US20110021011A1 - Carbon materials for carbon implantation - Google Patents

Abstract

A method of implanting carbon ions into a target substrate, including: ionizing a carbon containing dopant material to produce a plasma having ions; optionally co-flowing an additional gas or series of gases with the carbon-containing dopant material; and implanting the ions into the target substrate. The carbon-containing dopant material is of the formula C_wF_xO_yH_zwherein if w=1, then x>0 and y and z can take any value, and wherein if w>1 then x or y is >0, and z can take any value. Such method significantly improves the efficiency of an ion implanter tool, in relation to the use of carbon source gases such as carbon monoxide or carbon dioxide.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• The benefit of priority to U.S. Provisional Patent Application No. 61/227,875 filed Jul. 23, 2009 in the names of Joseph D. Sweeney, Oleg Byl and Robert Kaim for “Carbon Materials for Carbon Implantation” is hereby claimed under 35 USC 119. The disclosure of such U.S. Provisional Patent Application No. 61/227,875 is hereby incorporated herein by reference, in its entirety.
TECHNICAL FIELD
• The present disclosure relates to ion implantation methods and systems, and more particularly, to carbon materials for carbon ion implantation in such systems.
BACKGROUND
• Ion implantation is used in integrated circuit fabrication to accurately introduce controlled amounts of dopant impurities into semiconductor wafers and is one of the processes of microelectronic/semiconductor manufacturing. In such implantation systems, an ion source ionizes a desired dopant element gas, and the ions are extracted from the source in the form of an ion beam of desired energy. Extraction is achieved by applying a high voltage across suitably-shaped extraction electrodes, which incorporate apertures for passage of the extracted beam. The ion beam is then directed at the surface of a workpiece, such as a semiconductor wafer, in order to implant the workpiece with the dopant element. The ions of the beam penetrate the surface of the workpiece to form a region of desired conductivity.
• Several types of ion sources are used in ion implantation systems, including the Freeman and Bernas types that employ thermoelectrodes and are powered by an electric arc, microwave types using a magnetron, indirectly heated cathode (IHC) sources, and RF plasma sources, all of which typically operate in a vacuum. In any system, the ion source generates ions by introducing electrons into a vacuum arc chamber (hereinafter “chamber”) filled with the dopant gas (commonly referred to as the “feedstock gas”). Collisions of the electrons with atoms and molecules in the dopant gas result in the creation of ionized plasma consisting of positive and negative dopant ions. An extraction electrode with a negative or positive bias will respectively allow the positive or negative ions to pass through an aperture as a collimated ion beam, which is accelerated towards the target material.
• In many ion implantation systems, carbon, which is known to inhibit diffusion, is implanted into the target material to produce a desired effect in the integrated circuit device. The carbon is generally implanted from a feedstock gas such as carbon monoxide or carbon dioxide. The use of carbon monoxide or carbon dioxide gases can result in oxidation of the metal surfaces within the plasma source (arc chamber) of the ion implanter tool, and can also result in carbon residues depositing on electrical insulators. These phenomena reduce the performance of the implanter tool, thereby resulting in the need to perform frequent maintenance. Oxidation can result in inefficiencies in the implantation process.
• Frequency and duration of preventive maintenance (PM) is one performance factor of an ion implantation tool. As a general tendency the tool PM frequency and duration should be decreased. The parts of the ion implanter tool that require the most maintenance include the ion source, which is generally serviced after approximately 50 to 300 hours of operation, depending on operating conditions; the extraction electrodes and high voltage insulators, which are usually cleaned after a few hundred hours of operation; and the pumps and vacuum lines of vacuum systems associated with the tool. Additionally, the filament of the ion source is often replaced on a regular basis.
• Ideally, feedstock molecules dosed into an arc chamber would be ionized and fragmented without substantial interaction with the arc chamber itself or any other components of the ion implanter. In reality, feedstock gas ionization and fragmentation can results in such undesirable effects as arc chamber components etching or sputtering, deposition on arc chamber surfaces, redistribution of arc chamber wall material, etc. In particular, the use of carbon monoxide or carbon dioxide gases can result in carbon deposition within the chamber. This can be a contributor to ion beam instability, and may eventually cause premature failure of the ion source. The residue also forms on the high voltage components of the ion implanter tool, such as the source insulator or the surfaces of the extraction electrodes, causing energetic high voltage sparking. Such sparks are another contributor to beam instability, and the energy released by these sparks can damage sensitive electronic components, leading to increased equipment failures and poor mean time between failures (MTBF).
• In another instance of undesirable deposition, various materials (such as tungsten) can accumulate on components during extended ion implantation processes. Once enough tungsten is accumulated, the power used to maintain temperature sufficient to meet the beam current setpoint may not be sustainable. This causes loss of ion beam current, which leads to conditions that warrant the replacement of the ion source. The resultant performance degradation and short lifespan of the ion source reduces productivity of the ion implanter tool.
• Yet another cause of ion source failure is the erosion (or sputtering) of material. For example, metallic materials such as tungsten (e.g., the cathode of an IHC source or the filament of a Bernas source) are sputtered by ions in the plasma of the arc chamber. Because sputtering is dominated by the heaviest ions in the plasma, the sputtering effect may worsen as ion mass increases. In fact, continued sputtering of material “thins” the cathode eventually leading to formation of a hole in the cathode (“cathode punch-through” in the case of IHC), or for the case of the Bernas source, creates an opening in the filament. Performance and lifetime of the ion source are greatly reduced as a result. The art thus continues to seek methods that can maintain a balance between the accumulation and erosion of material on the cathode to prolong the ion source life.
SUMMARY
• In one aspect, the present disclosure relates to a method of implanting carbon ions into a target substrate. This method comprises: ionizing a carbon-containing dopant material to produce a plasma having ions; and implanting the ions into the target substrate. The carbon-containing dopant material is of the formula C_wF_xO_yH_zwherein if w=1, then x>0 and y and z can take any value, and wherein if w>1 then x or y is >0, and z can take any value.
• In another aspect, the present disclosure relates to another method of implanting carbon ions into a target substrate. This method comprises: ionizing a carbon-containing dopant material to produce a plasma having ions; co-flowing an additional gas or series of gases with the carbon-containing dopant material; and implanting the ions into the target substrate. The carbon-containing dopant material is of the formula C_wF_xO_yH_z, wherein w, x, y and z are as defined above.
• In another aspect, the present disclosure relates to a method of improving the efficiency of an ion implanter tool. This method comprises: selecting a carbon-containing dopant material of the formula C_wF_xO_yH_zfor use in the ion implanter tool in a chamber, wherein w, x, y and z are as defined above; ionizing the carbon-containing dopant material; and implanting a carbon ion from the ionized carbon-containing dopant material using the ion implanter tool. The selecting of the material of the formula C_wF_xO_yH_zminimizes the amount of carbon and/or non-carbon elements deposited in the chamber after the implanting of the carbon ion. In doing so, the performance of the ion source is optimized.
• Other aspects, features and embodiments of the present disclosure will be more fully apparent from the ensuing description and appended claims.
DETAILED DESCRIPTION
• In accordance with the present disclosure, carbon ions are implanted from a feedstock source material into the target material of a substrate via an ion implantation process. In one exemplary embodiment, an ion source generates the carbon ions by introducing electrons into a vacuum arc chamber filled with a carbon-containing dopant gas as the feedstock material. The chamber has tungsten walls on which a filament electrode and a repeller electrode are mounted and separated from the walls by ceramic insulators. Collisions of the electrons with molecules in the carbon-containing dopant gas result in the creation of ionized plasma consisting of positive carbon ions. The ions are then collimated into an ion beam, which is accelerated towards the target material. The beam may be directed through a mask having a plurality of openings therein to implant the carbon ions in the desired configuration. The present disclosure is not limited in this regard as other means of implanting carbon ions are within the scope of the present disclosure. Furthermore, the present disclosure is not limited to the implantation of carbon ions, as any ion other than carbon (or in addition to carbon) can be selected for implantation.
• In any embodiment, to generate the carbon ions, the carbon-containing dopant material has the formula C_wF_xO_yH_zwherein if w=1, then x>0 and y and z can take any value, and wherein if w>1 then x or y is >0, and z can take any value. The carbon atom is separated from the remainder of the molecule, thereby resulting in an ionized plasma that includes positive carbon ions. The positive carbon ions may be singular, or they may form clusters of two or more carbon atoms. Alternatively, molecular ions of the form C_aF_bO_cH_d⁺, wherein a>0, and b, c, and d can have any value, may be formed in order to co-implant multiple atomic species simultaneously. For example, implanting an ion such as CF⁺ may eliminate a later F⁺ implant. For cases in which co-implantation of species compromises the integrated circuit quality or performance, the carbon dopant material can be used to produce non-carbon ions for implantation. An example would be the implantation of F⁺. The benefit is that a second dopant material containing fluorine may not be required.
• The ratios of C, F, O, and H (as denoted by w, x, y, and z) are chosen to optimize ion source life and beam current. While the use of carbon achieves specific integrated circuit device characteristics, the carbon will deposit within the ion source chamber of the ion implanter, causing electrical shorts or particle generation. Additionally, the carbon can cause sputtering of the cathode (IHC source) or filament (Bernas source), resulting in shortened ion source life. The presence of oxygen within the dopant material helps to minimize the deposition of carbon by oxidizing carbon deposits to form CO or CO2. However, the oxygen can also oxidize components of the ion source, such as the cathode or the filament. The oxidation of these components may degrade the performance of the ion implant tool, thereby leading to frequent maintenance requirements. By adding fluorine to the dopant source, the oxidation of the cathode or filament can be minimized. However, fluorine can also react with the metallic walls of the arc chamber (usually tungsten or molybdenum), forming gases of the formula WF, or MoF_xwherein x=1-6. When these gases contact the cathode or filament, they tend to react and deposit tungsten. While this is beneficial in that it can help balance any sputtering due to the ions within the plasma, it may be desirable to add some hydrogen to the molecule to balance the tungsten deposition rate (hydrogen will restrict the ability of the fluorine from reacting with the metallic walls to form the metal fluorides that subsequently cause metal deposition on the cathode or filament).
• In one embodiment, the C_wF_xO_yH_zsource gas comprises COF₂. When COF₂is used as the source gas, the molecule is ionized in the arc chamber, and C⁺ ions are separated via mass analysis and then implanted into the target material. Within the arc chamber, O and F ions and neutrals are also present. The oxygen helps to minimize carbon deposits, while the fluorine serves to keep the cathode or filament from forming an oxide surface layer. In this manner, the performance of the ion source is greatly improved.
• The present disclosure also contemplates the simultaneous flowing of C_wF_xO_yH_zmaterial(s) with oxygen or an oxygen-containing gas such as air to modify or control the ratios of C, F, O, and H, thereby further modifying or controlling the amount of carbon ions implanted and optimizing the trade-off between carbon ions implanted and oxide formation. In particular, the C_wF_xO_yH_zcan be co-flowed with COF₂, CO₂, CO, or any other oxygen-containing gas. Without being bound by theory, it is contemplated that the co-flowing of COF₂or similar gases balances the deposition of the carbon ion with the coating of the arc chamber and etching.
• The present disclosure additionally contemplates the simultaneous flowing of C_wF_xO_yH_zmaterial(s) with gases such as fluorine and hydrogen or dilution with inert gases such as nitrogen, argon, xenon, helium, combinations of the foregoing, and the like. The use of inert gases helps to sustain a plasma when flowing dopant gases.
• By adjusting the ratios of elements in and generating carbon ions from a carbon-containing dopant gas having the formula C_wF_xO_yH_z(and optionally co-flowing the dopant gas with COF₂, CO₂, CO, (or another carbon-containing molecule) fluorine, hydrogen, nitrogen, argon, or the like), the amount of carbon implanted is maximized and the amounts of non-carbon elements are minimized with regard to the deposition thereof within the chamber. In such manner, the efficiency of the implanter tool can be improved. Additionally, the downtime of such a tool (for maintenance, cleaning, and the like) can also be reduced.
• Furthermore, the C_wF_xO_yH_zmaterial could be flowed simultaneously with up to four additional gases. Such gases include, but are not limited to, (1) CO+F₂+H₂+O₂; (2) CO+COF₂+H₂; and (3) CF₄+CH₄+O₂. The present disclosure is not limited in this regard as other gases are within the scope of the present invention.
• Although this disclosure has included various detailed embodiments, it will be understood by those of skill in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiments disclosed in the above detailed description, but that the disclosure will include all embodiments falling within the spirit and scope of the foregoing description.

Claims (16)

1. A method of implanting a carbon ion into a target substrate, comprising:

ionizing a carbon-containing dopant material to produce a plasma having ions; and

implanting the ions into the target substrate;

wherein the carbon-containing dopant material is of the formula C_wF_xO_yH_zwherein if w=1, then x>0 and y and z can take any value, and wherein if w>1 then x or y is >0, and z can take any value.

2. The method ofclaim 1, wherein the ions of the plasma produced are of the form C_aF_bO_cH_d⁺, wherein a>0, and b, c, and d can have any value.

3. The method ofclaim 1, wherein upon ionizing the carbon-containing dopant material, the carbon ions are clustered in groups of at least two carbon atoms.

4. The method ofclaim 1, wherein the carbon-containing dopant material is COF₂.

5. The method ofclaim 1, further comprising selecting the ratios of w, x, y, and z to produce a feed material of the formula C_wF_xO_yH_zprior to the step of ionizing to produce the plasma.

6. The method ofclaim 1, further comprising co-flowing an additional gas or series of gases with the carbon-containing dopant material, the additional gas comprising one or more of carbon, oxygen, fluorine, hydrogen, nitrogen, argon, xenon, air, and helium.

7. A method of implanting carbon ions into a target substrate, comprising:

ionizing a carbon-containing dopant material to produce a plasma having ions;

co-flowing an additional gas or series of gases with the carbon-containing dopant material; and

implanting the ions into the target substrate;

wherein the carbon-containing dopant material is of the formula C_wF_xO_yH_z.

8. The method ofclaim 7, wherein the ions of the plasma produced are of the form C_aF_bO_cH_d⁺, wherein a>0, and b, c, and d can have any value.

9. The method ofclaim 7, wherein upon ionizing the carbon-containing dopant material, the carbon ions are clustered in groups of at least two carbon atoms.

10. The method ofclaim 7, wherein the carbon-containing dopant material is COF₂gas.

11. The method ofclaim 7, further comprising selecting the desired additional gas or series of gases and desired ratios of w, x, y, and z to produce a feed material of the formula CC_wF_xO_yH_z, prior to the step of ionizing to produce the plasma.

12. The method ofclaim 7, wherein the additional gas comprises one or more of carbon, oxygen, fluorine, hydrogen, nitrogen, argon, xenon, air, and helium.

13. A method of improving the efficiency of an ion implanter tool, comprising:

selecting a carbon-containing dopant material of the formula C_wF_xO_yH_zfor use in the ion implanter tool in a chamber, wherein if w=1, then x>0 and y and z can take any value, and wherein if w>1 then x or y is >0, and z can take any value;

ionizing the carbon-containing dopant material; and

implanting a carbon ion from the ionized carbon-containing dopant material using the ion implanter tool;

wherein the selecting of the material of the formula C_wF_xO_yH_zminimizes the amount of carbon and/or non-carbon elements deposited in the chamber after the implanting of the carbon ion.

14. The method ofclaim 13, wherein the carbon-containing dopant material is COF₂.

15. The method ofclaim 13, further comprising providing an additional material with the carbon-containing dopant material.

16. The method ofclaim 13, wherein the ions of the plasma produced are of the form C_aF_bO_cH_d⁺, wherein a>0, and b, c, and d can have any value.