Hot-wire chemical vapor deposition low-loss hydrogenated amorphous silicon waveguides for silicon photonic devices

Swe Z. Oo; Antulio Tarazona; Ali Z. Khokhar; Rafidah Petra; Yohann Franz; Goran Z. Mashanovich; Graham T. Reed; Anna C. Peacock; Harold M. H. Chong

doi:10.1364/PRJ.7.000193

Journals >Photonics Research >Volume 7 >Issue 2 >Page 193 > Article

Photonics Research
Vol. 7, Issue 2, 193 (2019)

Hot-wire chemical vapor deposition low-loss hydrogenated amorphous silicon waveguides for silicon photonic devices

Swe Z. Oo^1、2、*, Antulio Tarazona², Ali Z. Khokhar², Rafidah Petra¹, Yohann Franz², Goran Z. Mashanovich², Graham T. Reed^2、3, Anna C. Peacock², and Harold M. H. Chong¹

Author Affiliations

¹School of Electronics and Computer Science, University of Southampton, SO17 1BJ, UK

²Optoelectronics Research Centre, University of Southampton, SO17 1BJ, UK

³School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore

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DOI: 10.1364/PRJ.7.000193 Cite this Article Set citation alerts

Swe Z. Oo, Antulio Tarazona, Ali Z. Khokhar, Rafidah Petra, Yohann Franz, Goran Z. Mashanovich, Graham T. Reed, Anna C. Peacock, Harold M. H. Chong. Hot-wire chemical vapor deposition low-loss hydrogenated amorphous silicon waveguides for silicon photonic devices[J]. Photonics Research, 2019, 7(2): 193 Copy Citation Text

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Extensive Raman characterization on the structural disorder of an a-Si:H network as a function of Tsub. (a) The Raman spectrum of an a-Si:H network deposited at 230°C of Tsub shows four Raman active modes and the structural information available from those, such as peak position, can indicate chemical species and symmetry; the ω shift can specify the stress and strain; and the FWHM can express the structural disorder and angular distortion of the material network. (b) TO peak position as a function of Tsub, where the dotted line is a guideline for standard TO peak frequency, ωTO of a-Si:H at 480 cm−1. Insets are the deconvolution of the TO peak into amorphous and micro-voids in the topology of a-Si:H deposited at 190°C and 320°C, where the solid line represents the TO peak of the Si-Si stretching mode of the deposited film and the dotted lines represent the Gaussian deconvolution of the TO peak. Red dotted lines suggest amorphous and green dotted lines suggest micro-voids. (c) TO peak width ΓTO as a function of Tsub, where dotted lines are guidelines for standard ΓTO at the fully amorphous condition and device-quality a-Si:H. (d) Dependence of the ratio of ITA to ITO on the hydrogen concentration in the diffusion control region. Schematic blue dotted arrows represent how bending modes vary with the hydrogen content in the H-role region and how the stretching mode changes with Tsub in the T-role region.

Fig. 1. Extensive Raman characterization on the structural disorder of an a-Si:H network as a function of Tsub. (a) The Raman spectrum of an a-Si:H network deposited at 230°C of Tsub shows four Raman active modes and the structural information available from those, such as peak position, can indicate chemical species and symmetry; the ω shift can specify the stress and strain; and the FWHM can express the structural disorder and angular distortion of the material network. (b) TO peak position as a function of Tsub, where the dotted line is a guideline for standard TO peak frequency, ωTO of a-Si:H at 480 cm−1. Insets are the deconvolution of the TO peak into amorphous and micro-voids in the topology of a-Si:H deposited at 190°C and 320°C, where the solid line represents the TO peak of the Si-Si stretching mode of the deposited film and the dotted lines represent the Gaussian deconvolution of the TO peak. Red dotted lines suggest amorphous and green dotted lines suggest micro-voids. (c) TO peak width ΓTO as a function of Tsub, where dotted lines are guidelines for standard ΓTO at the fully amorphous condition and device-quality a-Si:H. (d) Dependence of the ratio of ITA to ITO on the hydrogen concentration in the diffusion control region. Schematic blue dotted arrows represent how bending modes vary with the hydrogen content in the H-role region and how the stretching mode changes with Tsub in the T-role region.

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Fig. 2. (a) An Arrhenius plot shows the deposition rate versus the temperature (square symbol) and shows the propagation loss (dB/cm) corresponding to the deposited temperature (diamond symbol). (b) Cross-sectional SEM images of the a-Si:H films deposited at the different substrate temperatures. The red boxes represent the a-Si:H layer surrounded by silicon dioxide. Inset: the field intensity profile of the propagation mode (at λ=1.55 μm) obtained from the 2 μm width waveguide.

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Fig. 3. (a) Measured propagation loss, which is normalized to the coupling loss for different widths. (b) Measured propagation loss (black dots) (dB/cm) of the fully etched ridge waveguide as a function of waveguide width at excitation wavelength 1550 nm. The dotted line is for the eye guide. The squares are the analytically calculated propagation losses. Inset is the cross-sectional image of the measured waveguide, W=350 nm, H=400 nm.

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Fig. 4. (a) AFM images of the surface roughness of a-Si:H deposited at 230°C and 320°C. (b) 2D electric field profiles across the different waveguide widths, where all experimental defects [extinction coefficient, sidewall, surface roughness, air void (as shown in inset of Fig. 3(b)] are counted.

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Reference	Material	Deposition Method	Deposited Temperature (°C)	Propagation Loss (dB/cm)	Type	Dimension $(W \times H) (nm \times nm)$	Etched Depth (nm)	Upper Cladding	Remark
[5]	a-Si:H	PECVD	220	0.7	Rib	$15 \times 3000$	1200	Air	$λ = 1310 nm$ , without post processing
[6]	a-Si:H	PECVD	300	2	Rib	$1100 \times 1300$	380	Air	$λ = 1550 nm$ , without post processing
[7]	a-Si	PECVD	—	2.7	Wire	$700 \times 100$	100	${SiO}_{2}$	$λ = 1550 nm$ , 10 nm ${SiN}_{x}$ intercladding and nitrogen/argon plasma treatment
[8]	a-Si:H	PECVD	300	3.46	Wire	$480 \times 220$	220	${SiO}_{2}$	$λ = 1550 nm$ , CMP^b process on lower cladding
[8]	a-Si:H	PECVD	300	1.34	Ridge	$480 \times 220$	70	${SiO}_{2}$	$λ = 1550 nm$ , CMP^b process on lower cladding
[9]	a-Si:H	PECVD	400	3.2	Wire	$550 \times 220$	220	${SiO}_{2}$	$λ = 1550 nm$ , CMP^b process on lower cladding
[10]	a-Si	PECVD	300	3.8	Wire	$450 \times 220$	220	TEOS^a	$λ = 1550 nm$ , without post processing
[11]	a-Si:H	PECVD	250-300	2	Rib	$2100 \times 2100$	900	${SiO}_{2}$	$λ = 1550 nm$ , without post processing
[11]	a-Si:H	PECVD	250-300	5.3	Wire	$500 \times 200$	200	${SiO}_{2}$	$λ = 1550 nm$ , without post processing
[12]	a-Si:H	PECVD	250	0.6	Ridge	$780 \times 440$	100	TEOS^a	$λ = 1550 nm$ , CMP^b process on deposited a-Si:H
[20]	c-Si	—	—	3.6	Strip	$445 \times 220$	220	Air	$λ = 1550 nm$ , without post processing
[21]	c-Si	—	—	3.4	Wire	$630 \times 220$	220	Air	$λ = 1550 nm$ , sidewall smoothing by wet chemical oxidation
[22]	c-Si	—	—	0.92	Wire	$500 \times 265$	265	Air	$λ = 1550 nm$ , without post processing
This work	a-Si:H	HWCVD	230	0.8	Wire	$650 \times 400$	400	${SiO}_{2}$	$λ = 1550 nm$ , without post processing

Table 1. Summary of the Performance of a-Si Waveguides and Techniques Used in Silicon Photonics Applications

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Substrate Temperature, $T_{sub}$ (ºC)	$ω_{TO}$ ( ${cm}^{- 1}$ )	$Γ_{TO}$ ( ${cm}^{- 1}$ )	$Δ θ_{b}$ (°)	$I_{TA} / I_{TO}$	Deposition Rate (nm/s)	Surface Roughness (nm)
190	490	79.85	10.81	2.08	0.46	1.32
210	476.36	66.5	8.58	1.36	0.57	1.1
230	480.5	68.9	8.98	0.73	0.55	1
250	480	68.25	8.88	1.12	0.55	0.84
320	492.6	90.78	12.63	1.84	0.52	3.58