IEC 60749-38:2008 pdf download – Semiconductor devices – Mechanical and climatic test methods – Part 38: Soft error test method for semiconductor devices with memory
3Test apparatus
3.1Measurement equipment
The equipment shall be capable of measuring the functions of the integrated circuit devices,and capable of measuring the time taken for the change of stored data by the exposure toenergetic particles,such as alpha radiation to take place (i.e. the generation of a soft error).Alternatively, the test equipment (memory tester etc.) shall have the capability of counting thenumber of soft errors in unit time.
3.2Alpha radiation source3.2.1 Background information
Uranium and thorium impurities found in trace amounts in the various production andpackaging materials emit alpha particles.Alpha particles are strongly ionizing,so those thatimpinge on the active device create bursts of free electron-hole pairs in the silicon. Differenttypes of alpha sources can be used to simulate the alpha emission from uranium and thoriumimpurities. Sources that emit alpha particles with energy spectra similar to uranium andthorium impurities simulate the radiation environment of wirebonded componentsencapsulated in moulding compound. Sources that emit alpha particles with similar energyspectra to 21 0Po are used for simulating components in a flip-chip arrangement with solderbumps. The source should provide an aipha particle spectrum similar to that encountered inthe actual component.
3.2.2Preferred sources
238U or 232Th are the preferred sources for inducing SER in mould-resin compounds. 241Amand 210Po sources can be used as substitutes.
3.2.3Variation in results
Results will differ depending on the source used due to spectral variations. Alpha particlesources available on the market are usually only classified by their activities in pCi (ratherthan in the preferred unit,Bq, see 2.11) and the emission rates of alpha particle are seldomindicated.
The emission rate cannot be determined simply from the activities because of the effects ofabsorption of alpha particle in the source itself and its situation.For example,the activity of1uCi is 3,7 x104 decays/s.However, the alpha emission rate from the source would be lessthan 3,7 ×104 alphals.
Therefore, a measurement of the alpha emission rate of the source which is used in the SERtest is recommended.
As a consequence，the energy spectrum of the alpha radiation source shall be confirmedbecause different test values can result from differing energy spectra even if the alpharadiation sources have the same level of radioactivity.
NOTE If 241Am o 210Po are used, this should be documented in a report along with the statement that results candiffer if other sources have been used,due to energy spectra variationis,
3.2.4Effect of high radiation levels
In cases where the dose concentration delivered to the test sample is high,considerationshall be given to the effect of multiple hits.
3.2.5 Measurement accuracy If the emission area of the alpha radiation is significantly smaller than the chip area, absorption of the alpha radiation through the atmosphere and the chip protection film and incident angle effects will contribute to give erroneous values. Therefore, to perform the test accurately, the emission area of the alpha radiation shall not be significantly smaller than the chip area and, preferably, shall be larger. In Figure 1 , the curves apply for devices of about 1 0 mm diameter. Dimension “d” should be scaled up or down in proportion for devices with a different diameter (for more information, see Bibliography).
3.3Test sample
Any type of integrated circuits with memory may be tested. The device parameters(capacitance of the memory cell in the DRAM etc.) which can affect the soft error rate shall bewell understood.
4Procedure
4.1 Alpha radiation accelerated soft error test4.1.1Surface preparation
The surface of the sample shall be suitably prepared before irradiation.For accelerated alphaparticle testing,the surface of the sample shall be exposed using a method which does notaffect the electrical characteristics. When, however, the purpose of the test is to evaluate theeffect of chip coating, the chip coating shall not be removed.
NOTE As an example, the upper side of the package can be cut with a small knife or the moulding resin on theupper surface of the chip can be dissolved chemically etc.Unless otherwise specified, chip coatings should beremoved because alpha radiation from an 241Am source (peak energy 5 MeV approximately) is absorbed by thechip coating. Alpha radiation of higher energy can occur in the package materials or as natural radio-activity.
4.1.2Power supply voltage
This shall be set at the minimum voltage of the recommended operating condition (whenrequired,the supply voltage dependence on failure rate shall be measured). For latch uptesting, the voltage shall be set at the minimum and maximum voltage of the recommendedoperating condition.
