行政院國家科學委員會專題研究計畫 成果報告
製備合成氧化物在互補式金氧半閘極介電層及自旋電元件
應用之研究
計畫類別： 個別型計畫 計畫編號： NSC91-2215-E-009-037- 執行期間： 91 年 08 月 01 日至 92 年 09 月 30 日 執行單位： 國立交通大學電子物理學系 計畫主持人： 趙天生 計畫參與人員： 陳建豪 報告類型： 完整報告 報告附件： 國際合作計畫研究心得報告 處理方式： 本計畫可公開查詢中 華 民 國 92 年 11 月 20 日
行政院國家科學委員會專題研究計畫成果報告
製備合成氧化物在互補式金氧半閘極介電層及自旋電元件應用之研究
Deposition and Characterization of Compound Oxide Films for High-
κ
CMOS Gate Dielectrics and Spintronics Applications
計劃編號: NSC-91-2215-E-009-037 執行期間: 91/8/1~92/9/30
主持人：趙天生 交通大學電子物理系 教授
E-mail: [email protected]
ABSTRACT
In this study, we use metal-organic chemical vapour deposition (MOCVD) to fabricate hafnium oxides on silicon. An oxygen-free precursor, TDEAH (tetrakis diethylamido hafnium), was used in film deposition, with nitric oxide (NO) or oxygen (O2) as oxidant gas.
Nitrogen incorporation up to 11% in atomic ratio was obtained in NO oxidized films.
Hafnium silicate films were deposited using TDEAH and TDMAS (tetrakis dimethylamido silicon). Silane (SiH4) was also examined to replace
TDMAS as the silicon precursor. TDMAS needs higher temperature for surface decomposition, while SiH4 can
be used with lower temperature in deposition. When using SiH4, however,
further study is required to enhance silicon incorporation and eliminate particular generation.
1. Introduction
Due to the needs of device scaling,
traditional gate-dielectric material, SiO2,
was thinned to obtain higher coupling capacitance. However, with thinner and thinner oxide films, tunneling currents dominate the gate-leakage and SiO2
loses its insulating property. Thus, the requirement turns to finding an alternative high dielectric constant (high-κ) material as the gate dielectric.
Materials with a higher dielectric constant than SiO2 can be made thicker
while preserving the same capacitance per unit area, thus reducing the leakage current significantly. The new high-κ
material should have adequate band-gap energy and a high barrier height with a low interface-state density on silicon. Film morphology, CMOS-related process compatibility, and reliability are other important issues. [1]
In this project, MOCVD was utilized to deposit hafnium oxide and hafnium silicate. For MOCVD, alkoxide precursors are often used. A recent review [2] describing the latest precursors for ZrO2 deposition points out that using
oxygen-containing precursors invariably results in a SiO2-rich interfacial layer at
the Si interface. This has been our experience with mixed alkoxide β-diketonate precursors for Zr and Si. [3] Therefore, we decided to use precursors with amide ligands, which contain no oxygen. TDEAH, [(C2H5)2N]4Hf, and
TDMAS, [(CH3)2N]4Si, were used for
Hf and Si precursors, respectively. In MOCVD process, oxidants are needed to form oxides or silicates; O2 and NO
were used for this purpose.
2. Experiments
After an HF-last RCA clean, 4-inch p-type (100) wafers were sent into the MOCVD chamber for film deposition. The chamber is equipped with a liquid injection system (ATMI LDS-300B) for introducing precursors (Fig.1). An
in-situ ellipsometer (Rudolph 1000i) is
added to the MOCVD chamber in order to monitor the growth rate of oxides or silicates.
Fig.1 MOCVD chamber is equipped with a liquid injection system and a vaporizer. The sample wafer is face-down, sitting on a quartz ring, and heated by a set of halogen lamps.
During hafnium-oxide deposition, 0.1 M TDEAH solution was pumped at a rate of 0.2 ml/min and was vaporized while passing through the vaporizer, accompanied by a flow of 50 sccm Ar. The vaporizer was held at 150°C, as well as the lines into the deposition chamber and the gas distribution ring.
The oxidants, either O2 or NO,
were introduced into a separate gas distribution ring at a flow rate of 150 sccm. In the pulse-mode deposition we utilized, each deposition cycle consisted of 4 steps: a precursor (with Ar) introduction, a pump-down, an oxidant introduction, and another pump-down. A flow of 100 sccm N2 was maintained
throughout the deposition cycle. The total deposition pressure was in the range 3~11 mTorr where gas-phase collisions are rare. The sample stage temperature was controlled with a quartz-halogen heater-thermocouple combination. The base pressure of the MOCVD chamber was about 10-8 Torr. The deposition temperature was held at 400°C for the hafnium oxide deposition.
For the hafnium-silicate deposition, 0.1 M TDEAH and 0.3 M TDMAS solutions were mixed and then pumped through the vaporizer. The relative ratio of TDEAH versus TDMAS was tunable, and was held constant during film deposition. The vaporizer temperature was 150°C. Deposition temperature was set to be 500°C or 550°C when TDMAS was used.
tested for hafnium-silicate deposition. In a pulse-mode deposition cycle, we introduced 10 sccm SiH4 flow either in
the TDEAH introduction step, or in the O2 introduction step. When SiH4 was
used, the deposition temperature was held at 350°C, 375°C, or 400°C.
After film deposition, an in-situ rapid thermal anneal (RTA) was performed. The wafer was spike annealed at 800°C, while the chamber pressure was kept around 10-8 Torr.
Auger electron spectroscopy (AES)
and in-situ X-ray photoelectron
spectroscopy (XPS) were used to analyze the composition of hafnium oxide or hafnium silicate films. By proper calculation, atomic ratios of elements can be extracted from XPS results.
For micro-structural investigation, high resolution transmission electron microscopy (HRTEM) was utilized. The thermal stability of hafnium oxide or hafnium silicate was evaluated by investigating the crystallization behavior after RTA.
3. Results and Discussion
A. Hafnium oxinitride
Nitrogen incorporation was found in all hafnium oxide films, no matter oxidized by O2 or NO during deposition.
In those films deposited with O2, the
incorporated nitrogen can be attributed to the amide ligands in TDEAH. According to the calculation based on XPS results, the average nitrogen
composition was 4 at. % for films deposited with O2 and 11 at. % for those
deposited with NO. AES analysis in Fig.2 also provides evidence of nitrogen incorporation. In HRTEM images (Fig.3), retarded crystallization was observed in films with higher nitrogen incorporation. 0 5 10 15 20 25 0 20 40 60 80 100 At om ic Conc ent rat ion Sputter Time C 1s N 1s O 1s Si_Sub Hf 4f
Fig.2 AES depth profile of a 15 nm HfOxNy film
(a)
(b)
Fig.3 Cross-sectional HRTEM of HfOxNy films
annealed at 600°C for 1 minute in oxygen ambient. Crystallized regions were found in
HfOxNy deposited with O2
HfOxNy
HfOxNy deposited with NO
Interface
Si substrate
B. Hafnium silicates (with TDMAS) The composition [Hf]/([Hf]+[Si]) of the films is shown in Fig.4. At a substrate temperature of 500°C, the amount of hafnium in the films initially decreases as the TDMAS percentage in the precursor mixture increases but levels off at ~60% (i.e. silicon amount increases and levels off at ~40%). Increasing the Si precursor above 80% of the total precursor solution did not increase the silicon concentration further. Increasing the TDMAS percentage in the precursor mixture causes another drawback of lowering deposition rate, which is shown in Fig.5. The silicon concentration achieved in this study is much smaller than reported in reference [4], which is done at a much higher pressure (8 Torr). This suggests that the incorporation of silicon at high pressure is activated by gas-phase rather than surface reactions.
Fig.4 Composition (squares) obtained by in-situ XPS and root-mean-squared roughness (circles) obtained by AFM as a function of the fraction of TDMAS in the precursor mixture for silicate films deposited using TDMAS and TDEAH.
Fig.5 Interface layer thickness (squares) obtained by HRTEM and deposition rate (circles) as a function of the fraction of TDMAS in the precursor mixture for silicate films deposited using TDMAS and TDEAH.
Fig.6 Cross-sectional HRTEM image of the Hf0.6Si0.4O2 film deposited at 550°C using a
precursor mixture of 20% TDEAH and 80% TDMAS, with O2 as the oxidant.
C. Hafnium silicates (with SiH4)
Table1 summarizes the silicon amount in hafnium silicate films deposited using TDEAH and SiH4 with O2.
Table1: [Si]/([Si]+[Hf]) ratios in silicate films
SiH4 was introduced 400°C 375°C 350°C
with O2 0.12 0.19 0.16
with TDEAH 0.1 n/a n/a
with dilute TDEAH 0.16 n/a n/a Epoxy
4.59 nm
Si substrate 2.38 nm
The silicon concentration could not be effectively increased. Higher silicon concentration was obtained when SiH4
was introduced with dilute TDEAH (0.02 M TDEAH, diluted with octane). However, the deposition rate was dramatically decreased with dilute TDEAH precursor.
Although the silicon concentration in hafnium silicate films deposited with SiH4 is low, the deposition temperature
can be reduced to 400°C, as being used in hafnium oxide deposition with TDEAH. Tetra-ethoxy silane (TEOS) was reported to be used in MOCVD hafnium silicate.[5] However, the temperature TEOS needs for surface decomposition is a concern.
4. Conclusions
Hafnium oxinitride films with 11 % nitrogen in atomic ratio were deposited using TDEAH with NO gas. TDEAH and NO gas were introduced in separate steps of a pulse-mode MOCVD process. With nitrogen incorporation, the films showed higher crystallization temperature, and were less likely to interface-layer growth in air-exposure tests.
MOCVD hafnium silicate films were deposited using TDEAH and TDMAS. The silicon versus hafnium concentration ratio was increased to 4:6 by increasing TDMAS percentage in the precursor mixture, with a drawback of lowered deposition rate. However, the higher temperature needed by TDMAS for surface decomposition limits its feasibility in MOCVD uses.
In order to decrease the substrate temperature during hafnium silicate deposition, SiH4 was used as the silicon
precursor in MOCVD, but the silicon concentration in deposited films was low. With SiH4, further study is required to
optimize [Si]/([Si]+[Hf]) ratio and eliminate particulate generation.
5. Publications
[1] X. Wu, D. Landheer, M.J. Graham, H.-W. Chen, T.-Y. Huang, and T.-S. Chao, "Structure and thermal stability of MOCVD ZrO2 films
on Si(100)," Journal of Crystal Growth, 250, 479–485, 2003.
[2] H.-W. Chen, T.-Y. Huang, D. Landheer, X. Wu, S. Moisa, G. I. Sproule, J. K. Kim, W. N. Lennard, and T.-S. Chao, "Ultrathin Zirconium Silicate Films Deposited on Si(100) Using Zr(Oi-Pr)
2(thd)2, Si(Ot-Bu)2(thd)2, and
Nitric Oxide," Journal of The Electrochemical Society, 150 (7), C465-C471, 2003.
[3] X. Wu, J.-H. Chen, M.-S. Lee, S. Moisa, T.-F. Lei, T.-S. Chao, Z.-H. Lu, W.-T. Ng, and D. Landheer, "Analysis of Hafnium Silicate Films Deposited on Si (100) Using [(CH3)2N]4Si or SiH4 with O2 and NO," 11th
Canadian Semiconductor Technology Conference, 2003.
6. References
[1] G.D. Wilk et al., J. Appl. Phys., 89, 5243, 2001. (and references therein)
[2] R.C. Smith et al., Adv. Mater. Opt. Electron.,
10, 105, 2000.
[3] H.-W. Chen et al., J. Electrochem. Soc., 150, C465, 2003.
[4] B.C. Hendrix et al., Appl. Phys. Lett., 80, 2362, 2002.
