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REOXIDIZED NITRIC OXIDE (ReoxNO or RNO) PROCESS

IP.com Disclosure Number: IPCOM000007379D
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2002-Mar-20
Document File: 4 page(s) / 153K

Publishing Venue

Motorola

Related People

Bikas Maiti: AUTHOR [+5]

Abstract

Reoxidation ofan oxynitride gate dielectric grown by nitric oxide (NO) annealing ofthermal oxide has been studied. This process has demonstrated -3-5X improvement ofQao ofactive edge intensive capaci- tors in comparison to thermal oxide, NzO and NO oxynitride. This improvement is believed to be due to the reduction of mechanical stress at the active edge which leads to less local thinning ofgate oxide at the field oxide edge.

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MOTOROLA Technical Developments Volume 24 March 1995

REOXIDIZED NITRIC OXIDE (ReoxNO or RNO) PROCESS

by Bikas Maiti, Philip J. Tobin, Yoshio Okada, Sergio A. Ajuria and Kimberly G. Reid

ABSTRACT

INTRODUCTION

Reoxidation ofan oxynitride gate dielectric grown

by nitric oxide (NO) annealing ofthermal oxide has been studied. This process has demonstrated -3-5X improvement ofQao ofactive edge intensive capaci- tors in comparison to thermal oxide, NzO and NO oxynitride. This improvement is believed to be due to the reduction of mechanical stress at the active edge which leads to less local thinning ofgate oxide at the field oxide edge.

  The weakness of the gate oxide at the isolation edge can cause a serious long-term reliability prob- lem for dense ULWVLSI circuits since the length of active edge can exceed 50 meters. Oxide thin- ning [l] at the LOCOS edge has been reported to contribute to the degradation of oxide quality. Gate oxide thinning at the field oxide isolation edge, as shown in Figure 1, enhances the insulator electric field, and results in early breakdown.

Gate (polysilicon)

Gate Oxide (SiO,)

Substrate (Si) - - -

Figure 1. Schematic of gate oxide thinning at the field oxide isolation edge.

CVD/Thermal stacked oxide [2] and optimized

sacrificial oxide/annealing as in PELOX (Poly Encap- sulated Local Oxidation of Silicon) [3, 41 have been demonstrated to reduce local gate oxide thinning. But these processes require multiple furnaces, more processing steps and high thermal budget. Oxyni- trides grown in NaO and NO ambient have excel- lent reliability compared to thermal oxides as dem- onstrated by analysis of area intensive structures [5, 6, 7,8] but are less impressive for active edge inten- sive structures (this work).

In this work we compare the reliability of these dielectrics using active edge intensive structures for

the first time and also demonstrate a unique proc- ess to improve the quality for these structures. The process utilizes reoxidation after NO anneal ofther- ma1 oxide (ReoxNO or RNO). This approach enhances Qao by -3-5X under constant current stress for both gate and substrate injection in comparison to thermal oxide, N20 and NO oxynitride.

EXPERIMENTAL

  Area and active edge intensive capacitors with the same area as drawn on the mask were fabricated on Si substrates with FMPBL isolation [9] and n+-poly gates, A sacrificial oxide cycle was used to

90 0 Motorola. 1°C~ 1995

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MO-OLA Technical Developments Volume 24 March 1995

Step 2: Anneal thermal oxide in nitric oxide gas ambient.

Step 3: Reoxidize.

eliminate Kooi effect. The gate dielectrics were grown in a conventional horizontal furnace as described in [6, 71. A control thermal oxide was grown in O2 + 3% HCI. NO oxynitride was formed by annealing this oxide in NO/inert gas mixture. NlO oxynitride as described in [6, 71 was also used as a reference in this study. Reoxidized Nitric Oxid...