Method for ion implant using grid assembly

• US 8,697,552 B2
• Filed: 01/31/2012
• Issued: 04/15/2014
• Est. Priority Date: 06/23/2009
• Status: Active Grant

• Current Assignee: Intevac
• Original Assignee: Intevac
• Inventors: Adibi, Babak, Chun, Moon
• Primary Examiner(s): Smoot, Stephen W
• Assistant Examiner(s): Chin, Edward
• Application Number:
  US13/363,347
• Publication Number:
  US 20120129325A1
• Time in Patent Office: 805 Days
• Field of Search: 438/513, 257/E21.334, 257/E21.143
• US Class Current: 438/511
• 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
• 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 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 positioned in its respective 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 its respective 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 respective second position and thereafter 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 and selectively implanting the substrate with at least a portion of the second set of ions that flowed through the apertures in the grid plates, 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.

2. The method of claim 1, 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 method further comprises repelling ions in the plasma region from the chamber walls using an electric field.

3. The method of claim 1, further comprising the step of applying a pulsed voltage to the plasma.

4. The method of claim 1, further comprising the step of applying a pulsed voltage to the substrate.

5. The method of claim 1, 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.

6. The method of claim 1, wherein the adjusting step comprises adjusting the position of the substrate.

7. The method of claim 1, wherein the adjusting step comprises adjusting the position of one of the grid plates.

8. The method of claim 1, wherein the plurality of grid plates comprises a first grid plate and a second grid plate, and the method further comprising positively biasing the first grid plate and negatively biasing the second grid plate.

9. The method of claim 1, wherein homogeneously implanting a substrate comprises:

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

igniting plasma in the plasma generator to break up the first single type of dopant material into a first plurality of dopant species;

implanting a substrate with the first plurality of dopant species in a single implantation step, wherein each one of the dopant species is implanted into the substrate at a different depth.

10. The method of claim 4, further comprising causing the pulsed voltage to be directed towards a plurality of different locations on the substrate.

11. The method of claim 6, wherein adjusting the position of the substrate comprises moving the substrate closer to the grid assembly.

12. The method of claim 7, wherein adjusting the position of one of the grid plates comprises moving one of the grid plates closer to the substrate.

13. The method of claim 8, 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.

14. The method of claim 8, wherein the plurality of grid plates further comprises a third grid plate that is grounded.

15. The method of claim 8, 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 9, wherein the first single type of dopant material is phosphine.

17. The method of claim 9, wherein the first single type of dopant material is boron or arsenic.

18. The method of claim 9, further comprising:

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

igniting the plasma to 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

,

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

19. The method of claim 15, wherein a third grid plate is disposed between the second grid plate and the substrate, the third grid plate comprising a plurality of apertures, and the method further comprises:

flowing ions to pass through the third grid plate subsequent to the ions passing through the second grid plate.

20. The method of claim 16, wherein the first plurality of dopant species comprises P⁺, P⁺⁺, P⁺⁺⁺, P₂⁺, P₃⁺, and P₅⁺.

21. The method of claim 18, wherein the first single type of dopant material and the second single type of dopant material are each a precursor gas.

22. The method of claim 19, further comprising coupling the third grid plate to ground potential.

23. The method of claim 19, wherein adjusting the position of the substrate or at least one of the grid plates comprises changing the position of at least one of the first grid plate, second grid plate, the third grid plate, and the substrate holder and thereafter performing the steps:

maintaining a plasma within the plasma region;

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;

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; and

,

implanting a substrate with at least a portion of the ions that flowed through the apertures in the third grid plate;

wherein,

the implantation performed prior to changing the position of at least one of the first grid plate, second grid plate, the third grid plate, and the substrate holder 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 after changing the position of at least one of the first grid plate, second grid plate, the third grid plate, and the substrate holder 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.

24. The method of claim 21, wherein the first single type of dopant material is arsine and the second single type of dopant material is phosphine.