The way to zeros: The future of semiconductor device and chemical mechanical polishing technologies

Abstract

For the last 60 years, the development of cutting-edge semiconductor devices has strongly emphasized scaling; the effort to scale down current CMOS devices may well achieve the target of 5 nm nodes by 2020. Planarization by chemical mechanical polishing (CMP), is one technology essential for supporting scaling. This paper summarizes the history of CMP transitions in the planarization process as well as the changing degree of planarity required, and, finally, introduces innovative technologies to meet the requirements. The use of CMP was triggered by the replacement of local oxidation of silicon (LOCOS) as the element isolation technology by shallow trench isolation (STI) in the 1980s. Then, CMP’s use expanded to improving embedability of aluminum wiring, tungsten (W) contacts, Cu wiring, and, more recently, to its adoption in high-k metal gate (HKMG) and FinFET (FF) processes. Initially, the required degree of planarity was 50 nm, but now 0 nm is required. Further, zero defects on a post-CMP wafer is now the goal, and it is possible that zero psi CMP loading pressure will be required going forward. Soon, it seems, everything will have to be “zero” and perfect. Although the process is also chemical in nature, the CMP process is actually mechanical with a load added using slurry particles several tens of nm in diameter. Zero load in the loading process, zero nm planarity with no trace of processing, and zero residual foreign material, including the very slurry particles used in the process, are all required. This article will provide an overview of how to achieve these new requirements and what technologies should be employed.

Surface removal of a copper thin film in an ultrathin water environment by a molecular dynamics study

“…As is well known, a major requirement for the CMP process is the minimal dishing and erosion, as well as minimal levels of the surface defects [3]. Furthermore, approaching and even achieving the three-"zero" target of "0 nm planarity, 0 defects, and 0 polishing load" are the desired goals for the CMP technology [5]. Hence, it is important to evaluate the surface defect of a Cu thin film.…”

“…Owing to the shrinkage of ultralarge-scale integrated circuits, new challenges for CMP have emerged recently, one of which is the small root-mean-square roughness (of the order of subnanometer) [1−4]. The initial requirement of reducing the step-height differences to about 50 nm was first changed to 30 nm, then to 10 nm, and finally to a 0 nm difference [5,6]. Furthermore, a three-"zero" target, namely, "0 nm planarity, 0 defects, and 0 polishing load", is even proposed and desired to be reached by the year 2020 [5].…”

“…The initial requirement of reducing the step-height differences to about 50 nm was first changed to 30 nm, then to 10 nm, and finally to a 0 nm difference [5,6]. Furthermore, a three-"zero" target, namely, "0 nm planarity, 0 defects, and 0 polishing load", is even proposed and desired to be reached by the year 2020 [5]. With this order of size, the removal of the polishing material within a few and even only one atomic layer of the film or coating surface is still challenging.…”

Perspective—Electrochemical Assessment of Slurry Formulations for Chemical Mechanical Planarization of Metals: Trends, Benefits and Challenges

“…1,2 CMP of the metal components of logic devices constitute a major aspect of this technique and, like other areas of IC manufacturing, metal CMP has become quite complex while addressing the emerging demands of technology through the last decade. 3 The new challenges of metal CMP originate from both the scaling and the novel material aspects of these systems. 3,4 At the same time, published reports indicate that, many of these issues, especially those related to the slurry consumables, 5 can be addressed to a large extent through electroanalytical examinations of slurry functions using scaled down models of actual CMP systems.…”

“…3 The new challenges of metal CMP originate from both the scaling and the novel material aspects of these systems. 3,4 At the same time, published reports indicate that, many of these issues, especially those related to the slurry consumables, 5 can be addressed to a large extent through electroanalytical examinations of slurry functions using scaled down models of actual CMP systems. 6 Recent studies performed in industrial facilities have also identified a critical need to further advance the fundamental understanding of metal CMP.…”