(722c) Simulation of Contact Hole Rectification by Directed Self Assembly of Diblock Copolymers

Contact holes (CHs) are important components of microelectronic chips and memory devices. They are cylindrical channels that are used to establish electric connection between different layers on the chip. For optimal device performance it is desirable that the diameter (also referred to as critical dimension or CD) of all the CHs in a block of area be the same. However, as the feature size on the chips continues to shrink, maintaining the desired level of shape and size uniformity in CHs is becoming increasingly difficult. One promising approach to rectify non-uniformities in CHs utilizes directed self assembly of AB diblock copolymers in CHs. Typically this approach employs an asymmetric diblock copolymer, whose one block is attracted to the inner surface of the CHs. The polymer is coated over the CHs and annealed. During annealing the two blocks self-assemble in cylindrical symmetry due to the cylindrical shape imposed by the CH walls and the preferential attraction of one block to the walls (directed self assembly, DSA).

The efficacy of this approach in CH rectification depends on properties of both the given CH array and the selected block copolymer. In real application only the average size of the initial CHs and their uniformity (CDU, quantified by standard deviation in CDs) is known. The challenge is to design block copolymers and (if needed) perform modifications to the CHs such that the CDU after DSA can be minimized. There are three main parameters that go into diblock block copolymer design: (i) the Flory-Huggins interaction parameter, χ_AB, (ii) the composition of the block copolymer, and (iii) size of the polymer chain (degree of polymerization, N and Kuhn length, b). Understanding the role of each of these parameters on the uniformity of cylinders formed by the block copolymer inside CHs is essential for achieving desired levels of rectification. In this work theoretical methods including two-dimensional self consistent mean field theory (SCFT) derived simulations and strong segregation theory (SST) based calculations have been employed to garner such understanding.

Calculating CDU from a large population of CHs by SCFT simulations (or SST calculations) is highly computationally intensive. To make the problem more tractable the two main contributing factors to CDU, namely, hole-to-hole diameter (CD) variations and non-circularity of individual holes, were studied separately. Hole-to-hole CD variations were introduced by varying CDs of circular CHs, and CH non-circularity by imposing the simplest perturbation to the circular cross-section of the CHs, namely, an ellipse. Block copolymer morphologies were simulated in judiciously selected circular and elliptical CHs to determine how these perturbations to the CHs affected the size and shape of the BCP cylinder. This presentation will discuss results from systematic parametric studies which provide insights on how the CDU of the block copolymer cylinder domains is affected by both CH properties (CH wall attraction to the two blocks) and BCP properties (χ_AB, N and b).