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Surface cleaning and nitridation of compound semiconductors using gas-decomposition reaction in Cat-CVD method
ELSEVIER
Thin Sohd Films 343-34
( 1999) 5X-53
I
Surface cleaning and nitridation of compound semiconductors using gas-decomposition reaction in Cat-CVD method Akira Izumi’“. Atsushi Masuda. Hideki Matsumura
Abstract In this paper. we proposed a novel surface cleaning and nitridation technology of compound semiconductor> usinggas-decomposition reactions in a catalytic chemical vapor deposition (Cal-CVD) system. An NH? gab was used for the burfuce modificalion of GaAs( 100). X-ray photoelectron spectroscopy measurements revealed that. ( I) oxygen related peak vanished by a 3 min-nitridation treatment at 150°C. (1) nanometer-thick GaN films were formed on rhe surface by 30 min-nitridationtreatments,(3) nitridedG&4, hadgoodoxidationresistances. Atomic force microscope observations revealed that thebe surface, were wry smooth (root mean square roughness, 0.28 nm). C 1999
ElsevierScienceS.X. All rightsreserved. f&e\~v.t~rr/.s: Catalytic
chemical
vapor
deposition:
Hoi wire chemical
vclpor depoqition:
1. Introduction Surface modification processessuchascleaning and nitridation for compound semiconductors(GaAs. InP, etc.) are one of key issuesfor device fabrication. However. up to now. quite few appropriate surface cleaning and surface nitridation methods have been established. Especially in the caseof GaAs. a significant problem for GaAs structure is the difficulty of growing dielectric interfaces for metalinsulator-semiconductor (MIS) devices. Unlike Si. osidation of GaAs usually results in a high density of interface traps near the middle of the band gap. Nitridation is known to be beneficial in GaAs device fabrication. particularly in reducing diode leakage currents [I]. All these processes have to be made at low temperature below 100°C since compound semiconductorsare unstable\vith high temperature. Past attempt to prepare nitride passivation layers has been performed by a lot of methods.For example, an RF H: plasma followed by an RF N1 plasma [X3] or RF NH:, plasma[-F-6]. an electron cyclotron resonance(ECR) N2 + H2 plasma [7]. a microwave NH:, plasma [5]. an 5; ion beam [8] and a simultaneousirradiation with a molecular NH; flux and a pulsedexcimer laser [9] or an electron beam [ IO]. However. such methodsmake compoundsemiconductor devices degradedbecauseof plasmaor ion beamirrndiation damages.There are other methodsemploying aqueous ” Correspondin: 1149.
aurhor.
Tel.:
+ 51-761-51-1561:
fax:
- 51-761-jl-
Surfax
cleanin,. 0 Surfxe
nirrid~r~on:
GaAs;
GaN
solutions such as (&H,),S, [ 1l-l-l]. Na2S9H20 [ 1?.14.15] and P&‘(NH,‘)2S [ 16,171.Hoivever, such treatmentscause heavy metal contamination and have poor reproducibility. Thus, the development of a new surface treatment technology at low temperatureswithout any plasma. ion beam or aqueoussolution hasbeen strongly required. In this work. we propose a novel surface cleaning and stabilization technology of compound semiconductors at low temperatures.Our technique is basedon gas-decomposition reaction by catalytic chemical vapor deposition (CatCVD) [18]. In this method. deposition gasesare decomposedby catalytic cracking reactionswith ;1heatedcatalyzer placednear sub>trates.and sothat. films are depo4ted at low temperatureswithout help from plasmanor photochemical excitation. Actually. the authors have already succeededto deposit high quality SiN, thin films by this method using a SiHl and NH; gas mixture [19]. High quality amorphous silicon [20] and polycrystalline silicon films [?l] with low hydrogen content have also been already obtained by this method. Recently applying thib technique. direct Si nitridation hasbeen succeededusing only an NH,; gas [73].
2. Experimental Fig. 1 showsthe schematicdiagram of a Cat-CVD apparatus. A tungsten wire wirh a diameter of 0.5 mm was used asthe catalyzer. It wascoiled and spreadwidely. keeping it parallel to a substrate holder with a di\tJnce of 40 mm. Surface treatment gab. NH; with 99.99Y’:r purity, was
0010-6090/99/S - see ironi maurr F 1999 Elsevier Science S.A. All right< reserved PII: SO010-6090r98)016SS-5
Thermo-couP~l
Substrate
ptepr
N Is
hof&r
After
As 3d
Ga 3d
60 days,:.
After
NH3 *---l
Fig. 1. Schemaric
diagram
of a Cat-CVD
apparatus
Binding energy (eV) decomposedby catalytic cracking reactions between gas and the healed catalyzer near substrates.The flow rate of NH3 was fixed at 50 seem.The gaspressureduring nitridation was about X mTorr. The temperature of the substrate holder Cr+Jwas measuredby a thermocouple(TC) mounted on the same surface of the holder and just beside the substrate. The surface temperature CT,,.)which was calibrated using a TC directly mounted to the Si substratewas kept at about 150°C.The temperakne of tungsten catalyzer CT,,) which was monitored by an infrared thermometerwas kept at 1220°C. A semi-insulating GaAs(100) substrate without any chemical treatment was employed as a representative of compound semiconductors.The surface conditions of GaAs after treatmentswere characterized by es situ X-ray photoelectron spectroscopy (XPS) measurements using monochromatic Al K, radiation. The shift of signals due to electrical charging of the sample surface was corrected with the C(ls) signal from the carbon contami-
NIs
z.= 5 300 min
J
As 3d
Ga 3d
. Ga LMM ii 1 !\ ?.%..I i
Binding
energy
(eV)
Fig. 2. Changes in N(ls), As(3J) and Ga(3d) XF’S spectra for samples subjected to the treatment for various times. The closed triangles indicate oxygen related peaks.
Fig 3. XPS spectra for samples beforr zir e?;posure for 60 days.
treatment,
after rreaumrnt
and after
rant. The surface morphology of GaAs was observed bjr atomic force microscope (AFhilj using a tapping mode.
3. Results and discussion 3.1. XPS obsen*iifiorr
Fig. 2 shows,XPS spectra of h’( Is), As(3d) and Ga(3d) from the surface of GaAs. All spectrawere observed at the photoelectron take-08 angle 8 of 3.5”. It is found that the surface oxide was removed by this treatment for 3 min, which is known to give an XPS signal with higher binding energy (BE) than the signalboth in Ga(3d) and As(3dj from Ga,4s substrate.The oxygen related peaksare labeled with closed triangles in Fig. 2. The remarkable changewith the treatment observed in this figure is the appearanceof new peaks with higher BE in the Ga(3d) spectrum and the appearance of the N(ls) spectrum. Therefore, we can consider that the surface of GaAs is nitrided and thin GaN layer is formed. The peak before the treatment observed in the K( Is) specrrum can be considered as the Ga LMM Auger signal. In the case of 300 min treatment, As(3d) 2RS signal jvith higher BE appears.The origin of this signal is not clear at this moment. We are speculating that the appearanceof the signal is due to ox2ation of the GaAs which appearedpartially after the treatment whiie transferring the sampleto the XPS apparatusor formation of As-N bonds. These cleaning and nitridation efkcts were not observedunder molecukr N-Ix irradiation without cracking. According to the area1intensities of N(Is) and chemical shifted component of Ga(3d) spectrumand alomic sensitivity factors of them, in the caseof 3 and 30 min treatments, we can estimatethat composition of both the nin-idefilm is Ga:N + 1:l. ,4nd the thickness of the him is difficult to calculate, however both As(3d) and Ga(3di spectra from the GaAs substrate are still observed after treatments.
T ,,t=1220°C, Before
treatment
different nitridation treatment time. Each observation area was 1 Km’. In the case of 300 min treatment. the RMS roughnessincreasesto IS.4 nm and showsrugged inorphology. However. the RMS roughnessof nitrided surface is 0.35 nm for 3 min treatment and 0.78 nm for 30 min treatment. which are comparable to that without nitridation whose RMS roughnessis 0.10 nm.
T&50°C 3 min
4. Conclusions
RMS roughnes&I.10
nm
We have proposeda novel surface cleaning and nitridation technology of GnAs using gas-decompositionreaction in a Cat-CVD system.An NH! gas was usedfor the surface cleaning or nitridation of GaAs(lO0) without any aqueous solution treatment. XPS measurementsrevealed that, (I) oxygen related peakswere disappearedby 3 min-nitridation treatment at 15O”C, (2) nanometer-thick GaN films were formed on the surfaceby 30 min-nitridation treatment, (3) nitrided GaAs had good oxidation resistance.AFM obse_rvations revealed that thesesurfaceswere very smooth (RMS roughness:0.28 nmj.
0.25 nm
30 min
300 min
0.28 nm
18.4 nm
Acknowledgements
Fig. 1. Surface morphology and surface royhnea~ trenrrd sampler obherved by AFM techmques.
q lpm
of post-trcured
and pre-
Therefore. we can estimate that thicknessof GaIKis at least a few nm from considerationsof the photoelectron escape depth. We are speculating that the mechanisin of the cleaning and nitridation effects is as follows; hydrogen radicals are considered to have cleaning effect for GaAs [23]. so. the above result indicates that the NH; gas produceshydrogen radicals and these radicals remove surface oxide of GaAs. At the sametime. nitrogen radicals are producedfrom NH,, and these radicals may react with GaAs and form GaN simply via an anion eschangereacrion [8]. The osidation resistanceof nitrided GaAs was investigated. The change of XPS spectra for the sampleafter the treatment for 30 min is shown in Fig. 3. The XPS observations Lvere carried out after the air exposure at roo1n temperature for 60 days. Almost no signals due to oxide can be observed even after the air exposure for 60 days. These results support that this treatment is one of the pro1nisingtechniquesfor the passivation of GaPlssurface.
AFM analysis \vas performed on the nitrided surface of the samesampleswhich were mentioned at Section 3.1 to investigate the surface morphology and the surface roughness.Fig. -I showsAFM imagesof surface1norphologywith
The authors would like to expresstheir thanks to Prof. S. Horita at JAIST for his fruitful discussionsand encow_agemerit. This work is in part supportedby the R&D Projects in cooperation with Academic Institutions ‘Cat-CVD Fabrication Process for semiconductor devices’ from the yew Energy and Industrial Technology Development Organization (NEDO) to the Ishikawa Trial center. This work is in part supported by the Progressof New Chemistry and the ANELVA corporation. References Ill S.J. Penrron. [‘I F. Capasso. [3! A. Callegcri.
E.E. H&x, A.G. Elliot. Appl. Phys. Lert. 44 (19541651. G.F. Williams. I. Electrochcm. SW. 129 (1982) 821. D. Lacey, D.A. Buchanan. E. Ldtta, \I. Gsscr, A. Paccagnelld. Instrum Phyb. Cunf. Ser. 106 (1989) 399. IJI C.Y. Wu. MS. Lm. J. Appl. Phy, 60 (19861 2050. El ES. Aydil. K.P. Glpis. R.A. Go,itxho. V.?vl. Donnelly, E. Yoon, J. Vnc. SCI. Technol. B 1 I (1993) 195. Jpn. J. Appt. [Gl A. Masuda. Y. Yoneznwn. A. hlonmolo. T. Shim& Phys. 32 (1995) 1075. ;71 A. Tnmura M. tiiragawd. S. Nambu. Instrum. Phys. Conf. Ser. I I2 11990, ‘-99. lSl L.A. DeLouiac. J. Vat Sci. Technol. A IO (1992) 1637. [91 N.Y. Zhu. %I. Wolf. J.M. Whire. J. VW. Sci Technol. A I1 (1993) 818. [IO1 Y.kl. Sun. J.G. Ekcrdr. J. Vat. Sci. Technol. B I I (1993) 610. ;I 11 J.F. Fan. H. Oigawn. Y. Nnnnichl. Jpn. 1. Appl Phyx. 27 (1958) Ll331. !I?] M S. Carpenter, M.R. Melloch. h1.S. Lundwom. S.P. Tobin. Appl. Phy,. La. 52 (19%) 2157. I1.Y Y. Nannichi. J.F. Fan. H Oignw. A. Koma. Jpn. J. Appl Phyr. 27 (19SS) L1367. [IA] K. Sdro. \I. Sokata. H. Ikoma. Jpn. I. Appl. Phys. 32 (1993) 33SJ.
A. I:mi
fl5]
et ul. /Tirirr
Solid
C.J. Sat&off, R.N. Nottenburg, J,C. Bischuff, R. 3hat, Appl. Phys. iett. 51 (19573 33. [16] ICC. Piwang, S.S. Li, J. ilpp1. Phys. 67 (1990) 2161. [ 171 NJ. Chester, T. Jnch, J.A. Dagata. J. Vat. Sci Technol. A 11 ( 1993) 474. [ 1S] H. Matsumura, H. Tachibana, Appl. Phys. Lett. 47 i 1985) 833.
Fi!ms
363-344
(191 {ZOj [?I] [12j [23]
(i999)
S. H, H. A.
528-531
Okada. H. IvIatsumura, Jpn. J. Appl. Phys 36 (1997) 7035. Matsumura. Jpn. J. Appl. Phys. 3 119X6j L9-19. hlarsumura, Jpn. J. Appl. Phya. 30 (1994) L15?2. Izumi, H. Matsumura. Appi. Phys. Lctt. 71 (1997) 1371. T. Sugaya, M. Kawabe, Jpn. J. Appi. Phys. 30 [ 1991, L-to;?.
531
Thin Sohd Films 343-34
( 1999) 5X-53
I
Surface cleaning and nitridation of compound semiconductors using gas-decomposition reaction in Cat-CVD method Akira Izumi’“. Atsushi Masuda. Hideki Matsumura
Abstract In this paper. we proposed a novel surface cleaning and nitridation technology of compound semiconductor> usinggas-decomposition reactions in a catalytic chemical vapor deposition (Cal-CVD) system. An NH? gab was used for the burfuce modificalion of GaAs( 100). X-ray photoelectron spectroscopy measurements revealed that. ( I) oxygen related peak vanished by a 3 min-nitridation treatment at 150°C. (1) nanometer-thick GaN films were formed on rhe surface by 30 min-nitridationtreatments,(3) nitridedG&4, hadgoodoxidationresistances. Atomic force microscope observations revealed that thebe surface, were wry smooth (root mean square roughness, 0.28 nm). C 1999
ElsevierScienceS.X. All rightsreserved. f&e\~v.t~rr/.s: Catalytic
chemical
vapor
deposition:
Hoi wire chemical
vclpor depoqition:
1. Introduction Surface modification processessuchascleaning and nitridation for compound semiconductors(GaAs. InP, etc.) are one of key issuesfor device fabrication. However. up to now. quite few appropriate surface cleaning and surface nitridation methods have been established. Especially in the caseof GaAs. a significant problem for GaAs structure is the difficulty of growing dielectric interfaces for metalinsulator-semiconductor (MIS) devices. Unlike Si. osidation of GaAs usually results in a high density of interface traps near the middle of the band gap. Nitridation is known to be beneficial in GaAs device fabrication. particularly in reducing diode leakage currents [I]. All these processes have to be made at low temperature below 100°C since compound semiconductorsare unstable\vith high temperature. Past attempt to prepare nitride passivation layers has been performed by a lot of methods.For example, an RF H: plasma followed by an RF N1 plasma [X3] or RF NH:, plasma[-F-6]. an electron cyclotron resonance(ECR) N2 + H2 plasma [7]. a microwave NH:, plasma [5]. an 5; ion beam [8] and a simultaneousirradiation with a molecular NH; flux and a pulsedexcimer laser [9] or an electron beam [ IO]. However. such methodsmake compoundsemiconductor devices degradedbecauseof plasmaor ion beamirrndiation damages.There are other methodsemploying aqueous ” Correspondin: 1149.
aurhor.
Tel.:
+ 51-761-51-1561:
fax:
- 51-761-jl-
Surfax
cleanin,. 0 Surfxe
nirrid~r~on:
GaAs;
GaN
solutions such as (&H,),S, [ 1l-l-l]. Na2S9H20 [ 1?.14.15] and P&‘(NH,‘)2S [ 16,171.Hoivever, such treatmentscause heavy metal contamination and have poor reproducibility. Thus, the development of a new surface treatment technology at low temperatureswithout any plasma. ion beam or aqueoussolution hasbeen strongly required. In this work. we propose a novel surface cleaning and stabilization technology of compound semiconductors at low temperatures.Our technique is basedon gas-decomposition reaction by catalytic chemical vapor deposition (CatCVD) [18]. In this method. deposition gasesare decomposedby catalytic cracking reactionswith ;1heatedcatalyzer placednear sub>trates.and sothat. films are depo4ted at low temperatureswithout help from plasmanor photochemical excitation. Actually. the authors have already succeededto deposit high quality SiN, thin films by this method using a SiHl and NH; gas mixture [19]. High quality amorphous silicon [20] and polycrystalline silicon films [?l] with low hydrogen content have also been already obtained by this method. Recently applying thib technique. direct Si nitridation hasbeen succeededusing only an NH,; gas [73].
2. Experimental Fig. 1 showsthe schematicdiagram of a Cat-CVD apparatus. A tungsten wire wirh a diameter of 0.5 mm was used asthe catalyzer. It wascoiled and spreadwidely. keeping it parallel to a substrate holder with a di\tJnce of 40 mm. Surface treatment gab. NH; with 99.99Y’:r purity, was
0010-6090/99/S - see ironi maurr F 1999 Elsevier Science S.A. All right< reserved PII: SO010-6090r98)016SS-5
Thermo-couP~l
Substrate
ptepr
N Is
hof&r
After
As 3d
Ga 3d
60 days,:.
After
NH3 *---l
Fig. 1. Schemaric
diagram
of a Cat-CVD
apparatus
Binding energy (eV) decomposedby catalytic cracking reactions between gas and the healed catalyzer near substrates.The flow rate of NH3 was fixed at 50 seem.The gaspressureduring nitridation was about X mTorr. The temperature of the substrate holder Cr+Jwas measuredby a thermocouple(TC) mounted on the same surface of the holder and just beside the substrate. The surface temperature CT,,.)which was calibrated using a TC directly mounted to the Si substratewas kept at about 150°C.The temperakne of tungsten catalyzer CT,,) which was monitored by an infrared thermometerwas kept at 1220°C. A semi-insulating GaAs(100) substrate without any chemical treatment was employed as a representative of compound semiconductors.The surface conditions of GaAs after treatmentswere characterized by es situ X-ray photoelectron spectroscopy (XPS) measurements using monochromatic Al K, radiation. The shift of signals due to electrical charging of the sample surface was corrected with the C(ls) signal from the carbon contami-
NIs
z.= 5 300 min
J
As 3d
Ga 3d
. Ga LMM ii 1 !\ ?.%..I i
Binding
energy
(eV)
Fig. 2. Changes in N(ls), As(3J) and Ga(3d) XF’S spectra for samples subjected to the treatment for various times. The closed triangles indicate oxygen related peaks.
Fig 3. XPS spectra for samples beforr zir e?;posure for 60 days.
treatment,
after rreaumrnt
and after
rant. The surface morphology of GaAs was observed bjr atomic force microscope (AFhilj using a tapping mode.
3. Results and discussion 3.1. XPS obsen*iifiorr
Fig. 2 shows,XPS spectra of h’( Is), As(3d) and Ga(3d) from the surface of GaAs. All spectrawere observed at the photoelectron take-08 angle 8 of 3.5”. It is found that the surface oxide was removed by this treatment for 3 min, which is known to give an XPS signal with higher binding energy (BE) than the signalboth in Ga(3d) and As(3dj from Ga,4s substrate.The oxygen related peaksare labeled with closed triangles in Fig. 2. The remarkable changewith the treatment observed in this figure is the appearanceof new peaks with higher BE in the Ga(3d) spectrum and the appearance of the N(ls) spectrum. Therefore, we can consider that the surface of GaAs is nitrided and thin GaN layer is formed. The peak before the treatment observed in the K( Is) specrrum can be considered as the Ga LMM Auger signal. In the case of 300 min treatment, As(3d) 2RS signal jvith higher BE appears.The origin of this signal is not clear at this moment. We are speculating that the appearanceof the signal is due to ox2ation of the GaAs which appearedpartially after the treatment whiie transferring the sampleto the XPS apparatusor formation of As-N bonds. These cleaning and nitridation efkcts were not observedunder molecukr N-Ix irradiation without cracking. According to the area1intensities of N(Is) and chemical shifted component of Ga(3d) spectrumand alomic sensitivity factors of them, in the caseof 3 and 30 min treatments, we can estimatethat composition of both the nin-idefilm is Ga:N + 1:l. ,4nd the thickness of the him is difficult to calculate, however both As(3d) and Ga(3di spectra from the GaAs substrate are still observed after treatments.
T ,,t=1220°C, Before
treatment
different nitridation treatment time. Each observation area was 1 Km’. In the case of 300 min treatment. the RMS roughnessincreasesto IS.4 nm and showsrugged inorphology. However. the RMS roughnessof nitrided surface is 0.35 nm for 3 min treatment and 0.78 nm for 30 min treatment. which are comparable to that without nitridation whose RMS roughnessis 0.10 nm.
T&50°C 3 min
4. Conclusions
RMS roughnes&I.10
nm
We have proposeda novel surface cleaning and nitridation technology of GnAs using gas-decompositionreaction in a Cat-CVD system.An NH! gas was usedfor the surface cleaning or nitridation of GaAs(lO0) without any aqueous solution treatment. XPS measurementsrevealed that, (I) oxygen related peakswere disappearedby 3 min-nitridation treatment at 15O”C, (2) nanometer-thick GaN films were formed on the surfaceby 30 min-nitridation treatment, (3) nitrided GaAs had good oxidation resistance.AFM obse_rvations revealed that thesesurfaceswere very smooth (RMS roughness:0.28 nmj.
0.25 nm
30 min
300 min
0.28 nm
18.4 nm
Acknowledgements
Fig. 1. Surface morphology and surface royhnea~ trenrrd sampler obherved by AFM techmques.
q lpm
of post-trcured
and pre-
Therefore. we can estimate that thicknessof GaIKis at least a few nm from considerationsof the photoelectron escape depth. We are speculating that the mechanisin of the cleaning and nitridation effects is as follows; hydrogen radicals are considered to have cleaning effect for GaAs [23]. so. the above result indicates that the NH; gas produceshydrogen radicals and these radicals remove surface oxide of GaAs. At the sametime. nitrogen radicals are producedfrom NH,, and these radicals may react with GaAs and form GaN simply via an anion eschangereacrion [8]. The osidation resistanceof nitrided GaAs was investigated. The change of XPS spectra for the sampleafter the treatment for 30 min is shown in Fig. 3. The XPS observations Lvere carried out after the air exposure at roo1n temperature for 60 days. Almost no signals due to oxide can be observed even after the air exposure for 60 days. These results support that this treatment is one of the pro1nisingtechniquesfor the passivation of GaPlssurface.
AFM analysis \vas performed on the nitrided surface of the samesampleswhich were mentioned at Section 3.1 to investigate the surface morphology and the surface roughness.Fig. -I showsAFM imagesof surface1norphologywith
The authors would like to expresstheir thanks to Prof. S. Horita at JAIST for his fruitful discussionsand encow_agemerit. This work is in part supportedby the R&D Projects in cooperation with Academic Institutions ‘Cat-CVD Fabrication Process for semiconductor devices’ from the yew Energy and Industrial Technology Development Organization (NEDO) to the Ishikawa Trial center. This work is in part supported by the Progressof New Chemistry and the ANELVA corporation. References Ill S.J. Penrron. [‘I F. Capasso. [3! A. Callegcri.
E.E. H&x, A.G. Elliot. Appl. Phys. Lert. 44 (19541651. G.F. Williams. I. Electrochcm. SW. 129 (1982) 821. D. Lacey, D.A. Buchanan. E. Ldtta, \I. Gsscr, A. Paccagnelld. Instrum Phyb. Cunf. Ser. 106 (1989) 399. IJI C.Y. Wu. MS. Lm. J. Appl. Phy, 60 (19861 2050. El ES. Aydil. K.P. Glpis. R.A. Go,itxho. V.?vl. Donnelly, E. Yoon, J. Vnc. SCI. Technol. B 1 I (1993) 195. Jpn. J. Appt. [Gl A. Masuda. Y. Yoneznwn. A. hlonmolo. T. Shim& Phys. 32 (1995) 1075. ;71 A. Tnmura M. tiiragawd. S. Nambu. Instrum. Phys. Conf. Ser. I I2 11990, ‘-99. lSl L.A. DeLouiac. J. Vat Sci. Technol. A IO (1992) 1637. [91 N.Y. Zhu. %I. Wolf. J.M. Whire. J. VW. Sci Technol. A I1 (1993) 818. [IO1 Y.kl. Sun. J.G. Ekcrdr. J. Vat. Sci. Technol. B I I (1993) 610. ;I 11 J.F. Fan. H. Oigawn. Y. Nnnnichl. Jpn. 1. Appl Phyx. 27 (1958) Ll331. !I?] M S. Carpenter, M.R. Melloch. h1.S. Lundwom. S.P. Tobin. Appl. Phy,. La. 52 (19%) 2157. I1.Y Y. Nannichi. J.F. Fan. H Oignw. A. Koma. Jpn. J. Appl Phyr. 27 (19SS) L1367. [IA] K. Sdro. \I. Sokata. H. Ikoma. Jpn. I. Appl. Phys. 32 (1993) 33SJ.
A. I:mi
fl5]
et ul. /Tirirr
Solid
C.J. Sat&off, R.N. Nottenburg, J,C. Bischuff, R. 3hat, Appl. Phys. iett. 51 (19573 33. [16] ICC. Piwang, S.S. Li, J. ilpp1. Phys. 67 (1990) 2161. [ 171 NJ. Chester, T. Jnch, J.A. Dagata. J. Vat. Sci Technol. A 11 ( 1993) 474. [ 1S] H. Matsumura, H. Tachibana, Appl. Phys. Lett. 47 i 1985) 833.
Fi!ms
363-344
(191 {ZOj [?I] [12j [23]
(i999)
S. H, H. A.
528-531
Okada. H. IvIatsumura, Jpn. J. Appl. Phys 36 (1997) 7035. Matsumura. Jpn. J. Appl. Phys. 3 119X6j L9-19. hlarsumura, Jpn. J. Appl. Phya. 30 (1994) L15?2. Izumi, H. Matsumura. Appi. Phys. Lctt. 71 (1997) 1371. T. Sugaya, M. Kawabe, Jpn. J. Appi. Phys. 30 [ 1991, L-to;?.
531