Compound semiconductor wafer inspection
In-house Service
MONSTR Sense Technologies’ compound semiconductor inspection is the first of its kind. Based on our proprietary nonlinear imaging technology, this inspection technique is highly sensitive to any defects altering the band structure of the epitaxial layer. It is sensitive to surface, sub-surface, and even substrate defects. Our proprietary scanning technique enables the use of variable spatial resolution for wafer overview scans in conjunction with high-resolution small-area scans for wafer growth recipe research and development.
Now, for the first time ever, we open this novel inspection technique for use by semiconductor manufacturers.
We currently offer three service packages:
Inspect Base:
- Resonant linear reflectance data across a 100 mm (4″) square area with 4 um resolution
- Four-wave mixing data across a 100 mm square area with 4 um resolution
Inspect Preferred:
- Resonant linear reflectance data across a 100 mm (4″) square area with 4 um resolution
- Four-wave mixing data across a 100 mm square area with 4 um resolution
- High-resolution (<1 um) scan of 50 customer-selected areas
Inspect Premium:
- Resonant linear reflectance data across a 150 mm (6″) square area with 4 um resolution
- Four-wave mixing data across a 150 mm square area with 4 um resolution
- High-resolution (<1 um) scan of 200 customer-selected areas
- Defect report with location and classification (KLARF file)
| Materials | SiC, GaN, GaAs | |
| Wafer size | 2″, 4″, 6″ | |
| Spatial resolution | 1-4 um | |
| Lead time | 4 weeks | |
| Measured channels | Resonant reflection, Four-wave mixing | |
| Wavelength range (for selectivity) | 350 nm-500 nm, 690 nm-1000 nm |
Here’s why we think you should try our nonlinear imaging to inspect your SiC and GaN wafers:
- Nonlinear imaging is not a morphology measurement: we measure defects that impact electronic structure. There are many things lighting up in a scattering image: Killer defects as much as non-killer defects, particulates, and dust. Our technique is resonant – if the defect does not alter the bandstructure, we can tell.
- Surface, subsurface, and substrate defects. Scattering is only sensitive to surface defects. A photoluminescence excitation beam can only penetrate so deep into the material. Our excitation beam penetrates deep and is sensitive to surface, subsurface, and even substrate defects such as grain boundaries.
- Nonlinear imaging is coherent, and therefore it is fast. Our nonlinear imaging is a coherent technique. This means we can go to larger spots without compromising signal collection. It also means we can go to sub-microsecond pixel dwell times.
Nonlinear optical measurements solve some problems of white-light imaging and photoluminescence. Nonlinear measurements, particularly four-wave mixing, are sensitive to fundamental defects in the crystalline structure of the semiconductor that impact the carriers. Therefore, defects, even subsurface defects, will strongly impact the four-wave-mixing image if the defect has a strong impact on the electrical properties of the semiconductor.
Compound semiconductors are the backbone of high-power electronics, high-frequency electronics, and opto-electronics. As global demand for compound semiconductors grows, improving yield rates of materials such as gallium nitride (GaN) and silicon carbide (SiC) is more important than ever. By developing better optical inspection tools, we seek to help manufacturers identify yield-killing defects in epitaxy layers long before the material is used in device production.
MONSTR Sense Technologies’ current line of products is already being used in research labs worldwide to improve the development of GaN devices, two-dimensional materials such as graphene and transition metal dichalcogenides, perovskites, colloidal quantum dots, gallium arsenide (GaAs)-based devices, and quantum materials such as vacancy centers.
Our ultrafast nonlinear imaging inspection technique is rather versatile – we work with tunable excitation lasers that currently allow us to study materials with bandgaps over the broad ranges 2.5-3.5 eV (wavelengths 350-500 nm) and 1.25-1.75 eV (690-1000 nm). This makes the technique perfectly suitable for, but not limited to, most compound semiconductor materials of interest, including SiC, GaN, and GaAs.
Silicon Carbide
Silicon Carbide (SiC) is the current focus for many high-power electronics manufacturers. The crucial purpose of inspection tools is to distinguish between killer and non-killer defects. Because our nonlinear technique is highly sensitive to small changes in the bandstructure, the killer defects that will affect device performance show up more strongly by either glowing or darkening.
We currently image 6″ SiC wafers with a 4 um spot size and classify defects across the wafer. Upon request, we can take high-resolution scans with sub-micron resolution in specific areas. Examples of high-resolution scans of some defects of interest in SiC are shown below.
Surface triangles in SiC epilayers, like many other defects, alter the bandstructure. Depending on how the bandstructure is changed, defects can either glow or darken in the nonlinear (NL) image. For surface triangles, the inner area of the triangle glows in the nonlinear image. For carrot defects excited using the same laser wavelength, the inside of the carrot darkens in the nonlinear image. The inside of the carrot is mostly unaffected in the resonant linear (L) reflection, highlighting the additional information available in the nonlinear image.
Nonlinear imaging is not only sensitive to surface defects, though. Even substrate defects, such as grain boundaries, show up in the nonlinear image. Unlike photoluminescence (PL), our technique does not rely on above-gap excitation, therefore, we are more sensitive to deeper defects in the epilayer and substrate if the focus is set accordingly.
Gallium Arsenide
Gallium Arsenide (GaAs) has made it from the lab to the marketplace with applications including integrated circuits, LEDs, and solar cells. Defect inspection of GaAs and GaAs quantum wells remains at the forefront of the industry. However, correlating defects with their impact on device performance and measuring subsurface defects is challenging.
Full wafer scans of a multiple quantum well sample highlight some features unique to these samples. For one, thickness variations in the substrate lead to Fabry-Perot fringes in the wafer image. Secondly, many of the defects in the wafer manifest themselves through bright emission properties. The provided wafer excerpt has a diameter of 2″, though wafers of up to 6″ can be scanned with sub-10 um resolution. Moreover, we offer the option to provide high-resolution images of certain defect areas, as illustrated below.
Scratches, as well as crystallographic defects, show up strongly in the FWM. Additionally, defects that partially or fully emit brightly can also be found with our nonlinear inspection method. Those defects are crucial because conventional brightfield or darkfield microscopy is often not sensitive to them. However, they clearly alter the bandstructure of the material, affecting the electrical properties and hence often acting as a killer defect. Our nonlinear imaging is also sensitive to subsurface defects that do not show up in any surface-sensitive scattering technique.
Gallium Nitride
Check back soon for our measurements of Gallium Nitride (GaN) wafers.