Yoshiaki Wakashima

Moisture-Induced Aluminum Corrosion and Stress on the Chip in Plastic-Encapsulated LSIs

Stress of encapsulant resin which acts on LSI chip was measured to evaluate passivation defects by a new method. It was cleared that the resin thermal stress gave damage to the LSI passivation film and aluminum corrosion took place by moisture penetrating through the film damage up to the metal surface in a humid atmosphere. The stress values obtained by the new method for various resins showed good correlation to the passivation defect densities. When a resin with half stress was applied, the defect density was halved. To improve the moisture resistance of plastic-encapsulated LSIs, the application of the low stress resin is supposed to be a good method.

Rate-Determining Factor of Aluminum Corrosion and a Rapid Method of Assessing the Moisture Resistance of Plastic Encapsulated LSI

New information about the aluminum corrosion of plastic encapsuled LSI was derived from measuring the leakage current on the die surface. Aluminum corrosion at temperature/humidity tests depends upon the water film produced at the interface between the molding resin and die. The moisture resistance of plastic encapsulated LSI can be rapidly evaluated by electrical leakage which can be related to water film formation.

Silicone Elastomer Vulcanized by the Hydrosilation Reaction and its Influence on Properties of a Modified Mos Device

A p-MOS device in which the gate position is incompletely covered by the gate electrode has been used as a test device to estimate influence of silicone elastomer on residual current after gate operation. The elastomer was vulcanized by the hydrosilation reaction. It was found that the residual current could be represented as a function of the hardness and electrical conductivity of the silicone elastomer; that is, the current increased with decreasing hardness and increasing conductivity over the temperature range from 100 to 150°C. Comparison of activation energies measured by the residual current and by electrical conductivity indicated that different mechanisms of charge transport may be in operation, The differences may be due to the presence of dipole moments such as from unreacted hydrosilyl groups and of certain species such as water and chloride ions.

A Study of Parasitic MOS Formation Mechanism in Plastic Encapsulated MOS Devices

With a view to preventing the formation of parasitic MOS in plastic encapsulated MOS devices, we studied the mechanism of the formation and found that parasitic MOS is due not only to surface mobile charge on oxidized silicon but also to bulk charge in plastic materials. Concerning an epoxy resin for semiconductor use, which is the most widely used material for plastic encapsulation, the behavior of bulk charge under pressure was investigated by electrical measurement and that under application of high voltage dc was also investigated electrically and by EPMA analysis. As a result, it was established that the majority of the mobile charge is actually certain ions with a negative charge and containing chlorine, rather than electrons or dipoles. It was further confirmed that parasitic MOS formation is extremely scant in MOS devices encapsulated with the same type of epoxy resins with little hydrolyzable chloride ion, and hence that minimizing the ionizable component in plastic materials is highly effective in preventing parasitic MOS formation. Motion of charge along the interface between silicon oxide layer and plastic could not be clarified. However, it is thought that parasitic MOS formation due to this motion can be prevented by providing an appropriate guard ring.

Water vapor solubility and permeability of coating polymers and their effects on residual current of modified semiconductor devices.

シリコーン系, 熱可塑系, 及びイミド系などの各種ポリマーが, 恒湿度雰囲気下 (25℃, 0～75%RH) で半導体素子に及ぼす影響を調べるために, 各ポリマーの吸湿率, 及び透過係数などを測定し, 水分の拡散係数を算出した. 次に, ポリマー, 及び水分などの影響を評価できるように工夫した電界効果型トランジスタの残留電流を測定した。残留電流は, ポリマーの種類によって異なり, 印加時間の延長, 及び湿度の増加などによって増大する傾向を示した. この残留電流は, 拡散係数D, 時間t, 及び相対湿度 Px (%) などを含む関数として表せることを導き出した. log Ir=m・Px+n・log (D・t) +log C, ここで, m, n及びCなどは, ポリマーの種類及び, 素子の構造によって決定される係数である. 拡散係数を比較することにより, 恒湿度雰囲気下で残留電流が増大する機構について考察した.

Influencing factors and calculation of residual currents for modified metal‐oxide‐semiconductor devices covered with various silicone elastomers

An equation for the residual current induced by electric potential during charging of the gate electrode in modified transistors was derived by using electrical conductivity, Atalla’s model, and Ihantola’s equation for metal‐oxide‐semiconductor devices. The equation was examined by comparing calculated values with measured values of the residual current in a transistor covered with a silicone elastomer vulcanized by various reactions. Factors causing variations in hardness affect the electrical conductivity of the silicone elastomers. These are analyzed based on the vulcanization reaction system and the catalyst species.