The discharge voltage behaviour during reactive sputtering of oxides. R. De Gryse, D. Depla, J. Haemers

Transcription

1 The discharge voltage behaviour during reactive sputtering of oxides R. De Gryse, D. Depla, J. Haemers AIMCAL

2 Hysteresis behaviour /O 2 and /O 2 discharge voltage (V) oxygen addition oxygen removal /O 2 Discharge voltage INCREASES on addition of oxygen /O 2 Discharge voltage DECREASES on addition of oxygen oxygen flow (sccm) Measurements by S. Heirwegh AIMCAL

3 Thornton : revised V W 0 discharge = e 0 im e I SE g E E original : g effective W 0 : effective ionisation energy e i : ion collection efficiency (for magnetron : almost 1) e 0 : fraction of maximum possible number of ions (for magnetron : almost 1) m : multiplication factor : accounts for ionisation in the sheath E : effective ionisation probability : influenced by electron recapture g ISEE : ion induced secondary electron emission coefficient * G. Buyle, Simplified model for the DC planar magnetron discharge (PhD, UGENT,2005) AIMCAL

4 Relationship ISEE/Voltage inverse of the discharge voltage (x10-3 1/V Ag Au Ce Cr Cu Mg Nb Pt Re Ta Y Zr ISEE coefficient AIMCAL

5 Measuring scheme status status status voltage V O2 V oxar V Ar argon oxygen magnetron Discharge voltage V Ar Oxygen flow V O2 oxygen addition oxygen removal time Dt AIMCAL

6 Results for different metals 410 Ag discharge voltage (V) Pt Re Au Cr Mg Ta Y time (s) Ce Zr Cu Nb Discharge voltage (V) Ag Au Ce Cr Cu Mg Nb Pt Re Ta Y V Ar V O2 V ox,ar target material AIMCAL

7 ISEE : two groups Ce Mg Y Li discharge voltage (V) oxygen flow (sccm) oxygen addition oxygen removal Ag Au Cu Pt Cr Nb Re Ta Zr High ISEE coefficient Low ISEE coefficient See Phelps et al. (Plasma Sources Science and Technology 1999) AIMCAL

8 Discharge voltage in pure oxygen At constant current : W0 Vdischarge = e e m ge 0 i ISE E Energy loss per produced ion electron pair M.A. Lieberman, A.J. Lichtenberg, Principles of plasma discharges and materials processing (New York, Wiley) AIMCAL

9 Calculation of yield Discharge voltage (V) Ta Nb me (s) Y I Y d = n D t o d = R+ DR SRIM ion : O + energy : ev O2 /2 material : oxide (density,stoichiometry) (1) Todorov et al. :Appl. PHYS. Lett. 52 (1988): (2) SRIM can be downloaded from (2) p p (1) AIMCAL

10 Yields : results calculated total sputter yield (SRIM) experimental total sputter yield 2.0 exp. oxide sputter DH f yield (kj/mole) Ag 2 O O Au 2 O CeO Cr 2 O CuO Li 2 O MgO Nb 2 O PtO ReO Ta 2 O O Y 2 O ZrO SRIM sputter yields : calculated based on the surface binding energy following the model of Malherbe et al. (Appl. Surf. Sci. 27 (1986): ) AIMCAL

11 Hypothesis(1) Hypothesis : Sputter bombardment results in reduction of the oxide which will influence the ISEE coefficient V ox,ar V Ar 360 K. Wittmaack, Surf. Sci. 419 (1999) 249 Discharge voltage (V) x in O 2-x ISEE coefficient time (s) AIMCAL

12 Reduction no reduction reduction R = ISEE ox ( ) M O ( ) M O s b reduction R Ce Cr Li Mg Nb Re Ta Y Zr AIMCAL

13 Hypothesis(2) 0.11 ISEE coefficient O/M ratio AIMCAL

14 Oxygen metal ratio ISEE coefficient Cr 2 O 3 Nb 2 O 5 ReO 3 Ta 2 O 5 O 2 red. O 2-x 2 O 3 CeO 2 Li 2 O MgO Y 2 O 3 ZrO 2 Ce Cr Li Mg Nb Re Ta Y Zr bulk oxygen to metal ratio AIMCAL

15 Conclusions At constant current, during reactive sputtering : 1) Increase or decrease of the discharge voltage can be attributed to a change of the ISEE coefficient due to target oxidation 2) Strong ion bombardment reduction results in a low ISEE coefficient. 3) A linear relationship between the O/M and the ISEE coefficient has been shown. ISEE ox ISEE coefficient V W 0 discharge = e 0 im e I SE g E E no reduction reduction R reduction Cr 2 O 3 Nb 2 O 5 ReO 3 Ta 2 O 5 O 2 red. O 2-x 2 O 3 CeO 2 Li 2 O MgO Y 2 O 3 ZrO 2 Ce Cr Li Mg Nb Re Ta Y Zr Ce Cr Li Mg Nb Re Ta Y Zr bulk oxygen to metal ratio AIMCAL

16 Acknowledgements Acknowledgements The authors are indebted to the for financial support company AIMCAL