Effect of Post-Annealing Conditions on Cu-Cu Wafer Bonding Characteristics

장은정,Sarah Pfeiffer,Bioh Kim,Thorsten Matthias,Seungmin Hyun,이학주,박영배 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.3

We have evaluated the interfacial adhesion energy of Cu-to-Cu bonding by using a 4-point bending test. Cu films are sputter deposited on Si(100) wafers. The bonding of Cu to Cu is successfully achieved by using a thermo-compression method at 25000 mbar and 415℃ for 40 min. The interface between the Cu films before the bonding was not observed after thermo-compression bonding. Only a few voids were observed at the middle of the Cu bonding layer. The quantitative interfacial adhesion energy of the Cu bonding without post annealing was 10.4 J/m2. The interfacial adhesion energy was changed high post-annealing of the bonding until a temperature of 300℃. However, very weak interfacial adhesion energy is observed after post annealing under an oxygen environment at temperatures over 400℃. Growth of brittle interfacial oxides is suggested as possible explanation for the effect of the environment on the weak interfacial adhesion energy. We have evaluated the interfacial adhesion energy of Cu-to-Cu bonding by using a 4-point bending test. Cu films are sputter deposited on Si(100) wafers. The bonding of Cu to Cu is successfully achieved by using a thermo-compression method at 25000 mbar and 415℃ for 40 min. The interface between the Cu films before the bonding was not observed after thermo-compression bonding. Only a few voids were observed at the middle of the Cu bonding layer. The quantitative interfacial adhesion energy of the Cu bonding without post annealing was 10.4 J/m2. The interfacial adhesion energy was changed high post-annealing of the bonding until a temperature of 300℃. However, very weak interfacial adhesion energy is observed after post annealing under an oxygen environment at temperatures over 400℃. Growth of brittle interfacial oxides is suggested as possible explanation for the effect of the environment on the weak interfacial adhesion energy.

Direct, CMOS In‑Line Process Flow Compatible, Sub 100 °C Cu–Cu Thermocompression Bonding Using Stress Engineering

Asisa Kumar Panigrahi,Tamal Ghosh,C. Hemanth Kumar,Shiv Govind Singh,Siva Rama Krishna Vanjari 대한금속·재료학회 2018 ELECTRONIC MATERIALS LETTERS Vol.14 No.3

Diffusion of atoms across the boundary between two bonding layers is the key for achieving excellent thermocompressionWafer on Wafer bonding. In this paper, we demonstrate a novel mechanism to increase the diffusion across the bondinginterface and also shows the CMOS in-line process flow compatible Sub 100 °C Cu–Cu bonding which is devoid of Cusurface treatment prior to bonding. The stress in sputtered Cu thin films was engineered by adjusting the Argon in-let pressurein such a way that one film had a compressive stress while the other film had tensile stress. Due to this stress gradient, anominal pressure (2 kN) and temperature (75 °C) was enough to achieve a good quality thermocompression bonding havinga bond strength of 149 MPa and very low specific contact resistance of 1.5 × 10−8 Ω-cm2. These excellent mechanical andelectrical properties are resultant of a high quality Cu–Cu bonding having grain growth between the Cu films across theboundary and extended throughout the bonded region as revealed by Cross-sectional Transmission Electron Microscopy. Inaddition, reliability assessment of Cu–Cu bonding with stress engineering was demonstrated using multiple current stressingand temperature cycling test, suggests excellent reliable bonding without electrical performance degradation.

Characteristics of Copper Nitride Nanolayer Used in 3D Cu Bonding Interconnects

Haesung Park,Hankyeol Seo,Sarah Eunkyung Kim 대한금속·재료학회 2021 ELECTRONIC MATERIALS LETTERS Vol.17 No.5

Cu–Cu bonding is a key process in fine pitch Cu interconnect in 3-dimenssional Si integration. Despite the excellent electricalproperty and pattern ability of Cu material, the Cu–Cu bonding process is affected by the high bonding temperature and easyoxidation. Thus, the ability to protect the copper surface in a reactive air environment is very important in Cu–Cu bonding,especially for die–to–wafer Cu bonding applications. We studied Cu–Cu bonding using a copper nitride nanolayer as anantioxidant passivation layer and investigated the stability of the copper nitride nanolayer over 7 days and its decompositioncapability across temperatures of up to 400 °C. We found that the copper nitride (Cu4N) nanolayer formed by two-step Ar/N2 plasma treatment protected the copper surface from further oxidation in the air, and that the energy required for thermaldecomposition of the copper nitride nanolayer in this study was about 29.6 kJ/mol. It can be seen that the bonding temperatureof Cu–Cu bonding can be sufficiently lowered by using a low–temperature decomposition property of copper nitride.

황동층의 형성과 선택적 아연 에칭을 통한 구리 필라 상 다공성 구리층의 제조와 구리-구리 플립칩 접합

이완근,최광성,엄용성,이종현 한국마이크로전자및패키징학회 2023 마이크로전자 및 패키징학회지 Vol.30 No.4

대기 중 구리-구리 플립칩(flip-chip) 접합을 위해 제안된 효율적 공정의 실현 가능성을 평가하고자 구리(Cu) 필라(pillar) 상 다공성 구리층의 형성 및 액상 환원제 투입 후 열압착 접합을 실시하였다. 구리 필라 상 다공성 구리층은 아연(Zn) 도금-합금화 열처리-선택적 아연 에칭(etching)의 3단계 공정으로 제조되었는데, 형성된 다공성 구리층의 두께는 평균 약 2.3 ㎛였다. 본 플립칩 접합은 형성 다공성 구리층에 환원성 용제를 침투시킨 후, 반건조 과정을 거쳐 열압착 소결접합으로 진행하였다. 용제로 인한 구리 산화막의 환원 거동과 함께 추가 산화가 최대한 억제되면서 열압착 동안 다공성구리층은 약 1.1 ㎛의 두께로 치밀해지며 결국 구리-구리 플립칩 접합이 완수되었다. 그 결과 10 MPa의 가압력 하에서 대기 중 300 ℃에서 5분간 접합 시 약 11.2 MPa의 접합부 전단강도를 확보할 수 있었는데, 이는 약 50% 이하의 필라들만이접합된 결과로서, 공정 최적화를 통해 모든 필라들의 접합을 유도할 경우 20 MPa 이상의 강도값을 쉽게 얻을 수 있을 것으로 분석되었다. The feasibility of an efficient process proposed for Cu-Cu flip-chip bonding was evaluated by forming a porous Cu layer on Cu pillar and conducting thermo-compression sinter-bonding after the infiltration of a reducing agent. The porous Cu layers on Cu pillars were manufactured through a three-step process of Zn plating-heat treatment-Zn selective etching. The average thickness of the formed porous Cu layer was approximately 2.3 μm. The flip-chip bonding was accomplished after infiltrating reducing solvent into porous Cu layer and pre-heating, and the layers were finally conducted into sintered joints through thermo-compression. With reduction behavior of Cu oxides and suppression of additional oxidation by the solvent, the porous Cu layer densified to thickness of approximately 1.1 μm during the thermo-compression, and the Cu- Cu flip-chip bonding was eventually completed. As a result, a shear strength of approximately 11.2 MPa could be achieved after the bonding for 5 min under a pressure of 10 MPa at 300 ℃ in air. Because that was a result of partial bonding by only about 50% of the pillars, it was anticipated that a shear strength of 20 MPa or more could easily be obtained if all the pillars were induced to bond through process optimization.

파워 소자의 고속 다이 접합을 위한 5 μm Cu@Sn 입자 기반 프리폼의 천이액상 소결접합 특성

한병조,조상호,전강록,이종현 대한금속·재료학회 2024 대한금속·재료학회지 Vol.62 No.1

To ensure the high-temperature stability of a bondline under next-generation power devices suchas SiC semiconductors, a die bonding test was performed by transient liquid-phase (TLP) sinter-bonding usinga Sn-coated Cu (Cu@Sn) particle-based preform. Compared to the existing 20 min-bonding result using a 30μm Cu@Sn particle-based preform, a 5 μm Cu@Sn particle-based preform was used to significantly reducethe bonding time to 5 min, and the optimal levels of the amount of Sn in the Cu@Sn particles, the thicknessesof Sn surface finish layers on the chip and substrate, and compression pressure during the bonding wereinvestigated. The Sn content in the Cu@Sn particles significantly changed the microstructure, including theporosity of the prepared preform. The preform porosity of 0.01% was confirmed after the formation of sufficientSn shells with an average thickness of about 602 nm at Sn 30 wt%. In addition, in the preform with Sn 30wt% content, the Sn phase was almost depleted after 3 min after annealing at 250 °C. The Sn finish layerwas evaluated in the thickness range of 0.63−4.12 μm, and it was observed that the shear strength of theformed bondline tended to increase with increasing pressure for all Sn layer thicknesses. In particular, whenthe bonding was carried out at a pressure of 2 MPa using a dummy Cu chip and substrate coated with a 1.53μm thick Sn layer, the best shear strength value of 36.89 MPa was achieved. In this case, all the Sn phasestransformed into intermetallic compound phases of Cu6Sn5 and Cu3Sn, and all the phases formed within thebondline, including Cu, exhibited high melting-point characteristics. Therefore, it was determined that therewould be no remelting of the bondline or a drastic decrease in mechanical properties in a high-temperatureenvironment below 300 oC, as initially intended. By increasing the content of the Sn shell up to 30 wt%, itwas possible to achieve a nearly full density (porosity: 0.3%) bondline structure, due to the rearrangementbehavior of particles, by maintaining liquid Sn for a long time during the bonding process. In conclusion, theoptimal Sn finish thickness was determined to be at the level of 1.5 μm, and the optimal pressure was at thelevel of 2 MPa. The short bonding time of 5 min represents a significant advance in TLP bonding processes,and it is expected to contribute to a substantial improvement in the die bonding of future SiC power devices.

웨이퍼 레벨 Cu 본딩을 위한 Cu/SiO² CMP 공정 연구

이민재,김사라은경,김성동,Lee, Minjae,Kim, Sarah Eunkyung,Kim, Sungdong 한국마이크로전자및패키징학회 2013 마이크로전자 및 패키징학회지 Vol.20 No.2

Chemical mechanical polishing (CMP) has become one of the key processes in wafer level stacking technology for 3D stacked IC. In this study, two-step CMP process was proposed to polish $Cu/SiO_2$ hybrid bonding surface, that is, Cu CMP was followed by $SiO_2$ CMP to minimize Cu dishing. As a result, Cu dishing was reduced down to $100{\sim}200{\AA}$ after $SiO_2$ CMP and surface roughness was also improved. The bonding interface showed no noticeable dishing or interface line, implying high bonding strength. 본 연구에서는 웨이퍼 레벨 Cu 본딩을 이용한 3D 적층 IC의 개발을 위해 2단계 기계적 화학적 연마법(CMP)을 제안하고 그 결과를 고찰하였다. 다마신(damascene) 공정을 이용한 $Cu/SiO_2$ 복합 계면에서의 Cu dishing을 최소화하기 위해 Cu CMP 후 $SiO_2$ CMP를 추가로 시행하였으며, 이를 통해 Cu dishing을 $100{\sim}200{\AA}$까지 낮출 수 있었다. Cu 범프의 표면거칠기도 동시에 개선되었음을 AFM 관찰을 통해 확인하였다. 2단 CMP를 적용하여 진행한 웨이퍼 레벨 Cu 본딩에서는 dishing이나 접합 계면이 관찰되지 않아 2단 CMP 공정이 성공적으로 적용되었음을 확인할 수 있었다.

Cu-Cu₂O계 공융액상을 활용한 Cu/AlN 직접접합

홍준성,이정훈,오유나,조광준,류도형,오승탁,현창용,Hong, Junsung,Lee, Jung-Hoon,Oh, You-Na,Cho, Kwang-Jun,Riu, Doh-Hyung,Oh, Sung-Tag,Hyun, Chang-Yong 한국분말야금학회 2013 한국분말재료학회지 (KPMI) Vol.20 No.2

In the DBC (direct bonding of copper) process the oxygen partial pressure surrounding the AlN/Cu bonding pairs has been controlled by Ar gas mixed with oxygen. However, the direct bonding of Cu with sound interface and good adhesion strength is complicated process due to the difficulty in the exact control of oxygen partial pressure by using Ar gas. In this study, we have utilized the in-situ equilibrium established during the reaction of $2CuO{\rightarrow}Cu_2O$ + 1/2 $O_2$ by placing powder bed of CuO or $Cu_2O$ around the Cu/AlN bonding pair at $1065{\sim}1085^{\circ}C$. The adhesion strength was relatively better in case of using CuO powder than when $Cu_2O$ powder was used. Microstructural analysis by optical microscopy and XRD revealed that the interface of bonding pair was composed of $Cu_2O$, Cu and small amount of CuO phase. Thus, it is explained that the good adhesion between Cu and AlN is attributed to the wetting of eutectic liquid formed by reaction of Cu and $Cu_2O$.

Ar/N₂ 2단계 플라즈마 처리에 따른 저온 Cu-Cu 직접 접합부의 정량적 계면접착에너지 평가 및 분석

최성훈,김가희,서한결,김사라은경,박영배,Choi, Seonghun,Kim, Gahui,Seo, Hankyeol,Kim, Sarah Eunkyung,Park, Young-Bae 한국마이크로전자및패키징학회 2021 마이크로전자 및 패키징학회지 Vol.28 No.2

3 차원 패키징을 위한 저온 Cu-Cu직접 접합부의 계면접착에너지를 향상시키기 위해 Cu박막 표면에 대한 Ar/N₂ 2단계 플라즈마 처리 전, 후 Cu표면 및 접합계면에 대한 화학결합을 X-선 광전자 분광법(X-ray photoelectron spectroscopy)을 통해 정량화한 결과, 2단계 플라즈마 처리로 인해 Cu표면에 Cu₄N이 형성되어 Cu산화를 효과적으로 억제하는 것을 확인하였다. 2단계 플라즈마 처리하지 않은 Cu-Cu시편은 표면 산화막의 영향으로 접합이 제대로 되지 않았으나 2단계 플라즈마 처리한 시편은 효과적인 표면 산화방지효과로 인해 양호한 Cu-Cu접합을 형성하였다. Cu-Cu직접접합 계면의 정량적 계면접착에너지를 double cantilever beam 시험방법 및 4점 굽힘(4-point bending, 4-PB) 시험방법을 통해 비교한 결과, 각각 1.63±0.24, 2.33±0.67 J/m²으로 4-PB 시험의 계면접착에너지가 더 크게 측정되었다. 이는 계면파괴역학의 위상각(phase angle)에 따른 계면접착에너지 증가 거동으로 설명할 수 있는데 즉, 4-PB의 계면균열선단 전단응력성분 증가로 인한 계면거칠기의 효과에 기인한 것으로 판단된다. The effect of Ar/N₂ two-step plasma treatment on the quantitative interfacial adhesion energy of low temperature Cu-Cu bonding interface were systematically investigated. X-ray photoelectron spectroscopy analysis showed that Ar/N₂ 2-step plasma treatment has less copper oxide due to the formation of an effective Cu4N passivation layer. Quantitative measurements of interfacial adhesion energy of Cu-Cu bonding interface with Ar/N₂ 2-step plasma treatment were performed using a double cantilever beam (DCB) and 4-point bending (4-PB) test, where the measured values were 1.63±0.24 J/m² and 2.33±0.67 J/m², respectively. This can be explained by the increased interfacial adhesion energy according phase angle due to the effect of the higher interface roughness of 4-PB test than that of DCB test.

저온 Cu/Ag-Ag/Cu 본딩에서의 Ag 나노막 효과

김윤호,박승민,김사라은경,Kim, Yoonho,Park, Seungmin,Kim, Sarah Eunkyung 한국마이크로전자및패키징학회 2021 마이크로전자 및 패키징학회지 Vol.28 No.2

차세대 반도체 기술은 이종소자 집적화(heterogeneous integration)를 이용한 시스템-인-패키징(system-inpackage, SIP) 기술로 발전하고 있고, 저온 Cu 본딩은 SIP 구조의 성능 향상과 미세 피치 배선을 위해서 매우 중요한 기술이라 하겠다. 본 연구에서는 porous한 Ag 나노막을 이용하여 Cu 표면의 산화 방지 효과와 저온 Cu 본딩의 가능성을 조사하였다. 100℃에서 200℃의 저온 영역에서 Ag가 Cu로 확산되는 것보다 Cu가 Ag로 확산되는 것이 빠르게 관찰되었고, 이는 저온에서 Ag를 이용한 Cu간의 고상 확산 본딩이 가능함을 나타내었다. 따라서 Ag 나노막을 이용한 Cu 본딩을 200℃에서 진행하였고, 본딩 계면의 전단 강도는 23.27 MPa로 측정되었다. System-in-package (SIP) technology using heterogeneous integration is becoming the key of next-generation semiconductor packaging technology, and the development of low temperature Cu bonding is very important for high-performance and fine-pitch SIP interconnects. In this study the low temperature Cu bonding and the anti-oxidation effect of copper using porous Ag nanolayer were investigated. It has been found that Cu diffuses into Ag faster than Ag diffuses into Cu at the temperatures from 100℃ to 200℃, indicating that solid state diffusion bonding of copper is possible at low temperatures. Cu bonding using Ag nanolayer was carried out at 200℃, and the shear strength after bonding was measured to be 23.27 MPa.

저온 Cu-Cu본딩을 위한 12nm 티타늄 박막 특성 분석

박승민,김윤호,김사라은경,Park, Seungmin,Kim, Yoonho,Kim, Sarah Eunkyung 한국마이크로전자및패키징학회 2021 마이크로전자 및 패키징학회지 Vol.28 No.3

최근 반도체 소자의 소형화는 물리적 한계에 봉착했으며, 이를 극복하기 위한 방법 중 하나로 반도체 소자를 수직으로 쌓는 3D 패키징이 활발하게 개발되었다. 3D 패키징은 TSV, 웨이퍼 연삭, 본딩의 단위공정이 필요하며, 성능향상과 미세피치를 위해서 구리 본딩이 매우 중요하게 대두되고 있다. 본 연구에서는 대기중에서의 구리 표면의 산화방지와 저온 구리 본딩에 티타늄 나노 박막이 미치는 영향을 조사하였다. 상온과 200℃ 사이의 낮은 온도 범위에서 티타늄이 구리로 확산되는 속도가 구리가 티타늄으로 확산되는 속도보다 빠르게 나타났고, 이는 티타늄 나노 박막이 저온 구리 본딩에 효과적임을 보여준다. 12 nm 티타늄 박막은 구리 표면 위에 균일하게 증착되었고, 표면거칠기(R_q)를 4.1 nm에서 3.2 nm로 낮추었다. 티타늄 나노 박막을 이용한 구리 본딩은 200℃에서 1 시간 동안 진행하였고, 이후 동일한 온도와 시간 동안 열처리를 하였다. 본딩 이후 측정된 평균 전단강도는 13.2 MPa이었다. Miniaturization of semiconductor devices has recently faced a physical limitation. To overcome this, 3D packaging in which semiconductor devices are vertically stacked has been actively developed. 3D packaging requires three unit processes of TSV, wafer grinding, and bonding, and among these, copper bonding is becoming very important for high performance and fine-pitch in 3D packaging. In this study, the effects of Ti nanolayer on the antioxidation of copper surface and low-temperature Cu bonding was investigated. The diffusion rate of Ti into Cu is faster than Cu into Ti in the temperature ranging from room temperature to 200℃, which shows that the titanium nanolayer can be effective for low-temperature copper bonding. The 12nm-thick titanium layer was uniformly deposited on the copper surface, and the surface roughness (R_q) was lowered from 4.1 nm to 3.2 nm. Cu bonding using Ti nanolayer was carried out at 200℃ for 1 hour, and then annealing at the same temperature and time. The average shear strength measured after bonding was 13.2 MPa.