Aelan Mosden

Highly selective dry-plasma-free chemical etch technique for advanced patterning

Currently, the areal scaling of central processing units continues in accordance with Moore’s law for both the N7 and N5 (i.e., 7 and 5nm) semiconductor technology nodes.1, 2 To meet scaling targets and to maintain an aggressive gear ratio, however, achieving sub-30nm pitch line/space features at the back end of line (i.e., BEOL, the second stage of integrated-circuit fabrication where individual devices are interconnected with wiring on the wafer) is key. A number of patterning strategies enable the fabrication of such small features: extremeUV (EUV) direct print; 193nm immersion-based self-aligned quadruple patterning, SAQP; 193nm immersion-based lithographic etch, (LE)x; and directed self-assembly, DSA. Source power concerns preclude EUV direct print, and overlay and lineplacement roughness (LPR) preclude 193nm immersion-based (LE)x and DSA, respectively.3, 4 The only technique that is ready for high-volume-manufacture (HVM) applications is the 193nm immersion-based SAQP.5, 6 Although SAQP has been successfully implemented at the front end of line (FEOL, where individual devices are patterned onto the semiconductor) since the development of the N10 node, the technique is new to BEOL, and brings with it a different set of challenges. One such challenge is the limited choice of materials that can be used as films because of the lower temperature budget (i.e., below 400C). The films that can be deposited at such low temperatures are generally of poor quality compared to their analogous high-temperature versions because of differences in, for example, crystallinity and composition. Because of these characteristics, conventional plasma-etch techniques often have less than the required etch selectivity. This causes Figure 1. Option 1 shows the schematics and process performance of a sequence of etch steps in a typical SAQP process flow involving (I) mandrel definition, (II) spacer deposition, (III) spacer etch-back, and (IV) mandrel pull. Option 2 compares the impact of a mandrel/profile improvement step (I-A) with corresponding all-in-one spacer etch-back mandrel pull (step IV). Scanning electron microscope images underneath the schematics show experimental results.

Dry-plasma-free chemical etch technique for variability reduction in multi-patterning (Conference Presentation)

Scaling beyond the 7nm technology node demands significant control over the variability down to a few angstroms, in order to achieve reasonable yield. For example, to meet the current scaling targets it is highly desirable to achieve sub 30nm pitch line/space features at back-end of the line (BEOL) or front end of line (FEOL); uniform and precise contact/hole patterning at middle of line (MOL). One of the quintessential requirements for such precise and possibly self-aligned patterning strategies is superior etch selectivity between the target films while other masks/films are exposed. The need to achieve high etch selectivity becomes more evident for unit process development at MOL and BEOL, as a result of low density films choices (compared to FEOL film choices) due to lower temperature budget. Low etch selectivity with conventional plasma and wet chemical etch techniques, causes significant gouging (un-intended etching of etch stop layer, as shown in Fig 1), high line edge roughness (LER)/line width roughness (LWR), non-uniformity, etc. In certain circumstances this may lead to added downstream process stochastics. Furthermore, conventional plasma etches may also have the added disadvantage of plasma VUV damage and corner rounding (Fig. 1). Finally, the above mentioned factors can potentially compromise edge placement error (EPE) and/or yield. Therefore a process flow enabled with extremely high selective etches inherent to film properties and/or etch chemistries is a significant advantage. To improve this etch selectivity for certain etch steps during a process flow, we have to implement alternate highly selective, plasma free techniques in conjunction with conventional plasma etches (Fig 2.). In this article, we will present our plasma free, chemical gas phase etch technique using chemistries that have high selectivity towards a spectrum of films owing to the reaction mechanism ( as shown Fig 1). Gas phase etches also help eliminate plasma damage to the features during the etch process. Herein we will also demonstrate a test case on how a combination or plasma assisted and plasma free etch techniques has the potential to improve process performance of a 193nm immersion based self aligned quandruple patterning (SAQP) for BEOL compliant films (an example shown in Fig 2). In addition, we will also present on the application of gas etches for (1) profile improvement, (2) selective mandrel pull (3) critical dimension trim of mandrels, with an analysis of advantages over conventional techniques in terms of LER and EPE.