Akira Koshiishi

Investigation of Etch Rate Uniformity of 60 MHz Plasma Etching Equipment

When the driving frequency of etching equipment using capacitively coupled parallel-plate plasma (CCP) becomes high, the etch rate tends to indicate a center peak. In this paper we discuss the improvement of the etch rate by leveling the center peak. From the results of numerical simulation using FEM, it can be considered that the center peak shape of the RF electric field distribution, which is enhanced by the resistivity of plasma, causes the center peak shape of the etch rate. Experimental results using an improved CCP, which possesses the ability to control the electric field distribution, demonstrate a refined etch rate. That is to say, the improvement of making a cavity behind the electrode provides the ability to control the electric field distribution. This distribution is governed by the dimensions of the cavity and the resistivity of the electrode. Less than 3% uniformity is obtained at 60 MHz for a wafer of 200 mm diameter using the improved electrode.

Improvement in Etch Rate Uniformity Using Resistive Electrodes with Multistep Cavity

When the driving frequency of etching equipment using capacitively coupled parallel-plate plasma (CCP) increases, etch rate tends to rapidly increase at the center of a wafer (i.e., center peaked). The use of a resistive electrode with a cavity behind it at the center is an effective method of reducing the intensity of this peak. Even though the center peak is removed, the etch rate at the wafer edge is typically low. Because of this, controlling etch rate uniformity within 3% is problematic. The use of multistep cavity behind the resistive electrode has been found to be an effective method of improving the uniformity over the entire wafer and is described in this paper. Finite element method (FEM) simulations are performed to show that the use of a multistep cavity improves the ability of controlling sheath field when compared with the use of a single-step cavity configuration. Experiments confirm uniformity control within ±1.8% (3σ) with the multistep cavity configuration for 300 mm diameter wafers etched in 60 MHz plasma sources.

Implementation of atomic layer etching of silicon: Scaling parameters, feasibility, and profile control

Atomic or layer by layer etching of silicon exploits temporally segregated self-limiting adsorption and material removal steps to mitigate the problems associated with continuous or quasicontinuous (pulsed) plasma processes: selectivity loss, damage, and profile control. Successful implementation of atomic layer etching requires careful choice of the plasma parameters for adsorption and desorption steps. This paper illustrates how process parameters can be arrived at through basic scaling exercises, modeling and simulation, and fundamental experimental tests of their predictions. Using chlorine and argon plasma in a radial line slot antenna plasma source as a platform, the authors illustrate how cycle time, ion energy, and radical to ion ratio can be manipulated to manage the deviation from ideality when cycle times are shortened or purges are incomplete. Cell based Monte Carlo feature scale modeling is used to illustrate profile outcomes. Experimental results of atomic layer etching processes are illustr...

Influence of Gas Chemistry and Ion Energy on Contact Resistance

Reactive ion etching (RIE) damage in contact hole etching is studied. The significant oxidation retardation layer (ORL) on Si surfaces is observed followed by high V pp (peak-to-peak voltage of 380 kHz RF) RIE. The depth of the ORL is linearly proportional to V pp, and it consists of a Si–C bond layer, according to X-ray photoelectron spectroscopy (XPS) analysis. The increase in contact resistance is found to be due to the existence of the ORL, using the sacrificial oxidation method and secondary ion mass spectroscopy (SIMS) analysis. The etch chemistries based on fluorocarbon-containing gas mixtures are characterized in terms of contact resistance and ORL. When hydride-containing gas mixtures are used in RIE, the contact resistance is low and the ORL depth is small. When CO-containing gas mixtures are used, the contact resistance is high and ORL depth is large. These different properties result from the different amounts of carbon implanted at the silicon surface.