Studies of Pecvd and Ozone CVD Deposition Rate, Uniformity and Step Coverage
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(1) INTRODUCTION Chemical vapor deposition (CVD) has been used to deposit films such as silicon, silicon oxide, silicon nitride, tungsten, silicide, copper and titanium nitride in the semiconductor industry. The reaction driving forces for CVD are typically temperature for thermal CVD, plasma ionization for plasma enhanced CVD, or atomic oxygen for ozone CVD. In the recent years, plasma enhanced CVD (PECVD) and ozone CVD have found extensive applications in the semiconductor industry, due to the higher deposition rate and lower deposition temperature. For example, PECVD and ozone CVD are used to deposit almost all dielectric films such as silicon oxide and silicon nitride on a wafer. The dielectric films on wafers serve as insulating layers between conducting metal layers and as passivation layer on top of semiconductor devices. Theoretical calculation and modeling help the understanding and prediction of CVD processes and film properties. However, previous works are complex and mainly deal with the fundamental details of CVD reactions (such as plasma density, atomic interactions, or chemical bonding) [1,2]. It is difficult to use these models in industry, where simple and straight forward explanation and prediction of deposition rate, step coverage and uniformity are needed. In this paper, we will calculate the deposition rate trend, deposition uniformity, flow rate, and step coverage for PECVD and ozone CVD in a parallel plate CVD reactor. The calculated results will be compared to experimental results.
(2) EXPERIMENTAL SETUP The experiments were done in a newly developed parallel plate CVD reactor (fig.l), the
substrate (typically a 8" wafer) is heated on a pedestal at a pre-set temperature. The reaction gases (reactants) are mixed and uniformly distributed through a shower head with numerous gas distribution holes. The chamber pressure is controlled by a throttle valve. The temperature is used to enhance film density and is typically well below thermal reaction temperature, so the thermal reaction rate is small. The chemical reaction rate is greatly enhanced when radio frequency (RF) power is applied between shower head and heater, due to creation of ions and radicals. In the case of ozone CVD, ozone is distributed uniformly through the shower head, the free oxygen atoms enhance the chemical reaction.
Experimental setup
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Materials equipment
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in anApplied
RF
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Fig.1
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SHOWER HEAD HIIHO1HHINHHIIHIK1 • D --- •
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SUBSTRATE HEATED PEDESTAL 113 Mat. Res. Soc. Syrup. Proc. V/ol.363 ©1995 Materials Research Society
(3) DEPOSITION RATE In a plasma or ozone activated CVD process, only reactant ions and radicals have chemical reactions. The ions & radicals are produced by RF power, with area power density (W), in PECVD, or ozone, with flow rate (Q), in ozone CVD. The reactants are excited as they flow through plasma or ozone. For a unit time, the amount of new reactants entering the chamber is F, (flow rate). They are excited into ions and radicals over time. Here we assume the amount of ions or rad
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