4H-SiC pn Diode using Internal Ring(IR) Termination Technique G. H. Song, H. W. Kim, W. Bahng, S. C. Kim and N. K. Kim Power Semiconductor Research Group, Korea Electrotechnology Research Institute(KERI), Sung-ju dong 28-1, ChangWon-city, Gyungnam 641-120 Korea Tel: +82-55-280-1622, Fax: +82-55-280-1590, e-mail: ghsong@keri.re.kr In this paper, the breakdown characteristic of 4H-SiC pn diode using Internal Ring(IR) termination technique is investigated. N-type 4H-SiC wafer having a 10um epilayer with a doping concentration of 5.4×1015/cm3 was used to fabricate the pn diodes with one or two IRs. IR was formed by boron implantation of single energy of 360keV with 5×1014/cm2 dose and activation annealing at 1700oC for 30min in Ar ambient. In order to obtain an optimum breakdown voltage of pn diode with one or two IRs, the distance between p-base main junction and 1st ring is varied from 3um to 7um and the distance between 1st and 2nd IR is fixed at 5um. A pn diode with two IRs termination structure has exhibited a high breakdown voltage of 1812V. Due to the IRs, the peak electric field at the interface between SiC and oxide of the surface is lower than the peak electric field at the edge of the 2nd IR, which means that the breakdown of the device occurs at the edge of the 2nd IR. Therefore the IR structure is attractive planar termination techniques for obtain a high breakdown voltage of 4H-SiC power device.

4H-SiC pn Diode using Internal Ring(IR) Termination Technique G. H. Song, H. W. Kim, W. Bahng, S. C. Kim and N. K. Kim Power Semiconductor Research Group, Korea Electrotechnology Research Institute(KERI), Sung-ju dong 28-1, ChangWon-city, Gyungnam 641-120 Korea Tel: +82-55-280-1622, Fax: +82-55-280-1590, e-mail: ghsong@keri.re.kr Silicon carbide (SiC) is regarded as a promising semiconductor material for novel devices requiring high-power, high frequency, and high temperature operation owing to its electrical and thermal properties [1, 2]. In the case of high voltage devices, edge termination plays an important role in determining the breakdown voltage of the device. The mesa edge termination has been demonstrated to yield nearly ideal breakdown voltage for 6H-SiC pn diode. However, such an approach may not be attractive because of the nonplanar surface, which is difficult to passivate. Moreover, in case of 4H-SiC, ideal breakdown voltage could not be achieved using mesa edge termination [3]. For 4H-SiC, planar edge termination technique is more useful one rather than mesa edge termination. In this paper, the fabrication of 4H-SiC pn diode using IR edge termination is presented. The fabricated pn diode has an epilayer with doping concentration of 5.4×1015/cm3 and a thickness of 10um. In our research, one and two IRs is used to improve the breakdown voltage.

A cross-sectional view of the device is shown in figure 1. Single B+ and multiple Al+ implantations were carried out at 650oC to form 0.65um-deep IRs and 0.2um-deep surface p+ region, respectively. Total implant doses for IRs and p+ region were 5×1014/cm2 and 6×1014/cm2, respectively. Post-implantation annealing was performed in an activation furnace at 1700oC for 30min in Ar. The surface of the diodes was passivated with 55nm-thick thermal oxide grown by wet oxidation at 1150oC for 3 hours followed by the post-oxidation annealing at 1150oC for 30min in Ar. In order to form the ohmic contacts, Ni/Ti layers were deposited on p+ implanted region as well as the backside of the substrate and then annealed at 950oC for 90sec in Ar.

The distance between main junction and the first IR(W1) has been varied from 3um to 7um for obtain an optimum breakdown voltage. Distance between 1st and 2nd IR(W2) is fixed at 5um. The measured breakdown characteristic of the device is shown at figure 2. The maximum breakdown voltage of 1812V was obtained in the diodes with two IRs. The breakdown voltage of 1720V is also obtained in the diode with one IR. The breakdown voltage of the rectangular and circular shape cell is shown at figure 3. Each type of the device has two IRs and the distance of W1 and W2 is 3um and 5um. In the case of the rectangular shape cell, the radius of the corner is varied from 10um to 40um for investigate the effect of the radius. As can be seen in the figure, the shape of the cell and the radius of the corner do not affect to the breakdown voltage of the device. Electric field characteristics of the diode were verified by the device simulator ATLAS [4]. Figure 4 shows the simulated one dimensional electric field distribution along the a-a’ and b-b’ lines(figure 1) of the diode with two IRs at 1812V. Due to the internal rings, the peak electric field at the SiC and oxide interface of the surface is lower than the peak electric field at the outer edge of the 2nd IR, implying that the breakdown of the device occurs at the edge of the 2nd IR, which contributes to the improvement of breakdown voltage of the device. From the experimental and simulation results, IR edge termination technique is useful planar termination method to improve the breakdown voltage of the 4H-SiC pn diode. Acknowledgement This work was done as a part of SiC Device Development Program (SiCDDP) supported by MOCIE(Ministry of Commerce, Industry and Energy) Korea. References [1] M. Bhatnagar and B. J. Baliga, IEEE Trans. Electron Devices, vol. 40, pp. 645-655.(1993) [2] R. J. Trew, H. B. Yan, and P. M. Mock, Proc. IEEE, vol. 79, pp. 598-620.(1991) [3] Dev Alok, R. Raghunathan, and B. J. Baliga, IEEE Trans. Electron Devices, vol 43, pp.

1315-1317.(1996) [4] Silvaco TCAD Manuals, Atlas, Silvaco International, Co. USA

Fig. 1. Cross-sectional view of the device. Fig. 2. Measured breakdown characteristics

of pn diode with two IRs

Fig. 3. Breakdown voltage of the rectangular Fig. 4. Electric field distribution of the

and circular shape cell. diode with two IRs at 1812V

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Characterization of a thermal oxidation process on SiC preamorphized by Ar ion implantation Antonella Poggi*, Roberta Nipoti, Sandro Solmi, Massimo Bersani(1) , Lia Vanzetti(1) CNR- IMM Sezione di Bologna, via Gobetti 101, 40129 Bologna (1) ITC-irst, 38050 Povo, TN, Italy

*Corresponding author: A.Poggi tel.+39 051 6399203, fax number: .+39 051 6399216 e-mail: poggi@lamel.bo.cnr.it In this paper, we investigate the thermal growth of SiO2 films on Ar+ amorphized 6H-SiC. Wet oxidation was performed at 800°C for different times between 30 and 270 min. Such a low oxidation temperature was chosen to be sure to investigate the oxide thermal growth on the amorphized SiC also for long oxidation time. In fact, on ion-beam amorphized SiC the oxidation competes with the crystal regrowth and, for example, at temperature as high as 1100°C the oxidation process takes place on a reorganised polycrystalline structure. The thickness and the composition of the oxide film were evaluated by Rutherford Back Scattering Channeling (RBS-C) spectra. These analyses performed on samples oxidized for times longer than 90 min, show the presence of a C rich transition region between the pure stoichiometric layer of SiO2 and the substrate. Si, O and C compose this near-interface region. The depth profiles of these elements, evaluated by SIMS, confirm the presence of this C rich film at the SiC interface. X-ray photon spectroscopy (XPS) analyses were performed on the same sample at different depths after oxide thinning. These measurements indicate the presence of a large amount the C – C bonds. The correlation between the oxide growth kinetic and the near-interface region composition of the growing film will be carefully analyzed and discussed.

Characterization of a thermal oxidation process on SiC preamorphized by Ar ion implantation Antonella Poggi*, Roberta Nipoti, Sandro Solmi, Massimo Bersani(1) , Lia Vanzetti(1) CNR- IMM Sezione di Bologna, via Gobetti 101, 40129 Bologna (1) ITC-irst, 38050 Povo, TN, Italy

*Corresponding author: A. Poggi tel.+39 051 6399203, fax number: .+39 051 6399216 e-mail: poggi@lamel.bo.cnr.it In semiconductor device applications involving high power, frequency, voltage, and/or temperature, SiC appears a useful choice thanks its physical properties such as high thermal conductivity, breakdown voltage and, saturation electron drift velocity. Moreover, SiC is the only compound semiconductor that can be thermally oxidized to form SiO2, the most studied and used dielectric material in semiconductor technology. Although similarities exist between oxides thermally grown on SiC and on Si [1,2], the former exhibits worse electrical performance [3]. Therefore, investigations on oxidation mechanisms and oxide composition are mandatory to understand the phenomena tacking place during the thermal growth of SiO2 on SiC so to control the electrical characteristics of SiO2/SiC structure. Recent results [4] have pointed out that the main difference between Si and SiC thermal oxidation is the limiting processes involved in the growth. While oxide growth on Si is governed by diffusion of the oxidant species through the oxide layer for thickness above 20-30nm, growth on SiC is limited by the reaction in the near interface region. That is, for SiC the behavior can be explained by an oxide thermal growth mechanism in which the oxidant species reacts in a region near (and including) the oxide/ SiC interface and not at an abrupt interface as in the case of Si. In this near-interface reactive region carbon and/or excess silicon (from SiC not completely oxidized or from Si interstitials injected as a result of SiC oxidation) may also be present and involved in the oxidation process. Taking into account these results obtained on crystalline SiC, the investigation of the thermal oxidation on a amorphized SiC layer can introduce new insights for the understanding of the phenomena occurring in the near-interface region. In fact, due to the breakage of the strong covalent bond of the SiC lattice, a completely amorphized SiC surface acts as an easier source of Si and C atoms during the oxide growth. In this paper, we investigate the thermal growth of SiO2 films on ion amorphized 6H-SiC. Si-face, on-axis, n-type bulk substrates were used. Room temperature Ar+ implantation at a energy of 170 keV with a fluence of 1.1x1015 cm-2 was carried out to produce an amorphous layer about 200 nm thick. Wet oxidation was performed at 800°C for different times between 30 and 270 min. Such a low oxidation temperature was chosen to be sure to investigate the oxide thermal growth on the amorphized SiC also for long oxidation time. In fact, as argued in [5], on ion-beam amorphized SiC the oxidation competes with the crystal regrowth and, for example, at temperature as high as 1100°C the oxidation process takes place on a reorganised polycrystalline structure. The samples were analyzed by Rutherford Back Scattering in the Channeling mode (RBS-C). The thickness and the composition of the oxide film were calculated by simulating RBS spectra with the code RUMP. Fig. 1 shows the <0001> RBS-C spectrum of the sample oxidized for 270 min. The sample structure accounting for this spectrum shape is shown in the top of Fig. 1. RBS-C spectra similar to that of Fig. 1 were measured for process time longer than 90 min. For process time shorter than 90 min the C rich layer was so thin that the presence of a structure could not be

resolved. A sharp increase of the oxidation kinetic was measured since when the interface C rich oxide layer started to be revealed.

Information on the composition of the oxide grown in 90 min was obtained by secondary ion mass spectroscopy (SIMS) performed with a 10 keV Cs+ ions. SIMS profiles of O, C and Si are reported in Fig. 2. The measurements confirm the presence of a C rich layer between the pure stoichiometric layer of SiO2 and the substrate. X-ray photon spectroscopy (XPS) analyses were performed on the same sample at different depths after oxide thinning. These measurements indicate the presence of a large amount the C – C bonds. The correlation between the oxide growth kinetic and the near-interface region composition of the growing film will be carefully analyzed and discussed [1] K. McDonald, M.B. Huang, R.A. Weller, L.C. Feldman, J.R. Williams, F. C. Stedile, I.J.R. Baumvol, C. Radtke, Appl. Phys. Lett. 76 (2000), p. 568. [2] M.B. Johnson, M.E. Zvanut, O. Richardson, J. Electron. Mater. 29 (2000), p. 368. [3] C. Raynaud, J. Non-Cryst. Solids 1 (2001) 280. [4] I.C. Vickridge, I. Trimaille, J.-J. Ganem, S. Rigo, C. Radtke, I.J.R. Baumvol, F.C. Stedile, Phys. Rev. Lett. 89 (2002), p. 256102-1. [5] R. Nipoti, A. Parisini, Phil. Mag. B 80 (2000), p. 647.

300 600 900 12000

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CO

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eV m

sr )

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Fig. 1. He+ 2 MeV 170° RBS-C spectrum of the sample oxidized for 270 min. The RUMP simulation accounting for thisspectrum shape require to hypothesise a sample structure like that shown in the top of the figure.

0 20 40 60 80 100101

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Fig. 2. SIMS profile of the sample oxidized for 90 min. For comparison, the plot also shows the C profile measured on a preamorphized SiC sample where an SiO2 layer of the same thickness were deposited at 420°C by chemical vapor deposition (dashed line).

SiC donor doping by 300°C P implantation: characterization of the doped layer properties in dependence of the post-implantation annealing temperature

Antonella Poggi*, Roberta Nipoti, Francesco Moscatelli1, Gian Carlo Cardinali, Mariaconcetta Canino CNR- IMM Sezione di Bologna, via Gobetti 101, 40129 Bologna 1Dipartimento d’Ingegneria Elettronica e dell’Informazione, Università di Perugia, via G. Duranti 93, 06125 Perugia *Corresponding author: a. Poggi tel. +39 051 6399203, fax number: +39 051 6399216 e-mail: poggi@lamel.bo.cnr.it Ion implantation is an important technique for a successful implementation of commercial SiC devices. The emphasis is to find suitable implantation and annealing parameters for the operation of p+n and n+p junctions in forward injection or reverse blocking modes. To reach this goal, ion-implantation is often performed at an elevated temperature in the range of 500-1000°C. Most of the industrial implanters are not geared for implantation at so high temperature, therefore it is interesting to study the properties of the doped layers implanted at lower temperature. In this work we present the results obtained implanting high concentration (1020 cm-3) of P at 300°C. The effects of post-implantation annealing on the electrical properties and the surface morphology of the doped layer are investigated for different annealing temperatures: 1300, 1500 and 1650 °C. Sheet resistance of the 0.2 µm thick implanted layers was measured on the Van der Pauw geometry and the obtained values were in the range 300-900 Ω/sq when the annealing temperature changed between 1650 and 1300°C. The implanted and uniplanted SiC surface showed a different morphology only after 1650 °C annealing. I-V measurements were performed on the fabricated n+/p diodes to test the electrical performance of the n+/p junction obtained with different post-implantation annealing temperature. Leakage current densities in the range 10-9

Acm-2 were measured at 10V and most diodes exibit a break-down voltage higher than 100V.

SiC donor doping by 300°C P implantation: characterization of the doped layer properties in dependence of the post-implantation annealing temperature

Antonella Poggi*, Roberta Nipoti, Francesco Moscatelli1, Gian Carlo Cardinali, Mariaconcetta Canino CNR- IMM Sezione di Bologna, via Gobetti 101, 40129 Bologna 1Dipartimento d’Ingegneria Elettronica e dell’Informazione, Università di Perugia, via G. Duranti 93, 06125 Perugia 2 INFM……. *Corresponding author: A. Poggi tel. +39 051 6399203, fax number: +39 051 6399216 e-mail: poggi@lamel.bo.cnr.it Ion implantation is an important technique for a successful implementation of commercial SiC devices. The emphasis is to find suitable implantation and annealing parameters for the operation of p+n and n+p junctions in forward injection or reverse blocking modes. Problems of SiC ion-implantation technology include [1]: 1) incongruent evaporation of Si from SiC wafer during post-implantation annealing; 2) stoichiometric disturbances caused by ion-implantation; 3) difficulty in restoring the lattice. These problems result in poor implant electrical activations. To minimize some of these problems, ion-implantation is often performed at an elevated temperature in the range of 500-1000°C. Nitrogen and phosphorus are the most popular donor implant species in SiC. At high doping concentration (>5x1019cm-3) the electrical activation on N donor is poor, raising the minimum sheet resistence of the contact region of high power, high frequncy devices, limiting the optimum devices performance. P is the donor dopant candidate to achieve low sheet resistence, but 700°C implantation is reported as mandatory for this goal [2,3]. Most of the industrial implanters are not geared for implantation at so a high temperature, therefore it is interesting to study the properties of P doped layer implanted at lower temperature. In this work we present the results obtained implanting high concentration of P at 300°C. The effect of post-implantation annealing on the electrical properties and surface morphologies of the doped layers are investigated at different annealing temperatures. A 3.5° off-axis (1000) p-type 6H-SiC wafer with a 5 µm epitaxial layer on the top, p-type doped up to 8.5×1015 cm-3, was used for this study. Circular n+/p diodes and Van der Pauw geometries were fabricated by 300°C P+ implantation. Several P+ energy and fluence values were used so to produce an almost box shape doping profile 0.2 µm thick and 1020 cm-3 hight at the wafer surface. Three samples were prepared and annealed at 1300, 1500, 1650°C respectively for 20 min in Ar ambient. To contact the p-type bulk SiC a metal scheme composed of Al(350nm)/Ti(80nm) was deposited by sputtering and annealed at 1000°C in vacuum for 2 min. On n-type regions metal contacts were deposited by e-beam evaporation of Ni. Ni Schottky contacts were at the same time realized on the p-type epitaxial layer. Sheet resistance of the implanted layers was measured on the Van der Pauw geometries and the results as a function of the post-implantation annealing temperature are reported in Table 1. In the same table literature data obtained by P implantation at 600°C [3] are also collected. Taking into account the different thickness of the doped layers, the resistivity was calculated and added in the table in order to compare the results. The resistivities of the 300 °C implanted layers are slightly higher than thase obtained implanting at 700 °C, nevertheless the obtained values are yet interesting for thecnological application. Furthermore, the optical observation of the surface after the thermal treatment shows a change in the morphology only on the sample treated at 1650 °C.

Implantation Temperature

(°C)

Doped Thickness

(µm)

Annealing Temperature

(°C)

Sheet Resistance (Ω/sq)

Resistivity

(Ωcm)

300 0.2 1300 900 0.018 300 0.2 1500 380 0.008 300 0.2 1650 330 0.007 600 0.35 1200 600 0.021 600 0.35 1300 200 0.007 600 0.35 1500 100 0.0035 600 0.35 1700 51 0.0018

Table 1: Sheet resistences measured on 1020cm-3 phosphorus implanted layers annealed for 20 min. I-V measurements were performed on the fabricated diodes to test the electrical performance of the n+/p junction obtained with different post-implantation annealing temperature. Preliminary results are reported in Fig. 2.

(a)

(b) Fig.2 : Typical I-V characteristic is drawn for 1300 and 1500 °C annealed diodes: the current density as a function of the forward (a) and reverse (b) voltage is reported.

Doping concentration of the p-type epitaxial layer was calculated from C-V measurements performed on the Schottky diodes. The obtained value 1×1016 cm-3 is little higher than the nominal value given by the supplier. C-V measurements on n+/p diodes are planned to study the p-type epitaxial layer under the implanted region. [1] Malpuri V. Rao, Solid-State Electronics, Vol. 47 (2003), p. 213. [2] Evan M. Handy, Mulpuri V. Rao, O.W. Holland, K. A. Jones, M. A. Derenge, N. Papanicolaou, J. Appl. Phys., 82 (2000), p. 5630. [3] MA. Capano, R. Santhakumar, R. Venugopal, MR. Melloch, JA Cooper Jr., J. Electron Mater, 29 (2000), p. 210.

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Effect of implantation temperature on redistribution of Al in SiC during annealing.

I.O. Usov Los Alamos National Laboratory, MST-STC, Los Alamos, NM 87544, USA A.A. Suvorova Centre for Microscopy and Microanalysis, University of Western Australia, Crawley, Australia A.V. Suvorov Cree, Inc., Durham, NC 27703, USA Ion implantation is an irreplaceable technology for selective-area doping and isolation of SiC-based devices. However, this technique results in a high level of radiation damage, which has to be removed by annealing at temperatures higher than 1600oC. At such temperatures, diffusion of implanted species can take place. In this presentation, we report the effect of ion implantation temperature on Al redistribution in 6H-SiC during subsequent annealing. 6H-SiC (0001) n-type epitaxial films with a donor concentration on the order of 1×1017 cm-3 were used. The samples were implanted with 50 keV Al+ ions to a dose of 1.4×1016 cm-2 at temperatures (Timp) ranging from room temperature (RT) to 1800oC. The annealing was performed in vacuum at temperatures (Tann) of 1600 and 1800oC for 320 s. The depth profiles of Al were determined using secondary ion mass spectrometry (SIMS) and cross-sectional transmission electron microscopy (TEM) was utilized to identify the nature of the implantation damage. The Al profiles for implantation at RT and 1300oC before and after annealing are shown on Figures 1 and 2. Annealing of the samples implanted at RT resulted in significant out-diffusion of Al at Tann = 1600oC. After annealing at 1800oC, losses due to out-diffusion were as great as 96% and Al diffusion into the sample bulk took place. Implantation at 1300oC reduced both the in- and out-diffusion as shown on Figure 2. The results demonstrated that redistribution of Al implanted in SiC during post implantation annealing directly correlated with the amount and nature of residual damage. Corresponding author: Alexander_Suvorov@cree.com; Phone: 1-919-313-5334; Fax: 1-919-313-5687

Effect of implantation temperature on redistribution of Al in SiC during annealing.

I.O. Usov Los Alamos National Laboratory, MST-STC, Los Alamos, NM 87544, USA A.A. Suvorova Centre for Microscopy and Microanalysis, University of Western Australia, Crawley, Australia A.V. Suvorov Cree, Inc., Durham, NC 27703, USA Ion implantation is an irreplaceable technology for selective-area doping and isolation of SiC-based devices. However, this technique results in a high level of radiation damage, which has to be removed by annealing at temperatures higher than 1600oC. At such temperatures, diffusion of implanted species can take place. In this presentation, we report the effect of ion implantation temperature on Al redistribution in 6H-SiC during subsequent annealing. 6H-SiC (0001) n-type epitaxial films with a donor concentration on the order of 1×1017 cm-3 were used. The samples were implanted with 50 keV Al+ ions to a dose of 1.4×1016 cm-2 at temperatures (Timp) ranging from room temperature (RT) to 1800oC. The annealing was performed in vacuum at temperatures (Tann) of 1600 and 1800oC for 320 s. The depth profiles of Al were determined using secondary ion mass spectrometry (SIMS) and cross-sectional transmission electron microscopy (TEM) was utilized to identify the nature of the implantation damage. The Al profiles for implantation at RT and 1300oC before and after annealing are shown on Figures 1 and 2. Annealing of the samples implanted at RT resulted in significant out-diffusion of Al at Tann = 1600oC. After annealing at 1800oC, losses due to out-diffusion were as great as 96% and Al diffusion into the sample bulk took place. Implantation at 1300oC reduced both the in- and out-diffusion as shown on Figure 2. The results demonstrated that redistribution of Al implanted in SiC during post implantation annealing directly correlated with the amount and nature of residual damage. Corresponding author: Alexander_Suvorov@cree.com; Phone: 1-919-313-5334; Fax: 1-919-313-5687

Figure 1. SIMS profiles of 50 keV Al+ implanted into SiC at Timp = RT and annealed at Tann =

1600 and 1800oC for 320 s.

Figure 2. SIMS profiles of 50 keV Al+ implanted into SiC at Timp = 1300oC and annealed at Tann

= 1600 and 1800oC for 320 s.

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Thermal Oxidation of 4H-Silicon Carbide Using the Afterglow Method A.M. Hoff1, E. Oborina1, S.E. Saddow1, and A. Savtchouk2 1: NNRC @ The University of South Florida, 4202 E. Fowler Ave. MS:ENB118, Tampa, FL, USA 33620, 2: Semiconductor Diagnostics Inc., 3650 Spectrum Blvd. Suite 130, Tampa, FL, USA 33612. Tel: (813) 974-4958, Fax: (813) 974-3610, hoff@eng.usf.edu The thermal oxidation of SiC in an afterglow processing system opens new pathways to address oxide growth rate and quality issues. In this vacuum furnace process, neutral atomic or excited molecular species are generated in a clean microwave source and flow to the furnace region of the apparatus where they react with the SiC substrates at prescribed temperature. Therefore, oxidant production in this system is decoupled from the substrate surface generation processes that occur in conventional furnace oxidation. With the afterglow method oxide films nearly 700Å thick have been grown at 1100°C in one hour at 1 Torr. This rate is more than three times greater than we observe at the same temperature in steam at atmospheric pressure. Such results suggest that the reactivity of the afterglow species with SiC is orders of magnitude higher than that of steam reacting at atmosphere. The electrical properties of films grown by the afterglow and conventional methods were characterized using the state-of-the-art non-contact corona-metrology commonly used by silicon IC manufacturers. As compared to furnace growth, the afterglow method was found to produce films with superior effective dielectric constant, similar interface trap density, and the flatband voltage in the as-grown state shifted toward more negative values (p-type).

Thermal Oxidation of 4H-Silicon Carbide Using the Afterglow Method A.M. Hoff1, E. Oborina1, S.E. Saddow1, and A. Savtchouk2 1: NNRC @ The University of South Florida, 4202 E. Fowler Ave. MS:ENB118, Tampa, FL, USA 33620, 2: Semiconductor Diagnostics Inc., 3650 Spectrum Blvd. Suite 130, Tampa, FL, USA 33612. Tel: (813) 974-4958, Fax: (813) 974-3610, hoff@eng.usf.edu High quality thermal oxides on silicon carbide are a key to the fabrication of future generations of field effect and other passivated electronic device structures. Unfortunately, the application of oxidation processes that produce high film growth rates and excellent interface quality on silicon material has produced disappointing results in the case of SiC. A global effort to address these issues through chemical and procedural modifications to the oxidation and subsequent processes [1,2] has improved the situation somewhat but to date growth rates remain low and charge state densities at or near the film interface remain high when compared to films on silicon. The thermal oxidation of SiC in an afterglow or remote plasma processing system opens new pathways to address oxide growth rate and quality issues. In afterglow chemical processing [3,4], the generation of reactants is accomplished by exciting precursor gases in a clean microwave discharge. Charged species and light generated in this source are trapped while a high flux of reactants flow to the furnace region of the apparatus where they may react with the substrates at a prescribed temperature as shown in Fig. 1. In this work, thermal oxides were grown by conventional atmospheric pressure furnace processing at 1100ºC in a pyrogenic steam ambient and in the afterglow system over a temperature range from 800ºC to 1100ºC at 1 Torr. In both cases, oxides were grown on cleaned 4H-SiC samples consisting of either n- or p-type epitaxial films on heavily doped substrates. Post-oxidation processing included no further anneal, a re-oxidation anneal at 950ºC, or an in-situ argon anneal. Film thickness was determined by profilometry, ellipsometry, and by electrical means. A state-of-the-art non-contact capacitance method, commonly used in silicon IC manufacturing, was applied to the characterization of the as-grown and annealed films. This corona-based method, described in [5], facilitates the rapid evaluation of processing effects while the complications and cost associated with the fabrication of capacitor structures are avoided. Table 1 summarizes the physical and electrical properties of the films grown by these methods and Fig. 2 depicts C-V results for an afterglow oxide grown at 800ºC and for a re-oxidized 1100ºC furnace oxide. The afterglow film in Fig. 2 was not annealed. The most striking result is the accelerated film growth obtained with the afterglow method. With the afterglow method oxide films nearly 700Å thick have been grown at 1100°C in one hour at 1 Torr. This rate is more than three times greater than we observe at the same temperature in steam at atmospheric pressure. Such results suggest that the reactivity of the afterglow species with SiC is orders of magnitude higher than that of steam reacting at atmosphere. Considering film properties one shall notice the superior dielectric constant of the 800°C afterglow film near k=3.9 of SiO2. This could be a result of more effective removal of carbon in the afterglow process. Other electrical properties are comparable for afterglow and conventional techniques. Afterglow films were not thermally treated after growth. It is thus conceivable that they could be improved by a properly designed annealing cycle.

References [1] K.Y. Cheong, S. Dimitrijev, J. Han, and H.B. Harrison, J. Appl. Phys. 93, 5682-5686, (2003). [2] G.Y. Chung, J.R. Williams, C.C. Tin, K. McDonald, D. Farmer, R.K. Chanana, S.T. Pantelides, O.W. Holland and L.C. Feldman, Appl. Surf. Sci. 184, 399-, (2001). [3] A.M. Hoff and J. Ruzyllo, Apl. Phys. Lett., 52, 1264-1265, (1988). [4] J.M. Cook and B.W. Benson, J. Electrochem. Soc., 130, 2459-2464, (1983). [5] P. Edelman, A. Savtchouk, M. Wilson, J. D’Amico, N. Kochey, and J. Lagowski, Proc. of 2003 Int. Conf. on Characterization and Metrology for ULSI Technology, March 24-28, Austin, Texas, USA (2003).

Table 1. Growth Parameters Film Properties System T

(°C) P

(Torr) Gas Time

(hr) Rate

(Å/ hr.) Tox***

(Å) k

(eff.) VFB, V p-type

VFB, V n-type

Furnace* 1100 760 O2,H2 1.5 200 300 2.5 -4 5.5 Afterglow 800 1 O2,N2O 2 135 270 3.84 -6.6 7

Afterglow** 1100 1 O2,N2O 1 670 670 3.6 -22.7 1 Furnace** 1100 760 O2,H2 0.75 240 180 3.25 -4.6 0.7

* films annealed by re-oxidation process after growth. ** films in-situ annealed in argon. *** Tox measured by ellipsometry.

Primary gasSecondary gas

Microwave Cavity

LoadPort

Pump

Furnace

Substratesand holder

Fused SilicaTube

Plasma

Afterglow species

Fig. 1. Afterglow thermal oxidation system.

Fig. 2. Capacitance-voltage comparison of an 800°C afterglow film that received no anneal with an 1100°C atm. furnace film that has been given an in-situ 3 hr. re-oxidation anneal at 950°C.