Heterogeneous silicon integration by ultra-high vacuum wafer bonding

The two most important characteristics of any surface considered for wafer bonding are cleanliness, surface smoothness and macroscopic flatness. Silicon wafers in the as-received condition have a native oxide on the surface several nanometers thick [1], Figure la shows that they also have a layer of hydrocarbons. While they are not clean, they are smooth. Our wafers were plasma or ion cleaned, chemically treated, and ultra high vacuum (UHV) thermal desorption annealed in different combinations to find the best method for providing smooth, contamination free substrates that will produce an atomically flat, chemically clean Si/Si bonded interface.The first approach was a single step process to remove the contaminants and then bond the clean wafers. Cleaning was accomplished by ion bombardment of the surface in an UHV chamber with base pressure 1x109 Torr. This ion cleaning chamber is connected between the UHV (2x10-10 ) bonding chamber and UHV (1x10-10) analysis chamber, allowing wafers to be cleaned, analyzed, and bonded without breaking vacuum [2].

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Electrical characterisation of UHV-bonded silicon interfaces

MRS Proceedings ◽

10.1557/proc-681-i4.4 ◽

2001 ◽

Vol 681 ◽

Cited By ~ 3

Author(s):

A. Reznicek ◽

S. Senz ◽

O. Breitenstein ◽

R. Scholz ◽

U. Gösele

Keyword(s):

Current Density ◽

Wafer Bonding ◽

Applied Voltage ◽

High Current Density ◽

Strong Dependence ◽

High Vacuum ◽

Ultra High Vacuum ◽

Bonding Energy ◽

Constant Density ◽

Trap States

ABSTRACTDirect wafer bonding can be used to mechanically and electrically connect semiconductors. In our experiments two 100 mm diameter (100) Si wafers (n-doping: 1014 cm−3) are first cleaned by standard chemical cleaning (RCA 1, 2). The surface is terminated by hydrogen after a HF dipping. The wafers are prebonded in air to protect the surface. After introduction into the ultra high vacuum (UHV) system the wafers are separated again. The hydrogen termination is released in a heating chamber. RHEED confirmed a surface reconstruction. The wafers are then cooled down to room temperature and bonded in UHV. The bonding energy is very close to the bulk bonding energy.Measurements of whole n-n wafers showed a linear relationship of voltage and current at a low current density of 0.05 A/cm2. The current flow is inhomogeneous, which is visible in IR- thermography images. Above 0.1 V the current density first saturates, but increases super- linearly for higher voltages. The electrical properties of a grain boundary can be modeled by a double Schottky barrier. The barrier height decreases with increasing applied voltage. C-V measurements show a strong dependence of capacitance on frequency, temperature and applied voltage.The capacitance increases with higher temperature and lower frequency. The interface state density can be estimated from the low temperature and high frequency capacitance limit as Dit = 1·1011 cm−2 eV−1 assuming a constant density of states.We can conclude that in order to avoid the undesirable effect of the potential barrier and trap states at the bonding interface a high doping near the interface is required for the application of wafer bonding to devices with a high current density across the bonded interface.

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Thin Pyrolytic Graphite Films for Electron Microscope Substrates

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100065183 ◽

1971 ◽

Vol 29 ◽

pp. 226-227 ◽

Cited By ~ 1

Author(s):

George H. N. Riddle ◽

Benjamin M. Siegel

Keyword(s):

Vacuum Chamber ◽

Pyrolytic Graphite ◽

High Vacuum ◽

Dark Field ◽

Ultra High Vacuum ◽

Graphite Substrate ◽

Nickel Substrate ◽

Routine Procedure ◽

Field Electron Microscopy ◽

Dark Field Electron

A routine procedure for growing very thin graphite substrate films has been developed. The films are grown pyrolytically in an ultra-high vacuum chamber by exposing (111) epitaxial nickel films to carbon monoxide gas. The nickel serves as a catalyst for the disproportionation of CO through the reaction 2C0 → C + CO2. The nickel catalyst is prepared by evaporation onto artificial mica at 400°C and annealing for 1/2 hour at 600°C in vacuum. Exposure of the annealed nickel to 1 torr CO for 3 hours at 500°C results in the growth of very thin continuous graphite films. The graphite is stripped from its nickel substrate in acid and mounted on holey formvar support films for use as specimen substrates.The graphite films, self-supporting over formvar holes up to five microns in diameter, have been studied by bright and dark field electron microscopy, by electron diffraction, and have been shadowed to reveal their topography and thickness. The films consist of individual crystallites typically a micron across with their basal planes parallel to the surface but oriented in different, apparently random directions about the normal to the basal plane.

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A High Voltage Electron Microscopy Study of Sub-Oxide Formation in Vanadium

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100065110 ◽

1971 ◽

Vol 29 ◽

pp. 212-213

Author(s):

R. H. Geiss ◽

R. L. Ladd ◽

K. R. Lawless

Keyword(s):

High Vacuum ◽

Microscopy Study ◽

Electron Microscopy Study ◽

Ultra High Vacuum ◽

Pure Oxygen ◽

Pressure Oxidation ◽

High Voltage Electron Microscopy ◽

Oxidation Study ◽

Voltage Electron ◽

Good Agreement

Detailed electron microscope and diffraction studies of the sub-oxides of vanadium have been reported by Cambini and co-workers, and an oxidation study, possibly complicated by carbon and/or nitrogen, has been published by Edington and Smallman. The results reported by these different authors are not in good agreement. For this study, high purity polycrystalline vanadium samples were electrochemically thinned in a dual jet polisher using a solution of 20% H2SO4, 80% CH3OH, and then oxidized in an ion-pumped ultra-high vacuum reactor system using spectroscopically pure oxygen. Samples were oxidized at 350°C and 100μ oxygen pressure for periods of 30,60,90 and 160 minutes. Since our primary interest is in the mechanism of the low pressure oxidation process, the oxidized samples were cooled rapidly and not homogenized. The specimens were then examined in the HVEM at voltages up to 500 kV, the higher voltages being necessary to examine thick sections for which the oxidation behavior was more characteristic of the bulk.

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The High Resolution Scanning Transmission Electron Microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100051591 ◽

1974 ◽

Vol 32 ◽

pp. 316-317

Author(s):

A. V. Crewe

Keyword(s):

Electron Microscope ◽

High Resolution ◽

High Vacuum ◽

Scanning Transmission Electron Microscope ◽

Ultra High Vacuum ◽

Resolving Power ◽

Imaging Characteristics ◽

Transmission Electron ◽

Scanning Transmission ◽

The Moment

The high resolution STEM is now a fact of life. I think that we have, in the last few years, demonstrated that this instrument is capable of the same resolving power as a CEM but is sufficiently different in its imaging characteristics to offer some real advantages.It seems possible to prove in a quite general way that only a field emission source can give adequate intensity for the highest resolution^ and at the moment this means operating at ultra high vacuum levels. Our experience, however, is that neither the source nor the vacuum are difficult to manage and indeed are simpler than many other systems and substantially trouble-free.

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Structure of Palladium Single-Crystal Films Prepared by Flash Evaporation onto (001) NaCl Substrates

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100069272 ◽

1970 ◽

Vol 28 ◽

pp. 456-457

Author(s):

L. E. Murr ◽

G. Wong

Keyword(s):

Single Crystal ◽

High Vacuum ◽

Ultra High Vacuum ◽

High Rate ◽

Flash Evaporation ◽

Optimum Load ◽

Single Crystal Films ◽

Crystal Films ◽

A Current

Palladium single-crystal films have been prepared by Matthews in ultra-high vacuum by evaporation onto (001) NaCl substrates cleaved in-situ, and maintained at ∼ 350° C. Murr has also produced large-grained and single-crystal Pd films by high-rate evaporation onto (001) NaCl air-cleaved substrates at 350°C. In the present work, very large (∼ 3cm2), continuous single-crystal films of Pd have been prepared by flash evaporation onto air-cleaved (001) NaCl substrates at temperatures at or below 250°C. Evaporation rates estimated to be ≧ 2000 Å/sec, were obtained by effectively short-circuiting 1 mil tungsten evaporation boats in a self-regulating system which maintained an optimum load current of approximately 90 amperes; corresponding to a current density through the boat of ∼ 4 × 104 amperes/cm2.

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A Field Emission System For Transmission Electron Microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100071934 ◽

1973 ◽

Vol 31 ◽

pp. 298-299

Author(s):

Michel Troyonal ◽

Huei Pei Kuoal ◽

Benjamin M. Siegelal

Keyword(s):

Electron Microscope ◽

Field Emission ◽

Optical System ◽

High Vacuum ◽

Ultra High Vacuum ◽

Objective Lens ◽

Electron Optical System ◽

Cross Sectional ◽

Transmission Electron ◽

Emission System

A field emission system for our experimental ultra high vacuum electron microscope has been designed, constructed and tested. The electron optical system is based on the prototype whose performance has already been reported. A cross-sectional schematic illustrating the field emission source, preaccelerator lens and accelerator is given in Fig. 1. This field emission system is designed to be used with an electron microscope operated at 100-150kV in the conventional transmission mode. The electron optical system used to control the imaging of the field emission beam on the specimen consists of a weak condenser lens and the pre-field of a strong objective lens. The pre-accelerator lens is an einzel lens and is operated together with the accelerator in the constant angular magnification mode (CAM).

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Hetero-Epitaxy of Group Va Metals on Sapphire

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100095716 ◽

1972 ◽

Vol 30 ◽

pp. 492-493

Author(s):

J. E. O'Neal ◽

J. J. Bellina ◽

B. B. Rath

Keyword(s):

Thermal Contact ◽

High Vacuum ◽

Electron Beam Evaporation ◽

Ultra High Vacuum ◽

Backing Plate ◽

Sapphire Substrates ◽

Deposition Parameters ◽

Polishing Damage ◽

Reflection Electron Diffraction

Thin films of the bcc metals vanadium, niobium and tantalum were epitaxially grown on (0001) and sapphire substrates. Prior to deposition, the mechanical polishing damage on the substrates was removed by an in-situ etch. The metal films were deposited by electron-beam evaporation in ultra-high vacuum. The substrates were heated by thermal contact with an electron-bombarded backing plate. The deposition parameters are summarized in Table 1.The films were replicated and examined by electron microscopy and their crystallographic orientation and texture were determined by reflection electron diffraction. Verneuil-grown and Czochralskigrown sapphire substrates of both orientations were employed for each evaporation. The orientation of the metal deposit was not affected by either increasing the density of sub-grain boundaries by about a factor of ten or decreasing the deposition rate by a factor of two. The results on growth epitaxy are summarized in Tables 2 and 3.

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Atomic-level imaging of the surface structure of Ag2O

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100113160 ◽

1984 ◽

Vol 42 ◽

pp. 656-657

Author(s):

William Krakow

Keyword(s):

High Vacuum ◽

Atomic Level ◽

Ultra High Vacuum ◽

Research Groups ◽

Resolution Electron ◽

Surface Reconstructions ◽

Order Of Magnitude ◽

High Resolution Electron Microscope ◽

Saturated Structure ◽

Transmission And Reflection

In recent years electron microscopy has been used to image surfaces in both the transmission and reflection modes by many research groups. Some of this work has been performed under ultra high vacuum conditions (UHV) and apparent surface reconstructions observed. The level of resolution generally has been at least an order of magnitude worse than is necessary to visualize atoms directly and therefore the detailed atomic rearrangements of the surface are not known. The present author has achieved atomic level resolution under normal vacuum conditions of various Au surfaces. Unfortunately these samples were exposed to atmosphere and could not be cleaned in a standard high resolution electron microscope. The result obtained surfaces which were impurity stabilized and reveal the bulk lattice (1x1) type surface structures also encountered by other surface physics techniques under impure or overlayer contaminant conditions. It was therefore decided to study a system where exposure to air was unimportant by using a oxygen saturated structure, Ag2O, and seeking to find surface reconstructions, which will now be described.

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