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Vapour pressure measurement of low volatility precursors
Microelectronics Reliability 45 (2005) 1000–1002 www.elsevier.com/locate/microrel
Vapour pressure measurement of low volatility precursors S.A. Rushworth
b
a,*
, L.M. Smith a, A.J. Kingsley a, R. Odedra a, R. Nickson b, P. Hughes b
a Epichem Limited, Power Road, Bromborough, Wirral, CH62 3QF, UK MKS Instruments UK Ltd, 1 Ancorage Court, Caspian Road, Altrincham, Cheshire, WA14 5HH, UK
Received 28 June 2004; received in revised form 29 September 2004 Available online 20 December 2004
Abstract The introduction of new chemicals into semiconductor production processes is an expensive, time consuming exercise. A key parameter required to ensure equipment set up is well suited to the source from the outset of trials is reliable precursor volatility data. In this paper we present details of a newly commissioned vapour pressure (VP) measurement system and latest vapour pressure values for the technologically interesting Hf and Ta precursors pentakis(dimethylamido)tantalum (PDMAT) and tetrakis(ethylmethylamido)hafnium (TEMAH). Calibration data is also presented to illustrate the accuracy of the equipment. Ó 2004 Elsevier Ltd. All rights reserved.
1. Introduction The increasing interest in the fabrication of new materials for next generation semiconductor devices has led to the desire to test numerous novel compounds. These new chemicals include sources for high k and barrier layers and a key parameter in the selection of a precursor suited to chemical vapour deposition (CVD) or atomic layer deposition (ALD) or a number of other techniques is its vapour pressure (VP). It must be possible to Ôpick upÕ a chemical and transport it at sufficient rate to the deposition chamber to allow a process to be studied. Obviously if the source remains in its supply container it is not useable. The use of elevated source
*
Corresponding author. Tel.: +44 151 334 2774; fax: +44 151 334 2774/6422. E-mail address: [email protected] (S.A. Rushworth).
temperatures to increase gas phase concentrations entering the deposition chamber is feasible but again the vapour pressure is needed to predict the desired conditions and allow process investigation to be performed more readily. However, to establish accurate vapour pressure data for this type of new source material is not a trivial exercise, as demonstrated by the fluctuation in literature values for even well known CVD precursors [1–3], especially when the volatility range in question is low. To meet this customer requirement the development and installation of equipment capable of providing the desired information in a reliable fashion has been addressed. Commissioning of the measurement system has been performed using naphthalene due to its availability to high purity and the well reported vapour pressure data reported in the literature [4–6]. Subsequent trials using oxide and nitride CVD sources have begun and preliminary data on a Ta precursor (PDMAT) and a Hf precursor (TEMAH) is presented.
0026-2714/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.microrel.2004.11.007
S.A. Rushworth et al. / Microelectronics Reliability 45 (2005) 1000–1002
1001
plete. At high temperatures decomposition can also contribute making result interpretation more difficult. Once a steady reading has been recorded the temperature is raised and allowed to equilibrate before repeating the process to get a second point. The temperature is raised again to get a third and so on until a maximum temperature is reached. The series may then be performed in reverse to ensure product degradation has not occurred and also to check the validity of the first recorded results.
Fig. 1. Schematic of vapour pressure equipment. Grey line defines the oven enclosure.
4. Results 4.1. Calibration with naphthalene
Fig. 2. Picture of vapour pressure system.
The requirement to wait for system stabilisation is highlighted in Fig. 3 which shows the indicated vapour pressure (VP) variation with time at a fixed temperature of 54.3 °C for naphthalene. A dramatic change is seen in the first stage of the experiment indicating severe out gassing however this plateaus at a steady reading thereafter. Similar graphs have been obtained for each of the different temperatures studied to ensure the data plotted in a composite graph is representative of the true stable vapour pressure of the material in question. This degree of reliability is key to allow the correct VP equation to be calculated. Fig. 4 shows the composite graph for 800
2. Equipment Pressure (mTorr)
The key sections of the system are located inside an oven to ensure uniform heating of all parts is achieved to prevent condensation errors. The sample chamber is attached to a vacuum manifold equipped with a BaratronTM pressure measurement gauge and a second BaratronTM is located outside the oven along with the computer connections etc. The construction material is stainless steel with high integrity joints throughout. (Details of the layout are provided in Figs. 1 and 2.)
700 600 500 400 300 200 100 0
0
1
2
3
4
6
7
8
9 10
11 12 13 14 15
Time (hrs)
Fig. 3. VP reading variation for naphthalene at 54.3 °C.
3. Experimental
Experiment
0 0.003 -0.1 Lo g P (Torr)
The sample for study is placed in the test chamber and vacuum applied to remove inert atmosphere process gas. It should be noted that out gassing from the sample is of critical importance when investigating vapour pressure measurement, especially in the less than 1 Torr range as presented here. Also a leak test is performed prior to any data being recorded for the sample. The first temperature for trial is established and readings taken over several minutes to establish an accurate, stable value. Results 100–200% too high can be obtained if this waiting period is excluded and out gassing is not fully com-
5
0.00305
0.0031
Literature
0.00315
0.0032
0.00325
-0.2 -0.3 -0.4 -0.5 -0.6 -0.7 1/T (K)
Fig. 4. VP curve for naphthalene including literature values.
1002
S.A. Rushworth et al. / Microelectronics Reliability 45 (2005) 1000–1002 1000 Vapour Pressure (mTorr)
Vapour Pressure (mTorr)
100
10
1 25
30
35
40
45
50
55
60
100
10
1 25
30
35
40
45
50
55
60
65
70
Temperature (C)
Temperature (C)
Fig. 5. VP curve for PDMAT.
Fig. 6. VP curve for TEMAH.
naphthalene in the temperature range 40–55 °C. Also plotted is the literature vapour pressure values and it can be seen that the experimental data is in good agreement with previously published data [4–6]. The vapour pressure equation for naphthalene can be calculated from the points recorded in Fig. 4 resulting in Eq. (1)
The vapour pressure equation for TEMAH can be calculated from the points recorded in Fig. 6 resulting in Eq. (3)
log10 ðP Þ ¼ 2983:1=T þ 8:969
ð1Þ
P is the pressure in Torr, T is the temperature in K. 4.2. Pentakis(dimethylamido)tantalum The first precursor studied was pentakis(dimethylamido)tantalum (PDMAT) due to the interest in its use in CVD and ALD technologies to deposit a variety of TaN and Ta2O3 layers useful in new device structures. The vapour pressure plot for this compound is shown in Fig. 5. The vapour pressure equation for PDMAT can be calculated from the points recorded in Fig. 5 resulting in Eq. (2) log10 ðP Þ ¼ 4124:9=T þ 11:265
ð2Þ
P is the pressure in Torr, T is the temperature in K. 4.3. Tetrakis(ethylmethylamido)hafnium The second precursor to be evaluated was tetrakis(ethylmethylamido)hafnium (TEMAH) due to interest in its use in the CVD and ALD of HfO2 layers as high k gate dielectrics in next generation semiconductor devices. The vapour pressure plot for this compound is shown in Fig. 6.
log10 ðP Þ ¼ 3432:3=T þ 9:447
ð3Þ
P is the pressure in Torr, T is the temperature in K.
5. Conclusion A vapour pressure measurement system has been successfully commissioned and employed to provide key data on novel precursors to enable customer deposition process development to proceed based on accurate data. Measurements for PDMAT and TEMAH have been recorded and further compounds will be investigated in the future to extend the knowledge base in this area.
References [1] Fulem M et al. Vapour pressure of metalorganic precursors. J Cryst Growth 2003;248:99–107. [2] Griffiths CL et al. Dynamic vapour pressure measurements of the dimethyl zinc triethylamine adduct using an ultrasonic monitor. Appl Phys Lett 1996;68(9):1294–6. [3] Kayser O et al. Vapour pressure of MOCVD precursors. Chemtronics 1988;3:90–3. [4] Camin DL, Rossine FD. Physical properties of 14 American petroleum institute research hydrocarbons C9 to C15. J Phys Chem 1955;59:1173–9. [5] Fowler L, Trump NW. Vapour pressure of naphthalene. New measurements between 40 °C and 180 °C. J Chem Eng Data 1968;13(2):209–10. [6] Handbook of Chemistry and Physics, 80th ed., ISBN 0849304806. p. 6–87.
Vapour pressure measurement of low volatility precursors S.A. Rushworth
b
a,*
, L.M. Smith a, A.J. Kingsley a, R. Odedra a, R. Nickson b, P. Hughes b
a Epichem Limited, Power Road, Bromborough, Wirral, CH62 3QF, UK MKS Instruments UK Ltd, 1 Ancorage Court, Caspian Road, Altrincham, Cheshire, WA14 5HH, UK
Received 28 June 2004; received in revised form 29 September 2004 Available online 20 December 2004
Abstract The introduction of new chemicals into semiconductor production processes is an expensive, time consuming exercise. A key parameter required to ensure equipment set up is well suited to the source from the outset of trials is reliable precursor volatility data. In this paper we present details of a newly commissioned vapour pressure (VP) measurement system and latest vapour pressure values for the technologically interesting Hf and Ta precursors pentakis(dimethylamido)tantalum (PDMAT) and tetrakis(ethylmethylamido)hafnium (TEMAH). Calibration data is also presented to illustrate the accuracy of the equipment. Ó 2004 Elsevier Ltd. All rights reserved.
1. Introduction The increasing interest in the fabrication of new materials for next generation semiconductor devices has led to the desire to test numerous novel compounds. These new chemicals include sources for high k and barrier layers and a key parameter in the selection of a precursor suited to chemical vapour deposition (CVD) or atomic layer deposition (ALD) or a number of other techniques is its vapour pressure (VP). It must be possible to Ôpick upÕ a chemical and transport it at sufficient rate to the deposition chamber to allow a process to be studied. Obviously if the source remains in its supply container it is not useable. The use of elevated source
*
Corresponding author. Tel.: +44 151 334 2774; fax: +44 151 334 2774/6422. E-mail address: [email protected] (S.A. Rushworth).
temperatures to increase gas phase concentrations entering the deposition chamber is feasible but again the vapour pressure is needed to predict the desired conditions and allow process investigation to be performed more readily. However, to establish accurate vapour pressure data for this type of new source material is not a trivial exercise, as demonstrated by the fluctuation in literature values for even well known CVD precursors [1–3], especially when the volatility range in question is low. To meet this customer requirement the development and installation of equipment capable of providing the desired information in a reliable fashion has been addressed. Commissioning of the measurement system has been performed using naphthalene due to its availability to high purity and the well reported vapour pressure data reported in the literature [4–6]. Subsequent trials using oxide and nitride CVD sources have begun and preliminary data on a Ta precursor (PDMAT) and a Hf precursor (TEMAH) is presented.
0026-2714/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.microrel.2004.11.007
S.A. Rushworth et al. / Microelectronics Reliability 45 (2005) 1000–1002
1001
plete. At high temperatures decomposition can also contribute making result interpretation more difficult. Once a steady reading has been recorded the temperature is raised and allowed to equilibrate before repeating the process to get a second point. The temperature is raised again to get a third and so on until a maximum temperature is reached. The series may then be performed in reverse to ensure product degradation has not occurred and also to check the validity of the first recorded results.
Fig. 1. Schematic of vapour pressure equipment. Grey line defines the oven enclosure.
4. Results 4.1. Calibration with naphthalene
Fig. 2. Picture of vapour pressure system.
The requirement to wait for system stabilisation is highlighted in Fig. 3 which shows the indicated vapour pressure (VP) variation with time at a fixed temperature of 54.3 °C for naphthalene. A dramatic change is seen in the first stage of the experiment indicating severe out gassing however this plateaus at a steady reading thereafter. Similar graphs have been obtained for each of the different temperatures studied to ensure the data plotted in a composite graph is representative of the true stable vapour pressure of the material in question. This degree of reliability is key to allow the correct VP equation to be calculated. Fig. 4 shows the composite graph for 800
2. Equipment Pressure (mTorr)
The key sections of the system are located inside an oven to ensure uniform heating of all parts is achieved to prevent condensation errors. The sample chamber is attached to a vacuum manifold equipped with a BaratronTM pressure measurement gauge and a second BaratronTM is located outside the oven along with the computer connections etc. The construction material is stainless steel with high integrity joints throughout. (Details of the layout are provided in Figs. 1 and 2.)
700 600 500 400 300 200 100 0
0
1
2
3
4
6
7
8
9 10
11 12 13 14 15
Time (hrs)
Fig. 3. VP reading variation for naphthalene at 54.3 °C.
3. Experimental
Experiment
0 0.003 -0.1 Lo g P (Torr)
The sample for study is placed in the test chamber and vacuum applied to remove inert atmosphere process gas. It should be noted that out gassing from the sample is of critical importance when investigating vapour pressure measurement, especially in the less than 1 Torr range as presented here. Also a leak test is performed prior to any data being recorded for the sample. The first temperature for trial is established and readings taken over several minutes to establish an accurate, stable value. Results 100–200% too high can be obtained if this waiting period is excluded and out gassing is not fully com-
5
0.00305
0.0031
Literature
0.00315
0.0032
0.00325
-0.2 -0.3 -0.4 -0.5 -0.6 -0.7 1/T (K)
Fig. 4. VP curve for naphthalene including literature values.
1002
S.A. Rushworth et al. / Microelectronics Reliability 45 (2005) 1000–1002 1000 Vapour Pressure (mTorr)
Vapour Pressure (mTorr)
100
10
1 25
30
35
40
45
50
55
60
100
10
1 25
30
35
40
45
50
55
60
65
70
Temperature (C)
Temperature (C)
Fig. 5. VP curve for PDMAT.
Fig. 6. VP curve for TEMAH.
naphthalene in the temperature range 40–55 °C. Also plotted is the literature vapour pressure values and it can be seen that the experimental data is in good agreement with previously published data [4–6]. The vapour pressure equation for naphthalene can be calculated from the points recorded in Fig. 4 resulting in Eq. (1)
The vapour pressure equation for TEMAH can be calculated from the points recorded in Fig. 6 resulting in Eq. (3)
log10 ðP Þ ¼ 2983:1=T þ 8:969
ð1Þ
P is the pressure in Torr, T is the temperature in K. 4.2. Pentakis(dimethylamido)tantalum The first precursor studied was pentakis(dimethylamido)tantalum (PDMAT) due to the interest in its use in CVD and ALD technologies to deposit a variety of TaN and Ta2O3 layers useful in new device structures. The vapour pressure plot for this compound is shown in Fig. 5. The vapour pressure equation for PDMAT can be calculated from the points recorded in Fig. 5 resulting in Eq. (2) log10 ðP Þ ¼ 4124:9=T þ 11:265
ð2Þ
P is the pressure in Torr, T is the temperature in K. 4.3. Tetrakis(ethylmethylamido)hafnium The second precursor to be evaluated was tetrakis(ethylmethylamido)hafnium (TEMAH) due to interest in its use in the CVD and ALD of HfO2 layers as high k gate dielectrics in next generation semiconductor devices. The vapour pressure plot for this compound is shown in Fig. 6.
log10 ðP Þ ¼ 3432:3=T þ 9:447
ð3Þ
P is the pressure in Torr, T is the temperature in K.
5. Conclusion A vapour pressure measurement system has been successfully commissioned and employed to provide key data on novel precursors to enable customer deposition process development to proceed based on accurate data. Measurements for PDMAT and TEMAH have been recorded and further compounds will be investigated in the future to extend the knowledge base in this area.
References [1] Fulem M et al. Vapour pressure of metalorganic precursors. J Cryst Growth 2003;248:99–107. [2] Griffiths CL et al. Dynamic vapour pressure measurements of the dimethyl zinc triethylamine adduct using an ultrasonic monitor. Appl Phys Lett 1996;68(9):1294–6. [3] Kayser O et al. Vapour pressure of MOCVD precursors. Chemtronics 1988;3:90–3. [4] Camin DL, Rossine FD. Physical properties of 14 American petroleum institute research hydrocarbons C9 to C15. J Phys Chem 1955;59:1173–9. [5] Fowler L, Trump NW. Vapour pressure of naphthalene. New measurements between 40 °C and 180 °C. J Chem Eng Data 1968;13(2):209–10. [6] Handbook of Chemistry and Physics, 80th ed., ISBN 0849304806. p. 6–87.