A State-of-the-Art Review of Fracture Toughness of Silicon Carbide: Implications for High-Precision Laser Dicing Techniques

Abstract

Silicon carbide (SiC) stands out for its remarkable hardness, thermal stability, and chemical resistance, making it a critical material in advanced engineering applications, particularly in power electronics, aerospace, and semiconductor industries. However, its inherent brittleness and relatively low fracture toughness pose significant challenges during precision manufacturing processes, particularly during the laser stealth dicing—a pivotal process for wafer separation. This review provides a comprehensive analysis of the fracture toughness of SiC, exploring its dependence on microstructural factors, such as grain size, fracture mode (transgranular vs. intergranular), and toughening mechanisms, including the crack deflection and bridging. The effects of temperature and mechanical anisotropy on the fracture resistance of SiC are discussed. Particular attention is given to how SiC’s low fracture toughness and brittle nature affect the controlled crack propagation critical to the dicing process. The review synthesizes key experimental findings from various fracture-toughness measurement techniques, highlighting their relevance for optimizing the laser processing parameters. By linking the fracture mechanics of SiC to its performance in laser stealth dicing, this review provides critical guidance for enhancing the process, ensuring greater efficiency and reliability in SiC wafer separation for advanced technologies.

1. Introduction

Silicon carbide (SiC), a key representative of third-generation semiconductor materials, exhibits exceptional mechanical, thermal, electronic, and chemical properties, such as high hardness, thermal conductivity, breakdown electric-field strength, and corrosion resistance [1,2], which makes it an ideal choice for semiconductor devices for high-power and high-temperature applications [3,4,5]. In comparison to silicon and gallium nitride, SiC excels in thermal conductivity, chemical stability, and mechanical robustness, positioning it as a preferred material for demanding environments where durability under extreme temperatures and high-power conditions is essential. With a hardness ranging from 9 to 9.5 on the Mohs scale [6,7], SiC’s extreme hardness and brittleness pose significant challenges to conventional machining methods like wire-saw slicing, which often introduce microcracks and kerf-related material loss, thereby limiting wafer yields [8,9,10].

To address these issues, laser stealth dicing (LSD) is emerging as a precise, efficient processing method, offering precision and minimal material loss compared to conventional mechanical techniques. The LSD generally integrates a three-step procedure involving wafer modification and subsequent separation (Figure 1). First, an ultrashort pulsed laser is focused beneath the surface of the SiC wafer, inducing localized modifications, such as void formation and micro-fracture growth without direct surface ablation [1,2,3,4,5,6]. This internal modification alters the crystalline structure, causing a separation plane to form beneath the wafer’s surface. Following this, the separation is executed through thermal stress or vibration, ensuring precise, defect-free cuts with minimal kerf loss [11,12,13,14,15]. Subsequently, the surface quality is examined. The LSD significantly accelerates processing speed, enhances accuracy, optimizes material usage, and reduces particle generation, substantially enhancing both efficiency and yield in wafer processing [12,13,14,15,16].

Fracture mechanics plays a significant role in the laser stealth dicing of SiC due to the material’s inherent brittleness and high hardness, demanding a careful fracture control. Fracture toughness, which quantifies a material’s resistance to crack propagation, is critical to ensure LSD-induced damage is confined to a controlled path [17,18,19]. An in-depth understanding of the fracture mechanics mechanism and an accurate characterization of fracture toughness allow strategic control over crack initiation and propagation, minimizing unintended fractures that could compromise wafer integrity. Proper management of stress intensity factors and crack-tip behavior ensures that the wafer cleaves cleanly with minimal chipping, debris, or rough edges [20,21,22,23,24,25].

This review seeks to offer a thorough and in-depth evaluation of the current knowledge surrounding the fracture toughness of SiC. The discussion encompasses the material’s intrinsic mechanical properties, alongside the experimental methodologies used to assess its fracture toughness, and the diverse factors—from microstructural characteristics to environmental influences—that affect its performance. Furthermore, the review explores the cutting-edge developments in SiC processing techniques. By integrating these recent findings, the paper aims to underscore both the persistent challenges and emerging opportunities in quantifying SiC’s fracture toughness, thereby paving the way for its continued use in cutting-edge technologies of the third-generation semiconductors.

2. Stress Intensity Factor and Fracture Toughness

Fractures are classified into three main types, based on the relative displacement of crack faces under applied loads: Mode I (opening), Mode II (sliding), and Mode III (tearing) [17,18]. Mode I, the most common and extensively studied, involves tensile forces perpendicular to the crack plane, causing crack-face separation. The stress field under Mode I loading (Figure 2) is given by [20]:

$${\sigma }_{xx}={\displaystyle \frac{K_I}{\sqrt{2\pi r}}}\cos {\displaystyle \frac{\theta }{2}}\left(1-\sin {\displaystyle \frac{\theta }{2}}\sin {\displaystyle \frac{3\theta }{2}}\right)$$

(1)

$${\sigma }_{yy}={\displaystyle \frac{K_I}{\sqrt{2\pi r}}}\cos {\displaystyle \frac{\theta }{2}}\left(1+\sin {\displaystyle \frac{\theta }{2}}\sin {\displaystyle \frac{3\theta }{2}}\right)$$

(2)

$${\sigma }_{xy}={\displaystyle \frac{K_I}{\sqrt{2\pi r}}}\sin {\displaystyle \frac{\theta }{2}}\cos {\displaystyle \frac{\theta }{2}}\cos {\displaystyle \frac{3\theta }{2}}$$

(3)

where r denotes the distance from the crack tip, θ represents the angle relative to the crack plane, K is the stress intensity factor and the subscript I refers to mode I fracture.

$$K_I=\underset{r\to 0}{\lim }\sqrt{2\pi r}{\left.{\sigma }_{yy}\right|}_{\theta =0}.$$

(4)

The value of K depends on the applied load, crack size, and the geometry of the material or a structure. The stress intensity factor encapsulates the relationship between the external forces and the localized stresses at the crack tip, making it essential for assessing material failure. When the stress intensity factor K exceeds a critical threshold, known as the fracture toughness K_Ic, unstable crack growth occurs, leading to fracture [24,25].

Fracture toughness, defining SiC’s ability to resist crack propagation, is crucial to understanding its performance under the laser processing and mechanical separation. Advances in characterizing fracture toughness leverage experimental techniques and materials engineering, including microstructural refinement, secondary-phase incorporation, and crack-bridging methods, to enhance fracture resistance [26,27,28]. Computational models further reveal how temperature, environmental conditions, and loading rates influence SiC’s toughness. In the next section, we examine popular experimental approaches for quantifying fracture toughness of SiC.

3. Fracture-Toughness Measurement Techniques

Measuring the fracture toughness of ultra-brittle SiC requires precise methods to accurately assess its resistance to crack propagation [29,30,31,32,33,34,35]. Approaches range from mechanical fracture tests, such as Single-Edge Notched Beam (SENB), Single-Edge Precracked Beam (SEPB), Double Cantilever Beam (DCB), Double Torsion (DT), Surface Crack in Flexure (SCF), and Chevron Notched Beam (CNB), which evaluate the bulk toughness through controlled crack growth under specific loading conditions [27,31,34], to indentation techniques like Vickers, Knoop, Berkovich, and nano-indentation, which estimate toughness from localized deformation and crack patterns, useful for small-scale or surface-level analysis [32,36]. Each technique offers unique strengths and limitations, making method selection critical for accurately characterizing SiC toughness for specific applications.

3.1. Single-Edge Notched Beam (SENB) Tests

The Single-Edge Notched Beam (SENB) test involves introducing a sharp, pre-existing notch into a rectangular beam specimen, followed by loading the specimen in in a three- or four-point bending configuration (Figure 3). The notch functions as the initiation site for crack propagation, with the applied load driving the crack through the specimen. The test enables a direct measure of the fracture toughness under Mode I loading, calculated from the applied critical load, notch length, and specimen dimensions, as follows [23]:

$$K_{IC}={\displaystyle \frac{3P_{cr}S}{2B{W}^2}}\sqrt{a}[1.93-3.07({\displaystyle \frac{a}{W}})+14.53{({\displaystyle \frac{a}{W}})}^2-25.07{({\displaystyle \frac{a}{W}})}^3+25.80{\left({\displaystyle \frac{a}{W}}\right)}^4],$$

(5)

where P_cr represents the critical load, S is the inner span, a is the crack length, B is the thickness, and W is the width (or height) of the specimen (Figure 3).

The SENB tests offer reliable, reproducible data for bulk materials, making them ideal for evaluating SiC’s fracture toughness under various conditions, including high-temperature and corrosive environments. However, the need for sharp notches, difficult to machine in brittle SiC, poses a challenge. Furthermore, in SiC, the crack may not propagate as cleanly as it does in ductile materials, leading to potential discrepancies in the results.

3.2. Chevron Notched Beam (CNB) Tests

A key challenge in SENB testing is achieving a sharp crack tip in SiC, which can impact accuracy. The Chevron Notched Beam (CNB) test improves upon SENB by using a V-shaped notch to promote stable crack growth during the toughness assessment (Figure 4). This notch design in CNB tests allows for controlled crack propagation along a defined path, yielding more consistent toughness measurements. The CNB testing is especially beneficial for brittle materials like SiC, where controlled crack progression is essential to prevent the sudden fracture.

The fracture toughness is calculated from the critical load at which the crack propagates fully through the specimen, as in [23,27]:

$$K_{IC}={\displaystyle \frac{P_{\max }}{B\sqrt{W}}}[17.99+67.43({\displaystyle \frac{a}{W}})+69.65{({\displaystyle \frac{a}{W}})}^2+72.09{({\displaystyle \frac{a}{W}})}^3+636.8{({\displaystyle \frac{a}{W}})}^4],$$

(6)

where P_max is the maximum applied load during the test, B is the thickness of the specimen, W is the height of the specimen, and a is the crack length (Figure 4).

Despite its advantages, the CNB technique has limitations. Machining an accurate chevron notch can be intricate and time-intensive, and achieving reliable results requires a carefully controlled testing environment, which may limit its accessibility in standard laboratories. Both SENB and CNB techniques are useful for brittle materials, but care must be taken to ensure that the notch is carefully machined and that the loading is performed under controlled conditions to obtain accurate reproducible fracture-toughness measurements.

3.3. Single-Edge Precracked Beam (SEPB) Test

In the SEPB test, the specimen is fabricated from high-purity SiC and notched at the mid-span using a precision diamond blade to initiate a sharp, controlled precrack. Each sample is then subjected to a three-point bending test in which the load is applied at a constant displacement rate, carefully calibrated to minimize dynamic effects and achieve quasi-static conditions. A load-displacement curve is recorded for each specimen, from which the critical load is identified as the onset of rapid crack propagation. Fracture toughness is subsequently calculated as in [25]:

$$K_{IC}={\displaystyle \frac{3}{2}}{\displaystyle \frac{P_{cr}BS}{W^{\frac{3}{2}}}}{({\displaystyle \frac{a}{W}})}^{{\displaystyle \frac{1}{2}}}{\displaystyle \frac{1.99-\frac{a}{W}(1-\frac{a}{W})[2.25-3.93\frac{a}{W}+2.7{(\frac{a}{W})}^2]}{(1+2\frac{a}{W}){(1-\frac{a}{W})}^{\frac{3}{2}}}},$$

(7)

where P_cr is the critical applied load during the test, B is the thickness of the specimen, W is the height of the specimen, S is the inner span, and a is the crack length (Figure 5).

Careful alignment of the specimen, precise crack-length measurement, and a slow loading rate are essential to ensure accurate determination of the fracture toughness.

3.4. Double Torsion (DT) Tests

In the Double Torsion (DT) testing, a precracked specimen is loaded to create a torsional moment, driving stable crack growth along its length. The specimen, usually a rectangular slab with a central slit, is loaded at four points along the edges, perpendicular to the crack plane, generating tensile stress at the crack tip (Figure 6). The DT testing’s key advantage is its ability to maintain stable crack growth under constant load. A notch at the slit end initiates the crack, and incremental loading induces a twisting motion around the specimen’s axis, producing a Mode I fracture condition. Crack growth is monitored in real-time through optical or acoustic sensors to ensure controlled propagation. The fracture toughness is calculated from [37]:

$$K_{IC}=Ps\sqrt{{\displaystyle \frac{3(1+v)}{W{t}^{3}h}}},$$

(8)

where ν is the is Poisson’s ratio, P is the critical load at which stable crack propagation occurs, t is the specimen thickness, h is the thickness at the notch, and W is the specimen width (Figure 6).

The DT tests allow for continuous crack-propagation monitoring, making them valuable for studying crack resistance over time. However, specimen preparation can be complex, and careful alignment is needed to ensure that stable crack growth occurs during testing. One of the challenges of the DT method is the need for precise specimen alignment and load application to prevent premature failure or non-uniform crack growth.

3.5. Double Cantilever Beam (DCB) Tests

The DCB specimen consists of two beams that are typically bonded together, featuring a notch or precrack at the midline. By applying tensile loads at the ends of the beams, the crack is driven to propagate along the midline of the specimen. The specimen’s length and notch depth, and the loading rate are carefully chosen to control the fracture process and minimize deviations from ideal crack propagation. The crack length is monitored either visually or via strain gauges affixed along the beam, providing real-time data on crack growth behavior.

The key feature of DCB testing is the direct measurement of the energy release rate, providing a quantitative assessment of fracture toughness, as expressed by the following equation [18]:

$$K_{IC}={\displaystyle \frac{pa}{BH}}\sqrt{{\displaystyle \frac{12}{H}}},$$

(9)

where P is the critical load, B is the specimen thickness, a is the crack length, and H is the thickness of each cantilever beam (Figure 7).

3.6. Surface Crack in Flexure (SCF) Method

The Surface Crack in Flexure (SCF) method involves preparing a rectangular beam specimen that incorporates a surface crack, typically introduced through precision machining or controlled indentation methods. The specimen is then subjected to a three-point bending test, where it is supported at both ends while a load is applied at the midpoint, leading to tensile stresses at the crack tip. During the test, the applied load is incrementally increased until the crack propagation occurs, allowing for the determination of the critical stress at which failure initiates. The fracture toughness is subsequently calculated using the maximum applied load, the specimen dimensions, and a geometric factor that accounts for the crack size and shape, as follows [23]:

$$K_{IC}=Y\left({\displaystyle \frac{3P_{f}A}{2B{W}^2}}\right)\sqrt{a},$$

(10)

where P_f is the failure load applied to the specimen, B is the thickness of the specimen, W is the height of the specimen, A is the difference between the outer and inner spans, a is the crack depth in m, and c is the half-width of the crack in m (Figure 8). In the above, Y is the stress intensity factor coefficient, given as

$$\begin{gathered} Y=(\sqrt{\pi }MS{H}_1)/\sqrt{Q}, \\ \mathrm{where}S=[1.1+0.35{(a/W)}^2]{(a/c)}^{1/2},Q=1+1.464{(a/c)}^{1.65},H_1=1-[0.34+0.11(a/c)](a/W), \\ \hspace{1em}\hspace{1em}\hspace{1em}\mathrm{and} M=\left(1.13-0.9{\displaystyle \frac{a}{c}}\right)+\left(-0.54+{\displaystyle \frac{0.89}{0.2+a/c}}\right){\left({\displaystyle \frac{a}{W}}\right)}^2+\left[0.5-{\displaystyle \frac{1}{0.65+a/c}}+14{(1-{\displaystyle \frac{a}{c}})}^{24}\right]{\left({\displaystyle \frac{a}{W}}\right)}^4. \end{gathered}$$

3.7. Indentation Method (Vickers, Knoop, Berkovich, Nano-Indentation)

Indentation methods are invaluable for assessing the SiC’s fracture toughness, offering efficient, localized measurement approaches suited to its hardness and brittleness [38]. Traditional toughness tests are often labor-intensive, making indentation techniques—such as Vickers, Knoop, Berkovich, and nano-indentation—particularly advantageous. Vickers indentation, using a square pyramidal indenter, creates radial cracks at indentation corners, allowing direct toughness estimation based on crack length and load. Knoop indentation, with an elongated diamond-shaped impression, is ideal for investigating toughness anisotropy along specific crystallographic directions, critical for applications like laser dicing that demand precise crack control. The Berkovich method, with its three-sided pyramidal indenter, is suitable for assessing small-scale toughness in confined areas by generating stress concentrations that reveal microstructural features. Finally, nano-indentation enables nanoscale assessments of hardness, elastic modulus, and toughness, applying controlled loads for detailed insights into SiC’s mechanical properties. For nano-indentation (Figure 9), the fracture toughness is given by [38]:

$$K_{Ic}=0.0473{\left(c/a\right)}^{-1.56}{\left[H/\left(\varphi E\right)\right]}^{-0.4}H\sqrt{a},$$

(11)

where E is the Young’s modulus, H is the Mohs hardness, and $\varphi$ is the ratio of hardness to yield stress.

Indentation methods (Vickers, Knoop, Berkovich, and Nano-Indentation) are primarily surface-level tests that provide fast and localized measurements of fracture toughness but are sensitive to surface preparation and environmental factors. Although nano-indentation offers high precision, it is limited to small volumes, which can restrict its applicability to bulk material properties.

Mechanical methods, including DT, DCB, SENB, CNB, and SEPB, provide a more representative assessment of bulk fracture toughness, particularly for brittle ceramics such as SiC. However, these techniques necessitate meticulous specimen preparation, precise alignment, and controlled loading conditions to ensure accurate measurement outcomes. A comprehensive comparison of the various testing methods, along with their respective advantages and disadvantages, is presented in

Table 1. Comparison of toughness testing methods for SiC.

Testing Method	Advantages	Disadvantages
Single-Edge Notched Beam (SENB)	- Standardized method and widely used for brittle materials. - Simple to perform and provides consistent results for bulk materials.	- Requires careful machining of a sharp notch, which can be challenging for SiC. - Crack may not propagate as cleanly in SiC.
Chevron Notched Beam (CNB)	- Reduces variability by stabilizing the crack growth during testing. - V-shaped notch ensures consistent crack propagation.	- Machining the chevron notch can be difficult and time-consuming. - Requires highly controlled test setup. - Not as commonly available as SENB.
Single-Edge Precracked Beam (SEPB)	- Improved reproducibility over SENB. - Precrack eliminates initial notch limitations.	- Precracking introduces complexity - Sample preparation can be time-intensive. - Requires specialized equipment for precracking.
Double Torsion (DT)	- Allows stable, controlled crack growth under Mode I (tensile) loading. - Suitable for high-temperature fracture-toughness testing. - Crack-propagation monitoring is straightforward.	- Requires careful loading and test conditions for stable crack propagation. - Requires calibration for testing equipment.
Double Cantilever Beam (DCB)	- Provides stable crack growth and direct measurement of crack-growth resistance. -Rigorous analytical solution.	- Complex specimen preparation. - Limited applicability for certain geometries and thin specimens. - Alignment and measurement of crack length are critical for accuracy.
Surface Crack in Flexure (SCF)	- Simple experimental setup with fewer complex geometries. -Provides direct insights into the crack-tip stress field.	- Requires precise measurement of crack front geometry. - Possible existence of residual stress.
Vickers Indentation	- Simple and quick technique. - Provides localized fracture toughness. - Useful for small or thin samples.	- Sensitivity to crack pattern visibility. - Influenced by surface conditions and residual stresses. - May not reflect bulk fracture toughness of the material.
Knoop Indentation	- Good for anisotropic materials due to elongated indent shape. - Lower penetration depth, ideal for thin coatings or surface layers.	- Similar limitations as Vickers (e.g., sensitivity to surface quality). - Complex crack pattern analysis required.
Berkovich Indentation	- Triangular indenter offers better precision in measuring localized plastic deformation. - Effective for evaluating thin films and coatings.	- Need for advanced image processing techniques to improve crack pattern accuracy. - Limited to surface-level fracture toughness, not ideal for bulk analysis.
Nano-Indentation	- High spatial resolution; excellent for small-scale materials. - Can measure hardness, elastic modulus, and fracture toughness, simultaneously.	- Extremely sensitive to surface roughness and preparation. - Can only assess very small volumes of material, making it less representative of bulk properties.

.

4. Fracture Toughness and Influencing Factors

4.1. Fracture Toughness Value

A comprehensive review of the reported fracture toughness values of SiC under different experimental conditions was conducted, and is summarized in

Table 2. Fracture toughness values of SiC.

SiC Type	Testing Method	Testing Temperature	$\mathbf{Fracture}\mathbf{Toughness}(\mathbf{MPa}\sqrt{\mathbf{m}}$)	References
sintered α-SiC	Double torsion	Up to 1773 K	3.0	[39]
	Single-edge notched beam	Room	4.1–4.5	[36]
	Chevron notched beam	Room	2.8–3.6
	Vickers indentation	Room	3.6–4.4	[40]
	Chevron-notch and straight-notch three-point bending	Up to 1773 K	3.0	[41]
	Three-point bending with single-edge precracked beam	Room	$2.3\pm$ 0.25	[42]
sintered β-SiC	Single-edge notched beam	Room	3.5–4.3	[36]
	Chevron notched beam	Room	3.1–3.9
sintered SiC	Single-edge notched beam	Room	2.51	[43]
	Chevron notched beam	Room	3.5
	Modified Knoop indented bending	Room	2.3–3.5	[44]
	Chevron-notch and straight-notch three-point-bending	Room	2.3–3.3
	Single-edge notched beam	Room	2.6–3.6
	Single-edge precracked beam	Room	2.5–6.4	[45]
	Vickers indentation	Room	2.8	[46]
	Single-edge V-notched beam	Room	3.2 ± 0.15	[47]
	Single-edge notched beam	Room	3.5 ± 0.42	[48]
6H polycrystalline silicon carbide	Vickers indentation	Room	1.36–2.52	[49]
hot-pressed SiC	Four-point bending with straight through notches, Chevron notches, and Knoop indentation cracks	Up to 1773 K	2.5–5.0	[50]
SiC	Three- and four-point-bending of precracked specimen	Room	2.2 ± 0.2	[51]
	Single-edge precracked beam method	Room-1773 K	3.59 ± 0.17 Room2.42.67@1773 K	[52]
	Knoop indentation	Room to 1363 K	4.3–5.5	[53]
	Four-point bend of a Chevron-notched specimen	Room to 1363 K	2.8–3.9	[53]
4H-SiC	Vickers indentation	Room	1.6–3.1	[54]
	Knoop	Room	1.4–1.8	[55]
	Berkovich indentation	Room	3.33	[56]
	Berkovich indentation	Room	3.42	[57]
	Vickers and Berkovich indentations	Room	2.89	[58]
	Nano-indentation	Room	2.97–3.61
	Berkovich indentation	Room	2.1	[59]
	Vickers indentation	Room	1.9
	Knoop indentation	Room	2.4–2.7
6H-SiC	Single-edge notched beam	300 K, 873 K	3.3	[60]
	Single-edge notched beam	1773 K	5.8
	Berkovich indentation	Room	3.2 ± 0.3	[61]
	Vickers indentations	Room	3.2 ± 0.2
	Vickers indentation	Room	1.7–3.4	[54]
	Vickers indentation	Room	3.3	[62]
	Vickers indentation	Room	1.8	[63]
	Knoop indentation	Room	1.8
	Knoop	Room	1.5–1.9	[55]
	Double cantilever beam	Room	1.8 ± 0.26	[64]
	Berkovich indentation	Room	3.2	[65]
	Berkovich indentation	Room	3.45	[56]
	Three-point bending tests for Chevron-notched specimens	Room	1.37 ± 0.13	[66]
			1.57 ± 0.13

. The fracture toughness of SiC varies significantly depending on the testing method employed, reflecting both the material’s inherent properties and the constraints associated with each technique. Indentation techniques, such as Vickers, Knoop, and Berkovich, typically yield relatively lower fracture-toughness values, ranging between 1 and 4 MPa·m^1/2, as these methods are highly localized and susceptible to surface defects and stress concentrations. Nano-indentation further highlights this scale sensitivity, as even minor surface irregularities can significantly affect the measured toughness. In contrast, bulk fracture tests, such as SENB and CNB, tend to provide higher and more consistent values, generally in the range of 3–5 MPa·m^1/2, as these tests involve controlled crack propagation under well-defined stress fields. The DT and DCB methods also report comparable toughness values, particularly under similar testing conditions. These observed variations in fracture toughness highlight the importance of selecting the appropriate testing method, as the specific measurement technique can profoundly influence the interpretation of SiC’s fracture resistance, particularly in applications involving complex loading and environmental conditions.

4.2. Toughness Anisotropy

Fracture toughness anisotropy in SiC is fundamentally linked to its crystal structure and the intrinsic characteristics of its grain boundaries, leading to directionally dependent mechanical properties [67,68,69]. Both polycrystalline and single-crystal forms of SiC exhibit distinct fracture behaviors that vary with the orientation of applied stress relative to their crystallographic planes. In the case of a single-crystal SiC, the fracture toughness is generally higher along specific crystallographic directions, such as {111}, where atomic bonding is stronger, compared to other orientations like {110} or {100}, which are more prone to crack propagation. The scenario is more intricate in polycrystalline SiC, due to interactions at grain boundaries and the random orientation of grains, which can either mitigate or amplify the intrinsic anisotropy observed in single crystals. Grain size, shape, and orientation, as well as the presence of impurities or secondary phases, can further influence the directional fracture toughness. In textured polycrystalline SiC, where grains may have preferential orientation, the anisotropic fracture behavior becomes more pronounced, where the cracks can preferentially initiate along weaker grain boundaries. SiC’s mechanical anisotropy plays a crucial role in guiding crack propagation during laser dicing, significantly impacting the precision and quality of the process. The material’s crystallographic planes exhibit varying fracture toughness, leading to orientation-dependent crack paths under the localized thermal and mechanical stresses. When subjected to laser-induced heating, regions with lower toughness in specific crystallographic directions are more susceptible to crack initiation and propagation, potentially resulting in irregular or unintended crack paths that deviate from the dicing line. This anisotropy requires careful optimization of laser parameters, such as power, pulse duration, and focal depth, to ensure that the energy input aligns with SiC’s preferred cleavage planes, thereby promoting controlled crack propagation. Without addressing these directional variances, laser dicing can produce inconsistent cuts and excessive chipping, ultimately compromising device integrity and yield in applications demanding high precision.

4.3. Temperature Dependence of Fracture Toughness

The fracture toughness of SiC demonstrates a distinct temperature dependence, remaining relatively stable below 1000 °C but with marked sensitivity at elevated temperatures [70,71,72]. Below 1000 °C, the toughness remains relatively stable, as the robust atomic bonding within SiC’s crystalline structure effectively resists crack propagation. The limited atomic mobility at these lower temperatures restricts thermally activated mechanisms, ensuring that toughness is largely maintained across various conditions. In contrast, at temperatures exceeding 1000 °C, the fracture toughness begins to increase, driven by enhanced atomic vibrational energy and the activation of mechanisms that promote local plasticity near crack tips. This increase in toughness at elevated temperatures is attributed to the material’s ability to better accommodate stress and dissipate energy through processes such as crack deflection and improved crack-growth resistance.

4.4. Effect of Grain Size and Microstructure on Fracture Toughness

The fracture toughness of SiC is strongly influenced by its grain size and microstructure, key factors that govern its crack initiation and propagation behavior [73,74]. In polycrystalline SiC, smaller grain sizes generally enhance fracture toughness by impeding the crack growth; grain boundaries act as barriers to crack propagation, forcing cracks to deflect or branch as they encounter grains with different orientations. This crack deflection increases the energy required for crack advancement, thereby improving toughness. Conversely, in SiC with larger grain sizes, cracks can propagate more easily through individual grains, leading to lower fracture toughness.

Microstructural features, such as grain shape, texture, and the presence of secondary phases or impurities, further impact the fracture toughness. Elongated grains or textured microstructures can introduce anisotropy in fracture behavior, where toughness is higher along certain directions and lower in others, depending on the grain orientation relative to the applied stress. Additionally, the presence of secondary phases at grain boundaries, such as impurities introduced during processing, can either strengthen the material by pinning grain boundaries or weaken it by providing easy crack paths [75]. Recent advances in toughening SiC have explored mechanisms such as crack deflection, bridging, and grain boundary engineering to enhance its resistance to fracture, with several studies demonstrating promising approaches. Crack deflection, for example, has been effectively achieved through microstructural refinement, where the introduction of fine, interlocking grains promotes the deviation of crack paths, thereby increasing the energy required for crack propagation. Studies incorporating SiC-whisker reinforcements have shown that these whiskers act as bridging elements across crack surfaces, arresting or slowing crack growth and improving toughness. Additionally, the incorporation of secondary phases, such as A1₂O₃ and Y₂O₃, into SiC has been shown to create interfaces that impede crack movement by forcing cracks to navigate around tougher or more ductile regions [75]. These interfaces introduce crack-tip shielding effects, further enhancing the material’s toughness by redistributing stress away from critical points. Such strategies underscore the importance of microstructural engineering in developing SiC materials with enhanced fracture resistance for high-performance applications.

5. Fracture Mechanism

The fracture toughness of SiC is significantly influenced by the fracture modes and toughening mechanisms that govern the crack propagation [69,75,76]. In SiC, fracture can occur via two primary modes: transgranular and intergranular. Transgranular fracture involves crack propagation through the grains themselves, which is typical in fine-grained SiC where strong grain boundaries and high cohesive forces within the grains dominate. This fracture mode is generally associated with higher fracture toughness, as cracks must overcome the atomic bonding within the grains, requiring more energy. On the other hand, intergranular fracture occurs along the grain boundaries and is more common in coarser-grained SiC. In this mode, the fracture toughness tends to be lower because the grain boundaries, which may be weaker due to impurities or secondary phases, provide an easier path for crack propagation. The balance between the transgranular and intergranular fracture is often influenced by grain size, the presence of secondary phases, and processing conditions, all of which determine the mechanical response of SiC under complex stress.

The crack deflection, bridging, and other toughening mechanisms play crucial roles in enhancing the fracture toughness of SiC. Crack deflection occurs when a propagating crack is forced to change direction as it encounters obstacles, such as grain boundaries, secondary phases, or microstructural inhomogeneities. In SiC, deflection is often seen in polycrystalline materials where the random orientation of grains and differences in their fracture resistance cause the crack to deviate from a straight path. This deflection increases the fracture surface area, requiring more energy to propagate the crack and thereby improving toughness. Crack bridging, another important toughening mechanism, occurs when unbroken grains bridge the crack faces behind the crack tip, providing resistance to further crack opening. In SiC-based composites, for example, reinforcing particles or fibers can act as bridges, significantly enhancing fracture toughness by absorbing energy and arresting crack growth. Both deflection and bridging act synergistically in SiC, impeding crack propagation and contributing to improved fracture resistance.

6. Implications for Laser Processing

Laser stealth dicing, which relies on creating internal modifications through the localized heating and stress without fully penetrating the wafer, exploits the material’s fracture properties to achieve precise cuts while minimizing surface damage [72,77]. The fracture toughness of SiC significantly influences its response to high-precision laser dicing, a critical process in the manufacturing of microelectronic devices [78]. Due to SiC’s inherent brittleness and relatively low fracture toughness, the material is susceptible to microcracking and uncontrolled crack propagation under high-intensity laser stresses. These mechanical limitations demand careful consideration of laser parameters to ensure precise, defect-free dicing. By understanding and optimizing laser conditions, such as power, pulse duration, and spot size, manufacturers can mitigate unwanted damage and achieve cleaner cuts [79]. The role of fracture toughness, in this context, is twofold: it defines the material’s resistance to crack initiation and affects the crack-propagation paths, which are crucial for controlling separation along desired lines without inducing excessive lateral damage [80,81,82].

In SiC, where cracks may propagate intergranularly or transgranularly depending on grain size and laser-induced stresses, the laser processing parameters must account for these varying fracture pathways [83,84]. For instance, in fine-grained SiC, transgranular fracture dominates, generally requiring higher energy to initiate crack propagation across grains. Conversely, coarser-grained SiC, which favors intergranular fracture along grain boundaries, may need tailored laser settings to prevent spontaneous microcrack formation. The presence of impurities or secondary phases at grain boundaries can further complicate the process, as these regions may serve as weak points where cracks can initiate uncontrollably, impacting the precision of the dicing operation. Adjustments to laser speed and focal positioning can also help to control the heat-affected zones, ensuring that cracks follow pre-defined pathways rather than diffusing irregularly through the brittle microstructure. Such precise adjustments become essential for avoiding damage that can compromise the functional integrity of the separated devices.

The temperature-dependent behavior of SiC under laser irradiation adds further complexity to laser processing. Elevated local temperatures can enhance fracture toughness through temporary plasticity near the crack tip, potentially improving the stability of crack propagation. However, exceeding the critical thermal thresholds risks oxidation, phase changes, or microstructural degradation, which can weaken fracture resistance and induce uncontrolled fracture. The fine balance between sufficient laser energy to initiate the controlled fracture and the risk of inducing thermal degradation or excessive microcracking is closely tied to SiC’s temperature-dependent fracture behavior. Therefore, laser processing must balance energy input to optimize cutting precision while minimizing the risks of thermal and mechanical degradation.

To achieve the high-precision cuts in SiC, minimizing undesired cracking, and ultimately improving the efficiency and quality of the laser dicing process, we propose the tailored guidelines, as follows:

• Substrate Preparation: Prior to dicing, polish or treat the SiC substrate surface to remove any pre-existing surface defects that might propagate into larger cracks during cutting. For finer grains, a smooth surface is especially advantageous, as it enables the laser to follow a predictable path.
• Laser-Type Selection: For SiC dicing, ultrashort-pulse lasers, such as femtosecond or picosecond lasers, offer precise control over the heat-affected zone and are ideal for brittle materials. The nanosecond lasers, while effective, can introduce more heat into the surrounding area.
• Laser Speed: A higher laser speed can help manage the heat-affected zone while preventing excessive heat accumulation that could cause microcracks.
• Focal Positioning: Position the laser focal point at a shallow depth, around 30 μm below the surface. This setting promotes controlled surface-level heating that guides crack propagation along the cutting path, reducing unintended lateral cracking.
• Pulse Frequency and Power: Increase pulse frequency (e.g., >50 kHz) with moderate power to enhance the smoothness of the cut while controlling the crack direction. This balance minimizes rough edges and helps maintain the integrity of fine-grained SiC.
• Short Pulse Width: Set a short pulse width (e.g., <10 ps) to achieve precise energy delivery, confining heat to the immediate area around the laser path and minimizing diffusion into surrounding grains.

These settings aim to balance the fracture toughness with laser precision, effectively reducing microcracks and enhancing dicing efficiency across different grain structures. The above measures, while theoretically designed to optimize the laser dicing process of SiC, remain subject to experimental verification to further confirm their efficacy and refine parameters for practical applications.

7. Conclusions

This review highlights the fracture toughness characteristics of SiC and their critical implications for high-precision laser dicing techniques. SiC’s unique combination of hardness, thermal conductivity, and low fracture toughness poses both challenges and opportunities for achieving controlled, damage-free wafer separation. Key microstructural factors, such as grain size, fracture modes, and intrinsic toughening mechanisms, play the central roles in determining SiC’s resistance to fracture and, consequently, its behavior under laser-induced stresses. Temperature effects and mechanical anisotropy further influence crack-propagation pathways, impacting dicing precision and reliability.

Optimizing the laser parameters (including laser types, laser speed, focal positioning, pulse frequency and width) to accommodate SiC’s brittle fracture tendencies is essential to reduce microcracking and maintain device integrity. Insights from fracture-toughness measurement techniques provide valuable data for refining laser processing conditions, minimizing thermal damage, and enhancing precision. By bridging SiC’s fundamental fracture mechanics with the specific demands of laser dicing, this review offers guidance to improve dicing efficiency and supports SiC’s expanded application in advanced microelectronics and high-performance systems.