Method And Technology Research On Real-time Laser Differential Confocal Microscopy Without Sample Reflectivity

Confocal microscopy (CM) has unique optical section capability and superior lateralresolution compared with ordinary microscopy. Thus, CM has an important function inboth fundamental academic research and industrial applications, such as microelectronics,industrial precision detection, biomedicine and materials engineering. However, theexisting CM imaging method has the following deficiencies:(a) low imaging efficiencybecause of layer-by-layer scanning by the focus,(b) low axial depth resolution because ofthe detection focus corresponding to the axial response curve’s peak with the lowestsensitivity, and (c) low signal-to-noise ratio (SNR) because of ambient lighting and thepower disturbance of the light source.All of these deficiencies make CM cannot satisfy the increasingly urgent requirementof real-time surface imaging in device fabrication monitoring in situ, and observation ofmorphology changes or cellular membrane motion of live biological samples. Researchon surface imaging methods and techniques with real-time rapid high resolution and highSRN has become a major issue of modern measurement areas.The subject “Research of laser differential confocal microscopy method andtechnology”, on the basis of three-dimension imaging principle in CM, proposes a newthree-dimension imaging principle in differential confocal microscopy (DCM), studies anew real-time laser differential confocal microscopy (RLDCM) imaging methods andtechnology without sample reflectivity difference effects for rapid high resolution andhigh SRN sample surface imaging, and develop the laser differential confocal microscope.The study content can be widely used in semiconductor processing, high-resolutionimaging, detection optical ultra-precision machining and testing and biomedical field, andhas important theoretical and practical value.The subject is supported by National Natural Science Foundation of China“Development of super resolution differential confocal microscope (No.60927012)”,National Instrumentation Program “Laser differential confocal measurement instrumentdevelopment and application research”(No.2011YQ040136). The following are the maininnovative research work I have completed so far:A new real-time laser differential confocal microscopy (RLDCM) without sample reflectivity difference effects is proposed for imaging height topography of samplesurface, which adapts the same optical path as the differential confocal microscopy. Bydividing the difference of the two signals simultaneously detected from the differentialconfocal imaging paths by the higher signal between these two signals, RLDCMseparates the signal that comes from reflectivity heterogeneity from the topographicsignal in real time. A new theoretical model of three-dimension imaging principle inRLDCM is established. The key parameter affecting axial response characteristics ofRLDCM is studied and optimized. Theoretical analysis and experimental resultsdemonstrate that RLDCM realizes the axial response without reflectivity differenceeffects, the lateral response nearly the same as confocal microscopy and a better noiseand disturbance suppression characteristics.A differential confocal microscopy for edge contour detection and location isproposed based on the differential confocal optical paths. By dividing the difference ofthe two signals simultaneously detected from the differential confocal imaging paths bythe absolute value of the difference, the proposed method realizes the real-time sampleedge contour imaging in the form of binary image, and greatly improve the efficiency ofedge contour detection. Theoretical analysis and computer simulations show that theproposed method can precisely detect and locate the edge contour without being affectedby edge shape and direction, and has the ability of suppressing the interference caused bymultiplicative and additive noise.A confocal pore size measurement based on super-resolution image restoration isproposed to obtain a fast and accurate measurement for submicrometer pore size. Thismethod facilitates the online inspection of the pore size evolution during etching.Combining confocal microscopy with super-resolution image restoration significantlyimproves the lateral resolution of the NTEM image, yields a reasonable circleedge-setting criterion, and achieves precise pore edge detection. Theoretical analysisshows that the minimum measuring diameter can reach0.19μm, and the root meansquare of the residuals is only1.4nm. Edge response simulation and experiment revealthat the edge response of the proposed method is better than80nm. The NTEM pore sizemeasurement results obtained by the proposed method agree well with that obtained by scanning electron microscopy.The microscope based on RLDCM is developed，utilizing which3-D imaging of laserdifferential confocal microscopy is realized for the first time. Experiments demonstratethat laser differential confocal microscopy significantly reduces the height topographyimaging time by single-layer scanning for the sample surface with reflectivityheterogeneity and achieves the high axial resolution of2nm without losing lateralresolution by optimizing the axial detector offset. The experimental measurement is wellagreed with the atomic force microscope the measurement. The RLDCM achievescalibration result as263±22nm, k=2for HS-500G, which has an optical height of259.8±5.38nm when wavelength is632.8nm. Thus, laser differential confocal microscopehas good and accurate three-dimensional imaging and measurement performance.In conclusion, the three-dimension imaging principle in RLDCM enriches the theory ofCM; the RLDCM imaging method realizes the real-time rapid high resolution and highSRN surface imaging without sample difference effects; the laser differential confocalmicroscope has various imaging modalities for different samples and differentmeasurement purposes, can provide both optical and topographical tomographic imagesreal-time and synchronously and thus is a new precision microscopic imaging andmeasurement instrument of great development potential and broad application prospect.