In this paper a review of various methodologies for burr prediction and minimization in face milling is presented. In particular, the authors look into the geometric solutions employed, which typically consist of understanding and modifying tool engagement conditions. The extent of applicability of various approaches is discussed and the possible direction for future research is indicated.

All process elements of a reconfigurable manufacturing system should accommodate future changes. This paper looks at one such process element, tool paths, with focus on face milling and pocket milling. Tool paths for the first part are designed to optimize the process outcomes for the initial constraints. Change in market conditions or part design leading to change in cycle time requirements, geometry or complexity of the part, are met using incremental tool paths. Changes in cycle time are achieved by changing the feedrate and tool diameter. Changes in part design are tackled by modifying tool path segments. This system would provide a quick turn around time, less testing and quicker ramp up.

We are developing an integrated tribo-chemical model of copper CMP that considers abrasive and pad properties, process parameters (speed, pressure etc.), and slurry chemistry to predict material removal rates. In this paper, the framework of the model is explained, and two important constituents of the model are presented: transient passivation behavior and characteristics of mechanical interactions.

During copper CMP, abrasives and asperities interact with the copper at the nano-scale, partially removing protective films. The local Cu oxidation rate increases, then decays with time as the protective film reforms. In order to estimate the copper removal rate and other Cu-CMP output parameters with a mechanistic model, the passivation kinetics of Cu, i.e. the decay of the oxidation current with time after an abrasive/copper interaction, are needed. For the first time in studying Cu-CMP, microelectrodes were used to reduce interference from capacitive charging, IR drops and low diffusion limited currents, problems typical with traditional macroelectrodes. Electrochemical impedance spectroscopy (EIS) was used to obtain the equivalent circuit elements associated with different electrochemical phenomena (capacitive, kinetics, diffusion etc.) at different polarization potentials. These circuit elements were used to interpret potential-step chronoamperometry results in inhibiting and passivating solutions, notably to distinguish between capacitive charging and Faradaic currents. Chronoamperometry of Cu in acidic aqueous glycine solution containing the corrosion inhibitor benzotriazole (BTA) displayed a very consistent current decay behavior at all potentials, indicating that the rate of current decay was controlled by diffusion of BTA to the surface. In basic aqueous glycine solution, Cu (which undergoes passivation by a mechanism similar to that operating in weakly acidic hydrogen peroxide slurries) displayed similar chronoamperometric behavior for the first second or so at all anodic potentials. Thereafter, the current densities at active potentials settled to values around those expected from polarization curves, whereas the current densities at passive potentials continued to decline. Oxidized Cu species typically formed at ‘active’ potentials were found to cause significant current decay at active potentials and at passive potentials before more protective passive films form. This was established from galvanostatic experiments.

CMP faces numerous challenges, as we move towards 45-nm and 32-nm nodes. The most important of these, as identified by ITRS [1], are: a) reliably predicting and controlling post-CMP topography (dishing and erosion loss should be limited to within 10% of the interconnect height throughout the die); b) Integration of ultra low-K

dielectric materials, including predicting stresses and damage, and designing very low stress polishing processes; and c) designing new planarization processes for new materials and new requirements.

To address these, a multi-scale (feature/die/wafer) CMP modeling framework is being developed for enabling Design for Manufacturing (DfM) and Manufacturing for Design (MfD). Topographic evolution has been studied for Shallow Trench Isolation CMP and is now being extended to copper CMP. A detailed, quantitative understanding of the mechanism(s) of CMP is being elucidated, using fundamental experiments and a mechanistic model based on physical data. Stress issues in low-K dielectric during copper CMP, which can lead to fracture and delamination, are being studied using Finite Element Modeling.

CMP has been successfully used for shallow trench isolation (STI) process in front end semiconductor processing. In STI process, nitride covers active device area acting as the CMP stop layer. Amount of nitride erosion during CMP is directly related to the step height of oxide isolation structure after removing nitride, and affects device performance as well. As semiconductor technology node is decreasing beyond 90nm, variation of nitride erosion over a chip in CMP process should be controlled within tight specifications. A model based simulation tool for chip scale variation of nitride erosion would improve not only CMP compatible STI layout design but also help in optimization of high density plasma chemical vapor deposition (HDPCVD) process of oxide layer. In this paper, a chip scale modeling scheme for better prediction of nitride erosion map integrating HDPCVD oxide topography is presented. In addition, a simulation result for a specially designed test pattern resembling production level STI layout is presented.

Millisecond scale benzotriazole (BTA) adsorption kinetics in acidic aqueous solution containing 0.01 M glycine and 0.01 M BTA have been investigated. Chronoamperometry was used to measure current densities on the surface of a micro-copper electrode in pH 4 aqueous solutions containing 0.01 M glycine with or without 0.01 M BTA. In the presence of BTA the current density decreased as the inverse of the square root of time for a few seconds due to adsorption of BTA. At potentials above 0.4 V saturated calomel electrode the current leveled off after a second or so due to the formation of a Cu(I)BTA monolayer on the copper surface. Based on these data a governing equation was constructed and solved to determine the initial kinetics of BTA adsorption. Analysis shows that material removal during copper chemical mechanical planarization (CMP) in this slurry chemistry occurs mostly by direct dissolution of copper species into the aqueous solution rather than mechanical removal of oxidized or pure copper species and that each interaction between a pad asperity and a given site on the copper removes only a small fraction of the Cu(I)BTA species present at that site.