Grain Boundary Confinement in SOI Films using Patterned AR Coatings and Seeded Oscillatory Growth

  • PDF / 1,428,208 Bytes
  • 6 Pages / 417.6 x 639 pts Page_size
  • 64 Downloads / 189 Views

DOWNLOAD

REPORT


GRAIN BOUNDARY CONFINEMENT IN SOI FILMS USING PATTERNED AR COATINGS AND SEEDED OSCILLATORY GROWTH

C.I. DROWLEY, P. ZORABEDIAN, AND T.I. KAMINS Hewlett-Packard Laboratories, 3500 Deer Creek Road, Palo Alto, CA 94304

ABSTRACT Regular arrays of grain-boundary-free silicon strips several hundred microns long have been produced in a silicon-on-insulator (SOI) structure by using a patterned anti-reflection (AR) coating in combination with seeded oscillatory growth techniques. The AR coating pattern consists of a series of parallel stripes (typically 10 pm wide, separated by 10 um spaces) starting from a seeding window. A laser beam (typically a 50 pm x 250 um elliptical beam) is scanned perpendicular to the stripes, with the long axis of the beam parallel to the scan direction. The beam is stepped 1-2 pm between successive scans to advance the single crystal along the direction of the AR stripes. Grain boundaries are confined to the region under the AR stripes. Stereographic analysis of KOH etch pits formed in the singlecrystal strips has shown that the orientation of the stripes gradually rotates from (001)[110) to (013)[331) as the crystal propagates away from the seed. MOS transistors formed in the single-crystal strips have mobilities comparable to devices formed in bulk films. These mobilities are approximately 20% higher than those found in devices formed in large-grain recrystallized polysilicon films. INTRODUCTION A number of techniques have been proposed to control or eliminate grain boundaries in laser-recrystallizedsilicon-on-insulator by controlling lateral temperature gradients. One technique [1) uses polycrystalline silicon (polysilicon) islands in contact with a seeding window. The islands are surrounded by oxide regions which absorb more power than the islands; consequently, a concave melt front is produced when a laser beam is scanned across an island. When a beam is scanned perpendicular to the long axis of the island and stepped along the long axis, a single crystal may be propagated from the seed along the island. The above technique is called "seeded oscillatory growth" because of the geometry and the scan method. The technique suffers from the disadvantage that relatively complicated processing (a double local oxidation) must be used to produce the islands. An alternative method [2,3) of controlling the grain boundaries uses a patterned anti-reflection (AR) coating to control the shape of the beaminduced melt front. The beam is scanned parallel to a series of stripes of AR coating over the polysilicon film. Single-crystal material may be propagated between stripes near the center of the beam. Drawbacks of this technique are that the single crystal doesn't propagate well near the edges of the beam, and that overlapping successive scans can destroy the single crystal produced by the earlier scans (cf. Fig. 1 of ref. [3]). In this paper we present a recrystallization method which combines aspects of the two techniques outlined above while eliminating some of their drawbacks. The technique is capable