J H Liao 1, Jianshe Tang 2,b, Ching Hwa Weng 2, Wei Lu 2, Han Wen Chen 2, John TC Lee 2

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1 Solid State Phenomena Vol. 134 (2008) pp Online available since 2007/Nov/20 at (2008) Trans Tech Publications, Switzerland doi: / Metal Hard Mask Employed Cu/Low k Film post Ash and Wet Clean Process Optimization and Integration into 65nm Manufacturing Flow Miao Chun Lin 1, Mei Qi Wang 1,a, Joe Lai 1, Ren Huang 1, Cheng Ming Weng 1, J H Liao 1, Jianshe Tang 2,b, Ching Hwa Weng 2, Wei Lu 2, Han Wen Chen 2, John TC Lee 2 1 UMC, No.18 Nanke 2 nd road, Tainan Science Park, Tainan County741, Taiwan, ROC 2 Applied Materials, 3330 Scott Boulevard, M/S 0697, Santa Clara, CA 95054, USA a Mei_Qi_Wang@umc.com b Jianshe_Tang@amat.com Keywords: Metal hard mask, Single wafer clean, Etch/Ash, Cu/Low-k. Abstract As 65nm technology in mass production and 45nm technology under development, post etch ash and cleaning faces new challenges with far more stringent requirements on surface cleanliness and materials loss. The introduction and integration of new materials, such as metal hard mask, creates additional requirements for wafer cleaning due to the occurrence of new defect modes related to metal hard mask. We have optimized a post etch ash process and developed a novel aqueous solution (AQ) based single wafer cleaning process to address these new defect modes. Physical characterization results and process integration electrical data are presented in this paper. Introduction Metal hard mask is widely used in BEOL process flow in recent years due to its many advantages, e.g. prevention of low-k dielectric damage [1, 2]. However, with the implementation of metal hard mask for BEOL, new issues arise in both etch/ash and wet clean process steps that need to be resolved. In the past few years, extensive research has been done for metal hard mask integration. For example, G. Delagdino, et. al investigated how to minimize ashing damage to low-k material and how to avoid the photoresist poisoning issue associated with 193nm resist [2]. C. Weng, and M. Lin, et. al. successfully developed a multi-step cleaning process, which is used in mass production [3]. However, little research has been done on defectivity improvement from the etch/ash and wet clean integration standpoint We evaluated the individual impact of etch/ash and wet clean on defect, electrical and reliability performance. We optimized etch/ash and wet cleaning, and successfully developed a simplified one step aqueous cleaning process. This paper presents results of process characterization and parametric yield data from the newly developed process. Hardware The development was completed on an Applied Materials' Oasis single wafer clean system. The wet cleaning chamber is schematically shown in figure 1, the chemical dispense arm can deliver two different chemicals in sequence, and the DIW dispense arm can deliver both RT and hot DIW. Backside liquid could be either chemical or DIW. The full coverage megasonic introduces physical cleaning force into the process to help for the particle removing. Blanket Cu wafers are used for etch rate test, patterned wafers are used for checking residue removal and parametric yield. Scanning Electron Microscopy (SEM) is used to check post cleaning residues. Transmission Electron Microscopy (TEM) is used for checking Cu loss on patterned wafer. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, (ID: , Pennsylvania State University, University Park, United States of America-14/06/14,04:58:44)

2 360 Ultra Clean Processing of Semiconductor Surfaces VIII RT or hot DIW Chem 1or Chem 2 Wafe r 300nm Megasonic plate Backside liquid Figure 1: Experimental setup Polymer Figure 2: Polymer covers the top of metal mask Process Results and Discussion Post etch ash optimization: We apply the concept of physical bombardment to change the physical properties of the polymer, we directly bombard the polymer with dilute gas. As shown in figure 2, prior to this bombardment treatment with dilute gas, the polymer is tightly adhered to the metal hard-mask. After bombardment with dilute gas, the physical characteristics of the polymer has been altered, or softened, such that diffusion of fluorine radicals is allowed to react with the underlying metal hard-mask, see figure 3 [3]. Residue Characterization: Figure 3 shows the typical residue after etch and dilute gas bombardment. A soft layer of polymer residue is left on top of metal hard mask and on trench side wall. In addition, some crystallized residues appear above polymer residue, increasing in size and density with time. Due to the presence of fluoride and its tendency to precipitate, the residue is believed to be a metal fluoride compound. Figure 3 shows the residue which is strongly bonded to metal mask. It appears after removing the generic polymer residue. Because of the relatively higher carbon and metal contents in the residue, this residue is believed to be organometallic in nature. Organometallic Residue 300nm Generic Polymer Figure 3: Generic polymer residue, metal fluoride residue, and organometallic bonded to metal hard masks after etch and ash Residue removal: Undercutting the particle or residue is a traditional and effective method for wafer cleaning; to remove the organometallic residue, slightly etch the metal hard mask to undercut the residue is necessary. It is well documented that H2O2 is a suitable chemical for the typical metal hard mask etch [1], however, H2O2 can not mixed together with lower ph aqueous solution for Cu/low-k film cleaning. In the newly developed process in order to undercut metal hard mask to remove the organometallic residue, we added another aqueous chemical to a fluorine based aqueous chemical to remove both organometallic residue and metal fluoride. Figure 4 shows the result. Clearly, all residues are completely removed. Metal fluoride dissolution is proposed as metal fluoride removing mechanism and is schematically shown in figure 5.

3 Solid State Phenomena Vol Figure 4: All residues are completely removed with the new cleaning process MFx AQ AQ MFx A Metal hard mask Metal hard mask (c) CU Figure 5: Proposed metal fluoride remove mechanism. Metal fluoride precipitate out of metal hard mask, AQ chemical dissolves the metal fluoride and separates the residue from metal hard mask, (c) metal fluoride flushes away with the chemical Parametric yield: Kelvin via resistance and via chain resistance distribution is summarized in figure 6. Compared to baseline process, the RC distribution from the new process is about the same or even better, especially on Kelvin via. The same via resistance suggests that the residue removal capability of the one step wet cleaning process and three steps cleaning baseline are comparable. The same performance suggests that the newly developed one step cleaning process has equivalent residue removal capability as the three steps baseline cleaning process. Precent 100.0% 90.0% 80.0% 70.0% 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% 0.0% Resistance (Ω ) baseline AQ clean Precent 100.0% 90.0% 80.0% 70.0% 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% 0.0% Figure 6: Via chain and Kelvin via resistance yield baseline AQ clean 0 1 2Resistance 3 (Ω ) Cu loss and reliability: Electromigration is the atomic diffusion caused by momentum transfer from conducting electrons. Electromigration and stress migration are critical reliability parameters and closely related to Cu loss in BEOL [4]. Lateral Cu loss was observed from wafer processed with the H 2 O 2 followed by aqueous clean process, as shown in figure 7. Figure 7 and (c) show the Cu

4 362 Ultra Clean Processing of Semiconductor Surfaces VIII loss from the process without H 2 O 2 Clean step. Clearly, no lateral Cu-loss was observed. The vertical Cu loss could come from multiple sources, such as post SiN barrier etch and TaN barrier punch through. We are investigating the individual impact of SiN barrier etch and TaN barrier punch through on vertical Cu loss. (c) Figure 7: Cu loss from H 2 O 2 followed by aqueous clean two steps process, and (c) No lateral Cu loss is observed from the single step aqueous clean process Summary The objective of this research is to develop a new process for metal hard mask Cu/low k film post etch/ash residue cleaning. The following conclusions can be made: (1) In the Cu/low-k process flow with metal hard mask, there are three type of typical residues after etch/ash: generic polymer residue, organometallic residue which is strongly bonded to metal masks, and time-dependent metal fluoride residue. (2)We optimized post etch ash process by dilute gas treatment and employed a new chemical to undercut metal hard mask for organometallic residue removal. (3)We developed a fluorine based aqueous chemistry to address the metal fluoride residue, which proved highly effective. (4) The integration electrical data shows that the optimized ash plus new single step aqueous cleaning process generates equal or even better results than that from multiple step processes. References 1. C. Richard, et. al.; Barrier and seed layer wet etching, Solid State Phenomena, Vol. 103~104 (2005), p361~ G. Delgadino, A. Zhao, et. al.; Tungsten hard mask damascene integration scheme for 65nm, 206th Meeting of the Electrochemical Society/2004 Fall Meeting of the Electrochemical Society of Japan, 2004, p Cheng Ming Weng, Miao Chun Lin, Ren Huang, US patent pending. 4. J. Segura and C. Hawkins, CMOS Electronics, How It Works, How It fails, (Wiley Interscience, A John Wiley & Sons, INC., Publication) p159~178.

5 Ultra Clean Processing of Semiconductor Surfaces VIII / Metal Hard Mask Employed Cu/Low k Film Post Ash and Wet Clean Process Optimization and Integration into 65nm Manufacturing Flow /