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T. H. Kim

Bio: T. H. Kim is an academic researcher from University of Tokyo. The author has contributed to research in topics: Anodic bonding & Wafer. The author has an hindex of 5, co-authored 7 publications receiving 404 citations.

Papers
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Journal ArticleDOI
TL;DR: A low energy Ar ion beam of 40-100 eV was used to activate the Cu surface prior to bonding in this paper, which enables successful Cu-Cu direct bonding under an ultrahigh vacuum condition.
Abstract: Thin copper (Cu) 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 ...

269 citations

Journal ArticleDOI
TL;DR: In this paper, a sequential plasma activation process consisting of oxygen reactive ion etching (RIE) plasma and nitrogen radical plasma was applied for microfluidics packaging at room temperature.
Abstract: A sequential plasma activation process consisting of oxygen reactive ion etching (RIE) plasma and nitrogen radical plasma was applied for microfluidics packaging at room temperature. Si/glass and glass/glass wafers were activated by the oxygen RIE plasma followed by nitrogen microwave radicals. Then, the activated wafers were brought into contact in atmospheric pressure air with hand-applied pressure where they remained for 24 h. The wafers were bonded throughout the entire area and the bonding strength of the interface was as strong as the parents bulk wafers without any post-annealing process or wet chemical cleaning steps. Bonding strength considerably increased with the nitrogen radical treatment after oxygen RIE activation prior to bonding. Chemical reliability tests showed that the bonded interfaces of Si/Si could significantly withstand exposure to various microfluidics chemicals. Si/glass and glass/glass cavities formed by the sequential plasma activation process indicated hermetic sealing behavior. SiOx Ny was observed in the sequentially plasma-treated glass wafer, and it is attributed to binding of nitrogen with Si and oxygen and the implantation of N2 radical in the wafer. High bonding strength observed is attributed to a diffusion of absorbing water onto the wafer surfaces and a reaction between silicon oxynitride layers on the mating wafers. T-shape microfluidic channels were fabricated on glass wafers by bulk micromachining and the sequential plasma-activated bonding process at room temperature

65 citations

Journal ArticleDOI
TL;DR: A wafer level surface activated bonding (SAB) tool has been developed for microelectromechanical systems (MEMS) packaging at low temperature as mentioned in this paper, which accommodates 8 in. diam wafers to a margin of error within ± 1 μm and the X, Y and θ axis alignments with an accuracy of ± 0.5 μm.
Abstract: A wafer level surface activated bonding (SAB) tool has been developed for microelectromechanical systems (MEMS) packaging at low temperature. The tool accommodates 8 in. diam wafers. The principle features of the tool are the automatic parallel adjustment for 8 in. wafers to a margin of error within ± 1 μm and the X, Y, and θ axis alignments with an accuracy of ±0.5 μm. We have approached a new integration technique for the integration of ionic crystals with transparent and nontransparent thin intermediate layers using this tool. Various sizes of patterned and bare silicon, Al silicate glass, and quartz wafers cleaned by a low energy argon ion source in a vacuum have been successfully bonded by this technique at low temperature. Radioisotope fine leak and vacuum seal tests of sealed silicon cavities show leak rates of 1.0 X 10 -9 and 2.6 X 10 -16 Pa/m 3 s, respectively, which are lower than the American military standard encapsulation requirements for MEMS devices in harsh environments. Void-free interfaces with bonding strengths comparable to bulk materials are found. Low adhesion between SAB-processed ionic crystals without adhesive layers is believed to be due to radiation-induced discontinuous polarization.

61 citations

Proceedings ArticleDOI
01 Jun 2004
TL;DR: In this paper, a sequential plasma activation process consisting of oxygen reactive ion etching (RIE) plasma and nitrogen radical activation is proposed for wafer direct bonding at room temperature, where the Si wafer surface is activated by oxygen RIE plasma and subsequently exposed to nitrogen radicals.
Abstract: A sequential plasma activation process consisting of oxygen reactive ion etching (RIE) plasma and nitrogen radical activation is proposed for wafer direct bonding at room temperature. The Si wafer surface is activated by oxygen RIE plasma and subsequently exposed to nitrogen radicals. The activated wafers by the two-step process were brought into contact in air followed by keeping them in air for 24 h. The wafers were bonded throughout the whole area and the bonding strength of the interface is as strong as bulk Si without any post-annealing process and wet chemical cleaning steps. XPS study indicates that the silicon surface has thermodynamically unstable characteristics. IR transmission images reveal a considerable amount of water is absorbed in the wafer surfaces during exposure to air after the plasma activation process. The high bonding strength is thought to be due to a diffusion of absorbed water into the wafer surface and a reaction between silicon oxynitride layers on the opposing wafer. TEM images show that an intermediate amorphous layer with thickness of 15 nm is formed across the interface. The bonding is so intimate that no micro-voids are found at the bonding interface. Furthermore, strong bonding of crystalline quartz and fused quartz at room temperature was also obtained by the sequential activation process.

43 citations

Proceedings ArticleDOI
19 Nov 2001
TL;DR: In this article, the authors describe a copper wafer bonding process for three-dimensional integration and wafer-level packaging applications, where 8-inch silicon wafers were coated with 80 nm copper and the copper surfaces were cleaned by irradiation of 50-100 eV argon ion beam before mating them together.
Abstract: This paper describes a copper wafer bonding process for three-dimensional integration and wafer-level packaging applications. Cu-Cu direct bonding at low temperature using a low energy ion activation method was investigated. 8-inch silicon wafers were coated with 80 nm copper and the copper surfaces were cleaned by irradiation of 50-100 eV argon ion beam before mating them together. The cleaned surfaces were examined by Auger electron spectroscopy (AES). It was observed that carbon contamination and the native oxide layer on the copper surface were effectively removed by 1 min ion beam irradiation without any wet cleaning process. After cleaning the surfaces, two wafers were brought into contact and pressed up to 1000 kgf in the bonding chamber at ultra high vacuum (UHV) pressure. The surfaces were examined by atomic force microscopy (AFM) and the bonded interface was investigated by tensile tests. Details of characterization of bonding interface of Cu-Cu and the effects of low energy ion beam on the bonding are described.

15 citations


Cited by
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Journal ArticleDOI
TL;DR: This review provides easy-to-understand examples and targets the microtechnology/engineering community as well as researchers in the life sciences, and discusses both research and commercial activities.

375 citations

Patent
07 Aug 2006
TL;DR: In this paper, a method of three-dimensional integration of elements such as singulated die or wafers and an integrated structure having connected elements, including singulated dies or wafer, was proposed.
Abstract: A method of three-dimensionally integrating elements such as singulated die or wafers and an integrated structure having connected elements such as singulated dies or wafers. Either or both of the die and wafer may have semiconductor devices formed therein. A first element having a first contact structure is bonded to a second element having a second contact structure. First and second contact structures can be exposed at bonding and electrically interconnected as a result of the bonding. A via may be etched and filled after bonding to expose and form an electrical interconnect to interconnected first and second contact structures and provide electrical access to this interconnect from a surface. Alternatively, first and/or second contact structures are not exposed at bonding, and a via is etched and filled after bonding to electrically interconnect first and second contact structures and provide electrical access to interconnected first and second contact structure to a surface. Also, a device may be formed in a first substrate, the device being disposed in a device region of the first substrate and having a first contact structure. A via may be etched, or etched and filled, through the device region and into the first substrate before bonding and the first substrate thinned to expose the via, or filled via after bonding.

215 citations

PatentDOI
TL;DR: In this paper, a first substrate having a first set of metallic bonding pads, preferably connected to a device or circuit, and having a second non-metallic region adjacent to the metallic bonding pad on the second substrate, and a contact-bonded interface between the first and second set of metamodel interfaces formed by contact bonding of the first nonmetallic regions to the second nonmetal regions.
Abstract: A bonded device structure including a first substrate having a first set of metallic bonding pads, preferably connected to a device or circuit, and having a first non-metallic region adjacent to the metallic bonding pads on the first substrate, a second substrate having a second set of metallic bonding pads aligned with the first set of metallic bonding pads, preferably connected to a device or circuit, and having a second non-metallic region adjacent to the metallic bonding pads on the second substrate, and a contact-bonded interface between the first and second set of metallic bonding pads formed by contact bonding of the first non-metallic region to the second non-metallic region. At least one of the first and second substrates may be elastically deformed.

183 citations

Journal ArticleDOI
TL;DR: A surface activated direct bonding technique was developed to integrate a magneto-optical garnet crystal on the silicon waveguides and demonstrated an optical isolation of 30 dB and insertion loss of 13 dB at a wavelength of 1548 nm.

150 citations

Journal ArticleDOI
TL;DR: In this paper, self-assembled monolayer (SAM) of 1-hexanethiol is applied on copper surface to retard surface oxidation during exposure in the ambient to provide a clean Cu surface.
Abstract: Self-assembled monolayer (SAM) of 1-hexanethiol is applied on copper (Cu) surface to retard surface oxidation during exposure in the ambient. This SAM layer can be desorbed effectively with an annealing step in inert N2 ambient to provide a clean Cu surface. Using this passivation method with SAM, wafers covered with thin Cu layer are passivated, stored, desorbed, and bonded at 250 °C. The bonded Cu layer presents clear evidence of substantial interdiffusion and grain growth despite prolonged exposure in the ambient. This method of passivation is proven to be effective and can be further optimized to enable high quality Cu–Cu direct bonding at low temperature for application in three-dimensional integration.

143 citations