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A PROCESS FOR MEASURING NITROGEN IN ULTRA-THIN OXYNITRIDE DIELECTRIC FILM

IP.com Disclosure Number: IPCOM000008764D
Original Publication Date: 1998-Jun-01
Included in the Prior Art Database: 2002-Jul-10
Document File: 3 page(s) / 148K

Publishing Venue

Motorola

Related People

Rama I. Hegde: AUTHOR [+4]

Abstract

A process for measuring nitrogen in an ultra- thin (<30 A) oxynitride film by secondary ion mass spectrometry (SIMS) is reported in this paper. This process is not limited to nitrogen in oxynitride, but it can be used for any low level element (dopant or impurity) analysis in ultra-thin films. Further, this method can be extended to any depth profiling composition measurement tool such as Auger elec- tron spectroscopy (AES), Rutherford backscattering (RBS) and X-ray photoelectron spectroscopy (XPS).

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MOTOROLA Technical Developments

A PROCESS FOR MEASURING NITROGEN IN ULTRA-THIN OXYNITRIDE DIELECTRIC FILM

by Rama I. Hegde, Bikas Maiti, Philip J. Tobin and Kimberly G. Reid

ABSTRACT

  A process for measuring nitrogen in an ultra- thin (<30 A) oxynitride film by secondary ion mass spectrometry (SIMS) is reported in this paper. This process is not limited to nitrogen in oxynitride, but it can be used for any low level element (dopant or impurity) analysis in ultra-thin films. Further, this method can be extended to any depth profiling composition measurement tool such as Auger elec- tron spectroscopy (AES), Rutherford backscattering (RBS) and X-ray photoelectron spectroscopy (XPS).

INTRODUCTION

  Ultra-thin (230 A) NO and NzO oxynitrides are candidate gate dielectrics for deep submicron MOSFET devices, due to their excellent properties such as suppression of boron penetration and high immunity to hot carrier effects'-i. These improve- ments provided by the NzO and NO oxynitrides are due to the accumulation of nitrogen atoms at the SilSiOi interface'. A comprehensive study of the effect of the interfacial nitrogen concentration (Ni.,) on MOSFET characteristics has shown that optimum MOSFET device characteristics are obtained for the N:., range from 0.2 to 1.0 at. % as determined by SIMS'. However, N,., measurement of ultra-thin oxynitride films by SIMS depth profiling is problematic',i. The SIMS signals are not stable and reliable from top 20 - 30 8, region, (known as "pre-equilibrium zone")l. As a result we developed a new process for measuring the N;., in this low range for ultra-thin oxynitrides (530 A).

EXPERIMENT

The ultra-thin (<30 A) NO oxynitride films studied here were processed in a RTP furnace using

a two-step process. First, approximately 30 A of thermal oxide was grown by RTP at 1050 "C in a low pressure (80 torr) oxygen ambient. Then the NO oxynitride films were grown by annealing this oxide in a NO ambient at 1000 "C for 30 set and 60 sec. The thicknesses of the oxynitride films were measured by single wavelength ellipsometty assuming a refractive index of 1.465. The increase in the oxynitride thickness resulting from NO oxynitride growth for 30 set and 60 set is 1 8, and 4 A, respec- tively. After the NO oxynitride growth, a layer of SiO2 using tetraorthosilicate (TEOS) was deposited on the NO oxynitride surface. Typical TEOS layer thickness was = 50 A. The SIMS data shown here have been acquired using Cs+ bombardment while monitoring clustered secondary species CsN+ as described elsewhere].

RESULTS AND DISCUSSION

  Figure I shows an example of N;., measurement of a 31 8, NO oxynitride without a TEOS cap by SIMS depth profiling. As shown, nitrogen analysis is very problematic for the ultra-thin NO oxynitride film. Figure 2 presents N.,...