Measurement of amount of pattern trim and surface chemistry for organic resist etching in an inductively coupled plasma in so₂-O₂ gas mixtures

We experimentally investigated the amount of pattern trim of the organic photoresist and its relation to the chemical compositions of the photoresist surface, as a function of gas mixture ratio between SO₂ and O ₂ in an inductively coupled plasma (ICP) gaseous electronics conference (GEC) reference cell. Both the photoresist line pattern width loss and the photoresist thickness loss decreased along with the increase in the SO₂ percentage from 10 to 68%. The ratio of the line pattern width loss to the thickness loss (= lateral-to-vertical etch rate ratio) decreased. The ratio corresponds to the amount of pattern trim in the bottom anti reflective coating (BARC) layer etching. We confirmed that photoresist pattern trim can be achieved in the ICP GEC reference cell as well as the gate etching process on a fabrication line. As the SO₂ percentage increased, the density of atomic P in the bulk plasma decreased, while the atomic percentage of sulfur increased from 0.06 to 0.12 on the blanket photoresist surface. The reason why the lateral-to-vertical etch rate ratio decreased with the increase in the SO₂ percentage is that the isotropic etching component by P atoms becomes smaller, and the anisotropic etching component, which is relevant to the sulfur on the photoresist surface, becomes larger with the increase in the SO₂ percentage.