Ion source for controlling decomposition accumulation using chlorine co-gas.

Abstract

An ion source for producing an ion beam containing aluminum ions is disclosed. The ion source includes a first gas source for introducing an organoaluminum compound into the arc chamber of the ion source. A second gas, different from the first gas, which is a chlorine-containing gas, is also introduced into the arc chamber. The chloride co-flow reduces the accumulation of decomposition products within the arc chamber. This accumulation may occur in the gas bushing or extraction aperture, or near the repeller. In some embodiments, the second gas is introduced continuously. In other embodiments, the second gas is introduced periodically based on the operating time or the measured uniformity of the extracted ion beam. The second gas may be introduced from a second gas source or a vaporizer.

Description

[Technical Field]

[0001] This application claims priority to U.S. patent application Ser. No. 18 / 099,353, filed Jan. 20, 2023, the entire disclosure of which is incorporated by reference.

[0002] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate to ion sources, and more particularly to ion sources for producing aluminum ions that control decomposition buildup caused by the use of DMAC. [Background technology]

[0003] Various types of ion sources can be used to generate ions for use in semiconductor processing equipment. For example, an indirectly heated cathode (IHC) ion source operates by supplying current to a filament positioned behind a cathode. The filament emits thermionic electrons, which are accelerated toward the cathode, heating it and causing the cathode to emit electrons into the arc chamber of the ion source. The cathode is located at one end of the arc chamber. A repeller can be located at the end of the arc chamber opposite the cathode. The cathode and repeller can be biased to repel electrons and direct them back toward the center of the arc chamber. In some embodiments, a magnetic field is used to further confine the electrons within the arc chamber. Multiple sides are used to connect both ends of the arc chamber.

[0004] Along one of these sides, near the center of the arc chamber, is an extraction aperture through which ions generated within the arc chamber can be extracted.

[0005] In certain embodiments, it may be desired to extract an ion beam composed of aluminum ions. Some gases useful for creating an ion beam of aluminum ions are dimethyl aluminum chloride (DMAC) ((CH)AlCl) and trimethyl aluminum (TMA) ((CH)Al).

[0006] However, long-term use of DMAC in the ion source chamber can result in decomposition products (such as aluminum carbide). This buildup can form as whiskers in the extraction apertures or on the gas bushing or repeller. Whiskers in the extraction apertures cause the ion beam to become non-uniform. Buildup around the gas bushing reduces or prevents gas from entering the ion source. Buildup on the repeller can lead to shorting of this part.

[0007] Therefore, it would be beneficial to have an ion source that can operate using DMAC, TMA, or other aluminum-containing gases while preventing or controlling the buildup of decomposition products. In addition, it would be advantageous if the ion source could operate continuously without requiring a dedicated cleaning process. Summary of the Invention

[0008] An ion source for producing an ion beam containing aluminum ions is disclosed. The ion source includes a first gas source for introducing an organoaluminum compound into the arc chamber of the ion source. A second gas, different from the first gas, which is a chlorine-containing gas, is also introduced into the arc chamber. The chloride co-flow reduces the accumulation of decomposition products within the arc chamber. This accumulation may occur in the gas bushing or extraction aperture, or near the repeller. In some embodiments, the second gas is introduced continuously. In other embodiments, the second gas is introduced periodically based on the operating time or the measured uniformity of the extracted ion beam. The second gas may be introduced from a second gas source or a vaporizer.

[0009] According to one embodiment, an indirectly heated cathode ion source is disclosed. The indirectly heated cathode ion source includes an arc chamber having multiple walls, an indirectly heated cathode disposed within the arc chamber, a first valve in communication with the arc chamber and a first gas source, the first gas source comprising a first gas that is an organoaluminum compound, a second valve in communication with the arc chamber and a second gas source, the second gas source comprising a second gas that is different from the first gas and is a chlorine-containing gas, and a controller in communication with the first and second valves to limit the accumulation of molecular by-products resulting from decomposition of the first gas. In some embodiments, the first gas is dimethylaluminum chloride (DMAC) or trimethylaluminum (TMA). In some embodiments, the second gas is chlorine gas. In some embodiments, the controller controls the second valve to introduce the second gas whenever the first gas is flowing through the arc chamber. In certain embodiments, the controller controls the first valve and the second valve so that the flow rate of the second gas is between 30 and 70% of the flow rate of the first gas. In some embodiments, the controller controls the second valve to periodically introduce the second gas. In certain embodiments, the controller controls the second valve based on the number of hours the indirectly heated cathode ion source has been in operation. In certain embodiments, a beam profiler is used to measure the uniformity of the ion beam extracted from the arc chamber, and the controller controls the second valve based on the uniformity of the ion beam extracted from the arc chamber.

[0010] According to another embodiment, an indirectly heated cathode ion source is disclosed. The indirectly heated cathode ion source includes an arc chamber having multiple walls, an indirectly heated cathode disposed within the arc chamber, a first valve in communication with the arc chamber and a first gas source, the first gas source containing a first gas that is an organoaluminum compound, a vaporizer in communication with the arc chamber, a heater for heating a dopant material disposed in the vaporizer to produce a second gas, and a controller in communication with the first valve and the heater to limit the accumulation of molecular by-products resulting from decomposition of the first gas. In some embodiments, the first gas is dimethylaluminum chloride (DMAC) or trimethylaluminum (TMA). In some embodiments, the dopant material is indium chloride, aluminum chloride, or another chloride-containing solid. In some embodiments, the controller controls the heater to introduce the second gas from the vaporizer whenever the first gas is flowing in the arc chamber. In certain embodiments, the controller controls the first valve and heater so that the flow rate of the second gas is between 10 and 70% of the flow rate of the first gas. In some embodiments, the controller controls the heater to periodically introduce the second gas. In certain embodiments, the controller controls the heater based on the number of hours the indirectly heated cathode ion source has been in operation. In certain embodiments, a beam profiler is used to measure the uniformity of the ion beam extracted from the arc chamber, and the controller controls the heater based on the uniformity of the ion beam extracted from the arc chamber.

[0011] According to another embodiment, a method of operating an indirectly heated cathode ion source adapted to produce aluminum ions is disclosed. The method includes introducing a first gas containing an organoaluminum compound into an arc chamber of the indirectly heated cathode ion source, ionizing the first gas to extract an ion beam containing aluminum ions from the arc chamber, and introducing a second gas containing chlorine, different from the first gas, into the arc chamber, where the introduction of the second gas extends operation of the indirectly heated cathode ion source. In some embodiments, the second gas is introduced periodically. In certain embodiments, the second gas is introduced based on the number of hours the indirectly heated cathode ion source has been in operation. In certain embodiments, the uniformity of the extracted ion beam is monitored, and the second gas is introduced if the uniformity is not within a predetermined threshold.

[0012] For a better understanding of the present disclosure, reference is made to the accompanying drawings, which are incorporated herein by reference. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is an indirectly heated cathode (IHC) ion source, according to one embodiment. [Figure 2] 1 is an indirectly heated cathode (IHC) ion source according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] FIG. 1 illustrates a first embodiment of an IHC ion source 10 that overcomes problems associated with the long-term use of DMAC or TMA. The IHC ion source 10 includes an arc chamber 100 having two opposing ends and a plurality of walls 101 connecting the two ends. The walls 101 of the arc chamber 100 may be constructed of an electrically conductive material, and the walls 101 may be in electrical communication with each other. In some embodiments, a liner may be disposed near one or more of the walls 101. A cathode 110 is disposed within the arc chamber 100 at a first end 104 of the arc chamber 100. A filament 160 is disposed behind the cathode 110. The filament 160 is in communication with a filament power supply 165. The filament power supply 165 is configured to apply a current to the filament 160 such that the filament 160 emits thermal electrons. Cathode bias power supply 115 negatively biases filament 160 with respect to cathode 110, so that thermal electrons are accelerated from filament 160 toward cathode 110 and heat the cathode 110 when they strike the backside of the cathode 110. Cathode bias power supply 115 may, for example, bias filament 160 so that it has a voltage that is between 200 V and 1500 V more negative than the voltage of cathode 110. Cathode 110 then emits thermal electrons on its front surface into arc chamber 100.

[0015] Thus, filament power supply 165 provides current to filament 160. Cathode bias power supply 115 biases filament 160 so that it is more negative than cathode 110, thereby attracting electrons from filament 160 toward cathode 110. In certain embodiments, cathode 110 may be biased with respect to arc chamber 100, for example, by bias power supply 111. In other embodiments, cathode 110 may be electrically connected to arc chamber 100 so that it is at the same voltage as walls 101 of arc chamber 100. In these embodiments, bias power supply 111 may not be used, and cathode 110 may be electrically connected to walls 101 of arc chamber 100. In certain embodiments, arc chamber 100 is connected to ground.

[0016] A repeller 120 may be disposed at a second end 105 opposite the first end 104. The repeller 120 may be biased relative to the arc chamber 100 by a repeller bias power supply 123. In other embodiments, the repeller 120 may be electrically connected to the arc chamber 100 so that it is at the same voltage as the walls 101 of the arc chamber 100. In these embodiments, the repeller bias power supply 123 may not be used, and the repeller 120 may be electrically connected to the walls 101 of the arc chamber 100. In yet other embodiments, the repeller 120 is not used.

[0017] The cathode 110 and the repeller 120 are each made of an electrically conductive material (such as a metal or graphite).

[0018] In certain embodiments, a magnetic field is generated within the arc chamber 100. This magnetic field confines electrons along one direction. The magnetic field typically extends parallel to the wall 101 from the first end 104 to the second end 105. For example, electrons may be confined to a column parallel to the direction from the cathode 110 to the repeller 120 (i.e., the y-direction). Therefore, electrons moving in the y-direction are not affected by any electromagnetic forces. However, electron movement in other directions may be affected by electromagnetic forces.

[0019] One side of the arc chamber 100 (referred to as the extraction plate 103) may have extraction apertures 140. In Figure 1, the extraction apertures 140 are located on the side parallel to the YZ plane (perpendicular to the page).

[0020] Additionally, the IHC ion source 10 may be in communication with at least two gas sources. The first gas source 170 may contain a first gas that is an organoaluminum compound. Organoaluminum compounds are compounds in which an aluminum atom is bonded to a carbon atom, such as dimethylaluminum chloride (DMAC) ((CH3)2AlCl) or trimethylaluminum (TMA) (CH3)3Al). A first valve 171 may be used to control the flow of the first gas from the first gas source 170 to the arc chamber 100. The second gas source 172 may contain a second gas that is a chlorine-containing gas, such as Cl2 or HCl. The second gas is carbon-free and different from the first gas. A second valve 173 may be used to control the flow of the second gas from the second gas source 172 to the arc chamber 100. A third gas source 175 may also be present and may contain various diluent gases (such as hydrogen, argon, or other gases). A third valve 176 may be utilized to control the flow of diluent gas from a third gas source 175 to the arc chamber 100. The first valve 171, the second valve 173, and the third valve 176 may be mass flow controllers (MFCs) such that the flow rate of each gas may be controlled. Gas bushings may be used to connect the outputs from the valves to the arc chamber 100.

[0021] Controller 180 may be in communication with one or more of the power supplies, thereby modifying the voltage or current provided by such power supplies. Controller 180 may also be in communication with first valve 171, second valve 173, and third valve 176. Controller 180 may include a processing unit (such as a microcontroller, a personal computer, a dedicated controller, or another suitable processing unit). Controller 180 may also include non-transitory storage elements (such as semiconductor memory, magnetic memory, or another suitable memory). This non-transitory storage element may contain instructions and other data that enable controller 180 to perform the functions described herein.

[0022] In the embodiment shown in FIG. 1, the controller 180 is configured to enable the IHC ion source 10 to generate an ion beam including aluminum ions while minimizing the buildup of decomposition products within the arc chamber 100.

[0023] FIG. 2 illustrates a second embodiment of the IHC ion source 11 that can be used to minimize or reduce the accumulation of decomposition products. In this embodiment, the second gas source 172 and the second valve 173 can be eliminated. The other components are as described above. In this embodiment, a vaporizer 190 can be in communication with the arc chamber 100. For example, the vaporizer can be located outside the arc chamber 100 but can include a conduit 191 connecting the output of the vaporizer to the arc chamber 100. A heater 195 can be located near the vaporizer 190 to heat and vaporize a dopant material 197 located within the vaporizer 190. The heater 195 can be a resistive heater or another type. The heater design is implementation specific and is not limited by this disclosure. In certain embodiments, the dopant material 197 in the vaporizer 190 can be a solid compound containing chlorine. For example, dopant material 197 can be aluminum chloride, indium chloride, or another chloride-containing solid. Because the first gas contains carbon, and carbon produces decomposition products, dopant material 197 does not contain carbon. When heater 195 is activated, vaporizer 190 generates a chlorine-containing gas.

[0024] In this embodiment, the controller 180 can be in communication with one or more of the power supplies, thereby modifying the voltage or current provided by such power supplies. The controller 180 can also be in communication with the first valve 171, the third valve 176, and the heater 195.

[0025] During operation, to generate the ion beam, controller 180 may allow a first gas to flow into arc chamber 100. In addition, the controller may provide current to filament 160, provide a cathode bias voltage using cathode bias power supply 115, and provide a bias voltage using bias power supply 111. The thermal electrons ionize the first gas to generate a plasma. An electrode located outside arc chamber 100 is then used to extract positive aluminum ions from arc chamber 100.

[0026] However, as discussed above, in certain embodiments, ions in the plasma may combine to generate other molecular by-products (referred to as decomposition products), such as aluminum carbide. Specifically, when DMAC is ionized, carbon ions and aluminum ions may recombine to form molecular by-products. Over time, these decomposition products may deposit inside the arc chamber 100 and may accumulate in the gas bushing, repeller 120, and / or extraction aperture 140.

[0027] Another mechanism of decomposition is thermal decomposition, which causes molecules to break down when they come into contact with a surface above their threshold temperature. Organometallic molecules (e.g., DMAC) are particularly susceptible to thermal decomposition. The threshold temperature for thermal decomposition of DMAC is approximately 400 ° C. This pyrolysis can also result in carbon-rich deposits inside the arc chamber 100 of the ion source.

[0028] The introduction of excess chlorine into the arc chamber 100 can be beneficial in breaking down deposits or controlling deposition rates. Excess chlorine can combine with excess hydrogen from the first gas to form HCl. For example, chlorides can be This can promote the chemical reaction TIFF2026501961000002.tif13170.

[0029] Methane (CH4) is a gas that can be easily extracted from the arc chamber 100. Aluminum chloride (AlCl3) can be ionized to produce additional aluminum ions. Furthermore, because AlCl3 sublimes at low temperatures, both of these compounds remain in gaseous form at the temperatures used in the arc chamber 100. Therefore, this reaction removes the buildup of decomposition products from within the arc chamber 100 and may also allow for the production of additional aluminum ions.

[0030] In certain embodiments, the controller 180 may enable the flow of chloride-containing gas (either from the second gas source 172 in FIG. 1 or the vaporizer 190 in FIG. 2) whenever the ion source is in use. Therefore, the constant presence of excess chlorine may prevent the buildup of decomposition products. In some embodiments, the flow rate of the chlorine-containing gas may be related to the flow rate of the first gas. For example, when the second gas source 172 is used, the flow rate of the chlorine-containing gas may be 30-70% of the flow rate of the first gas. When the vaporizer 190 is used, the flow rate of the chlorine-containing gas may be 10-70% of the flow rate of the first gas. This may be due to the fact that there are other factors associated with the vaporizer species, such as the stoichiometry of the vaporized material and the mass of chlorine contained in the vaporized gas.

[0031] In another embodiment, the controller 180 may periodically enable the flow of chloride-containing gas to facilitate the cleaning process. In this embodiment, the controller 180 may enable the flow of chlorine-containing gas after a predetermined number of hours of operation to remove buildup of decomposition products. For example, the controller 180 may enable the chlorine-containing gas after 12-24 hours of operation. The chlorine-containing gas may be flowed into the ion source for 1-2 hours to remove or reduce buildup. While the chlorine-containing gas is flowing into the arc chamber 100, the first gas may also be flowed, allowing aluminum ions to be generated and extracted from the arc chamber 100 during the cleaning process. After the buildup is removed, the flow of chlorine-containing gas may be terminated. A timer may then be reset, and this sequence may be repeated multiple times. In another embodiment, the controller 180 may use feedback from a sensor to determine when the chlorine-containing gas is introduced into the arc chamber 100. For example, a beam profiler may be used to measure the uniformity of the extracted ion beam. If the uniformity is not within a predetermined threshold (e.g., within 1%), the controller 180 may enable the flow of a chlorine-containing gas to remove deposits inside the ion source arc chamber 100 and enable extraction of a more uniform beam. The flow of chlorine gas may be for a predetermined period of time (e.g., 1-2 hours) or may be related to the uniformity of the extracted ion beam.

[0032] The above-described embodiments of this application may have numerous advantages. As mentioned above, long-term use of DMAC can result in the accumulation of molecular by-products in the ion source. In one test, flakes formed on the extraction plate 103 near the extraction aperture 140 after approximately 150 hours. This leads to a decrease in uniformity. Uniformity can be defined as the maximum deviation of the beam current along the entire beam width from the average beam current. In other words, 0% uniformity indicates that the beam current is the same along the entire beam width. Furthermore, after 250 hours of operation, decomposition products accumulated in the gas bushing to the extent that gas flow was blocked. Furthermore, tests observed that excessive accumulation could cause the repeller 120 to short circuit with the wall. Introducing excess chlorine into the arc chamber 100 can reduce or eliminate this problem. One test showed that introducing a chlorine-containing gas resulted in less than 50% blockage of the gas bushing due to decomposition products after 285 hours of operation. This indicates that the addition of a chlorine-containing gas allows the ion source to operate for over 500 operating hours before the gas bushing becomes completely clogged with decomposition products. Additionally, the addition of a chlorine-containing gas significantly reduces overall deposition and flake generation in the ion source, allowing beam uniformity to be maintained for a longer period of time.

[0033] The present disclosure is not limited in scope by the specific embodiments described herein. Indeed, in addition to the embodiments and modifications to the present disclosure described herein, various other embodiments and modifications will be apparent to those skilled in the art from the foregoing description and accompanying drawings. Accordingly, such other embodiments and modifications are intended to be included within the scope of the present disclosure. Moreover, while the present disclosure is described herein in the context of particular implementations in particular environments for particular purposes, those skilled in the art will recognize that the utility of the present disclosure is not limited to such contexts, and that the present disclosure may be beneficially implemented in several environments for several purposes. Accordingly, the claims set forth below should be construed in light of the full scope and nature of the present disclosure as described herein.

Claims

1. 1. An indirectly heated cathode ion source comprising: an arc chamber having a plurality of walls; an indirectly heated cathode disposed within the arc chamber; a first valve in communication with the arc chamber and a first gas source, the first gas source comprising a first gas that is an organoaluminum compound; a second valve in communication with the arc chamber and a second gas source, the second gas source comprising a second gas different from the first gas, the second gas being a chlorine-containing gas; a controller in communication with the first valve and the second valve to limit the accumulation of molecular by-products resulting from decomposition of the first gas; an indirectly heated cathode ion source comprising:

2. 2. The indirectly heated cathode ion source of claim 1, wherein the first gas is dimethylaluminum chloride (DMAC) or trimethylaluminum (TMA).

3. 2. The indirectly heated cathode ion source of claim 1, wherein the second gas is chlorine gas.

4. 2. The indirectly heated cathode ion source of claim 1, wherein the controller controls the second valve to introduce the second gas whenever the first gas is flowing in the arc chamber.

5. 5. The indirectly heated cathode ion source of claim 4, wherein the controller controls the first valve and the second valve such that the flow rate of the second gas is between 30 and 70% of the flow rate of the first gas.

6. The indirectly heated cathode ion source of claim 1 , wherein the controller controls the second valve to periodically introduce the second gas.

7. The indirectly heated cathode ion source of claim 6 , wherein the controller controls the second valve based on the number of hours the indirectly heated cathode ion source has been in operation.

8. 7. The indirectly heated cathode ion source of claim 6, further comprising a beam profiler for measuring a uniformity of the ion beam extracted from the arc chamber, wherein the controller controls the second valve based on the uniformity of the ion beam extracted from the arc chamber.

9. 1. An indirectly heated cathode ion source comprising: an arc chamber having a plurality of walls; an indirectly heated cathode disposed within the arc chamber; a first valve in communication with the arc chamber and a first gas source, the first gas source containing a first gas that is an organoaluminum compound; a vaporizer in communication with the arc chamber; a heater for heating a dopant material disposed in the vaporizer to produce a second gas; a controller in communication with the first valve and the heater to limit the accumulation of molecular by-products resulting from decomposition of the first gas; an indirectly heated cathode ion source comprising:

10. 10. The indirectly heated cathode ion source of claim 9, wherein the first gas is dimethylaluminum chloride (DMAC) or trimethylaluminum (TMA).

11. 10. The indirectly heated cathode ion source of claim 9, wherein the dopant material is indium chloride, aluminum chloride, or another chloride-containing solid.

12. 10. The indirectly heated cathode ion source of claim 9, wherein the controller controls the heater to introduce the second gas from the vaporizer whenever the first gas is flowing in the arc chamber.

13. 13. The indirectly heated cathode ion source of claim 12, wherein the controller controls the first valve and the heater such that the flow rate of the second gas is between 10 and 70% of the flow rate of the first gas.

14. The indirectly heated cathode ion source of claim 9 , wherein the controller controls the heater to periodically introduce the second gas.

15. The indirectly heated cathode ion source of claim 14 , wherein the controller controls the heater based on the number of hours the indirectly heated cathode ion source has been in operation.

16. 15. The indirectly heated cathode ion source of claim 14, further comprising a beam profiler for measuring a uniformity of the ion beam extracted from the arc chamber, wherein the controller controls the heater based on the uniformity of the ion beam extracted from the arc chamber.

17. 1. A method of operating an indirectly heated cathode ion source adapted to produce aluminum ions, comprising: introducing a first gas comprising an organoaluminum compound into an arc chamber of the indirectly heated cathode ion source; ionizing the first gas and extracting an ion beam containing aluminum ions from the arc chamber; introducing a second gas into the arc chamber, the second gas comprising chlorine and different from the first gas; wherein the introduction of the second gas extends operation of the indirectly heated cathode ion source.

18. 18. The method of claim 17, wherein the second gas is introduced periodically.

19. 20. The method of claim 18, wherein the second gas is introduced based on the number of hours the indirectly heated cathode ion source has been in operation.

20. 20. The method of claim 18, wherein the uniformity of the ion beam is monitored and the second gas is introduced if the uniformity is not within a predetermined threshold.

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