Patent Application
20090183679
1. Field of the Invention
The present invention relates to gas reaction chamber which feeds an ion source for use in ion implantation of semiconductors and more particularly to a gas reaction chamber which converts gaseous materials into a particular gas feed material for ion beam production, for example, conversion of molecular gas material into other molecular or atomic species.
2. Description of the Prior Art
Ion implantation is a key enabling technology in the manufacture of integrated circuits (IC's). In the manufacture of logic and memory IC's, ions are implanted into substrates, formed from, for example, silicon and GaAs wafers, to form the transistor junctions. Ions are also implanted to dope the well regions of the pn junctions. By varying the energy of the ions, the implantation depth of the ions into the substrate can be controlled, allowing three-dimensional control of the dopant concentrations introduced by ion implantation. The dopant concentrations control the electrical properties of the transistors, and hence the performance of the IC's.
A number of different electrically active materials are known to be used as dopant materials including As, B, P, In, Sb, Bi and Ga. Many of these materials are available in gaseous form, for example as AsH3, PH3, BF3, and SbF5.
Known ion implanters are manufacturing tools which ionize the dopant-containing feed materials, (e.g., by an arc plasma, electron impact, RF or microwave, as is well known in the art,) and extract the dopant ions of interest; accelerate the dopant ion to the desired energy; filter away undesired species; and then transport the dopant ion of interest to the wafer. In order to achieve the desired implantation profile, the following variables must be controlled for a given implantation process:
Dopant feed material (e.g., BF3 gas)
Dopant ion (e.g., B+)
Ion energy (e.g., 5 keV)
Chemical purity of the ion beam (e.g., <1% contaminants)
Energy purity of the ion beam (e.g., <2% FWHM)
ion dose, temperature and angular uniformity during implant.
An area of great importance in the technology of ion implantation is the ion source. The “standard” technology for commercial ion sources, namely the “Enhanced Bernas” ion source is well known. This type of source is commonly used in high current, high energy, and medium current ion implanters. The ion source is mounted to the vacuum system of the ion implanter, e.g., through a mounting flange which may also accommodate vacuum feed-throughs for cooling water, thermocouples, dopant gas feed, N2 cooling gas, and power. A feed gas is fed into the source arc chamber in which the gas is cracked and or ionized to form the dopant ions.
The feed gas is frequently a material which is a gas under normal conditions. In some cases, the gas feed is derived from hot solid materials. In these cases, the gas feeding system includes a vaporizer or oven depending upon the type of solid feed material to be converted to a gas for introduction into the ion source chamber for ionization. Vaporizers or ovens (hereinafter referred to as “vaporizers”) are typically provided in which solid feed materials such as As, Sb2O3, B18H22, B10H14, C14H14 C16H10 and P are vaporized,
In one example known in the art, the ovens, gas feed, and cooling lines are contained within a cooled machined aluminum block. The water cooling is required to limit the temperature excursion of the aluminum block while the vaporizers, which operate between 100 C. and 800 C., are active, and also to counteract radiative heating by the arc chamber when the source is active. The arc chamber is mounted to, but in poor thermal contact with, the aluminum block.
Traditionally, Bernas-type ion sources have been used in ion implantation equipment. Bernas-type ion sources are known as hot plasma or arc discharge sources and typically incorporate an electron emitter, either a naked filament cathode or an indirectly-heated cathode. This type of source generates a plasma that is confined by a magnetic field. Recently, cluster implantation ion sources have been introduced into the equipment market place. These cluster ion sources are unlike the Bernas-style sources in that they have been designed to produce “clusters”, or conglomerates of dopant atoms in molecular form, including ions of the form Asn+, Pn+, CnHm or BnHm+, where n and m are integers, and m,n≧1. Such ionized clusters can be implanted much closer to the surface of a substrate and at higher dose rates relative to their monomer (n=1,m=0) counterparts. Therefore, cluster ion sources are of great interest for forming ultra-shallow p-n transistor junctions, for example, in transistor devices of the 65 nm, 45 nm, or 32 nm generations. For example, the method of cluster implantation and cluster ion sources is described in detail in U.S. Pat. Nos. 6,452,338; 6,686,595; 6,744,214 and 7,107,929, all hereby incorporated by reference. These cluster ion sources preserve the parent molecules (or utilize a different species thereof, e.g., C14H14 converts to C7H7) of the feed gases introduced into the ion source in generating the ion beam. The use of As4+, P4+or P7+ as an implant material for ion implantation in making semiconductor devices is disclosed in applicant's assignee's pending U.S. patent application Ser. No. 60/856,994, incorporated by reference. Other materials for use in implantation may include CnHm and As7.
The vaporizers disclosed in the prior art, such as the above-identified patents, are suitable for vaporizing solid materials, such as decaborane (B10H14), C14H14, C16H10, B18H22 and TMI (trimethyl indium), which have relatively high vapor pressures at room temperature, and thus vaporize at temperatures around 100° C. The ovens traditionally associated with the Bernas type sources typically operate at temperatures greater than 100° C., e.g. from 100° C. to 800° C., due to the feed material to be converted to a gas for introduction into the ion source.
As known in the prior art, gaseous material may be fed directly into the ion source chamber, however, the feed material of interest in connection with semiconductor manufacturing purposes in gaseous form is limited. With regard to feed materials such as arsenic and phosphorous, a gaseous form, e.g., a hydride, is available for use in monomer atom implantation purposes. However, tetramer beams have been shown to be of interest with regard to efficiency of operation of the semiconductor manufacturing facility and may also offer process benefits. At present, tetramers, such as, As4, P4, and others, are difficult to create in standard Bernas type sources.
In the case of gaseous feed materials, such as, AsH3 and PH3, being used as a feed material in a Bernas type ion source, monomer forms of the dopant molecules are available in the ionization chamber, and so the formation of the tetramer molecule is known to be suppressed. To the extent a tetramer is formed, it is likely to be formed from metallic As (or P) deposited on walls of the ionization chamber which then forms the tetramer. The chamber walls are likely very hot or very cold with respect to the usual 350-400° C. vaporization temperatures used in ovens and hence the walls are not a very copious or repeatable source of tetramer molecules, e.g. As4 or P4.
Currently, the most generous source for generating tetramer molecules is known to be a vaporizer oven, operated at 350-400° C. with solid arsenic (As) or solid phosphorus (P). The major inadequacies of this method are numerous, including:
requirements to handle toxic or flammable materials in loading the oven;
slow heat up and cool down times of the materials, which affects the overall responsiveness of the system and tool throughput;
non-repeatability of the system, that is, different temperatures are often needed to reach the same operating pressures as the supply of feed material in the oven ages and the pressure can vary over short time periods depending on the nature of the solid feed material surface (e.g. native oxide layers) or even trapped volumes of gas which release at unpredictable times;
deposition of non-volatile, toxic or flammable metals on vacuum surfaces, which affects time of operation when cleaning of the oven inputs to the chamber is required; and
the inability to readily control, i.e., turn on and shut-off the flow of the tetramer material to the ion source chamber.
Molecular beam epitaxy (MBE) equipment is known which utilizes gaseous hydrides as a feed material. See, for example, Calawa, A. R., Applied Physics Letters (1981), 38(9), p. 701-703; Shiralagi, K. T., J. Vac. Sci. Technol. A (1992) 10(1), p 46-50; Panish, M. B., Prog. Crystal Growth and Charact. (1986) 12, p. 1-28; “Dimer and Tetramer Formation in an AsH3 Cracker Studied by Calibrated Quadrupole Mass Spectrometry”, C. Lohe and C. D. Kohl, J. Vac. Sci. Techno. B7 (2) March/April 1998; and “Gas Crackers” by Veeco, Compound Semiconductor, MBE Operations, St. Paul, Minn., USA.
In such systems, hydrides in gaseous form are used as feed materials. In order to generate molecular and atomic species of interest, “crackers” are known for “cracking” the gaseous hydride material into various molecular and atomic species. Such “crackers” are known to be ovens or furnaces which operate at temperatures in the range 800° K to 1300° K and which heat the gaseous hydrides producing various molecular and atomic species, including H2, As4, As2, As, AsH and AsH3 in the case of solid As material.
In the case of gaseous feed materials (AsH3 and PH3) primarily monomer forms are available in the ionization chamber, and so the formation of the four-fold tetramer molecule is suppressed. To the extent it happens, it is likely to be from metallic As (or P) deposited on walls which then form the tetramer. The chamber walls are likely very hot or very cold with respect to the usual 350-400° C. vaporization temperatures used in ovens and hence the walls are not a very copious or repeatable source of tetramer molecules (As4 or P4). Currently, the most generous source of tetramer molecules is a solid oven, operated at 350-400° C. with lump As or phosphorus.
The major inadequacies of this method are numerous, including: requirements to handle toxic or flammable materials in loading the oven; slow heat up and cool down times of the materials, which affects the overall responsiveness of the system and tool throughput; non-repeatability of the system, that is, different temperatures are often needed to reach the same operating pressures as the supply of feed material in the oven ages and the pressure can vary over short time periods depending on the nature of the solid feed material surface (e.g. native oxide layers) or even trapped volumes of gas which release at unpredictable times; deposition of non-volatile, toxic or flammable metals on vacuum surfaces, which affects time of operation when cleaning of the oven inputs to the chamber is required; and the inability to readily control, i.e., turn on and shut-off the flow of the tetramer material to the ion source chamber.
In order to generate atomic arsenic, the system disclosed in the '407 utilizes a two (2) step process that includes a vaporizer oven and a “cracker” which includes an atomizer to achieve the desired atomic species. More particularly, the arsenic atoms are produced in two steps. In the first step, a sublimator vaporizes solid arsenic, producing a molecular beam of arsenic tetramers and/or dimers. The molecular beam source can optionally include a cracker to produce As2 from As4. In the second step, the molecular beam impinges on a surface of a heated element, termed an atomizer, producing an output beam containing atomic arsenic.
The system disclosed in the '407 has several disadvantages. For example, it requires two (2) steps. That system also requires a vaporizer in addition to a cracker and is unsuitable for use with gaseous hydride materials.
Thus, there is a need for a system for use with gaseous hydrides to generate tetramer source materials that can be accomplished in a single step without the need for a separate vaporizer oven, which overcomes the problems associated with prior art methods for converting gaseous hydrides into various molecular and atomic species.
Briefly, the present invention relates to an ion source which includes a gas reaction chamber. The invention also includes a method of converting a gaseous feed material into a tetramer, dimer, other molecule or atomic species by supplying the feed material to the gas reaction chamber wherein the feed material is converted to the appropriate gas species to be supplied to the ion source and ionized. More particularly, the gas reaction chamber is configured to receive hydride and other feed materials in gaseous form, such as, AsH3 or PH3, and generate various molecular and atomic species for use in ion implantation, heretofore unknown. In one embodiment of the invention, the gas is heated to provide relatively accurate control of the molecular or atomic species generated. In an alternate embodiment of the invention, the gas reaction chamber uses a catalytic surface to convert the feed gas into the different source gas specie required for implantation, such as, hydrides into tetramer molecules. In yet another embodiment of the invention, the gas reaction chamber is configured so that a catalytic or thermodynamic or pyrolytic reaction (herein catalytic) occurs in the presence of an appropriate material including glass or metals such as, W, Ta, Mo stainless steel, ceramics, boron nitride or other refractory metals, raised to an appropriate temperature.
The present invention provides various advantages over the prior art. For example, the invention allows the gaseous feed material to be handled with safety and easily with common practice, for example, with a safe delivery system, such as a gas cylinder. The invention also resolves problems associated with the prior art including providing responsive start up and shut down times as the delivery of the ion source gas stops when the feed gas is removed, the repeatability of the delivery rate is good since it depends on the gas feed rate and the build up of solid materials in the ionization chamber and vacuum system may be less due to the on-demand conversion of the feed material to the source material, e.g., hydrides into tetramers, rather than the slower heating and cooling of solids.
These and other advantages of the present invention will be readily understood with reference to the following specification and attached drawing wherein:
The present invention relates to an ion source which includes a gas reaction chamber or reactor. The gas reaction chamber is configured to receive hydride feed materials in gaseous form of hydrides, for example, AsH3 or PH3, and generate various molecular and atomic species for use in ion implantation, heretofore unknown. More particularly, the gas reaction chamber converts feed supply gases, such as, but not limited to hydrides, (e.g., AsH3 or PH3) into tetramers (As4 or P4), dimers or other desirable monomer or molecular species for implant in a single step without the use of a separate vaporizer oven.
Referring to
When the vaporizer valve 3 is in the open position, vaporized gases from the vaporizer 2 flow through the vaporizer valve 3 to an inlet channel 15 into the open volume of an ionization chamber 16. These gases are ionized, for example, by interaction with the electron beam transported from an electron source 12 to an electron beam dump 11. The ions produced in the ionization chamber 16 exit the ion source 1 by way of an exit aperture 37, where they are collected and transported by the ion optics of the ion implanter in a manner generally known in the art.
The body of vaporizer 2 houses a liquid, e.g., water bath 17 which surrounds a crucible 18 containing a solid feed material. The water bath 17 is heated by a resistive heater plate 20 and cooled by a heat exchanger coil 21 to keep the water bath at the desired temperature. The heat exchanger coil 21 is cooled by de-ionized water provided by water inlet 22 and water outlet 23. The temperature difference between the heating and cooling elements provides convective mixing of the water, and a magnetic paddle stirrer 24 continuously stirs the water bath 17 while the vaporizer is in operation. A thermocouple 25 continually monitors the temperature of the crucible 18 to provide temperature readback for a PID) vaporizer temperature controller (not shown). The ionization chamber body 5 is made of aluminum, graphite, silicon carbide, or molybdenum, and operates near the temperature of the vaporizer 2 through thermal conduction. In addition to low-temperature vaporized solids, the ion source can receive gases through gas feed 26, which feeds directly into the open volume of the ionization chamber 16 by an inlet channel 27.
In order to operate with gaseous feed materials, ion implanters typically use gas bottles which are coupled to a gas distribution system within the ion implanter. The gases are fed to the ion source via metal gas feed lines which directly couple to the ion source 1 through a sealed gas fitting, such as a, VCR or VCO fitting.
In the embodiment illustrated in
A control system, including a thermocouple 121, may be used to control the temperature of the gas reaction chamber 100 to temperatures greater than 800° C. by known temperature control systems, well known in the art. The gas reaction chamber 100 includes a gas feed inlet 104 which may be coupled to the semiconductor facility gas supply or a gas bottle (not shown). The gas distributed by the gas feed inlet 104 may be controlled by known gas control systems, also well known in the art.
Within the volume of the evacuated chamber 101 may be disposed a flow channeling device 105, formed, for example, in a cylindrical shape. The flow channeling device 105 may be fabricated from a metal, glass or a ceramic, such as, pyrolytic boron nitride, pBN. When the flow channeling device 105 is disposed within the evacuation chamber 101, an annular gas distribution plenum 120 is defined in fluid communication with the gas feed inlet 104. The inner diameter of the evacuation chamber 101 and the outer diameter of the flow channeling device 105 creates an annular gap or flow channel 107 for the gas from the annular gas distribution plenum 120 to allow the gas to uniformly distribute itself around the inner sidewalls of the evacuation chamber 101.
As shown in
The flow channeling device 105 includes a longitudinal bore 106 that is in fluid communication with a nozzle 102 extending into the ionization chamber 16. As the gas is heated by the heating coils, the gas expands and flows into a cavity 110, formed between the inner wall 111 of the evacuation chamber 101 and the horizontal bore 106. The heated gas flows through the bore 106 and into the ionization chamber 16 by way of the nozzle 102.
The embodiment of the gas reaction chamber device 100, illustrated in
As is known in the prior art heating feed gases to specific temperatures can crack those gases to other molecular and atomic species. Temperatures for cracking various known source gases, such as gaseous hydrides, into other molecular and atomic species are generally known in the art, e.g., 200 degrees C. to 1000 degrees C.
As such, the gas reaction chamber 100 is adapted to breakup, “crack”, various molecular species, such as hydrides, e.g., AsH3 or PH3 into intermediate species which in the presence of the catalytic material conveniently form tetramers (AS4 or P4), dimers (As2 or P2) or other desirable monomer or molecular species, e.g., BF3 to form BF2 and/or B for implant in a single step without the use of a separate vaporizer oven.
Other gas species (including gas species other than hydrides), such as, BF3, SbH3, GeH4, SiH4 etc., may also be successfully processed in the gas reaction chamber 100 to form other desired molecular and atomic species. In general, the gas reaction chamber 100 in accordance with the present invention is configured to convert gaseous supply material, typically gases, of the form AnCmRzHx, where A is a dopant atom such as B, P, or As, C is carbon, R is a molecule, radical or ligand which contain atoms that are not injurious to the implantation process or semiconductor device performance, and H is hydrogen, n, m, x, and z are with n≧2, m≧0 and x and z≧0 into other desired molecular and atomic species for use in ion implantation.
In accordance with an important feature of the invention, the gas reaction chamber 100 may also be used to generate lower forms of gases passed therethrough. For example, the gas reaction chamber 100 may be configured to generate lower forms of BF3 into lower forms, such as BF2, BF and even B.
In a further embodiment of the invention, the gas reaction chamber device 100 may optionally include a catalytic material surface 108 shown here as disposed on or as part of the outside wall of the flow channeling device 105 and forming part of the flow surfaces of the flow channel 107 through which the feed gas communicates with the ion source chamber. Alternately, the catalytic material surface may form or be a part of any surface which the gas feed material comes into contact. In another alternate embodiment, a fine mesh of tungsten, W, may be inserted in to the flow channeling device 105 forming a convenient catalytic surface 108 allowing gas flow. In yet another alternate embodiment, thin sheets of metal may be used to form the catalytic surface 108. These metal sheets may be formed from various metals including tungsten, W, and molybdenum, Mo. The metal sheets forming the catalytic surface 108 are shaped to fit the flow channel 107.
In another alternate embodiment, the catalytic surface 108 material, such as tantalum, Ta, can be disposed within the bore 106. It is understood that many other materials can be used or in combination to form the catalytic material surface 108, such as stainless steel, pyrolytic boron nitride, graphite, refractory metals and quartz or a hot filament. In addition, the catalytic surface 108 may be formed in other shapes including mesh, solid surface, wires and wool.
The flow of gas through the gas reaction chamber 100 may be arranged alternatively to the configuration, illustrated in
In a further embodiment of the gas reaction chamber device 100, the gaseous feed material interacts with the catalytic material surface 108 in the presence of the heat from heating coils 103, wrapped around the conduit 110, converting the hydride or other gaseous feed material into a tetramer molecule or other specie, such as a dimer molecule. Alternatively the catalytic material itself may be heated by current flow (as in a filament) or inductively, thus providing a directly heated material distinct from the indirectly heated catalysts.
In operation, the gas feed material is allowed to flow through the reactor 100 on its way to the ionization chamber 16. The heating coils 103 are energized to raise the temperature of the gas reaction chamber 100, such that the gas feed material, for example; a gaseous hydride, is converted to the desired molecular or atomic species, for example, a tetramer molecule for ionization within the ion source 1. A temperature monitoring device (not shown) is used for closed loop control of the conduit temperature as discussed above.
In yet another embodiment of the invention, the gas reaction chamber 100 may be configured so that a catalytic (or pyrolytic) reaction occurs in the presence of an appropriate material including glass or metals, such as, W, Ta, Mo stainless steel, ceramics, boron nitride or other refractory metals, raised to an appropriate temperature, e.g., 600 degrees C. to 1000 degrees C., by the heating coils 103.
Obviously, many modifications and variations of the present invention are possible in light of the above teachings. Thus, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above.
This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/022,562, filed on Jan. 22, 2008, hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61022562 | Jan 2008 | US |
