cause of half voltage on microcontroller reset pin
Tony is probably correct in his comment about voltage reversal- note that SMT tantalum caps have the polarity bar on the positive side, rather than the negative (which is common with most other electrolytic capacitors), and I have seen that cause confusion before. If the cap has been reversed you should replace it with a new one.

If you do not have a series resistor to the reset input, shorting the MCU power supply will discharge the cap through the input protection diodes, potentially permanently damaging them. In the future, a few hundred ohms is sufficient if this is a possibility.