Masayasu Nihei

Study on step coverage and (111) preferred orientation of aluminum film deposited by a new switching bias sputtering method

A new switching bias sputtering method capable of improving both the step coverage at the small contact holes and the quality of aluminum film has been developed for the formation of reliable interconnection of very large scale integrated circuits. The method features alternating operation of standard and bias sputtering in 5×10−4 Torr of argon. Aluminum film deposited using this method is seen to have seven times higher (111) orientation and four times higher electromigration resistance than simple bias‐sputtered aluminum film. Additionally, the step coverage is raised to 50% for a perpendicular step with 1 μm depth and 1 μm width.

Development of A New High-Frequency, High-Peak Current Power Source for High Constricted Arc Formation

A new power source, able to generate high-frequency, up to 20 kHz, and high-peak pulse current, up to 500 A, has been developed. By using the new power source, arc pressure and bead depth 3 times as high and twice as deep as those obtained from the DC power source were obtained. The new power source achieved a stable arc in a narrow groove with high aspect ratio due to high constriction. Welding speeds using the new power source are twice as fast as the DC arc.

A Void Free Soldering Process in Large-Area, High Power Insulated Gate Bipolar Transistor Modules

We have developed a new void free process for making the solder joint between the chip mounted AlN substrate and the metal substrate in large-area, high power insulated gate bipolar transistor (IGBT) modules. This new process consists of two steps. First, Ar+ were used to clean the surfaces of Ni plated film on a metal and AlN substrates which were then coated with 0.5-µm-thick Ag film. Second, 50 wt% Pb–Sn solder was sandwiched between the two substrates and heated to 503 K in a vacuum for 5 min before being cooled in a N2 atmosphere. By using this process, the area percentage of voids in a soldering area up to 130×190 mm2 can be reduced to less than 0.1%. IGBT modules made by this process were also found to exhibit satisfactory current-voltage characteristics.

Formation of W underlayer by switching bias sputtering to plug 0.25 μm contact holes

Physical vapor deposion by a newly developed switching bias sputtering method for the formation of both adhesion and barrier metal underlayers on 0.25 μm contact/via holes with sufficient step coverage has been investigated as a hole filling process. The method features alternating operation of sputtering to deposit and resputtering of the film to enhance step coverages of the side walls by resputtering of the bottom. It was found that W films formed for holes with aspect ratios of 3.0–3.5 gave step coverages of 17%–23% for the side wall and 30%–33% for the bottom. The resistivity of W films deposited on planar surfaces was 10.5 μΩ cm, similar to values for W films deposited by conventional direct current (dc) sputtering. The deposition rate of the sputtering was 50%–80% of the rate of conventional dc sputtering.

High-reliability interconnection formation by a two-step switching bias sputtering process

Abstract A two-step switching bias sputtering method which can considerably improve both step coverage and electromigration resistance compared with that attainable by conventional d.c. and d.c. bias sputtering has been developed for the formation of reliable interconnections for LSIs. One-step switching bias sputtering consists of alternating operations of d.c. and d.c. bias sputtering. This method features two-step bias, which consists of deep bias followed by shallow bias sputtering. The first bias enhances step coverage of walls by resputtering Al films at the base of the holes. The second bias removes the contaminated Al layer using Ar. Al films of good quality and electromigration resistance values comparable with those attained by conventional d.c. sputtering can be formed by reducing the cyclic number of alternating operations of two-step switching bias sputtering from 18 to 1. The step coverage of Al films at small contact holes by this method is three times higher than that obtained by conventional d.c. sputtering.

Submicron contact hole filling by electron bias sputtering

A new electron bias sputtering method capable of filling Al into submicron contact holes without degradation of the quality has been developed for the formation of reliable interconnections of very large scale integrated circuits. The method features intermittent electron irradiation to enhance Al flow during sputtering. The Al film deposited contains little Ar and has low resistivity. Contact holes with 0.4‐μm diameter and 0.9‐μm depth can be filled with Al.