A Study of Haze Generation as Thin Film Materials

Transcription

1 A Study of Haze Generation as Thin Film Materials Ju-Hyun Kang, Han-Sun Cha*, Sin-Ju Yang, Chul-Kyu Yang, Jin-Ho Ahn*, Kee-Soo Nam, Jong-Min Kim**, Manish Patil**, Ik-Bum Hur** and Sang-Soo Choi** Blank Mask R&D Center, S&S TECH CORPORATION 9, Horim-Dong, Dalseo-Gu, Daegu-City, , Korea * Division of Advanced Materials Science Engineering, Hanyang University 17, Haengdang-Dong, Seongdong-Gu, Seoul-City, , Korea ** R&D Center, Photronics-PKL 493-3, Sungsung-Dong, Cheonan-City, Choongnam-Do, , Korea Phone: Fax: [email protected] ABSTRACT For high quality products in the semiconductor and photomask industries, exposure wavelength has been shortening from i-line to ArF to embody the high resolution as critical dimension (CD) shrinkage and the specifications have been restricted. However, a new defect issue called haze has appeared that is shortening the wavelength. This defect is caused by the photoreaction of chemical residues exposed to SO 4 2-, NH 4 + and other chemicals. Accordingly, in this paper we investigated the generation of haze in thin film materials. For fabrication of various thin films, the materials which were metal, compound material without nitrogen, and compound material with nitrogen, were deposited on a quartz substrate using sputtering. Then, we chemically treated the thin film materials using various conditions including sulfuric peroxide mixture (SPM) and standard cleaning (SC-1). First, the concentration of ions on the thin film materials was measured using ion chromatography (IC) analysis. Second, haze defects were inspected after exposure in order to evaluate the difference in haze generation on the thin film materials. Also, we investigated the numbers and shape of the occurrences of haze. Keywords: haze, ion chromatography, thin film material, exposure, SO 4 2-, NH INTRODUCTION The critical dimension (CD) has been minimized and the exposure wavelength has been shortened to embody the higher integration and larger capacity of semiconductors. However, exposure energy has been increasing as the exposure wavelength shortening, and this causes the issue called haze. This defect is caused by the exposure of high energy on the photomask surface, and reduces the lifetime of the photomask, so this defect eventually decreases productivity in the lithography. Accordingly, the haze issue must be overcome to improve productivity. As shown in previous reports, the residual ions SOx, NOx and NH 4 adhered to the photomask surface during the cleaning process, and these caused a photoreaction due to exposure to high energy. Therefore, the haze defect was caused by photoreaction. From the result of these reports, it was shown that the haze was also generated by outgassed contaminants from pellicle materials such as frames, films, adhesives and other materials. However, most of the studies focused on the photomask process. Accordingly, we investigated haze generation on the mask blanks of thin film materials. Photomask Technology 2007, edited by Robert J. Naber, Hiroichi Kawahira Proc. of SPIE Vol. 6730, 67304K, (2007) X/07/$18 doi: / Proc. of SPIE Vol K-1

2 2. EXPERIMENTAL 2.1 Process Flow Ion Extraction Treatment by Quartz Container with DI Water IC Analysis Thin Film by Sputtering Chemical Treatment as Conditions 1 st Exposure with 7, 10 kj Haze Inspection 2nd Exposure with 5 kj Haze Inspection Figure. 1 Process Flow We studied the generation of haze on thin film materials in figure 1. Figure 1 shows the process flow of this study. As shown in figure 1, thin films were deposited using the sputtering system and treated with various chemical conditions. And then, the adsorbed ion concentration on the surface was analyzed using IC analysis. Also we inspected the number and shape of occurrence of haze by microscope after ArF laser acceleration. 2.2 Thin Film Condition In this paper, we prepared the three categories of material such as pure metal, compound materials without nitrogen and compound materials with nitrogen as shown in table 1. Materials A ~ D were pure metals, and materials E and F which are phase shift mask (PSM) materials were compound materials without nitrogen. Materials G and H were compound materials based on material E with nitrogen, and material G had a relatively higher composition of nitrogen than material H. Finally, materials I and J were compound materials based on material F with nitrogen, and material I had a relatively higher composition of nitrogen than material J. Materials G ~ J were also PSM materials. Table 1. Types of Samples Pure Metal Compound Material without Nitrogen Compound Material with Nitrogen Materials A, B, C, D E F G, H (Material E based) I, J (Material F based) We chemically treated the materials with various conditions as shown in table 2 for thin film materials. Condition 1 did not apply SPM or SC-1, and condition 2 applied only SPM for 10 minutes using the dipping method. Condition 3 applied both SPM and SC-1 for 10 minutes using the dipping method. After treatment, the thin film materials with chemical treatment were kept in shipping boxes. Table 2. Chemical Treatment as Conditions Conditions SPM SC 1 1 No Dipping No Dipping 2 Dipping for 10 min No Dipping 3 Dipping for 10 min Dipping for 10 min Proc. of SPIE Vol K-2

3 2.3 IC Analysis Condition We measured the ion concentrations of the thin films material using IC analysis. First, we extracted ions with deionized (DI) water using a quartz container as shown in figure 2. Gasket Cover Teflon bolt 6 Inch Quartz Quartz Figure. 2 Quartz Container for Ion Extraction Figure 2 shows the quartz container for ion extraction. Quartz was selected as the container material to minimize the impurities from the container and to prevent re-adsorption of the impurities. Gasket and teflon bolt were used to seal the container. The ion extraction progressed through heat treatment in the DI water. The IC analysis was done using a DIONEX-320 series from the ion extracted DI water. 2.4 ArF Laser Acceleration Condition ArF laser acceleration was applied for haze generation as in the conditions of table 3. After ArF laser acceleration, we inspected the surface of the thin film materials using microscopy. Table 3. Conditions of ArF Laser Acceleration Items Energy Source Beam Size on Sample Energy Fluency Condition 193 mm 5 mm x 5 mm 150 Hz Humidity 45 % Temperature 23 Air Flow 0.5 LPM Proc. of SPIE Vol K-3

4 3. RESULTS AND DISCUSSION 3.1. IC Analysis Results IC analysis progressed for thin film materials. Table 4 shows the results of the IC analysis for condition 1, which did not apply. Despite no chemical treatment for the thin film materials, ions were detected for all thin film materials, because ions were generated form the shipping box and environmental condition such as cleanroom. There was also a slight difference in ion concentrations for all the materials. As shown in table 4, F -, Cl -, SO 2-4 and NH + 4 ions were detected for all of the thin film materials. The total ion concentration for all of the thin film materials was from 4 ppbv to 7 ppbv. Table 4. Ion Analysis Results of Condition 1 by IC (unit : ppbv) Materials Description F - Cl SO 4 NH 4 Total Material A Pure Metal Material B Pure Metal Material C Pure Metal Material D Pure Metal Material E Compound Material without Nitrogen Material F Compound Material without Nitrogen Material G Compound Material with Nitrogen Material H Compound Material with Nitrogen Material I Compound Material with Nitrogen Material J Compound Material with Nitrogen NO 3, Na, K, Mg, Ca ions were not defected. Table 5 shows the results of the IC analysis for condition 2, which was treated only with SPM. More SO 4 2- ions were detected compared to condition 1. First, in the case of materials A ~ D, which were the pure metals, around 5 ppbv ion concentrations were analyzed from materials A ~ C, but material D generated 20 ppbv, which was 4 times higher than the other materials. This difference in ion concentration occurred due to diversion of the ion adsorption rate of the materials. For material E, which was PSM material without nitrogen, ppbv of SO 4 2- was deteced and material F had 9.45 ppbv, so the ion concentrations in material E was 1.2 times higher than material F s concentration, and the difference of the ion adsorption rate was caused by the different composition of the transition metal. For PSM material G and H without nitrogen, which were based on material E, the difference in the total ion concentration between materials G and H was 26 ppbv. The highest concentration of SO 4 2- ion was detected in material G. Therefore, we could find that the difference of ion concentration was due to nitrogen composition in materials G and H. Also in the PSM materials I and J with nitrogen, which were based on material F, the total ion concentration of material I, with a high composition of nitrogen, was ppbv, and this concentration was higher than material J s concentration, with a low composition of nitrogen. This tendency was similar to materials G and H. However, the difference in the ion concentrations due to nitrogen composition was as small as 6 ppbv. There was twice as much ion concentration among PSM materials in materials G ~ H, and this difference due to a mother material difference. Due to the results of the IC analysis of the thin film materials, we could conclude that the difference in the ion concentration of the thin film materials was caused by a variation in the ion adsorption rate that occurred due to the different surface energy state of the material types and their compositions. Also the concentrations of F -, Cl - and NH 4 + ions increased compared to condition 1 because of impurities in the SPM solution. Therefore, selection of SPM solution is needed. We rinsed after the SPM treatment for 10 minutes, but SO 4 2- ions were detected. Accordingly, more rinse time is needed to remove SO 4 2- ions, which also have a sticky characteristic in cleaning process. Proc. of SPIE Vol K-4

5 Table 5. Ion Analysis Results of Condition 2 by IC (unit : ppbv) Materials Description F - Cl - 2- SO 4 + NH 4 Total Material A Pure Metal Material B Pure Metal Material C Pure Metal Material D Pure Metal Material E Compound Material without Nitrogen Material F Compound Material without Nitrogen Material G Compound Material with Nitrogen Material H Compound Material with Nitrogen Material I Compound Material with Nitrogen Material J Compound Material with Nitrogen Table 6 shows the results of the IC analysis for condition 3, which was treated with both SPM and SC-1. Concentrations of NH + 4 ions increased. First, in the case of materials A ~ D, which were pure metals, around 25 ppbv of NH + 4 ion concentration was analyzed from materials A ~ C, but material D generated 90 ppbv, which was about 4 times higher than the other materials. Material E, which was PSM material without nitrogen, showed ppbv of NH + 4, and material F was analyzed to be ppbv. This concentration was 4 times higher than material F s concentration. For PSM material G and H without nitrogen, which were based on material E, the total ion concentration of material G was ppbv, which was about 2 times higher than material H`s concentration. The highest concentration of NH + 4 ions was detected from material G. On the other hand, the total ion concentration and NH + 4 of material H was ppbv and ppbv, and this concentration were lower than material G. Therefore, we could find the same tendency that ion concentrations are different due to the composition ratio of nitrogen in the case of materials G and H. Also, for PSM materials I and J with nitrogen, which were based on material F, the total ion concentration of Material I was higher than material J, where material I s concentration was ppbv. TheNH + 4 ion concentration of materials I and J were ppbv and 20.2 ppbv, respectively. However, the difference in the total ion concentration between materials I and J was small, only 18 ppbv. Table 6. Ion Analysis Results of Condition 3 by IC (unit : ppbv) Materials Description F - Cl SO 4 NH 4 Total Material A Pure Metal Material B Pure Metal Material C Pure Metal Material D Pure Metal Material E Compound Material without Nitrogen Material F Compound Material without Nitrogen Material G Compound Material with Nitrogen Material H Compound Material with Nitrogen Material I Compound Material with Nitrogen Material J Compound Material with Nitrogen Proc. of SPIE Vol K-5

6 As shown in the results of the IC analysis of these conditions, the pure metal materials such as A ~ C had a relatively low total ion concentration compared to materials D ~ J. For PSM materials E and F without nitrogen, the total ion concentration of these materials was high compared to those of the pure metal materials and was low compared to those of the PSM materials with nitrogen, because the ion adsorption rate was different for the PSM material composition, and we could find that total the ion concentration was determined as a composition ratio of nitrogen. Therefore, types and composition of the materials and nitrogen composition were the dominant factors for low ion concentrations in the selection of materials for binary and PSM as the mask blanks Haze Generation as ArF Acceleration Results Counts of Haze Defects We did ArF laser acceleration to generate the haze and count the number of occurrences of haze. In the case of condition 1, the energy of the ArF laser acceleration was 10 kj due to no chemical treatment and the energy of the ArF laser acceleration was 7 kj in conditions 2 and 3 due to chemical treatment. An additional ArF laser acceleration was done using an additional 5 kj to investigate the haze generation from exposure energy. In condition 1, no haze defect was found at 10 kj and 15 kj of exposure energy, because the concentration of ions, such as SO 4 2- and NH 4 +, was very low Q 7kJ PiLls 5 kj a Sulfate a Total Ion 15 mm Spot Area 5 mm 5 mm 5 mm 30 a 15 mm = 0 I- C C0 1) n iø-; /1 I I I I I I A B C D E F G H I J -- Pure Metal Compound Material Compound Material without Nitrogen with Nitrogen Figure. 3 Haze Defect Count Results by ArF Laer Acceleration of Condition 2 Figure 3 shows the haze inspection results of condition 2. The haze inspection area was 15 mm x 15 mm around a spot area of 5 mm x 5 mm as shown in figure 3. For pure metal materials A ~ D, number of occurrence of the haze defect in the pure metal materials A ~ C, which had low ion concentrations of about 25 ppbv, was under 3 EA/cm2, and in material D, which had high ion concentrations of 50 ppbv, the number of occurrence of the haze defect was 15 EA/cm2. The Proc. of SPIE Vol K-6

7 2- variations of total ion concentrations were twice as large, SO 4 ion concentrations were 4 times as large, and the difference in the number of haze defects was 5 times as large between materials A ~ C and material D. Therefore, we could find that relationship between the number of haze defects and the SO 2-4 ion concentration was in direct proportion. For PSM materials E and F without nitrogen, the number of haze defects in material E was 10 EA/cm2, and material F s number of haze defect was 5 EA/cm2, so material E s haze numbers were twice that of material F. The concentration of the total ions and SO 2-4 ion concentrations in material E were 42 ppbv and ppbv, and for material F were ppbv and 9.45 ppbv, respectively. Therefore, the relationship between SO 2-4 ion concentrations and haze defects was in direct proportion in the case of PSM materials E and F. For PSM materials G and H with nitrogen, which were based on material E, 22.9 EA/cm2 of haze defects was generated in material G and 12.4 EA/cm2 in material H. The number of haze defects in material G was 1.5 times higher than material H. The concentration of total ions and SO 2-4 ion was ppbv and ppbv in material G, and ppbv and ppbv in material H. SO 4 ion concentration in material G were 1.5 times higher than material H. Accordingly, the variation of total ion concentration was almost the same as the difference of haze defects in materials G and H. We could find that the relationship between the haze defect and the total ion concentration was in direct proportion here, too. For PSM materials I and J with nitrogen, which were based on material F, 8.5 EA/cm2 of haze defects were generated in material I and 7.1 EA/cm2 in material J. For the ion concentration in Materials I and J, the concentrations of total ions and SO 2-4 were ppbv and ppbv for material I, and that of material J were ppbv and ppbv, respectively. The variation of ion concentrations and the difference in the haze defects between material I and J were small. In accordance with above results, we could identify that the concentration of total ions and the SO 2-4 ions was a very important factor in the generation of haze defects c' 30 C, 7 kj -, Plus 5 kj Ammonia Total Ion Uncountable r Uncountable Uncountable 15 mm Spot Area 5 mm 5 mm 5 mm 15 mm C U 0 A B C D E F G H I J 0 Pure Metal Compound Material without Nitrogen Figure. 4 Results of Haze Acceleration Test as condition 3 Compound Material with Nitrogen Proc. of SPIE Vol K-7

8 Figure 4 shows the haze inspection results for condition 3. For the pure metal materials A ~ D, the number of haze defects in pure metal materials A ~ C with ion concentrations of about 80 ppbv was small, at just 17 EA/cm2, when compare to material D with ion concentrations of 170 ppbv at 12 kj. The number of haze defects of material D was uncountable at 12 kj. The total ion concentration in materials A ~ C was twice that of material D, and the NH + 4 ion concentrations were 4 times that of material D. Therefore, the difference in the haze defects in materials A ~ D was caused by the different concentrations of total ions and NH + 4 ions. NH + 4 ion concentrations were an important factor for haze generation in condition 3. That is, number of haze defects increased as the NH + 4 ion concentration increased. For PSM materials E and F without nitrogen, the number of haze defects in material E was uncountable, and 10 EA/cm2 of haze defects were generated in material H. The concentration of total ions and the NH + 4 ions in material E were ppbv and ppbv, and these of material F were 75.7 ppbv and ppbv, respectively. Accordingly, the number of haze defects increased with the NH + 4 ion concentration in materials E and F. This tendency was the same in materials A ~ D. For PSM materials G and H with nitrogen, which were based on material E, uncountable haze defects was generated in + material G and haze defects of 25.8 EA/cm2 was generated in material H. The concentration of total ions and the NH 4 ions in material G were higher than material H at ppbv and ppbv. Accordingly, the number of haze defects rapidly rose with concentration of total ions and the NH + 4 ions. This was the same for the results of the pure metal materials and material E and F, above. For PSM materials I and J with nitrogen, which were based on material F, haze defects of 16.9 EA/cm2 was counted in material I, twice that of material J, and haze defects of 8.5 EA/cm2 were generated in material J. The ion concentrations and number of haze defects were twice that of material J. As a result, the relationship between ion concentrations and the number of haze defects was in direct proportion for materials I and J. In accordance with the results of the haze inspection of the conditions, the number of haze defects increased as the ion concentration increased. We confirmed that ions such as SO 2-4 and NH + 4 were especially important factors in the generation of haze defects Shape Investigation of Haze Defects The shape of the haze defects was analyzed with respect to the materials and conditions in this paper. At the same time, the change of shape was analyzed with respect to the exposure energy. First, we could not find a difference due to the condition in the shape of the haze defects in the pure metals. The shape was circle type. Circle Haze Circle Haze a 1- Lens Contamination 100 Lens Contamination Figure. 5 Representative Haze Defect Images of Material A ~ D Figure 5 shows a representative haze defect images of materials A ~ D. As shown in figure 5, the generated haze defects in the pure metal materials has the shape of circle, and the size of the haze defect was slightly different, because the concentrations of SO 4 2- and NH 4 + ions and the surface state of the materials was almost the same due to the same Proc. of SPIE Vol K-8

9 material group of the metals. The ion concentration of material D was higher than the other pure metal materials, but the shape of the haze defects was circle type. Only material D has many number of haze defect. PSM materials E and F without nitrogen had circle type haze defects, and they were similar to those of the pure metal materials. Circle Haze Circle Haze Lens Contamination (a) Material E (b) Material F Fig. 6 Representative Haze Defect Images of Material E, F Figure 5 shows the representative haze defect images of materials E and F. As shown in figure 6, the haze defects in materials E and F were circle type haze with varying size. Oval 0Haze Spot Group Haze t Flower Haze (a) Material G 00 (b) Material H Distorted Circle Haze (c) Material I (d) Material J Figure. 7 Representative Haze Defect Images of Material G ~ J Proc. of SPIE Vol K-9

10 Figure 7 shows a representative haze defect images of materials G ~ H with nitrogen. The type of haze defect in materials G and H was like oval shaped as in fig 7 (a), or spot group shaped as in figure 7 (b). The type of haze defects in materials I and J were different compared to material G and H as shown in figure 7 (c) and (d). In accordance with the results of the inspection of haze type, the types of haze in pure metal materials and PSM materials without nitrogen in materials A ~ F were a similar circle type haze defects, but the types of haze in the PSM materials with nitrogen in materials G ~ J were different than material A ~ F. The ion concentrations of materials G ~ J were higher than the other materials, and haze generation was more unstable as the haze occurrence rate increased because the ion concentration was higher. Next, the shape of the haze was analyzed after 5 kj of ArF laser acceleration was added to each material. 7 kj + 5 kj Just Size Increased 3.5 EA/cm2 5.1 EA/cm2 Figure. 8 Representative Haze defect Images of Material A ~ D as Exposure Energy Figure 8 shows the representative haze defect images of materials A ~ D after 5 kj ArF laser acceleration was added. As shown in figure 8, there was no difference in the shape of the haze defect, but the size became bigger. We could confirm the same results in the other pure metal materials. 7 kj + 5 kj Just Size Incressed (b) 21.9 EA/cm2 Uncountable Figure. 9 Representative Haze defect Images of Material E, F as Exposure Energy Figure 9 shows representative haze defect images of PSM materials E and F after 5 kj ArF laser acceleration was added. As shown in figure 9, there was no difference in the shape of the haze but the size and number of haze defects increased. Proc. of SPIE Vol K-10

11 7 kj + 5 kj 4j7 p ;-_. The shape of Haze Defect changed '- t cc. 'I -' -? ij Growth 'k. I rt X50 20 (a) Material G 7 kj + 5 kj The Size and Shape of Haze Defect Changed Nucleation of Haze (b) Material H.. The Size and Shape of Haze Defect Changed 7 kj + 5 kj S 0 lao I Ice (c) Material I 7 kj + 5 kj The Size and Shape of Haze Defect Changed (d) Material J Figure. 10 Representative Haze defect Images of Material G ~ J as Exposure Energy Proc. of SPIE Vol K-11

12 Figure 10 shows the representative haze defect images of PSM materials G ~ J after 5 kj of ArF laser acceleration was added. As shown in figure 10, the shape and size of the haze defect changed. For material G, the shape of the haze defect was circle type haze early on, but the shape of the haze defect changed to a branch type haze and the size increased as 5 kj ArF laser acceleration was added. Additionally, large number of haze defects was generated. For material H, a large numbers of nucleations were generated as the ArF laser acceleration was increased. There was also changing of shape and increasing size in the haze defects in materials I and J. In materials G and H, which were based on material E, and in material I and J, which were based on material F, there was a different changing of shape, because the surface energy was different then the composition of the transition metal in the mother materials. In accordance with the results of the haze defect shape inspection, pure metal materials A ~ D and PSM materials E and F without nitrogen had circle type haze in the initial exposure, and there was no difference in the shape of the haze as exposure energy was increased. Only the size of haze defects was increased with increasing exposure energy. PSM materials G ~ H with nitrogen had a different type of haze defect in each material in the initial exposure, and the shape of the haze defects changed as exposure energy was increased. The shape change and size and number increase in material G were much larger than materials H ~ J, because the instability of the haze generation increased especially due to differences in the composition and adsorbed ion concentrations. 4. CONCLUSION As a result, we could confirm that the adsorbed ion concentration on the surface was different in the thin film materials, because the materials have different surface energy due to composition: the composition of the transition metals and the composition ratio of nitrogen. Therefore, the number and shape of the haze defects were different after the ArF laser acceleration. Also, PSM materials with and without nitrogen have unstable characteristics in their haze generation compared to the pure metal materials, and PSM materials without nitrogen were more stable than PSM materials with nitrogen for haze generation. Accordingly, it is very important to select a thin film material to reduce the haze defect. We need more research to investigate the mechanism of haze generation in the thin film materials. 5. ACKNOWLEDGEMENTS This work was supported by Research and Development (2007. May ~ Apr) project of Small and Medium Business Administration. REFERENCE 1. H. B. Kang et al., A study for the control of chemical residuals on photomask by using a thermal treatment for 65-nm node, Proc. SPIE, vol. 5853, 2005, F. Eschbach et al., Photomask lifetime issues in ArF lithography, Proc. SPIE, vol. 5853, 2005, K. Bhattacharyya et al., An Investigation of a New Generation of Progressive Mask Defects on Pattern Side of Advanced Photomasks, Proc. SPIE, vol. 5853, 2005, F. Eschbach et al., ArF lithography reticle crystal growth contributing factors, Proc. SPIE, vol. 5567, 2004, S. J. Han et at., The Study on Characteristics and Control of Haze Contamination induced by Photochemical Reaction, Proc. SPIE, vol. 5130, 2003, Proc. of SPIE Vol K-12