Room temperature Cu–Cu direct bonding using surface activated bonding method

Abstract

Thin copper ͑Cu͒ films of 80 nm thickness deposited on a diffusion barrier layered 8 in. silicon wafers were directly bonded at room temperature using the surface activated bonding method. A low energy Ar ion beam of 40-100 eV was used to activate the Cu surface prior to bonding. Contacting two surface-activated wafers enables successful Cu-Cu direct bonding. The bonding process was carried out under an ultrahigh vacuum condition. No thermal annealing was required to increase the bonding strength since the bonded interface was strong enough at room temperature. The chemical constitution of the Cu surface was examined by Auger electron spectroscope. It was observed that carbon-based contaminations and native oxides on copper surface were effectively removed by Ar ion beam irradiation for 60 s without any wet cleaning processes. An atomic force microscope study shows that the Ar ion beam process causes no surface roughness degradation. Tensile test results show that high bonding strength equivalent to bulk material is achieved at room temperature. The cross-sectional transmission electron microscope observations reveal the presence of void-free bonding interface without intermediate layer at the bonded Cu surfaces.

Fast atom bombardment onto vertically aligned multi-walled carbon nanotube bumps to achieve low interconnect resistance with Au layer

“…By this treatment, contaminants on the surfaces are removed and the surfaces become activated, after which strong direct bonding between the surfaces occurs [18][19][20]. The SAB method is available for metal-tometal bonding [18,21], semiconductor-to-semiconductor bonding [19,22,23], ceramic-to-metal bonding [18,20], and especially diamond-tometal [24]. Accordingly, Ar-FAB is expected to open several graphite layers of MWNTs as conductivity paths via their activation effect.…”

Fine-pitch bump-less Cu-Cu bonding for wafer-on-wafer stacking and its quality enhancement

“…A number of methods have been developed to achieve Cu-Cu bonding at low temperature. One method is to remove the surface oxide with energetic ions and bond the Cu surfaces in ultra-high vacuum (UHV) ambient but this method is less manufacturing worthy [4]. Oxide removal with wet cleaning such as acetic acid [5] has been used with some success.…”

Pressureless Bonding Using Sputtered Ag Thin Films

“…12,13 In this method, the bonding interface forms by interdiffusion of Cu atoms, available under high temperature and pressure, in an ultrahigh vacuum to prevent oxidation. 12 Room-temperature Cu-Cu bonding has been rarely studied, and bonding in an ultrahigh vacuum induces an additional surface activation process.…”

“…12 Room-temperature Cu-Cu bonding has been rarely studied, and bonding in an ultrahigh vacuum induces an additional surface activation process. 13 These processes have many issues to be solved before mass production, mainly the high cost and low throughput of bonding in an ultrahigh vacuum, caused by the surface activation process. This bonding technology must be studied to make it practical for producing high volumes of power devices that will operate reliably in harsh working environments.…”