A. Sagara

B. Tsuchiya

K. Tsuzuki

M. "Natsir

O. Motojima

Y." Hasegawa

National Institute for Fusion Science (NIFS-Repository)

§60. Control of Discharge Conditions to Reduce Hydrogen Content in Boron Films Coating Natsir M., Tsuzuki, K.(Grad. Univ. Advanced Studies) Sagara, A., Motojima, 0. Tsuchiya, B. (Dep. Crystalline Matel. Nagoya Univ.) Hasegawa, Y. (Dep. Energy Eng. Nagoya Univ.) Aiming at the reduction of H content in boron fihns at near romn temperature by controlling glow discharge conditions, the systetnatic study has been perfonned in plasma processing teststand (PPT). So far, flash filament tnethod (FF) at floating potential is used to measure H concentration 1 ,2). To investigate the effect of the electric potential, boron films are prepared on AI samples at electrically floating or cathode potential, and the hydrogen concentration is measured by elastic recoil detection tnethod (ERD) and a new rnodified norn1alizing technique with Rutherford back scattering (RBS)3). Figure I shows a typical RBS spectrmn taken from the cathode potential B coated AI sample, on which B cannot be clearly observed, probably due to surface roughness of AI target. However, the B fihn thickness was measured from the shift of the AI surface edge as shown in Fig; 1. Then AI edge intensity with calculated scattering cross section a and energy stopping power £ under the B film was used as the measure of the probing He+ fluences which was used to obtain absolute H concentration frotn ERD spectra. This tnethod was newly established in this work for the case of low Z thin films. Figure 2 shows the typical hydrogen depth profiles in boron films formed on floating or cathode potential AI samples. Frmn this figure it is observed that the H profile on the cathode potential sample is tnore dense, flat, and thick in comparison with the floated one. We have investigated H/B dependence on the discharge power and the total pressure. The results showed that the H/B of the cathode potential samples, which are exposed to energetic ions, are higher than that of the floating potential ones in every case. The H/B are reduced with increasing the fihn growth rate (increasing the flux of boron contained radicals and/or ions), in good agreement with our results obtained so far frotn the FF method or RGA. Thus, it is conjectured that energetic ions flux should be reduced but the radical one should be increased for the reduction of H concentration. We can also conclude that FF is a usable method for quick and in-situ measurement in coated film. 6000 ,.----::-., __________ ---b.liJ.i!LIWI, 4800 ~ 3600 ~ ::s '-'\ . •. 0 u 2400 "'\~B ·"'-,.. AI under B film _ "":.. -< pure-<-Discharge conditions Tot~1 pressure: 200 mTorr 1200 Disclmge power: 100 Watt Mixing r<Jtio : 5 % (B21VIIe) Deposition time : 13 min () Samp1~ temp. - 90 OC I 00 200 300 400 ~. AI ' ·.f-<-----------8 film- 259 11111 500 GOO 700 800 Detected energy E d (ke V) 900 Fig. I. RBS spectrum taken from B film prepared on the electrically cathode potential AI sample, and the schematic illustration of the ion beam analysis system. ,---..... 815 .!2_ V) 8 0 ....... C\$ N JQ 01 0 Discharge conditions; Total pressure : 200mTorr Discharge power: 100 Wall Deposition time : 13 min Mixing ratio : 5 % ( Bzl~/1-le) Sample temp. - 90 0C Cathode potential ~ . ... -.~~ I . ~.. ' !'~~ 100 200 Depth ( ntn) 300 Fig.2. Depth profiles of hydrogen atom in boron films on electrically floating or cathode potential AI samples. References 1) M. Natsir, A. Sagara, et. al, J. Nucl. Mater., 220-222 ( 1995) 865-868. 2) M. Natsir, A. Sagara, et. al, Trans. of Fusion. Tech., 27 (1995) 527-531. 3) M. Natsir, A. Sagara, et. al, in print in Vacuum. 65 

Control of Discharge Conditions to Reduce Hydrogen Content in Boron Films Coating

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