An accelerated electromigration life-test method has been developed to evaluate the large electromigration resistance of Cu interconnects in a ve~. short period of test time. The essence of the acceleration technique employed here is to use stress current more. than 107 A/cm 2 and to utilize the self-heating of the test interconnect for giving temperature stress. Moreover, to avoid uncontrollable thermal runaway and resultant interconnect melting, we adopted an efficient cooling technique that immediately removes the joule heat and keeps the interconnect temperature constant. As a result, it has been demonstrated that large grain copper interconnects created by a low-kinetic-energy particle process and the thermal annealing that follows exhibit approximately three orders of magnitude larger electromigration lifetime at 300 K than Al-alloy interconnects formed by a conventional sputtering process. Additionally, a new expression for electromigration lifetime was proposed based on Black's equation through the comparative studies of electromigration endurance of various materials.Enhancement in integration density and speed performance of ULSI circuits requires miniaturization of transistors and interconnects as well as higher current driving capabilities for transistors. As a result, large currents must be conducted through long interconnects with small cross sections. Therefore the establishment of a metallization scheme which ensures high electromigration reliability as well as low interconnect resistance is important.Aluminum-based alloys, such as A1-Si and A1-Si-Cu, are major materials used to form interconnects in integrated circuits. However, their resistivities are not low enough to operate ULSI circuits at ultrahigh speed. Furthermore, these alloys are liable to show high susceptibility to electromigration and stress-migration failures. Copper(Cu) is drawing considerable attention as an alternative to A1 alloys due to its low bulk resistivity (1.72 ~ 9 cm) and large electromigration resistance. 1 We have reported the establishment of a high performance copper metallization technology by employing a low-kinetic-energy particle process. 2' 3 Cu films deposited on SiO2 with relatively high ion bombardment energies undergo crystal orientation conversion from Cu(lll) to Cu(100) upon thermal annealing, which is accompanied by the growth of giant grains as large as 100 ~m. 3 The room temperature resistivity of such giant-grain Cu films is 1.76 ~ 9 cm which is almost equal to the bulk resistivity of 1.72 ~s -cm. At 12 K, the resistivity is reduced further to 18.3 n~ 9 cm, due to the reduction in the grain-boundary scattering. Such a low resistance feature of Cu films is attractive in the formation of interconnects for high speed LSIs. However, the evaluation of electromigration resistance of Cu interconnects so far has not been conducted extensively due to the difficulty in conducting life tests within a reasonable span of testing time. The conventional technique for accelerated life test of metal interconnects is g...

The hardness of single-crystal gallium nitride of 500 µm thickness at elevated temperatures is measured and compared with those of other semiconductors. A Vickers indentation method was used to determine the hardness under an applied load of 0.5-5 N in the temperature range 20-1200 °C. The average hardness is 10.8 GPa at room temperature, which is comparable to that of Si. At elevated temperatures, GaN shows higher hardness than Si, GaAs, and ZnSe. A high mechanical stability for GaN at high temperature is deduced.

The hardness of single-crystal gallium nitride at elevated temperatures is measured and compared with that of other semiconductors. A Vickers indentation method was used to determine the hardness under an applied load of 0.5 N in the temperature range 20-1200 • C. The average hardness was measured as 10.8 GPa at room temperature, which is comparable to that of Si. At elevated temperatures, GaN shows higher hardness than Si and GaAs. A high mechanical stability for GaN is deduced.

A large-electromigration-resistance copper interconnect technology has been developed using the low-kinetic energy particle process [l]. We have found that giant grains as large as 100 pm grow in the copper film formed on SiO, upon the thermal annealing performed after the film growth process. The resistivity of the copper film is as low as 1.78 pQcm at a room temperature which is almost identical to the bulk resistivity. The electromigration lifetime of the copper interconnect is three to five orders of magnitude larger than that of Al-Si based alloy interconnects. Furthermore, a new accelerated-electromigrationtesting method has been developed to evaluate such longlifetime copper interconnects within a short period of test time. That has enabled us for the first time to perform comparative studies of various interconnect materials in a very efficient way to establish large-electromigration-resistance interconnection technology.