Chemical vapor deposition TiN process for contact/via barrier applications

Abstract

Chemical vapor deposition (CVD) TiN is an attractive replacement for PVD TiN as a barrier and glue layer for subhalf-micron contacts and vias. CVD TiN films have been deposited in a commercial reactor via the thermal decomposition of tetrakis-dimethyl-amino-titanium (TDMAT) precursor in an N2 ambient. The deposition can be characterized by a simple Arrhenius rate expression with a half-order dependence on TDMAT concentration and an activation energy of 0.53 eV. Designed experiments show that the deposition transitions from being kinetically limited at high TDMAT flow rates and low temperatures to transport limited at the other extreme. In the kinetically limited regime, the deposition rate increases with increasing TDMAT mole fraction and increasing temperature. Step coverage simulations have been performed by coupling SPEEDIE (a profile evolution program) with the Arrhenius rate expression. Experimental and simulated step coverages show good agreement over a wide range of process conditions. Step coverage improves with increasing deposition rate and decreasing temperature. Adequate deposition rates (≳400 Å/min) with good deposition uniformity and high step coverage (50%–85%) can be achieved. Film stress and roughness are mostly invariant with process conditions. These films are close to stoichiometric (i.e., 1:1 Ti:N ratio), but contain up to 30% carbon. Exposure of these films to air causes rapid oxidation with a steady state concentration of 15%–20% oxygen after 24 h of air exposure. The high carbon concentration results in high film resistivity (5000 μΩ cm), which doubles after 24 h of air exposure due to oxidation of the film. Film resistivity decreases and film stability improves with increasing N2 flow rate. Electrical characterization of two process variants have been performed. The first provides a film with 85% step coverage with a resistivity of 5600 μΩ cm, while the second process achieves a lower resistivity of 3700 μΩ cm and a lower step coverage of 50%. Electrical performance of both films is similar. Contact induced diode leakage is lower for CVD TiN compared to PVD TiN. Contact resistance for 100–200 Å CVD TiN is comparable or lower than 500 Å PVD TiN. A 100 Å CVD TiN barrier is adequate; 300 Å CVD TiN is too thick because of high film resistivity. An Al–Cu/100–300 Å CVD TiN/Si stack shows lower resistance increase after 450–500 °C, 30 min N2 anneal compared to a Al–Cu/200 Å PVD TiN/Si stack indicating that CVD TiN is a superior barrier and is more inert than PVD TiN.

Characteristics of chemically vapor deposited TiN films prepared using tetrakis-ethylmethyl-amido-titanium

“…7 The growth rate of a TiN film in the presence of NH 3 has also been investigated. A substrate temperature of 300°C was chosen to minimize the effect of mass transfer or feed rate control on film growth rate.…”

Titanium nitride: A new Ohmic contact material for n-type CdS

“…[27][28][29] The high value might be partly due to so-called 'current crowding' at the contacts, which means that only part of the TiN contact area is active in the transport of current from and to the CdS. This effect occurs because the diameter of the contact is much larger than the film thickness, and the current always chooses the path of the least resistance.…”

Chemical vapor deposition of titanium nitride thin films from tetrakis(dimethylamido)titanium and hydrazine as a coreactant

“…4,8 The two most extensively used thermal CVD precursor systems are: (i) the inorganic halide, TiCl 4 and ammonia; 3,7,[9][10] or (ii) the organometallic compounds, tetrakis(dimethylamido)titanium (TDMAT) or tetrakis-(diethylamido)titanium (TDEAT) and ammonia. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] The first system requires temperatures too high (500-700°C) for most device applications, and the films are contaminated with unacceptable levels of chlorine. In the case of the organometallic precursor, it is difficult to obtain films with a combination of low impurity levels, low resistivity, and sufficient conformality for future generation devices with submicron features.…”