DEPOSITION OF CRYSTALLINE LAYERS ON POLYMER SUBSTRATES USING NANOPARTICLES AND LASER NANOFORMING

Abstract

A method of forming crystalline semiconducting layers on low melting or low softening point substrates includes the steps of providing an aqueous solution medium including a plurality of semiconductor nanoparticles dispersed therein having a median size less than 10 nm, and applying the solution medium to at least one region of a substrate to be coated. The substrate has a melting or softening point of <200® C. The solution medium is evaporated and the at least one region is laser irradiated for fusing the nanoparticles followed by annealing to obtain a continuous film having a recrystallized microstructure. An article includes a polycrystalline semiconducting layer including a plurality of crystallites predominately in the size range of 2 to 50 μm, and a substrate having a melting or softening point of <200° C. supporting the semiconducting layer. An average grain size of the crystallites is less at an interface proximate to the semiconducting layer as compared to an average grain size further away from the interface.

Description

BRIEF DESCRIPTION OF FIGURES

There is shown in the drawings embodiments which are presently preferred, it being understood, however, that the invention can be embodied in other forms without departing from the spirit or essential attributes thereof.

FIG. 1( a) shows steps in a likely mechanism of film formation during laser nanoforming of thin film polycrystalline silicon from an aqueous nanoparticle comprising dispersion, including a cross sectional schematic of an exemplary article according to the invention formed after coalescence and film formation.

FIG. 1( b) shows a cross sectional view of an article 180 comprising a dielectric layer 185 disposed between a semiconducting layer which comprises a plurality of spaced apart crystalline (single crystal or polycrystalline) regions 195 and the substrate 190.

FIG. 2 is a schematic of an exemplary deposition system for depositing thin films using nanoparticles and laser nanoforming according to the invention.

FIG. 3 provides DSC data for single crystal silicon, 5 nm and 30 nm silicon particles showing bulk melting point of nanoparticles ˜1149° C. approximately 279° C. lower than the bulk melting temperature of silicon ˜1428° C. Point A corresponds to 90% of T_mn=1149° C. and point B corresponds to 110% of T_mn for curves 1 and 2.

FIG. 4 shows a comparison of melting temperatures obtained by various techniques. The theoretical calculated values for the melting temperature is T_mn=1094° C., using DSC is T_mn=1149° C., using optical pyrometer is T_mn=1188° C. and for bulk silicon is T_mb=1428° C.

FIG. 5 is a scanned SEM image of a laser nanoformed film at 9 W in CW mode on flexible polymer substrate.

FIG. 6 is an EDS analysis on silicon nanoparticles laser treated on flexible polymer substrate showing Si, C and O along with Na, Cl and Ca.

FIG. 7 is an XPS analysis of laser nanoformed silicon film on rigid polymer substrates showing 17% Si, 0.5% N, 0.7% Ca, 41.0% O and 40.6% C.

FIG. 8( a) is a plot of Raman peak position observed with increasing incident laser power in CW mode for laser nanoformed thin films on polymer substrates. The standard used is a single crystal silicon sample.

FIG. 8( b) is a plot of Raman peak position observed with increasing annealing time for laser nanoformed thin films on polymer substrates at 1 W in CW mode on rigid polymer substrate.

Claims

1. A method of forming crystalline semiconducting layers on low melting or low softening point substrates, comprising the steps of: providing an aqueous solution medium including a plurality of semiconductor nanoparticles dispersed therein having a median size less than 10 nm;applying said solution medium to at least one region of a substrate to be coated, said substrate having a melting or softening point of <200° C.;evaporating said solution medium, andlaser irradiating said at least one region for fusing said nanoparticles in said at least one region followed by annealing obtain a continuous film having a recrystallized microstructure.

2. The method of claim 1, wherein said fusing is performed at a first power for a first time, and said annealing is performed at a second power for a second time, wherein said second power is lower than said first power, and said second time is longer than said first time.

3. The method of claim 1, wherein said laser irradiating step comprises continuous wave (CW) laser beam heating.

4. The method of claim 1, wherein said aqueous solution consists essentially of water and said nanoparticles.

5. The method of claim 1, wherein said evaporating step comprises laser evaporating.

6. The method of claim 1, wherein said at least one region is a single continuous film.

7. The method of claim 1, wherein said at least one region comprises a plurality of spaced apart regions.

8. The method of claim 1, wherein said nanoparticles comprise silicon nanoparticles, further comprising the step of in situ doping of said silicon nanoparticles, wherein dopants from said doping are activated during said laser irradiating step.

9. The method of claim 1, further comprising the step of placing a plurality of single crystal seeds on said substrate before said applying step.

10. An article, comprising: a polycrystalline semiconducting layer comprising a plurality of crystallites predominately in the size range of 2 to 50 μm, anda substrate having a melting or softening point of <200° C. supporting said semiconducting layer, wherein an average grain size of said crystallites is less at an interface proximate to said substrate as compared to an average grain size in the semiconducting layer remote from said interface.

11. The article of claim 10, wherein said semiconducting layer comprises silicon or germanium.

12. The article of claim 10, further comprising a silicon dioxide layer disposed between said semiconducting layer and said substrate, wherein said semiconducting layer comprises a plurality of spaced apart regions.

13. The article of claim 10, wherein said substrate comprises a polymer.