Impact of Physical Stress on Gate Dielectric in Ultrathin Si Gate-Stack for Next-Generation Flexible CMOS Technology

In this article, we report the fabrication and characterizations of sub-20-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>m thin flexible Si die containing active devices. Thermally grown 2.62-nm silicon dioxide (SiO2), atomic layer deposition (ALD)-deposited 3-nm HfO2 (high-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\kappa $ </tex-math></inline-formula>), and 10-nm TiN layers are used to fabricate an array of MOSCAPs on Si wafers. The fabricated devices are characterized to analyze the doping density (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N} _{a}$ </tex-math></inline-formula>), flat-band voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {fb}}$ </tex-math></inline-formula>), threshold voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {th}}$ </tex-math></inline-formula>), fixed oxide charge (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q} _{f}$ </tex-math></inline-formula>), and interface trap densities (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${D} _{\text {it}}$ </tex-math></inline-formula>). Then, a deep reactive ion etching (DRIE) reduces the die thickness to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 15\mu $ </tex-math></inline-formula>m for flexibility. The encapsulated flexible devices are found to have relatively better breakdown performances when tested in compressive stressing and no variations when in tensile stress. The time-dependent dielectric breakdown (TDDB) measurement shows a minimal variation in flexible and bulk devices. The TDDB and a voltage acceleration slope are projected in flexible devices after performing a 10000 times bending and relaxation process (cycling).