Adam Ticknor

Post Copper CMP Hybrid Clean Process for Advanced BEOL Technology

A “hybrid” post Cu CMP cleaning process that combines acidic and basic clean in sequence is developed and implemented. The new process demonstrates the strengths of both acidic and basic cleans and achieves a more than 60% reduction in CMP defects, such as polish residues, foreign materials, slurry abrasives, scratches, and hollow metal, relative to an all-basic clean process. It also eliminates the circular ring defects that occur intermittently during roller brush cleans. TXRF scans confirm the reduction of AlOx defects when using the hybrid clean process. XPS spectra show similar Cu surface oxidation states between the basic and hybrid clean processes. As revealed by XRD analysis, surface Cu oxide is dissolved into aqueous solution by the acidic clean chemical. The formation mechanism of circular ring defects and the key to their elimination is discussed.

Post Cu CMP cleaning process evaluation for 32nm and 22nm technology nodes

Optimization of post Cu CMP cleaning performance can be accomplished through dilution ratio tuning and pad rinse of clean chemicals. Excessive chemical etching as well as megasonic power can induce high Cu roughness. Generation of hollow metal and Cu dendrite defects depends not only on the clean chemistry but also the queue time between plating and anneal and between CMP and cap. AFM and XPS provide insights into the cleaning mechanism. EM and TDDB tests are the ultimate tests for the effectiveness of post Cu CMP cleaning.

Fixed Abrasive Technology for STI CMP on a Web Format Tool

Shallow trench isolation (STI) requires a high quality oxide with superior fill capability provided by High Density Plasma (HDP) oxide. Unfortunately, the HDP deposition process can create large within die topographies that are difficult to polish directly using conventional silica slurries. As a result, etch back integration schemes have traditionally been incorporated for STI polish. A more revolutionary approach is the use of Fixed Abrasive (FA) CMP [1]. FA CMP allows direct STI polish with good planarization/process stability, eliminating the need for prior etch back. The planarization efficiency is strongly dependent on the shape of the pad composites that hold the CeO 2 mineral. Fixed abrasive pads with pyramid and pole shapes are available. In this work, three different fixed abrasive pads supplied by 3M corporation were evaluated for STI CMP polish performance using the Obsidian 8200C web format CMP tool. Basic polish characteristics such as planarity (dependence on sub-pad/pattern density), selectivity to topography, oxide dishing and nitride erosion are presented. The FA pads discussed here have been classified as “slow”, “medium” or “fast” depending on blanket oxide removal rate. The slow rate pad had a very high selectivity to topography and very low dishing of the down area oxide. The removal rate of blanket oxide was less than 100 A/min. The pad was best suited to the polish of isolation trench structures with small, controlled overfill (> 200 A) across the wafer. A large process window was demonstrated. The removal rate of the “medium” pad also decreased significantly at the onset of planarization with a blanket oxide removal rate of ca. 200 A/min. Unlike the slow rate pad, the medium rate pad did not provide a suitable overpolish process window required for a manufacturable STI process. It is believed this pad would be a good choice for BPSG polish. In contrast to the slow and medium rate pads, the blanket oxide removal rate of the fast pad was ca. 2000 A/min with no self-stopping capability at the onset of planarization. The removal rate was extremely center fast, such that it could not be compensated by adjustment of tool parameters. Use of a modified process developed within the DRAM development alliance (DDA) at East Fishkill (IBM/ Infineon) enabled the fast pad to polish deep STI structures that would otherwise be impossible using the slow or medium rate pads.

Hybrid clean approach for post-copper CMP defect reduction

A “hybrid” post-Cu CMP cleaning process that combines acidic and basic cleans in sequence is developed and implemented. The new process demonstrates the advantages of both acidic and basic cleans and achieves a more than 60% reduction in CMP defects, such as polish residues, foreign materials, slurry abrasives, scratches, and hollow metal, relative to an all-basic brush clean process. It also eliminates the circular ring defects that occur intermittently during roller brush clean. TXRF scans confirm the reduction of AlOx defects when using the hybrid clean process. XPS spectra show similar Cu surface oxidation states between the basic and hybrid clean processes. Both short and open yields can be improved by using the new clean process. The underlying mechanism of the huge defect reduction benefits is discussed.

Microreplicated pad conditioner for copper and copper barrier CMP applications

Metal-free micro-replicated conditioning disks are applied to the development of Cu and Cu barrier CMP processes for 22nm technology nodes. Compared with traditional pad conditioners with diamond grits embedded in metal matrix, the micro-replicated conditioners demonstrate lower within-wafer non-uniformity, more stable end-point time, more uniform and controllable pad wear, lower defectivity, and longer pad life time. Used pad analyses provide insights into the effectiveness of conditioning and guidelines for further process improvement.