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Control of electrostatic discharge damage to semiconductors
World Abstracts on Microelectronics and Reliability tests have revealed that the aluminum devices are susceptible to at least two failure mechanisms, emitter-base degradation and electromigration. Electromigration was also observed on the gold devices. The aluminum devices tested fail, typically, after 150 hr at 280°C and 700 hr at 250 °. If this data is extrapolated to a more normal junction temperature of 150°C, a mediantime to failure of 5 x 105 hr is obtained. The gold metallized devices have been life tested at junction temperatures of 340°C for as long as 2000 hr without failing.
A life-test study of electromigration in microwave power transistors. S. GOTTESFELD. Proc. IEEE Reliab. Phys. Syrup. 94 (1974). A life-test study was made of a microwave power transistor employing aluminum metallization. The life tests were conducted under dc overstress conditions to accelerate the rate of failure as a result of electromigration of the metaliization system. Extrapolation of the data obtained showed a predicted MTF of approximately one hundred years for the device under test at a typical operating-current density of 8.4x 10" A/cm ~ and junction temperature of 150°C. Analysis of the failures revealed the presence of both aluminum and silicon electromigration, with the latter the primary cause of failure. A failure-rate model was constructed from the data relating MTF to activation energy, temperature and current density. Susceptibility of semiconductor devices to thermal second breakdown. N. S. COI-1N. Proc. IEEE Reliab. Phys. Syrup. 90 (1974). A method for determining the susceptibility of semiconductor devices to damage from an electromagnetic pulse (EMP) due to induced thermal second breakdown is described. The method can be used as a nondestructive screening test. It is based on the increase in junction reverse breakdown voltage with temperature and can be used to find the most EMP resistant devices of a given device type. A mathematical explanation is presented and other tentative applications are proposed. Reliability study of an N-channel silicon gate FET with field shield. E. S. ANOLICK,J. F. PROSSER and B. R. REMIS. Proc. IEEE Reliab. Phys. Syrup. 70 (1974). A reliability study was performed on an N-channel PET with a selfaligned gate and a field shield. It was found that the field shield was very successful in reducing leakage and did not add significantly to the failure rate of the structure. It was further found that in terms of dielectric shorts and VT stability, the silicon gate structure was as good as or better than comparable metal-gate devices. Control of electrostatic discharge damage tO semiconductors. E. R. FREEMAN and J. R. BEALL. Proc. IEEE Reliab. Phys. Syrup. 304 (1974). Numerous semiconductor failures have been experienced in the Viking Lander, Skylab and Titan III launch Vehicle programs. These included junction field effect transistors (J-PET), planar diodes, bipolar digital integrated circuits in discrete and hybrid packages, internally compensated operational amplifiers and inputprotected MOS LSI circuits (Metal Oxide Semiconductor Large Scale Integrated circuits). All parts had passed high-reliability 100% screening tests and came from lots that had met rigorous sample acceptance test requirements. All of the failures were encountered during some phase of handling or test of the parts or circuit assemblies. Junction failures exhibited significant increases in reverse leakage current and degradation of reverse breakdown voltage. Failure sites were isolated to minute rediffusion of the junction at the silicon/silicon-dioxide interface. MOS failures were classic ruptures of the silicon dioxide dielectric under the gate or capacitor metallization, which produced shorts in the affected area. The hypothesis that these failures were caused by elec-
265
trostatic discharge through the affected areas was based on the limited degree of damage to the parts and was empirically verified through damage threshold tests on good parts. An equivalent circuit model for a charged human body was utilized in these tests. Identical failure modes and mechanisms were produced using this circuit at 1500-2000 V. These static levels are well below normal shock sensation. Susceptibility guidelines were established for all planar and MOS devices based on leakage current and breakdown voltage characteristics. Surveys of receiving, assembly and test areas revealed that stored charge levels from 5 to 20 kV were present on personnel, fixturing and packaging materials. These large electrostatic potentials were attributed to the use of cleanroom gowns, containers, trays, protective wrappings made of synthetic materials and the absence of chargeneutralizing media in work areas.
The accelerated testing of plastic encspsulated semiconductor components. R. W. LAWSON. Proc. IEEE Reliab. Phys. Syrup. 243 (1974). Elevated temperature and elevated humidity have been studied as stress factors for predicting the reliability of plastic encapsulated bipolar semiconductor components. The test transistors used in the study were encapsulated in a variety of epoxy resins and a silicone resin the purity of which were characterised by a deiermination of the conductivity of an aqueous extract of the resin. Both stress conditions induce failure modes due to gain degradation, leakage growth and increase in saturation voltages and, under humidity stress, the degree of degradation could be related to the resin purity. It is concluded that elevated temperature is not useful for predicting the reliability of epoxy encapsulated components but is useful for silicone encapsulated components operating above about 100°C. Humidity stress testing is shown to be valid and relevant for both epoxy and silicone encapsulated components operating below 100°C because of the water that will be present in the encapsulants in normal environmental conditions. It is proposed that the humidity stress factor for life predictive purposes is (RH) 2 because this is directly related to the water content of the encapsulating resin and can be used as the basis of a physical model that explains the experimental observations in terms of the ionic impurity content of the resin. Degradation of gold-germanium ohmic contact to nGaAs. K. OHATA and M. OGAWA. Proc. IEEE Reliab. Phys. Syrup. 278 (1974). The metallurgical and electrical investigations were carried out on the Pt/Au-Ge and Ni/Au-Ge ohmic contacts to n-GaAs in focusing the degradation during aging. The characteristic structures in the alloyed regions and their metallurgical changes during aging (3300C) were examined by means of Electron Probe Micro-Analysis. The thick Pt and Ni films in the contact systems caused the reaction during aging to proceed. The degradation of the contact resistance during aging was found to take place with the progress of the metallurgical reaction. The details of the investigation including the discussions on the degradation mechanism will be described. *Failure analysis of AUTODIN microeleetronics, technical rept. E. B. HAKIM and R. HOLEVlNSKI. Army Electronics Command, Fort Monmouth, N.J. ECOM-4187 1-S762705-A-05601 DA-1-S-762705-A-05. 21pp. January (1974). A total of 401 integrated circuits (IC), both monolithic and hybrid, were investigated. These devices were obtained from AUTODIN systems, which were being repaired at the Tobyhanna Army Depot, Tobyhanna, Pa. Results are discussed.
A life-test study of electromigration in microwave power transistors. S. GOTTESFELD. Proc. IEEE Reliab. Phys. Syrup. 94 (1974). A life-test study was made of a microwave power transistor employing aluminum metallization. The life tests were conducted under dc overstress conditions to accelerate the rate of failure as a result of electromigration of the metaliization system. Extrapolation of the data obtained showed a predicted MTF of approximately one hundred years for the device under test at a typical operating-current density of 8.4x 10" A/cm ~ and junction temperature of 150°C. Analysis of the failures revealed the presence of both aluminum and silicon electromigration, with the latter the primary cause of failure. A failure-rate model was constructed from the data relating MTF to activation energy, temperature and current density. Susceptibility of semiconductor devices to thermal second breakdown. N. S. COI-1N. Proc. IEEE Reliab. Phys. Syrup. 90 (1974). A method for determining the susceptibility of semiconductor devices to damage from an electromagnetic pulse (EMP) due to induced thermal second breakdown is described. The method can be used as a nondestructive screening test. It is based on the increase in junction reverse breakdown voltage with temperature and can be used to find the most EMP resistant devices of a given device type. A mathematical explanation is presented and other tentative applications are proposed. Reliability study of an N-channel silicon gate FET with field shield. E. S. ANOLICK,J. F. PROSSER and B. R. REMIS. Proc. IEEE Reliab. Phys. Syrup. 70 (1974). A reliability study was performed on an N-channel PET with a selfaligned gate and a field shield. It was found that the field shield was very successful in reducing leakage and did not add significantly to the failure rate of the structure. It was further found that in terms of dielectric shorts and VT stability, the silicon gate structure was as good as or better than comparable metal-gate devices. Control of electrostatic discharge damage tO semiconductors. E. R. FREEMAN and J. R. BEALL. Proc. IEEE Reliab. Phys. Syrup. 304 (1974). Numerous semiconductor failures have been experienced in the Viking Lander, Skylab and Titan III launch Vehicle programs. These included junction field effect transistors (J-PET), planar diodes, bipolar digital integrated circuits in discrete and hybrid packages, internally compensated operational amplifiers and inputprotected MOS LSI circuits (Metal Oxide Semiconductor Large Scale Integrated circuits). All parts had passed high-reliability 100% screening tests and came from lots that had met rigorous sample acceptance test requirements. All of the failures were encountered during some phase of handling or test of the parts or circuit assemblies. Junction failures exhibited significant increases in reverse leakage current and degradation of reverse breakdown voltage. Failure sites were isolated to minute rediffusion of the junction at the silicon/silicon-dioxide interface. MOS failures were classic ruptures of the silicon dioxide dielectric under the gate or capacitor metallization, which produced shorts in the affected area. The hypothesis that these failures were caused by elec-
265
trostatic discharge through the affected areas was based on the limited degree of damage to the parts and was empirically verified through damage threshold tests on good parts. An equivalent circuit model for a charged human body was utilized in these tests. Identical failure modes and mechanisms were produced using this circuit at 1500-2000 V. These static levels are well below normal shock sensation. Susceptibility guidelines were established for all planar and MOS devices based on leakage current and breakdown voltage characteristics. Surveys of receiving, assembly and test areas revealed that stored charge levels from 5 to 20 kV were present on personnel, fixturing and packaging materials. These large electrostatic potentials were attributed to the use of cleanroom gowns, containers, trays, protective wrappings made of synthetic materials and the absence of chargeneutralizing media in work areas.
The accelerated testing of plastic encspsulated semiconductor components. R. W. LAWSON. Proc. IEEE Reliab. Phys. Syrup. 243 (1974). Elevated temperature and elevated humidity have been studied as stress factors for predicting the reliability of plastic encapsulated bipolar semiconductor components. The test transistors used in the study were encapsulated in a variety of epoxy resins and a silicone resin the purity of which were characterised by a deiermination of the conductivity of an aqueous extract of the resin. Both stress conditions induce failure modes due to gain degradation, leakage growth and increase in saturation voltages and, under humidity stress, the degree of degradation could be related to the resin purity. It is concluded that elevated temperature is not useful for predicting the reliability of epoxy encapsulated components but is useful for silicone encapsulated components operating above about 100°C. Humidity stress testing is shown to be valid and relevant for both epoxy and silicone encapsulated components operating below 100°C because of the water that will be present in the encapsulants in normal environmental conditions. It is proposed that the humidity stress factor for life predictive purposes is (RH) 2 because this is directly related to the water content of the encapsulating resin and can be used as the basis of a physical model that explains the experimental observations in terms of the ionic impurity content of the resin. Degradation of gold-germanium ohmic contact to nGaAs. K. OHATA and M. OGAWA. Proc. IEEE Reliab. Phys. Syrup. 278 (1974). The metallurgical and electrical investigations were carried out on the Pt/Au-Ge and Ni/Au-Ge ohmic contacts to n-GaAs in focusing the degradation during aging. The characteristic structures in the alloyed regions and their metallurgical changes during aging (3300C) were examined by means of Electron Probe Micro-Analysis. The thick Pt and Ni films in the contact systems caused the reaction during aging to proceed. The degradation of the contact resistance during aging was found to take place with the progress of the metallurgical reaction. The details of the investigation including the discussions on the degradation mechanism will be described. *Failure analysis of AUTODIN microeleetronics, technical rept. E. B. HAKIM and R. HOLEVlNSKI. Army Electronics Command, Fort Monmouth, N.J. ECOM-4187 1-S762705-A-05601 DA-1-S-762705-A-05. 21pp. January (1974). A total of 401 integrated circuits (IC), both monolithic and hybrid, were investigated. These devices were obtained from AUTODIN systems, which were being repaired at the Tobyhanna Army Depot, Tobyhanna, Pa. Results are discussed.