Effect of Growth Temperature during the Atomic Layer Deposition of the SrTiO₃ Seed Layer on the Properties of RuO₂/SrTiO₃/Ru Capacitors for Dynamic Random Access Memory Applications

Kim, Sang Hyeon,Lee, Woongkyu,An, Cheol Hyun,Kwon, Dae Seon,Kim, Dong-Gun,Cha, Soon Hyung,Cho, Seong Tak,Hwang, Cheol Seong American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.48

<P>The atomic layer deposition process of SrTiO<SUB>3</SUB> (STO) films at 230 °C was studied with Sr(<SUP>i</SUP>Pr<SUB>3</SUB>Cp)<SUB>2</SUB> and Ti(CpMe<SUB>5</SUB>)(OMe)<SUB>3</SUB> (Pr, Cp, and Me are propyl, cyclopentadienyl, and methyl groups, respectively) on Ru substrates. The growth behavior and properties of STO films grown at 230 °C were compared with those deposited at 370 °C. With the limited over-reaction of the Sr precursor during the initial growth stage at a lower temperature, the cation composition was more controllable, and the surface morphology after crystallization annealing at 650 °C had more uniform grains with fewer defects. Here, the excess reaction of the Sr precursor means the chemical-vapor-deposition-like growth of the SrO component mediated through the thermal decomposition of the adsorbed Sr precursor molecules. It was by the reaction of the Sr precursor with the oxygen supplied from the partly oxidized Ru substrate. The second STO was grown at 370 °C (main layer) on the annealed first STO layer (crystallized seed layer) to lead to the in situ crystallization of the main layer. Due to the improved microstructure of STO films induced by the seed layer deposited at 230 °C, the bulk dielectric constant of 167 was obtained for the main layer, which was higher than the value of 101 where the seed layer was deposited at 370 °C, even though the crystallization annealing condition of the seed layer and the deposition condition of the main layer were consistent. The seed layer grown at 230 °C, however, had a lower dielectric constant of only ∼49, whereas the high-temperature seed layer had a dielectric constant of ∼106. Therefore, the low-temperature seed layer posed a severe limitation in acquiring an advanced capacitor property with the involvement of a low-dielectric interfacial layer.</P> [FIG OMISSION]</BR>

N-doped Al₂O₃ thin films deposited by atomic layer deposition

Kim, Minjae,Kang, Kyung-Mun,Wang, Yue,Park, Hyung-Ho Elsevier 2018 THIN SOLID FILMS - Vol.660 No.-

<P><B>Abstract</B></P> <P>The present study focused on nitrogen doped Al<SUB>2</SUB>O<SUB>3</SUB> thin films using atomic layer deposition, varying the deposition temperature from 55 to 170 °C. Al<SUB>2</SUB>O<SUB>3</SUB> thin film growth rate and electrical properties were mostly dependent on deposition temperature. Nitrogen concentration decreased from 2.7 to 2.4% with increasing deposition temperature. X-ray photoelectron spectroscopic analysis confirmed that nitrogen doping in Al<SUB>2</SUB>O<SUB>3</SUB> decreased formation of oxygen related defects, including non-lattice oxygen. Surface morphology analyses also showed that N-doping reduced Al<SUB>2</SUB>O<SUB>3</SUB> film surface roughness. Reduced oxygen related defects significantly reduced leakage current by 1000 times when comparing with as-deposited films. Minimum leakage current (5 × 10<SUP>−10</SUP> A/cm<SUP>2</SUP>) was observed for N-doped Al<SUB>2</SUB>O<SUB>3</SUB> film deposited at 170 °C and post-annealed at 400 °C, including a decrease by 10 times through N-doping.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Al<SUB>2</SUB>O<SUB>3</SUB> thin films with doped nitrogen were deposited using atomic layer deposition. </LI> <LI> N was incorporated up to 2.72 at.% at the deposition temperature of 55 °C by ALD. </LI> <LI> RMS roughness of Al<SUB>2</SUB>O<SUB>3</SUB> thin film was reduced to under 1 nm through N-doping. </LI> <LI> Leakage current of Al<SUB>2</SUB>O<SUB>3</SUB> thin film was reached to 5 × 10<SUP>−10</SUP>A/cm<SUP>2</SUP> by N-doping. </LI> </UL> </P>

Atomic-layer-deposited buffer layers for thin film solar cells using earth-abundant absorber materials: A review

Sinha, Soumyadeep,Nandi, Dip K.,Kim, Soo-Hyun,Heo, Jaeyeong North-Holland 2018 Solar Energy Materials and Solar Cells Vol. No.

<P><B>Abstract</B></P> <P>Atomic layer deposition (ALD) is not just a thin film deposition technology limited to the semiconductor IC industries to grow high-<I>k</I> gate dielectric or a Cu diffusion barrier layer. In recent times, it has found plenty of applications in the field of renewable energy due to its precise thickness control up to few angstroms and its unique feature of conformal and uniform coating on any randomly shaped 3D structure. ALD has far-reaching applications in this field, including electrochemical storage, fuel cells, solar photovoltaics (PV), and catalysis for water splitting to produce H<SUB>2</SUB> as a green fuel. In solar PV technology, ALD is now being extensively used as an efficient tool to deposit surface passivation layers, absorber or sensitizer, transparent conducting oxide, and barrier and buffer layers in several kinds of solar cells. Out of all the different layers associated with a solar cell, ALD is majorly used for the development of a very thin <I>n-</I>type buffer layer. This review article presents a systematic chronological study on such ALD-grown buffer layers for thin film solar cells (TSFCs). The study is carried out in detail based on different earth-abundant absorber materials, such as Cu<SUB>2</SUB>ZnSn(S,Se)<SUB>4</SUB> (CZTSSe), Cu<SUB>2</SUB>O and SnS, for which ALD is successfully used to deposit the buffer layer.</P> <P><B>Highlights</B></P> <P> <UL> <LI> ALD buffer layers for TFSCs based on emerging absorbers are reviewed. </LI> <LI> Correlation between cell performance and ALD process parameters is investigated. </LI> <LI> Progress on the efficiency of the TFSCs based on ALD buffers is reported. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Simulation and deposition of near-IR anti-reflection layers for silicon substrates

Kim, Kyeeun,Song, Gwang Yeom,Kim, Yong Tae,Moon, Jong Ha,Heo, Jaeyeong Elsevier 2017 Surface & coatings technology Vol.332 No.-

<P><B>Abstract</B></P> <P>Anti-reflection (AR) layers for Si were investigated for potential application in optical communications in the wavelength range of 1270–1330nm. The optical simulation module of the Essential Macleod program was used to find the optimal thickness of single-layer and double-layer structures using Al<SUB>2</SUB>O<SUB>3</SUB> and TiO<SUB>2</SUB>. Al<SUB>2</SUB>O<SUB>3</SUB> was found to be a better AR single-layer because of a lower reflectance. Less than 1% reflectance was simulated using double-layer structures for both stack sequences Si/TiO<SUB>2</SUB>/Al<SUB>2</SUB>O<SUB>3</SUB> and Si/Al<SUB>2</SUB>O<SUB>3</SUB>/TiO<SUB>2</SUB>. For experimental work, atomic layer deposition (ALD) of Al<SUB>2</SUB>O<SUB>3</SUB> and TiO<SUB>2</SUB> was employed to fabricate two different stacks. Reflectance measurements were conducted and 1.9% and 1.7% maximum reflectance was recorded in the wavelength range 1270–1330nm. This reflectance establishes the possibility that the two stacks can be used as effective AR layers for Si lenses designed for optical communications. Resistance against humidity was tested for the two structures and only the Si/Al<SUB>2</SUB>O<SUB>3</SUB>/TiO<SUB>2</SUB> structure was impermeable. Analyses using Fourier transform infrared spectroscopy and atomic force microscopy revealed that ALD-Al<SUB>2</SUB>O<SUB>3</SUB> is easily hydroxylated while ALD-TiO<SUB>2</SUB> acts as a good humidity barrier.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Single- and double-layers were investigated for near-IR anti-reflection coatings for silicon. </LI> <LI> Reflectance less than 2% was fabricated for Al<SUB>2</SUB>O<SUB>3</SUB>/TiO<SUB>2</SUB> and TiO<SUB>2</SUB>/Al<SUB>2</SUB>O<SUB>3</SUB> stacks. </LI> <LI> Atomic-layer-deposited-Al<SUB>2</SUB>O<SUB>3</SUB> was prone to water permeation at 80°C. </LI> <LI> Atomic-layer-deposited-TiO<SUB>2</SUB> acted as good barrier for water permeation. </LI> </UL> </P>

Degradation of the Deposition Blocking Layer During Area-Selective Plasma-Enhanced Atomic Layer Deposition of Cobalt

이한보람,Jaemin Kim,김형준,Woo-Hee Kim,Jeong Won Lee,황인찬 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.1

The effects of plasma on the degradation of the deposition blocking layer during area-selective atomic layer deposition were investigated. Co atomic layer deposition (ALD) processes were developed by using Co(iPr-AMD)2 (bis(N,N0-diisopropylacetamidinato)cobalt(II)) as a precursor, and two different reactants, NH3 gas for thermal ALD (TH-ALD) and NH3 plasma for plasma-enhanced ALD (PE-ALD). TH- and PE-ALD were applied to area selective ALD (AS-ALD) by using an octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) as a blocking layer. Both ALD processes produced pure Co films with resistivities as low as 50 µΩcm. For PE-ALD, however, no selective deposition was achieved due to a degradation of the OTS hydrophobicity caused by the NH3 plasma exposure. The effects of the plasma on the blocking efficiency of SAM were studied.

Reducing the nano-scale defect formation of atomic-layer-deposited SrTiO₃ films by adjusting the cooling rate of the crystallization annealing of the seed layer

Lee, Woongkyu,Yoo, Sijung,Jeon, Woojin,Yoo, Yeon Woo,An, Cheol Hyun,Chung, Min Jung,Kim, Han Joon,Lee, Sang Woon,Hwang, Cheol Seong Elsevier 2015 THIN SOLID FILMS - Vol.589 No.-

<P><B>Abstract</B></P> <P>SrTiO<SUB>3</SUB> (STO) thin films, grown by atomic layer deposition (ALD), were studied for capacitors in dynamic random access memory. The STO ALD process consisted of two steps: the growth of seed layer followed by a rapid thermal annealing (RTA) process at 650°C to crystallize it, and the deposition of the main layer on top of the seed layer at 370°C to induce the in-situ crystallization. During single cooling process after the RTA of the seed layer, voids and nano-cracks were formed due to the thermal expansion mismatch between STO film and Si substrate. This problem was well mitigated by adopting the stepwise cooling process, wherein the holding time of 30s at 500, 350, and 200°C suppressed the defect formation in the seed layer. Therefore, the main layer grown on that seed layer showed an improved microstructure with a high bulk dielectric constant of 135. However, the increase in total annealing time degraded the interface quality between the STO and the bottom electrode, which finally worsened the insulating property. As a result, the minimum equivalent oxide thicknesses with low leakage current densities (<10<SUP>−7</SUP> A/cm<SUP>2</SUP> at 0.8V) for the single and stepwise cooling processes were 0.39nm and 0.46nm, respectively.</P> <P><B>Highlights</B></P> <P> <UL> <LI> SrTiO<SUB>3</SUB> films with high dielectric constant were grown by atomic layer deposition. </LI> <LI> Two kinds of cooling processes after crystallization annealing were examined. </LI> <LI> Microstructure was improved by adopting the stepwise cooling process. </LI> <LI> Bulk dielectric constant was improved by adopting the stepwise cooling process. </LI> <LI> Amorphous STO was grown on the void region of STO seed layer. </LI> </UL> </P>

Characteristics of NiO films prepared by atomic layer deposition using bis(ethylcyclopentadienyl)-Ni and O2 plasma

지수현,장우성,손정욱,김도형 한국화학공학회 2018 Korean Journal of Chemical Engineering Vol.35 No.12

Plasma-enhanced atomic layer deposition (PEALD) is well-known for fabricating conformal and uniform films with a well-controlled thickness at the atomic level over any type of supporting substrate. We prepared nickel oxide (NiO) thin films via PEALD using bis(ethylcyclopentadienyl)-nickel (Ni(EtCp)2) and O2 plasma. To optimize the PEALD process, the effects of parameters such as the precursor pulsing time, purging time, O2 plasma exposure time, and power were examined. The optimal PEALD process has a wide deposition-temperature range of 100-325 oC and a growth rate of 0.037±0.002 nm per cycle. The NiO films deposited on a silicon substrate with a high aspect ratio exhibited excellent conformality and high linearity with respect to the number of PEALD cycles, without nucleation delay.

Permeation barrier properties of an Al2O3/ZrO2 multilayer deposited by remote plasma atomic layer deposition

이상훈,최학영,신석윤,박주현,함기열,정현수,전형탁 한국물리학회 2014 Current Applied Physics Vol.14 No.4

We report the permeation barrier properties of Al2O3/ZrO2 multi-layers deposited by remote plasma atomic layer deposition. Electrical Ca degradation tests were performed to derive the water vapor transmission rate (WVTR) of Al2O3, ZrO2 and Al2O3/ZrO2 multi-layers at 50 C and 50% relative humidity (RH). Al2O3/ZrO2 multi-layers exhibit better barrier properties than Al2O3 and ZrO2 layers, and when more individual layers were deposited in the same total thickness, the WVTR value was reduced further, indicating a better barrier property. The WVTR of the Al2O3 and ZrO2 layers were 9.5 103 and 1.6 102 g/m2 day, respectively, but when deposited alternatively with 1 cycle of each layer, the WVTR decreased to 9.9 104 g/m2 day. X-ray diffraction results indicated that ZrO2 has a monoclinic structure but Al2O3 and Al2O3/ZrO2 multi-layers show an amorphous structure. Cross sectional Al2O3/ZrO2 multilayer structures and the formation of a ZrAlxOy phase are observed by transmission electron microscopy (TEM). X-ray photoelectron spectrometry (XPS) results indicate that Al2O3 and ZrO2 contain 33.7% and 37.8%, respectively, AleOH and ZreOH bonding. However, the ZrAlxOy phase contained 30.5% AleOH and ZreOH bonding. The results of transmittance measurement indicate that overall, Al2O3, ZrO2 and Al2O3/ ZrO2 multi-layers show high transmittance greater than 80% in the visible region.

ALD ZnO 버퍼층 증착 온도가 전착 Cu₂O 박막 태양전지 소자 특성에 미치는 영향

조재유,트란 휴 만,허재영,Cho, Jae Yu,Tran, Man Hieu,Heo, Jaeyeong 한국태양광발전학회 2018 Current Photovoltaic Research Vol.6 No.1

Beside several advantages, the PV power generation as a clean energy source, is still below the supply level due to high power generation cost. Therefore, the interest in fabricating low-cost thin film solar cells is increasing continuously. $Cu_2O$, a low cost photovoltaic material, has a wide direct band gap of ~2.1 eV has along with the high theoretical energy conversion efficiency of about 20%. On the other hand, it has other benefits such as earth-abundance, low cost, non-toxic, high carrier mobility ($100cm^2/Vs$). In spite of these various advantages, the efficiency of $Cu_2O$ based solar cells is still significantly lower than the theoretical limit as reported in several literatures. One of the reasons behind the low efficiency of $Cu_2O$ solar cells can be the formation of CuO layer due to atmospheric surface oxidation of $Cu_2O$ absorber layer. In this work, atomic layer deposition method was used to remove the CuO layer that formed on $Cu_2O$ surface. First, $Cu_2O$ absorber layer was deposited by electrodeposition. On top of it buffer (ZnO) and TCO (AZO) layers were deposited by atomic layer deposition and rf-magnetron sputtering respectively. We fabricated the cells with a change in the deposition temperature of buffer layer ranging between $80^{\circ}C$ to $140^{\circ}C$. Finally, we compared the performance of fabricated solar cells, and studied the influence of buffer layer deposition temperature on $Cu_2O$ based solar cells by J-V and XPS measurements.

Influences of surface treatment on In_0.53Ga_0.47As epitaxial layer grown on silicon substrate using trimethylaluminum

Kim, Soo Bin,Lee, Seung Hyun,Jung, Hae Jun,Seo, Myung Su,Kim, Sung Min,Lee, Soonil,Park, Ji-Yong,Park, Tae Joo,Jeong, Hae-Yong,Jun, Dong-Hwan,Park, Kyung Ho,Park, Won-Kyu,Lee, Sang Woon Elsevier 2018 THIN SOLID FILMS - Vol.646 No.-

<P><B>Abstract</B></P> <P>A development of high quality In<SUB>x</SUB>Ga<SUB>1−x</SUB>As epitaxial layers on Si substrates is essential for high-performance logic transistors due to the low fabrication cost and high compatibility with a conventional Si technology. We investigate the surface of In<SUB>0.53</SUB>Ga<SUB>0.47</SUB>As epitaxial layers grown by metal-organic chemical vapor deposition on a Si substrate (with InP/GaAs buffer layers) to obtain a high capacitance using high-k films (HfO<SUB>2</SUB>/Al<SUB>2</SUB>O<SUB>3</SUB> bilayer). The high-k films were grown on In<SUB>0.53</SUB>Ga<SUB>0.47</SUB>As epitaxial layers by atomic layer deposition (ALD). The interface between the high-k bilayer and the In<SUB>0.53</SUB>Ga<SUB>0.47</SUB>As epitaxial layer was analyzed depending on a surface treatment of the In<SUB>0.53</SUB>Ga<SUB>0.47</SUB>As epitaxial layer, and the surface treatment of the In<SUB>0.53</SUB>Ga<SUB>0.47</SUB>As epitaxial layer using trimethylaluminum (TMA) enhanced the electrical performances of Pt/high-k film/In<SUB>0.53</SUB>Ga<SUB>0.47</SUB>As capacitors. The TMA was introduced on the In<SUB>0.53</SUB>Ga<SUB>0.47</SUB>As epitaxial layer in the ALD chamber, which reduced native oxides (such as gallium and arsenic oxides) of the In<SUB>0.53</SUB>Ga<SUB>0.47</SUB>As surface and minimized a formation of interfacial layers between the high-k film and In<SUB>0.53</SUB>Ga<SUB>0.47</SUB>As layer. A capacitance equivalent thickness (CET) of ~1.5nm was achieved with a low leakage current (~10<SUP>−4</SUP> A/cm<SUP>2</SUP> at 1V). A CET as low as ~1.3nm and a capacitance >2.5μF/cm<SUP>2</SUP> was attained by optimizing the high-k/In<SUB>0.53</SUB>Ga<SUB>0.47</SUB>As interface. The TMA treatment on the In<SUB>0.53</SUB>Ga<SUB>0.47</SUB>As epitaxial layer is compatible with the conventional Si technology and provides promising opportunities for the development of state-of-the-art field-effect transistor technology using In<SUB>x</SUB>Ga<SUB>1−x</SUB>As epitaxial layers.</P> <P><B>Highlights</B></P> <P> <UL> <LI> High capacitance on In<SUB>0.53</SUB>Ga<SUB>0.47</SUB>As epitaxial layers grown on Si substrates </LI> <LI> Achievement of capacitance equivalent thickness lower than 1.5nm with low leakage current </LI> <LI> Enhancement of electrical performances by a surface treatment using trimethylaluminum. </LI> </UL> </P>