• 전기전자학회논문지
• /
• 제25권1호
• /
• pp.1-9
• /
• 2021

본 논문에서는 고전압, 고전류 동작에 적합한 4H-SiC UMOSFET에 대해서 연구하였다. 일반적으로 SiO2는 SiC MOSFET에서 gate dielectric으로 가장 많이 사용되는 물질이다. 하지만 4H-SiC보다 유전 상수 값이 2.5배 낮아서 높은 전계를 갖게 되므로 SiO2/SiC 접합 부분에서 열악한 특성을 갖는다. 따라서 high-k 물질을 gate dielectric으로 적용한 소자를 SiO2를 적용한 소자와 TCAD 시뮬레이션을 통해 전기적 특성을 비교하였다. 그 결과 BV 감소, VTH 감소, gm 증가, Ron 감소를 확인하였다. 특히 온도가 300K일 때, Al2O3와 HfO2의 Ron은 66.29%, 69.49%가 감소하였으며 600K일 때도 39.71%, 49.88%가 감소하였다. 따라서 Al2O3와 HfO2가 고전압 SiC MOSFET의 gate dielectric 물질로써 적합함을 확인하였다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2001년도 하계학술대회 논문집
• /
• pp.832-835
• /
• 2001

We report the structural and electrical properties of hafnium oxide (HfO$_2$) films with tungsten silicide (WSi$_2$) metal gate. In this study, HfO$_2$thin films were fabricated by oxidation of sputtered Hf metal films on Si, and WSi$_2$was deposited directly on HfO$_2$by LPCVD. The hysteresis windows in C-V curves of the WSi$_2$HfO$_2$/Si MOS capacitors were negligible (<20 mV), and had no dependence on frequency from 10 kHz to 1 MHz and bias ramp rate from 10 mV to 1 V. In addition, leakage current was very low in the range of 10$^{-9}$ ~10$^{-10}$ A to ~ 1 V, which was due to the formation of interfacial hafnium silicate layer between HfO$_2$and Si. After PMA (post metallization annealing) of the WSi$_2$/HfO$_2$/Si MOS capacitors at 500 $^{\circ}C$ EOT (equivalent oxide thickness) was reduced from 26 to 22 $\AA$ and the leakage current was reduced by approximately one order as compared to that measured before annealing. These results indicate that the effect of fluorine diffusion is negligible and annealing minimizes the etching damage.

• 한국전기전자재료학회논문지
• /
• 제24권12호
• /
• pp.939-943
• /
• 2011

In this paper, reliability of the two sandwiched MIM capacitors of $Al_2O_3-HfO_2-Al_2O_3$ (AHA) and $SiO_2-HfO_2-SiO_2$ (SHS) with hafnium-based dielectrics was analyzed using two kinds of voltage stress; DC and AC voltage stresses. Two MIM capacitors have high capacitance density (8.1 fF/${\mu}m^2$ and 5.2 fF/${\mu}m^2$) over the entire frequency range and low leakage current density of ~1 nA/$cm^2$ at room temperature and 1 V. The charge trapping in the dielectric shows that the relative variation of capacitance (${\Delta}C/C_0$) increases and the variation of voltage linearity (${\alpha}$/${\alpha}_0$) gradually decreases with stress-time under two types of voltage stress. It is also shown that DC voltage stress induced greater variation of capacitance density and voltage linearity than AC voltage stress.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
• /
• pp.378.1-378.1
• /
• 2014

In this study, we investigated that the resistance switching characteristics of Nb-doped HfO2 films with increasing Nb doping concentration. The Nb-doped HfO2 based ReRAM devices with a TiN/Nb-doped HfO2/Pt/Ti/SiO2 were fabricated on Si substrates. The Nb-doped HfO2 films were deposited by reactive dc magnetron co-sputtering at $300^{\circ}C$ and oxygen partial ratio of 60% (Ar: 16sccm, O2: 24sccm). Microstructure of Nb-doped HfO2 films and atomic concentration were investigated by XRD, TEM, and XPS, respectively. The Nb-doped HfO2 films showed set/reset resistance switching behavior at various Nb doping concentrations. The process voltage of forming/set is decreased and whereas the initial current level is increased in doped HfO2 films. However, the switching properties of Nb-doped HfO2 were changed above the specific doping concentration of Nb. The change of resistance switching behavior depending on doping concentration was discussed in terms of concentration of non-lattice oxygen and micro-structure of Nb-doped HfO2.

• 반도체디스플레이기술학회지
• /
• 제8권2호
• /
• pp.55-58
• /
• 2009

Density functional theory was used to investigate the adsorption and reaction of $HfCl_4$ with two hydroxyls on Si (001)-$2{\times}1$ surface in atomic layer deposition (ALD) process. We prepared a reasonable Si substrate which consisted of six inter-dimer dissociated $H_2O$ molecules and two intra-dimer dissociated $H_2O$ molecules. The $HfCl_4$must react with two hydroxyls to be a bulk-like structure. When $HfCl_4$ was adsorbed on a hydroxyl, there was energy benefit of -0.55 eV. Though there was energy loss for $HfCl_4$ to react with H of hydroxyl, thermal energy of ALD chamber would be enough to pass the energy barriers. There were five reaction pathways for $HfCl_4$ to react with two hydroxyls; inter-dimer, intra-dimer, cross-dimer, inter-row, and cross-row. Inter-row, inter-dimer and intra-dimer were relatively favorable among the five reaction pathways based on the energy difference. The electron densities between O and Hf in these three reactions were higher than the others and they had shorter Hf-O and O-O bond lengths than the other two reaction pathways.

• 한국전기전자재료학회논문지
• /
• 제24권5호
• /
• pp.370-373
• /
• 2011

We investigated the effects of low temperature ($500^{\circ}C$) $O_2$ annealing on the characteristics of hafnium silicate ($HfSi_xO_y$) films deposited on a Si substrate by atomic layer deposition (ALD). We found that the post deposition annealing under oxidizing ambient causes the oxidation of residual Hf metal components, resulting in the improvement of electrical characteristics such as flat band voltage shift (${\Delta}V_{fb}$) by hysteresis without oxide capacitance reduction. We suggest that post deposition annealing under oxidizing ambient is necessary to improve the electrical characteristics of $HfSi_xO_y$ films deposited by ALD.

• 한국재료학회지
• /
• 제27권1호
• /
• pp.48-52
• /
• 2017

In this study, we used I-V spectroscopy, photoconductivity (PC) yield and internal photoemission (IPE) yield using IPE spectroscopy to characterize the Schottky barrier heights (SBH) at insulator-semiconductor interfaces of Pt/$HfO_2$/p-type Si metal-insulator-semiconductor (MIS) capacitors. The leakage current characteristics of the MIS capacitor were analyzed according to the J-V and C-V curves. The leakage current behavior of the capacitors, which depends on the applied electric field, can be described using the Poole-Frenkel (P-F) emission, trap assisted tunneling (TAT), and direct tunneling (DT) models. The leakage current transport mechanism is controlled by the trap level energy depth of $HfO_2$. In order to further study the SBH and the electronic tunneling mechanism, the internal photoemission (IPE) yield was measured and analyzed. We obtained the SBH values of the Pt/$HfO_2$/p-type Si for use in Fowler plots in the square and cubic root IPE yield spectra curves. At the Pt/$HfO_2$/p-type Si interface, the SBH difference, which depends on the electrical potential, is related to (1) the work function (WF) difference and between the Pt and p-type Si and (2) the sub-gap defect state features (density and energy) in the given dielectric.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2010년도 하계학술대회 논문집
• /
• pp.382-382
• /
• 2010

The etch characteristics of the $HfAlO_3$ thin films and selectivity of $HfAlO_3$ to $SiO_2$ in $Cl_2/BCl_3$/Ar plasma were investigated in this work. The maximum etch rate was 108.7 nm/min and selectivity of $HfAlO_3$ to $SiO_2$ was 1.11 at $Cl_2$(3sccm)/$BCl_3$(4sccm)/Ar(16sccm), RF power of 500 W, DC-bias voltage of - 100 V, process pressure of 1 Pa and substrate temperature of $40^{\circ}C$. As increasing RF power and DC-bias voltage, etch rates of the $HfAlO_3$ thin films increased. Whereas as decreasing of the process pressure, those of the $HfAlO_3$ thin films were increased. The chemical reaction on the surface of the etched the $HfAlO_3$ thin films was investigated with X-ray photoelectron spectroscopy (XPS).

• JSTS:Journal of Semiconductor Technology and Science
• /
• 제1권2호
• /
• pp.95-102
• /
• 2001

Hafnium oxide thin films for gate dielectric were deposited at $300^{\circ}C$ on p-type Si (100) substrates by plasma enhanced chemical vapor deposition (PECVD) and annealed in $O_2$ and $N_2$ ambient at various temperatures. The effect of hydrogen treatment in 4% $H_2$ at $350^{\circ}C$ for 30 min on the electrical properties of $HfO_2$for gate dielectric was investigated. The flat-band voltage shifts of $HfO_2$capacitors annealed in $O_2$ambient are larger than those in $N_2$ambient because samples annealed in high oxygen partial pressure produces the effective negative charges in films. The oxygen loss in $HfO_2$films was expected in forming gas annealed samples and decreased the excessive oxygen contents in films as-deposited and annealed in $O_2$ or $N_2$ambient. The CET of films after hydrogen forming gas anneal almost did not vary compared with that before hydrogen gas anneal. Hysteresis of $HfO_2$films abruptly decreased by hydrogen forming gas anneal because hysteresis in C-V characteristics depends on the bulk effect rather than $HfO_2$/Si interface. The lower trap densities of films annealed in $O_2$ambient than those in $N_2$were due to the composition of interfacial layer becoming closer to $SiO_2$with increasing oxygen partial pressure. Hydrogen forming gas anneal at $350^{\circ}C$ for samples annealed at various temperatures in $O_2$and $N_2$ambient plays critical role in decreasing interface trap densities at the Si/$SiO_2$ interface. However, effect of forming gas anneal was almost disappeared for samples annealed at high temperature (about $800^{\circ}C$) in $O_2$ or $N_2$ambient.

• 한국결정학회:학술대회논문집
• /
• 한국결정학회 2002년도 정기총회 및 추계학술연구발표회
• /
• pp.42-43
• /
• 2002

반도체 디바이스의 발전은 높은 직접화 및 동작 속도를 추구하고 있으며, 이를 위해서 MOSFET의 scale down시 발생되는 문제를 해결해야만 한다. 특히, Channel이 짧아짐으로써 발생하는 device의 열화현상으로 동작전압의 조절이 어려워 짐을 해결해야만 하며, gate oxide 두께를 줄임으로써 억제할 수 있다고 알려져 왔다. 현재, gate oxide으로 사용되고 있는 SiO2박막은 비정질로써 ～8.7 eV의 높은 band gap과 Si기판 위에서 성장이 용이하며 안정하다는 장점이 있으나, 두께가 1.6 nm 이하로 얇아질 경우 전자의 direct Tunneling에 의한 leakage current 증가와 gate impurity인 Boron의 channel로의 확산, 그리고 poly Si gate의 depletion effect[1,2] 등의 문제점으로 더 이상 사용할 수 없게 된다. 2001년 ITRS에 의하면 ASIC제품의 경우 2004년부터 0.9～l.4 nm 이하의 EOT가 요구된다고 발표하였다. 따라서, gate oxide의 물리적인 두께를 증가시켜 전자의 Tunneling을 억제하는 동시에 유전막에 걸리는 capacitance를 크게 할 수 있다는 측면에서 high-k 재료를 적용하기 위한 연구가 진행되고 있다[3]. High-k 재료로 가능성 있는 절연체들로는 A1₂O₃, Y₂O₃, CeO₂, Ta₂O, TiO₂, HfO₂, ZrO₂,STO 그리고 BST등이 있으며, 이들 재료 중 gate oxide에 적용하기 위해 크게 두 가지 측면에서 고려해야 하는데, 첫째, Si과 열역학적으로 안정하여 후속 열처리 공정에서 계면층 형성을 배제하여야 하며 둘째, 일반적으로 high-k 재료들은 유전상수에 반비례하는 band gap을 갖는 것으로 알려줘 있는데 이 Barrier Height에 지수적으로 의존하는 leakage current때문에 절연체의 band gap이 낮아서는 안 된다는 점이다. 최근 20이상의 유전상수와 ～5 eV 이상의 Band Gap을 가지며 Si기판과 열역학적으로 안정한 ZrO₂[4], HfiO₂[5]가 관심을 끌고 있다. HfO₂은 ～30의 고유전상수, ～5.7 eV의 높은 band gap, 실리콘 기판과의 열역학적 안전성 그리고 poly-Si와 호환성등의 장점으로 최근 많이 연구가 진행되고 있다. 또한, Hf은 SiO₂를 환원시켜 HfO₂가 될 수 있으며, 다른 silicide와 다르게 Hf silicide는 쉽게 산화될 수 있는 점이 보고되고 있다.