Heat treatment, also known as annealing, is a common step in the semiconductor fabrication process. A buildup of radiation-induced localized charge within the semiconductor and insulator alters local field distribution, threshold voltage, and leakage current. NASA's patent-pending technology implements an annealing process on a system level directly on a chip for annealing defects and improving device performance with heating done in the laboratory.
The annealing may be performed inside an oven or upon a hotplate. A sys-tem-on-microheater provides defect annealing capability for recovering bulk trapped charges and interface states. The healing starts simply by heating the chip in a process that can be compared to that of a human's immune system — something capable of detecting and quickly responding to any number of possible assaults in order to keep the larger system working optimally.
A microheater is monolithically integrated on the backside of a generic Complementary Metal Oxide Semiconductor (CMOS) chip for an on-chip annealing system (figure, left (b)). Compared to a stacked microheater, the monolithic integration reduces the die profile that accordingly enhances the heating power efficiency and heating/ cooling rates, which was verified experimentally and numerically. The self-healing microheater is controlled by a temperature feedback circuit to maintain the desired temperature.
All circuits under the treatment are unbiased in order to avoid any side effects on normal devices. A control circuit block is programmed to monitor a device parameter shift, such as the threshold voltage on the same chip, in order to determine the need for treatment. A control circuit triggers the micro hotplate and senses the temperature to adjust the target temperature and duration. The microheater and the system-on-chip are fabricated separately and stacked into a single package that can be implemented on any arbitrary commercial off-the-shelf device as a generic approach.