A low temperature Cu-Cu direct bonding method with VUV and HCOOH treatment for 3D integration

Sakai, Taiji; Imaizumi, Nobuhiro; Sakuyama, Seiki

doi:10.1109/icep-iaac.2015.7111059

Cited by 9 publications

(5 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Moreover, low pre-treatment temperature below Cu re-crystallization point does not promote the coalescence of Cu fine grains, which should proceed during the bonding process instead of the pre-treatment process. Interfacial gap/void filling by the Cu coalescence also plays a key role during low-temperature wafer bonding [ 16 ].…”

Section: Resultsmentioning

confidence: 99%

“…In addition, a pre-treatment process should be implemented at lower than Cu re-crystallization temperature, because the coalescence of Cu fine grains during the bonding process plays an important role in filling interfacial gaps and voids which cause air leaking [ 14 , 15 ]. Typical Cu re-crystallization temperature is reported as the range of 120–150 °C [ 16 ].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Bonding-Based Wafer-Level Vacuum Packaging Using Atomic Hydrogen Pre-Treated Cu Bonding Frames

et al. 2018

View full text Add to dashboard Cite

A novel surface activation technology for Cu-Cu bonding-based wafer-level vacuum packaging using hot-wire-generated atomic hydrogen treatment was developed. Vacuum sealing temperature at 300 °C was achieved by atomic hydrogen pre-treatment for Cu native oxide reduction, while 350 °C was needed by the conventional wet chemical oxide reduction procedure. A remote-type hot-wire tool was employed to minimize substrate overheating by thermal emission from the hot-wire. The maximum substrate temperature during the pre-treatment is lower than the temperature of Cu nano-grain re-crystallization, which enhances Cu atomic diffusion during the bonding process. Even after 24 h wafer storage in atmospheric conditions after atomic hydrogen irradiation, low-temperature vacuum sealing was achieved because surface hydrogen species grown by the atomic hydrogen treatment suppressed re-oxidation. Vacuum sealing yield, pressure in the sealed cavity and bonding shear strength by atomic hydrogen pre-treated Cu-Cu bonding are 90%, 5 kPa and 100 MPa, respectively, which are equivalent to conventional Cu-Cu bonding at higher temperature. Leak rate of the bonded device is less than 10−14 Pa m3 s−1 order, which is applicable for practical use. The developed technology can contribute to low-temperature hermetic packaging.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Bonding-Based Wafer-Level Vacuum Packaging Using Atomic Hydrogen Pre-Treated Cu Bonding Frames

et al. 2018

View full text Add to dashboard Cite

show abstract

“…As pointed out by the authors, flux-less soldering became already an active research area in the early 1990s, and formic-acid vapor (HCOOH) appeared to be a very promising reaction gas for flux-less flip-chip bonding technique. HCOOH reacts with metal oxides already at temperatures above 150 • C, attracting its use for low-temperature processes in 3-D integrations, for example for a Cu-Cu direct bonding method [22]. Between 150 • C and 200 • C, the compound M(COOH) is formed by the chemical reaction…”

Section: Flip-chip Bondingmentioning

confidence: 99%

Fluxless flip-chip bonding using a lead-free solder bumping technique

et al. 2017

View full text Add to dashboard Cite

With the LHC exceeding the nominal instantaneous luminosity, the current barrel pixel detector (BPIX) of the CMS experiment at CERN will reach its performance limits and undergo significant radiation damage. In order to improve detector performance in high luminosity conditions, the entire BPIX is replaced with an upgraded version containing an additional detection layer. Half of the modules comprising this additional layer are produced at DESY using fluxless and lead-free bumping and bonding techniques. Sequential solder-jetting technique is utilized to wet 40-µm SAC305 solder spheres on the silicon-sensor pads with electroless Ni, Pd and immersion Au (ENEPIG) under-bump metallization (UBM). The bumped sensors are flip-chip assembled with readout chips (ROCs) and then reflowed using a flux-less bonding facility. The challenges for jetting low solder volume have been analyzed and will be presented in this paper. An average speed of 3.4 balls per second is obtained to jet about 67 thousand solder balls on a single chip. On average, 7 modules have been produced per week. The bump-bond quality is evaluated in terms of electrical and mechanical properties. The peak-bump resistance is about 17.5 mΩ. The cross-section study revealed different types of intermetallic compounds (IMC) as a result of interfacial reactions between UBM and solder material. The effect of crystalline phases on the mechanical properties of the joint is discussed. The mean shear strength per bump after the final module reflow is about 16 cN. The results and sources of yield loss of module production are reported. The achieved yield is 95%.

show abstract

“…Another developing surface modification pretreatment for direct Cu bonding is a combined process with diamond cutting, formic acid vapor and vacuum ultraviolet irradiation [9,10,11]. The bonding can be achieved even at 175 o C. It was reported that nano-sized grains underneath the diamond cut surface accelerate metallurgical interdiffusion between Cu-Cu interface.…”

Section: Introductionmentioning

confidence: 99%