Chromium oxide as a hard mask material better than metallic chromium

Abstract

In nanofabrication, use of thin resist is required to achieve very high resolution features. But thin resist makes pattern transferring by dry etching difficult because typical resist has poor resistance to plasma etching. One widely employed strategy is to use an intermediate hard mask layer, with the pattern first transferred into this layer, then into the substrate or sublayer. Cr is one of the most popular hard etching mask materials because of its high resistance to plasma etching. Cr etching is carried out in O 2 and Cl 2 or CCl 4 environment to form the volatile etching product CrO 2 Cl 2 , but addition of O 2 gas leads to fast resist etching. In this work, the authors show that Cr 2 O 3 can be etched readily in a Cl 2 /O 2 gas mixture with less oxygen than needed for Cr etching, because Cr 2 O 3 contains oxygen by itself. Thus it is easier to transfer the resist pattern into Cr 2 O 3 than into Cr. For the subsequent pattern transferring into the substrate here silicon using nonswitching pseudo-Bosch inductively coupled plasma-reactive ion etching with SF 6 /C 4 F 8 gas and Cr or Cr 2 O 3 as mask, it was found that the two materials have the same etching resistance and selectivity of 100:1 over silicon. Therefore, Cr 2 O 3 is a more suitable hard mask material than Cr for pattern transferring using dry plasma etching.

Highly Ordered Porous Inorganic Structures via Block Copolymer Lithography: An Application of the Versatile and Selective Infiltration of the “Inverse” P2VP-b-PS System

“…To study the capacity and the versatility of P2VP in creating ordered domains, selective metal infiltration via spin coating of the precursor solutions onto the highly ordered BCP thin films was studied followed by the conversion of the metal ions to their metal oxides by UVO treatment. Four different metal ions (chromium (Cr 3+ ), nickel (Ni 2+ ), iron (Fe 3+ ), and gallium (Ga 3+ )) were selected to be infiltrated into the ordered BCP thin films based on previous reports. ,,, In metal infiltration studies, an ethanol swelling treatment is commonly applied to increase interaction between the metal and the desired block by creating a porous structure. ,, However, for the BCP analyzed in this research (P2VP-majority), it was not possible to apply this procedure. The EtOH swelling led to the film destruction and the loss of pattern, possibly due to ethanol’s selectivity toward the P2VP block, thus resulting in a complete collapse of the matrix (SI Figure S2).…”

Etching of iron and iron–chromium alloys using ICP-RIE chlorine plasma

“…The first study dedicated to chromium etching was provided by Abe et al [42]. They analysed the etching process using plasma mixtures with Cl 2 and O 2 and attributed it to the formation of CrCl 2 O 2 volatile compounds (CrCl 2 O 2 is volatile at room temperature [43]). Curtis et al [44] studied the evolution of Cr etching by varying the percentage of O 2 in CCl 4 /O 2 mixtures and observed a maximum of chromium etch rate for 50 %O 2 .…”

Ultrahigh aspect ratio etching of silicon in SF6-O2 plasma: The clear-oxidize-remove-etch (CORE) sequence and chromium mask

“…the temperature and applied power during plasma ashing. [35][36][37][38] Below 100°C, almost no erosion is observed and the erosion is only substantial at the maximum power. Nitrogen or CF 4 plasmas do not attack chromium; only O 2 supports ashing.…”

“…However, it is known that chromium is damaged (or etched) when exposed to plasma ash systems and O 2 is a basic ingredient of the CORE sequence. [35][36][37][38] Therefore, a further task of this study is to find the limits of ultra-HAR etching using chromium as a hard mask.…”