4D Reflectometer

Characterize transparent patterns

Transparent pattern characterization by DHM® is a unique solution to measure 3D topography and thicknesses of transparent structures on a reflective substrate.

Measures topography, thickness and refractive indices of transparent structures

  • Measurement of surface structures from 10 nanometers to several microns
  • Measurement of refractive indices
  • Characterization of deposited or etched structures composed of up to 3 layers

Flexible instrument

  • Non-contact method, ideal to measure liquids and soft materials
Typical transparent SiO2 pattern characterized by DHM reflectometry analysis tool

The 3D topography as well as the thicknesses and refractive indices of patterned transparent samples are retrieved by a dedicated post-analysis software by computing the complete reflected wavefront based on the laws of physics. Therefore DHM® provides a solution to measure the correct topography while measurements with alternative optical profilometer are affected by the multiple reflections of the light signal occurring in transparent materials. Structures of Transparent materials such SiO2 and thin metal layers, widely used in coating, isolating, protective or structuring layers in semiconductor and MEMS industries, are typical samples easily characterized by DHM®. Dynamical topography of liquids on microfluidics devices and on functional surfaces is critical to characterize because of multiple interferences occurring between the liquid and the substrate. DHM® with the Reflectometry analysis software enables to provide accurate dynamical measurements. This solution encompasses a holographic microscope instrument by Lyncée Tec with a full range of microscope objectives, the dedicated Koala acquisition and analysis software and the dedicated Reflectometry post-analysis software.

Benefits

DHM® technology and its dedicated Reflectometry post-analysis software offer significant benefits.

Be innovative by extending your range of measurable samples

  • Perform Reflectometry analysis with a single DHM® instrument
  • Measure the topography on coated materials with metrological precision
  • Study surface topography of semiconductors with photoresist
  • Study dynamical dielectric constant variation (Hall effect)
  • Measure the 3D topography of liquids and soft materials

Get instantaneous results

  • Combien DHM® Reflectometry analysis software with live profilometry, stroboscopic synchronization and industrial solutions

Competitive Strengths

ŸDHM® provides a unique solution to measure 3D topography of transparent structures on reflective substrates. It also overcomes the standard limitations of scanning methods and covers a large range of applications. It provides unique advantages to measure structures and their thicknesses in the nanometer and micrometer range and as well as to retrieve information on material dielectric properties. Samples without structures, i.e. thin films, or with many layers, e.g. with anti-reflective coating, are not adapted to DHM®. DHM® Reflectometry analysis can be compared to the following alternative systems.

DHM® vs. Mechanical Profilometer

Mechanical profilometers are widespread for direct measurement of transparent structures without any assumption on the sample composition. The drawback is that, additionally of being a time consuming scanning method, they cannot provide any information on the material and cannot measure layer thicknesses without the presence of steps. Moreover, the measurement by contact profilometer can be affected by elastic deformation on the surface, dirt dragged by the tip or by a damaged tip. Soft materials and liquids cannot be measured. DHM® is a non-contact and non-scanning method. Combined with specific Reflectometry software it enables quick topography and thickness measurements of transparent patterns without any surface damage.
Features DHM® Mechanical profilometer
Non-damaging    
Non-scanning    
Soft materials & liquids    
Topography measurement   no scanning   XY scanning
Measurement of refractive index    
Measurement of dynamical and moving sample    

DHM® vs. Ellipsometer

Ellipsometry is a well-known optical technique for investigating dielectric properties (refractive index) and thicknesses of thin films. It requires use of a model of the sample, similarly to DHM. The drawbacks are, additionally of being a time consuming scanning method, the high price and the lateral resolution limited by the beam diameter.
DHM and Reflectometry analysis measure the thickness, from a few nanometers to several microns, and the topography of transparent patterns with interferometric resolution.
Features DHM® Ellipsometer
Non-scanning  
Thickness measurement [10nm – 50μm] transparent materials
[0.1nm – 0.01mm] non-metals
[0.1nm – 50nm] metals
Measurement of refractive index  
Topography measurement w/o scanning XY scanning
Measurement of dynamical and moving sample  
Lateral resolution ++ objective resolution limited by laser spot diameter
Cost competitive ++

DHM® vs. Spectral Reflectance (SR)

Spectral Reflectance (SR) analyzes reflected light and determines the thickness and dielectric constant of films. The main difference between Ellipsometry and SR is that the first one uses light reflected at low incident angle, while the second uses light reflected perpendicular (normal) to the surface of the sample. SR is a simple and low-cost instrument but measurements are not instantaneous since a spectral analysis has to be performed. Moreover, it requires a lateral XY scanning to retrieve 3D information. SR usual application is films with a limited numbers of layers, and with thickness larger than 10 μm.

DHM® and Reflectometry analysis measure the thickness, from a few nanometers to several microns, and the topography of transparent patterns with interferometric resolution.
Features DHM® Spectral Reflectance
Non-scanning  
Thickness measurement [10nm – 50μm] transparent materials
[1nm – 1mm] non-metals
[0.5nm – 50nm] metals
Measurement of refractive index  
Topography measurement w/o scanning XY scanning
Measurement of dynamical and moving sample  
Lateral resolution ++ objective resolution limited by laser spot diameter

DHM® vs. Confocal Laser Scanning Microscope (CLSM)

Confocal Laser Scanning Microscope (CLSM) measures transparent layers by discriminating the signal reflected by each interface from the multi-layer sample. To be able to use this procedure, layer thicknesses must be large enough compared to the size of the focal point. This one decreases when the objective Numerical Aperture (NA) and magnification increase. To characterize layers with thin thicknesses, objectives with high NA, large magnification, and thus with limited field of view have to be used. Thin layers on large structure cannot be measured since objectives with low NA and low magnification cannot be used.

DHM® Reflectometry analysis does not require discrimination of each layer interface. It considers the global reflected signal and uses the laws of optics to provide accurate measurement of thicknesses from a few nanometers to several microns. Moreover, without any scanning, DHM® retrieves the 3D topography of transparent patterns with interferometric resolution as well as the refractive index.

Features DHM® CLSM
Non-scanning  
Thickness range  10nm – μm  >um
Topography measurement  
Measurement of refractive index  
Measurement of dynamical and moving sample  
Complete reflected signal considered  

DHM® vs. White Light Interferometry (WLI)

WLI, as self-explained by its name, uses white light illumination. For layer thicknesses larger than a few microns, WLI uses the coherence vertical scanning mode similarly to CLSM: the signal reflected by the various interfaces is discriminated. For thinner structures, WLI uses the phase shifting mode. It does not provide an efficient solution as the recorded signal is averaged over the full wavelength spectrum of the source. The system of equations determining the reflected signal cannot unequivocally resolve thicknesses and refractive indices of the layers.
By using a laser monochromatic source DHM® records a set of data enabling unequivocal calculation using the equations from the laws of optics. It provides accurate measurement of topography and thicknesses from a few nanometers to several microns with interferometric resolution.
Features DHM® WLI
Use of monochromatic light source  
Non-scanning  
Thickness range  10nm – μm >um
Topography measurement  
Measurement of refractive index limited
Measurement of dynamical and moving sample  
Large collection of objectives from standard optical microscopy  

Application Cases

In 2009, on request of a DHM® user measuring SIMS, Lyncée Tec has developed the solution to interpret optical measurement of samples with transparent structures. Since then, the Reflectometry analysis software has been continuously improved with new features and tools. Among many samples, Lyncée Tec has published the comparative measurements of geometrical topography for the following sample configurations:

SiO2 staircase on Si wafer

  • Height measurement of transparent multi-layered steps
  • Non-contact and complete 3D topography without any scanning
  • Step edges precisely highlighted

Crater dug through layers of Au-SiO2-Si

  • Depth measurement of a crater dug through transparent multi-layers on reflective substrate
  • Complete 3D topography of relatively large crater area
  • Depth determination with subnanometric vertical resolution

Fluid topography on substrate

  • Topography measurement of Liquid (TetraEthylenGlycol, TEG) drop on Si substrate
  • Non-contact, i.e. non damaging measure
  • Unique solution for complete 3D characterization of liquid or soft material drop
SiO2 Nano-staires on Si substrate