Improved Quality Alkylhydrazine Precursors - Sigma …. Rushworth, R. Odedra, L. Wyatt, I. Hovland...
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www.safchitech.com Figure 5. Discussion The correlation between the FWHM of the –NH 2 peak in the NMR to the calculated spiking level established experimentally was found to be very high. The range in FWHM values obtained for the TBHZ 20-10000ppm water content samples allowed a line plot to be made that could be extrapolated to lower and higher water contents giving a quick and simple way of using NMR to measure the water levels in alkylhydrazines. It should be noted that the correlation plot was not linear but exponential in nature with only very small change in the FWHM values observed for the driest samples. At the low ppm range the correlation line was found to fit a linear relationship. Similarly for the MMHZ a line plot suitable for determining water content of samples from FWHM values in a quantitative manner was produced. In prior work the NMR detection limit for DMHZ was stated as 50ppm however in this study with a higher sensitivity NMR tool the detection limit was markedly reduced to less than 10ppm. Conclusions For the first time a correlation between the quantity of water in methylhydrazine and tertiarybutylhydrazine and the full width half maximum of the –NH 2 peak in the 1 H NMR spectrum. The highest purity tertiarybutylhydrazine obtained has been reported with <10 ppm of water by extrapolation of the experimental results. These high purity alkylhydrazines may now be used to grow GaInNAs for laser diode fabrication with reduced threshold current density compared to devices deposited using water contaminated precursors. References S. Miyoshi, K. Onabe, N. Oohkouchi, H. Yaguchi, R.I to, S. Fukatsu and Y. Shiyaki, 1. J. Cryst. Growth, 124 (1992) 439. S. Akram and I. Bhat, 2. J. Cryst. Growth, 138 (1994) 105. A. Ougazzaden, Y. Le Bellego, E. V. K. Rao, L. Leprince, G. Patriarch and M. Juhel, 3. EW MOVPE VII, Berlin, 1997, A7. D. J. Friedman, J. F. T. Geist, S. R. Kurtz and J. M. Olson, 4. J. Cryst. Growth, 195 (1998) 409. D. K. Gaskill, N. Bottka and M. C. Lin, 5. Appl. Phys. Lett., 48 (1986) 1449. G. Zhang et al, 6. J. Cryst. Growth, 128 (1993) 536. H. Tsuchiya, A. Tageuchi, M. Kurihara and F. Hasegawa, 7. J. Cryst. Growth, 152 (1995) 21. S. Yoshida and J. Suzuki, 8. J. Cryst. Growth, 191 (1998) 279. A. Ougazzaden, Y. Le Bellego, E.V. K. Rao, M. Juhel, L. Leprince and G. Patriarche, 9. Appl. Phys Lett., 70 (1997) 2861. O. W. Pohl, K. Knorr, C. Möller, U. Gernert, W. Richter, J. Blasing, J. Christen, J. Gottfriedsen and H. Schumann, Jpn. 10. J. Appl. Phys., 38 (1999) L1007. O. W. Pohl, C. Möller, K. Knorr, W. Richter, J. Gottfriedsen, H. Schumann, K. Rademann and A. Fielicke, 11. Mat. Sci. and Eng., B, 59 (1999) 20. R. Odedra, L.M. Smith, S.A. Rushworth, M.S. Ravetz, J. Clegg, R. Kanjolia, S.J.C. Irvine, M.U. Ahmed, E.D. Bourret- 12. Courchesne, N.Y. Li and J. Cheng, J. Elec. Mat., 29 (2000) 161 Acknowledgements This work was partially funded by the Technology Strategy Board (UK) under contract AF045L (ETOE II) and AM092J (PROMISE). Introduction Due to the interest in InGaAsN because of its potential to improve the performance of long wavelength lasers and 1-eV solar cells. 3,4 there is a demand for higher efficiency, higher purity nitrogen sources for use in the preferred deposition technique MOVPE. Alkylhydrazines have been investigated as such sources because their first thermal decomposition step is a facile N-N bond cleavage that allows film growth at the reduced temperatures needed to incorporate N more effectively. A variety of derivatives have been investigated (hydrazine, 5 phenylhydrazine, 2,6 methylhydrazine (MMHZ), 7 1,1-dimethylhydrazine (DMHZ), 1,4,8,9 and tertiarybutylhydrazine (TBHZ) 10,11 ) with DMHZ most commonly employed. Due to this popularity, improved purification routes and analysis techniques were developed for DMHZ 12 but little evidence for similar data on the other potential precursors is available. Application of the optimum analysis techniques identified for DMHZ to the other molecules MMHZ and TBHZ has been applied using state of the art equipment and results indicate that similar correlations between characterisation data and quantitative determination of the major impurity water can be made. The availability of a suitable high sensitivity accurate analysis technique has enabled purification technologies to be developed to remove water to low levels thus improving performance in actual MOVPE processes. Experimental Initial samples of “high purity” MMHZ and TBHZ were spiked with varying amounts of water and analysed by proton NMR on a Bruker 400MHz spectrometer. This technique was chosen as the simplest and fastest to use, and the spectra obtained were very simple to interpret. Initially neat samples were employed, however, due to spectral lock difficulties, it was found that better results were obtained when C 6 D 6 was present in the NMR tube. From prior work the FWHM of the –NH 2 peak was proposed to be influenced by hydrogen-bonded water to provide a measurable effect on the signal shape hence the attention to detail to obtain the optimum resolution and reproducibility for all sample characterisation. (See Figures 1 and 2). The spiking of MMHZ and TBHZ samples in the 10-10000ppm range was achieved by adding controlled amounts of water to bulk samples and agitating for several hours prior to sampling to ensure uniform dispersion of the contaminant. Achieving controlled levels in the 10ppm range proved dif ficult and necessitated very large sample sizes thus introducing a higher potential error. Following spiking correlation trials improve purity samples were characterised in an analogous manner. Results As expected the water signal itself was not observed in the 1H NMR traces, but there was a significant difference in the –NH 2 peak found in spectra from the different samples. The –NH 2 peak became much sharper as the water was removed. Initial trails with TBHZ covered a wide range as shown in Figure 3 whilst for the other compounds trials were limited to the lower impurity concentartion levels. The full width at half maximum (FWHM) of the relevant peaks are presented in Table 1 and plotted in Figures 3-5. The highest purity samples investigated (EpiPure) proved to have less than 10ppm water present in all cases. Improved quality alkylhydrazine precursors as determined by an enhanced sensitivity water analysis technique S. Rushworth, R. Odedra, L. Wyatt, I. Hovland SAFC Hitech Ltd, Power Road, Bromborough, Wirral, CH62 3QF, UK; e-mail: [email protected] Phone: +(44) 151 224 3774 KEY WORDS – Alkylhydrazines, MOVPE, ALD, nitrogen source, analysis. Abstract Alkylhydrazine derivatives are attractive low temperature nitrogen sources for use in MOVPE due to their reduced thermal stability compared to ammonia. In dilute nitrides (ie InGaAsN), where deposition temperatures must be markedly lower than for other nitride systems, this is a key advantage. However, quantification of contaminant levels in these compounds in the ppm range has proved difficult by normal techniques thus establishing ultimate purity, particularly for water content, requires improved technologies. Previous studies for 1,1-dimethylhydrazine {(CH 3 ) 2 N-NH 2 } provided a baseline methodology using 1H nuclear magnetic resonance spectroscopy (NMR), gas chromatography-atomic emission detection (GC-AED) and cryogenic mass spectroscopy (Cryogenic-MS) techniques. Detection limits of around 20-50ppm were achieved but a further increase to identify 10ppm or below levels was targeted to allow the best films to be deposited. In this work we report the extension of the NMR and GC-AED approach to other alkylhydrazine precursors. Similar relationships between water content and FWHM of the –NH 2 peak have been confirmed demonstrating the robustness of the analytical techniques. Furthermore using state-of-the-art equipment and a number of process refinements an enhanced sensitivity has been achieved such that the industry demanded detection limits can be achieved routinely. With an accurate assessment capability in place purification protocols have been optimised to remove water to below the current detection limits. The higher purity of these materials offers improved layer quality and the potential to fabricate advanced device structures. -C(CH 3 ) 3 peak FWHM -NH 2 peak Figure 1. Proton NMR spectrum for TBHZ highlighting –NH 2 peak Figure 2. Proton NMR spectrum for MMHZ with a) high and b) low water content 0.05 0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 water content (ppm) Figure 3. Correlation graph of water content vs FWHM for TBHZ Figure 4. Figure 6. Table 1. Spiked water content for TBHZ, MMHZ and DMHZ and NMR –NH 2 peak FWHM data * Actual spiking level = 5ppm and 20ppm for these samples Experimental water spiking level NH 2 NMR peak FWHM TBHZ MMHZ DMHZ 10ppm Void 0.01268 0.0064* 25ppm 0.02191 0.01378 0.0113* 50ppm 0.02223 0.01667 0.0292 100ppm 0.02896 0.01802 0.0572 EpiPure sample 0.01936 0.01311 0.00752 FWHM of -NH 2 peak in NMR in ppm FWHM of -NH 2 peak in NMR in ppm FWHM of -NH 2 peak in NMR in ppm
Transcript of Improved Quality Alkylhydrazine Precursors - Sigma …. Rushworth, R. Odedra, L. Wyatt, I. Hovland...
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Figure 5.
Discussion
The correlation between the FWHM of the –NH2 peak in the NMR to the calculated spiking level established experimentally was found to be very high. The range in FWHM values obtained for the TBHZ 20-10000ppm water content samples allowed a line plot to be made that could be extrapolated to lower and higher water contents giving a quick and simple way of using NMR to measure the water levels in alkylhydrazines. It should be noted that the correlation plot was not linear but exponential in nature with only very small change in the FWHM values observed for the driest samples. At the low ppm range the correlation line was found to fi t a linear relationship. Similarly for the MMHZ a line plot suitable for determining water content of samples from FWHM values in a quantitative manner was produced. In prior work the NMR detection limit for DMHZ was stated as 50ppm however in this study with a higher sensitivity NMR tool the detection limit was markedly reduced to less than 10ppm.
ConclusionsFor the fi rst time a correlation between the quantity of water in methylhydrazine and tertiarybutylhydrazine and the full width half maximum of the –NH2 peak in the 1H NMR spectrum. The highest purity tertiarybutylhydrazine obtained has been reported with <10 ppm of water by extrapolation of the experimental results. These high purity alkylhydrazines may now be used to grow GaInNAs for laser diode fabrication with reduced threshold current density compared to devices deposited using water contaminated precursors.
ReferencesS. Miyoshi, K. Onabe, N. Oohkouchi, H. Yaguchi, R.I to, S. Fukatsu and Y. Shiyaki, 1. J. Cryst. Growth, 124 (1992) 439.
S. Akram and I. Bhat, 2. J. Cryst. Growth, 138 (1994) 105.
A. Ougazzaden, Y. Le Bellego, E. V. K. Rao, L. Leprince, G. Patriarch and M. Juhel, 3. EW MOVPE VII, Berlin, 1997, A7.
D. J. Friedman, J. F. T. Geist, S. R. Kurtz and J. M. Olson, 4. J. Cryst. Growth, 195 (1998) 409.
D. K. Gaskill, N. Bottka and M. C. Lin, 5. Appl. Phys. Lett., 48 (1986) 1449.
G. Zhang et al, 6. J. Cryst. Growth, 128 (1993) 536.
H. Tsuchiya, A. Tageuchi, M. Kurihara and F. Hasegawa, 7. J. Cryst. Growth, 152 (1995) 21.
S. Yoshida and J. Suzuki, 8. J. Cryst. Growth, 191 (1998) 279.
A. Ougazzaden, Y. Le Bellego, E.V. K. Rao, M. Juhel, L. Leprince and G. Patriarche, 9. Appl. Phys Lett., 70 (1997) 2861.
O. W. Pohl, K. Knorr, C. Möller, U. Gernert, W. Richter, J. Blasing, J. Christen, J. Gottfriedsen and H. Schumann, Jpn. 10. J. Appl. Phys., 38 (1999) L1007.
O. W. Pohl, C. Möller, K. Knorr, W. Richter, J. Gottfriedsen, H. Schumann, K. Rademann and A. Fielicke, 11. Mat. Sci. and Eng., B, 59 (1999) 20.
R. Odedra, L.M. Smith, S.A. Rushworth, M.S. Ravetz, J. Clegg, R. Kanjolia, S.J.C. Irvine, M.U. Ahmed, E.D. Bourret-12. Courchesne, N.Y. Li and J. Cheng, J. Elec. Mat., 29 (2000) 161
AcknowledgementsThis work was partially funded by the Technology Strategy Board (UK) under contract AF045L (ETOE II) and AM092J (PROMISE).
IntroductionDue to the interest in InGaAsN because of its potential to improve the performance of long wavelength lasers and 1-eV solar cells.3,4 there is a demand for higher effi ciency, higher purity nitrogen sources for use in the preferred deposition technique MOVPE. Alkylhydrazines have been investigated as such sources because their fi rst thermal decomposition step is a facile N-N bond cleavage that allows fi lm growth at the reduced temperatures needed to incorporate N more effectively. A variety of derivatives have been investigated (hydrazine,5 phenylhydrazine,2,6 methylhydrazine (MMHZ),7 1,1-dimethylhydrazine (DMHZ),1,4,8,9 and tertiarybutylhydrazine (TBHZ)10,11) with DMHZ most commonly employed. Due to this popularity, improved purifi cation routes and analysis techniques were developed for DMHZ12 but little evidence for similar data on the other potential precursors is available.
Application of the optimum analysis techniques identifi ed for DMHZ to the other molecules MMHZ and TBHZ has been applied using state of the art equipment and results indicate that similar correlations between characterisation data and quantitative determination of the major impurity water can be made. The availability of a suitable high sensitivity accurate analysis technique has enabled purifi cation technologies to be developed to remove water to low levels thus improving performance in actual MOVPE processes.
ExperimentalInitial samples of “high purity” MMHZ and TBHZ were spiked with varying amounts of water and analysed by proton NMR on a Bruker 400MHz spectrometer. This technique was chosen as the simplest and fastest to use, and the spectra obtained were very simple to interpret. Initially neat samples were employed, however, due to spectral lock diffi culties, it was found that better results were obtained when C6D6 was present in the NMR tube. From prior work the FWHM of the –NH2 peak was proposed to be infl uenced by hydrogen-bonded water to provide a measurable effect on the signal shape hence the attention to detail to obtain the optimum resolution and reproducibility for all sample characterisation. (See Figures 1 and 2).
The spiking of MMHZ and TBHZ samples in the 10-10000ppm range was achieved by adding controlled amounts of water to bulk samples and agitating for several hours prior to sampling to ensure uniform dispersion of the contaminant. Achieving controlled levels in the 10ppm range proved diffi cult and necessitated very large sample sizes thus introducing a higher potential error.
Following spiking correlation trials improve purity samples were characterised in an analogous manner.
Results
As expected the water signal itself was not observed in the 1H NMR traces, but there was a signifi cant difference in the –NH2 peak found in spectra from the different samples. The –NH2 peak became much sharper as the water was removed. Initial trails with TBHZ covered a wide range as shown in Figure 3 whilst for the other compounds trials were limited to the lower impurity concentartion levels. The full width at half maximum (FWHM) of the relevant peaks are presented in Table 1 and plotted in Figures 3-5. The highest purity samples investigated (EpiPure) proved to have less than 10ppm water present in all cases.
Improved quality alkylhydrazine precursors as determined by an enhanced sensitivity water analysis technique
S. Rushworth, R. Odedra, L. Wyatt, I. HovlandSAFC Hitech Ltd, Power Road, Bromborough, Wirral, CH62 3QF, UK; e-mail: [email protected] Phone: +(44) 151 224 3774KEY WORDS – Alkylhydrazines, MOVPE, ALD, nitrogen source, analysis.
AbstractAlkylhydrazine derivatives are attractive low temperature nitrogen sources for use in MOVPE due to their reduced thermal stability compared to ammonia. In dilute nitrides (ie InGaAsN), where deposition temperatures must be markedly lower than for other nitride systems, this is a key advantage. However, quantifi cation of contaminant levels in these compounds in the ppm range has proved diffi cult by normal techniques thus establishing ultimate purity, particularly for water content, requires improved technologies. Previous studies for 1,1-dimethylhydrazine {(CH3)2N-NH2} provided a baseline methodology using 1H nuclear magnetic resonance spectroscopy (NMR), gas chromatography-atomic emission detection (GC-AED) and cryogenic mass spectroscopy (Cryogenic-MS) techniques. Detection limits of around 20-50ppm were achieved but a further increase to identify 10ppm or below levels was targeted to allow the best fi lms to be deposited.
In this work we report the extension of the NMR and GC-AED approach to other alkylhydrazine precursors. Similar relationships between water content and FWHM of the –NH2 peak have been confi rmed demonstrating the robustness of the analytical techniques. Furthermore using state-of-the-art equipment and a number of process refi nements an enhanced sensitivity has been achieved such that the industry demanded detection limits can be achieved routinely. With an accurate assessment capability in place purifi cation protocols have been optimised to remove water to below the current detection limits. The higher purity of these materials offers improved layer quality and the potential to fabricate advanced device structures.
-C(CH3)3 peak
FWHM
-NH2 peak
Figure 1. Proton NMR spectrum for TBHZ highlighting –NH2 peak
Figure 2. Proton NMR spectrum for MMHZ with a) high and b) low water content
0.05
0.06
0.07
0.08
0.09
0.1
0.11
0.12
0.13
0.14
0.15
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
water content (ppm)
Figure 3. Correlation graph of water content vs FWHM for TBHZ
Figure 4.
Figure 6.
Table 1. Spiked water content for TBHZ, MMHZ and DMHZ and NMR –NH2 peak FWHM data
* Actual spiking level = 5ppm and 20ppm for these samples
Experimental water spiking level
NH2 NMR peak FWHM
TBHZ MMHZ DMHZ
10ppm Void 0.01268 0.0064*
25ppm 0.02191 0.01378 0.0113*
50ppm 0.02223 0.01667 0.0292
100ppm 0.02896 0.01802 0.0572
EpiPure sample 0.01936 0.01311 0.00752
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-NH
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HM
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-NH
2 p
eak
inN
MR
in p
pm
FW
HM
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-NH
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eak
inN
MR
in p
pm
