ZnO/Cu/ZnO (ZCZ) thin films were deposited at room temperature on a glass substrate using direct current (DC) and radio frequency (RF, 13.56 MHz) magnetron sputtering and then the effect of post-deposition electron irradiation on the structural, optical, electrical and transparent heater properties of the films were considered. ZCZ films that were electron beam irradiated at 500 eV showed an increase in the grain sizes of their ZnO(102) and (201) planes to 15.17 nm and 11.51 nm, respectively, from grain sizes of 13.50 nm and 10.60 nm observed in the as deposited films. In addition, the film’s optical and electrical properties also depended on the electron irradiation energies. The highest opto-electrical performance was observed in films electron irradiated at 500 eV. In a heat radiation test, when a bias voltage of 18 V was applied to the film that had been electron irradiated at 500 eV, its steady state temperature was about 90.5 °C. In a repetition test, it reached the steady state temperature within 60 s at all bias voltages.

Dry etching of copper thin films is performed using high density plasma of ethylenediamine (EDA)/ hexafluoroisopropanol (HFIP)/Ar gas mixture. The etch rates, etch selectivities and etch profiles of the copper thin films are improved by adding HFIP to EDA/Ar gas. As the EDA/HFIP concentration in EDA/HFIP/Ar increases, the etch rate of copper thin films decreases, whereas the etch profile is improved. In the EDA/HFIP/Ar gas mixture, the optimal ratio of EDA to HFIP is investigated. In addition, the etch parameters including ICP source power, dc-bias voltage, process pressure are varied to examine the etch characteristics. Optical emission spectroscopy results show that among all species, [CH], [CN] and [H] are the main species in the EDA/HFIP/Ar plasma. The X-ray photoelectron spectroscopy results indicate the formation of CuCN compound and C-N-H-containing polymers during the etching process, leading to a good etch profile. Finally, anisotropic etch profiles of the copper thin films patterned with 150 nm scale are obtained in EDA/HFIP/Ar gas mixture.

This study reports the effects of H2S gas concentration on the properties of Cu2ZnSnS4(CZTS) thin films. Specifically, sulfurization process with low H2S concentrations of 0.05% and 0.1%, along with 5% H2S gas, was studied. CZTS films were directly synthesized on Mo/Si substrates by chemical bath deposition method using copper sulfate, zinc sulfate heptahydrate, tin chloride dihydrate, and sodium thiosulfate pentahydrate. Smooth CZTS films were grown on substrates at optimized chemical bath deposition condition. The CZTS films sulfurized at low H2S concentrations of 0.05 % and 0.1% showed very rough and porous film morphology, whereas the film sulfurized at 5% H2S yielded a very smooth and dense film morphology. The CZTS films were fully crystallized in kesterite crystal form when they were sulfurized at 500 oC for 1 h. The kesterite CZTS film showed a reasonably good room-temperature photoluminescence spectrum that peaked in a range of 1.4 eV to 1.5 eV, consistent with the optimal bandgap for CZTS solar cell applications.

To realize high-performance thin film solar cells, we prepared CIGS by the co-evaporation technique on both sodalime and Corning glass substrates. The structural and efficient properties were investigated by varying the thickness of the Mo:Na layer, where the total thickness of the back contact was fixed at 1μm. As a result, when the Mo:Na thickness was 300 nm on soda-lime glass, the measured Na content was 0.28 %, the surface morphology was a plate-like compact structure, and the crystallinity by XRD showed a strong peak of (112) preferential orientation together with relatively intense (220) and (204) peaks as the secondary phases influenced crystal formation. In addition, the substrates on soda-lime glass effected the lowest surface roughness of 2.76 nm and the highest carrier density and short circuit current. Through the optimization of the Mo:Na layer, a solar conversion efficiency of 11.34% was achieved. When using the Corning glass, a rather low conversion efficiency of 9.59% was obtained. To determine the effects of the concentration of sodium and in order to develop a highefficiency solar cells, a very small amount of sodium was added to the soda lime glass substrate.

The aim of this work was to investigate the effects of electrodeposition conditions on the microstructural characteristics of copper thin films. The microstructure of electroplated Cu films was found to be highly dependent on electrodeposition conditions such as system current and current density, as well as the bath solution itself. The current density significantly changed the preferred orientation of electroplated Cu films in a DC system, while the solution itself had very significant effects on microstructural characteristics in a pulse-reverse pulse current system. In the DC system, polarization at high current above 30 mA, changed the preferred orientation of Cu films from (220) to (111). However, Cu films showed (220) preferred orientation for all ranges of current density in the pulse-reverse pulse current system. The grain size decreased with increasing current density in the DC system while it remained relatively constant in the pulse-reverse pulse current system. The sheet resistance increased with increasing current density in the DC system due to the decreased grain size.

Cu2ZnSn(Sx,Se1-x)4 (CZTSSe) thin films were prepared by sulfurization of evaporated precursor thin films. Precursor was prepared using evaporation method at room temperature. The sulfurization was carried out in a graphite box with S powder at different temperatures. The temperatures were varied in a four step process from 520˚C to 580˚C. The effects of the sulfurization temperature on the micro-structural, morphological, and compositional properties of the CZTSSe thin films were investigated using X-ray diffraction (XRD), Raman spectra, field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The XRD and Raman results showed that the sulfurized thin films had a single kesterite crystal CZTSSe. From the FE-SEM and TEM results, the Mo(Sx,Se1-x)2 (MoSSe) interfacial layers of the sulfurized CZTS thin films were observed and their thickness was seen to increase with increasing sulfurization temperature. The microstructures of the CZTSSe thin films were strongly related to the sulfurization temperatures. The voids in the CZTSSe thin films increased with the increasing sulfurization temperature.

Cu2ZnSn(S,Se)4 material is receiving an increased amount of attention for solar cell applications as an absorber layer because it consists of inexpensive and abundant materials (Zn and Sn) instead of the expensive and rare materials (In and Ga) in Cu(In,Ga)Se2 solar cells. We were able to achieve a cell conversion efficiency to 4.7% by the selenization of a stacked metal precursor with the Cu/(Zn + Sn)/Mo/glass structure. However, the selenization of the metal precursor results in large voids at the absorber/Mo interface because metals diffuse out through the top CZTSe layer. To avoid the voids at the absorber/Mo interface, binary selenide compounds of ZnSe and SnSe2 were employed as a precursor instead of Zn and Sn metals. It was found that the precursor with Cu/SnSe2/ZnSe stack provided a uniform film with larger grains compared to that with Cu2Se/SnSe2/ZnSe stack. Also, voids were not observed at the Cu2ZnSnSe4/Mo interface. A severe loss of Sn was observed after a high-temperature annealing process, suggesting that selenization in this case should be performed in a closed system with a uniform temperature in a SnSe2 environment. However, in the experiments, Cu top-layer stack had more of an effect on reducing Sn loss compared to Cu2Se top-layer stack.

The Cu2ZnSnS4 (CZTS) thin film solar cell is a candidate next generation thin film solar cell. For the application of an absorption layer in solar cells, CZTS thin films were deposited by pulsed laser deposition (PLD) at substrate temperature of 300˚C without post annealing process. Deposition time was carefully adjusted as the main experimental variable. Regardless of deposition time, single phase CZTS thin films are obtained with no existence of secondary phases. Irregularly-shaped grains are densely formed on the surface of CZTS thin films. With increasing deposition time, the grain size increases and the thickness of the CZTS thin films increases from 0.16 to 1μm. The variation of the surface morphology and thickness of the CZTS thin films depends on the deposition time. The stoichiometry of all CZTS thin films shows a Cu-rich and S-poor state. Sn content gradually increases as deposition time increases. Secondary ion mass spectrometry was carried out to evaluate the elemental depth distribution in CZTS thin films. The optimal deposition time to grow CZTS thin films is 150 min. In this study, we show the effect of deposition time on the structural properties of CZTS thin film deposited on soda lime glass (SLG) substrate using PLD. We present a comprehensive evaluation of CZTS thin films.

Cu(In, Ga)Se2 (CIGS) precursor films were electrodeposited on Mo/glass substrates in acidic solutions containingCu2+, In3+, Ga3+, and Se4+ ions at −0.6V (SCE) and pH 1.8. In order to induce recrystallization, the electrodepositedCu1.00In0.81Ga0.09Se2.08 (25.0at.% Cu+20.2at.% In+2.2at.% Ga+52.0at.% Se) precursor films were annealed under a highSe gas atmosphere for 15, 30, 45, and 60 min, respectively, at 500oC. The Se amount in the film increased from 52at.% to62at.%, whereas the In amount in the film decreased from 20.8at.% to 9.1at.% as the annealing time increased from 0 (as-deposited state) to 60 min. These results were attributed to the Se introduced from the furnace atmosphere and reacted withthe In present in the precursor films, resulting in the formation of the volatile In2Se. CIGS precursor grains with a cauliflowershape grew as larger grains with the CuSe2 and/or Cu2-xSe faceted phases as the annealing times increased. These faceted phasesresulted in rough surface morphologies of the CIGS films. Furthermore, the CIGS layers were not dense because the emptyspaces between the grains were not removed via annealing. Uniform thicknesses of the MoSe2 layers occurred at the 45 and60 min annealing time. This implies that there was a stable reaction between the Mo back electrode and the Se diffused throughthe CIGS film. The results obtained in the present research were sufficiently different from comparable studies where therecrystallization annealing was performed under an atmosphere of Ar gas only or a low Se gas pressure.

The microstructure and Cu diffusion barrier property of Ta-Si-N films for various Si and N compositions were studied. Ta-Si-N films of a wide range of compositions (Si: 0~30 at.%, N: 0~55 at.%) were deposited by DC magnetron reactive sputtering of Ta and Si targets. Deposition rates of Ta and Si films as a function of DC target current density for various N2/(Ar+N2) flow rate ratios were investigated. The composition of Ta-Si-N films was examined by wavelength dispersive spectroscopy (WDS). The variation of the microstructure of Ta-Si-N films with Si and N composition was examined by X-ray diffraction (XRD). The degree of crystallinity of Ta-Si-N films decreased with increasing Si and N composition. The Cu diffusion barrier property of Ta-Si-N films with more than sixty compositions was investigated. The Cu(100 nm)/Ta-Si-N(30 nm)/Si structure was used to investigate the Cu diffusion barrier property of Ta-Si-N films. The microstructure of all Cu/Ta-Si-N/Si structures after heat treatment for 1 hour at various temperatures was examined by XRD. A contour map that shows the diffusion barrier failure temperature for Cu as a function of Si and N composition was completed. At Si compositions ranging from 0 to 15 at.%, the Cu diffusion barrier property was best when the composition ratio of Ta + Si and N was almost identical.

Cu(In,Ga)Se2(CIGS) photovoltaic thin films were electrodeposited on Mo/glass substrates with an aqueous solution containing 2 mM CuCl2, 8 mM InCl3, 20 mM GaCl3 and 8mM H2SeO3 at the electrodeposition potential of -0.6 to -1.0 V(SCE) and pH of 1.8. The best chemical composition of Cu1.05In0.8Ga0.13Se2 was found to be achieved at -0.7 V(SCE). The precursor Cu-In-Ga-Se films were annealed for crystallization to chalcopyrite structure at temperatures of 100-500˚C under Ar gas atmosphere. The chemical compositions, microstructures, surface morphologies, and crystallographic structures of the annealed films were analyzed by EPMA, FE-SEM, AFM, and XRD, respectively. The precursor Cu-In-Ga-Se grains were grown sparsely on the Mo-back contact and also had very rough surfaces. However, after annealing treatment beginning at 200˚C, the empty spaces between grains were removed and the grains showed well developed columnar shapes with smooth surfaces. The precursor Cu-In-Ga-Se films were also annealed at the temperature of 500˚C for 60 min under Se gas atmosphere to suppress the Se volatilization. The Se amount on the CIGS film after selenization annealing increased above the Se amount of the electrodeposited state and the MoSe2 phase occurred, resulting from the diffusion of Se through the CIGS film and interaction with Mo back electrode. However, the selenization-annealed films showed higher crystallinity values than did the films annealed under Ar atmosphere with a chemical composition closer to that of the electrodeposited state.

(hfac)Cu(1, 5-DMCOD)(1, 1, 1, 5, 5, 5-Hexafluoro-2, 4-pentanedionato Cu(I) 1, 5-dimethyl-cyclooctadine) 전구체와 He 운반기체를 이용하여 MOCVD(Metal Organic Chemical Vapor Deposition) 방법으로 Cu 박막을 형성하였으며, He 운반기체와 함께 H2 gas 및 H(hfac) Ligand의 첨가가 Cu 박막 형성에 미치는 영향에 대하여 조사하였다. He운반기체만을 사용한 경우, Cu 박막의 증착율은 기판온도 180~230˚C에서 20~125Å/min 정도로 낮은 값을 보였으며, 특히 기판온도 190˚C에서는 매우 얇은 두께 (700Å)이면서 낮은 비저항(2.8μΩcm)을 갖는 Cu 박막이 형성됨을 알 수 있었다 He 운반기체와 함께 환원가스(H2) 및 화학첨가제 (H (hfac) ligand)의 첨가 실험에서는 낮은 기판온도 (180~190˚C) 구간에서 현저하게 증착율이 증가하였으며 얇은 두께 (~500Å)의 Cu 박막이 낮은 비저항(3.6~2.86μΩcm)을 갖는 것으로 나타났다. 또한 얇은 두께의 MOCVD Cu박막들의 표면 반사도(reflectance)는 300˚C에서 열처리한 sputter Cu의 반사도에 근접하는 우수한 surface morphology를 보였다 결국, (hfac)Cu(1,6-DMCOD) 전구체를 이용하여 얻어진 MOCVD Cu박막은 얇은 두께에서 낮은 비저항을 갖는 우수한 막질을 보였으며, Electrochemical deposition공정에서 conformal seed layer로써의 적용이 가능할 것으로 기대된다.

(hfac)Cu(vtmos) [C10H13O5CuF6Si: 1,1,1,5,5,5-hexafluoro-2,4- pentadionato (vinyltrimethoxysilane) copper (I)] 구리원을 액체분사법으로 공급하여 반응성 스퍼터 증착된 PVD-TiN과 급속열처리 변환된 RTP-TiN 기판상에 구리를 유기금속 화학증착법으로 성장시키고, 증착조건과 기판 종류가 박막의 증착율, 결정구조 및 미세조직, 전기비저항 등에 미치는 영향을 분석하였다. 구리원 유량 0.2ccm에서 증착반응은 Ar 유량 200sccm까지 물질전달 지배과정과 전압 1.0Torr 이상에서 기화기에서의 공급율속을 보였다. 전압 0.6Torr일 때 활성화에너지는 155~225˚C의 표면반응 지배영역에서 12.7~14.1kcal/mol의 값을 나타내었으며, 225˚C 이상의 기판온도에서는 H2 첨가에 따른 증착율 개선이 간응한 것으로 판단되었다. 증착층은 기판온도 증가에 따라 3차원 island 양식으로 성장하였으며, 증착초기 구리 핵생성밀도가 큰 RTP-TiN상 증착층이 PVD-TiN상보다 현저한 (111) 우선방위와 낮은 전기비저항값을 나타내었다. 구리박막의 전기비저항은 결정립간 연결성이 양호한 165˚C에서 가장 낮았으며, 증착온도에 따른 박막 미세구조 변화로 인해 그 거동은 3개의 영역으로 구분되어 나타났다.

본 연구에서는 기존에 알려진 구리 전구체와 새롭게 개발된 전구체인 hfac (hexafluoroacetylacetonate) Cu(I) DMB (3,3-dimethyl-1-butene)를 비교 평가해보았다. (Hfac)Cu(I) (DMB)의 증가압은 40˚C에서 3 torr 정도로 기존에 잘 알려진 (hfac)Cu(I) vinyltrimethylsilane (VTMS) 보다 10배 정도 높은 것으로 나타났으며 그럼에도 불구하고 상당히 안정하여 65˚C에서 일주일 이상 가열하여도 변하지 않았다. 이 전구체로 100-280˚C에서 구리 박막을 증착할 수 있었으며 150-250˚C온도 범위에서 2.0μΩ-cm의 순수한 구리 박막을 얻었다. 구리 박막의 증착 속도는 기존의 전구체보다 7~8배 정도 높은 것으로 나타났다.

비정질 실리콘 박막 위에 구리용액을 스콘코팅하여 구리이온을 흡착시킨 후 이를 표면 핵생성 site로 이용하는 새로운 저온 결정화 방법에 관하여 연구하였다. 구리 흡착으로 LPCVD비정질 실리콘 박막의 결정화온도를 500˚C까지 낮출 수 있었고 결정화시간도 크게 단축되었다. 530-600˚C에서 어닐링시 구리가 흡착된 비정질 실리콘 막은 나뭇가지 형태의 fractal을 이루며 결정화되었다. 이때 fractal크기는 구리용액의 농도에 따라 30-300μm로 성장하였다. Fractal의 내부는 새 털 모양의 타원형 결정립으로 구성되어 있으며 TEM 에 의한 최종 결정립의 크기는 0.3-0.4μm로 intrinsic 비정질 실리콘 박막을 600˚C에서 어닐링하였을 때화 크기가 비슷하였다. 구리용액의 농도 증가에 따라 핵생성 활성화 에너지와 결정성장 활성화 에너지가 감소하였다. 결과적으로 구리 흡착이 표면에서 우선 핵생성 site를 증가시키고 핵생성 및 fractal 성장에 필요한 활성화 에너지를 모두 낮추어 저온에서도 결정화가 촉진되었음을 알 수 있었다.

TiN 기판상에 CVD와 무전해 도금을 이용하여 구리막을 성장시킬 때 여러 가지 전처리에 따른 증착 양상의 변화에 관하여 조사하였다. Cu(hfac)2를 선재(precursor)로 사용하여 CVD 증착을 실시할 때 각 전처리에 따른 TiN상의 구리막의 덮힘성(coverage)향상은 Pd-HF 활성화 처리>>HF dip> RF remote plasma의 순이었다. 특히 Pd-HF 활성화 처리를 해줄 경우 거의 완전한 연속막을 얻을수 있었으며 scotch tape peel test 결과 매우 양호한 부착특성을 보였으나, 이에 비해 전처리를 해주지 않은 경우에는 오랜 시간이 경과되어도 연속막으로 성장하지 못하고 섬모양의 큰 결정립을 이룰 뿐이었다. 이러한 차이는 Pd-HF 활성화 처리에 의해 표면에 미세하게 형성된 Pd층이 구리의 핵생성과 부착특성을 크게 향상시켰기 때문인 것으로 사료되며 이러한 효과는 무전해 도금의 경우에도 마찬가지였다. 그리고 기판과 증착온도에 따른 선택성을 보면 350˚C이하에서는 pd-HF 활성화 처리에 의해서 SiO2에 대하여 TiN으로의 선택성을 가지나 그 이상의 온도에서는 선택성이 상실되었다.

CVD와 무전해 도금법을 이용하여 TiN 기판상에 구리막을 성장시켰고 그 각각에 대해 증착조건에 따른 성장막의 morphology, 성장기구 및 비저항, 막의 치밀성 등의 물리적 특성을 조사하였다. CVD 증착막의 결정립 크기와 입간의 기공은 막두께에 비례하여 커지는 경향을 나타내었으며 비저항은 4.7μΩcm로 구리의 체적비저항값과 거의 비슷한 것으로 나타났다. 무전해 도금막은 초기에는 layer-by-layer mode로 나중에는 is-land growth mode로 성장하는 경향을 보였다. CVD구리막의 막질은 후열처리 분위기에 따라서도 상당한 차이를 보였다. CVD구리막의 막질은 후열처리 분위기에 따라서도 상당한 차이를 보였으며, 활성화 에너지로부터 350˚C를 기준으로 증착기구가 변하는 것을 확인할 수 있었던 반면, 무전해 도금은 60-80˚C의 온도 구간에서 증착기구는 변하지 않았으나 도금 온도가 높을수록 막표면이 거칠어지는 경향을 나타내었다. 7:1 BHF 에칭 실험의 결과 무전해도금에 의한 구리막에 비해 CVD구리막의 에칭속도가 더 빨랐으며 막질도 덜 치밀한 것으로 나타났다.