Ion source with extended charge life

Abstract

An ion source that is capable of extending the life of a charge material in a vaporizer is disclosed. A controller uses information about the desired beam current and the amount of charge material remaining in the vaporizer to determine the temperature experienced by the vaporizer. The temperature of the vaporizer determines the rate at which the charge material is consumed. By considering both the amount of charge material left, as well as the desired beam current, the temperature of the vaporizer may be maintained at a lower temperature than would otherwise be possible. This serves to extend the life of the charge material, while still supplying the desired beam current.

Description

[0001] ION SOURCE WITH EXTENDED CHARGE LI FE

[0002] This application claims priority of U . S . Provisional Patent Application Serial No . 63 / 729 , 771 , filed December 9 , 2024 , the disclosure of which is incorporated herein by reference in its entirety .

[0003] FIELD

[0004] Embodiments of the present disclosure relate to an ion source and more particularly, an ion source with extended charge li fe due to temperature control of the vaporizer .

[0005] BACKGROUND

[0006] Various types of ion sources may be used to create the ions that are used in semiconductor processing equipment . For example , an indirectly heated cathode ( IHC ) ion source operates by supplying a current to a filament disposed behind a cathode . The filament emits thermionic electrons , which are accelerated toward and heat the cathode, in turn causing the cathode to emit electrons into the arc chamber of the ion source . The cathode is disposed at one end of an arc chamber . A repeller may be disposed on the end of the arc chamber opposite the cathode . The cathode and repeller may be biased so as to repel the electrons , directing 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 . A plurality of sides is used to connect the two ends of the arc chamber . An extraction aperture is disposed along one of these sides, proximate the center of the arc chamber, through which the ions created in the arc chamber may be extracted.

[0007] In some embodiments, the ions are created by the vaporization of a solid or liquid material. Typically, the solid material, referred to as the charge material, is disposed in a vaporizer. The vaporizer is heated so as to sublimate the charge material to produce vapor containing the species of interest. This vapor travels to the arc chamber, where it is ionized to produce ions of the species of interest.

[0008] However, a vaporizer is limited in the amount of charge that it may hold, which limits the amount of time that the ion source may operate before the vaporizer is replenished. Extending the charge life would reduce down time for the ion source, reduce cost of ownership, and improve throughput.

[0009] Therefore, an ion source that is capable of extending the life of the charge material while delivering the desired beam current would be beneficial.

[0010] SUMMARY

[0011] An ion source that is capable of extending the life of a charge material in a vaporizer is disclosed. A controller uses information about the desired beam current and the amount of charge material remaining in the vaporizer to determine the temperature experienced by the vaporizer. The temperature of the vaporizer determines the rate at which the charge material is consumed. By considering both the amount of charge material left, as well as the desired beam current , the temperature of the vaporizer may be maintained at a lower temperature than would otherwise be possible . This serves to extend the li fe of the charge material , while still supplying the desired beam current .

[0012] According to one embodiment, an ion source to extract an ion beam having a desired beam current is disclosed . The ion source comprises an arc chamber comprising a plurality of walls ; a plasma generator ; a vapori zer in communication with the arc chamber ; a heater to heat charge material disposed within the vapori zer ; and a controller in communication with the heater, wherein the controller operates the heater so as to heat the vapori zer to a temperature that is based on the desired beam current and an amount of charge material disposed in the vaporizer . In some embodiments , a set temperature to be used for the vapori zer at a maximum beam current is calibrated, and temperature of fsets are provided for beam currents less than the maximum beam current, where the temperature of fsets are defined as a number of degrees less than the set temperature to be used at lower beam currents . In certain embodiments , the temperature of fsets are provided using an equation based on desired beam current . In certain embodiments , the temperature offsets are provided in a table that associates desired beam current to temperature of fset . In some embodiments , the controller estimates the amount of charge material disposed in the vaporizer based on hours of operation . In certain embodiments , the controller increases temperature over time based on a temperature ramp rate , defined as degrees per hour, wherein the temperature ramp rate is di f ferent for dif ferent beam currents . In some embodiments , a set temperature to be used for the vapori zer at a maximum beam current is calibrated, and temperatures are provided for beam currents less than the maximum beam current , where the temperatures are defined based on a ratio of the desired beam current to the maximum beam current . In some embodiments , the plasma generator comprises an indirectly heated cathode disposed in the arc chamber . In some embodiments , the plasma generator comprises an RF antenna .

[0013] According to another embodiment , an ion source to extract an ion beam having a desired beam current is disclosed . The ion source comprises an arc chamber comprising a plurality of walls ; a plasma generator ; a vapori zer in communication with the arc chamber ; a heater to heat charge material disposed within the vapori zer ; and a controller in communication with the heater, wherein the controller operates the heater so as to heat the vapori zer to a temperature , wherein the controller : uses a temperature of fset to determine the temperature when a desired beam current is changed; and uses a temperature ramp rate to adj ust the temperature as the charge material is consumed . In some embodiments , the temperature of fset is calculated for a plurality of dif ferent beam currents . In certain embodiments , temperature ramp rates are calculated for the plurality of di f ferent beam currents . In certain embodiments , the plurality of beam currents are grouped into a number of bins , wherein beam currents within a bin are assigned a same temperature of fset and temperature ramp rate . In some embodiments , values of the temperature offset and temperature ramp rate are determined using a calibration process and remain constant thereafter . In some embodiments , initial values of the temperature offset and temperature ramp rate are determined using a calibration process and at least one is updated thereafter based on feedback regarding actual beam current . In some embodiments , initial values of the temperature of fset and temperature ramp rate are determined using a calibration process and at least one is updated thereafter based on feedback regarding cathode power . In some embodiments , initial values of the temperature offset and temperature ramp rate are determined using a calibration process and at least one is updated thereafter based on feedback regarding total extracted current from the ion source. In some embodiments, the plasma generator comprises an indirectly heated cathode disposed in the arc chamber. In some embodiments, the plasma generator comprises an RF antenna.

[0014] According to another embodiment, a method of operating an ion source is disclosed. The ion source comprises a controller, an arc chamber, a vaporizer in communication with the arc chamber, and a heater to heat charge material in the vaporizer. The method comprises selecting a desired beam current; and using the controller to determine a temperature for the vaporizer based on the desired beam current; and changing the temperature of the vaporizer if a different beam current is selected. In some embodiments, the method also comprises using the controller to adjust the temperature of the vaporizer as the charge material is consumed. In certain embodiments, a rate at which the temperature is adjusted is determined based on the desired beam current.

[0015] BRIEF DESCRIPTION OF THE FIGURES

[0016] For a better understanding of the present disclosure, reference is made to the accompanying drawings, which are incorporated herein by reference and in which:

[0017] FIG. 1 is an indirectly heated cathode (IHC) ion source with extended charge material life in accordance with one embodiment; and

[0018] FIGs. 2A-2B show the relationship between desired beam current and set temperature;

[0019] FIG. 3 shows the relationship between temperature and hours of operation for different beam currents; FIG . 4 is a table that shows the relationship between beam current , temperature of fset and temperature ramp rate according to one embodiment ;

[0020] FIG . 5 is a flowchart showing the operation of the controller according to one embodiment ;

[0021] FIG . 6 is a flowchart showing the operation of the controller according to another embodiment ;

[0022] FIG . 7 shows the temperature of the vaporizer as a function of beam current and hours of operation; and

[0023] FIG . 8 shows an ion implanter that may utili ze the IHC ion source of FIG . 1 .

[0024] DETAILED DESCRIPTION

[0025] As noted above , certain dopants , such as indium, antimony, and aluminum are usually supplied in solid form for use in an ion source . These charge materials are disposed in a vaporizer, which is heated to cause the charge material to sublimate . The resulting vapor is then ionized in the arc chamber to produce ions of the desired species . However, the amount of charge material that may be contained in the vapori zer may be limited . Thus , the availability of the ion source may be limited by the amount of time that the ion source may operate before replenishing the charge material .

[0026] FIG . 1 shows an IHC ion source 10 that overcomes these issues . The IHC ion source 10 includes an arc chamber 100 , comprising two opposite ends , and walls 101 connecting to these ends . The walls 101 of the arc chamber 100 may be constructed of an electrically conductive material and may be in electrical communication with one another . In some embodiments , a liner may be disposed proximate one or more of the walls 101 . A cathode 110 is disposed in 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 pass a current through the filament 160 , such that the filament 160 emits thermionic electrons . Cathode bias power supply 115 biases filament 160 negatively relative to the cathode 110 , so these thermionic electrons are accelerated from the filament 160 toward the cathode 110 and heat the cathode 110 when they strike the back surface of cathode 110 . The cathode bias power supply 115 may bias the filament 160 so that it has a voltage that is between, for example , 200V to 1500V more negative than the voltage of the cathode 110 . The cathode 110 then emits thermionic electrons on its front surface into arc chamber 100 .

[0027] Thus , the filament power supply 165 supplies a current to the filament 160 . The cathode bias power supply 115 biases the filament 160 so that it is more negative than the cathode 110 , so that electrons are attracted toward the cathode 110 from the filament 160 . In certain embodiments , the cathode 110 may be biased relative to the arc chamber 100 , such as by bias power supply 111 . In other embodiments , the cathode 110 may be electrically connected to the arc chamber 100 , so as to be at the same voltage as the walls 101 of the arc chamber 100 . In these embodiments , bias power supply 111 may not be employed and the cathode 110 may be electrically connected to the walls 101 of the arc chamber 100 . In certain embodiments , the arc chamber 100 is connected to electrical ground .

[0028] On the second end 105 , which is opposite the first end 104 , a repeller 120 may be disposed . The repeller 120 may be biased relative to the arc chamber 100 by means of a repeller bias power supply 123 . In other embodiments , the repeller 120 may be electrically connected to the arc chamber 100 , so as to be at the same voltage as the walls 101 of the arc chamber 100 . In these embodiments , repeller bias power supply 123 may not be employed and the repeller 120 may be electrically connected to the walls 101 of the arc chamber 100 . In other embodiments , the bias power supply 111 may be used to bias the repeller 120 as well . In still other embodiments , a repeller 120 is not employed .

[0029] The cathode 110 and the repeller 120 are each made of an electrically conductive material , such as a metal or graphite .

[0030] In certain embodiments , a magnetic field is generated in the arc chamber 100 . This magnetic field is intended to confine the electrons along one direction . The magnetic field typically runs parallel to the walls 101 from the first end 104 to the second end 105 . For example , electrons may be confined in a column that is parallel to the direction from the cathode 110 to the repeller 120 . Thus , electrons do not experience any electromagnetic force to move in this direction . However, movement of the electrons in other directions may experience an electromagnetic force .

[0031] Disposed on one side of the arc chamber 100 , referred to as the extraction plate 103 , may be an extraction aperture 140 . In FIG . 1 , the extraction aperture 140 is disposed on a side that is parallel to the X-Y plane (perpendicular to the page ) .

[0032] Further, the IHC ion source 10 may be in communication with at least one gas source . The gas source 170 may contain a gas , which may be an inert gas , such as argon . A valve 171 may be utilized to control the flow of the gas from the gas source 170 to the IHC ion source 10 . The valve 171 may be a mass flow controller (MFC) such that the flow rate may be controlled . A vaporizer 190 may be in communication with the arc chamber 100. For example, the vaporizer 190 may be disposed outside the arc chamber 100, but may include a conduit 191 connecting the output of the vaporizer 190 with the arc chamber 100. A heater 195 may be disposed proximate the vaporizer 190 to heat and vaporize the charge material 197 disposed within the vaporizer 190. The heater 195 may be a resistive heater or another type. The design of the heater is implementation specific and not limited by this disclosure. In certain embodiments, the charge material 197 within the vaporizer 190 may be a solid compound containing the dopant of interest, such as aluminum chloride, aluminum iodide, gallium iodide, indium iodide, antimony fluoride, lanthanum fluoride or another solid compound. A temperature sensor 198 may also be located proximate to the vaporizer 190 to monitor the temperature of the vaporizer 190. This temperature sensor 198 may be a thermocouple or another suitable device. In certain embodiments, a cooling device, such as a Peltier cooling element may also be disposed proximate the vaporizer to actively cool the vaporizer 190. In other embodiment, cooling is achieved passively.

[0033] Located outside the extraction aperture 140 is an extraction electrode 150. This extraction electrode 150 is biased by extraction power supply 155 at a voltage that is more negative than the arc chamber 100 so as to attract positive ions. Note that, in another embodiment, the extraction electrode 150 may be grounded and the extraction power supply 155 may be used to positively bias the arc chamber 100. In both scenarios, a difference in voltage is created between the arc chamber 100 and the extraction electrode 150, which attracts positive ions to exit through the extraction aperture 140. While FIG . 1 shows an IHC ion source, it is understood that this disclosure is also applicable to other ion sources , such as ion sources that utili ze an RF antenna to generate a plasma . Thus , the disclosure is applicable to any ion source that includes an arc chamber and a plasma generator, wherein the plasma generator may be an indirectly heated cathode , an RF antenna or another device .

[0034] A controller 180 may be in communication with one or more of the power supplies such that the voltage or current supplied by these power supplies may be modified . The controller 180 may also be in communication with the valve 171 , the temperature sensor 198 and the heater 195. The controller 180 may include a processing unit, such as a microcontroller, a personal computer, a special purpose controller, or another suitable processing unit . The controller 180 may also include a non-transitory storage element , such as a semiconductor memory, a magnetic memory, or another suitable memory . This non-transitory storage element may contain instructions and other data that allows the controller 180 to perform the functions described herein .

[0035] The IHC ion source 10 may be part of an ion implantation system, such as that shown in FIG . 8 . The ion implantation system may include the IHC ion source 10 , extraction optics 201 , a mass analyzer 210 , a mass resolving device 220 , one or more components 230 disposed downstream from the mass resolving device 220 and a process chamber 260 that contains the workpiece holder 270 . Specifically, disposed outside and proximate the extraction aperture 140 of the IHC ion source 10 are extraction optics 201 . The extraction optics 201 include the extraction electrode 150 ( see FIG . 1 ) . Located downstream from the extraction optics is the mass analyzer 210 . The mass analyzer 210 uses magnetic fields to guide the path of the extracted ions. The magnetic fields affect the flight path of ions according to their mass and charge. A mass resolving device 220 that has a mass resolving aperture 221 is disposed at the output, or distal end, of the mass analyzer 210. By proper selection of the magnetic fields, only those ions that have a selected mass and charge will be directed through the mass resolving aperture 221. Other ions will strike the mass resolving device 220 or a wall of the mass analyzer 210 and will not travel any further in the system.

[0036] One or more components 230 are located downstream from the mass resolving device. In the case where the IHC ion source 10 outputs a ribbon beam, a collimator may be one of the one or more components 230. The collimator accepts the extracted ions that pass through the mass resolving aperture 221 and creates a ribbon ion beam formed of a plurality of parallel or nearly parallel beamlets. Located downstream from the collimator may be an acceleration / decelerat ion stage. The acceleration / deceleration stage may be an electrostatic filter. The electrostatic filter is a beam-line lens component configured to independently control deflection, deceleration, and focus of the ion beam.

[0037] In other embodiments, the ion beam extracted from the IHC ion source 10 may be a spot beam. In this embodiment, the one or more components 230 may include an electrostatic scanner located downstream from the mass resolving device 220. The electrostatic scanner is used to move the spot beam in the first direction.

[0038] In both embodiments, the ion beam 250 exits the one or more components 230 and enters the process chamber 260. Located downstream from the one or more components 230 is the workpiece holder 270, disposed within the process chamber 260. The ions extracted from the IHC ion source 10 may be directed toward a workpiece disposed on the workpiece holder 270 . The workpiece may be a silicon wafer, a silicon carbide wafer, a gallium nitride wafer or another semiconductor wafer . A current sensor 280 may be disposed in the process chamber 260 . This current sensor 280 may be used to measure the beam current that reaches the workpiece . This may be compared to the desired beam current to determine the temperature of the vapori zer as described in more detail below .

[0039] The controller 180 is aware of the desired beam current . Based on the amount of charge material remaining in the vapori zer 190 and the desired beam current, the controller 180 determines an appropriate temperature for the vaporizer 190 .

[0040] Both of these factors play a part in the determination of the temperature that the controller 180 uses for the vapori zer . For example , when there is a large amount of charge material 197 , a certain amount of vapor is created at a certain temperature . However, as the charge material 197 is consumed, that temperature is insuf ficient to maintain the same flow of vapor . Therefore , the temperature used by the vapori zer 190 may be increased as the amount of charge material 197 is reduced .

[0041] A similar relationship exists with beam current . For example , to generate a high beam current , a large amount of vapor is created, facilitating the creation of many ions of the dopant of interest . However, for a lower beam current , a smaller amount of vapor may be acceptable to produce the requisite number of ions . Thus , the temperature of the vapori zer may be related to the desired beam current . Thus, to extend the life of the charge material, the controller 180 may select the temperature of the vaporizer based on the amount of charge material 197 remaining in the vaporizer 190 and the desired beam current.

[0042] Each of the components that the controller 180 uses to determine the temperature are now discussed in more detail.

[0043] First, regarding beam current, a relationship between desired beam current and temperature of the vaporizer 190 may be created. For example, for a vaporizer that is full of charge material, assume that to generate the maximum beam current, there is a certain set temperature. This set temperature may be established using a calibration procedure. For example, the temperature of the vaporizer 190 may be varied while the resulting beam current is measured. Based on this calibration procedure, the set temperature may be established.

[0044] To generate a smaller beam current, a temperature lower than this set temperature may be utilized. Therefore, an equation or table may be created to define the relationship between desired beam current and vaporizer temperature for a fully loaded vaporizer 190. Alternatively, a relationship between the set temperature and the desired beam current may be defined. For example, a relationship may be defined relating desired beam current to the offset from the set temperature. FIG. 2A shows an example of this relationship. In this figure, the horizontal axis represents the beam current, as a percentage of the maximum beam current. The vertical axis represents the offset from the set temperature (which may be determined using a calibration procedure) . Note that, in certain embodiments, this relationship may be roughly linear. Thus, the temperature offset may be defined as follows: wherein k is a constant that may depend on the species of the charge material.

[0045] Thus, for any desired beam current, the temperature to be used for the vaporizer 190 may be determined from this relationship and is defined as the set temperature plus the temperature offset. Note that, in certain embodiments, this relationship is constant regardless of the amount of charge material 197 in the vaporizer 190. In other words, this offset temperature relationship is constant regardless of whether the vaporizer is full, half-full, or even almost empty of charge material 197.

[0046] While FIG. 2A and the above describes the creation of an equation relating desired beam current to temperature offset, other implementations are possible. For example, rather than creating an equation, a table that associates a range of desired beam currents to a temperature offset may be used. For example, FIG. 2B shows a table that may be created based on the chart shown in FIG. 2A. This table groups beam currents within a predetermined range into a single bin, wherein the temperature offset for all desired beam currents in that bin are the same. This table may simplify the computations performed by the controller 180, while still providing the advantages described herein. Grouping beam currents in bins also limits the number of crucible temperature changes which can help speed up transitions from beam current to beam current. Note that the table in FIG. 2B shows 5 bins, however, any number of bins may be defined in the table. Further, while FIG. 2A shows a linear relationship between percentage of maximum beam current and temperature offset, other relationships may also be used to determine the temperature to be used at lower beam currents. For example, in another embodiment, rather than adding a temperature offset to the set temperature, a multiplication factor may be used. In this embodiment, the temperature to be used at a lower beam current may be defined as: temperature, where m is a constant.

[0047] As noted above, the temperature used for the vaporizer 190 is also dependent on the amount of charge material 197 that remains in the vaporizer. The rate at which the charge material 197 is consumed is related to the temperature used for the vaporizer 190. Thus, the charge material 197 is consumed more quickly when operating at maximum beam current, and is consumed at slower rates at lower beam currents. Further, as noted above, as the charge material 197 is consumed, the temperature used for the vaporizer 190 increases to maintain the desired beam current.

[0048] Thus, a relationship between amount of charge material 197 and temperature may also be created. For example, at maximum beam current, the charge material 197 is consumed at the highest rate. Therefore, the depletion rate of charge material 197 as a function of time is the greatest. The depletion rate at lower beam currents will be slower. Thus, time and beam current may be used to estimate the amount of charge material 197 that remains in the vaporizer 190. As noted above, to compensate for this depletion of charge material 197, the temperature may be increased as a function of time . At high beam currents , the rate at which the temperature is increased as a function of time , is greater than at lower beam currents .

[0049] FIG . 3 shows a representative graph that shows the relationship between hours of operation and vaporizer temperature for various beam currents . Line 300 shows the temperature profile used to achieve maximum current . Note that the rate of temperature change is steepest for this line . Also note that , as expected, the number of hours of operation is smallest , since the charge material 197 is consumed quickest in this scenario . Line 310 represents the temperature profile for a medium beam current . Note that the slope of line 310 is less steep than that of line 300 . Therefore , the charge material 197 lasts longer . Finally, line 320 represents the temperature profile of the vapori zer 190 for a low beam current . Note that the slope of line 320 is less steep than that of line 310 .

[0050] Based on this information, it is possible to derive a relationship between the rate of temperature change ( also referred to as temperature ramp rate ) and the desired beam current . In some embodiments , the relationship between temperature ramp rate and desired beam current may be linear . Thus , in some embodiments , the temperature ramp rate may be expressed as : wherein j is a constant and MaxRamp is the temperature ramp rate used for the maximum beam current . However, to simplify this, the temperature ramp rates may be included in the table shown in FIG. 2B. FIG. 4 shows a table that shows the relationship between desired beam current, temperature offset and temperature ramp rate.

[0051] Using all of this information, the operation of the controller 180 may now be described, with respect to FIG. 5.

[0052] First, as shown in Box 500, the controller 180 is made aware of the desired beam current and the set temperature. Based on this, as shown in Box 510, the controller 180 may determine the temperature offset and the temperature ramp rate. This temperature offset is then subtracted from the set temperature to arrive at the initial temperature to be applied to the vaporizer 190, as shown in Box 520. The controller 180 controls the heater 195 to achieve this initial temperature, as shown in Box 530. As shown in Box 540, the controller 180 also monitors the duration of time that the vaporizer 190 is in use. As time passes, the controller 180 may adjust the temperature of the vaporizer 190 by multiplying the temperature ramp rate associated with this beam current by the number of hours of operation, as shown in Box 550. Note that the adjustment of the temperature of the vaporizer 190 may be performed continuously, at regularly intervals, or at some other event. For example, the temperature is adjusted by the controller 180 whenever the recipe is changed or a tuning event occurs.

[0053] FIG. 5 shows a simple example where the beam current remains constant throughout the life of the charge material 197. However, in many embodiments, the beam current is changed multiple times using the same charge material 197. FIG. 6 shows a flowchart showing the operation of the controller 180 in this embodiment. First, as shown in Box 600 of FIG. 6, the controller 180 is provided with the set temperature and the temperature ramp rate for the maximum beam current. In some embodiments, the controller 180 may be provided with a table of values, such as that shown in FIG. 4. In other embodiments, the controller 180 may be provided with equations relating temperature to desired beam current and temperature ramp rate to desired beam current.

[0054] Next, as shown in Box 610, the controller 180 is provided with the desired beam current. Based on this desired beam current, the controller 180 subtracts the appropriate temperature offset to arrive at the temperature to apply to the vaporizer 190, as shown in Box 620. Then, as shown in Box 630, the controller 180 heats the vaporizer 190 to this temperature. The controller 180 then monitors the hours of operation and uses the temperature ramp rate associated with the desired beam current to adjust the temperature of the vaporizer 190, as shown in Box 640. The controller 180 also continually checks to see if the desired beam current has been changed, as shown in Decision Box 650. If the desired beam current has not changed, the controller 180 continues to adjust the temperature of the vaporizer 190 using the temperature ramp rate associated with the desired beam current. However, if the desired beam current has changed, the controller 180 determines a new desired temperature, as shown in Box 660. This may be done in a number of ways. In one embodiment, the controller 180 compares the temperature offset associated with the new desired beam current to the temperature offset associated with the previous desired beam current. It uses the difference between these two values to determine the step change be to made to get to the proper temperature. For example, assume that the vaporizer 190 is currently operating at a desired beam current with an associated temperature offset of -15°. If the new desired beam current has an associated temperature offset of -10°, the controller calculates that the temperature of the vaporizer 190 is to be increased by 5°. Additionally, the temperature ramp rate is now that associated with the new desired beam current.

[0055] FIG. 7 shows the temperature profile of the vaporizer 190 following the process shown in FIG. 6. FIG. 7 shows a maximum temperature profile 710, which is defined as the temperature to be applied to the vaporizer 190 if the maximum beam current is desired. In other words, temperatures to be used for all other beam currents may be calculated from this maximum temperature profile by subtracting the appropriate temperature offset. Temperature profile 720 shows the actual temperature of the vaporizer 190 during operation. In this graph, the desired beam current is changed a plurality of times. In this figure, it is assumed that the bins defined in FIG. 4 are used. Thus, bin 1 is maximum temperature and steepest temperature ramp rate, while bin 5 is the lowest temperature and least steep temperature ramp rate. Note that when the desired beam current changes, there is an immediate change to the temperature of the vaporizer 190, corresponding to the process described in Box 660. Additionally, between changes in beam current, the temperature ramp rate is set according to the desired beam current, and is therefore different in each bin.

[0056] This sequence continues until the vaporized reaches a predetermined temperature, which may be referred to as the empty temperature. FIG. 3 shows this empty temperature.

[0057] In some embodiments, as described above, the values in the table of FIGs. 2B and 4 are determined based on a calibration process and remain constant thereafter. However, other embodiments are also possible. For example, in another embodiment, the initial values of these parameters are determined using a calibration process. However, these parameters may be modified during operation. Specifically, the controller 180 may monitor the actual beam current using current sensor 280 (see FIG. 8) . If the measured beam current is less than desired within the defined recipe parameters, this may imply that an insufficient amount of vapor is being generated, which indicates that the temperature of the vaporizer 190 is too low. Therefore, to increase the beam current, the temperature of the vaporizer 190 may be increased. This may be done by changing the temperature offset values, the temperature ramp rate values or both. As an example, assume an ion beam having a beam current that is 75% of the maximum beam current is desired. The controller would begin by using the values in the second row of the table in FIG. 4, with a temperature offset of -5°C and a temperature ramp rate of 1.2°. However, over time, it may be determined by the controller 180 that the beam current is less than desired. To correct this, the controller may update the temperature offset to a value closer to the value in the first row (i.e. 0°) , or may increase the temperature ramp rate to a value closer to the value in the first row (i.e. 1.5°) . As another example, assume an ion beam having a beam current that is 40% of the maximum beam current is desired. The controller would begin by using the values in the third row of the table in FIG. 4, with a temperature offset of -10°C and a temperature ramp rate of 0.9°. However, over time, it may be determined by the controller 180 that the beam current is more than desired. To correct this, the controller may update the temperature offset to a value closer to the value in the fourth row (i.e. -15°) , or may decrease the temperature ramp rate to a value closer to the value in the fourth row (i.e. 0.6°) . Note that these are only examples. Note that this dynamic feedback may also be used if equations are used to determine the vaporizer temperature rather than tables.

[0058] There are other means of determining the lack or abundance of vapor flow from the vaporizer over time. In one embodiment, the cathode power used to create the desired beam current may be monitored. Specifically, the controller 180 may be configured to receive an indication of the total power output by bias power supply 111. In one embodiment, this may be performing by monitoring the current supplied by the bias power supply 111 to the cathode 110. If there is insufficient vapor provided by the vaporizer over time, the cathode power will increase over the same time period. Conversely, if there is an abundance of vapor flow, the cathode power may decrease over time. Thus, after calibration, the temperature offset and / or the temperature ramp rate may be adjusted based on the cathode power. Similarly, the total current extracted from the ion source to achieve the desired beam current may be monitored. This may be done by monitoring the current supplied by extraction power supply 155. If the total extracted current used to generate a specified beam current decreases, this may indicate that there is an abundance of vapor provided and the vaporizer temperature offset and / or temperature ramp rate may be modified accordingly. Conversely, if the total extracted current used to generate the specified beam current increases, this may indicate that there is insufficient vapor provided by the vaporizer and the vaporizer temperature offset and / or temperature ramp rate may be modified accordingly. Thus, after calibration, the temperature offset and / or the temperature ramp rate may be adjusted based on the total current extracted from the ion source. The embodiments described above in the present application may have many advantages . Ions for certain dopant species are typically obtained using a vaporizer . However, unlike typical gas sources , which are cannisters that are easily accessible and replaceable , adding charge material to a vapori zer is a more laborious task . Thus , the ability to extend the li fe of the charge material results in longer uptime for the ion source and increases throughput . In one test, it was found that when operating at maximum beam line , the charge material in the vaporizer lasted for a certain duration . Further, in traditional systems where the temperature of the vapori zer is not controlled based on beam current , the charge material would last this amount of time , regardless of beam current . However, by using the beam current to determine appropriate temperatures for the vaporizer, longer li fe of the charge material may be achieved . In another test , using the ion source described herein, the ion source was operated at medium and low beam currents . The result was that the charge material lasted more than twice as long as it did in the first test . This reduces maintenance and down time . Additionally, some charge material may be very expensive . Thus , this system also reduces operating expenses .

[0059] The present disclosure is not to be limited in scope by the specific embodiments described herein . Indeed, other various embodiments of and modi fications to the present disclosure , in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings . Thus , such other embodiments and modifications are intended to fall within the scope of the present disclosure . Furthermore , although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose , those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes . Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein .

Claims

What is claimed is:

1. An ion source to extract an ion beam having a desired beam current, comprising: an arc chamber comprising a plurality of walls; a plasma generator; a vaporizer in communication with the arc chamber; a heater to heat charge material disposed within the vaporizer; and a controller in communication with the heater, wherein the controller operates the heater so as to heat the vaporizer to a temperature that is based on the desired beam current and an amount of charge material disposed in the vaporizer.

2. The ion source of claim 1, wherein a set temperature to be used for the vaporizer at a maximum beam current is calibrated, and temperature offsets are provided for beam currents less than the maximum beam current, where the temperature offsets are defined as a number of degrees less than the set temperature to be used at lower beam currents.

3. The ion source of claim 2, wherein the temperature offsets are provided using an equation based on desired beam current .

4. The ion source of claim 2, wherein the temperature offsets are provided in a table that associates desired beam current to temperature offset.

5. The ion source of claim 1, wherein the controller estimates the amount of charge material disposed in the vaporizer based on hours of operation.

6. The ion source of claim 5, wherein the controller increases the temperature over time based on a temperature ramp rate,defined as degrees per hour, wherein the temperature ramp rate is different for different beam currents.

7. The ion source of claim 1, wherein a set temperature to be used for the vaporizer at a maximum beam current is calibrated, and temperatures are provided for beam currents less than the maximum beam current, where the temperatures are defined based on a ratio of the desired beam current to the maximum beam current.

8. The ion source of claim 1, wherein the plasma generator comprises an indirectly heated cathode disposed in the arc chamber or an RF antenna.

9. An ion source to extract an ion beam having a desired beam current, comprising: an arc chamber comprising a plurality of walls; a plasma generator; a vaporizer in communication with the arc chamber; a heater to heat charge material disposed within the vaporizer; and a controller in communication with the heater, wherein the controller operates the heater so as to heat the vaporizer to a temperature, wherein the controller: uses a temperature offset to determine the temperature when a desired beam current is changed; and uses a temperature ramp rate to adjust the temperature as the charge material is consumed.

10. The ion source of claim 9, wherein the temperature offset is calculated for a plurality of different beam currents.

11. The ion source of claim 10, wherein temperature ramp rates are calculated for the plurality of different beam currents .

12. The ion source of claim 11, wherein the plurality of different beam currents are grouped into a number of bins,wherein beam currents within a bin are assigned a same temperature of fset and temperature ramp rate .13 . The ion source of claim 11 , wherein values of the temperature of fset and temperature ramp rate are determined using a calibration process and remain constant thereafter .14 . The ion source of claim 11 , wherein initial values of the temperature of fset and temperature ramp rate are determined using a calibration process and at least one is updated thereafter based on feedback regarding actual beam current .15 . The ion source of claim 11 , wherein initial values of the temperature of fset and temperature ramp rate are determined using a calibration process and at least one is updated thereafter based on feedback regarding cathode power .16 . The ion source of claim 11 , wherein initial values of the temperature of fset and temperature ramp rate are determined using a calibration process and at least one is updated thereafter based on feedback regarding total extracted current from the ion source .17 . The ion source of claim 9 , wherein the plasma generator comprises an indirectly heated cathode disposed in the arc chamber or an RF antenna .18 . A method of operating an ion source , wherein the ion source comprises a controller, an arc chamber, a vaporizer in communication with the arc chamber, and a heater to heat charge material in the vapori zer, the method comprising : selecting a desired beam current ; and using the controller to determine a temperature for the vaporizer based on the desired beam current ; and changing the temperature of the vaporizer i f a di f ferent beam current is selected .19 . The method of claim 18 , further comprising :using the controller to adjust the temperature of the vaporizer as the charge material is consumed.

20. The method of claim 19, wherein a rate at which the temperature is adjusted is determined based on the desired beam current.

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