Patent Application
20230135525
The present invention relates generally to ion implantation systems, and more specifically to an ion source for an ion implantation system configured to generate an ion beam, whereby a gas inlet for introducing a source gas to the ion source is shielded to mitigate a degradation of source materials at high temperatures, such as when forming aluminum ions from gaseous dimethylaluminum chloride (DMAC).
There is increasing demand for ion implants using metal ions. For example, aluminum implants are important for the power device market, which is a small but fast-growing segment of the market. For many metals, including aluminum, supplying feed material to the ion source is problematic. Systems have been previously provided that utilize a vaporizer, which is a small oven that is external to the arc chamber of the ion source, whereby metal salts are heated to produce adequate vapor pressure to supply vapor to the ion source. The oven, however, is remote from the arc chamber and takes time to heat up to the desired temperature, establish the vapor flow, start the plasma, start the ion beam, etc. Further, if a change from one metal species to some other species is desired, time is taken in waiting for the oven to cool down adequately for such a change in species.
Another conventional technique is to place a metal-containing material such as aluminum or another metal inside the arc chamber. For aluminum, the metal-containing material may comprise aluminum oxide, aluminum fluoride, or aluminum nitride, all of which can withstand the approximately 800C temperatures of the plasma chamber. In such a system, ions are sputtered directly off the material in the plasma. Another technique is to use a plasma containing an etchant such as fluorine to attain chemical etching of the metal. While acceptable beam currents can be attained using these various techniques, compounds of aluminum oxide, aluminum chloride, and aluminum nitride, all of which are good electrical insulators, tend to be deposited on electrodes adjacent to the ion source in a relatively short period of time (e.g., 5-10 hours). As such, various deleterious effects are seen, such as high voltage instabilities and associated variations in dosage of ions being implanted.
The present disclosure thus provides a system and apparatus for generating an ion beam when utilizing a thermally unstable gas, such as forming an ion beam comprising ions from gaseous dimethylaluminum chloride (DMAC), diborane, or other gases. Accordingly, the following presents a simplified summary of the disclosure in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
In accordance with one aspect of the disclosure, an ion implantation system is provided. Broadly, the disclosure is directed toward an ion implantation and ion source for implantation of ions. In one particular example, a thermally unstable gas such as a gaseous aluminum-based ion source material is provided, wherein an ion source is configured to receive and ionize the gaseous aluminum-based ion source material and to form an ion beam therefrom. A beamline assembly is configured to selectively transport the ion beam, and an end station is configured to accept the ion beam for implantation of ions into a workpiece.
The gaseous aluminum-based ion source material, for example, comprises, or is comprised of, dimethylaluminum chloride (DMAC). In one example, the DMAC is stored as a liquid that transitions into vapor phase at room temperature when under vacuum. A pressurized gas bottle, for example, is configured to contain the DMAC and to provide the DMAC to the ion source. The ion source, for example, comprises an arc chamber, wherein the pressurized gas bottle is configured provide the DMAC to the arc chamber. One or more dedicated supply lines can be further provided and configured to transfer the DMAC from the pressurized gas bottle to the arc chamber. A low-pressure gas bottle, for example, is configured to contain the DMAC and to provide the DMAC to an arc chamber of the ion source as a gas via a primary gas line.
In accordance with some examples of the present disclosure, an ion source is provided, wherein an arc chamber has one or more radiation generating features defined therein. The arc chamber, for example, comprises an arc chamber body generally enclosing an internal volume. The arc chamber, for example, has at least one gas inlet aperture defined therein. One or more shields, for example, are positioned proximate to the gas inlet aperture. The one or more shields, for example, provide a fluid communication between the gas inlet aperture and the internal volume. The one or more shields are further configured to substantially prevent thermal radiation from reaching the gas inlet aperture from the one or more radiation generating features.
In accordance with various aspects of the disclosure, an ion source is provided, wherein an arc chamber has one or more radiation generating features defined therein. The arc chamber comprises an arc chamber body generally enclosing an internal volume, wherein the arc chamber body has a gas inlet aperture defined therein. A gas source, for example, is configured to provide a gas through the gas inlet aperture, and one or more shields are positioned proximate to the gas inlet aperture. In one example, the gas comprises dimethylaluminum chloride (DMAC).
The one or more shields, for example, provide a fluid communication between the gas inlet aperture and the internal volume, wherein the one or more shields minimize a line-of-sight from the one or more radiation generating features to the gas inlet aperture and are configured to substantially prevent thermal radiation from reaching the gas inlet aperture from the one or more radiation generating features.
The gas inlet temperature, for example, can be defined at the gas inlet aperture, wherein the one or more shields are configured to maintain the gas inlet temperature below a predetermined maximum temperature, and wherein the predetermined maximum temperature is based on a decomposition temperature of the gas. In another example, the ion source is configured to form a plasma within the arc chamber from a source material comprising a dopant species. At least one shield of the one or more shields, for example, can be comprised of a shield material that comprises the dopant species, wherein the shield material is configured to be chemically etched by the gas. The dopant species, in one example, comprises aluminum, wherein the gas comprises a halide. In another example, the one or more shields comprise a plurality of shields, wherein the at least one shield comprises a closest one of the plurality of shields that is in closest proximity to the gas inlet aperture and is comprised of the dopant species, and wherein a farthest one of the plurality of shields that is farthest from the gas inlet aperture is comprised of a refractory metal, a ceramic, or graphite.
The one or more radiation generating features, for example, can comprise one or more of a plasma column defined within the internal volume, a cathode, a repeller, the arc chamber body, and an arc slit plate. The one or more shields, for example, are configured to generally prevent the plasma column from forming a plasma at the gas inlet aperture.
In accordance with another example, the one or more shields comprise a plurality of rigid plates in a stacked formation. The plurality of rigid plates, for example, are positioned directly over the gas inlet aperture while not contacting the gas inlet aperture. The arc chamber body, for example, can further comprise one or more liners, wherein the plurality of rigid plates are recessed behind an innermost liner and the arc chamber body. The plurality of rigid plates, for example, can be spaced apart from each other by a predetermined spacing distance.
In another example, the one or more shields are comprised of a plurality of shields, wherein one or more of the plurality of shields have one or more shield apertures defined therein. The one or more shield apertures, for example, are defined in the two or more of the plurality of shields and are offset from one another, thereby preventing the line-of-sight from the one or more radiation generating features to the gas inlet aperture through the one or more shield apertures.
The one or more shields, for example, are symmetrically arranged with respect to the arc chamber body. In yet another example, the one or more shields are comprised of one or more a refractory material, a ceramic, and graphite.
In another example, the arc chamber body comprises one or more liners, and wherein the one or more shields are operably coupled to the one or more liners. The one or more liners, for example, can comprise one or more thermal breaks defined therein, wherein the one or more thermal breaks are configured to reduce a heat transfer to the gas inlet aperture. The one or more thermal breaks, for example, can comprise one or more of a groove defined in the one or more liners, a region of the one or more liners that has a smaller cross section than a remainder of the one or more liners, and a machined periphery defined around the gas inlet aperture configured to limit a thermal conduction through the one or more liners to the gas inlet aperture.
One or more fastening devices can be further provided, wherein the one or more fastening devices, for example, operably couple the one or more shields to one or more of the arc chamber body and the one or more liners. The one or more fastening devices, for example, comprise one or more screws and/or one or more standoffs. In another example, a plurality of slots are defined in the one or more liners, wherein the one or more shields are configured to slidingly engage the plurality of slots, thereby operably coupling the one or more shields to the one or more liners.
In accordance with another example, an ion source is provided, wherein an arc chamber is configured to form a plasma column. A gas inlet aperture, for example, is defined in a wall of the arc chamber, and one or more shields are provided, wherein the one or more shields generally prevent a line of sight from the plasma column to the gas inlet aperture. The one or more shields, for example, generally define one or more walls of the arc chamber.
In another example, the ion source further comprises a cathode and a repeller respectively positioned at opposite ends of the arc chamber, wherein the arc chamber is symmetrical, and whereby the one or more shields are configured to provide a uniform erosion of the cathode and repeller.
The one or more shields, for example, are further configured to lower a temperature proximate to the gas inlet aperture concurrent with the formation of the plasma column. In another example, the one or more shields further minimize a decomposition and/or plugging of the gas inlet aperture concurrent with the formation of the plasma column.
According to another example, one or more of a size, a shape, and a quantity of the one or more shields is configured to prevent the line of sight from the plasma column to the gas inlet aperture based, at least in part, on a temperature sensitivity of a gas provided through the gas inlet aperture. For example, the one or more shields are configured to reduce a temperature of the arc chamber concurrent with the formation of the plasma column.
To the accomplishment of the foregoing and related ends, the disclosure comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
The present disclosure is directed generally toward an ion implantation system and an ion source material associated therewith. More particularly, the present disclosure is directed toward components for said ion implantation system when using a gas that is highly reactive and/or thermally unstable, whereby high temperatures within an ion source increase a reactivity or reaction rate of the gas. For example, an ion source material is provided as a source gas for producing atomic ions to electrically dope silicon, silicon carbide, or other semiconductor substrates at various temperatures. In particular, the present disclosure advantageously minimizes degradation of such a source gas at high temperatures, such as when using dimethylaluminum chloride (DMAC) as the ion source material. Further, when using a highly reactive gas such as fluorine, by achieving a lower temperature at a gas inlet of the ion source in accordance with the present disclosure, a reduction of an etch rate of components adjacent to, or in contact with, the gas inlet is further achieved, such as in a case where NF3 is utilized, whereby its decomposition into nitrogen and fluorine is reduced.
Accordingly, the present invention will now be described with reference to the drawings, wherein like reference numerals may be used to refer to like elements throughout. It is to be understood that the description of these aspects are merely illustrative and that they should not be interpreted in a limiting sense. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be evident to one skilled in the art, however, that the present invention may be practiced without these specific details. Further, the scope of the invention is not intended to be limited by the embodiments or examples described hereinafter with reference to the accompanying drawings, but is intended to be only limited by the appended claims and equivalents thereof.
It is also noted that the drawings are provided to give an illustration of some aspects of embodiments of the present disclosure and therefore are to be regarded as schematic only. In particular, the elements shown in the drawings are not necessarily to scale with each other, and the placement of various elements in the drawings is chosen to provide a clear understanding of the respective embodiment and is not to be construed as necessarily being a representation of the actual relative locations of the various components in implementations according to an embodiment of the invention. Furthermore, the features of the various embodiments and examples described herein may be combined with each other unless specifically noted otherwise.
It is also to be understood that in the following description, any direct connection or coupling between functional blocks, devices, components, or other physical or functional units shown in the drawings or described herein could also be implemented by an indirect connection or coupling. Furthermore, it is to be appreciated that functional blocks or units shown in the drawings may be implemented as separate features in one embodiment, and may also or alternatively be fully or partially implemented in a common feature in another embodiment. For example, several functional blocks may be implemented as software running on a common processor, such as a signal processor.
Ion implantation is a physical process that is employed in semiconductor device fabrication to selectively implant dopant into semiconductor and/or wafer material. Thus, the act of implanting does not rely on a chemical interaction between a dopant and semiconductor material. For ion implantation, dopant atoms/molecules from an ion source of an ion implanter are ionized, accelerated, formed into an ion beam, analyzed, and swept across a wafer, or the wafer is translated through the ion beam. The dopant ions physically bombard the wafer, enter the surface and come to rest below the surface, at a depth related to their energy.
Ion sources in ion implanters typically generate the ion beam by ionizing a source material in an arc chamber, wherein a component of the source material is a desired dopant element. The desired dopant element is then extracted from the ionized source material in the form of the ion beam.
In order to gain a general understanding of the disclosure, and in accordance with one aspect of the present disclosure,
Generally speaking, an ion source 108 in the terminal 102 is coupled to a power supply 110 to ionize a dopant gas into a plurality of ions from the ion source to form an ion beam 112. Individual electrodes in close proximity to the extraction electrode may be biased to inhibit back streaming of neutralizing electrons close to the source or back to the extraction electrode.
The ion beam 112 in the present example is directed through a beam-steering apparatus 114, and out an aperture 116 towards the end station 106. In the end station 106, the ion beam 112 bombards a workpiece 118 (e.g., a semiconductor such as a silicon wafer, a display panel, etc.), which is selectively clamped or mounted to a chuck 120 (e.g., an electrostatic chuck or ESC). Once embedded into the lattice of the workpiece 118, the implanted ions change the physical and/or chemical properties of the workpiece. Because of this, ion implantation is used in semiconductor device fabrication and in metal finishing, as well as various applications in materials science research.
The ion beam 112 of the present disclosure can take any form, such as a pencil or spot beam, a ribbon beam, a scanned beam, or any other form in which ions are directed toward end station 106, and all such forms are contemplated as falling within the scope of the disclosure.
According to one exemplary aspect, the end station 106 comprises a process chamber 122, such as a vacuum chamber 124, wherein a process environment 126 is associated with the process chamber. The process environment 126 generally exists within the process chamber 122, and in one example, comprises a vacuum produced by a vacuum source 128 (e.g., a vacuum pump) coupled to the process chamber and configured to substantially evacuate the process chamber. Further, a controller 130 is provided for overall control of the vacuum system 100.
The present disclosure appreciates that workpieces 118 having silicon carbide-based devices formed thereon have been found to have better thermal and electrical characteristics than silicon-based devices, and in particular, in applications used in high voltage and high temperature devices, such as electric cars, etc. Ion implantation into silicon carbide, however, utilizes a different class of implant dopants than those used for silicon workpieces. In silicon carbide implants, aluminum, phosphorous, and nitrogen implants are often performed. Nitrogen implants, for example, are relatively simple, as the nitrogen can be introduced as a gas, and provides relatively easy tuning, cleanup, etc. Aluminum, however, is more difficult, as there are presently few good gaseous solutions of aluminum known.
The present disclosure contemplates that an ion source material 132, for example, is provided to an arc chamber 134 of the ion source 108 for forming the ion beam 112. Heretofore, there has been no materials that could be safely and effectively delivered to the ion source 108 in a gaseous form in order to produce the ion beam 112 for subsequent implantation of aluminum ions. In the past, either a solid source material (not shown) has been placed in a heated vaporizer assembly (not shown), whereby the resulting gas is fed into the arc chamber 134, or a solid high-temperature ceramic (not shown) such as Al2O3 or AIN has been placed into the arc chamber where it is etched by a fluorine-based gas.
Both of these techniques, however, can have substantial limitations. For example, the time for a vaporizer to achieve a temperature needed to transition the solid material into a vapor phase can be greater than 30 minutes, thus impacting tool productivity. Further, when a different dopant gas is desired to be introduced into the arc chamber, the time needed to subsequently reduce the temperature of the vaporizer such that the source material is no longer in a vapor phase can be greater than 30 minutes. This is commonly referred to as the transition time between species, whereby the transition time can reduce the productivity of the ion implanter.
Still further, when etching an aluminum oxide (Al2O3) or aluminum nitride (AIN) ceramic using a fluorine-based dopant gas (e.g., BF3, NF3, PF3, PF5), the resulting byproducts of the reaction (e.g., AlFx, Al, N and neutrals of AIN and AL2O3) can form an insulating coating on the extraction electrode (e.g., at a negative voltage), which, in turn, can cause a charge build up and subsequent discharging to an ion source arc slit optics plate (e.g., at a positive voltage), thus further reducing the productivity of the tool.
In order to overcome the limitations or the prior art, the ion implantation system 101 of the present disclosure provides gaseous dimethylaluminum chloride (C4H10AlCl, also referred to as DMAC) as the ion source material 132 to advantageously deliver an aluminum-based material into the arc chamber 134 of the ion source 108 in a gaseous form. Providing DMAC to the arc chamber 134 in a gaseous form, for example, advantageously allows for faster transition times between species (e.g., less than 5 minutes), no wait times for material warm-up and cool-down, and no insulating material forming on the extraction electrode seen in conventional systems. The ion source material 132 (e.g., DMAC), for example, is selectively delivered to the arc chamber 134 via a dedicated, primary gas line 136, as it is a highly reactive material (pyrophoric). A fluorine-containing gas source 138 (e.g., BF3, PF3, etc.) is selectively provided to the arc chamber 134 via a secondary gas line 140, wherein the primary gas line 136 and secondary gas line are distinct and separate gas lines. The fluorine-containing gas source 138, for example, is a molecule or a pre-mixture of gases wherein at least one component thereof is fluorine.
Using a gas such as DMAC as a source material to generate an aluminum ion beam has benefits in terms of fast transitions and stability of the ion source; however, exposure of the DMAC gas to temperatures greater than 400° C. will tend to decompose the DMAC.
Accordingly, the present disclosure provides a number of apparatuses, systems, and methods for generally preventing such plugging, fouling, or contamination of a gas inlet aperture associated with an ion source. Thus, in accordance with one example aspect of the disclosure,
The arc chamber body 306, for example, can further comprise one or more liners 320, wherein the one or more liners generally serve to thermally, chemically, or otherwise protect the arc chamber body 306. The one or more liners 320, for example, and can comprise or be comprised of a material such as a graphite or other protective material. In one example, the arc chamber 302 comprises at least one gas inlet aperture 322 for introduction of a gas from a gas source 324 to the internal volume 308, as will be discussed further, infra. The gas inlet aperture 322 (e.g., a hole, channel, or other opening), for example, is defined in or through one or more of the arc chamber body 306 and the one or more liners 320.
According to one example of the present disclosure, one or more shields 326 are positioned proximate to the gas inlet aperture 322, wherein the one or more shields provide a fluid communication between the gas inlet aperture and the internal volume 308 while shielding the gas inlet aperture from thermal radiation associated with the internal volume. The one or more shields 326 illustrated in
The one or more shields 326, for example, are configured to not substantially interfere with the plasma column 318 within the arc chamber 302. For example, the one or more shields 326 comprise shields 334A, 334B, and 334C shown in
For example,
The present disclosure thus appreciates, that while here may be operational advantages to generally providing symmetry of the interior volume 308 associated with the one or more shields 326 and the arc chamber 302, such as illustrated in the examples shown in
Referring again to
During operation any of the arc chambers 302, 350, 370 of
According to another example, the one or more shields 326 are further configured to generally prevent a formation of a plasma at, or proximate to, the gas inlet aperture 322. For example, at least one of the one or more shields 326 can be positioned directly over the gas inlet aperture 322 of any of
According to another example, as illustrated in
In accordance with another illustrative example of various aspects of the present disclosure, the ion source 300 of
Accordingly, the present disclosure appreciates that by positioning the one or more shields 326 over, or in proximity to, the gas inlet aperture 322 (e.g., based on a temperature sensitivity of the source gas or molecule), a surface or area proximate to the gas inlet aperture is accordingly protected from heat associated with the plasma column 318, the cathode 310 (e.g., an indirectly heated cathode or IHC), the arc chamber body 306, or the repeller 312. The one or more shields 326, for example, also generally prevent the formation of a plasma at or proximate to the gas inlet aperture 322 due to localized high pressure in the region, thus lowering a temperature of the area or region surrounding the gas inlet aperture and/or preventing plasma intrusion into the inlet aperture. The one or more shields 326, for example, can comprise or be comprised of a refractory metal that has a low thermal conductivity, such as tantalum. Alternatively, the one or more shields 326 can comprise or be comprised of other various materials such as tungsten, molybdenum, graphite, aluminum nitride and aluminum oxide.
In accordance with another example, a configuration of the one or more shields 326 (e.g., a length, width, height, shape, etc.) can be based, at least in part, on the temperature sensitivity of the gas introduced to the ion source 300 via the gas inlet aperture 322. The one or more shields 326 can be planar or any non-planar shape, such as being curved or bell-shaped. In another example, a width and height of the one or more shields 326 may have a staggered or stepped configuration, such as to cover or generally prevent line-of-sight from the plasma column 318 to the gas inlet aperture 322.
The one or more shields 326, for example, are coupled to the arc chamber body 306 or one or more liners 320 via the one or more fastening devices 328, such as one or more screws, standoffs, clamps, interference-fit members, slots, etc. The one or more fastening devices 328, for example, comprise or are comprised of one or more of a refractory metal, ceramic or graphite, whereby the one or more fastening devices are configured to withstand high temperatures, reactive gases such as fluorine gas, and have low impurity levels. The one or more fastening devices 328, for example, are constructed from a material with low thermal conductivity, such as tantalum, whereby heat is not readily transferred to the arc chamber body 306 or the one or more liners 320.
In one example, the one or more liners 320 can be constructed such that two end pieces may be bridged together via one or more of the radiation shields. One or more of the one or more liners 320, for example, can comprise at least one thermal break 388 machined on, or otherwise defined in or on one or more sides of the gas inlet aperture 322. In another example, the thermal heat break 388 can be machined around the gas inlet aperture 322. The one or more liners 320 may also be thinned proximate to the gas inlet aperture 322 so as to further reduce mass and subsequent thermal conduction. While not shown, the one or more liners 320 can comprise a one-piece U-shaped liner (e.g., two side liners and a rear liner are combined to form the U-shaped liner), and one or more of the one or more shields 326 can be positioned over the gas inlet aperture 322. The one or more liners 320, for example, can be flat or shaped to follow various contours of a shield closest to the plasma. Various underlying U-shaped liners can be spaced apart to further reduce thermal conduction to the arc chamber body.
The present disclosure, for example, thus provides one or more thermal shields to reduce a temperature of various components in proximity to the gas inlet aperture and/or generally prevent the plasma from flowing to the region of the gas inlet aperture that can be an area of higher pressure than the remainder of the arc chamber. The present disclosure is thus particularly applicable when introducing various thermally-unstable stable gases to the arc chamber, such when introducing gases such as dimethylaluminum chloride (DMAC), Diborane, Halides or other such gases. DMAC, for example, can be utilized as a source of aluminum for implantation of aluminum ions in high power devices.
It is noted that the present disclosure is also applicable to various applications where highly-reactive gases are introduced to an arc chamber. In such applications, the present disclosure ameliorates concerns previously seen where high temperatures and highly-reactive gases are present, such as fluorine reacts with tungsten to form volatile WFx. For example, highly-reactive gases such as such as fluorine, XeF2, or other reactive gases can be provided through the gas inlet aperture, whereby the one or more shields of the present disclosure advantageously protect the region of the gas inlet aperture.
In accordance with one exemplary aspect, in act 402 of
Although the invention has been shown and described with respect to a certain embodiment or embodiments, it should be noted that the above-described embodiments serve only as examples for implementations of some embodiments of the present invention, and the application of the present invention is not restricted to these embodiments. In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiments of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several embodiments, such feature may be combined with one or more other features of the other embodiments as may be desired and advantageous for any given or particular application. Accordingly, the present invention is not to be limited to the above-described embodiments, but is intended to be limited only by the appended claims and equivalents thereof.
This application claims the benefit of U.S. Provisional Application Serial No. 63/273,338 filed Oct. 29, 2021, entitled, “SHIELDED GAS INLET FOR AN ION SOURCE”, the contents of all of which are herein incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63273338 | Oct 2021 | US |
