Ichiharu Kondo

Formation of high adhesive and pure Pt layers on TiO2

The formation of a high adhesive noble metal layer on an oxide layer has been investigated in the Pt/(Ti)/TiO2/SiO2/Si system, prepared in a vacuum evaporation apparatus. The thermosonic ball bonding test and the conventional pull test were successively applied to the evaluation of adhesion. The Ti inserted layer between the Pt and the TiO2 layer was found to improve the adhesion. A Ti layer of approximately 10 nm was found to be necessary for stronger adhesion. Auger electron spectroscopy (AES) depth profile results showed that a part of the Ti atoms in the inserted layer were segregated to the Pt surface from the interface by annealing at 1373 K for 30 min, while the rest of Ti atoms in the inserted layer remained and acted as a ‘‘glue’’ at the interface between the Pt and the TiO2 layer. It should be noted that Ti could not be detected in the Pt layer within the AES detection limits. Scanning electron microscope and energy dispersive x‐ray spectroscopy observations showed that Ti diffusion occurred thr...

Evaluation of adhesion strength of Ti films on Si(100) by the internal stress method

Abstract Titanium films were sputter deposited onto Si(100) surface. Adhesion strength of the Ti film was evaluated by the internal stress method. The Ti film was overcoated by a Ni coating in the state of a high internal stress, the value of which was about 0.5 GPa (tensile). The internal stress induces large normal and shear stress at the interface between the Ti film and the Si(100) surface. Those stresses increase with the increase of the Ni coating thickness. The stress distribution was evaluated by the finite element method. The evaluation shows that the normal stress on the interface is extremely large at the edge of the sample. This result suggests that a peeling of the Ti film is initiated at the edge and is consistent with observed spontaneous peeling phenomena. We could determine the adhesion strength of the Ti film by measuring the thickness of the Ni coating to peel off the Ti film. The value was found to range in 0.1–1 GPa region. The effect of the Ar ion bombardment of Si substrate on the adhesion enhancement was investigated in detail by this method.

Adhesion measurement of Ti thin films on Si substrate using internal stress in overcoated Ni films

Adhesion strength between sputtered Ti thin films and Si substrate has been evaluated by using an internal stress in Ni thin films deposited onto the Ti thin films. The adhesion of the Ni film to the Ti film is very strong and the internal stress in the Ni film was found to be large enough to peel off the Ti film from the Si substrates. The tensile stress generated by the internal stress in the Ni film at the interface between the Ti film and the Si substrate was evaluated by finite element method. By this method, it became clear that when the value of the Ni film internal stress times the Ni film thickness was 150 N/m, the corresponding tensile stress at the interface was 10 MPa and this stress was enough to peel off the Ti film on an Ar ion bombarded Si substrate.

Effects of different pretreatments on the surface structure of silicon and the adhesion of metal films

Interface structures and adhesion to silicon after different surface pretreatments have been investigated for Ni(500–1000 nm)/Ti(250 nm) films prepared in a dc planar magnetron sputtering apparatus. In order to obtain high adhesion, a chemical pretreatment (with buffered HF) has been found to be favorable in comparison with a conventional Ar ion bombardment pretreatment (with cathodic voltage: 400 V). High resolution transmission electron microscopy (HRTEM) showed that there were two layers between Ti and Si in the case of Ar ion bombardment pretreatment. Energy dispersive x‐ray spectroscopy (EDS) and electron diffraction (ED) showed that they were amorphous Ti–Si alloy and amorphous Si containing Ar. Moreover, a peeling pattern, after the test with adhesive tape, could be found at the boundary between the amorphous Ti–Si alloy layer and the amorphous Si layer containing Ar by using x‐ray photoelectron spectroscopy (XPS). In the case of chemical pretreatment, only an amorphous Ti–Si alloy layer was observ...

Interface structure and adhesion of sputtered metal films on silicon: The influence of Si surface condition

Ni(100–1000 nm)/Ti(250 nm) films were prepared by dc planar magnetron sputtering on Si(100) surfaces. Interface structures between Ti and Si and adhesion of the Ti films to Si after different surface pretreatments have been investigated. Before the film deposition, the Si substrate received an Ar ion bombardment or a chemical etching treatment. In the case of the Ar ion bombardment, we have investigated the effect of the cathodic voltage. A low cathodic voltage (50 V) resulted in high adhesion. The results by Rutherford backscattering spectroscopy showed that the amount of Ar incorporated in the Si surface during the Ar ion bombardment is increased with the cathodic voltage. The existence of Ar at the interface between the Si substrate and the Ti–Si mixed layer seems to lower the adhesion. In the case of the chemical pretreatment, we have investigated the effect of the exposure time in the atmosphere after the chemical etching treatment. A shorter exposure time (within 1 h) has been found to be preferred ...

Interface structure and adhesion of sputtered Ti layers on Si: the effect of heat treatment

Abstract Interface structure and adhesion of the Ti films on Si substrates pretreated by an Ar ion bombardment have been investigated by high resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron diffraction and Auger electron spectroscopy (AES). Two extra layers were observed between the Ti layer and Si substrate in the as-deposited condition. One was an amorphous Si (a-Si) layer about 2 nm thick which contain Ar atoms on the single-crystal Si surface, and the other is an amorphous TiSi (a-TiSi) mixed layer about 3 nm thick on the a-Si layer. A peeling test indicates that complete detachment occurred at the interface between the a-Si and the a-TiSi mixed layer. However, the adhesion was increased by the heat treatment at 723 K for 30 min, and peeling ratio was reduced to about 10%. Ar atoms distributed at the interface seem to cause the reduction of the adhesion. The heat treatment changed the distribution of Ar atoms at the interface. The profile of the interface was also changed to increase the area of direct contact between the TiSi mixed layer and the Si substrate. Both effects seem to enhance the adhesion.

Adhesion measurement of thin metal films by scratch, peel, and pull methods

Scratch, peel, and pull methods for adhesion measurement were applied to deposited thin film/solid substrate combinations. Scatter in the experimental data was observed and its origin is discussed. The interface between the thin film and the substrate was investigated by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and Auger electron spectroscopy (AES), and the correlation of the interface structure with the adhesion strength was investigated. Ion bombardment and heat treatment were carried out to enhance the adhesion. Accumulation of bombarding gas ions at the interface was observed and the role of ion bombardment in improving adhesion is considered.

Thin film structure and adhesion of sputtered TiNi layers on silicon

Abstract Thin film stress, adhesion and structure at different argon pressures have been investigated in the system Ni(200–800 nm)/Ti(100–400 nm)/Si, prepared in a d.c. planar magnetron sputtering apparatus. The adhesion between titanium and silicon has been found to decrease at low argon pressure (0.67 Pa (5 mTorr)) and to increase at high argon pressure (2.67 Pa (20 mTorr)) X-ray diffraction analysis revealed a highly oriented Ni(111) layer near the boundary between nickel and titanium, and the X-ray fluorescence method showed that the density was higher at an argon pressure of 0.67 Pa. The adhesion change is considered to be influenced mainly by the change in stress of the nickel film; that is, the modulus of elasticity seems to vary with crystalline orientation and density, which are affected by the argon pressure.

Formation of compositionally graded multilayer films by discharge gas flow modulation in magnetron sputtering

Abstract A new method to form compositionally graded multilayer films by using a single deposition source has been developed. In this method, the reactive gas flow rate has been changed periodically to form multilayers. As a result, the composition of the multilayer films obtained by this technique changes periodically without any interrupted interfaces. To form multilayers using this technique, a non-linear relationship between the reactive gas flow rate and the deposition parameters such as deposition rate and reactive gas consumption should be considered because they cause a non-linear relationship between the reactive gas flow rate and the composition distribution towards the film depth of deposited films. Without considering this, the film with a sinusoidal component distribution that is assumed to originate novel properties cannot be obtained. By comparing the oxygen distribution towards the film depth obtained by Auger electron spectroscopy with that calculated from O 2 consumption during film deposition, it was found that oxygen diffused towards the metal-rich underlayers during deposition of oxygen-rich layers. This diffusion makes it difficult to estimate and control film layer composition distribution from deposition parameters. By optimizing the gas flow rate change a TiO x multilayer film with a 5-layered sinusoidal component distribution has been obtained.

Growth mechanism of Si nodules on BPSG

Abstract Si nodules that appear in the metal electrodes of integrated circuits often reduce their reliability. The growth process of Si nodules generated on boro-phospho silicate glass (BPSG) in the Al-1 wt.% Si film electrode has been investigated. The Al-1 wt.% Si films sputter deposited on BPSG films were annealed at 723 K for 30 min according to the usual integrated circuit procedure. Scanning electron microscopy and atomic force microscopy observations revealed that the Si nodules seemed to precipitate along Al grain boundaries particularly on the BPSG film and their shape appeared pyramidal. To make clear the mechanism of the growth of the Si nodule on the BPSG film, the interface between the Si nodule and the BPSG film was investigated in detail by transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. As the result, it was found that there existed an amorphous silicon oxide region in the central part of the interface under the Si nodule. The amorphous silicon oxide is considered to be formed by diffusion of oxygen from the BPSG film to the Si nodule during the annealing. The amorphous silicon oxide may act as an embryo for the formation of the Si nodule and the migration of Si atoms dissolved in Al towards the embryo seems to enhance the growth of the Si nodule.