A scalable submicron contact technology using conformal LPCVD TiN

Abstract

A scalable submicron contact technology has been developed using a fully conformal LPCVD titanium nitride barrier metal that provides low contact resistance to salicide, low leakage, excellent adhesion and high thermal stability. Owing to the uniform step coverage, especially in deep, straight wall contacts, the CVD TiN overcomes the metal reliability and junction leakage issues associated with the physical sputtering of metals in high aspect ratio, submicron contacts. LPCVD TiN withstands 550°C thermal stress, maintaining low contact resistance and leakage, while physically deposited TiN fails at 500°C. The applicability of CVD TIN barrier technology to VLSI devices has been successfully demonstrated on production circuits. INTRODUCI'IONCVD titanium nitride has received attention from several sources (1,2) as a hard coating for steel and other metals. Recently CVD TiN has been evaluated as a barrier metal (3,4,5) for semiconductor devices due to its conformal step coverage and high thermal stability. As a result of these properties CVD TiN films can find applications a t the submicron level a s a barrier for laserplanarized, high-temperature or bias-sputtered aluminum as well as a glue layer for tungsten. In this work, we describe a scalable contact technology for submicron integrated circuits using CVD TiN as a barrier metal. Contact resistance, diode leakage, chemical and physical properties of the film are discussed. The excellent conformality of LPCVD TiN has been demonstrated in contacts as small as 0 . 4~ and in trenches with an aspect ratio greater than six. The use of LPCVD TiN as a reliable adhesion layer for tungsten in sub-half micron contacts is demonstrated for the first time. Trace concentrations of C1, a reactant byproduct, are a concern which is addressed with corrosion reliability data. EXPERIMENTALTwo submicron contact process sequences utilizing LPCVD TIN as a barrier and/or a n adhesion layer have been studied (Fig. 1). Both techniques were used to produce silicided contacts, yielding a low interfacial resistance for the resulting SiR'iSiR'iN structure. TiN films were deposited from Tic14 and N H 3 at 650°C in a single wafer LPCVD system to obtain uniform, reproducible films. Barrier integrity under thermal stress is a more critical issue for aluminum than for tungsten metallization. For this reason, the electrical results described in this paper were obtained with conventional Al/Cu/Si metal. In order to illustrate the use of LPCVD TiN as a n adhesion layer, its application with blanket tungsten as metal 1 or in conjunction with tungsten etchback for plug purposes is also demonstrated (Fig. 2).Diode leakage measurements were performed a t 10 V reverse bias. To distinguish the leakage contribution of the contacts from other sources, two structures were measured: a 15000 pm2 diode with three (1p.m dia) contacts, and a similar diode with 2904 contacts. Measurements are reported after wafer processing, as well as after a series of half hour thermal stresses starting at 450°C and including 550°C....

Kinetic and Mechanistic Studies of the Chemical Vapor Deposition of Tungsten Nitride from Bis(Tertbutylimido)Bis(Tertbutylamido)Tungsten

“…First, high-quality TiN is commonly deposited by sputtering techniques. Because of the nature of this latter deposition technique, this can lead to poor surface coverage of high aspect ratio features such as contact plugs and vias due to shadowing. ,− While CVD methods can obviate this limitation, it remains that the growth of TiN generally yields an underdense, mixed (111/002) texture in the film. , Such structures adversely impact the stability of the metallization levels of the device. It has recently been shown, however, that dense, fully (111)-textured TiN thin films can be obtained using a reactive magnetron sputtering method …”

Characteristics of PECVD grown tungsten nitride films as diffusion barrier layers for ULSI DRAM applications

“…Despite the significantly improved step-coverage, these processes bring with them challenges with respect to film characteristics and process characteristics, such as high resistivity, high impurity contents of the films or high processing temperature2 , 4 Tungsten nitride (W-Nitride) films grown by sputtering or CVD methods have been investigated for barrier material applications as an alternative to TiN films. Particularly, the technologies of the diffusion barrier between the interconnection materials and the silicon in the contact hole, or between interconnection materials play a critical role with the continued scalingdown of devices.…”