• PDF / 301,350 Bytes
• 5 Pages / 420.48 x 639 pts Page_size
• 60 Downloads / 306 Views

DOWNLOAD

REPORT

---

Ultrafast UV-Laser Induced Oxidation of Silicon T.E. ORLOWSKI AND H. RICHTER

Xerox Webster Research Center Rochester, NY 14644

ABSTRACT A new low temperature method of forming high quality patterned silicon dioxide (Si0 2 ) layers up to a thickness of 1 ,.m on silicon substrates is presented. UV pulsed laser excitation in an oxygen environment is utilized. IR absorption spectroscopy, CV and IV measurements are employed to characterize the oxide films and the Si-Si0 2 interface. No shift but a significant broadening of the Si-0 stretching mode compared with thermally grown oxides is found indicating that the laser grown oxide is stoichiometric but with a higher degree of disorder. From CV measurements we deduce a fixed oxide charge near the Si-Si0 2 interface of 6x10 1 0 /cm 2 for oxides that have been thermally annealed in 02 following the laser induced growth making this material a candidate for applications in semiconductor devices.

INTRODUCTION There has been considerable activity in the search for efficient low temperature techniques for depositing thin dielectric films in semiconductor device fabrication processes to eliminate problems such as substrate warpage, dopant redistribution and defect generation and propagation [1] associated with conventional high temperature processing steps. Much progress has been made in rapid low temperature deposition of Si3 N4 and Si0 2 using laser-initiated CVD techniques [2,3] utilizing UV lasers to photolyze gas phase reactants which combine at the substrate surface to form the insulating film. Other studies have shown that oxygen trapped in laser-induced amorphous silicon layers during pulsed laser annealing of silicon wafers rapidly forms Si0 2 [4]. The work reported here is concerned with a new low temperature method of rapidly forming high quality patterned silicon dioxide layers on silicon substrates involving pulsed UV laser excitation and characterizing the electrical properties of the resulting insulating films. EXPERIMENTAL Shown in Figure 1 is the apparatus developed for laser induced oxidation of silicon. The technique involves electronic excitation and subsequent rapid heating of a silicon substrate (p-type, 10-20 Qcm, (100) surface) to near or above its melting point in an oxygen environment using a XeCI excimer laser which provides 5 nsec pulses with up to 5mJ energy at 308 nm. Focusing the beam to 1.0 x 0.5 mm spot on the sample results in energy densities up to 1.0 J/cm2 . The laser penetration depth at 308 nm in silicon is less than 100 A and with a laser pulse duration of 5 nsec there is no residual substrate heating (i.e., the sample cools within 1 p.sec of excitation). In order to reduce the strain in the substrate during the rapid heating and cooling, the substrate was resistively heated to 4000C. Sample temperature was measured using an optical pyrometer. Repetitive pulses (100Hz) combined with scanning the focused laser beam over the sample surface produced patterned oxide layers large enough to perform IR and electrical measurements. Growth Kineti