Formation of Chemically Clean and Morphologically Smooth PtSi/Si Interfaces
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Schottky diode by damage created by the high energy (in the order of 100 keV) ion beams. Therefore, in attempting to develop a platinum salicide process for application in sub-half micron technology, we have adopted an alternate approach to form a planar ex-situ PtSi/Si interface comprising the following steps: (i) chemical cleaning employing gigabit purity chemicals and a modified RCA process which has been used elsewhere [8] to reduce metal preoxidation contamination and silicon surface roughness in (ii) cleaning procedures for improved gate-oxide integrity; sputter-deposition of the Pt layer in an ultraclean, ultrahigh environment to maintain the integrity of the (UHV) vacuum chemically cleaned silicon surface and minimize deposition related particle low-kinetic-energy in-situ (iii) contamination; bombardment during film growth to cause localized atomic mixingat the interface (in the case of a sputter-discharge with Ar as the sputter gas, these particles are Ar ions drawn from the plasma to ex-situ silicidation by rapid the substrate [9,10]); and (iv) The compositional and microstructural thermal annealing (RTA). properties of PtSi/Si interfaces, so prepared, are reported in this paper. EXPERIMENTAL DETAILS Platinum layers, of thickness in the range of 20-40 nm, were sputter-deposited onto lightly P doped, 3-5 ohm-cm, n-type Si (100) substrates
in
a
stainless
cryo-pumped
steel,
VCTI
cryotorr
8)
deposition chamber with a base pressure of 2.5xi0" Torr, utilizing a 2.5 cm diameter, UHV, planar magnetron sputter gun powered by an power supply through a tuning circuit. Advanced Energy RFX 600 r.f. The Pt target purity was 99.99%. Gigabit purity chemicals were used chemically clean the silicon surface utilizing a modified to first RCA process. The final HF dip (in 1:100 HF:H 20) and subsequent rinse in deionized water (17.7 megohm) was done immediately prior to loading the substrates in the loadlock chamber. A base pressure of 6x10 Torr was routinely obtained in the loadlock chamber which was pumped by a Balzers TPU 062 turbopump backed by a molecular drag pump and a diaphragm pump. A constant flow of ultrahigh purity N2 (ppb impurity levels) was maintained in the loadlock chamber during substrate loading and unloading operations. Typically, pumpdown of the loadlock chamber to 2x10 Torr took 10 min at which point the substrates were transferred to the deposition chamber. Research Grade Ar (ppb impurity levels) was used as the sputter gas. To minimise Ar consumption and maintain reasonable flow-rates a throttle valve had to be employed to reduce the cryopump throughput. The residual base pressure with the throttle closed was 5x10 9 Torr. The deposition conditions were: Argon pressure of 5.1 power of 100 W, and a mTorr, an Ar flow rate of 96 sccm, r.f. target self-bias of -446 V. The bias on the substrate holder, which was kept floating, was measured to be about -2 V. Under these conditions, the deposition rate was 7.2 nm/min. Silicidation was done ex-situ in N2 ambient using an AG Associates Heatpulse 410 anne
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