電漿化學氣相沉積技術成長超低應力之紫外光可透性氮化矽薄膜

Abstract

反應氣體的流量(如NH3與SiH4)以及RF功率對薄膜特性的影響很大。當RF功率充足時，較高的SiH4流量可以獲得較快的薄膜沉積速率，而且因為中和了單位厚度的離子轟擊，因此也擁有較輕微的薄膜壓縮式應力。此外，NH3流量的上升可以得到Si-H鍵含量更少且紫外光可透性更高的氮化矽薄膜，同時也具有極低的濕蝕刻速率。 PECVD氮化矽薄膜中的Si-H鍵結含量直接反應出薄膜的紫外光穿透率的高低。同時，紫外光可透性氮化矽薄膜(N/Si ratio較高)，也會呈現出比非紫外光可透性氮化矽薄膜(Si-rich)更低的折射率。當RF功率不足時，除了會形成很高的伸張式薄膜內應力外，也將形成鬆散的高蝕刻速率薄膜，而且因為薄膜中的Si-H鍵含量較高，所以紫外光可透性也較差。 透過適當的製程參數調整，我們成功的得到了具有極低薄膜內應力(~-17MPa)的高紫外光可透性(>70%@254nm)氮化矽薄膜，而且此薄膜的BOE濕蝕刻速率很低(~4.9Å/min)，只有一般PECVD Si-rich氮化矽薄膜蝕刻速率(10.9 Å/min)的一半，是品質很高的PECVD氮化矽薄膜。

Material and physical properties of silicon nitride (Si3N4) films deposited by plasma enhanced chemical vapor deposition (PECVD) are significantly affected by the gas flow rate of NH3 and SiH4 during the film deposition. When RF power is sufficient, a higher SiH4 gas flow rate increases the deposition rate, and also relieves compressive stress because the increased deposition rate alleviates the ion bombardment damage per unit volume of the film. On the other hand, the increase in the NH3 flow rate can reduce the density of the Si-H bonds and decrease the BOE etch rate, resulting in a high UV-transmittance and superior film quality for the nitride film. This is due to that a PECVD Si3N4 film with a higher N/Si ratio has a higher UV-transmittance and a lower refractive index. When the RF power is not sufficient enough, PECVD nitride films have a higher content of Si-H bonds and exhibit a large tensile stress, leading to a lower UV-transmittance. By properly controlling the process gas flow rate and the RF power during the PECVD process, we can produce highly UV-transparent (>70%@254nm) Si3N4 thin films with an extremely low stress (~-17MPa). The nitride film has an etching rate (~4.9Å/min) as small as half the etching rate of conventional PECVD silicon nitride films (10.9 Å/min).