Apparatus and methods for ion implantation

• US 4,847,504 A
• Filed: 02/24/1986
• Issued: 07/11/1989
• Est. Priority Date: 08/15/1983
• Status: Expired due to Term

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Aitken, Derek
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Aronoff, Michael
• Application Number:
  US06/832,327
• Time in Patent Office: 1,233 Days
• Field of Search: 250/492.2, 250/492.21, 250/296, 250/298, 250/492.1, 250/492.3, 250/285, 250/423 R, 250/426, 313/360.1, 313/361.1, 313/636.1
• US Class Current: 250/492.2
• CPC Class Codes: H01J 27/022 Details
• CPC Class Codes: H01J 27/028 Negative ion sources
• CPC Class Codes: H01J 27/14 Other arc discharge ion sources using an applied magnetic field
• CPC Class Codes: H01J 37/05 Electron or ion-optical arrangements for separating electrons or ions according to their energy or massparticle separator tubes H01J49/00
• CPC Class Codes: H01J 37/08 Ion sources; Ion guns
• CPC Class Codes: H01J 37/3171 for ion implantation
• CPC Class Codes: H01J 49/30 using magnetic analysers , e.g. Dempster spectrometer

Abstract

A system for implanting ions into a target element including a source arrangement for producing an ion beam; a beam analyzing arrangement for receiving the ion beam and selectively separating various ion species in the beam on the basis of mass to produce an analyzed beam; and a beam resolving arrangement disposed in the path of the analyzed beam for permitting a preselected ion species to pass to the target element. The analyzing arrangement has an ion dispersion plane associated therewith. The source arrangement has an associated ion emitting envelope including an area of substantial extension in a plane parallel to the ion dispersion plane and producing ions entering said analyzing arrangement which are travelling substantially either toward or from a common apparent line object lying in a plane perpendicular to the ion dispersion plane.

Claims

1. In a system for implanting ions into a target element, ion source means including an ion exit aperture means through which generated ions may freely pass and being electrically biased to a preanalysis acceleration voltage;

an extraction electrode means positioned in the vicinity of said ion exit aperture means and biased to a voltage value relative to said preanalysis acceleration voltage to extract and accelerate ions from said ion source means; and

a deceleration electrode means positioned downstream of said extraction electrode means and being biased to a voltage relative to said extraction voltage value, the voltage value of the deceleration electrode means relative to the extraction electrode means being of the same order of magnitude as the voltage value of the extraction electrode means relative to the preanalysis acceleration electrode means, substantially to decrease the velocity of ions passing through the region between said extraction electrode means and said deceleration electrode means.

2. The system of claim 1, further comprising a stabilized power supply means for supplying said preanalysis acceleration voltage and an unstabilized power supply means for supplying said voltage to said extraction electrode means so that said extraction electrode voltage will rapidly drop in magnitude when a spark discharge occurs between said ion source means and said extraction electrode means, such that the energy of said spark is limited and said spark is quickly quenched without substantially affecting the velocity of extracted ions entering said analyzing means.

3. In a system for implanting ions into a target element, ion source means for producing an ion beam;

beam analyzing means for receiving said ion beam and separating various ion species in said beam on the basis of mass to produce an analyzed beam; and

beam resolving means disposed in the path of said analyzed beam for permitting a preselected ion species to pass to said target element;

said beam resolving means comprising a plurality of beam resolving elements each having a resolving aperture, and means for selectively positioning one of said beam resolving elements in the path of said analyzed beam.

4. The system of claim 3, wherein each of said beam resolving elements is dedicated to a particular ion species so that contamination from other ion species deposited on the edges of other resolving elements can not be sputtered off during ion implanting process.

5. The system of claim 3, wherein said beam resolving means further comprises an ion drift tube communicating at one end with said beam analyzing means and having an ion beam exit aperture at the opposite end thereof, said beam resolving elements being positioned adjacent said ion beam exit aperture and comprising a mounting frame with a plurality of beam resolving slits carried thereon, and said positioning means comprises means for selectively positioning one of said beam resolving slits in position to communicate with said ion beam exit aperture.

6. The system of claim 5, wherein said positioning means comprises a shaft rotatably mounted at said end of said drift tube communicating with said analyzing means, a coupling arm mounted at one end to said shaft and at the other end to said mounting frame such that said mounting frame translates across said other end of said ion drift tube in front of said ion beam exit aperture as said shaft rotates, and an actuator means for producing a precisely controlled rotation of said shaft to predefined rotary positions to position one of said beam resolving slits in a precise location in front of said ion beam exit aperture.

7. In a system for implanting ions into a target element, ion source means for producing an ion beam;

beam analyzing means for receiving said ion beam and selectively separating various ion species in said beam on the basis of mass to product an analyzed beam exiting said analyzing means, and beam resolving means disposed in the path of said analyzed beam for permitting a preselected ion species to pass to said target element;

said ion source means comprising an ion source arc chamber having a front plate with a rectangualr ion exit aperture therein, an extraction electrode means mounted in front of said ion exit aperture means and electrically biased with respect to said front plate to extract a beam of ions from said ion source arc chamber through said ion exit aperture means, said ion exit aperture means having a width substantially greater than three millimeters such that a high current beam of ions is extracted from said ion source arc chamber.

8. The system of claim 7, wherein said front plate of said ion source arc chamber is about six millimeters in thickness, said ion exit aperture means is formed to a width of about five millimeters, and said ion exit slit has a cross-sectional configuration comprising a first wall portion about 0.25 millimeter long extending substantially perpendicular to the back surface of said front plate and a second wall portion extending from said first wall portion toward the front wall surface of said front plate at an angle of about forty five degrees.

9. The system of claim 7, wherein said analyzing means comprises an analyzing magnet system including a pair of magnet pole pieces having inner surfaces spaced from each other by substantially equal distances thereacross, the front entry edges of said pole pieces being angled substantially to the entrance path of the ion beam traversing the region between said poles to provide a strong fringe focussing field at the beam entrance end of said pole pieces for producing a converging lens action on the ion beam in the non-dispersion plane of the magnet system, said ion exit aperture means width producing an ion beam with substantially greater divergence than an aperture with more narrow width, and said fringe focussing field of said entry face of said analyzing magnet assisting in converging said diverging beam into said pole gap.

10. The system of claim 9, wherein a beam entry magnetic field shunt is provided at the beam entry end of said magnet pole pieces and spaced a short distance away from said magnet poles and spaced a short distance away from said magnet poles to provide a magnetic field free entry region for said ion beam prior to encountering said fringe focussing field of said angled pole piece edges and to enhance the effectiveness of said fringe focussing field.

11. The system of claim 10, wherein said magnet pole pieces have rear exit edges angled substantially to the exit path of the ion beam, and further comprising a beam exit magnetic field shunt located at the beam exit end of said magnet pole pieces and spaced a short distance away from said magnet poles to provide a magnetic field free exit region for said ion beam after passing through said fringe focussing field.

12. The system of claim 7, wherein said ion source means further comprises a deceleration electrode means mounted downstream of said extraction electrode means, said front plate of said ion source arc chamber being biased to a preanaylsis acceleration voltage, said extraction electrode means being biased to a voltage value relative to said preanalysis acceleration voltage to extract and accelerate ions from said source;

and said deceleration electrode means being biased to a voltage value relative to said extraction voltage to decrease substantially the velocity of ions passing through the region between said extraction electrode means and said deceleration electrode means.

13. The system of claim 12, further comprising a stabilized power supply means for supplying said preanalysis acceleration voltage and an unsabilized power supply means for supplying said voltage to said extraction electrode means so that said extraction electrode voltage will rapidly drop in magnitude when a spark discharge occurs between said source front plate and said extraction electrode means, to limit the energy of, and quickly quench, said spark without substantially affecting the velocity of extracted ions entering said analyzing means.

14. The system of claim 12, wherein said bias voltage on said extraction electrode means has a magnitude at least about ten percent of the difference in magnitudes of said preanaylsis acceleration voltage and the voltage applied to said deceleration electrode means.

15. The system of claim 7, further comprising a deceleration electrode means mounted downstream from said extraction electrode means, said ion source means and said extraction and deceleration electrodes means being mounted within a source chamber housing, and further comprising a support arrangement for said extraction electrode means and said deceleration electrode means including an electrode support base, a first support pillar arrangement mounted on one side of said electrode support base for supporting said extraction electrode means thereon in a cantilevered manner and having a shielded insulator section remote from said extraction electrode means, and a second support pillar arrangement for supporting said deceleration electrode means thereon in a cantilevered manner above and separated from said extraction electrode means;

said source chamber housing including an opening in one wall thereof running parallel to said support pillar arrangements and said support pillar arrangements and said cantilevered mounting of said electrodes providing a region of high vacuum pumping conductance thereat, such that gas from a gas fed ion source is more readily removed from said source chamber to avoid such gas entering the beam analyzing means and other portions of the system.

16. The system of claim 7, wherein said ion source means further comprises an elongated filament-cathode disposed lengthwise within said source chamber, and an elongated anode disposed adjacent said filament-cathode;

means applying a current generating electrical potential difference across said filament-cathode;

means applying an arc creating bias between said chamber and said filament-cathode to generate ions within said chamber; and

magnetic means applying a magnetic field parallel to said filament-cathode with a non-uniform field strength from one end of said filament cathode to the other to counteract non-uniform ion generation characteristics from one end of said source to the other.

17. The system of claim 16, wherein said magnetic means includes a pair of magnetic pole pieces positioned at opposite ends of said ion source means and substantially aligned with said filament-cathode and separate field coils positioned on said pole pieces for separately controlling the magnetic field intensity generated in the vicinity of each pole piece.

18. In a system for implanting ions into a target element, ion source means for producing an ion beam;

beam analyzing means for receiving said ion beam and selectively separating various ion species in said beam on the basis of mass to produce an analyzed beam exiting said analyzing means, and beam resolving means disposed in the path of said analyzed beam for permitting a preselected ion species to pass to said target element, said ion source means including a source chamber housing and an electrode module and a source module mounted within said housing;

said source module comprising a source mounting flange, an ion source carried on said source mounting flange, and a source insulator carried on said source mounting flange and being removably mounted along with said source mounting flange to said electrode module mounting flange such that said ion source module comprises a separately removable module.

19. The system of claim 18, wherein said electrode module includes a mounting flange, and electrode support base carried on said mounting flange, and an electrode assembly carried on said support base, said mounting flange being removably mounted to said source chamber housing such that said mounting flange, said support base and said electrode assembly comprise a separately removable module;

said source mounting flange and said source insulator being mounted to said electrode mounting flange.

20. The system of claim 19, wherein said electrode assembly comprises an extract in electrode, a deceleration electrode, a first support pillar arrangement mounted on one side of said electrode support base for supporting said extraction electrode thereon in a cantilevered manner and having a shielded insulator section remote from said extraction electrode, and a second support pillar arrangement mounted on the opposite side of said electrode support base for supporting said deceleration electrode thereon in a cantilevered manner above and separated from said extraction electrode;

said source chamber housing including an opening in one wall thereof running parallel to said support pillar arrangements and said support pillar arrangements and said contilevered mounting of said electrode providing a region of high vacuum pumping conductance thereat, such that gas from a gas fed ion source is more readily removed from said source chamber to avoid such gas entering the beam analyzing means and other portions of the system.

21. The system of claim 20, wherein said electrode module further comprises a beam control vane assembly carried on said electrode module mounting flange, said beam control vane assembly comprising a pair of upper vanes positioned downstream of said deceleration electrode, a vane support element mounted at one end of each of said vanes and extending past the outside edges of said support pillars for said electrodes and said electrode support base, rotation mounting means coupling to the other end of each of said vane support elements for rotationally mounting said vanes and said vane support element to said electrode assembly mounting flange, and vane driving means for driving said rotation mounting means to selectively position said vane support elements and said vanes so that said vanes intercept a preselected portion of the length of said ion beam passing through said deceleration electrode.

22. The system of claim 21, wherein said beam control vane assembly further comprises means for selectively driving only one of said vanes into and out of said beam while maintaining the other vane in a position which fully blocks one-half of the ion beam so that the characteristics of said ion beam can be analyzed by gradually passing incremental additional portions of one-half of said ion beam to said analyzing means.

23. In a method for operating an ion source system comprising an ion source having an ion emitting region, an extraction electrode positioned in the vicinity of said ion emitting region, and a second electrode positioned substantially adjacent said extraction electrode, the steps of:

applying a preanalysis acceleration voltage to said ion source;

applying to said extraction electrode a bias potential having a value relative to said preanalysis acceleration voltage to extract and accelerate ions from said source; and

applying to said second electrode a bias potential having a value relative to said bias potential value on said extraction electrode of the same order of magnitude as the value of the bias potential on the extraction electrode relative to the preanalysis acceleration voltage, to reduce substantially the velocity of ions travelling between said extraction electrode and said second electrode.

24. The method of claim 23, wherein the step of applying said preanalysis acceleration voltage to said ion source comprises applying a stabilized potential thereto and the step of applying a bias potential to said extraction electrode comprises applying an unstabilized potential thereto so that said potential with rapidly drop in magnitude when a spark discharge occurs between said ion source and said extraction electrode, to limit the energy of, a quickly quench, said spark without substantially affecting the velocity of extracted ions entering said analyzing means.

25. In a method for implanting ions of substantially a single preselected ions species into a target element, the steps of:

generating an ion beam of substantially uniform velocity and having a plurality of ion species therein, including said preselected ion species;

analyzing said ion beam to separate ions having different values of charge to mass ratio into different beam paths;

selecting from a group of beam resolving elements a particular beam resolving element; and

positioning said selected beam resolving element in the path of the ion beam of said preselected ion species to pass said ions to said target element.

26. In an ion source system, a source chamber with an elongated ion exit aperture in one wall thereof;

an elongated filament-cathode disposed lengthwise within said source chamber;

means applying a current generating electrical potential difference across said filament-cathode;

means applying an arc creating bias between said chamber and said filament-cathode to generate ions within said chamber; and

means applying a magnetic field parallel to said filament-cathode with a non-uniform field strength to counteract non-uniform ion generating characteristics from one end of said source to the other.

27. In an ion source system, a source chamber with an elongated ion exit aperture formed in one wall thereof;

an elongated filament-cathode disposed lengthwise within said source chamber and substantially parallel to said aperture;

a plurality of separate anode elements mounted within said source chamber with electrical isolation therebetween; and

means for applying separate bias voltages to said separate anode structures for independent control of the ion current generated in the vicinity of each of said anode structures.

28. The ion source system of claim 27, further comprising means for separately detecting the current flow between each of said separate anode elements and said filament-cathode.

29. In a method for generating an ion beam of selecting energy for an ion implantation system, the steps of:

creating a plasma of ions within a generally confined volume;

extracting a beam of ions from said plasma with an accelerating voltage; and

decelerating said beam of ions with a substantial decelerating voltage relative to said accelerating voltage, said deceleration voltage being of the same order of magnitude as said accelerating voltage.

30. The method of claim 29, wherein said deceleration of said beam produced by said deceleration voltage has a magnitude at least ten percent of the selected energy of the beam.

31. In a method for implanting ions of substantially a single preselected ion species into a target element, the steps of:

generating an ion beam having a plurality of ion species therein, including said preselected ion species;

analyzing said ion beam to separate ions having different values of charge to mass ratio into different focused ion beam paths; and

passing the focused ion beam of said preselected ion species through a preselected one of a plurality of beam resolving elements into said target element.