Effect of surface kinetics on the step coverage during chemical vapor deposition
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Effect of surface kinetics on the step coverage during chemical vapor deposition Gyeong Soon Hwanga) and Sang Heup Moon Department of Chemical Engineering, Seoul National University, Seoul 151-742, South Korea
Suk Woo Nam Battery and Fuel Cell Research Center, Korea Institute of Science and Technology, Seoul 136-791, South Korea
Chee Burm Shinb) Department of Chemical Engineering, Ajou University, Suwon 442-749, South Korea (Received 24 April 1998; accepted 12 February 1999)
Profile evolution simulations during chemical vapor deposition based on a 2D continuum model reveal that the type of surface kinetics plays an important role in determining step coverage of films deposited in high aspect ratio trenches and vias. Linear surface kinetics, resulting from an adsorption rate limited process, is found to cause difficulty in bringing about conformal step coverage in deep narrow trenches without reducing the growth rate considerably. Under such condition, void-free filling cannot be achieved while maintaining a growth rate acceptable to integrated circuit (IC) manufacturing. The numerical study also suggests that the high tendency of the precursor for chemical equilibrium on a surface, resulting in nonlinear kinetics by a surface reaction limited process, is crucial to achieve a uniform step coverage as typically observed in SiO2 deposition from tetraethylorthosilicate (TEOS). As device dimensions decrease, the control of the step coverage of thin films deposited in vias and trenches becomes of great concern in the fabrication of very large scale integrated (VLSI) circuits. A number of techniques have been developed to improve the step coverage of silicon dioxide films from various gas sources. Chemical vapor deposition (CVD) from tetraethylorthosilicate (TEOS) is widely used for interlayer dielectrics1,2 because it provides better step coverage than other gap-filling techniques. Several mechanisms have been proposed to explain the behavior of step coverage of oxide films deposited in various structures. Oh et al.3 investigated theoretically the factors controlling step coverage in atmospheric pressure chemical vapor deposition (APCVD) based on the continuum transport equation and surface kinetics, and suggested that the ratio of surface reaction rate to gas phase diffusion rate, k兾D, played a key role in the step coverage; lower k兾D resulted in better step coverage. Based on the same mechanism, Li et al.4 suggested that low k兾D was responsible for the conformal step coverage usually observed in SiO2 depositions from TEOS in APCVD. The gas phase diffusivity (D) of the gaseous reactant is inversely proportional to the total pressure, whereas the reaction rate constant (k) is hardly affected by the total pressure. a)
Present address: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125. b) Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 14, No. 6, Jun 1999
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