Improvement of Heating Characteristics of Molybdenum Silicide Thin FilmElectric Heaters

YUKI ITO, MASASHI SATO, KENICHI WAKISAKA, and SHINZO YOSHIKADODoshisha University, Japan

SUMMARY

Molybdenum silicide (MoSi2) has an electrical con-ductivity as high as that of a metal, and greater chemicalstability than that of, for example, SiC, in various atmos-pheres. Therefore, many kinds of MoSi2 bulk-type heatersare used in practical operations up to 1800 °C, which ishigher than the temperature of SiC heaters. However,MoSi2 is fragile at room temperature and has low creepresistance at high temperature. The purpose of this study isto fabricate heaters using thin films of MoSi2 deposited onalumina substrates and crucibles by RF magnetron sputter-ing and to evaluate their characteristics. MoSi2 thin film wasdeposited on the outside of an alumina crucible withoutheating the substrate and then Pt wire was attached using aPt paste with sintering in a vacuum. This MoSi2 thin filmheater showed almost linear resistance–temperature (R–T)characteristics and a uniform heating state. It also showedgood controllability of voltage and stability in the power–Tcharacteristics for operations up to 1000 °C. However, at aheating temperature of 1300 °C, the heating area of MoSi2thin film decreased because of the reaction between Pt andMoSi2 in the case of long-term heating. Thus, Mo thin filmwas deposited as a buffer layer between Pt and MoSi2 thinfilm to prevent such a reaction. This thin film heater showedgood linear R–T characteristics up to 1200 °C. However,the temperature coefficient of resistance changed with re-peated heating operation as a result of the diffusion of Moatoms into MoSi2. Thus, a thin film heater was fabricatedwith Mo3Si, having a higher Mo content than MoSi2. Thisheater showed a low degree of diffusion of Mo or Pt atomsinto the thin film and had excellent practical characteristicsup to 1000 °C. © 2009 Wiley Periodicals, Inc. Electr EngJpn, 168(2): 11–19, 2009; Published online in Wiley Inter-Science (www.interscience.wiley.com). DOI 10.1002/eej.20806

Key words: thin film high-temperature heater;MoSi2 film; RF magnetron sputtering; alumina substrate;improvement of heaters; MoSi3 film.

1. Introduction

Molybdenum silicide (MoSi2) has a high meltingpoint of 2030 °C and is widely and practically used as amaterial for heaters that can be operated at high tempera-tures in an oxidizing atmosphere, similar to SiC heaters.Molybdenum silicide can also be used practically up to1800 °C, which is higher than the temperature of SiCheaters. Furthermore, it has a greater chemical stability thanSiC in various atmospheres. However, MoSi2 is fragile atroom temperature, and therefore attention is required in itsuse. In particular, MoSi2 is easily softened above 1300 °C,so that new strategies are needed for its installation and forthe form of heaters [1]. We fabricated and evaluated heatersusing molybdenum silicide deposited on the substrate byRF magnetron sputtering. Currently, the heaters are fabri-cated by depositing MoSi2 thin films on alumina substratesand installing Pt electrodes. It has been reported that suchheaters deteriorate with increasing heating time [2]. It isspeculated that PtSi is generated by the reaction between Ptand MoSi2. The temperature coefficient of the resistance ofPtSi is semiconductor-like, and the resistance is lower thanthat of MoSi2 at high temperature. Therefore, the heatingof the PtSi area decreases, and the heating area of MoSi2thin film decreases substantially at high temperature. In thisstudy, a method that reduces the deterioration of the heatingcharacteristics due to the generation of PtSi is reported.

2. Experiment

2.1 Evaluation and fabrication of MoSi2 thinfilms

MoSi2 powders were pressed at 25 MPa on a plate-type target holder that was made of anoxic copper and had

© 2009 Wiley Periodicals, Inc.

Electrical Engineering in Japan, Vol. 168, No. 2, 2009Translated from Denki Gakkai Ronbunshi, Vol. 127-A, No. 8, August 2007, pp. 452–458

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a diameter of 12 cm. That target holder was placed in an RFmagnetron sputtering apparatus assembled by combiningthe magnetron sputtering apparatus shown in Fig. 1 with anRF power supply. The substrate on which to deposit the thinfilm was placed facing the opposite side of the target holder.The distance between the target and the substrate wasapproximately 50 mm. A high-purity alumina substratewith a thickness of 1.0 mm was used. The sputtering con-ditions were as follows: discharge frequency 13.56 MHz;discharge power 200 W; discharge gas pressure 0.53 Pa;argon discharge gas at a constant flow rate of 400 ml/min;substrate temperature 700 °C or no substrate heating; dis-charge time 1 to 3 h. Without substrate heating, the substratetemperature increased to 180 °C because of pilot dischargewhen the shutter opened, and settled at approximately 350°C 1 hour after the start of fabrication. The crystal structureof the thin film was analyzed by X-ray powder diffractionanalysis (XRD). Composition analysis of the thin film wascarried out using a scanning electron microscope (SEM)with energy-dispersive X-ray spectroscopy (EDX) underthe conditions of an acceleration voltage of 20 kV, a scan-ning area of 40 × 30 µm2, a beam current of 200 pA, asampling time of 300 s, and a count rate of 1100 cps. Pt andMo atoms were analyzed using the Lα line, and Si wasanalyzed using Kα lines.

2.2 Evaluation and fabrication of the crucible

A rotation device was introduced from the outsideinto the RF magnetron sputtering apparatus in order toevenly deposit the thin film on the crucible. Then, MoSi2sputtering was carried out. A high-purity alumina cruciblewith a bore of 11 mm, a radius of 6.5 mm, and a length ofabout 61 mm was used. The crucible was not heated, andthe discharge time was 1 to 3 hours. The rotation rate of thecrucible was 1 rpm.

We believed that to fabricate heater electrodes usingPt, which has a high melting point of 1770 °C and highchemical stability, the paste-burning method would be ap-propriate. However, in the case of heating in an oxidizingatmosphere, the paste-burning method is irrelevant becauseSi in MoSi2 thin film oxidizes. Therefore, after depositinga MoSi2 thin film, Pt wire was wound around both ends ofthe thin film and Pt paste was applied in a band. The MoSi2thin film was inserted into a quartz pipe. Afterwards, theinside of the quartz pipe was exhausted to approximately 1Pa using a rotary pump, and the quartz pipe was insertedinto an electric furnace held at 1000 °C. After 1 hour, thequartz pipe was extracted from the electric furnace so thatthe temperature decreased rapidly.

To carry out this process, heaters with Pt paste as theelectrodes were fabricated. The length of the heating areaamong the electrodes was 35 to 40 mm. The thin filmheaters were placed in an ultrahigh-vacuum chamber (ap-proximately 10–7 Pa). Heating power was supplied by a DCconstant-voltage source. The heating temperature inside thecrucible was measured by inserting an Alumel-chromelthermocouple into the crucible filled with alumina powder(approximately 0.3 µm grain size). Resistance–temperature(R–T) characteristics of heaters were calculated using thesemeasured values.

2.3 Evaluation and fabrication of Mo5Si3 andMo3Si thin films

To prevent the migration of Mo described in Section3.2 into the MoSi2 thin film, heaters using Mo5Si3 or Mo3Sithin film were fabricated. The reason for using Mo5Si3 orMo3Si thin film is that even if migration of Mo occurs, thecomposition of the heating area does not change very much.The Mo5Si3 and Mo3Si thin films were deposited using atarget which was a mixture of Mo and MoSi2 powders. Ahigh-purity alumina substrate with a thickness of 1.0 mmor a high-purity alumina crucible was used. The sputteringconditions were the same as those for MoSi2, and thedischarge time was 2 hours. The thin films were analyzedby XRD and EDX. The conditions of analysis also were thesame as for MoSi2. Heaters using these thin films depositedon the crucible were also fabricated under the same condi-tions as described in Section 2.2. The discharge time of theMo5Si3 or Mo3Si thin film was 1 hour.

3. Results and Discussion

3.1 Evaluation of MoSi2 thin films depositedon alumina substrate

MoSi2 thin films deposited on the alumina substratehad a hexagonal crystal structure, contrary to the tetragonal

Fig. 1. Schematic drawing of apparatus for thin filmdeposition by RF magnetron sputtering.

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one of the target material, under all conditions. However,the orientation changed greatly with the sputtering condi-tions. It was found that sputtering conditions strongly af-fected the deposited MoSi2 thin film. The XRD patterns areshown in Fig. 2. The compositions were close toMo:Si=1:2, which is the stoichiometric composition ratio,under all conditions. Furthermore, it has been reported thatwhen a thin film is deposited by sputtering using Ar gas, itoften has the so-called column structure, where all thecrystals inside the thin film are arrayed in columns on thesubstrate [3, 4]. It was confirmed from SEM images that theMoSi2 thin films deposited on the alumina substrate alsohad the column structure.

3.2 Evaluation of alumina crucible heaters

Figure 3 shows the heating characteristics in theultrahigh-vacuum chamber of the thin film heater withMoSi2 film deposited on the outside of the alumina cruci-ble, taking practical use into consideration. This thin filmhad high stability, and the heating temperature of this heaterreached 1000 °C, with an electric power of approximately190 W. At a low heating temperature, the pressure increasedbecause of gas generated from the heater and then sub-sequently decreased with increasing temperature. However,the pressure increased again at a high temperature of about900 °C, and the resistance of the heater decreased markedly.It was speculated that the decrease of resistance was caused

by the reaction between MoSi2 thin film and Pt, wherebyplatinum silicide (PtSi) was generated. Because no peculiarphenomena such as a decrease in resistance were observedon repetition of heating to 1000 °C, heating was repeatedto 1300 °C. This R–T characteristic is shown in Fig. 4. Asin the first process of heating to 1000 °C, the resistancedecreased rapidly at approximately 1000 °C in the firstprocess of heating up to 1300 °C. However, the resistance

Fig. 2. XRD patterns of thin MoSi2 films deposited onalumina substrate.

Fig. 3. Heating characteristics of MoSi2 thin film heaterdeposited on outside of aluminum crucible.

Fig. 4. Repeated R–T characteristics of MoSi2 thin filmheater deposited on outside of aluminum crucible and

heated to 1300 °C.

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changed linearly with temperature despite the repetition ofheating. The resistance was almost constant, although itvaried slightly with the repetition of heating. The rapiddecrease in resistance from the first heating process to thesecond heating process appears to be due to the generationof PtSi. Therefore, it is inferred that the resistance of theheater decreased because PtSi has a lower resistance thanMoSi2, and the contact resistance was reduced between theelectrodes and the thin film.

The temperature characteristics of heating with anelectric power source were stable. The heating temperaturereached approximately 1300 °C with an electric power ofapproximately 300 W. In addition, the heating temperaturecould be controlled well by adjusting the electric power.The pressure increased owing to gas generated from theheaters and then decreased with increasing heating tem-perature. However, the pressure began to increase again atapproximately 1000 °C. The reason for the increase intemperature is mainly the gas generated from the vacuumchamber. This is confirmed by the dominance of the in-crease in temperature of the vacuum chamber owing toradiant heat at high temperature and by a comparison of thepressure change during the heating and cooling processes.

To investigate evaporation from the crucible, aquartz-crystal-vibration-type film thickness sensor wasplaced approximately 50 mm from a MoSi2 thin film heater.However, contamination due to evaporation from the heatermaterials was not detected. Thus, it appears that the amountof evaporation from the heater materials is nominal. Fur-thermore, compared with the temperature inside the cruci-ble measured with a thermocouple, the surface temperatureof MoSi2 thin films, measured with a radiation thermome-ter, was more than 100 °C higher.

3.3 Heating characteristics using aluminacrucible for a long term

Long-term heating using the crucible described inSection 3.2 was carried out at 1300 °C. When the heatingtemperature reached 1300 °C, the voltage was adjusted toa constant value, and the heating test was started. Theheating characteristics over a period of 10 hours are shownin Fig. 5. Although the heating area spread uniformly atfirst, it tended toward the center area with increasing heat-ing time. It appears that PtSi was generated with the migra-tion of Pt into the MoSi2 thin film, as described in Section3.2. The resistance of the thin film, where PtSi was formed,was lower than that at the center of the MoSi2 thin filmbecause of the semiconductor-like property of the resis-tance, which decreased at higher temperature. This resultled to a difference in Joule heating at the same current.Therefore, the amount of heat at both ends of the heater

decreased and the heating area moved to the center area ofthe heater.

To characterize this phenomenon, the composition ofthe MoSi2 thin film heater was analyzed by EDX. Table 1shows the amounts of Mo, Si, and Pt. The composition wasanalyzed at three points: at the Pt electrodes, at the MoSi2thin film near the Pt electrodes, and at the center of theMoSi2 thin film far from the Pt electrodes. The compositionratio of Pt in the MoSi2 thin film near the Pt electrodes washigh, as shown in Table 1. Considering this result and thedecrease in the resistance shown in Figs. 3 and 4 in the firstprocess of heating, it is concluded that the decrease of theheating area was caused by reaction between Pt and Si. Toprevent the reaction between Pt and MoSi2 at high tempera-tures, a Mo thin film buffer layer was inserted between theMoSi2 thin film and the Pt electrodes, because the resistanceand temperature coefficient of MoSi2 thin film are stableeven if Mo of the Mo thin film buffer layer diffuses into theMoSi2 thin film.

The Mo thin film buffer layer was deposited for 30min under the same sputtering conditions as those used inthe deposition of the MoSi2 thin film on the alumina cruci-ble. After the deposition of the thin film, Pt electrodes wereattached to the Mo thin film buffer layer. A schematicdrawing of this process is shown in Fig. 6. The improved

Fig. 5. Photograph of heating state at 1300 °C.

Table 1. Composition ratios of MoSi2 thin film heaterafter heating

(a) 0 h (b) 6 h later (c) 10 h later

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heater was placed in the ultrahigh-vacuum chamber and theheating characteristics of the improved heater with the Mothin film buffer layer were evaluated under the same condi-tions as described in Section 3.2. Heating was repeated 10times between room temperature and 1000 °C, then 20times between room temperature and 1200 °C. The re-peated R–T characteristics between room temperature and1200 °C are shown in Fig. 7. For this heater, a decrease inthe resistance in the first process of increasing the tempera-ture did not occur. This result indicates that the reactionbetween the MoSi2 thin film and Pt electrodes was inhibitedby the buffer layer and the decrease in the contact resistanceowing to the formation of PtSi between the electrodes andthe thin film was prevented.

After the first heating cycle, the resistance decreasedgradually as the heating was repeated, similarly to theMoSi2 thin film discussed in Section 3.2. However, as theheating was further repeated, the resistance began to in-crease gradually after reaching the minimum value. Fur-thermore, the rate of resistance rise with temperatureincreased after the heating was repeated 20 times, as shownin Fig. 7. Considering that the temperature coefficient ofMo is 5.0 × 10–3 °C–1 and that of MoSi2 is 7.489 × 10–4 °C–1,as calculated from Fig. 4, it is speculated that the ratio ofMo in the MoSi2 thin film increased owing to the separationof Si from MoSi2 as the heating was repeated. Conse-quently, the temperature coefficient of the heater increased.To explain the cause, the composition of the MoSi2 thin filmwith the Mo buffer layer was analyzed by EDX. Table 2

shows the compositions of Mo, Si, and Pt. The analyzedpoints were at the Mo thin film buffer layer, at the MoSi2thin film near the Mo thin film, and at the center of theMoSi2 thin film far from the Mo thin film.

By the composition analysis, it was confirmed thatthe migration of Pt into the center of the MoSi2 thin filmwas prevented. However, the quantity of Mo in the MoSi2thin film near the Mo thin film and at the center of the MoSi2thin film increased. This result is different from thestoichiometric composition ratio given by Mo:Si=1:2, anda marked increase in Mo content was observed. From theabove results, it was found that Mo of the Mo buffer layer,instead of Pt, diffuses into the MoSi2 thin film. Thus, thedecrease in the resistance is also explained by the diffusion

Fig. 7. Repeated R–T characteristics of MoSi2 thin filmheater deposited on outside of aluminum crucible with

Mo buffer layer and heated to 1200 °C.

Fig. 6. Fabrication process of MoSi2 thin film heaterwith Mo buffer thin film.

Table 2. Composition ratios of MoSi2 thin film heaterwith Mo buffer layer after heating

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of Mo. However, the decrease of the heating area, whichwas observed in the MoSi2 thin film without a Mo bufferlayer, did not occur. Therefore, the heater was improved byusing the Mo buffer layer. In the next section, we describean attempt to prevent the migration of Mo using molybde-num silicide that contains much Mo, taking the aboveresults into consideration.

3.4 Evaluation of Mo5Si3 and Mo3Si thin films

Mo5Si3 and Mo3Si were prepared by dry mixing ofMo and MoSi2 powders in an agate bowl in such a way thatthe composition mol ratio of Mo and Si was 5 to 3 or 3 to1. The X-ray diffraction peaks of Mo5Si3 and Mo3Si werenot observed after dry mixing, although those of Mo andMoSi2 were observed. Then, thin films were deposited onthe alumina crucible substrate with a target of Mo5Si3 orMo3Si thin film. For both Mo5Si3 and Mo3Si thin filmdeposited without substrate heating, diffraction peaks ofMo5Si3 and Mo3Si were not observed. Therefore, the thinfilms were annealed in a vacuum under the same conditionsas for sintering the Pt paste. In the case of the Mo5Si3 thinfilm annealed after deposition with substrate heating at 700°C, the diffraction peaks did not agree with those of Mo5Si3obtained from the JCPDS card. On the other hand, thediffraction peaks of Mo3Si thin film annealed after deposi-tion with substrate heating at 700 °C corresponded to thoseof a Mo3Si cubic crystal obtained from the JCPDS card.These XRD patterns are shown in Fig. 8.

These results indicate that the deposition of a thinfilm of Mo3Si cubic crystals on the alumina crucible sub-strate is possible by annealing at 1000 °C in spite of thedifficulty of substrate heating. Moreover, it was found, bycomposition analysis, that the composition of each thin filmwas close to the stoichiometric composition ratio ofMo:Si=3:1 despite the substrate heating.

3.5 Characteristics of Mo5Si3 thin film heater

Figure 9 shows the repeated R–T characteristics ofthe Mo5Si3 thin film heater with the same Mo buffer layeras described in Section 3.4. Heating of this heater wasrepeated 5 times between room temperature and 1000 °Cand then repeated between room temperature and 1200 °C.The resistance did not decrease markedly in the first processof heating, unlike the case of MoSi2 thin film with a Mobuffer layer, but decreased gradually. Then, the number ofrepetitions of heating at which the resistance of Mo5Si3 thinfilm reached a minimum was smaller than that given inSection 3.4. This is because the Mo5Si3 thin film reachedthe limit of solid solution of Mo sooner than did the MoSi2

thin film. Comparing the resistances at the 4th, 10th, and16th repetitions after reaching 1200 °C, it was found that

Fig. 9. Repeated R–T characteristics of Mo5Si3 thinfilm heater deposited on outside of aluminum crucible

with Mo buffer layer and heated to 1200 °C.

Fig. 8. XRD patterns of Mo3Si thin films deposited onaluminum substrate under various conditions.

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the resistance increased and the temperature coefficientvaried as the number of heating repetitions increased. Table3 shows the composition analysis of this heater after heat-ing. The analyzed points were at the Mo thin film bufferlayer, at the Mo5Si3 thin film near the Mo thin film, and atthe center of the Mo5Si3 thin film far from the Mo thin film.It was confirmed that the ratio of Mo to Si increased at thecenter of the Mo5Si3 thin film. This result is considerablydifferent from the stoichiometric composition ratio ofMo:Si=5:3 and indicates that migration of Mo into theMo5Si3 thin film also occurred. In addition, Si was detectedfrom the Mo buffer layer. This result suggests an increasein the contact resistance, that is, an increase in the resistanceof the heater. This is because Mo5Si3 thin film originallycontains a large amount of Mo and the diffusion of Monegligibly affects the resistance of the heater.

3.6 Characteristics of Mo3Si thin film heater

The Mo3Si thin film heater with a Mo buffer layerwas heated 20 times between room temperature and 1000°C in the ultrahigh-vacuum chamber. The repeated R–Tcharacteristics of this heater are shown in Fig. 10. Theresistance of this heater reached the minimum value asquickly as the heater described in Section 3.5. Heatingresulted in almost linear R–T characteristics, in approxi-mate agreement with those of the MoSi2 thin film heater,and the heating temperature reached 1000 °C for an electricpower of approximately 140 W. Table 4 shows the compo-sition of this heater after repeated heating. The analyzedpoints were at the Mo thin film buffer layer, at the Mo3Sithin film near the Mo thin film, and at the center of theMo3Si thin film far from the Mo thin film. It is seen in Table4 that the amount of Si on the Mo thin film is low. This resultsuggests that the diffusion of Si was hindered. Therefore,the reason for the slight increase in the resistance observedduring the repetition of heating for the MoSi2 or Mo5Si3thin film heater appears to be that the increase in the contactresistance or the resistance of the electrodes due to diffusionof Si was hindered. Although the Mo-to-Si composition

ratio in the Mo3Si thin film near the Mo thin film increasedslightly, that at the center of the Mo3Si thin film afterheating was the same before and after heating.

The above results confirmed that the migration of Mois reduced for the Mo3Si thin film heater compared with theMoSi2 or Mo5Si3 heater. This phenomenon results from thedifference in the crystal structures of the two types of thinfilms. MoSi2 originally has the tetragonal CaC crystal struc-ture, in which the volume-filling factor of atoms is high,making the displacement and migration of atoms difficult.However, as mentioned in Section 3.1, the crystal structureof MoSi2 changes from tetragonal to hexagonal during thedeposition of the thin film. Moreover, an accurate crystalstructure of the Mo5Si3 thin film was not obtained. On theother hand, Mo3Si has a cubic A15 crystal structure inwhich the displacement and migration of atoms are also

Table 3. Composition ratios of Mo5Si3 thin film heaterwith Mo buffer layer after heating

Table 4. Composition ratios of Mo3Si thin film heaterwith Mo buffer layer after heating

Fig. 10. Repeated R–T characteristics of Mo3Si thinfilm heater deposited on outside of aluminum crucible

with Mo buffer layer up to 1000 °C.

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difficult. Hence, the cubic crystal structure of Mo3Si re-mained after the deposition of the thin film, as described inSection 3.4. The volume-filling factor of atoms in hexago-nal-crystal-structure MoSi2 thin films is approximately27.34%. Meanwhile, that in tetragonal-crystal-structureMo3Si thin films is approximately 69.20%. Therefore, it isspeculated that the migration of atoms such as Mo or Pt washindered since the Mo3Si thin film heater has a fairly highvolume-filling factor of atoms. In addition, the suppressionof the diffusion of Si into electrode was also explained bythe high volume-filling factor of atoms for Mo3Si. On thebasis of the above discussion, it is concluded that thedecrease of the heating area observed in the MoSi2 heatercan be improved by using Mo3Si thin film with a highvolume-filling factor of atoms.

4. Conclusions

The results of this study are summarized as follows.

(1) The heating characteristics of a MoSi2 thin filmheater with a Mo buffer layer inserted to prevent the gen-eration of PtSi were almost linear and as good as those ofthe MoSi2 thin film heater without the Mo buffer layer. Itappears that the generation of PtSi was prevented, becauseno marked decrease in the resistance was observed in thefirst process of heating. However, the temperature coeffi-cient of resistance changed during the repetition of heating.This is caused by the migration of Mo instead of Pt.

(2) The fabrication of Mo5Si3 or Mo3Si thin film wasattempted using a target made of Mo and MoSi2 powdersmixed in such a way that the composition molar ratio of Moto Si corresponds to that of Mo5Si3 or Mo3Si. Under thiscondition, X-ray diffraction peaks of Mo5Si3 were notobserved from the deposited thin film. However, the peaks

of tetragonal Mo3Si crystal were observed from the depos-ited thin film with substrate heating at 700 °C or withannealing instead of substrate heating.

(3) In the case of the Mo5Si3 thin film heater with theMo buffer layer, the amount of Mo at the center of theMo5Si3 thin film increased after heating, as in the case ofthe MoSi2 thin film, and the migration of Mo could not beprevented. On the other hand, for the Mo3Si thin film heaterwith the Mo buffer layer, the composition ratio at the centerof the Mo3Si thin film was the same before and afterheating. Therefore, it was concluded that the migration ofMo into the MoSi2 thin film was prevented.

(4) The lack of migration of Mo in the case of theMo3Si thin film is attributed to the difference in crystalstructure. MoSi2 changes from the tetragonal crystal struc-ture to the hexagonal crystal structure upon the depositionof the thin film. On the other hand, the cubic crystal struc-ture of Mo3Si is retained after the deposition of the thin film.The volume-filling factor of atoms for Mo3Si with cubiccrystal structure is higher than that for MoSi2 with hexago-nal crystal structure, and hence the migration and displace-ment of atoms such as Mo and Pt are difficult.

REFERENCES

1. Nakagawa K, Tamamizu T, Umeda N, Kawanami T.Fine ceramics. Giken; 1982. p 100–107. (in Japanese)

2. Wakisaka K, Ito Y, Kado H, Yoshikado S. Fabricationand application of thin MoSi2 film electric heaters.Trans IEE Japan 2006;126-A:135–142. (in Japanese)

3. Hayashi S, Sofue S, Yoshikado S. Fabrication andevaluation of LaCrO3 thin film heaters. Trans IEEJapan 2001;121-A:269–275. (in Japanese)

4. Kinbara A. Sputtering phenomena. Tokyo UniversityPublishing; 1984. p 177–182. (in Japanese)

AUTHORS

Yuki Ito (nonmember) received his B.S. degree in electrical engineering from Doshisha University in 2004 and joinedMitsubishi Electric Corporation.

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AUTHORS (continued) (from left to right)

Masashi Sato (student member) received his B.S. degree in electrical engineering from Doshisha University in 2006 andis now in the M.S. degree program.

Kenichi Wakisaka (nonmember) received his B.S. degree in electrical engineering from Doshisha University in 2002 andjoined Fujifilm Corporation.

Shinzo Yoshikado (member) completed the M.E. program in material science at the University of Electro-Communicationsin 1978. He has been a professor in the Electronics Department at Doshisha University since 1995. His principal researchinterests are in electronic materials technology. He is a member of the Japanese Physical Society and Applied Physics Society.

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