Improvement of PECVD-SiN_x for TFT Gate Insulator by Controlling Ion Bombardment Energy

Yasuhiko KASAMA, Tadahiro OHMI, Koichi FUKUDA, Hirobumi FUKUI, Chisato IWASAKI, Shoichi ONO

Summary :

It has been revealed that ion bombardment energy and ion flux density play an essentially critical role in SiN_x deposition process of PECVD in TFT-LCD production. Ion energy and ion flux density bombarding onto substrate surface are known to be extracted from waveform of RF applied to an electrode. Using this method, we investigated film quality of SiN_x formed in the conventional parallel plate PECVD equipment. When N₂ + H₂ or N₂ + Ar is employed as a carrier gas in source gas (SiH₄ + NH₃), we have defined normalized ion flux density as ion flux density divided by deposited SiN_x molecule which must be increased to obtain high quality SiN_x film while ion energy is suppressed at low level as not giving damages on the film surface. This technique has made it possible to securely form SiN_x film (2500 ) featuring dielectric break-down field intensity of 8.5 MV/cm at 250 on a glass substrate with Cr gate interconnects of 1000 having vertical step struc-ture. One of the important factors to improve film quality of SiN_x deposited in PECVD is to increase ion flux density while keeping ion bombardment energy low enough to protect growing surface against any damages. Using this technique inverse-staggered TFT-array featuring field effect mobility of 0.96 cm²/V・s has been demonstrated which gate insulator SiN_x, non-doped a-Si: H and a-Si: H(n⁺) were formed continuously at the identical substrate temperature of 250.

• Publication: IEICE TRANSACTIONS on Electronics Vol.E79-C No.3 pp.398-406
• Publication Date: 1996/03/25
• Type of Manuscript: Special Section PAPER (Special Issue on Scientific ULSI Manufacturing Technology)
• Category: Device Issues

Authors

Yasuhiko KASAMA
Tadahiro OHMI
Koichi FUKUDA
Hirobumi FUKUI
Chisato IWASAKI
Shoichi ONO

Keyword

TFT,  gate insulator,  PECVD,  ion flux,  ion energy