Cu Deposition And ·OH Concentration Distribution In Photoinduced Confined Etching System

Confined etchant layer technique(CELT),a copy processing of three-dimensional ultra-micro(nano)graphics,has been successfully applied in the three-dimensional complex morphology processing of conductors,semiconductors,and insulators.Since CELT can control the degree of etching effectively and is sensitive to distance,it can also be developped to an unstressed polishing technology.Though copper(Cu)interconnect is widely used in the large scale of the integrated circuit,the process is still not good for the low damage,low scratch of the polishing of Cu.Our group has developed a chemical polishing technology based on the photoinduced confined etching system,and the application to the planarization of Cu was preliminarily realized.But the technology still has the following two key problems to be solved:(1)It was found that the Cu deposits may exist on the surface of the tool in the process of photoinduced confined etching of Cu workpiece,will the deposits influence the TiO2 pholocatalyst to the decrease of the photoinduced planarization effect?How to inhibit the deposits?(2)It is desiderated to establish methods to characterize the concentration distribution of the photoinduced confined etching layer for the evaluation and optimization of the scavenging agents,and the etching conditions.In this paper,I focused on the mechanism of Cu deposits on the tool surface and the simultaneous influence on the photoinduced confined etching system,and try to inhibit the Cu deposits;Two strategies to evaluate the concentration distribution of OH in the photoinduced confined etching system were proposed.The main research contents and results are as follows:1.Two kinds of TiO2 pholocatalyst layers were prepared by liquid-phase deposition using ZnO as a template and TiO2 nanoparticles by electric field deposition.Scanning electron microscope combined with fluorescence were used for screening the appropriate conditions of the preparation of TiO2 nanotubes.The former is more manageable but the procedures are much more complex,and the raw materials are also more expensive;while the latter has a weaker fixation with the substrate and is easier to fall off the surface,and the diffusion path of the carrier was not as short as that of TiO2 nanotubes,the degree of recombination is higher,but the procedures are easier and cheap.2.The photoinduced confined etching systems based on the TiO2 nanotubes and the TiO2 nanoparticles were established respectively.It was found that the deposits on the TiO2 surface were Cu and a small amount of Cu2O by scanning electron microscope,energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy in the photoinduced confined chemical planarization of Cu.The mechanism of the photo-deposition of Cu was investigated,which took place in the micro/nano-scale liquid layer between the tool and workpiece.A cupric simulated solution was used to study the influence of the Cu deposits on the photoinduced confined etching system.The deposition of Cu and its influence on TiO2 were studied by the simulated solution,the mechanism of deposition was investigated further and the results showed that the Cu deposits enhanced the photocatalytic performance of TiO2,but the enhancement of mechanism would change with the increase of Cu deposits,and the original morphology of TiO2 was changed by the excess Cu deposits,the increase of the Cu deposits is not beneficial to the control of etching rate and the accuracy of the planarization.Finally,several routes including stirring,adding complexing agent and external field were exploited to investigate the inhibition of Cu deposition on the TiO2 surface and the simultaneous influence on the etching of Cu workpiece.Trying to inhibit Cu deposits by improving mass-transfer can lead to the increase of the etching of Cu;adding complexing agent combined with enhanced mass-transfer can inhibit the Cu deposit,and may improve the planarization effect in the meanwhile.So,the choice of inhibition methods and the conditions should balance the influence on the multiple chemical reactions and mass transfer processes of the micro/nano-scale liquid layer between the tool and workpiece.3.First,a method used for the characterization of the concentration distribution of· OHf in photoinduced confined etching system based on the device and the SG/TC mode of scanning electrochemical microscopy(SECM)was explored.Second,the deposition-etching-stripping of Cu on a SECM tip was explored to establish a new characterization strategy of the concentration distribution of OHf in photoinduced confined etching system.The influence of glycine on the concentration distribution of ·OHf was studied by these two methods and the effective thicknesses of the etching agent layers were estimated.These two methods can both provide analytical tools for the evaluation of concentration distribution of ·OHf,the first one was easy and convenient,can provide the two-dimensional characterization with spatial resolution,but there are some deviations in measurement.While the second one can provide a more accurate characterization for the concentration distribution of ·OHf,the measurement environment was closer to the real situation,but the procedures are more complex.These methods have a significance on the evaluation and optimization of the effect of photocatalytic layer,the scavenging agents,and other influencing factors in the confined layer,and for further research on the etching and confining mechanisms.