Plasma immersion method for ion implantation

Abstract

The present invention relates to a method of plasma immersion ion implantation using multiple precursor gases, particularly for the purpose of controlling the amount of a particular atomic dopant species implanted into a workpiece relative to other atomic species also implanted into the workpiece during the implantation process.

Description

Technical Field

[0001] The following description relates to plasma immersion ion implantation methods using multiple precursor gases, particularly for the purpose of controlling the amount of a particular atomic dopant species implanted into the workpiece relative to other atomic species also implanted into the workpiece during the implantation process. Background Art

[0002] In the materials and semiconductor processing industries, there are various reasons for modifying the chemical composition of a solid material by introducing one or more additional chemical species into the chemical composition of the solid material. Adding small amounts of different atoms or ions to the ordered structure of a solid material can have a useful and significant effect on the material properties of the solid material. For example, small amounts of dopant atoms are routinely added to semiconductor materials to affect the conductivity of the semiconductor material. Nitrogen or carbon atoms can be added to solid materials to improve mechanical properties (such as strength or wear resistance). In other examples, small amounts of impurities can be added to solid materials to affect the optical properties of the solid material.

[0003] A common technique for implanting dopants or impurities into solid materials is ion beam implantation. Ion beam implantation techniques implant relatively pure single ion species into solid materials to cause desired modifications to the chemical, optical, or mechanical properties of the implanted material. A typical ion beam implantation system includes an ion chamber that is used to form an ion plasma containing a mixture of many ion species. The ion mixture passes through an aperture in the ion chamber and into a high vacuum region where the ions are accelerated by an electric field to form an ion beam. The ion beam then passes through a mass analyzer to select and isolate a single ion species for implantation. In this way, an ion beam can be formed to include a high concentration of an ion species selected from the mixture of ion species in the plasma for implanting the single ion species into a workpiece.

[0004] Another technique for ion implantation is plasma immersion ion implantation. In plasma immersion ion implantation, a plasma is generated in a chamber, and the plasma contains a mixture of different chemical ion species. A workpiece is placed in the chamber and surrounded by the plasma containing the mixture of ion species. An electric potential is placed near the workpiece, such as below the workpiece, so that ions with opposite charge (relative to the electric potential) are accelerated toward the workpiece and implanted into the workpiece.

[0005] Comparisons between plasma immersion and beam-line techniques reveal a balance between cost, complexity, and performance characteristics. The high-energy ion beams produced by conventional (beam-line) ion implantation chambers penetrate relatively deeper into the workpiece than the low-energy ions implanted by ion immersion ion implantation. The ions provided by ion immersion ion implantation generally do not have the same high energy and are typically implanted to shallower depths than beam-line implantation. Consequently, the energy required to perform plasma immersion ion implantation is less than that required for beam-line ion implantation. The higher energy required by beam-line ion implantation allows for higher implantation energies for ions to penetrate deeper from the substrate surface, but at the expense of increased cost and operational complexity. In contrast, ion immersion ion implantation uses RF power (radio frequency power generator) to dissociate ions into a plasma, which requires less energy and reduces equipment complexity. Similarly, plasma immersion ion implantation can deliver high-dose implants in a relatively short time, thereby improving throughput. Therefore, compared to beam-line implantation, plasma immersion ion implantation can be considered a cost-effective ion implantation technique for certain low-energy and high-dose processes.

[0006] The performance difference caused by the elimination of the ion beam is a reduction in the selectivity of the ionic and atomic species implanted by the plasma immersion method. Plasma immersion technology does not involve an ion beam that can be filtered to isolate (select) the desired ionic species of the plasma for implantation. Plasma ion implantation technology cannot effectively select specific ion species from the plasma for implantation. All ions with a common charge in the plasma are accelerated toward the workpiece and will be implanted into the workpiece, meaning that many different types of ionic and atomic species will be implanted into the wafer. If the plasma contains a mixture of ionic species that includes boron, fluorine, and hydrogen atoms as atomic species, some amount of boron, fluorine, and hydrogen will be implanted into the workpiece.

[0007] Due to the non-selective nature of this implantation technique, a significant technical challenge facing plasma immersion technology is the limited level of control over the relative amounts of different atomic species implanted within the workpiece. While the ratio of implanted atomic species can be influenced to some extent by adjusting plasma tool parameters, the level of control afforded in this manner is limited. Therefore, techniques are needed to better control the ratio of the amounts of implanted atomic species when using plasma immersion technology. Summary of the Invention

[0008] The present invention describes techniques that allow for improved control over the relative amounts of atomic species implanted into a workpiece ("implanted atomic species") using plasma immersion ion implantation techniques. The methods include selecting and using a combination of two or more different gaseous precursors to generate a plasma used in a plasma immersion ion implantation process. The chemical compositions of the gaseous precursors and their relative amounts are selected to increase the amount of a selected atomic species (e.g., a "dopant") implanted into the workpiece relative to other, less desirable or undesirable, atomic species that are also implanted into the workpiece during the implantation process.

[0009] In one aspect, the present invention relates to a method of ion implantation. The method includes supporting a workpiece in a chamber; generating a plasma from a precursor mixture including a first precursor and at least one additional precursor different from the first precursor, wherein the ions include at least two different plasma ion species, and the at least two different plasma ion species include a selected atomic species and one or more additional atomic species. The method also includes applying an electric potential to the workpiece to accelerate the at least two different plasma ion species toward the workpiece to implant the selected atomic species and the one or more additional atomic species onto a surface of the workpiece. The at least one additional precursor causes an increased amount of the selected atomic species to be implanted into the workpiece.

[0010] In another aspect, the present invention relates to a plasma immersion ion implantation system comprising a chamber including a plasma generator comprising an RF antenna, a workpiece support, and an electrode. The system further comprises a source of a first precursor and a source of at least one additional precursor different from the first precursor. The system is adapted to support a workpiece on the workpiece support and generate a plasma from the precursors. The plasma comprises at least two different plasma ion species, and the two plasma ion species comprise a selected atomic species and one or more additional atomic species. The system is also adapted to accelerate the at least two different plasma ion species toward the workpiece to implant the selected atomic species and the one or more additional atomic species onto a surface of the workpiece. The at least one additional precursor causes an increased amount of the selected atomic species to be implanted into the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Example plasma immersion ion implantation tools and systems are described for use in describing the method. DETAILED DESCRIPTION

[0012] The following describes a plasma immersion ion implantation technique that uses two or more chemically distinct gaseous precursors to form a plasma.

[0013] Plasma immersion technology is non-selective with respect to the ion species of the plasma mixture implanted into the workpiece. The technology generally involves the non-selective implantation of ion species from a plasma containing a mixture of multiple chemically different ion species. The number and type of ion species produced will depend on the chemical composition of the gaseous precursor used to generate the plasma. Each ion species may contain one or more atomic species and may exhibit a positive or negative charge. The workpiece is placed in a chamber and surrounded by the mixture of ion species of the ions. An electric potential causes ions having an opposite charge relative to the electric potential to be accelerated toward the workpiece and implanted into the workpiece. The implantation is non-selective, i.e., uncontrolled, with respect to the different types of ions (having a common charge) and the amount of different atomic species present in the plasma. Regardless of the chemical composition, all ion species in the plasma having an opposite charge to the electric potential are accelerated toward the workpiece.

[0014] According to the present invention, applicants have identified techniques that allow for improved control over the relative amounts of atomic species implanted into a workpiece using plasma immersion ion implantation techniques. The methods include selecting and using a combination of two or more chemically distinct gaseous precursors to generate a plasma for use with the ion immersion ion implantation technique. The chemical compositions of the two or more different gaseous precursors and the relative amounts of each selected and used to generate the ions can be selected and controlled to cause an increase in the amount of a particularly desired atomic species (e.g., a "dopant") (referred to herein as the "selected atomic species") implanted into the workpiece relative to other, less desirable or undesirable atomic species ("additional atomic species") that are also implanted into the workpiece during the implantation process.

[0015] The plasma immersion ion implantation method of the present disclosure involves generating a plasma from two or more chemically distinct gaseous precursors for implantation via a plasma immersion implantation technique. At least one of the gaseous precursors includes an atomic species desired for implantation into a workpiece (a "selected" atomic species), such as a dopant species when present in a component of the workpiece. The method as described allows for improved control over the relative amount of the selected atomic species implanted into the workpiece compared to other implanted atomic species, particularly allowing for implantation of a higher amount (percentage) of the selected atomic species compared to the amount of other (additional) atomic species implanted into the workpiece.

[0016] Based on two specific (non-limiting) examples of the method as described, the atomic species implanted into the workpiece may be boron, fluorine, or a combination of boron and fluorine. Boron and fluorine are commonly used as dopant species in semiconductor materials.

[0017] Although this description uses boron and fluorine as two specific examples of implanted (e.g., "dopant") species, either of which may be the "selected" atomic species, the methods of this description may be effective for use with other atomic species as implanted species; for example, the methods described herein may be used to control or increase the amount (percentage) of a particular selected atomic species (other than fluorine or boron) implanted in a workpiece relative to the total amount of atomic species implanted.

[0018] The amount of the selected atomic species implanted in the workpiece can be increased by at least 5%, 10%, 20%, 30%, 50%, or, in some example methods, by as much as 100%, compared to the controlled amount (percentage) achieved in a process using only one gaseous precursor (i.e., a single gaseous precursor) to prepare the plasma (i.e., in the absence of one or more additional precursors). For example, if the amount of a selected implanted atomic species implanted by a method of generating a plasma using a gaseous precursor (in the absence of one or more additional precursors) is 35% of the total atomic species implanted in the workpiece by the method, the increase in the amount of the selected implanted atomic species may be at least 5%, 10%, 20%, 30%, 50% or 100% greater than the 35% base number, that is, at least 36.75%, 38.5%, 42%, 45.5%, 52.5% or 70% of the total amount of implanted atomic species is the selected species (and the remaining 63.25%, 61.5%, 58%, 54.5%, 47.5% and 30% of the total implanted atomic species are one or more additional implanted atomic species).

[0019] In this example, the 35% value for the selected atomic species is a baseline ("base") value for the amount of the selected species implanted to prepare a plasma using a plasma ion immersion implantation technique using a single gaseous precursor. As an example, when BF3 is used alone as the single gaseous plasma precursor to prepare a plasma using a plasma ion immersion implantation technique, the baseline percentage of boron implanted as the implanted atomic species may be in the range of approximately 34 to approximately 35 atomic percent, with the remainder of the implanted atomic species (i.e., approximately 65 to approximately 66 atomic percent) being fluorine. The increased relative amount of boron as the selected implanted atomic species may be an amount that is at least 5, 10, 20, 30, 50, or 100 atomic percent greater than the 35% base, as the percentage of the total implanted atomic species, for example, the amount of implanted boron, based on the total amount of all implanted atomic species, is at least 36.75, 38.5, 42, 45.5, 52.5, or 70 atomic percent.

[0020] According to typical (previous and current) commercial methods for implanting boron or fluorine as the selected atomic species, BF3 or B2H6 is used as a gaseous precursor. When BF3 is the precursor, the plasma will contain B + 、F+ , BF + 、BF2 + and BF3 + These various ionic species and atomic species of boron and fluorine from these ions will be implanted into the workpiece, and neither the ionic species nor the atomic species are selective to control the relative amounts of implanted boron and fluorine.

[0021] According to the methods of the present description, a plasma can be generated from two or more chemically distinct gaseous precursors, and the gaseous precursors can be specifically selected to cause a relatively higher or increased amount of a particularly desired (i.e., "selected") atomic species to be implanted in a workpiece relative to all implanted (selected and unselected) atomic species. The amount of the selected implanted atomic species implanted in the workpiece as a percentage of the total implanted atomic species (total selected implanted species and implanted unselected species) can be at least 20%, e.g., 25%, 35%, 45%, 55%, 65%; that is, the amount of the selected implanted atomic species can be at least 20%, e.g., 25%, 35%, 45%, 55%, 65%, or more, of the total amount of implanted selected and implanted unselected atomic species. As described herein, using two or more chemically distinct gaseous precursors to generate a plasma is a technique that can be used to increase the amount of the selected atomic species implanted in a workpiece relative to the total amount of all implanted atomic species when compared to a similar plasma immersion ion implantation method in which the plasma is generated from only a single gaseous precursor. According to the methods described herein, a plasma is generated from a precursor mixture comprising a first precursor and at least one additional precursor different from the first precursor. The ions comprise at least two different plasma ion species, and the at least two different plasma ion species comprise a selected atomic species and one or more additional atomic species. The at least one additional precursor used to form the plasma causes an increase in the amount (percentage) of the selected atomic species implanted in a workpiece relative to all implanted atomic species, compared to performing the method without using the at least one additional precursor to form the plasma, i.e., by forming the plasma with only the first precursor.

[0022] According to useful and preferred examples of the methods described herein, the selected atomic species may be boron or fluorine, and the gaseous precursors that can be used to generate the plasma may include one selected from the following groups (e.g., both precursors may be selected from a single group), or a combination of two or more chemically different gaseous precursors selected from two or more of the following groups.

[0023] Group A - Boron fluoride gas: BF3, B2F4, B x F y .

[0024] Group B - Boron hydride gas: B2H6, Bx H y .

[0025] Group C - Mixed boron fluoride: BHF2, BH2F, B x H y F z .

[0026] Group D - other boron gases: BCl3, B x A y (A may be an element other than fluorine).

[0027] Group E - Fluorine or fluoride gases (non-boron): F2, SiF4, Si2F6, GeF4, Ge2F6, CF4, C2F6, XeF2, PF3, PF5, AsF3, AsF5, NF3, SF6, A x F y (A may be an element other than boron).

[0028] Group F - Inert gases: He, Ne, Ar, Kr, Xe and N2.

[0029] Group G - Hydrogen and hydride gases: H2, SiH4, Si2H6, GeH4, Ge2H6, PH3, AsH3, CH4, C2H6, NH3, A x H y .

[0030] Group H - oxygen and oxide gases: O2, O3, N2O, N4O, NO2, N2O3, N2O4, N2O5, CO, CO2, A x O y .

[0031] In these and other example methods, the plasma may be generated from a gaseous precursor containing a combination of two chemically distinct gaseous precursors as described herein, selected from one or more of Groups A, B, C, D, and E, and may additionally include one or more gases selected from Groups F, G, and H. The relative amounts of the first precursor and the second precursor may be any effective or preferred amount, such as a relative amount of 10:90 to 90:10 (molar), such as a relative amount in the range of 40:60 to 60:40.

[0032] According to other example methods, the plasma may include one or more of a third gaseous precursor, a fourth gaseous precursor, and a fifth or additional gaseous precursor, each selected from any one of Groups A, B, C, D, and E.

[0033] In certain specific example methods, the selected atomic species is boron, and both gaseous precursors can be selected from Group A. Alternatively, the two gaseous precursors can be selected by using one gaseous precursor from Group B and one gaseous precursor from Group D. As examples: the first gaseous precursor can be BF3, and the second gaseous precursor can be B2F4; or the first gaseous precursor can be BF3, and the second gaseous precursor can be B2H6; or the first gaseous precursor can be B2F4, and the second gaseous precursor can be B2F6.

[0034] In these example methods, boron is the selected atomic species, and fluorine and, optionally, hydrogen are unselected atomic species. The amount of boron implanted into the workpiece as the selected atomic species may be at least 20%, e.g., 25%, 35%, 45%, 55%, 65%, 75%, 85%, or 95% (atomic), of the total implanted atomic species; that is, the amount of implanted boron is at least 20%, e.g., 25%, 35%, 45%, 55%, 65%, 75%, 85%, or 95% (atomic), of the total amount of implanted boron and implanted non-boron atomic species. In preferred example methods, when the plasma is derived from a combination of two or more chemically distinct gaseous precursors as described herein, the amount (percent, atoms) of boron implanted in the workpiece, relative to the total amount of all implanted atomic species (boron plus non-boron atomic species) in the workpiece, can be greater than the amount (percent, atoms) of boron implanted using the same workpiece by a similar (e.g., the same) plasma immersion ion implantation method in which the plasma is generated from only a single gaseous precursor compound (e.g., BF3 or B2F4) rather than a mixture of two or more gaseous precursors (compounds).

[0035] As an additional potential benefit of the methods described herein, selecting useful or preferred types and amounts of two or more gaseous precursors for implanting boron as the selected atomic species can result in reduced levels of boron particles or boron coating materials that are present or accumulate on interior surfaces of the chamber of a plasma immersion ion implantation tool during plasma immersion ion implantation. Reducing particle formation and deposition within the chamber can also increase system operating time (uptime) by reducing downtime and can also increase the useful life of a plasma immersion ion implantation system.

[0036] In other example methods, the dopant atomic species is fluorine, and both gaseous precursors can be selected from Group E. As examples: the first gaseous precursor can be F2, and the second gaseous precursor can be BF3 or HF; or the first gaseous precursor can be NF3, and the second gaseous precursor can be CF4.

[0037] In these example methods, fluorine is the selected atomic species, and one or more non-fluorine atomic species of any of the two or more gaseous precursors may be unselected atomic species. The amount of fluorine implanted into the workpiece may be at least 40%, for example, 45%, 55%, 65%, 75%, 85%, or 95% (atomic) of the total implanted atomic species, i.e., the amount of implanted fluorine may be at least 40%, for example, at least 45%, 55%, 65%, 75%, 85%, or 95% (atomic) of the total amount of implanted fluorine and any implanted non-fluorine atomic species. In preferred methods, when the plasma is derived from a combination of two or more chemically distinct gaseous precursors as described herein, the amount (percentage, atoms) of fluorine implanted into the workpiece relative to the total amount of all implanted atomic species (fluorine plus non-fluorine atomic species) in the workpiece may be greater than the amount (percentage, atoms) of fluorine implanted using the same workpiece by a similar plasma immersion ion implantation method in which the plasma is generated from only one gaseous precursor (e.g., BF3).

[0038] The methods described herein for using multiple gaseous precursors to generate a plasma in a plasma immersion ion implantation process can be used with any desired gaseous precursor, any selected atomic species, and any desired workpiece into which the selected atomic species is to be implanted. Certain methods are suitable for increasing the relative amount (percent, atoms) of the selected atomic species implanted in the workpiece relative to the total amount of implanted atomic species (selected and unselected atomic species). These preferred methods can increase the amount (percent, atoms) of the selected atomic species implanted in a workpiece relative to the amount of the selected atomic species implanted in a comparable (e.g., identical) workpiece prepared using a comparable implantation process that is identical to the present invention but uses only a single gaseous precursor to generate the plasma.

[0039] Plasma immersion ion implantation techniques can be used for surface doping or modification by extracting ions from a plasma containing a mixture of different ions, as described herein, and applying a high voltage to a workpiece (retained within the plasma) or an electrode supporting the workpiece to accelerate the ions toward a substrate. The accelerated ions from the plasma penetrate into the workpiece. The workpiece can be any object or device into which one or a combination of ions can be desirably introduced, such as a semiconductor wafer or a microelectronic device substrate. Compared to beamline implantation tools, plasma immersion implantation tools are less complex due to the lack of a mass analyzer (required in beamline ion implantation systems) that can select the desired ions for implantation from a plasma containing many different ion species. Ion immersion ion implantation tools do not require equipment for generating, focusing, and refining an ion beam. Consequently, plasma immersion ion implantation techniques can yield advantages such as: lower power requirements; lower energy or higher dose of ions delivered to the workpiece, or both; relatively better conformal doping; reduced overall hardware and operating costs; or two or more of these.

[0040] The methods described herein can be performed using conventional plasma immersion tools operating according to known plasma immersion ion implantation principles and using a combination of two or more gaseous precursors as described herein. A plasma produced from a mixture of different ion species derived from two or more gaseous precursors can be formed by applying a high voltage RF or any other form of EM field (microwave or DC) to a process chamber containing the gaseous precursors. The ions are then deflected toward the workpiece surface and implanted to a desired depth from the substrate surface.

[0041] Figure 1 An example plasma immersion ion implantation chamber suitable for use in performing methods as described herein is shown. Figure 1 The chamber is suitable for performing plasma immersion ion implantation methods, but can also be used to expose a substrate to high energy ions without implanting the ions below the surface. Thus, as used herein, the term "implantation" refers to placing ions or atoms at or below the surface of a workpiece by a method as described herein.

[0042] The processing chamber 100 includes a chamber body 102 having a bottom 124, a top 126, and sidewalls 122 that enclose the chamber interior 104. A substrate support assembly 128 is supported from the bottom 124 of the chamber body 102 and includes a support plate 200 adapted to receive a substrate 300 for processing. Optionally, the substrate support assembly 128 may include embedded heater elements or cooling elements (not shown) adapted to control the temperature of the support plate 200 supported by the substrate 300.

[0043] A vacuum port 132 is defined in the chamber body 102 and is coupled to a vacuum pump (not shown) for evacuating the chamber 104 during operation.

[0044] Gaseous precursors are introduced into the chamber 104 from various sources, for example, through one or more inlet ports 130 , to supply the gaseous precursors into the chamber 104 for processes performed on the substrate 300 .

[0045] Also present within the chamber 104 is an RF antenna 310 that is connected to an RF generator (not shown) to activate the RF antenna and generate a plasma 320 by dissociating gaseous precursor compounds.

[0046] In use, a process gas comprising two or more gaseous precursors as described herein is supplied to the chamber 104 from a process gas source (not shown) through one or more inlet ports 130 and converted into a plasma 320 by the RF antenna 310. The RF antenna and RF generator may be configured to effectively dissociate the compound of the two or more gaseous precursors into implantable ionic species, which are directed toward the surface of the substrate 300 by the potential generated by the pulse generator 330. The operating parameters of the system described herein, such as the power of the RF generator and the power and frequency of the pulse generator, may be selected to produce ionic species of the plasma that can be accelerated toward the substrate surface and implanted to a desired depth below the top surface of the substrate 300 at a desired ion concentration.

[0047] In example operation, the power of RF power dissociates the gaseous precursor to produce the required ion flux on the surface of the substrate. The RF power is controlled to accelerate the ion energy dissociated from the process gas toward the substrate surface and implanted into the desired depth below the top surface of the substrate with the required ion concentration. In exemplary terms, a relatively low bias voltage (e.g., 50V) can result in a relatively low ion energy, for example, within the range of 50eV. Dissociated ions with low ion energy can be implanted into a shallower depth from the substrate surface. Alternatively, a higher bias voltage of about 100kV can produce higher ion energy, for example, within the range of 100keV. Dissociated ions with high ion energy provided and produced by relatively high RF power and bias voltage (such as higher than about 100keV) can be implanted into a substrate much deeper from the substrate surface.

Claims

1. An ion implantation method comprising: supporting the workpiece in the chamber; generating a plasma from a precursor mixture comprising a first precursor and at least one additional precursor different from the first precursor, wherein the plasma comprises at least two different plasma ion species, and wherein the at least two different plasma ion species include a selected atomic species and one or more additional atomic species; applying an electric potential to the workpiece to accelerate the at least two different plasma ion species toward the workpiece to cause the selected atomic species and the one or more additional atomic species to be implanted onto a surface of the workpiece; wherein the at least one additional precursor causes an increased amount of a selected atomic species to be implanted into the workpiece, wherein the amount of the selected atomic species implanted into the workpiece is at least 5% greater than the amount of the selected atomic species implanted by a method lacking the at least one additional precursor. 2 . The method of claim 1 , wherein the amount of the selected atomic species implanted in the workpiece is at least 20% of the total amount of implanted atomic species.

3. The method of claim 1 , wherein the selected atomic species is boron or fluorine, the one or more additional atomic species comprise boron, fluorine, hydrogen, or a combination thereof, and the first precursor and the at least one additional precursor comprise: a first precursor selected from Groups A, B, C, D, or E, and a second precursor selected from Group A, B, C or D different from the first precursor, in: Group A includes boron fluoride gases; Group B includes boron hydride gases; Group C includes mixed hydrogen fluoride and boron gases; Group D includes boron gas; and Group E includes fluorine or fluoride gases.

4. The method according to any one of claims 1 to 3, wherein the precursor mixture comprises One or more precursors of Group F, G or H, wherein: Group F includes inert gases; Group G includes hydrogen and hydride gases; and Group H includes oxygen and oxide gases.

5. The method of any one of claims 1 to 3, wherein the selected atomic species is boron, and The amount of boron implanted into the workpiece is at least 20% of the total amount of implanted atomic species.

6. The method of any one of claims 1 to 3, wherein the selected atomic species is fluorine, and The amount of fluorine implanted into the workpiece is at least 40% of the total amount of implanted atomic species.

7. The method according to any one of claims 1 to 3, wherein the first precursor is selected from HF, F2, SiF4, Si2F6, GeF4, Ge2F6, CF4, C2F6, XeF2, PF3, PF5, AsF3, AsF5, NF3, SF6 and A x F y Wherein A is an element other than boron. The method according to claim 3 , wherein a molar ratio of the first precursor to the second precursor is in the range of 10:90 to 90:

10.

9. A plasma immersion ion implantation system comprising: a chamber comprising: a plasma generator comprising an RF antenna, workpiece supports, and electrode, the source of the first precursor, and a source of at least one additional precursor different from said first precursor, The system is suitable for: supporting a workpiece on the workpiece support; generating a plasma from the precursor, wherein the plasma comprises at least two different plasma ion species, and the at least two different plasma ion species include a selected atomic species and one or more additional atomic species; and accelerating the at least two different plasma ion species toward the workpiece to cause the selected atomic species and the one or more additional atomic species to be implanted onto a surface of the workpiece; wherein the at least one additional precursor causes an increased amount of a selected atomic species to be implanted into the workpiece, and wherein the amount of the selected atomic species implanted into the workpiece is at least 5% greater than the amount of the selected atomic species implanted by a method lacking the at least one additional precursor.

10. The method of claim 3, wherein group D comprises BCl3 or another boron gas having the general formula BxAy, A being an element other than fluorine.

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