DC 마그네트론 스퍼터로 증착한 Reoxidized HfO_(2) 박막의 열처리에 따른 물리적 특성 및 전기적 특성 연구

이동원 연세대학교 대학원 2002 국내석사

DC 마그네트론 스퍼터링 방법으로 Si(100) 기판에 증착한 Hf 박막를 ∼50nm, ∼15nm, ∼10nm 두께로 증착하고 다양한 열처리 방법을 통해 Hf박막의 산화과정을 Si(100)기판과의 계면 및 박막의 미세구조 변화와 전기적 특성을 관찰하였다. Hf(∼50nm)/Si시스템과 Hf(∼15nm)/Si시스템에서 600℃이상에서의 열처리시 박막 표면의 Hf 산화반응과 더불어 Si기판에서는 Hf실리사이드 반응이 동시에 일어남을 관찰하였다. 또한, 800℃에서의 열처리 시간을 30분으로 진행하였을 때, 초기에 생성된 Hf실리사이드가 박막표면에서 확산되어 들어온 산소와 반응하여 HfO_(2)와 SiO_(2)가 형성되는 분해반응이 일어나며, 이때 생성된 Si가 산소와 반응하여 Si기판과의 계면에서 불균일하게 SiO_(2) 계면층이 형성됨을 관찰할 수 있었다. Hf(∼10nm)/Si시스템를 Vertical Furnace에서 열처리시 RMS Roughness가 크게 증가하지 않아 균일한 reoxidized HfO_(2) 박막을 얻을 수 있었다 HRTEM과 XPS분석을 통해 Hf박막을 증착 후 대기에 노출되었을 때 자연산화가 되며, 열처리를 통해 산소가 확산되어 들어와 Si기판과 반응하여 SiO_(2)계면층이 성장하여 N_(2)분위기, 800℃로 5분간 열처리한 시편의 경우 20Å 인것을 관찰하였다. CET는 51.5A˚이며 유전상수는 ∼15.5로 계산되었으며, 전하밀도는 4.07×10^(+12) #/㎠, -1V에서의 누설전류는 0.018A/㎠ 나타냈다. N_(2)분위기, 600℃에서 열처리 시간에따른 시편과 O_(2)분위기에서 열처리한 시편의 경우에도 위와 유사한 결과를 얻었다. We investigated the change of the microstructure which depended on the thickness of Hf films deposited by DC magnetron sputtering on Si substrate for gate dielectric application. Also, we estimated the electrical property. The Hf films that were reoxidized by the RTA (rapid thermal annealing) were analyzed by AFM, XRD, XPS, AES and HR-TEM. For ∼50nm thick as-deposited Hf film, the HfO_(2) layer at the surface was observed about 5nm by HR-TEM. The HfO_(2) layer increased to be 15nm at 600℃ in N_(2) ambient. Especially, the HfO_(2) grains were shown not only at the surface of the Hf film but also at the silicide(Hf_(5)Si_(4)) grain boundaries. These grains of silicides on the Si substrate were not observed at this sample that annealed at 800℃ for 30min in N_(2) ambient, due to decompositing into HfO_(2) and Si. And then the Si reacted with the oxygen that diffused from surface and accumulated on the interface of Si-substrate. We observed small grains of the HfO_(2) film due to the local crystallization of the ∼10nm as-deposited Hf films by HR-TEM. The thickness of the interfacial layer between hafnium oxide and Si substrate was about 8Å. After annealing by Furnace for increasing anneal time and temperature in N_(2) or O_(2) ambient, the thickness of interfacial layer was increased to that of as-deposited film.

CHARACTERIZATION OF INTERFACES BETWEEN HfO2 THIN FILM AND METAL ELECTRODE

김영남 성균관대학교 일반대학원 2013 국내박사

Structural characteristics and electrical properties of HfO2 single layer, Al2O3/ HfO2 bi-layer and HfO2/Al2O3/ HfO2 Stack film in MIS and MIM structure were studied in terms of the capacitance in the memory cell as a function of the thickness, annealing temperature, under layer and pre-post treatment. Characteristics of HfO2 single layer are given in Chapter 4-1. It can be understood that there is the excess Oxygen concentrations of the HfO2 films and the interfacial Hf-Silicate. The interfacial layers and HfO2 bulk films thickness was slightly decreased after annealing using RTA. Because the decrease in thickness with annealing at 650 and 750 °C for 2min might be due to the effect of densification and the removal of residual, such as excess oxygen and residual carbon using as a precursor, from the films. The carbon concentration of the HfO2 was decreased due to the depo temperature increasing and the better electrical performance, such as a smaller leakage current, at the higher deposition temperature in condition of a similar equivalent oxide thickness (EOT). A phase transition from amorphous to monoclinic of HfO2 structure can be found up to 100 Å deposition thickness, even at the as-deposited state. After RTA, we can see the phase transition from amorphous to monoclinic of HfO2 structure in annealing temperature up to 500 °C, even at the 50 Å deposition thickness. After annealing, it was observed to accumulate in grain boundaries of HfO2 at 200 Å deposition thickness sample may be present in amorphous Hf-Silicate (HfxSiyO4) phase. Properties of Al2O3/HfO2 bi layer are reported in Chapter 4-2. With postannealing 750 °C for 2min, there are Hf silicate and Al silicate phase, and a slightly partial transition from the amorphous phase to the monoclinic phase of HfO2 in the HfO2 /Al2O3 film. If PN process in the NH3 treatment using by plasma tube at 650 °C is skipped at interface between HfO2 /Al2O3 and Si-sub. It can be identified that the physically undefined intermediate layer of Hf silicate and Al silicate are a lot of created between HfO2 /Al2O3 and Si-sub. J-V data measured using the HfO2 single layer and Al2O3/HfO2 stack structure with same EOT of 26 Å. The leakage current density at -3V is 8.0 × 10−8 A/cell, 7.0 × 10−13 A/cell at the HfO2 single layer and Al2O3/HfO2 stack structure, respectively. Al2O3/HfO2 stack structure leakage current is approximately 105 times smaller than that of HfO2 single layer with same equivalent oxide thickness (EOT). And also, the leakage current at -3V is 8.0 × 10−12 A/cell, 7.0 × 10−13 A/cell at the Al2O3 single layer and Al2O3/HfO2 stack structure, respectively. Al2O3/HfO2 stack structure leakage current is approximately 101 times smaller than that of Al2O3 single layer with similar equivalent oxide thickness (EOT). Capacitance is more increased as HfO2 to Al2O3 thickness Ratio is increased. However, leakage current was rapidly increased when Al2O3 thickness is less than 25Å because of the direct tunneling problem, regardless of HfO2 thickness. The thickness of HfO2 is reduced by 5Å and the increase of the Cmin 0.5fF/Cell and 0.03 V reduction of BV are occurred, and thickness of Al2O3 is reduced by 2 Å and the increase of the Cmin 0.5fF/Cell and 0.03 V reduction of BV are occurred. Characteristics of HfO2/Al2O3 bi layer at the MIS are described in Chapter 5-1. The phenomenon that Hf-Oxide Thickness is reduced after TiCl4 treatment could be confirmed. And also, it could be noted that Hf-Aluminate created between HfO2 and Al2O3 caused by TiCl4 effect. The rms roughness of the HfO2 single layer with the TiCl4 post-treatment is 30 times larger than that of the films in HfO2/Al2O3 stack film with TiCl4 post-treatment. In case of TiCl4 Based PECVD, the thickness of HfNx and HfO2 more decreased than PVD, caused by TiCl4 effect between TiN and HfO2 interface. HfNx more created caused by NH3 preflow, and also this layer was affected reaction barrier layer to TiCl4. In PECVD sample, TiOx peak more increase at the TiN/HfO2 single layer interface. It should be noted that TiO2 created between TiN and HfO2 caused by TiCl4 effect of oxygen molecular dissociation of HfO2. However, it may be confirmed that HfO2 vacancy created due to TiO2 creation in single HfO2 film. HfO2 vacancy at the HfO2 film may be more disadvantageous in terms of electrical properties such as leakage current and low equivalent oxide thickness due to non stoichiometry. Properties of HfO2/Al2O3 bi layer at the MIM are discussed in Chapter 5-2. It was confirmed that Carbon and Oxygen in TiN decrease due to Plasma Power increase, and the thickness of TiN was decreased due to the Plasma power increase. And also HfNx was observed. In particular, a significant source of defects in this system is the interface between TiN and HfO2, which has been shown to consist of HfNx with dielectric constant lower than that of HfO2. Therefore, It may be noted that HfNx is defect material which is more disadvantageous in terms of electrical properties, such as equivalent oxide thickness and leakage current. Equivalent oxide thickness of MIM Al2O3/HfO2 stack structure is approximately 1.5 times smaller than that of MIS Al2O3/HfO2 stack structure at the same leakage current. Characteristics of HfO2/Al2O3/HfO2 stack films at the MIM are given in Chapter 5-3. The results suggest that the local crystallization is much more pronounced for the sample annealed at 550 ˚C than at 500 ˚C. It was confirmed by HRTEM diffraction pattern analysis that the crystal structures of the HfO2 dielectric films were monoclinic HfO2, [(111)- or (11-1)- oriented] and cubic HfO2, [(111)- oriented]. The TEM crystal structure data clearly showed that the leakage current in the I-V measurement of the TiN/HfO2/Al2O3/HfO2/TiN device rapidly increased owing to the distinct local crystallization created at interface between the HfO2 films and the TiN bottom electrode. Leakage current of the 500 ˚C annealing temperature is approximately 2.5 times smaller than that of 550 ˚C annealing temperature of the TiN/ HfO2/Al2O3/ HfO2/TiN structure. The characterization of interfaces between HfO2 and TiN with pre-post treatments is discussed in Chapter 6. HfO2/TiN structure after O3 feeding treatments, confirming that the C impurity intensity inside the HfO2 films gradually decreases with increasing O3 feeding time. Good leakage current properties were observed when the O3 feeding time increased. The decrease in peak count in the N 1s spectra with an increase in O3 feeding time also confirms the presence of HfNx materials caused by reaction of the excess Hf and dissociated N. The HfNx bonds formed as a result of nitrogen dissociation, made by plasma damage and Ti oxidation in TiN films, may work as inside film trap sites, which may lower the characteristic leakage current in the film. With O2 plasma pre-treatment, it is confirmed that the concentration of TiO2 remarkably increased with the plasma exposure time. Therefore, we can understand the phenomenon which is N 1s peak decreased in the interface. And also, there is a decrease in the amount of Cl impurity it also notable. It is confirmed that the residual Cl in the HfO2 bulk and the HfNx in the interface, which are created by reaction via out-diffusion of N and Cl from TiN, are highly diminished due to the hindrance of the TiO2 formed on the top of the TiN bottom electrode. It is confirmed that a gradual enhancement of m-HfO2 (111) peak with an increase in the plasma exposure time from 0 to 300 sec which suggest the local crystallization HfO2 at the interface. The increase in the concentration of TiO2 at the interface with an increase in the plasma exposure time may be the reason for the enhanced crystallization of the HfO2 layer. The concentration of HfNx was decreased caused by HfO2 and TiO2 creation due to supply the sufficient oxygen during O2 plasma pre-treatment. It may be indicates that a partial transition from the HfNx phase to m-HfO2. A local crystallization of HfO2 was clearly observed at the interface in the cases of the 150 and 300 sec plasma exposures the non treated sample showed an amorphous structure by HRTEM.

Characterization of interfaces between HfO2 thin film and metal electrode

Kim, Youngnam Sungkyunkwan University 2013 국내박사