Solid State Modulators for PIII Applications

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1 Solid Sae Modulaors for P Applicaions Dr. Marcel P.J. Gaudreau, P.E., Dr. Jeffrey A. Casey, Timohy J. Hawkey, Michael A. Kempkes, J. Michael Mulvaney; Diversified Technologies, nc. Absrac One of he key echnologies in P is he delivery of fas, ighly regulaed high volage, high curren pulsed power o he plasma implanaion chamber. This requires a nearly ideal high volage swich capable of operaing a shor pulsewidhs, fas rise and fall imes, and high pulse repeiion raes. Exising swich echnologies are limied in providing he ideal swiching required. Using new solid sae power modulaors, he required power can be delivered more effecively and reliably han by older, ube-based echnologies such as gridded vacuum ubes, hyrarons, and Pulse Forming Neworks (PFNs). Solid-sae high power echnology is now available o allow P o be a cos-effecive, commercially viable process, ready for widespread commercializaion. nroducion A recenly developed surface reamen process is Plasma Source on mplanaion (PS) or Plasma mmersion on mplanaion (P). The componen o be reaed wih P is placed in a vacuum chamber, in which a plasma is generaed conaining he ions of he species o be implaned. The P sysem repeiively pulses he arge a high negaive volages (in he - kv range) o implan he surface wih a flux of energeic plasma ions. Because he plasma surrounds he sample (i is immersed ), and because he ions are acceleraed normal o he sample surface, plasma-source implanaion occurs over he enire surface, hereby eliminaing he need o manipulae non-planar samples in fron of an ion beam. The P echnique hus circumvens he line-of-sigh resricions inheren in convenional ion implanaion. Objecs wih complex geomery can be reaed wihou elaborae arge manipulaion. P disinguishes iself from convenional coaing and implanaion processes by being: a.) a bach process, able o coa large dies and complex surfaces wihou arge manipulaion (demonsraed by he reamen of a pison run a Los Alamos Naional Laboraory) b.) a low emperaure process, which does no disor or modify die dimensions c.) able o produce high coaing adherence (such as in DLC) n many respecs, P can be considered an exension of radiional plasma processes, such as PVD. The vacuum chamber, plasma source, and many of he conrols are common o boh P and PVD sysems. For P, however, ighly regulaed, high volage pulsed power is criical. Pulsed power sources mus be able o deliver nearly ideal, repeaable, consisen pulses o opimize he properies of he reaed componens. As P echnology has evolved, high volage, high power sysems have emerged as he criical echnology issue. The deal Pulse Power Circui The op drawing in Figure shows he ideal pulse power circui for P, powered by an ideal volage source, wih unlimied curren and consan volage. also conains an ideal swich having he following characerisics: he swich is boh an opening and closing swich he swiching ime is infiniesimal (fracions of a microsecond) i has nearly zero series impedance when closed and infinie impedance when open V Power Source Off On Swich Off Load Figure : deal Circui (op) and deal Pulse (boom)

2 Wih such an ideal circui, he plasma acceleraing volage will be a perfec square pulse, as shown in he boom drawing in Figure. This ideal volage pulse has a minimal rise and fall ime and a fla op, independen of load, curren and repeiion rae. Real World Pulsed Power Figure shows a simplified, bu realisic P circui. This circui reains he ideal swich, as in Figure, bu adds several real world facors: a variable DC power supply wih finie curren capabiliy, a sorage capacior for achieving high peak curren, and series and parallel (pulldown) oupu impedances. The series impedance is inheren in any circui, as is he cable capaciance beween he power deal Swich R pulldown source and he plasma. The pulldown resisor is added o provide a discharge pah for his cable capaciance when he swich is off. Finally, real world plasma loads are complex so he plasma load is represened as a complex RC circui. Figures 3 and 4 show ypical volage and curren pulses seen by he load in his model. Several criical observaions are apparen from his simple model. Firs, even wih an ideal swich, he pulse shape is no longer a perfec square wave. The riseime ( ) represens he charging ime of he cable and plasma capaciance hrough he series impedance where, C sorage R series V R R Power Supply Modulaor L series Closing Swich C cable Cable Figure : Real World P Circui Model C Plasma C R C C series cable plasma () The pulse op can be kep nearly fla by choosing a large enough value of sorage capacior, such ha he volage droop, V, from he pulse curren is small. Noe ha longer pulsewidhs or higher pulse currens will require larger sorage capaciors. V C sorage where pulldown plasma () The fall ime of he pulse ( 3 ) is given by he RC consan of he cable and plasma capaciance and he pulldown and plasma impedance. n all cases, i is desirable o keep he series impedance as low as possible. A radeoff mus be made, however, wih he pulldown resisor value. A low resisance speeds fall ime, bu also shuns power from he load when he swich is closed. This power is: P V R pulldown f * (3)

3 where f is he pulse repeiion frequency. This shuned power can represen a significan load a high volages for small values of pulldown resisance, and also represens a significan cooling load o he overall sysem. Balancing he compeing desires for fas fall ime and power efficiency is a criical facor V V 3 Figure 3: Volage Waveform for he Figure Circui in selecing he value of pulldown resisor. Alernaely, a second swich can be placed in series wih he pulldown resisor, which closes briefly o discharge he plasma afer he main swich has opened a he compleion of he pulse. Figure 4 shows he ypical curren drawn from he pulsed power source during a volage pulse. is he iniial charging curren, approximaely given by provided ha L C L cable C series V Lseries Rseries Ccable C C R series (4) (5) 3 is he seady sae plasma curren represened by: 3 V R (6) where R seady sae effecive plasma resisance and ypically R R series 3 is he ypical pulse curren normally considered in sizing P average power and dose rae sysems. A key here is o noe ha he magniude of he peak curren ( ), while relaively shor in duraion, will ofen be many imes his average curren ( 3 ). The ransiion curren ( ) beween he peak curren and he pulse curren is given by: V where RC (7) R e Finally, he curren and volage fall imes are: V V e V R e 3 3 (8) (9) cable pulldown where C C C R R 3 3

Again, R pulldown can be made exremely low, and he fallime minimized, if a second swich is placed in series wih i o discharge he cable and plasma capaciance a he end of he pulse.

The swich, power supply, and sorage capaciance mus have he abiliy o suppor very fas d/d a he beginning of he pulse, and high peak curren, while mainaining V.

Primarily, his can 3 be achieved by minimizing he cable lengh from he swich o he plasma, and by careful design of he feedhrough for minimum capaciance.

A high curren levels, cable inducance 4 will dominae his series impedance, and he circui mus be designed o minimize his Figure 4: Curren Waveform for P Circui inducance.

4 Again, R pulldown can be made exremely low, and he fallime minimized, if a second swich is placed in series wih i o discharge he cable and plasma capaciance a he end of he pulse. Three major conclusions can be drawn from his model. Firs, he sabiliy of he volage pulse is criical over a wide range of curren levels during he pulse. The swich, power supply, and sorage capaciance mus have he abiliy o suppor very fas d/d a he beginning of he pulse, and high peak curren, while mainaining V. This requires low series equivalen resisance and inducance. Second, while he plasma characerisics are a funcion of he process, he P sysem should be designed o minimize exernal capaciance. Primarily, his can 3 be achieved by minimizing he cable lengh from he swich o he plasma, and by careful design of he feedhrough for minimum capaciance. Minimizing his capaciance will reduce he peak curren required from he pulse power sysem, and improve boh he rise and fall imes of he 3 pulse. A high curren levels, cable inducance 4 will dominae his series impedance, and he circui mus be designed o minimize his Figure 4: Curren Waveform for P Circui inducance. Finally, noe ha all of hese effecs are seen wih an ideal swich model. The resul is ha, even wih an ideal swich, i is no possible o achieve perfec P pulses. The objecive is o minimize he effecs of each of he previously discussed facors on he pulse. The nex secion will discuss opions for realizable high volage swiches. High Volage Swiching Opions So far, we have discussed several requiremens for high volage swiching for P. These requiremens include: High Volage -kv Low swich impedance Very fas volage rise and fall imes (ypically under µs). High peak curren handling (-3A) Very high d/d capabiliy ( - A/µS) Three basic echnologies are in use oday o address hese requiremens: () vacuum elecron swich ubes (e.g., erodes); () pulse forming neworks wih hyrarons; and (3) he relaively new approach of high volage, solid sae swiching developed by DT. Of he hree, solid sae swiching comes closes o providing he ideal characerisics demanded by P processes. Solid sae modulaors feaure insulaed gae bipolar ransisor (GBT) swiches in series and parallel configuraions ha allow nearly arbirary high volages (kv-kv) and currens (A-5kA). They operae as boh opening and closing swiches, providing exensive flexibiliy in pulsewidh, and very fas faul proecion. A 3 MW solid sae pulsed power sysem is exemplified by DT s PowerMod HVPM -5 Pulse Modulaor, shown in Figure 5. This solid sae modulaor conains he series GBT modules, pull down resisor, sorage capacior, conrols, and proecion circuiry required o provide kv, 5A pulses, a arbirary pulsewidhs from µs o Seleced by R&D Magazine as One of he Mos Significan Technological New Producs of 997. Figure 5: HVPM -5 Pulse Modulaor Figure 6: HVPM -5 Pulse; kv, A, µs/cm 4

DC, a up o 3kHz, in a single 9 rack-mounable uni. A ypical kv, A pulse from his uni is shown Figure 6. This solid sae swich is very nearly ideal.

When he swich is closed, he volage drop across i is less han 3 V / kv, so he swich adds very low series impedance ino he P sysem.

Finally, he curren rae limi for larger GBT swiches can be as high as 5 A / µs.

5 DC, a up o 3kHz, in a single 9 rack-mounable uni. A ypical kv, A pulse from his uni is shown Figure 6. This solid sae swich is very nearly ideal. Curren hrough he swich has very minimal impac on oupu volage. Figure 6, shows ha ypical swich imes for his approach are ypically 5 ns - independen of volage. When he swich is closed, he volage drop across i is less han 3 V / kv, so he swich adds very low series impedance ino he P sysem. The DC power supply volage required wih hese swiches is virually he same as he implan volage required - a kv process requires only a.3 kv power supply. Finally, he curren rae limi for larger GBT swiches can be as high as 5 A / µs. For high curren low volage, commercial-scale P processes such as DLC, he mos cos effecive soluion uses high curren (+A), high volage (3.3kV+) GBTs in series. Figure 7: Consan Volage of 6.5kV, µs ino Varying Plasma load (Source: LANL) Figure 8: Varying Curren (475A peak) of 6.5kV, µs Figure 7 and Figure 8 show ypical volage and Pulse ino Plasma Load (Source: LANL) curren pulses in he P processing of auomoive engine pisons a LANL. The flaop of he volage pulse, during which he curren varies by a facor of hree, demonsraes he nearly ideal performance of he solid sae modulaor used in he processing (Figure 9). DT s HVPM - solid sae modulaor, which uses series conneced, high curren GBTs, provides up o 4 MW of peak power a kv. For very high volage (-kv) implanaion, eiher a direcly coupled power supply and modulaor; or a lower volage power supply / modulaor wih a sep-up pulse ransformer may be uilized. DT has buil muliple pulsed power sysems using boh approaches. The primary deerminan of he opimal approach is, in general, he required peak curren. The ransformer coupled approach is generally limied o peak currens below A, while direc coupled sysems can suppor housands of amperes of peak curren. Oher radeoffs beween hese wo approaches include cos, efficiency, waveform shape, and pulse flexibiliy. Direcly Coupled A ypical commercial high power kv direc-coupled modulaor is shown in Figure. DT s HVPM -5 PowerMod modulaor conains a.75 µf sorage capacior, a kv, 5A peak, solid sae GBT swich, and all he conrol monioring and proecion circuiry required o pulse up o 5 khz or more. A represenaive volage pulse from his uni is shown in Figure. The clean pulse shape shows he near ideal behavior of he swich sysem. Transformer Coupled Figure 9: PowerMod - 5

is also possible o use a lower volage modulaor (such as he HVPM -5), coupled wih a pulse ransformer o achieve high volage, low curren pulses - albei wih consrained flexibiliy in pulsewidh due o he

The sizing of he peak curren on he primary side of he pulse ransformer is criical o his approach.

Charging his capaciance a he beginning of each pulse can lead o very high surge currens. This problem is greaer by he urns raio squared when using a pulse ransformer.

Using a kv modulaor and a 5: pulse ransformer o achieve kv pulses requires a primary (modulaor) curren approximaely 3 imes he peak curren seen a he load.

6 is also possible o use a lower volage modulaor (such as he HVPM -5), coupled wih a pulse ransformer o achieve high volage, low curren pulses - albei wih consrained flexibiliy in pulsewidh due o he limied vol-second capabiliy of he ransformer core. The major advanage of his approach is ha i is ypically half he cos of a direc coupled solid sae modulaor a low curren. The sizing of he peak curren on he primary side of he pulse ransformer is criical o his approach. No only is he primary peak curren increased by he volage sep-up raio, bu he cable capaciance seen by he modulaor will be muliplied by his raio squared. Charging his capaciance a he beginning of each pulse can lead o very high surge currens. This problem is greaer by he urns raio squared when using a pulse ransformer. Figure shows an oupu pulse from a from a 5.5: pulse ransformer driven by he HVPM -5. Using a kv modulaor and a 5: pulse ransformer o achieve kv pulses requires a primary (modulaor) curren approximaely 3 imes he peak curren seen a he load. n eiher configuraion, cable capaciance can be a major source of inefficiency in he P sysem. For example, he power los o repeiively charge and discharge he cable capaciance of six fee of coaxial cable beween he modulaor and P chamber a kv and 5kHz is: Figure : DT PowerMod HVPM -5 P fe fcv 9kW () is criical ha he DC power supply is capable of providing he power required by he P process iself, and he addiional power dissipaion associaed wih charging he power cable, feedhrough, and plasma. Discussion The key requiremen, unique o P in comparison o esablished processes like PVD, is high volage pulsed power o achieve implanaion of ions ino a subsrae. These pulses mus mainain very igh volage conrol during a pulse in which he curren may vary by an order of magniude. There are wo obsacles o he efficien applicaion of consan volage-acceleraing pulses in P applicaions. Firs, he peripheral passive circuiry plays a significan role in pulse shaping and power loss. Second, non-ideal swiching elemens can significanly degrade pulse shape, efficiency, sysem complexiy, and cos of a P sysem. Regardless of he swich characerisics, he passive elemens of he P should be opimized o minimize cable and feedhrough capaciance; minimize inducance (especially for high curren sysems); and allow for large peak currens many imes he average pulse curren. Figure : Nearly deal Curren Pulse ino a Resisive Load; 8kV, 9A Pulse,.5 µs/cm. Pulse curren A/div. Figure : Sample Uncompensaed Pulse Transformer Pulse (8kV, 5µ/cm ino Capaciive Load Solid sae pulse modulaors offer he following advanages: () shor pulse o DC flexibiliy; () high power efficiency resuling in lower coss for DC power and cooling; (3) fas riseime and fas opening for arc proecion; (4) a modular design which can be scaled o specific P sysems and processes; (5) very high reliabiliy; (6) small fooprin, and (7), no x-ray emissions. 6

Table of Contents. 3.0 SMPS Topologies. For Further Research. 3.1 Basic Components. 3.2 Buck (Step Down) 3.3 Boost (Step Up) 3.4 Inverter (Buck/Boost)

Table of Contents. 3.0 SMPS Topologies. For Further Research. 3.1 Basic Components. 3.2 Buck (Step Down) 3.3 Boost (Step Up) 3.4 Inverter (Buck/Boost) Table of Conens 3.0 SMPS Topologies 3.1 Basic Componens 3.2 Buck (Sep Down) 3.3 Boos (Sep Up) 3.4 nverer (Buck/Boos) 3.5 Flyback Converer 3.6 Curren Boosed Boos 3.7 Curren Boosed Buck 3.8 Forward Converer