Selective LPCVD Tungsten for Contact Barrier Applications

Abstract

This study assesses the use of selective LPCVD tungsten as a contact barrier in VLSI circuits. Measurements of the contact resistance and leakage current are evaluated as a function of variations in W deposition parameters, implant type, implant dosage, and metallization heat‐treatment. Addition of SiF4 to alter the equilibrium of the displacement reaction is seen to cause minimal erosion and encroachment of the Si contacts as well as produce low and thermally stable contact resistances to both n+ and p+ diffusions. For surface doping concentrations of 1.44×1020 cm−3 normalAs and 0.62×1020 cm−3B , measured values of the contact resistance for 2.0 μm sized vias are near 30Ω. Such values are quite compatible with high performance CMOS device requirements. Further reductions in these values are achieved with use of a self‐aligned normalPtSi/W contact barrier metallization. The contact resistance for 2.0 μm sized vias are, in this case, near 4 and 15OHgr; for the n+ and p+diffusions, respectively. Sporadic leakage across shallow n+/P‐Tub junctions remains, however, a serious problem associated with this selective LPCVD W process. Understanding the origin of this leakage and eliminating it can lead to numerous applications of this technology in VLSI manufacturing.

Low Pressure Chemical Vapor Deposition of Tungsten and Aluminum for VLSI Applications

“…An extrapolation of MTF to typical device operating conditions of 80~ and 10 ' ~ Alcm ~ yielded a value of 9.1 x 104h. This is indeed comparable to MTF values of evaporated A1 under equivalent device operating conditions but are significantly lower than the values (18). This effect, i l l u s t r a t e d in Fig.…”

“…In the initial stages of W deposition, displacement will precede hydrogen reduction when hydrogen is present, and will occur exclusively when hydrogen is absent. The free energy of t h e s e reactions is equal to -1 5 kcal/mol of W and -147 kcal/ tool of W for the h y d r o g e n and Si reductions, respectively (both calculated at 327~ This study, primarily based on the above authors' work (17)(18)(19)(20), reviews the deposition chemistries, as well as the properties and applications of L P C V D W and A1 films in VLSI processing.…”

“…13, i n d i c a t in the case of the B -i m p l a n t e d Si (i.e., only a small a m o u n t of Si, -300A, was eroded). Several factors were observed to i n f u e n c e the excessive erosion of the N+Si by WF6 (18). A m o n g these, variations in W deposition parameters, such as lowering the WF~ partial pressure and deposition temperature as well as increasing t h e carrier gas flow rate, appeared to alleviate the problem.…”

“…In an effort to inhibit this Si d i s p l a c e m e n t reduction, so as to m i n i m i z e Si erosion of contact areas and also avoid formation of subfluoride by-products that may adversely affect the contact resistance, the effect of adding SiF4 to the reactant gases (i.e., WF6 and H2) in a one-step process was investigated (18). The choice of SiF4 was based on the fact that its p r e s e n c e would shift the disp l a c e m e n t reaction to the left according to the equilibrium quotient Q = [SiF4]3/[WF~] 2.…”

Investigation of Chemically Vapor Deposited Tantalum for Medium Caliber Gun Barrel Protection

“…In the microelectronics industry, CVD metal coatings (e.g., Ta, W, Cu, Al, etc.) are routinely used to conformally cover sub-micron-sized trenches (< 0.12 µm) with severe aspect ratios (hole depth/diameter ratio ~ 20:1) [8][9][10][11][12][13][14][15]. This feature uniquely offered by the CVD process is highly beneficial in achieving the required uniform coating coverage along the interior rifled surface of the gun barrel.…”