Self-aligned Contact Process Research Articles

ChemInform Abstract: A Stacked Capacitor Cell with a Fully Self-Aligned Contact Process for High-Density Dynamic Random Access Memories (DRAM).

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W-Polymetal Gate with Low W/Poly-Si Interface Resistance for High-Speed/High-Density Embedded Memory

A new W-polymetal gate electrode with the structure of W/WN/WSi/poly-Si is proposed. The W-polymetal gate is suitable for high-density memories since it has low resistance and is compatible with the self-aligned contact process. In our study, however, it is found that the interface of W and poly-Si has non-ohmic and quite high resistance in the case wherein only WN is used as a barrier film. This resistance increases the delay in complementary metal-oxide-semiconductor (CMOS) logic circuits and prevents high-speed operation. Our new process includes the deposition of thin WSi on poly-Si, followed by rapid thermal annealing, which results in ohmic and sufficiently low contact resistance between W and poly-Si. It is also demonstrated that selective gate reoxidation is successfully applied for this new structure, and the insertion of thin WSi does not cause any adverse effect on the electrical characteristics of metal-oxide-semiconductor field-effect transistor (MOSFET). This process is promising for high-speed and high-density embedded memory.

High yielding self-aligned contact process for a 0.150-μm DRAM technology

This paper describes improvements in the self-aligned contact process for 0.150 /spl mu/m and 0.175 /spl mu/m technology generations. Using a dynamic random access memory cell layout, we show that self-aligned contacts can be formed at 0.175 /spl mu/m ground rules and beyond by using a C/sub 4/F/sub 8/-CH/sub 2/F/sub 2/ chemistry. With the improved etch selectivity, gate cap nitride thickness can be reduced, resulting in a smaller aspect ratio for the gate etch, borophosphosilicate glass fill, and contact etch. With a rectangular contact, the area can be increased and the process windows for lithography and etch are improved. The process window for lithography increases by up to 40%, the aspect ratio for the etch and the contact fill is less, and the sensitivity to misalignment is reduced. The combination of rectangular contacts and C/sub 4/F/sub 8/-CH/sub 2/F/sub 2/ chemistry greatly enhances the product yield.

Analysis of SiO2-to-Si3N4 selectivity in reactive ion etching using additional O2 gas

The mechanism for control of the Si3N4 etch rate in a self-aligned contact process when C4F8/Ar/O2 gas is used was investigated. The Si3N4 surfaces after dry etching were analyzed by x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy. After dry etching, a polymer-like residue film less than 15 nm thick and an oxidized layer between the polymer layer and the Si3N4 surface were observed. In the CF polymer layer, the etching product of CN or CNO was characterized. CN or CNO components are widely distributed in the CF polymer layer, while the SiO2 layer is more localized on the Si3N4 surfaces. We found that the thicknesses of the CF polymer and SiO2 layer strongly depend on the Si3N4 etch rate, which is determined by the flow rate of the additional O2 gas. The thickness of the CF polymer, which was decreased from 10.1 to 4.1 nm, is considered to act as an inhibitor. The thickness of the SiO2 layer, which is easy to etch, was increased from 1.4 to 2.7 nm. The CF polymer thickness and the etching path of Si3N4 oxidation are important factors in controlling the Si3N4 etch rate.

Experimental investigations and analysis for high-quality Nb/Al-AlOx/ Nb Josephson junctions

We have made a detailed study of the fabrication process of Nb/Al-AlOx/Nb Josephson junctions with the aim of introducing guiding principles to obtain high-quality junctions. Junctions were fabricated by a novel process named the self-aligned contact process. We investigated the deposition conditions of Nb and Al films and optimized them. Oxidation conditions for obtaining target critical current were also investigated. Then composition of the tunneling barrier material and the coverage of the thin Al layer on the base electrode were analyzed by x-ray photoelectron spectroscopy, Auger electron spectroscopy, etc. We investigated aging and annealing effects on the junctions. We confirmed that the current-voltage (I-V) characteristics of the junctions did not change after storage for 450 days at room temperature or when subjected to temperatures of up to 150 °C for shorter periods. Applying the McMillan theory to our experimental results, we explained the characteristics of the junctions. As a result, we have demonstrated that the characteristics are determined by two proximity layers: The first is a double proximity layer composed of an elemental Al layer and Nb/Al alloy layer in the base electrode, and the second is a Nb layer with low transition temperature in the counterelectrode. We have demonstrated that the characteristics are drastically improved by reducing the Nb/Al alloy layer and the Nb layer with low transition temperature and have obtained high-quality junctions with little leakage current.

All refractory Nb/Yb-YbOx/Nb Josephson junction

A new all refractory Josephson junction, in which Yb oxide is used as a tunneling barrier, has been fabricated by the self-aligned contact process. The heat formation energy of Yb oxide is higher than that of Al oxide. It is expected that a junction with Yb oxide would be more stable than one with Al oxide. The obtained current-voltage characteristic is Vm=15 mV at the critical current density jJ=1500 A/cm2. Its dielectric constant and barrier height are compared with Al oxide.

Self-aligned contact process for Nb/Al-AlOx/Nb Josephson junctions

High quality Nb/Al-AlOx/Nb Josephson junctions have been fabricated by a novel process named the self-aligned contact process. After the definition of the junction area by a reactive ion etching (RIE) technique, the exposed Nb layer and the junction edge are anodized to protect against electrical shorts and an Al film is deposited as the etching stopper layer. After base electrode patterning by RIE, an insulation layer is deposited. The contact hole, with the diameter of the junction, for connecting a counter electrode and a wiring layer, can be made without registration because of the deposited Al film. The junctions fabricated by this process have exhibited excellent current-voltage characteristics (Vm =70 mV at the critical current density jJ =1.8 kA/cm2, Vm =11 mV at jJ =20 kA/cm2).