Silicon carbide (SiC) is a wide bandgap semiconductor material used in high-power, high-temperature, and high-frequency electronic devices. 4H-SiC substrates feature distinct characteristics including high thermal conductivity, high breakdown voltage and superior chemical inertness, making them ideal for power electronics, radio frequency devices and sensors.

Ion implantation is crucial for the fabrication of SiC devices (Figure 1) and requires meticulous control of dopant distribution. Accurate characterization of wafer drop or erroneous cutting angle is essential to achieve high device performance and reliability.

Bruker QCVelox The High Resolution X-ray Diffraction (HRXRD) system is a robust instrument to determine the cutting angle precisely, thereby maximizing the ion implantation process for 4H-SiC substrates.

Chart 1. Representation of the ion implantation process on a SiC power device. Image credit: Bruker Nano Surfaces and Metrology

Importance of Precise Cutting Angle in 4H-SiC in Ion Implantation

The drop angle of a 4H-SiC substrate plays a central role in calculating the quality and performance of SiC devices. SiC defects occur parallel to the growth direction. Because of this, an intentional drop is applied to SiC substrates to protect the underlying 4H-SiC crystal and allow defects to have a predictable orientation throughout epitaxial growth.

Precise cutting angle control is essential for crystal quality, channel removal and technical defect accuracy.

Crystal quality

• Reduce defect density: Precise cutting ensures high crystal quality, reducing defect density and improving device reliability.
• Improve material uniformity: Precise drops result in uniform epitaxial growth and crystal morphology, thereby improving material quality and device performance.

Channel suppression

• Improve the precision of ion implantation: Precise cutting maximizes ion implantation, reducing the risk of ion channeling and improving device performance.
• Guarantee uniform distribution of dopants: Precise cutting ensures uniformity of ion implantation, reducing channeling effects and improving device uniformity.

Defect Engineering Accuracy

• Improve the activation of dopants: Precise cutting facilitates controlled defect engineering, maximizing dopant activation and improving device performance.
• Improve device reliability: Accurate drops facilitate the generation of customized defect profiles, thereby improving the reliability and durability of 4H-SiC-based electronic devices.

Although drops are essential for Si and SiC wafers, their accuracy is also crucial due to their increased sensitivity to crystal defects. The cutting angle in Si wafers impacts crystal defects and dislocations.

The effect is generally less drastic than that of SiC due to SiC’s wider bandgap and high operating temperatures, where defects propagate and result in a higher density of crystallographic and surface defects.

Precise cutting in SiC is essential for device performance and reliability, as it reduces defects and ensures high crystal quality.

Role of HRXRD in 4H-SiC ion implantation

HRXRD offers multiple advantages for accurately evaluating wafer rake angles in 4H-SiC substrates, such as:

• High precision: HRXRD offers precise assessments of grating orientation and cutting angles (magnitude and direction) with sub-degree resolution, ensuring the accurate detection of small deviations in the expected orientation of the 4H-SiC wafer.
• Non-destructive analysis: HRXRD allows characterization of wafer drops without damaging the sample, thus enabling online metrology.
• Versatility: HRXRD can be applied to multiple SiC substrates with various orientations, sizes, doping levels, and polytypes, making it flexible for many SiC device fabrication processes.

Bruker HRXRD for rapid drop determination

HRXRD is a power reference metrology approach in silicon and compound semiconductor manufacturing.

Bruker’s sophisticated HRXRD systems enable an additional level of sensitivity to discrete wafer drop variations, with unrivaled precision and accuracy achieved by evaluating various high-resolution rocker curves (ω scans) at different azimuth angles (φ) to quantify both the magnitude and direction of falls. from the diffracted angles, as shown in Figure 2.

This sequence of assessments is entirely recipe-based and analysis can be automated using Bruker analytical software.

Chart 2. Illustration of the calculation of drops by measuring the tilt curves ω at different slice azimuths in the recipe. Image credit: Bruker Nano Surfaces and Metrology

If the nominal slice thickness and expected scrap data are given as a reference for scrap refinement, accurate scrap assessments could be improved and achieved more quickly. This is particularly advantageous in high volume manufacturing, where nominal wafer thicknesses and scraps are well controlled.

Recent tests performed on a dedicated high-intensity Bruker QCVelox HRXRD diffractometer have shown how a typical 200mm 4H-SiC wafer with an expected drop of 4° can be evaluated in less than 60 seconds with an accuracy and precision of <0.005° for the magnitude of the fall and <0.01° for the direction of the falls compared to the conventional approach displayed in Figure 2.

This method is suitable for the characterization of all common semiconductor substrates, such as SiC, Si, GaAs, InP and GaN.

Optimize Ion Implantation by Leveraging HRXRD

Ion implantation is crucial in the fabrication of 4H-SiC semiconductors and necessary for precise control of dopant distribution and device properties.

By using HRXRD for precise wafer drops, semiconductor manufacturers can maximize ion implantation processes and improve device performance in 4H-SiC-based electronics, accelerating innovation and facilitating new applications in the electronics industry.

This information was obtained, reviewed and adapted from materials provided by Bruker Nano Surfaces and Metrology.

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