Novel Photo Resist Stripping for Single Wafer Process

Transcription

1 Solid State Phenomena Vols (2005) pp Online available since 2005/Apr/01 at (2005) Trans Tech Publications, Switzerland doi: / Novel Photo Resist Stripping for ngle Wafer Process Atsushi Okuyama 1,a, Kazumi Asada 1, Hitoshi Abe 1, Hayato Iwamoto 1, Yoshio Okamoto 2 and Takuya Wada 2 1 Semiconductor Solutions Network Company Sony Corporation Asahi-cho, Atsugi-shi, Kanagawa, Japan 2 Semiconductor Equipment Company DAINIPPON SCREEN MFG. CO., LTD , Mikami, Yasu-cho, Yasu-gun, Shiga , Japan a Atsushi.Okuyama@jp.sony.com Keywords: resist stripping, single wafer process, high dose ion implantation, non ashing Introduction It is common to use the mixed-solution of H 2 SO 4 and H 2 O 2 (SPM : Sulfuric Peroxide Mixture) for dip process after ashing at the stripping process of the high dose ion implanted photo resist [1, 2]. However, the attack on a substrate by ASH+WET is posing problems to high performance devices [3]. Figure 1 shows the mechanism of the attack on a substrate by ASH+WET and the dose-profile in the depth direction of the ion implanted substrate was shown in Figure 2. The ion implanted substrate surface is attacked by oxidization by ashing, and O 2 etching by wet cleaning, and, as a result, the dose-loss arises. Figure 2 expresses dose-loss by ASH+WET arised in one process, and the extent of attack to a substrate becomes still larger by repeating this process. On the other hand, it is also required to strip resist by single process in order to deal with wafers of large diameter and a small quantity of multi-kind conditions from the viewpoint of cost and environment. For the purpose of fulfilling these requirements, the resist stripping method of controlling the consumption of the chemicals, and having a high stripping performance by single wafer process (following SHARK cleaning : SH Advanced Resist Killer) was developed. Experimental The reactions are as follows in SPM : H 2 SO 4 + H 2 O 2 => H 2 SO 5 + H 2 O The resist stripping performance has correlation with the amount of generation and reactivity of H 2 SO 5 (peroxosulfuric acid). Although it is difficult to measure the amount of generation of H 2 SO 5 directly because of the dependence on H 2 O 2 concentration, concentration change of H 2 O 2 in SPM solution was investigated (Figure 3). Although the concentration of H 2 O 2 is low in the conventional dip process (several hours passed after mixture of chemicals), it is expected that a higher stripping performance is obtained by using SPM solution with high concentration just after mixture of chemicals. SHARK cleaning is the resist stripping method aimed at supplying H 2 SO 5 generated in the very high state on a wafer by mixing the chemicals just before the supply. Chemicals are made to react efficiently by the chemicals mixture part attached just before a nozzle, as shown in Figure 4. The samples which are implanted with various ions and the amounts of dose into patterned i-line resist were used for evaluation. For SHARK cleaning, it processed in order of Figure 5 using the cleaning equipment of a single wafer spray system. Moreover, the concentration of H 2 SO 4 and H 2 O 2 used for SHARK is 96% and 31%, respectively. 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-04/06/14,08:42:31)

2 298 Ultra Clean Processing of licon Surfaces VII Firstly, the way of mixing chemicals, the rotation rate of a wafer, the mixture ratio of chemicals, the flow rate of chemicals, the temperature of the chemicals, the supply method, the shape of a supply nozzle, etc. were changed and the optimal condition in SHARK was found. Secondly, the number of the resist residue was investigated in order to compare the resist stripping performance of the optimal condition of the SHARK, and that of the conventional dip process. Thirdly, in order to estimate the amount of attack on a substrate by SHARK cleaning or conventional process (Ashing+SPM), the change of O 2 thickness before and after these processes was investigated. Results and Discussion As a poiont of mixing chemicals, on a wafer, in a nozzle, just before a nozzle, etc. were compared. Consequently, the point which showed the highest stripping performance was the mixture just before a nozzle which can mix chemicals most efficiently. The example of an optimization result is shown in Figure 6. Figure 6 (a) is the plot of the number of resist residue as a function of the mixture ratio of H 2 SO 4 and H 2 O 2. If the mixture ratio shifts from an optimal condition, the stripping performance becomes worse because one of chemicals remains and it doesn t react efficiently. Figure 6 (b) is the plot of the number of resist residue as a function of the rotation speed of the wafer during chemicals supply. Although the stripping performance improves when the fresh chemicals just after mixture are continuously supplied by rotating a wafer at high speed so that the chemicals are shaken off from a wafer, if the rotation speed is too high, the chemicals are shaken off before reacting with the resist, and the resist stripping performance becomes worse. Figure 6 (c) is the plot of the number of resist residue as a function of the flow rate of the chemicals. When the total amount of the chemicals was fixed and the flow rate was changed, it turns out that the resist stripping performance is saturated by the optimal flow rate. It is expected that this optimal flow rate is the flow rate at which the chemicals contribute to a resist stripping reaction most efficiently. Figure 6 (d) is the plot of the number of resist residue as a function of the temperature of the chemicals. Although the resist stripping performance improves as temperature of chemicals becomes high as expected, when the temperature reaches a certain point, it turns out that the resist stripping performance is saturated. The stripping performance evaluation results for the resist with various implantation doses by the optimal condition of SHARK are shown in Table I (a). On the other hand, the results by the conventional dip process are shown in Table I (b). It is shown that the stripping performance of SHARK is higher than conventional dip process. The number of the resist residue with implants ion of 1E15 dose after SHARK and conventional dip process were compared (Figure 7). The resist with implants ion of 1E15 dose which has not been stripped by conventional dip process could be stripped by SHARK. This is the effect of highly reactive H 2 SO 5 by supplying chemicals just after mixture. The thickness change of O 2 before and after resist stripping and after-stripping treatment was compared between SHARK and ashing+conventional process(spm) (Figure 8). Although the difference in each final thickness of O 2 is not so large, it is shown that the thickness after ashing+conventional is thicker than that after SHARK. This thickness difference suggests that a substrate was attacked by oxidation from ashing and O 2 etching from after-stripping treatment (Figure 1). Conclusions We established a novel photo resist stripping method for single wafer process (SHARK cleaning). SHARK can strip high dose ion implanted resist (over 1E15) by non ashing because of highly reactive H 2 SO 5 by mixing chemicals just before supplying on a wafer.

3 Solid State Phenomena Vols References [1] M.Itano et al; IEEE Trans. On Semicond.Manufact., 6 (3), pp , [2] M.M. Heyns et al; Proc. AMDP, March , pp.59-66, Sendai, Japan. [3] K.Hirose et al; Ion-implanted photoresist and damage-free stripping, J. Electrochem. Soc., Vol.141, No.1, pp , Ashing Wet O 2 O 2 Figure 1: The Mechanism of the Attack for a Substrate. O 2 Attack for a Substrate Ion Conc.(/cm3) Dose-Profile of the Ion Implanted substrate Low Concentrations High SHARK H2SO4 H2O2 Conventional (SPM) Depth (nm) Dose-Loss by Ash.+Wet Figure 2: Dose-Profile of the Ion Implanted Substrate. H 2 O 2 H 2 SO 4 Mixture Part Nozzle H 2 SO 4 / H 2 O 2 Substrate Figure 4: The Schematic of SHARK Cleaning. Figure 3: Concentration Change of H 2 SO 4 and H 2 O 2 as a Function of Elapsed Time. SHARK Hot DIW DIW Dry Elapsed Time APM DIW Figure 5: The Process Flow of SHARK Cleaning. 100 H2SO4 0 0 H2O2 100 (a) Mixture Ratio Low Rotation Speed High (b) Rotation Speed

4 300 Ultra Clean Processing of licon Surfaces VII Low Chem. Flow Rate High Low Chem. Temperature High (c) Flow Rate (d) Temperature Figure 6: Mixture Ratio of H 2 SO 4 and H 2 O 2 (a) and Rotation Speed of Wafer (b) and Chemical Flow Rate (c) and Temperature of Chemicals (d) for Resist Stripping. Table I: Resist Stripping Performances by SHARK Cleaning (a) and Conventional (b). Implant Ion (a) SHARK Implant Dose 1E+13 1E14 Implant Dose 1E15 1E+13 1E14 1E15 B B Implant Ion (b) Conventional (SPM) P P As As (a) SHARK (b) Conventional (SPM) Figure 7: Stripping Results of Ion Implant Resist (As-1E15) by SHARK (a) and Conventional (b). SHARK Cleaning Ashing+Conventional(SPM) O2 Thickness(nm) Initial Ashing SHARK APM or SPM Figure 8: The change of O 2 Thickness by SHARK and Ashing+Conventional (SPM).

5 Ultra Clean Processing of licon Surfaces VII / Novel Photo Resist Stripping for ngle Wafer Process /