濕式清洗製程改善快閃記憶體金屬佈線與通道連接電阻降低研究

Abstract

在高密度快閃記憶體元件上，為了從有邊界通道金屬線製程上，獲得更小的晶格尺寸，所以使用無邊界通道製程，但是IMD內金屬介電層物質，將會因為蝕刻和蝕刻後清洗，而被侵蝕後退。這將會導致Rv電阻值升高，和EM電子遷移信賴度產生的問題〔1〕。 關於這個狀況，在58nm快閃記憶體元件上，利用氨化物和氟化物的化學品來進行研究，我們發現鋁銅金屬側蝕狀況會因為氨化合物與鋁金屬反應形成氧化鋁/鋁金屬/氨化合物的膠狀物質，附著於鋁銅金屬表面上方式來減輕其狀況。 縮短氨化合物清洗時間以及足夠的異丙醇浸潤，產生類似膠狀物質在去離子水清洗時，將可減少鋁銅金屬側蝕狀況在四甲基氫氧化銨與雙氧水混合物方式，金屬蝕刻後的聚合物物質將可因為氫氧基與鋁反應產生氫氧化鋁物質而去除；而雙氧水將會與鋁銅金屬表面產生氧化物層使來避免金屬腐蝕。 另外，利用稀釋的硫酸/雙氧水加微量氫氟酸化合物(DSP+) 清洗鋁及氧化鋁表面聚合物物質，DSP+本身氟離子〔F-〕會與鋁金屬反應形成鋁氟化合物(AlFx)然後在去離子水清洗這一步被帶走，而硫酸與雙氧水會讓鋁銅金屬表面形成氧化物質，讓氫氟酸在去離子水清洗後不致於因殘留而繼續侵蝕鋁銅金屬，鋁銅金屬側蝕現象在DSP+清洗後依然還是存在的。

Borderless (BDL) vias landing on metal lines were demanded in high-density flash memory devices due to the reduced die size, internal dielectric (IMD) material recess in un-landed via dry etching and the Al-Cu metal line undercut caused by post-etch cleaning may lead to a high via resistance (Rv) and the EM reliability issue〔1〕. In this work, the Al-Cu loss mechanism in BDL-via cleaning by using amine- and fluoride-based chemicals was studied for 58 nm flash devices. We found that the Al-Cu undercut can be alleviated in heptadecylamine containing solvent by minimizing the formation of Al2O3/Al/HDA gel-like material; the shorter heptadecylamine processing time with sufficient IPA rinses generated a thinner gel-like layer, leading to a small Al-Cu undercut in the deionizer water rinse step. For Tetra Methyl Ammonium Hydroxide/H2O2-containing semi-aqueous solution, metal contained etched-residues can be removed by reaction of OH- with Al to form dissolved Al(OH)4-; addition of H2O2 will form an oxidized passivation layer on the metal surface to prevent from metal corrosion. On the other hand, the Al/Al2O3 contained polymer was removed by fluoride-based solvent or Dilution Sulfuric acid with Hydrogen peroxide and 100ppm of Hydrofluoric acid through the reaction with F- to form deionizer water dissolved AlFx byproducts; while H2SO4 and H2O2 in DSP+ will oxidize Al to form Al2O3, that will be further etched by HF, resulting in a severe Al-Cu undercut.