520, the ion beam is accelerated to higher and higher energies by successive stages. In the first, RFP stage 522, the ions are accelerated from the energy of ˜30 keV, to an energy of about 1.1 MeV. In a second linac stage 524, the ions are accelerated to about 2.1 MeV. In the third and final linac stage 526, the ions are accelerated to energies of about 3.5 MeV or even greater.
Upon exiting the linac section 520, the ion beam enters the High Energy Beam Transport (HEBT) section 540. The function of the HEBT section 540 is to shape the highly energetic ion beam exiting from the final linac stage 526 (e.g. from elliptical to circular), to bend the path of the highly energetic ion beam, and, if appropriate, to achieve scanning of the beam on the target.
Specifically, the highly energized ion beam is first exposed to analyzing magnet 542, which alters the direction of the beam and performs the cleansing function described throughout the instant application, such that initial contaminants of the high energy beam are routed to beam dump 544.
In accordance with certain embodiments, the analyzing magnet 542 exerts a force over the beam that is consistent over time, such that the resulting direction of the of the cleansed beam does not vary. In accordance with alternative embodiments, however, the analyzing magnet may exert a force over the beam that does change over time, such that the direction of the beam does in fact vary. As described in detail below, such a change in beam direction accomplished by the analyzing magnet, may serve to accomplish the desired scanning of the beam along one axis.
Upon exiting the analyzing magnet, the cleansed ion beam enters beam scanner 548.
While the particular embodiment of the beam scanner shown in
While the particular embodiment shown in
The scanning stage 562 may function to translate the position of the workpieces or bulk materials receiving the particle beam. In accordance with certain embodiments, the scanning stage may be configured to move along a single axis only. In accordance with still other embodiments, the scanning stage may be configured to move along two axes. As shown in the particular embodiment of
The various components of the apparatus of
The various components of the coupon system described above may be implemented with a computer system having various features.
As noted, mouse 670 can have one or more buttons such as buttons 680. Cabinet 640 houses familiar computer components such as disk drives, a processor, storage device, etc. Storage devices include, but are not limited to, disk drives, magnetic tape, solid state memory, bubble memory, etc. Cabinet 640 can include additional hardware such as input/output (I/O) interface cards for connecting computer system 610 to external devices external storage, other computers or additional peripherals, further described below.
Any of the software components or functions described in this application, may be implemented as software code to be executed by a processor using any suitable computer language such as, for example, Java, C++ or Perl using, for example, conventional or object-oriented techniques. The software code may be stored as a series of instructions, or commands on a computer readable medium, such as a random access memory (RAM), a read only memory (ROM), a magnetic medium such as a hard-drive or a floppy disk, or an optical medium such as a CD-ROM. Any such computer readable medium may reside on or within a single computational apparatus, and may be present on or within different computational apparatuses within a system or network.
In one embodiment, the beam filter, although changing the beam direction, causes little energy change of the energy level of the selected first ion specie to form the second beam 216. In other words, the energy level of particle beam 216 may still in the desired range of 1 MeV to 5 MeV obtained by the linear accelerator 205. Of course, there can be other variations, modifications, or alternatives. For example, the energy level and beam confinement level of the first particle beam 215 may affect the beam profile of the output second particle beam 216. Also, the particle accelerator could be of a type other than a linear accelerator, such as a cyclotron or the like.
In yet another specific embodiment, the beam filter 210 or 210B respectively is installed in a vacuum chamber 212 or 212B. The chamber 212 or 212B has an independent pumping unit (not shown) which may control the internal pressure to a certain value of Pbf during the operation. The chamber 212 or 212B also includes a high-energy beam transport unit at the exit aperture 219 for extracting the particle beam 216. The High Energy Beam Transport (HEBT) includes the entire beam path from the exit of 205 to the entrance of 220 or exit aperture 219. The exit aperture 219 is directly coupled to end-station 220 which includes a process chamber for performing a high-energy implantation process. In one embodiment, the process chamber includes its own pumping unit to control its own internal pressure of another predetermined level of Pes. Of course, there can be other variations, alternatives, and modifications.
As an example, the high-energy charged particle beam extracted at the exit 219 is a H+ ion beam. In the end-station 220 the H+ ion beam are guided onto the surface of the workpiece. While the impinging high-energy H+ ions predominantly penetrate into some distances into the bulk, some surface atoms or molecules, especially, some light weighted surface contaminates with higher vapor pressure, may be sputtered away by the high-energy H+ ions. These sputtered surface atoms or molecules may redeposit on the surface of the workpiece causing damages or increasing surface roughness. The surface contaminate re-deposition may alter the continued ion implantation process resulting a domino effect that lead to poor non-uniform cleaving planes not suit for subsequent film transfer process. In a preferred embodiment, in order to prevent the sputtered surface atoms or molecules from re-depositing on the processed surface of the workpiece, the pressure level Pbf of the beam filter chamber 212 or 212B is intentionally set to be lower than the pressure level Pes of the end-station chamber 220. Because of the pressure difference, the sputtered contaminate atoms or molecules can be pulled backward due to the negative differential pressure to the beam filter chamber away from, instead of being deposited to, the surface of the workpiece. The desired pressure difference may depend on the ion beam energy level, beam profile, or scanning mechanism, and material types and surface conditions of the workpiece. For example, a typical pressure Pes of the chamber at the end-station 220 could be less than about 1×10−3 Torr. The chamber pressure Pbf that houses the beam filter 210 then can be set to be one or two order magnitude lower than the pressure Pes so that the sputtered contaminates may be sucked away. This arrangement also tends to keep any neutral or sputtered atoms generated within the accelerator or high-energy beam transport prior to the analyzing beam filter away from the end-station. Of course, there can be other variations, alternatives, and modifications.
As shown in
If beam scanning over the target material is desired, in particular embodiments an electromagnetic X-Y type scanning system can be added to the output side of the beam filter assembly. One of the scanning axes can also be combined with the analyzing beam filter system to “wobble” or add/subtract an angle from the last stage of the beam filter, in order to effectuate the scanning along that specific axis.
In an specific embodiment, the end-station includes a second chamber that is part of a cluster tool (not shown) For example, the cluster tool may include an open-air tile-staging station for loading multiple bulk workpieces. The cluster tool may include one more load locks that are directly coupled to the second chamber for transferring the workpiece in/out of the second chamber from/to atmosphere environment or in/out of different chambers with different processing pressures. In one embodiment, the workpiece is first loaded on to a rack with a proper clamping mechanism. The workpiece can be various types including but not limiting to a film coating on a substrate, a tile, a wafer, and a bulk material with a planar surface. In another embodiment, a plurality of bulk workpieces can be loaded on the rack and packed in certain order. Then the loaded rack with a plurality of bulk workpieces is transferred into the second chamber for batch processing. Through one or more load locks other process stations/chambers may be included/added for the cluster tool. For example, there is a process chamber for polishing or re-lapping the surfaces of the bulk workpieces before or after ion implantation process. In another example, a rack of loaded bulk workpieces can be annealed or inspected before a cleaving process in a post-processing chamber after the high-energy implantation. Furthermore, another process chamber can be coupled to the post-processing chamber for completing a controlled cleaving process to manufacture free-standing thick films or tiles out of those bulk workpieces. After one layer film or tile is removed, the remaining bulk workpieces on the rack will be transferred back to the second chamber of the end-station in the cluster tool for further ion implantation as a cycled direct film transfer process. Of course, there can be other variations, alternatives, and modifications.
If beam scanning over the target material is desired, an electromagnetic X-Y type scanning system can be added to the output side of the last beam filter assembly 312. One of the scanning axes can also be combined with the analyzing beam filter system to “wobble” or add/subtract an angle from the last stage of the beam filter to effectuate the scanning along that specific axis. Of course, there can be other variations, alternatives, and modifications.
1. Generate 402 a plurality of ionic particles by an ion source, which contains multiple species including at least a first ion specie (for example H+ ions);
2. Accelerate and confine 404 the plurality of ionic particles to a first particle beam with energy level of the first specie at least in a range of 1 MeV to 5 MeV or greater using a particle accelerator apparatus such as a linear accelerator apparatus;
3. Extract 406 the first particle beam through a first exit aperture to a first chamber;
4. Process 408 the first particle beam in the first chamber to separate the first ion specie out of the multiple species;
5. Optionally scan 410 the second particle beam using an electric/magnetic or electro-magnetic scanning system electro-magnetic to generate a scanned second particle beam;
6. Extract 412 a second particle beam through a second exit aperture into a second chamber, which contains substantially the first ion specie (for example H+ ions) only;
7. Irradiate 414 the scanned second particle beam to implant the first ion specie into one or more planar surfaces of one or more bulk workpieces loaded in the second chamber, where the pressure of the second chamber is set to be higher than the first chamber;
8. Perform other steps 416, as desired.
The above sequence of steps provides a method according to an embodiment of the present invention. Other alternatives can also be provided where steps are added, one or more steps are removed, or one or more steps are provided in a different sequence without departing from the scope of the claims herein. Alternatively, there can be other ways of reducing contaminate during the high-energy implantation. Further details of the present method can be found throughout the present specification and more particularly below.
As shown in
In one specific embodiment, the plurality of charged particles are accelerated and confined to a charged particle beam by a linear accelerator apparatus. For example, a linear accelerator apparatus based on RFQ-linac technology and/or RFI technology or combination of both can produce a high-energy ionic beam. In other embodiments, the particle accelerator apparatus may comprise a DC electrostatic accelerator or a non-linear accelerator such as a cyclotron. For example, the H+ ions in the beam can be accelerated to an energy level ranging from 1 MeV to 5 MeV or greater. Depending on different ionic species with different mass or charges, the corresponding energy level could vary. Of course, there can be other variations, modifications, and alternatives.
In another specific embodiment, the accelerated particle beam will be firstly extracted through an exit aperture of the linear accelerator apparatus into a first chamber where a beam filter apparatus is installed to receive the particle beam and an input beam. The first chamber should be a vacuum chamber with an independent pumping unit and a gauge for measure the pressure. Again, the input beam includes multiple ionic species, though one specie, e.g., the H+ ion may be a dominant specie. The beam filter is designed for separating the dominant ion specie from the total ionic species and dumping the rest impurity species. In one embodiment, the beam filter may be one based on electric sector to separate the H+ ion. In another embodiment, the beam filter may be one based on magnetic sector to separate the H+ ion. In an alternative embodiment, the mass-selection mechanism may be based on charge-to-mass ratio. In another alternative embodiment, a charge-to-mass ratio may be utilized for specie-selection. Of course, there can be other variations, modifications, and alternatives.
Typically, any combination of electric sectors, electric/magnetic sections (e.g. ExB fields) or magnetic sectors plus certain drift channels may be used to build the beam filter. The charged particle beams, depending on its mass or charges, may be curved to certain angle. In one embodiment, the beam filter is designed to transform the input beam with multiple species to an output beam with only desired ionic specie through an exit aperture of the first chamber while dumping the other species to side channels. The exit aperture of the first chamber may point to a different spatial direction, either horizontally or vertically, than the exit aperture of the linear accelerator apparatus. For example, the output beam may be in a horizontal plane with the input beam but turn 90 degrees away. In another example, the output beam may be in a vertical plane with the input beam and change a 90 degree angle from horizontal direction to downward direction. In another embodiment, because the first chamber is held in a high vacuum environment and the magnetic sector would change little of the speed of the charged particles, the output beam now contains substantially desired ionic species having an energy level substantially the same as the original beam. For example, the output H+ ion beam may be still in energy level of 1 MeV and above.
If the accelerator system is to have the capability of generating a range of energy levels for allowing different Direct Film Transfer thicknesses to be made using an implant system, the beam filter can be advantageously made using a electric or electro-magnetic section where the second beam of a different energy can be selected by setting a voltage or current to change the beam bending characteristics of the beam filter. Of course, there can be other variations, modifications, and alternatives.
In yet another embodiment, the output beam is extracted and optionally scanned into a second chamber which is part of an end-station where the charged particles are used for performing various kinds of processes including one or more steps of a Direct Film Transfer process for manufacturing free-standing thick silicon films from ingot for solar cell applications. Typically, the second chamber is held at a high vacuum environment with a pressure of about 5×10−6 Torr for performing the certain steps of the Direct Film Transfer process. In particular, referring to
In another specific embodiment, during the implantation process, the method 400 provides a process of keeping a pressure difference between the first chamber and the second chamber. In particular, the pressure in the first chamber will be kept lower than the pressure in the second chamber. For example, the pressure in the first chamber is one or two orders of magnitude lower than the pressure in the second chamber. Because of this pressure difference, any impurity atoms or molecules possibly sputtered by the high-energy ion beam can be sucked away from the surface back to the first chamber through the exit aperture and are pumped out. This inherently reduces the possibility of a re-deposition of the sputtered atoms and molecules back onto the implanting surface. Otherwise, the re-deposition of these atoms/molecules may alter the surface morphology and/or implantation profile. For example, some contaminate atoms on the surface may change the EOR of the implanted ion so that the defect network becomes scattered. In another example, the surface tends to become rough quickly and unable to be performed a repeated Direct Film Transfer process so to greatly lower the manufacture yield. In general the embodiments for keeping the pressure difference between the first and second chambers provides a method of low contaminate processing. Of course, there can be other variations, modifications, and alternatives.
According to an preferred embodiment, a system of introducing a linear accelerator particle beam for low contaminate processing includes a linear accelerator with at least an ion source for generating a plurality of charged particles and an apparatus for accelerating and confining the plurality of charged particles in a first particle beam in a first spatial direction. The first particle beam includes at least a first ion specie in an energy level ranging from 1 MeV to 5 MeV and is outputted to a first exit aperture. Additionally, the system includes a beam filter apparatus configured to receive the first particle beam. The beam filter apparatus includes a first chamber housing a mass-selection device to process the first particle beam and generate a second particle beam. The second particle beam includes substantially the first ionic specie only and being outputted to a second exit aperture in a second spatial direction that is different from the first spatial direction. In one embodiment, the first ionic specie is H+ ion. In another embodiment, the first ion specie is H2+ ion. Moreover, the system includes an end-station with a second chamber configured to receive the second particle beam. The second chamber houses a pre-loaded workpiece with a planar surface configured to be irradiated by the second particle beam for implanting the first ionic specie. The first chamber is associated with a first pressure and the second chamber is associated with a second pressure that is higher than the first pressure. For example, the system is one of system 200, 200B, 300, or 300B.
According to an alternative embodiment, a system of introducing a linear accelerator particle beam for low contaminate processing includes a linear accelerator apparatus configured to generate a first particle beam comprising at least a first ionic specie in an energy level of at least 1 MeV. The system further includes a beam filter coupled to the linear accelerator apparatus to receive the first particle beam. The beam filter is in a first chamber and is configured to generate a second particle beam with substantially the first ionic specie only. In one embodiment, the first ionic specie is H+ ion. In another embodiment, the first ion specie is H2+ ion. Moreover, the system includes an end-station with a second chamber coupled to the first chamber for extracting the second particle beam. The second particle beam is irradiated onto a planar surface of a workpiece loaded in the second chamber for implanting the first ionic specie. The first chamber is associated with a first pressure and the second chamber is associated with a second pressure that is higher than the first pressure. In one embodiment, the system is system 200 in
According to still another alternative embodiment, the invention provides a method of introducing linear accelerator particle beam for low contaminate processing. The method includes generating a plurality of ionic particles by an ion source. The plurality of ionic particles contain multiple species including a first ion specie. Additionally, the method includes accelerating and confining the plurality of ionic particles to a first particle beam with energy level of the first specie at least in a range of 1 MeV to 5 MeV and higher using a linear accelerator. The method further includes extracting the first particle beam through a first exit aperture to a first chamber. The first chamber is associated with a first pressure. Moreover, the method includes processing the first particle beam in the first chamber to separate the first ion specie out of the multiple species and extracting a second particle beam through a second exit aperture into a second chamber. The second particle beam includes substantially the first ion specie only. In one embodiment, the first ionic specie is H+ ion. In another embodiment, the first ion specie is H2+ ion. Furthermore, the method includes irradiating the second particle beam to one or more planar surfaces of one or more bulk workpieces loaded in the second chamber to implant the first ion specie. The second chamber is associated with a second pressure that is higher than the first pressure. In one preferred embodiment, the method is method 400 in
Numerous benefits are achieved using embodiments of the present invention. In particular, embodiments of the present invention use a linear accelerator based on RFQ-linac and/or RFI technology that has been proven to be a cost effective way to obtain high-energy proton beam in at least 1 MeV. According to certain embodiments of the invention with proper dosage and temperature controls these high-energy H+ ions can be utilized for deep implantation down to 200 μm beneath a surface of a selected bulk semiconductor with minimum surface damage to form a desired cleave region thereof. Subsequently, through various controlled cleaving processes or direct layer transfer processes a free-standing thick film (with thickness about 200 μm or less) can be produced. Some embodiments of the invention can be used to produce free-standing single crystalline silicon or polycrystalline silicon thick films for manufacture photovoltaic cells.
Some other embodiments of the present invention provide a method of introducing high energy particles for ion implantation with a less contaminate process. The method utilizes a beam filter to separate a desired ionic specie, for example, the H+ ion, from other ionic species with different mass or charge, so that the less contaminate ions will be implanted which otherwise may cause wide-spreading defects instead of forming the cleave region as a predominant 2-D defect network. Additionally, the beam filter according to certain embodiments of the invention can bend the beam angle, either horizontally or vertically, providing a geometric flexibility for system arrangement. Particularly, the end-station is such a system can be easily incorporated into a cluster processing tool. Some specific embodiments of the present invention also provide method of performing ion implantation with a less contaminate process by setting a pressure difference between the end-station chamber and the beam filter chamber so that any impurity atoms or molecules sputtered by the particle beam can be prevented from re-depositing onto the implanting surface. Depending upon the embodiment, one or more of these benefits may be achieved.
At least the following embodiments are understood as following within the scope of the present invention.
A system wherein the first chamber is associated with a first pressure and the second chamber is associated with a second pressure, the first pressure being set to be at least 10× lower relative to the second pressure. A system wherein the second pressure in the second chamber is about (1×10−3) torr and lower.
A system wherein ion source is an electron cyclotron resonance (ECR) ion source. A system wherein the apparatus for accelerating and confining the plurality of charged particles in a first particle beam is a linear accelerator (linac) system. A system wherein the linac system comprises a stage selected from a radio frequency quadrupole (RFQ) stage, a RF-Focused Interdigitated (RFI) stage, a Drift-Tube Linac (DTL) stage, or a Quadrupole-Focused Interditigated (QFI) stage. A system wherein the apparatus for accelerating and confining the plurality of charged particles in a first particle beam comprises multiple stages.
A system wherein the first particle beam is in an energy level at least 1 MeV. A system wherein the first particle beam is in an energy level ranging from 0.5 MeV to 5 MeV.
A system wherein the first particle beam comprises the first ionic specie and a plurality of contaminate species originated from either the ion source or generated during the propagation through the linear accelerator. A system wherein the first ion specie is H+ ion. A system wherein the first ion specie is H2+ ion. A system wherein the plurality of contaminate species is selected from the group of Hydrogen isotope specie, Helium specie, Oxygen specie, Nitrogen specie, Carbon specie, Aluminum Specie, Iron Specie, Copper Specie, and constituent elements of aluminum and steel alloys.
A system wherein the mass-selection device comprises an electric sector. A system wherein the mass-selection device comprises a magnetic sector. A system of claim 1 wherein the mass-selection device comprises any combination of an electric sector, a magnetic sector, electric/magnetic (E×B), and one or more drift channels. A system wherein the mass-selection device is based on a mechanism of generating separate trajectories with different radius of curvature for particles with different charge-to-mass ratio. A system wherein the mass-selection device is based on a mechanism for differentiating particles by charge-to-mass ratio.
A system wherein the first spatial direction relative to the second spatial direction forms an angle in a horizontal plane. A system wherein the angle is about 90 degrees. A system wherein the angle is about 45 degrees. A system wherein the angle is about 135 degrees. A system wherein the first spatial direction relative to the second spatial direction forms an angle in a vertical plane. A system wherein the angle is about 90 degrees.
A system wherein the beam filter apparatus is a two-stage mass-selection device further comprising a third chamber housing a second mass-selection device coupled to the first mass-selection device in series to produce the second particle beam. A system wherein the third chamber is associated with a third pressure that is set to be lower relative to the second pressure.
A system wherein the end-station including a second chamber coupled to the second exit aperture is configured to receive the second particle beam in horizontal direction. A system wherein the end-station is part of a cluster tool configured to integrate with a plurality of chambers including the second chamber. A system wherein the second chamber is configured to couple with one or more load locks for loading in/out the workpiece.
A system wherein the workpiece is a thick film on a substrate, a tile workpiece, a wafer workpiece, or a bulk workpiece. A system wherein the bulk workpiece comprises a shaped ingot of single-crystalline or polycrystalline silicon, germanium, III/V group compound semiconductor.
A system wherein the second chamber is further configured to load/unload a plurality of bulk workpieces each including a planar surface for batch processing. A system wherein the second chamber is configured to allow each planar surface of the plurality of bulk workpieces being irradiated by the extracted second particle beam in a substantially perpendicular direction. A system wherein the plurality of bulk workpieces are loaded on a rack that is movable in a plane allowing the second particle beam effectively scanning over all the planar surfaces of the plurality of bulk workpieces.
A system wherein the end-station including a second chamber coupled to the first chamber is configured to receive the second particle beam in horizontal direction. A system wherein the end-station including a second chamber coupled to the first chamber is configured to receive the second particle beam in vertical direction.
As described in detail above, various embodiments of the present invention relate to methods and apparatuses for processing a workpiece with a particle beam. One potentially important application for such processing is in the performance of a controlled cleaving process. For example, in one embodiment, hydrogen, helium, and/or a rare gas are implanted into a substrate to define a subsurface cleave region, followed by a controlled cleaving action to separate a thin film of material from the implanted substrate. Such a controlled cleaving process is described more fully in U.S. Pat. No. 6,013,563 incorporated by reference in its entirety herein for all purposes. A system for achieving such controlled cleaving may include one or more energy sources configured to achieve initiation and propagation of a cleave front in the substrate. Examples of such energy sources include but are not limited to a thermal source or sink, a chemical source, a mechanical source, and an electrical source.
It is understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.
The instant nonprovisional patent application claims priority to U.S. Provisional Patent Application 60/997,684 filed Oct. 3, 2007, which is incorporated by reference in its entirety herein for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 60997684 | Oct 2007 | US |
