1. Equipment and technological processes for manufacturing GaAs MMICs METALISATION TWO TALK 9

2. Sputtering Sputtering: When a solid or liquid is bombarded by high energy atomic particles, it is possible for individual atoms to obtain enough energy to escape from the surface of the material being bombarded. Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

3. Sputtering  When power is supplied to a magnetron a negative voltage of typically -300V or more is applied to the target. This negative voltage attracts positive ions to the target surface at speed.  Generally when a positive ion collides with atoms at the surface of a solid an energy transfer occurs. If the energy transferred to a lattice site is greater than the binding energy, primary recoil atoms can be created which can collide with other atoms and distribute their energy via collision cascades.  A surface atom becomes sputtered if the energy transferred to it normal to the surface is larger than about 3 times the surface binding energy (approximately equal to the heat of sublimation). Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

4. Sputtering Advantages – Good film adhesion – Accurate control of process – Good ‘step’ coverage, e.g. coats round corners – Lift off Possible with long throw distance and coating chimneys – Easily automated – With appropriate power input virtually anything can be sputtered Disadvantages – Small source to substrate distance can make film thickness uniformity difficult – Films thicker than 5 microns difficult – Hardware & target material costs are high Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

5. Sputtering There are two basic methods for sputtering materials – DC Sputtering - limited to materials which are electrically conductive. Can’t be used to sputter insulators. Generally high deposition rate. – RF Sputtering - Used to sputter non-conductive materials. Will also work for conductive (anything can be RF sputtered). Deposition rate lower than DC for metallic materials. Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

6. Magnetron sputtering - Magnets enable lower pressures to be used During the sputter process a magnetic field can be used to trap secondary electrons close to the target. The electrons follow helical paths around the magnetic field lines undergoing more ionizing collisions with neutral gaseous near the target than would otherwise occur. This enhances the ionisation of the plasma near the target leading to a higher sputter rate. It also means that the plasma can be sustained at a lower pressure. The sputtered atoms are neutrally charged and so are unaffected by the magnetic trap. Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

7. What a magnetron looks like Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

8. Key parts of a magnetron Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

9. Magnetrons come in all sorts of shapes and sizes!! Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

10. Also during the sputtering process a glow is observed, this is caused by excited ions relaxing to a lower energy state and emitting energy in the form of light. Different elements emit the visible light at a different wavelength and therefore a different colour will be observed. However this highlights one of the problems of magnetron the so called “racetrack” – caused by non–uniformity of the magnetic field behind the target This means parts of the target get sputtered way faster than others which leads to reduced efficiency and poor use of material – if the target is an expensive material (e.g. Au) this is a problem Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

11. Many very complex designs of magnets have been employed by vendors in order to improve this effect. Usage can be as low as low as 30% if nothing is done High usage around 80% is possible but at a price! Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

12. The term balanced and unbalanced magnetrons are commonly used The balanced term is generally used to describe conventional magnetrons The term unbalanced is used to describe magnetrons that are also capable of producing ion bombardment of the thin film at the same time as deposition The term balanced and unbalanced magnetrons are commonly used The balanced term is generally used to describe conventional magnetrons The term unbalanced is used to describe magnetrons that are also capable of producing ion bombardment of the thin film at the same time as deposition Magnetron Concepts Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

13. Unbalanced magnetrons An unbalanced magnetron possesses stronger magnets on the outside resulting in the expansion of the plasma away from the surface of the target towards the substrate. The effect of the unbalanced magnetic field is to trap fast moving secondary electrons that escape from the target surface. These electrons undergo ionizing collisions with neutral gas atoms away from the target surface and produce a greater number of ions and further electrons in the region of the substrate considerably increasing the substrate ion bombardment. Effectively a secondary plasma is formed in the region of the substrate. When a negative bias is applied to the substrate, ions from this secondary plasma are accelerated to the substrate and bombard it; this ion bombardment is used to control the many properties of the growing film. Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

14. An unbalanced magnetron, the outer North poles are stronger than the inner South poles therefore the field lines stretch further into the vacuum chamber Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

15. Completely balanced Type 1. unbalancedType 2. unbalanced. Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

16. RELATIVE THICKNESS 100% CENTER OF WAFER EDGE OF WAFER VACUUM CHAMBER ATOM SOURCE EVAPORATION FLUX WAFER LOW DENSITY FLUXHIGH DENSITY FLUX ON AXIS COATINGS & UNIFORMITY COATING GEOMETRIES Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

17. COATING GEOMETRIES RELATIVE THICKNESS 100% CENTER OF WAFER EDGE OF WAFER VACUUM CHAMBER ATOM SOURCE EVAPORATION FLUX ROTATING WAFER LOW DENSITY FLUX HIGH DENSITY FLUX OFF AXIS COATINGS AND UNIFORMITY Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

18. Fig. 1. 6” source, 8” substrate, 100mm height separation (target to substrate), 130mm offset distance(centre of target to centre of substrate) Fig. 2. 6” source, 8” substrate, 175mm height separation (target to substrate), 130mm offset distance(centre of target to centre of substrate) Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

19. VACUUM PUMPING OPTIONS ROUGH VACUUM 2 STAGE ROTARY PUMPING 1.5-80 cu m 3 h -1 2 STAGE ROTARY PUMPS Oxygen pumping options (Fomblinised systems using Fomblin oils) SCROLL PUMPING WITH OIL FREE OPERATION These pumps are totally oil free to avoid oil contamination inside the vacuum chamber. They are suited for oxygen pumping and have reduced maintenance schedules. Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

20. VACUUM PUMPING OPTIONS HIGH VACUUM PUMPING DIFFUSION LOWEST COST HIGH VACUUM PUMPS. MEDIUM BASE VACUUM WITH GOOD WATER VAPOUR PUMPING SPEED TURBO MOLECULAR FAST START UP TIMES WITH MAGNETICALLY LEVITATED BEARING OPTIONS. THESE PUMPS HAVE POOR WATER VAPOUR PUMPING PERFORMANCE WITH HIGH BASE VACUUM LEVELS. CRYOGENIC PUMPING SLOW START UP TIMES, NO BACKING REQUIRED WITH FASTED WATER VAPOUR PUMPING. HIGH BASE VACUUM. Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

21. PROCESS PRESSURE OPTIONS – MORE IMPORTANT THAN YOU THINK! BASIC OPEN LOOP CONTROL Fixed gas flow from Auto Gas Bleed, and fixed vacuum pumping speed UP-STREAM PRESSSURE CONTROL Mass flow gas control with closed loop connection to process vacuum gauge Constant vacuum pumping speed Pressure is maintained constant by varying the process gas flow in a PID closed loop control system DOWN-STREAM PRESSURE CONTROL Operator selectable mass flow values for process gas flow. Operator selectable pumping speed via continuously variable throttle valve in high vacuum pumping line, with PID closed loop control from process pressure gauge Individual settings for both process gas flow and process pressure. Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

22. Pressure control Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

23. workholders Simple rotation Planetary motion Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

24. Reactive sputtering and alloys -1 You can carry out sputtering in the presence of a reactive gas (like O 2 ) instead of the usual Ar Its one way of creating oxides – but be warned!! Reactive sputtering is hard to control – final stoichiometry of deposited films tends to vary a lot and the process is hard to make reproducible Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

25. Co-sputtering Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

26. Reactive sputtering and alloys -2 Same goes for alloys. You can co-sputter alloys by having 2 magnetrons working at once but again be warned that its hard to:-  Get the geometry of the system right  Get the sputter rate of the two films right and in the correct ratio and stable at that  Get good uniformity over a large substrate If you want to sputter an alloy buy a composite target but be careful again as the composition of the target may well not be the composition of the film you get but it will be reproducible! Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

27. TargetSputterPowerTargetTotalCrystalAtomicinteratomic Static rate - different separationsrate factor materialyielddensitydiameterpowerstructureradiusspacing microns per minute -600VW/cm 2 cmwattsnm 6 cm10 cm14 cm atoms/ion Ag3.4210157FCC0.1440.2890.3540.2140.1390.128 Al1.2210157FCC0.1430.2860.1240.0750.0490.128 Au2.8210157FCC0.1440.2880.2900.1760.1140.128 C0.2210157HEX0.0770.1540.0110.0070.0040.128 Co1.4210157CPH0.1250.250.1260.0760.0500.128 Cr1.3210157BCC0.1280.250.1170.0710.0460.128 Cu2.3210157FCC0.1280.2550.2110.1280.0830.128 Fe1.3210157BCC0.1280.2480.1160.0700.0460.128 Ge1.2210157DIAMOND0.1390.2780.1200.0730.0470.128 Mo0.9210157BCC0.140.2750.0890.0540.0350.128 Nb0.65210157BCC0.1470.2860.0670.0410.0260.128 Ni1.5210157FCC0.1250.2490.1340.0820.0530.128 Os0.95210157CPH0.1350.270.0920.0560.0360.128 Pb2.15210157FCC0.1740.3480.2690.1630.1060.128 Pd2.4210157FCC0.1370.2740.2370.1440.0930.128 Pt1.6210157FCC0.1380.2770.1600.0970.0630.128 Re0.9210157CPH0.1380.2760.0890.0540.0350.128 Rh1.5210157FCC0.1340.2690.1450.0880.0570.128 Si0.5210157DIAMOND0.1170.2340.0420.0260.0170.128 Ta0.6210157BCC0.1470.2860.0620.0370.0240.128 Th0.7210157FCC0.180.360.0910.0550.0360.128 Ti0.6210157CPH0.1470.2990.0650.0390.0250.128 U1210157ORTHO0.1380.2750.0990.0600.0390.128 W0.6210157BCC0.1410.2740.0590.0360.0230.128 Y0.6210157CPH0.1810.3620.0780.0470.0310.128 Zr0.75210157CPH0.160.3180.0860.0520.0340.128 Sputter data – different materials Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2

28. Do it yourself sputtering!! Unlike many technologies described in these talks there is nothing so difficult about sputtering that does not allow anybody with a decent understanding of vacuum and thin films to build their own system Many suppliers of sputter systems, especially for smaller size substrates, are just assemblers of parts and add very little value to the process that is being carried on inside the system There is so much literature on the properties of sputtered films and the conditions needed to create them, you should be able to establish exactly what you want quite easily – SO if money is short do it yourself!! Equipment and technological processes for manufacturing GaAs MMICs METALLISATION 2