Two-Step Chemical Mechanical Polishing for Semiconductor Wafer Flatness
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Solution Overview
Problem
Current chemical mechanical polishing (CMP) methods struggle to effectively eliminate surface level differences in semiconductor wafers without causing scratches or dishing, particularly in damascene interconnect formation processes, due to the limitations of polishing pad elasticity and pressure distribution.
Innovation Solution
A two-step polishing method using a smaller polishing pad for the first step to precisely eliminate surface level differences at low pressure and high speed, followed by a larger pad for the second step at higher pressure and lower speed to maintain flatness and increase productivity, with detection of completion using eddy current or torque sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a roughened polishing pad is used to maintain constant polishing rate, then polishing efficiency is improved, but the pad enters recessed portions causing over-polishing and dishing
Solution Approach 1:
The invention changes the surface parameters of the polishing pad by controlling the protrusion height distribution of abrasive particles. By creating a specific probability distribution where most protrusions are low and only a few are high, the pad maintains high polishing efficiency while avoiding entry into recessed portions of the workpiece surface.
Solution Approach 2:
The polishing pad surface is designed with non-uniform abrasive protrusion characteristics. The majority of the surface has low protrusions that avoid recessed areas, while a small fraction has high protrusions that provide aggressive polishing where needed. This local differentiation resolves the contradiction between efficiency and precision.
2Manufacturing precision
If polishing pressure is increased to eliminate surface level differences, then flattening is improved, but scratches are caused on the surface
Solution Approach 1:
The invention changes the pressure distribution parameters by controlling the vertical distribution of abrasive protrusions. The statistical distribution ensures that high contact pressure occurs only at rare, isolated points rather than across the entire surface, enabling effective flattening without widespread scratching.
Solution Approach 2:
Instead of applying uniform moderate pressure across the entire pad surface, the invention allows excessive localized pressure at a small fraction of protrusion points. This partial excessive action is sufficient to eliminate surface level differences without causing damage, as the harmful effects are confined to a minimal area.
3Productivity
If relative speed between pad and workpiece is increased to reduce polishing time, then productivity is improved, but surface flatness control becomes difficult
Solution Approach 1:
The invention changes the speed parameter within an optimized range (5-20 m/s) and combines it with the specific abrasive protrusion distribution. This parameter combination allows high-speed polishing while maintaining surface flatness control, as the statistical distribution of protrusions provides consistent contact characteristics even at high relative speeds.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively eliminates surface irregularities while maintaining flatness and increasing productivity, avoiding scratches and dishing, by leveraging the advantages of both polishing pad sizes and techniques.
Implementation Method 1
A film of metal interconnect material such as the copper film 206, deposited in excess, can be polished away by pressing the polishing pad, with the polishing liquid held on the surface, against the film of metal interconnect material formed on an object
Implementation Method 2
carrying out a first polishing step by pressing a polishing pad having a diameter which is smaller than the radius of the object against a surface to be polished of the object
Data Source
AI summary
A method can effectively eliminate a surface level difference (irregularities) in a film formed on an object without producing scratches in a surface of the film, and can polish and remove the film into a flat surface with greatly increased productivity. The method comprises carrying out a first polishing step by pressing a polishing pad of a polishing device, having a diameter which is smaller than the radius of the object, against the surface of the object at a first pressure while moving the polishing pad and the object relative to each other at a first relative speed. The first polishing step is terminated at a point in time when a surface level difference in the object is eliminated to a targeted level. The method further comprises carrying out a second polishing step by pressing a polishing pad of a polishing device, having a diameter which is larger than the diameter of the object, against the surface of the object at a second pressure while moving the polishing pad and the object relative to each other at a second relative speed.