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Inc.

Laser andElectron-Beam Solid Interactions 133

and Materials Processing

REAL TIME MONITORING OF THE OPTICAL PROPERTIES OF CW LASER ANNEALED SILICON

JOHN F. READY+,

B.

THOMPSON MCCLURE+,

TERRY L.

+Honeywell Corporate Technology Center,

BREWER++ AND WILLIAM L. LARSON++

10701 Lyndale Avenue South,

Bloomington, MN 55420, USA; ++Honeywell Solid State Electronics Center, 12001 Highway 55, Plymouth, MN 55441, USA

ABSTRACT The surface reflectivity of ion implanted silicon is a function of the entire past history of the material, including the nature of the implanted species and the implant dose. It is influenced by interference effects, arising from discontinuities in index of refraction at the surface and at the boundary between damaged and undamaged material. The reflectivity may be either higher or lower than that of the unimplanted silicon. As the crystalline silicon regrows from below, the reflectivity changes because of variable constructive or destructive interference. This paper describes monitoring of the surface reflectivity during continuous laser annealing. The beam from a continuous argon ion laser is scanned in a raster pattern over the silicon surface. The surface reflectivity for a HeNe laser beam is monitored as a function of time during crystalline regrowth. The reflectivity contains an oscillatory component which arises because of changes in interference due to the decreasing thickness of the noncrystalline layer. The oscillatory behavior produces a signature characteristic of the annealing. The reflectivity monitoring technique is useful for investigating the influence of parameters such as the spatial profile of the laser beam and the implantation dose on the annealing characteristics. The results are correlated with measurements of the depth profile of the implanted ions, as revealed by anodic oxidation and stripping.

INTRODUCTION The reflectivity of the surface of silicon and other semiconductors has been used previously as a probe to monitor the processes that occur during laser annealing. Time-resolved measurements made during pulsed laser annealing 2 demonstrate the melting and resolidification of the surfacel, . Non-timeresolved measurements of reflectivity during continuous laser annealing also 3 show the progression of annealing and melting . These measurements show features that suggest constructive interference between light reflected from the sample surface and from the regrowth interface. This paper describes time-resolved monitoring of the reflectivity of the surface of arsenic-implanted silicon during CW laser annealing. High dose implantation creates regions of amorphous material as well as contiguous regions of imperfect crystallinity that are "damaged" but not completely amorphized. For the purpose of formulating a simple optical model, we idealize this situation to a discontinuity between an amorphous layer and a crystalline substrate. This discontinuity implies optical reflection from the interface because of the change in index of refraction. The reflected light may