Study On Material Removal Process Of Copper Chemical Mechanical Polishing At Pad Asperity Scale

With the rapid development of integrated circuits,the requirements for chip integration and electrical performance have become higher and higher.In recent years,3D packaging technology has developed rapidly.Copper as an interconnect material is widely used in three-dimensional packaging technology due to its low impedance and high conductivity.Among 3D packaging technologies,the chemical mechanical polishing(CMP)process is a common technical means which can achieve the local and global planarization of copper.There are high removal rate and planarization requirements in interconnection technology.The following problems exist in the process of meeting the requirements: the numerous polishing parameters in the CMP process make it difficult to control the process parameters;It is difficult to analyze the characteristics of new polishing pads and polishing solutions during use;Improper control of the chemical and mechanical actions of the polishing conditions will cause problems such as dishing and copper protrusions,which will affect the subsequent process.Therefore,it is meaningful to understand the material process of copper and accurately adjust the proportion of mechanical and chemical actions to meet the requirements of interconnection technology.At the same time,the asperity contact state is related to the material removal in the copper polishing process,and it is also related to the dressing parameters in the process.Therefore,this research is based on the scale of polishing pad asperities to study the copper CMP material removal process,so as to optimize and guide the copper CMP process.The main research contents of this research are:(1)Through the single POM(polyoxymethylene)ball scratching experiment method to study the material removal process of copper chemical mechanical polishing,a single POM ball is used to simulate a single pad asperity,and the load,chemical reaction time interval,oxidant concentration,and the p H of polishing solutions are explored.The protrusion of the groove edge morphology is explained based on the influence of the contact interface temperature,It is speculated that the frictional heat at the scratching interface promotes the phenomenon of protrusion.And the material removal mechanism is analyzed by monitoring the current changes on the copper surface during the scratching process based on electrochemical analysis methods.The results showed that the material removal process is a process of mechanical wear accelerated chemical corrosion.(2)The polishing pad scratching experiment under reciprocating motion is carried out on the copper surface,and the influence of different loads and chemical reaction time intervals on the material removal rate is explored.At the same time,the etching rate under different conditions during the scratching process is analyzed and the impact of load and reaction time interval on the etching rate is summarized.The material removal profiles after scratching are analyzed in combination with the removal model of single pad asperity to elaborate the chemical-mechanical synergy under the contact of multiple pad asperities.(3)The actual contact state image of the pad asperities is taken with a CCD camera and binarized and the influence of asperity contact on the planarization process of the copper pattern wafer is explored.A series of polishing experiments are carried out on the wafer using a millimeter-scale polishing pad and the material removal amount of the up and down areas on the surfaces of wafer is analyzed by comparing with the expanded GW model.By measuring the compression of pad asperity and the change of the contact area under different pressures,the difference between the removal rate of up and down areas at different positions is analyzed.