6G wireless communication will use the sub-THz frequency band (100 GHz to 300 GHz) and support new technologies such as holographic communication, brain-computer interfaces, immersive communication and AI-driven satellite communication. The sub-THz band offers a wide spectrum that can meet the growing demand for high-speed data and low-latency services which a good candidate for the 6G communication. 6G requires new hardware systems for operating this frequency range, therefore, it is important to study the effects of hardware impairments on sub-THz communication. In the 6G communication the key impairments include phase noise, power amplifier nonlinearity, and filtering, which can reduce spectral efficiency. In this work, these impairments are analyzed using adjacent channel power ratio (ACPR) and error vector magnitude (EVM) performance metrics, followed by performance analysis of 6G waveforms under different modulation schemes, including QPSK, 16-QAM, and up to 1024-QAM. Simulation results show that higher-order modulation schemes perform well, even in the presence of hardware impairments.