Surface planarization of thin silicon films during and after processing by the sequential lateral solidification method

• US 6,830,993 B1
• Filed: 02/04/2002
• Issued: 12/14/2004
• Est. Priority Date: 03/21/2000
• Status: Expired due to Term

• Current Assignee: Trustees Of Columbia University In The City Of New York (Columbia University)
• Original Assignee: Trustees Of Columbia University In The City Of New York (Columbia University)
• Inventors: Sposili, Robert S., Im, James S., Crowder, Mark A.
• Primary Examiner(s): Niebling, John F.
• Assistant Examiner(s): Roman, Angel
• Application Number:
  US09/979,201
• Time in Patent Office: 1,044 Days
• Field of Search: 438/479
• US Class Current: 438/479
• CPC Class Codes: B23K 2101/40 Semiconductor devices
• CPC Class Codes: B23K 26/06 Shaping the laser beam, e.g. by masks or multi-focusing
• CPC Class Codes: B23K 26/0622 by shaping pulses
• CPC Class Codes: B23K 26/066 by using masks
• CPC Class Codes: B23K 26/0853 Devices involving movement of the workpiece in at least in two axial directions, e.g. in a plane
• CPC Class Codes: B23K 26/3576 Diminishing rugosity, e.g. grinding; Polishing; Smoothing
• CPC Class Codes: H01L 21/02532 Silicon, silicon germanium, germanium
• CPC Class Codes: H01L 21/02678 Beam shaping, e.g. using a mask
• CPC Class Codes: H01L 21/02686 Pulsed laser beam
• CPC Class Codes: H01L 21/02691 Scanning of a beam
• CPC Class Codes: H01L 21/302 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
• CPC Class Codes: H01L 21/32115 Planarisation
• CPC Class Codes: H01L 21/67253 Process monitoring, e.g. flow or thickness monitoring
• CPC Class Codes: Y10S 438/942 Masking

Abstract

Systems and methods for reducing a surface roughness of a polycrystalline or single crystal thin film produced by the sequential lateral solidification process are disclosed. In one arrangement, the system includes an excimer laser (110) for generating a plurality of excimer laser pulses of a predetermined fluence, an energy density modulator (120) for controllably modulating the fluence of the excimer laser pulses such that the fluence is below that which is required to completely melt the thin film, a beam homoginizer (144) for homoginizing modulated laser pulses in a predetermined plane, a sample stage (170) for receiving homoginized laser pulses to effect melting of portions of the polycrystalline or single crystal thin film corresponding to the laser pulses, translating means for controllably translating a relative position of the sample stage (170) with respect to the laser pulses, and a computer (110) for coordinating the excimer pulse generation and fluence modulation with the relative positions of the sample stage (170) to thereby process the polycrystalline or single crystal thin film by sequential translation of the sample stage (170) relative to the laser pulses.

Claims

1. A method for reducing a surface roughness of a polycrystalline or single crystal thin film produced by the sequential lateral solidification process, comprising the steps of:

(a) generating a plurality of excimer laser pulses of a predetermined fluence;

(b) controllably modulating said fluence of said excimer laser pulses emitted by said excimer laser such that said fluence is below that which is required to completely melt said polycrystalline or single crystal thin film;

(c) homogenizing said modulated laser pulses in a predetermined plane;

(d) effecting partial melting of portions of said polycrystalline or single crystal thin film corresponding to said homogenized laser pulses; and

(e) controllably translating a relative position of said polycrystalline or single crystal thin film with respect to said homogenized laser pulses to process said polycrystalline or single crystal thin film by sequential translation of said sample stage relative to said homogenized laser pulses at corresponding sequential locations thereon.

2. The method of claim 1, wherein said excimer laser pulses comprise ultraviolet excimer laser pulses.

3. The method of claim 1, wherein said homogenizing step comprises homogenizing said modulated laser pulses with a tophat profile in both the x and y directions.

4. The method of claim 1, wherein said modulating step comprises attenuating said fluence of said excimer laser pulses to approximately 25% to 75% of the full melt threshold of said polycrystalline or single crystal thin film.

5. The method of claim 1, wherein said translating step comprises controllably translating said polycrystalline or single crystal thin film in one direction orthogonal to a direction of said homogenized laser pulses.

6. The method of claim 5, wherein said homogenizing step comprises homogenizing said modulated laser pulses with a tophat profile in at least said direction orthogonal to a direction of said modulated laser pulses, and wherein said translating step comprises translating said polycrystalline or single crystal thin film in said direction orthogonal to a direction of said homogenized laser pulses, such that sequential homogenized laser pulses are incident on slightly overlapping regions of said polycrystalline or single crystal thin film.

7. The method of claim 1, wherein said translating step comprises controllably translating said polycrystalline or single crystal thin film in two orthogonal directions that are perpendicular to a path formed by said homogenized laser pulses.

8. The method of claim 7, wherein said homogenizing step comprises homogenizing said modulated laser pulses with a tophat profile in said two directions orthogonal to a direction of said modulated laser pulses, and wherein said translating step comprises translating said polycrystalline or single crystal thin film in said two directions such that sequential homogenized laser pulses are incident on slightly overlapping regions of said polycrystalline or single crystal thin film in said two directions.

9. The method of claim 1, wherein said translating step comprises translating said polycrystalline or single crystal thin film after at least two homogenized beam pulses irradiate said portion of said polycrystalline or single crystal thin film.