Fluorine based molecular co-gas when running dimethylaluminum chloride as a source material to generate an aluminum ion beam

Abstract

An ion implantation system, ion source, and method are provided having a gaseous aluminum-based ion source material. The gaseous aluminum-based ion source material can be, or include, dimethylaluminum chloride (DMAC), where the DMAC is a liquid that transitions into vapor phase at room temperature. An ion source receives and ionizes the gaseous aluminum-based ion source material to form an ion beam. A low-pressure gas bottle supplies the DMAC as a gas to an arc chamber of the ion source by a primary gas line. A separate, secondary gas line supplies a co-gas, such as a fluorine-containing molecule, to the ion source, where the co-gas and DMAC reduce an energetic carbon cross-contamination and/or increase doubly charged aluminum.

Claims

1. An aluminum ion implantation source apparatus, comprising: an arc chamber; a process gas supply line in fluid communication with the arc chamber, the process gas supply line configured to selectively introduce a dimethylaluminum chloride (DMAC) process gas into the arc chamber; a co-gas supply line in fluid communication with the arc chamber, the co-gas supply line being distinct from the process gas supply line, and configured to selectively introduce a fluorine containing co-gas into the arc chamber; a refractory metal shaft disposed within the arc chamber; and an aluminum containing ceramic target disposed on or proximate to the refractory metal shaft, wherein the refractory metal shaft is configured to be biased to a negative potential so as to achieve a desired etch rate of the aluminum containing ceramic target that, in combination with the DMAC process gas and the fluorine containing co-gas introduced into the arc chamber, generates a desired ion beam current of doubly charged aluminum ions (Al++).

2. The aluminum ion implantation source apparatus of claim 1, wherein the aluminum containing ceramic target comprises one or more of Al.sub.2O.sub.3 and AlN.

3. The aluminum ion implantation source apparatus of claim 1, wherein the fluorine containing co-gas comprises one or more of BF.sub.3, SiF.sub.4, PF.sub.3, PF.sub.5, NF.sub.3, He+F.sub.2, and He+F.sub.2+Ar.

4. The aluminum ion implantation source apparatus of claim 1, wherein the desired ion beam current of Al++ is greater than approximately 5 ma.

5. The aluminum ion implantation source apparatus of claim 1, wherein biasing of the refractory metal shaft to the negative potential, in combination with the DMAC process gas and the fluorine containing co-gas introduced into the arc chamber, causes one or more of the following reactions:
AlN+F.sub.2.fwdarw.AlF.sub.3+N.sub.2(1), and
Al.sub.2O.sub.3+F.sub.2.fwdarw.AlF.sub.3+O.sub.2(2).

6. The aluminum ion implantation source apparatus of claim 1, wherein biasing of the refractory metal shaft to the negative potential, in combination with the DMAC process gas and the fluorine containing co-gas introduced into the arc chamber, causes a sputtering of the aluminum containing ceramic target to form neutrals comprising one of more of nitrogen, oxygen and aluminum, which neutrals are ionized so as to facilitate a reduced flow of the DMAC process gas into the arc chamber and thereby reduce an internal pressure of the arc chamber.

7. The aluminum ion implantation source apparatus of claim 1, wherein biasing of the refractory metal shaft to the negative potential, in combination with the DMAC process gas and the fluorine containing co-gas introduced into the arc chamber, facilitates the following reaction of fluorine and hydrogen to facilitate the generation of the desired ion beam current of Al++:
H+F.fwdarw.HF.

8. The aluminum ion implantation source apparatus of claim 1, wherein a chlorine component of the DMAC process gas etches the aluminum containing ceramic target in accordance with the following reaction:
Al+Cl.sub.2.fwdarw.AlCl.sub.3.

9. The aluminum ion implantation source apparatus of claim 1, wherein biasing of the refractory metal shaft to the negative potential, in combination with the DMAC process gas and the fluorine containing co-gas introduced into the arc chamber, facilitates a reduction in energetic carbon contamination by virtue of fluorine scavenging hydrogen atoms from carbon.

10. The aluminum ion implantation source apparatus of claim 1, wherein the fluorine containing co-gas breaks carbon-to-carbon bonds (CC) in accordance with the following reaction:
C.sub.2H.sub.3+5F.fwdarw.2CF+3HF.

11. An aluminum ion implantation source apparatus, comprising: an arc chamber; a process gas supply means for selectively introducing a dimethylaluminum chloride (DMAC) process gas into the arc chamber; a co-gas supply means for selectively introducing a fluorine containing co-gas into the arc chamber, wherein the co-gas supply means is distinct from the process gas supply means; a refractory metal shaft disposed within the arc chamber; an aluminum containing ceramic target disposed on or proximate to the refractory metal shaft; and a means for generating a desired ion beam current of doubly charged aluminum ions (Al++), whereby in combination with the DMAC process gas and the fluorine containing co-gas, the refractory metal shaft is electrically biased to achieve a desired etch rate of the aluminum containing ceramic target.

12. The aluminum ion implantation source apparatus of claim 11, wherein the means for generating the desired ion beam current of Al++ electrically biases the refractory metal shaft to a negative potential, thereby etching the aluminum containing ceramic target and causing one or more of the following reactions:
AlN+F.sub.2.fwdarw.AlF.sub.3+N.sub.2(1), and
Al.sub.2O.sub.3+F.sub.2.fwdarw.AlF.sub.3+O.sub.2(2).

13. The aluminum ion implantation source apparatus of claim 11, wherein the aluminum containing ceramic target comprises one or more of Al.sub.2O.sub.3 and AlN.

14. The aluminum ion implantation source apparatus of claim 11, wherein the fluorine containing co-gas comprises one or more of BF.sub.3, SiF.sub.4, PF.sub.3, PF.sub.5, NF.sub.3, He+F.sub.2, and He+F.sub.2+Ar.

15. The aluminum ion implantation source apparatus of claim 11, wherein the desired ion beam current of Al++ is greater than approximately 5 ma.

16. The aluminum ion implantation source apparatus of claim 11, wherein the means for generating the desired ion beam current of Al++ electrically biases the refractory metal shaft to a negative potential and causes a sputtering of the aluminum containing ceramic target to form neutrals comprising one of more of nitrogen, oxygen and aluminum, which neutrals are ionized so as to facilitate a reduced flow of the DMAC process gas into the arc chamber and thereby reduce an internal pressure of the arc chamber.

17. The aluminum ion implantation source apparatus of claim 11, wherein the means for generating the desired ion beam current of Al++ electrically biases the refractory metal shaft to a negative potential, thereby facilitating the following reaction:
H+F.fwdarw.HF.

18. The aluminum ion implantation source apparatus of claim 11, wherein a chlorine component of the DMAC process gas etches the aluminum containing ceramic target in accordance with the following reaction:
Al+Cl.sub.2.fwdarw.AlCl.sub.3.

19. The aluminum ion implantation source apparatus of claim 11, wherein the means for generating the desired ion beam current of Al++ electrically biases the refractory metal shaft to a negative potential, thereby facilitating a reduction in energetic carbon contamination by virtue of fluorine scavenging hydrogen atoms from carbon.

20. The aluminum ion implantation source apparatus of claim 11, wherein the fluorine containing co-gas breaks carbon-to-carbon bonds (CC) in accordance with the following reaction:
C.sub.2H.sub.3+5F.fwdarw.2CF+3HF.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a block diagram of an exemplary vacuum system utilizing dimethylaluminum chloride as an ion source material in accordance with several aspects of the present disclosure.

(2) FIG. 2 is a graph illustrating various spectra of an aluminum ion beam according to several examples.

(3) FIG. 3 is a chart illustrating a comparison of various spectra values according to several examples.

(4) FIG. 4 illustrates an exemplary method for implanting aluminum ions into a workpiece using dimethylaluminum chloride as a gaseous ion source material.

DETAILED DESCRIPTION

(5) 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 using dimethylaluminum chloride as an ion source material for producing atomic ions to electrically dope silicon, silicon carbide, or other semiconductor substrates at various temperatures. The present disclosure advantageously minimizes energetic cross-contamination of carbon in an aluminum implant when using dimethylaluminum chloride as the ion source material. Further, the present disclosure minimizes various deposits on extraction electrodes and source chamber components. The present disclosure will thus reduce associated arcing and glitching, and will further increase overall lifetimes of the ion source and associated electrodes.

(6) 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.

(7) 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.

(8) 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.

(9) 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.

(10) 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.

(11) In order to gain a general understanding of the disclosure, and in accordance with one aspect of the present disclosure, FIG. 1 illustrates an exemplary vacuum system 100. The vacuum system 100 in the present example comprises an ion implantation system 101, however various other types of vacuum systems are also contemplated, such as plasma processing systems, or other semiconductor processing systems. The ion implantation system 101, for example, comprises a terminal 102, a beamline assembly 104, and an end station 106.

(12) 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. The ion beam 112 in the present example is directed through a mass analyzer 114 (e.g., a beam-steering apparatus), and out an aperture 116 towards the end station 106. The mass analyzer 114, for example, includes a field generating component, such as a magnet, and operates to provide a field across a path 117 of the ion beam 112 so as to deflect ions from the ion beam at varying trajectories according to mass (e.g., mass-to-charge ratio). Ions traveling through the magnetic field experience a force which directs individual ions of a desired mass along the path 117 and which deflects ions of undesired mass away from the path. 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.

(13) 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.

(14) 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.

(15) 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, 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.

(16) 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. The ion beam 112 is extracted through an extraction aperture 140 of the arc chamber 134 via an electrical biasing of an extraction electrode 142 associated therewith. Heretofore, there has been no material 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 Al.sub.2O.sub.3 or AlN has been placed into the arc chamber where it is etched by a fluorine-based gas.

(17) 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, which can impact 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.

(18) Still further, when etching an aluminum oxide (Al.sub.2O.sub.3) or aluminum nitride (AlN) ceramic using a fluorine-based dopant gas (e.g., BF.sub.3, NF.sub.3, PF.sub.3, PF.sub.5), the resulting by-products of the reaction (e.g., AlF.sub.x, Al, N and neutrals of AlN and AL.sub.2O.sub.3) 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 the ion source arc slit optics plate (e.g., at a positive voltage), thus further reducing the productivity of the tool.

(19) In order to overcome the limitations or the prior art, the ion implantation system 101 of the present disclosure provides gaseous dimethylaluminum chloride (C.sub.4H.sub.10AlCl, 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.

(20) The DMAC, for example, is stored in a pressurized gas bottle as a liquid that transitions into vapor phase at room temperature at a predetermined pressure (e.g., a vacuum). 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 144 (e.g., BF.sub.3, PF.sub.3, etc.) is selectively provided to the arc chamber 134 via a secondary gas line 146, wherein the primary gas line 136 and secondary gas line are distinct and separate gas lines. The fluorine-containing gas source 144, for example, is a molecule or a pre-mixture of gases wherein at least one component thereof is fluorine.

(21) The inventors have observed that high beam currents (e.g., greater than approximately 30 ma) of singly-charged aluminum (Al+) can be achieved, but that beam currents of doubly-charged (Al++) are substantially lower (e.g., less than approximately 5 ma). In order to augment the production of doubly-charged aluminum, for example, a ceramic target consisting of either AlN or Al.sub.2O.sub.3 can be positioned on, or in close proximity to, a shaft comprised of a refractory metal that can be biased to a negative potential. Biasing the shaft to a negative potential, for example, generates a negative electric field that accelerates ions to the surface (e.g., increasing the ion current), which, in-turn, increases the temperature of the refractory metal shaft and the aluminum-based ceramic target. This increase in temperature, when using a fluorine-based gas molecule, thus increases the etch rate of the aluminum-based ceramic to form AlF.sub.x which is then cracked in the plasma to form AL+ and F. For example, the following reactions can occur:
AlN+F.sub.2.fwdarw.AlF.sub.3+N.sub.2(1), and
Al.sub.2O.sub.3+F.sub.2.fwdarw.AlF.sub.3+O.sub.2(2).

(22) There is also incidental sputtering of the ceramic target to form neutrals of nitrogen, oxygen, and aluminum, whereby such neutrals can be further ionized in the plasma. The provision of an aluminum-based sputter/etch target in conjunction with DMAC and one or more of a fluorine-containing molecule (e.g., BF.sub.3, PF.sub.3, PF.sub.5, etc.) and a pre-mix of other gases where at least one component is fluorine (e.g., BF.sub.3+Ar, He+F.sub.2), thus allows for lower flows of DMAC to the ion source. As such, an internal pressure of the arc chamber can be lowered (e.g., due to reduced charge exchange, longer mean free path), which can be further beneficial to the formation of doubly-charged aluminum ions.

(23) The reaction of fluorine and hydrogen, for example, is beneficial to the production of doubly-charged aluminum, as high hydrogen levels correlate to lower doubly-charged aluminum beam currents by the reaction,
H+F.fwdarw.HF(3).
Further, the chlorine component of DMAC will also etch the AlN and/or Al.sub.2O.sub.3 to form AlCl.sub.x, as
Al+Cl.sub.2.fwdarw.AlCl.sub.3(4),
which can then be ionized in the plasma.

(24) In accordance with another example, a further advantage of using a fluorine-based molecule as a co-gas when running DMAC is a reduction in energetic carbon cross-contamination. The co-gas may comprise one or more of a fluorine-containing molecule and a mixture of fluorine and one or more inert gases. In one example, the co-gas comprises one or more of BF.sub.3, SiF.sub.4, PF.sub.3, PF.sub.5, NF.sub.3, He+F.sub.2 (sometimes referred to as HeF.sub.2), and He+F.sub.2+Ar (sometimes referred to as HeF.sub.2Ar). For example, the addition of a fluorine-based molecule (e.g., BF.sub.3) or a pre-mixture of other gases where at least one component is fluorine (e.g., He+F.sub.2) to the provision of DMAC has been observed to reduce the contamination level by approximately 50% from 2.05e17 to 1e17, as seen when comparing an 85V biased electrode AMU spectra 202 to an 85V biased electrode with the provision of BF.sub.3 AMU spectra 204, as illustrated in the graph 200 of FIG. 2.

(25) Based, at least in part on the comparisons of the AMU spectras 202, 204, 206, and 208 of FIG. 2 and AMU spectra value comparisons 300 shown in FIG. 3, the present disclosure appreciates potential mechanisms for such variations. For example, fluorine (F) can be scavenging hydrogen (H) atoms from carbon (C), thus reducing a formation of C.sub.2H.sub.x+ species (e.g., where C.sub.2H.sub.3 is approximately the same atomic mass as Al+). In other examples, fluorine (F) can also be breaking carbon-to-carbon bonds (CC), or following reaction can occur to form CF.sub.x:
C.sub.2H.sub.3+5F.fwdarw.2CF+3HF(5).

(26) FIG. 4 illustrates an exemplary method 400 for implanting aluminum ions into a workpiece. It should be further noted that while exemplary methods are illustrated and described herein as a series of acts or events, it will be appreciated that the present invention is not limited by the illustrated ordering of such acts or events, as some steps may occur in different orders and/or concurrently with other steps apart from that shown and described herein, in accordance with the invention. In addition, not all illustrated steps may be required to implement a methodology in accordance with the present invention. Moreover, it will be appreciated that the methods may be implemented in association with the systems illustrated and described herein as well as in association with other systems not illustrated.

(27) In accordance with one exemplary aspect, in act 402 of FIG. 4, a gaseous ion source material is provided in the form of dimethylaluminum chloride (DMAC). The gaseous ion source material, for example, may be provided in a low pressure bottle (e.g., approximately 10-15 torr), whereby the DMAC is flowed from the low pressure bottle as a gas to an arc chamber of an ion source in act 404. In act 406, the ion source material comprising DMAC is ionized in the ion source to produce aluminum ions. In act 408, the aluminum ions are extracted from the ion source to form an ion beam comprising the aluminum ions, and in act 410, the aluminum ions are implanted into a workpiece.

(28) 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.