Al₂O₃ Coating on Silicon Substrate

As semiconductor devices continue to develop towards high integration, low power consumption, and high reliability, interface engineering and the selection of dielectric materials have become key factors determining device performance. Aluminum oxide (Al₂O₃) is widely used in key structures such as high-k gate dielectrics, surface passivation layers, and anti-reflection layers in silicon-based devices due to its wide bandgap (about 6eV), moderate high dielectric constant (k≈7-9), and excellent chemical stability. This structure combines excellent interface characteristics, passivation effect, and optical properties, which can meet the application requirements of high-quality Al₂O₃/Si heterojunctions in high-performance microelectronics, nanoelectronics, and photovoltaic devices. PAM-XIAMEN can provide Al₂O₃ coating on silicon substrate. Please refer to the following specifications for details:

1. Specification Value of Al₂O₃ Coating on Silicon Substrate

PAM250909-Al2O3/Si

Substrate
Diameter	200 ±0.3mm
Material	CZ Silicon
Grade	Prime
Thickness	725 ±25μm
Orientation	<100>
Type/Dopant	P/B
Surface Metals	<1E10 at/cm²
Resistivity	1-100Ohm.cm
Surface Finish	Single Side Polished
Notch	1, SEMI Std. @ <110> ±1°
TTV	<5μm
STIR / SFQR	≤0.35μm (25 x 25, PUA 100%)
Bow	<30μm
Warp	<30μm
Particles ≥0.2μm	<20
Particles ≥0.3μm	<10
Coating
Al2O3 Thickness	100nm
Al2O3 Uniformity	≤5%

 

2. Al₂O₃/Si Interface Characteristics and Structure

According to the study by Shulakov et al. on the 100nm Al₂O₃/Si interface, the interface thickness is approximately 60 nm and exhibits a complex layered structure:

• Upper layer (near the Al₂O₃ side): Mainly composed of Al₂O₃ molecules, along with Al atoms whose coordination state resembles that of metallic aluminum. These Al atoms tend to form relatively large metal clusters.
• Middle layer (approximately 10–50nm from the substrate): Contains Si atoms in an unusual chemical state, which is neither amorphous Si nor c-Si, nor is it SiO₂ or SiOₓ. It is speculated that these Si atoms form small-sized clusters consisting of a few atoms.
• Near-substrate layer (<10nm): Rich in stoichiometric SiO₂, immediately adjacent to the c-Si substrate.

This interfacial structure is formed by a combination of oxygen in-diffusion, silicon out-diffusion, and chemical reactions during the deposition process. For an Al₂O₃ layer with a thickness of 100nm, the interfacial structure is considerably more complex than that of thin layers (tens of nanometers), yet it exhibits good consistency and reproducibility.

Fig. 1 Decomposition of Al and Si L₂,₃ X-ray emission spectra of the 100nm Al₂O₃/Si sample

3. Surface Passivation Performance of Al₂O₃

Al₂O₃ thin films provide excellent field-effect passivation on p-type silicon, primarily attributed to a high density of fixed negative charges (Qfix > 10¹²cm⁻²) located near the interface within the film, as well as a low interface state density (Dit ≈ 10¹¹cm⁻² eV⁻¹). Studies by Zhu et al. demonstrate:

• For p-type silicon coated with 30nm Al₂O₃, after annealing at 350°C, the minority carrier lifetime can reach 4.7ms, and the effective surface recombination velocity is as low as 4 cm/s.
• For p-type silicon coated with 100nm Al₂O₃, the optimal annealing temperature is 600°C, yielding an effective lifetime of approximately 750μs and a surface recombination velocity of about 25cm/s.
• For an uncoated bare p-type silicon wafer, the lifetime is only about 6μs, and the surface recombination velocity is as high as 3170cm/s.

The study indicates that 100nm Al₂O₃ can significantly suppress surface recombination and enhance the internal quantum efficiency of devices under appropriate annealing conditions.

Fig. 2 (a) Effective minority carrier lifetime and (b) effective surface recombination velocity of p-type silicon wafers coated with 30nm and 100nm Al₂O₃ as a function of post-deposition annealing temperature

4. Anti-Reflection Performance of Al₂O₃ Coated Silicon

The refractive index of Al₂O₃ in the visible spectrum is approximately 1.6 (at λ = 630nm), forming a good refractive index match with crystalline silicon (approximately 3.5), making it suitable as an anti-reflection coating. Research shows:

• After coating textured silicon surfaces with 100nm Al₂O₃, the average reflectance can be as low as 2.8%, close to the 2.9% of the industrial standard SiNₓ anti-reflection coating.
• For single-side polished substrates, 100nm Al₂O₃ still significantly reduces surface reflectance, particularly in the short-wavelength region (300–600nm).
• The extinction coefficient of Al₂O₃ is nearly zero across wavelengths above 200nm, indicating no absorption loss in this range, with an optical bandgap of approximately 6eV.

Therefore, the silicon substrate coated with Al₂O₃ can simultaneously achieve both passivation and anti-reflection functions in photovoltaic cells or photodetectors.

Fig. 3 (a) Refractive index (n) and extinction coefficient (k) of 100nm ALD Al₂O₃ as a function of wavelength; (b) Reflectance spectra of textured Si coated with different Al₂O₃ thicknesses

5. Process Compatibility and Thermal Stability

Al₂O₃ thin films are deposited by ALD or molecular deposition, typically at a deposition temperature of 200°C, which is compatible with back-end-of-line (BEOL) CMOS processes. The films exhibit good thermal stability:

• Annealing in the range of 300–600°C (in ambient atmosphere) progressively improves passivation performance.
• Performance degrades above 650°C, primarily due to an increase in interface state density.
• Rapid thermal annealing (900°C, 3 seconds) still retains a moderate level of passivation (τeff ≈ 120μs).

This temperature window allows for the integration of subsequent processes such as electrode sintering and alloying.

6. Typical Applications of Al₂O₃ Thin Films

• High-k gate dielectric: Used in MOSFETs, MIM capacitors, etc., to replace SiO₂, reducing leakage current and enhancing drive capability.
• Photovoltaic cells: Serves as a field-effect passivation layer for p-type silicon emitters and as a front-side anti-reflection coating.
• Sensors and MEMS: Provides chemical protection and electrical insulation.
• Advanced packaging: Functions as a barrier layer or dielectric isolation layer.

Whether you need silicon wafers for research or for industrial applications, please contact us email at [email protected] and [email protected].

 

References:

1. Shulakov, A. S., Braiko, A. P., Bukin, S. V., & Drozd, V. E. (2004). Properties of an Al2O3/Si interface. Physics of the Solid State, 46(10), 1935-1939.
2. Zhu, L. Q., Li, X., Yan, Z. H., Zhang, H. L., & Wanb, Q. Dual functions of anti-reflectance and surface passivation of the atomic layer deposited Al2O3 films on crystalline silicon substrates.