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OXYGEN PLASMA SURFACE TREATMENT OF (111) IRIDIUM FOR LITHOGRAPHY PROCESSING

IP.com Disclosure Number: IPCOM000008791D
Original Publication Date: 1998-Sep-01
Included in the Prior Art Database: 2002-Jul-12
Document File: 4 page(s) / 281K

Publishing Venue

Motorola

Related People

Sean Lian: AUTHOR [+4]

Abstract

For embedded dynamic random access memory (EmDRAM) devices, Iridium (Ir) has been found to be a good electrode material for DRAM capacitors, in conjunction with high dielectrics materials such as barium strontium titanate (BST). However, we have found that photoresist can not be stripped using downstream oxygen plasma etching when the resist is in direct contact with Ir. It is suspected that Ir is such a strong catalyst that it catalyzes a cross link- ing chemical reaction at the resist / Ir interface and hardens the resist during the subsequent high tem- perature processes, resulting in the inability to strip the resist using the aforementioned oxygen plasma process. After ashing, residue with same resist pat- tern was observed optically on Ir surface and was characterized by AFM and cross section SEM at about ZOOOA in thickness, Organic and ionic conta- minants were detected by TOF-SIMS analysis of the Ir surface prior to the resist coating without O2 plas- ma treatment. This may relate to the formation of the residue after ashing. A 0, plasma pre-treatment of Ir surface is shown to clean and passivate the Ir surface resulting in the easy removal of resist during the ashing process.

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MOTOROLA Technical Developments

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OXYGEN PLASMA SURFACE TREATMENT OF (111) IRIDIUM FOR LITHOGRAPHY PROCESSING

by Sean Lian, Patrick Montgomery, Bill Chu and J. J. Lee

ABSTRACT

   For embedded dynamic random access memory (EmDRAM) devices, Iridium (Ir) has been found to be a good electrode material for DRAM capacitors, in conjunction with high dielectrics materials such as barium strontium titanate (BST). However, we have found that photoresist can not be stripped using downstream oxygen plasma etching when the resist is in direct contact with Ir. It is suspected that Ir is such a strong catalyst that it catalyzes a cross link- ing chemical reaction at the resist / Ir interface and hardens the resist during the subsequent high tem- perature processes, resulting in the inability to strip the resist using the aforementioned oxygen plasma process. After ashing, residue with same resist pat- tern was observed optically on Ir surface and was characterized by AFM and cross section SEM at about ZOOOA in thickness, Organic and ionic conta- minants were detected by TOF-SIMS analysis of the Ir surface prior to the resist coating without O2 plas- ma treatment. This may relate to the formation of the residue after ashing. A 0, plasma pre-treatment of Ir surface is shown to clean and passivate the Ir surface resulting in the easy removal of resist during the ashing process.

Pt"" that generates alpha particles resulting in an alpha-ray emissivity of 5x10-' counts/hr, which is 100 times the acceptable level (3). Furthermore, poor adhesion also increases the difficulty of usi~ng Pt in device integration. These disadvantages in using Pt have prompted the search for other alterna- tives.

  Several merits of Iridium (Ir) have made it attractive as an electrode material for BST thin film capacitors. Ir does not have any known radioactive isotopes that generate alpha particles. It has been studied as an electrode material for PbZrTi03 (PZT) and SeBi,TaO, (SBT) capacitors (4). It has better adhesion to SiO, compared to Pt (5) and chemical vapor deposition (CVD) of Ir is available (6). However, when photoresist is coated on Ir surfaces for electrode patterning, the resist, at high tempera- tures, can be converted to higher hydrocarbons via oxidative coupling using Ir as a catalyst (7). The activation energy of this reaction at the defect sites is much less than the reaction barrier at the terrace sites (8). Due to the impurity level of the Ir source target in the deposition chamber, there are defects on Ir surface and this undesirable reaction is not avoidable when resist is subjected to the subsequent high temperature processes. Therefore, it is very difficult to ash away the resist during the postetch resist strip either before patterning etch, if rework is needed, or after patterning etch. A treatment of Ir surface before resist coating was studied to passi- vate the Ir surface and therefore improve the resist ashing process.

INTRODUCTION

  (Ba,Sr)TiO, (...