P.K.Skorobogatov, A.Y.Nikiforov, A.A.Demidov
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The laser simulation of dose rate effects is based on laser beam capability to ionize IC's semiconductor structures [1]. The basic limiting factor is the influence of metallization shadowing on semiconductor ionization uniformity [2]. It was proposed that the influence of metallization may be reduced by using of optical homogenizer that converts the coherent output laser radiation into the diffused radiation of finite-size source.  
To investigate this possibility the TSCPHXX and TSCLUXX test structure sets were manufactured in conventional 2-mm bulk CMOS process. Each structure set includes well-substrate p-n junction (48x78 mm) with strip contacts and various metallization coverage from 8.3 up to 91.7%. The structure set TSCLUXX is similar to TSCPHXX but with different disposition of highly doped regions in order to form SCR (latch-up).
Pulsed laser simulator "RADON-5E" with 1.06 mm wave-length and 11 ns pulse width was used [3]. The simulator is supplied by homogenizer that converts purely coherent parallel laser irradiation into diffused mode. 
The numerical simulator "DIODE-2D" optical model was modified in order to take into account the diffuse feature of "RADON-5E" output radiation. We analyzed the effect of metallization shadowing on dose rate laser simulation adequacy taking into account the nonparallel light propagation and bottom chip reflection.
As a result a good agreement is obtained between numerical simulation results and test data for all test structures. It was found that usage of homogenizer improves the laser intensity uniformity within chip area and decrease the influence of metallization shadowing on test structure ionizing current. For TSCPHXX test structure set when metallization coverage increase from 8.3 to 91.7 (11 times) the ionizing current amplitude  decrease only from 10 to 5 mA (2 times) at laser intensity 9.7·103 W/cm2. For TSCLUXX test structure set the latch-up threshold level increase only from 2.7.103 to 4.3.103 W/cm2  (1.7 times) when metallization coverage increase from 8.3 to 75 % (9 times). These results can be explained by nonparallel feature of diffused irradiation and by contribution of reflected irradiation from chip bottom.
Obtained results demonstrate the advantage of diffused laser irradiation for dose rate effects simulation in highly-metallized silicon IC’s.

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A diffused laser irradiation was used to improve laser simulation adequacy of dose rate effects in silicon IC’s with high metallization density. The conversion of coherent output laser irradiation into the diffused one was made by specialized  homogenizer. Test structures with various metallization coverage were designed. Numerical simulations together with laser tests were performed in order to clarify the advantage of diffused laser irradiation before coherent one. 
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