PLASMA GRID IMPLANT SYSTEM FOR USE IN SOLAR CELL FABRICATIONS

• US 20100323508A1
• Filed: 06/22/2010
• Published: 12/23/2010
• Est. Priority Date: 06/23/2009
• Status: Active Grant

• Current Assignee: Intevac
• Original Assignee: Solar Implant Technologies, Inc. (Intevac, Inc.)
• Inventors: Chun, Moon, Adibi, Babak
• Granted Patent: US 8,749,053 B2
• Time in Patent Office: Days
• US Class Current: 438/513
• CPC Class Codes: C23C 14/042 using masks
• CPC Class Codes: C23C 14/48 Ion implantation
• CPC Class Codes: H01J 2237/0437 Semiconductor substrate
• CPC Class Codes: H01J 2237/184 Vacuum locks
• CPC Class Codes: H01J 2237/201 for mounting multiple objects
• CPC Class Codes: H01J 2237/327 Arrangements for generating the plasma
• CPC Class Codes: H01J 2237/3365 Plasma source implantation
• CPC Class Codes: H01J 37/185 Means for transferring objects between different enclosures of different pressure or atmosphere
• CPC Class Codes: H01J 37/3171 for ion implantation plasma immersion ion implantation H01J37/32412
• CPC Class Codes: H01J 37/32412 Plasma immersion ion implantation
• CPC Class Codes: H01J 37/32422 Arrangement for selecting ions or species in the plasma
• CPC Class Codes: H01L 21/2236 from or into a plasma phase
• CPC Class Codes: H01L 31/068 the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
• CPC Class Codes: H01L 31/0682 back-junction, i.e. rearside emitter, solar cells, e.g. interdigitated base-emitter regions back-junction cells
• CPC Class Codes: H01L 31/1804 comprising only elements of Group IV of the Periodic Table
• CPC Class Codes: H01L 31/1864 Annealing
• CPC Class Codes: H01L 31/1876 Particular processes or apparatus for batch treatment of the devices
• CPC Class Codes: Y02E 10/547 Monocrystalline silicon PV cells
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

A method of ion implantation comprising: providing a plasma within a plasma region of a chamber; positively biasing a first grid plate, wherein the first grid plate comprises a plurality of apertures; negatively biasing a second grid plate, wherein the second grid plate comprises a plurality of apertures; flowing ions from the plasma in the plasma region through the apertures in the positively-biased first grid plate; flowing at least a portion of the ions that flowed through the apertures in the positively-biased first grid plate through the apertures in the negatively-biased second grid plate; and implanting a substrate with at least a portion of the ions that flowed through the apertures in the negatively-biased second grid plate.

Claims

1. A plasma grid implantation system comprising:

a plasma source configured to provide plasma;

a first grid plate comprising a plurality of apertures configured to allow ions from the plasma in a plasma region to pass therethrough, wherein the first grid plate is configured to be positively biased by a power supply;

a second grid plate comprising a plurality of apertures configured to allow the ions to pass therethrough subsequent to the ions passing through the first grid plate, wherein the second grid plate is configured to be negatively biased by a power supply; and

a substrate holder configured to support a substrate in a position where the substrate is implanted with the ions subsequent to the ions passing through the second grid plate.

2. The system of claim 1, wherein:

the first grid plate is positively biased by a power supply; and

the second grid plate is negatively biased by a power supply.

3. The system of claim 1, wherein:

the position of at least one of the first grid plate, the second grid plate, and the substrate holder is configured to be adjusted between a homogeneous implantation position and a selective implantation position;

the homogeneous implantation position is configured to enable a single laterally-homogeneous ion implantation across the substrate on the substrate holder, wherein the single laterally-homogeneous ion implantation is formed from a combination of ions that have passed through different apertures of the second grid plate; and

the selective implantation position is configured to enable a plurality of laterally spaced-apart ion implantations of the substrate on the substrate holder, wherein the plurality of laterally spaced-apart ion implantations is formed from ions that have passed through the different apertures of the second grid plate.

4. The system of claim 1, further comprising a third grid plate disposed between the second grid plate and the substrate holder, the third grid plate comprising a plurality of apertures configured to allow the ions to pass therethrough subsequent to the ions passing through the second grid plate.

5. The system of claim 4, wherein the third grid plate is grounded.

6. The system of claim 4, wherein:

the position of at least one of the third grid plate and the substrate holder is configured to be adjusted between a homogeneous implantation position and a selective implantation position;

the homogeneous implantation position configured to enable a single laterally-homogeneous ion implantation across the substrate on the substrate holder, wherein the single laterally-homogeneous ion implantation is formed from a combination of ions that have passed through different apertures of the second grid plate; and

the selective implantation position configured to enable a plurality of laterally spaced-apart ion implantations of the substrate on the substrate holder, wherein the plurality of laterally spaced-apart ion implantations is formed from ions that have passed through the different apertures of the second grid plate.

7. The system of claim 1, wherein the apertures of at least one of the first grid plate and the second grid plate are substantially circular holes.

8. The system of claim 1, wherein the apertures of at least one of the first grid plate and the second grid plate are elongated slots.

9. The system of claim 1, wherein each one of the apertures of at least one of the first grid plate and the second grid plate comprises a top end and a bottom end, wherein the bottom end is closer to the substrate holder than the top end, and wherein the diameter of each aperture gradually increases from the top end to the bottom end.

10. The system of claim 1, wherein the first grid plate and the second grid plate comprise a material chosen from the group consisting of:

silicon, graphite, silicon carbide, and tungsten.

11. The system of claim 1, further comprising a chamber defined by chamber walls, wherein the plasma region, the first grid plate, and the second grid plate are housed within the chamber, and wherein the chamber walls are configured to repel ions in the plasma region using an electric field.

12. The system of claim 11, wherein one or more magnets are coupled to the chamber walls.

13. A method of ion implantation comprising:

providing a plasma within a plasma region of a chamber;

positively biasing a first grid plate, wherein the first grid plate comprises a plurality of apertures and is disposed in a first position;

negatively biasing a second grid plate, wherein the second grid plate comprises a plurality of apertures and is disposed in a first position;

flowing ions from the plasma in the plasma region through the apertures in the positively-biased first grid plate;

flowing at least a portion of the ions that flowed through the apertures in the positively-biased first grid plate through the apertures in the negatively-biased second grid plate; and

implanting a substrate with at least a portion of the ions that flowed through the apertures in the negatively-biased second grid plate, wherein the substrate is disposed in a first position.

14. The method of claim 13, wherein a shadow mask comprising a plurality of openings formed therethrough is disposed a predetermined distance away from the substrate, and the method further comprises:

flowing at least a portion of the ions that flowed through the apertures in the negatively-biased second grid plate through the openings in the shadow mask before implanting the substrate.

15. The method of claim 13, wherein a photoresist mask comprising a plurality of openings formed therethrough is placed in contact with the substrate, and the method further comprises:

flowing at least a portion of the ions that flowed through the apertures in the negatively-biased second grid plate through the openings in the photoresist mask before implanting the substrate.

16. The method of claim 13, further comprising:

adjusting the position of at least one of the first grid plate, second grid plate, and the substrate holder to a second position;

providing a plasma within the plasma region subsequent to the adjustment to the second position;

flowing ions from the plasma in the plasma region through the apertures in the positively-biased first grid plate subsequent to adjustment to the second position;

flowing at least a portion of the ions that flowed through the apertures in the positively-biased first grid plate through the apertures in the negatively-biased second grid plate subsequent to adjustment to the second position; and

implanting a substrate with at least a portion of the ions that flowed through the apertures in the negatively-biased second grid plate subsequent to adjustment to the second position,

wherein the implantation performed when the at least one of the first grid plate, second grid plate, and the substrate holder was in the first position forms a single laterally-homogeneous ion implantation across the substrate, wherein the single laterally-homogeneous ion implantation is formed from a combination of ions that have passed through different apertures of the second grid plate, and

wherein the implantation performed when the at least one of the first grid plate, second grid plate, and the substrate holder was in the second position forms a plurality of laterally spaced-apart ion implantations of the substrate, wherein the plurality of laterally spaced-apart ion implantations is formed from ions that have passed through the different apertures of the second grid plate.

17. The method of claim 13, wherein a third grid plate is disposed between the second grid plate and the substrate, the third grid plate disposed in a first position and comprising a plurality of apertures configured to allow the ions to pass therethrough subsequent to the ions passing through the second grid plate.

18. The system of claim 17, wherein the third grid plate is grounded.

19. The method of claim 17, further comprising:

adjusting the position of at least one of the first grid plate, second grid plate, the third grid plate, and the substrate holder to a second position;

providing a plasma within the plasma region subsequent to the adjustment to the second position;

flowing ions from the plasma in the plasma region through the apertures in the positively-biased first grid plate subsequent to adjustment to the second position;

flowing at least a portion of the ions that flowed through the apertures in the positively-biased first grid plate through the apertures in the negatively-biased second grid plate subsequent to adjustment to the second position;

flowing at least a portion of the ions that flowed through the apertures in the negatively-biased second grid plate through the apertures in the third grid plate subsequent to adjustment to the second position; and

implanting a substrate with at least a portion of the ions that flowed through the apertures in the third grid plate subsequent to adjustment to the second position,

wherein the implantation performed when the at least one of the first grid plate, second grid plate, the third grid plate, and the substrate holder was in the first position forms a single laterally-homogeneous ion implantation across the substrate, wherein the single laterally-homogeneous ion implantation is formed from a combination of ions that have passed through different apertures of the third grid plate, and

wherein the implantation performed when the at least one of the first grid plate, second grid plate, the third grid plate, and the substrate holder was in the second position forms a plurality of laterally spaced-apart ion implantations of the substrate, wherein the plurality of laterally spaced-apart ion implantations is formed from ions that have passed through the different apertures of the third grid plate.

20. The method of claim 13, wherein the apertures of at least one of the first grid plate and the second grid plate are substantially circular holes.

21. The method of claim 13, wherein the apertures of at least one of the first grid plate and the second grid plate are elongated slots.

22. The method of claim 13, wherein each one of the apertures of at least one of the first grid plate and the second grid plate comprises a top end and a bottom end, wherein the bottom end is closer to the substrate holder than the top end, and wherein the diameter of each aperture gradually increases from the top end to the bottom end.

23. The method of claim 13, wherein the first grid plate and the second grid plate comprise a material chosen from the group consisting of:

silicon, graphite, silicon carbide, and tungsten.

24. The method of claim 13, wherein the plasma region, the first grid plate, and the second grid plate are housed within a chamber that is defined by chamber walls, and wherein the chamber walls are configured to repel ions in the plasma region using an electric field.

25. The method of claim 13, further comprising the step of applying a pulsed voltage to the plasma.

26. The method of claim 13, further comprising the step of applying a pulsed voltage to the substrate.

27. The method of claim 26, wherein the pulsed voltage is directed towards a plurality of different locations on the substrate.

28. The method of claim 13, further comprising:

passing the substrate through a first plurality of differentially-pumped stages prior to the substrate being implanted with the ions, wherein each stage in the first plurality of differentially-pumped stages comprises a lower pressure than the previous stage in the first plurality of differentially-pumped stages;

passing the substrate from the first plurality of differentially-pumped stages directly to an implantation stage;

passing the substrate from the implantation stage directly to a second plurality of differentially-pumped stages subsequent to the substrate being implanted with the ions, and

passing the substrate through the second plurality of differentially-pumped stages, wherein each stage in the second plurality of differentially-pumped stages comprises a higher pressure than the previous stage in the second plurality of differentially-pumped stages,

wherein the implantation stage comprises a lower pressure than any of the stages in the first plurality and second plurality of differentially-pumped stages.

29. A plasma grid implantation system comprising:

a plasma source configured to provide plasma;

a grid assembly comprising a plurality of grid plates, wherein each grid plate comprises a plurality of apertures configured to allow ions from the plasma to pass therethrough; and

a substrate holder configured to support a substrate in a position where the substrate is implanted with the ions subsequent to the ions passing through the plurality of apertures of the grid plates,

wherein at least one of the substrate holder and the grid plates is configured to be adjusted between a homogeneous implantation position and a selective implantation position,

wherein the homogeneous implantation position is configured to enable a single laterally-homogeneous ion implantation across the substrate on the substrate holder, the single laterally-homogeneous ion implantation being formed from a combination of ions that have passed through different apertures of the second grid plate, and

wherein the selective implantation position is configured to enable a plurality of laterally spaced-apart ion implantations of the substrate on the substrate holder, the plurality of laterally spaced-apart ion implantations being formed from ions that have passed through the different apertures of the second grid plate.

30. The system of claim 29, wherein the plurality of grid plates comprises:

a first grid plate comprising a plurality of apertures configured to allow ions from the plasma in a plasma region to pass therethrough; and

a second grid plate comprising a plurality of apertures configured to allow the ions to pass therethrough subsequent to the ions passing through the first grid plate.

31. The system of claim 30, wherein the first grid plate is configured to be positively-biased, either continuously in DC mode or in pulsed mode, by a power supply.

32. The system of claim 31, wherein the second grid plate is configured to be negatively-biased, either continuously in DC mode or in pulsed mode, by a power supply.

33. The system of claim 32, wherein the plurality of grid plates further comprises a third grid plate comprising a plurality of apertures configured to allow the ions to pass therethrough subsequent to the ions passing through the second grid plate.

34. The system of claim 33, wherein the third grid plate is configured to be grounded.

35. The system of claim 30, wherein the first grid plate, the second grid plate, and the substrate holder are all configured to have their positions adjusted.

36. A method of ion implantation comprising:

providing a plasma within a plasma region of a chamber;

providing a grid assembly comprising a plurality of grid plates, wherein each grid plate comprises a plurality of apertures;

flowing a first set of ions from the plasma in the plasma region through the apertures in each of the grid plates in the grid assembly while each of the grid plates is in a first position;

homogeneously implanting a substrate with at least a portion of the first set of ions that flowed through the apertures in the grid plates while the substrate is supported in a first position by a substrate holder, thereby forming a single laterally-homogeneous ion implantation across the substrate from a combination of the first set of ions that have passed through different apertures of the same grid plate;

adjusting the position of the substrate or at least one of the grid plates to a second position;

flowing a second set of ions from the plasma in the plasma region through the apertures in each of the grid plates in the grid assembly subsequent to the adjustment to the second position;

selectively implanting the substrate with at least a portion of the second set of ions that flowed through the apertures in the grid plates subsequent to the adjustment to the second position, thereby forming a plurality of laterally spaced-apart ion implantations on the substrate from a portion of the second set of ions that have passed through different apertures of the same grid plate.

37. The method of claim 36, wherein the adjusting step comprises adjusting the position of the substrate.

38. The method of claim 37, wherein adjusting the position of the substrate comprises moving the substrate closer to the grid assembly.

39. The method of claim 36, wherein the adjusting step comprises adjusting the position of one of the grid plates.

40. The method of claim 39, wherein adjusting the position of one of the grid plates comprises moving one of the grid plates closer to the substrate.

41. The method of claim 36, wherein the plurality of grid plates comprises a first grid plate and a second grid plate, the first grid plate being positively-biased, and the second grid plate being negatively biased.

42. The method of claim 41, wherein the plurality of grid plates further comprises a third grid plate that is grounded.

43. A method of ion implantation comprising:

providing a first single type of dopant material to a plasma generator;

the plasma generator breaking up the first single type of dopant material into a first plurality of dopant species; and

implanting a substrate with the first plurality of dopant species.

44. The method of claim 43, wherein the substrate is implanted with the first plurality of dopant species in a single implantation step.

45. The method of claim 43, wherein each one of the dopant species is implanted into the substrate at a different depth.

46. The method of claim 43, wherein the first single type of dopant material is phosphine.

47. The method of claim 46, wherein the first plurality of dopant species comprises P⁺, P⁺⁺, P⁺⁺⁺, P₂⁺, P₃⁺, and P₅⁺.

48. The method of claim 43, wherein the first single type of dopant material is boron or arsenic.

49. The method of claim 43, wherein:

a second single type of dopant material is provided to the plasma generator;

the plasma generator breaks up the second single type of dopant material into a second plurality of dopant species during the same period that the plasma generator breaks up the first single type of dopant material into the first plurality of dopant species; and

the second plurality of dopant species is implanted into the substrate during the same period that the first plurality of dopant species is implanted into the substrate.

50. The method of claim 49, wherein the first single type of dopant material and the second single type of dopant material are each a precursor gas.

51. The method of claim 50, wherein the first single type of dopant material is arsine and the second single type of dopant material is phosphine.