Plasma grid implant system for use in solar cell fabrications

• US 8,749,053 B2
• Filed: 06/22/2010
• Issued: 06/10/2014
• Est. Priority Date: 06/23/2009
• Status: Active Grant

• Current Assignee: Intevac
• Original Assignee: Intevac
• Inventors: Adibi, Babak, Chun, Moon
• Primary Examiner(s): Kraig, William F
• Assistant Examiner(s): Chin, Edward
• Application Number:
  US12/821,053
• Publication Number:
  US 20100323508A1
• Time in Patent Office: 1,449 Days
• Field of Search: 438/513, 156/345, 257/E21.334
• US Class Current: 257/715
• 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 for fabricating solar cells from a substrate, comprising:

a plasma source configured to provide plasma in a plasma region;

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

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

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 through the third grid plate subsequent to the ions passing through the second grid plate, wherein the third grid plate is coupled to ground potential;

a substrate holder configured to support the substrate in a position where the substrate is implanted with the ions subsequent to the ions passing through the third grid plate to thereby dope the substrate and fabricate a solar cell;

a chamber defined by chamber walls, wherein the plasma region, the first grid plate, the second grid plate, and the third grid plate are housed within the chamber; and

, a conveyor belt transporting the substrates from an atmospheric side to vacuum side inside the chamber;

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 for 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 beamlets that have passed through different apertures of the third grid plate and combined by space charge expansion into a uniform beam;

the selective implantation position is configured for 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 individual ion beamlets that have passed through the different apertures of the third grid plate; and

, wherein the first grid plate, the second grid plate and the third grid plate form a grid plate assembly, wherein the grid plate assembly is configured to focus the beamlets into known shapes onto the substrate to thereby form the selective implantation.

2. The system of claim 1, wherein:

the conveyor is configured to transport multiple substrate for simultaneous homogeneous implantation, followed by simultaneous selective implantation.

3. 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.

4. 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.

5. The system of claim 3, wherein each one of the circular hole 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.

6. 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.

7. The system of claim 1, wherein the chamber walls are configured to repel ions in the plasma region using a magnetic field to push the plasma off the chamber walls.

8. The system of claim 7, wherein one or more magnets are coupled to the chamber walls.

9. The system of claim 1, wherein the first grid plate is configured to be DC positively-biased, either in continuous mode or in pulsed mode.

10. The system of claim 1, further comprising a first pulse forming network coupled to the second grid plate such that the second grid plate is configured to be DC negatively-biased, in pulsed mode.

11. The system of claim 1, wherein the first grid plate, the second grid plate, and the substrate holder are all configured to have their positions adjustable.

12. The system of claim 1, wherein the third grid plate is removable.

13. The system of claim 1, wherein the first grid plate and the second grid plates are configured to accelerate ions from the plasma and minimize back streaming electrons.

14. The system of claim 10, further comprising a second pulse-forming network coupled to the plasma source and in modulation with the first pulse-forming network.

15. The system of claim 1, further comprising a high-voltage pulser coupled to the substrate holder to negatively bias the substrate.

16. The system of claim 1, further comprising a shadow mask positioned close to the third grid plate.

17. The system of claim 1, further comprising a hard mask placed in contact with the substrate.

18. The system of claim 1, wherein the chamber walls are configured to enclose multiple substrates for simultaneous implantation.