In-Situ Studies of the Formation Sequence of Silicides During Vacuum (10 -7 TORR) Thermal Annealing of TI/Polysilicon Bi
- PDF / 1,031,572 Bytes
- 5 Pages / 420.48 x 639 pts Page_size
- 50 Downloads / 190 Views
IN-SITU STUDIES OF THE FORMATION SEQUENCE OF SILIClDES DURING VACUUM (10-7 TORR) THERMAL ANNEALING OF TI/POLYSILICON BILAYERS Z.MAa), L.H.ALLENa), and S.LEEb) a) Department of Materials Science and Engineering, Illinois at Urbana-Champaign, Urbana, IL 61801 b)
Universioty of
NCR Corporation, Microelectronic Division, Colorado Springs, CO 80916
ABSTRACT The formation of siuicides during the thermal reaction of Ti/polysilicon bilayers has been investigated using both in-stu four point sheet resistance measurements and ex-situ measurements including X-ray diffraction, cross-sectional transmission electron microscopy and Auger electron spectroscopy. For a series of samples annealed at a ramp rate of 10°C/min the following sequence of changes in the bilayers occurred. At temperatures exceeding 350°C and prior to the silicidation oxygen from the vacuum system diffuses into the Ti
film forming a solid solution of Ti(O) with 0 levels up to 20
%.
An
amorphous TixSiy layer is the first major silicide reaction observed at temperatures near 440°C. The first major crystalline phase is observed at 500°C and identified as C49 TiSi2. This phase was found to coexist at these temperatures with the partially consumed Ti(O) and the amorphous TixSiy layers. Further annealing above 700 °C results in the final structural transformation from C49 TiSi2 to C54 TiSi2.
INTRODUCTION Reactions between Ti and single crystal or amorphous Si have been extensively studied'- 7 in last several years because of the importance of the C54 phase of Ti silicide as contact material in the microelectronic industry. Most of the work to date has been done with samples of Ti on single crystal Si substrates 2' 3 ,8 ' 9 which has leadl to a fairly complete understanding of the general silicide reaction. This investigation focuses on the sequential formation of the reactions which takes place during the annealing process of the Ti and polysilicon bilayers. By measuring the sheet resistance of the bilayer in situ during annealing a more complete, continuous picture of the
Mat. Res. Soc. Symp. Proc. Vol. 237. ©1992 Materials Research Society
662
overall reaction is obtained. Each change in the Ti/polysilicon bilayer during annealing including the oxidation of the initial Ti layer and the three silicidation reactions is easily observed by a complimentary change in the sheet resistance of the film. More direct measurements of the composition and microstructure of the film during annealing is obtained by XRD, TEM and Auger analysis. EXPERIMENTAL PROCEDURES The substrates used in this study were made with commercially available p-type Si (100) wafers with resistivity of 14-21 0-cm. They were cleaned and then subsequently thermally oxidized to obtain an Si02 layer of thickness 7,500A. This SiO2 layer acts as a electrically isolating layer between the Ti/polysilicon layer and the conducting Si substrate. A 3500A polysilicon layer was then deposited using LPCVD techniques. XRD data of the polysilicon layers showed the Si is polycrystalline with (220) preferred
Data Loading...
