Effects of Conductivity of Polysilicon on Profile Distortion

Abstract

The profile distortion, notch, in the etching of gate lines with high-density plasmas is becoming more deleterious as ULSI devices are being further scaled down. Dependence of the etch profiles on the polysilicon conductivity was studied for various spacings of line-and-space patterns. The notch depth was deeper for polysilicon with higher conductivity. The image potential was employed to account for the dependence of notch on conductivity. To measure the net positive charges which are known to contribute to the notch phenomenon, we observed the ion and electron current waveforms from patterned and unpatterned wafers as a function of bias power. The results showed that the surface of the patterned wafer is more positively charged than that of the unpatterned wafer, and the net charge can be reduced by raising the bias power. However, an increase in the bias power lowers the selectivities over both thin gate oxide and photoresist.

Notch formation by stress enhanced spontaneous etching of polysilicon

“…Stress may enhance the spontaneous etching by reducing the energy barrier for Cl ͑or Cl Ϫ , assuming a field enhanced spontaneous etching mechanism 21 ͒ to penetrate into the silicon lattice and attack the underlying Si-Si bonds. Greater notching with increased polysilicon conductivity ͑n ϩ type͒ has been reported, 23 in agreement with the proposed mechanism. 21 In these cases above, spontaneous etching has been attributed to the increased penetration of halogen atoms into the polysilicon substrate.…”

Plasma etching: Yesterday, today, and tomorrow

“…Charging in high aspect ratio features is believed to be responsible for "etch stop" that is often observed for dielectric materials. [188][189][190][191][192][193][194][195][196][197][198][199][200][201] Etch stop can also be caused by deposition of fluorocarbon polymer at the bottoms of high aspect holes in insulating films. 153 The combination of charging and polymer deposition can cause other interesting phenomena.…”

On the origin of the notching effect during etching in uniform high density plasmas

“…The notching phenomenon [1][2][3] describes the opening of a long narrow groove ͑the ''notch''͒ in a conductive material at the interface with an underlying insulator. The notch occurs perpendicularly to the normal ion direction and appears during the overetching step in high density plasma tools.…”

“…3 Various scenarios for notching have been proposed in the literature; all are based on the difference between the potential of the poly-Si line, which attracts excess electrons at the side facing the open area, and the potential at the trench bottom ͑SiO 2 ͒, which charges up positively. One school of thought suggests that this potential difference causes ion migration to the sidewall foot of the outermost poly-Si line, 2,3 where they cause localized etching. However, evidence for such surface ion migration on adsorbate ͑e.g., Cl͒ covered SiO 2 is hard to find; furthermore, this mechanism fails to explain the wide notches frequently seen experimentally.…”