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edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 22 NO. 4 14 APPLICATION EXAMPLE: MOBILITY ENGINEERING IN P-TYPE SILICON-GERMANIUM CHANNELS For sub-10 nm process nodes, high mobility channel material optimization requires significant process engi- neering. Direct feedback in terms of mobility values in the very near surface layers has not been easy for char- acterization methods. This example describes applica- tion of DHEM to characterization of SiGe p-type channel materials with significant strain in the matrix due to high Ge content and a laser anneal basedprocess. [13] Lasermelt annealing has been used here to demonstrate a localized annealing method that selectively regrows the matrix after implant without diffusing the implanted species including dopants. Wafers in this exampleweren-type300mmSi thatwere plasma implanted first with Ge and then with B. The GeH 4 energy was 3 kV and B 2 H 6 energy was 500 V to achieve a shallow Ge amorphous layer < 10 nm and B-doped ultra- shallow junction < 10 nm. The first sample was implanted to the 1x10 17 cm -2 level with Ge and then implanted with 4 x10 16 cm -2 B 2 H 6 , while the second samplewas implanted to the 1x10 16 cm -2 level withGe and4 x10 15 cm -2 level withB 2 H 6 . Extensive analysis of thematerialswas also performed in between the process steps to track possiblemovement of the implanted species and track the retention of strain. Near-surface XPS analysis of the 1x10 17 cm -2 Ge sample indicated a peak Ge content of 55% in the < 5 nm region, while the 1x10 16 cm -2 Ge sample showed a 20% peak Ge content. The sampleswere then laser annealedat fluences from 0.5 Jcm -2 to 5 Jcm -2 . X-ray diffraction (XRD) strain analysis was performed on the samples where only the 55% Ge wafer annealed at 2.5 Jcm -2 showed a shoulder indicating strain in the surface layer as can be seen in Fig. 4a. DHEM was used to obtain the mobility depth pro- files for the 20%and55%Ge samples annealedat 2.5 Jcm -2 as shown in Fig. 4b. The 0% Ge mobility reference value (for p-type doped Si) is ~38 cm 2 /V-s. As can be seen from this data, 20% Ge content increased the hole mobility by 70% up to ~63 cm 2 /V-s, while for the 55% Ge sample the near-surface mobility (< 5 nm) increased to ~160 cm 2 /V-s. This is 4.3x higher surface hole mobility and it is equiva- lent to 75% Ge or 1.5 GPa of compressive strain including surface strain. CONCLUSION Depth profiling of electrical parameters such asmobil- ity and carrier concentration through semiconductor layers is important for process development to optimize performance of devices to be fabricated on such layers. DHEM is a technique that can measure both mobility and carrier concentrationprofiles at nm-level depth resolution. Accurate characterization of electrical properties in the near-surface regionof a filmprovides valuable information about surface dopant activation and behavior of contact resistance. Similarly, such measurements make mobility engineeringpossible for channelmaterials tobeemployed in advanced device structures. (b) (a) Fig. 4 a) XRD for SiGe sample with 55% Ge showed a shoulder in XRD data indicating strain in the matrix using 2.5 Jcm -2 annealing; b) DHEMmobility depth profiles for the 55% Ge and 20% Ge content samples annealed at 2.5 Jcm -2 . (continued on page 16)