HF PECVD SiNx：H薄膜的机械应变在纳米光子应用中的研究

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"这篇科研文章探讨了使用高频等离子体增强化学气相沉积（HF PECVD）技术在低温下制备氢化非晶硅氮化物（SiNx：H）薄膜的方法，着重研究了等离子体频率和功率密度对薄膜特性，特别是应力的影响。通过傅立叶变换红外光谱（FTIR）分析了薄膜中的化学键信息，并利用衬底曲率测量确定了薄膜的应力。实验结果显示，等离子体频率对SiNx：H薄膜的应力控制至关重要，以40.68MHz频率生长的氮化硅层表现出拉伸应力在400MPa至700MPa之间，这种应力水平适用于应变硅光子学的应用。" 本文是关于硅光子学的一个研究，其中涉及的关键知识点包括： 1. **硅光子学**：这是一种利用硅材料作为光子器件的基础来处理光信号的技术。硅光子学因其与现有电子集成电路的兼容性，成为高性能光通信、计算和传感器系统的重要研究领域。 2. **氢化非晶硅氮化物（SiNx：H）薄膜**：SiNx：H是一种广泛使用的光子学材料，因其优良的光学性能、稳定性以及可以通过PECVD技术在低温下沉积而受到青睐。这种薄膜可以作为光波导、光隔离器和光调制器等光子组件的组成部分。 3. **高频等离子体增强化学气相沉积（HF PECVD）**：这是一种薄膜沉积方法，通过引入高频等离子体激发反应气体，使得在较低温度下也能有效地沉积高质量的薄膜。HF PECVD常用于半导体制造和微电子领域。 4. **等离子体频率和功率密度**：这两个参数在HF PECVD过程中决定了薄膜的物理和化学特性。更高的等离子体频率可能导致更紧密的原子排列，从而影响薄膜的应力状态。等离子体功率密度则影响化学反应速率和薄膜的生长速率。 5. **应力测量**：通过对衬底曲率的测量，可以评估薄膜的应力状态。拉伸应力是薄膜向内收缩的趋势，对于应变硅光子学特别重要，因为它可以改变硅基材料的光学性质，实现对光信号的控制。 6. **傅立叶变换红外光谱（FTIR）**：这是一种分析化学技术，通过检测物质对红外光的吸收，来获取其分子结构和化学键信息。在本研究中，FTIR被用来揭示SiNx：H薄膜中的化学成分和键合状态。通过这些研究，科学家们能够优化制备工艺，获得具有特定应力特性的SiNx：H薄膜，这对于开发新型的硅光子器件和提高其性能具有重要意义。

Chin. Phys. B Vol. 24, No. 10 (2015) 106801

Mechanical strains in pecvd SiN

𝑥

:H ﬁlms

for nanophotonic application

∗

O. Semenova

a)†

, A. Kozelskaya

, Li Zhi-Yong

, and Yu Yu-De

Rzhanov Institute of Semiconductor Physics, Siberian Branch of Russian Academy of Sciences, Novosibirsk, Russia

Institute of Strength Physics and Materials Science, Siberian Branch of Russian Academy of Sciences, Tomsk, Russia

Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China

(Received 25 February 2015; revised manuscript received 4 June 2015; published online 20 August 2015)

Hydrogenated amorphous silicon nitride ﬁlms (SiN

:H) are deposited at low temperature by high-frequency plasma-

enhanced chemical vapor deposition (HF PECVD). The main effort is to investigate the roles of plasma frequency and

plasma power density in determining the ﬁlm properties particularly in stress. Information about chemical bonds in the

ﬁlms is obtained by Fourier transform infrared spectroscopy (FTIR). The stresses in the SiN

:H ﬁlm are determined from

substrate curvature measurements. It is shown that plasma frequency plays an important role in controlling the stresses in

SiN

:H ﬁlms. For silicon nitride layers grown at plasma frequency 40.68 MHz initial tensile stresses are observed to be in

a range of 400 MPa–700 MPa. Measurements of the intrinsic stresses of silicon nitride ﬁlms show that the stress quantity

is sufﬁcient for ﬁlm applications in strained silicon photonics.

Keywords: silicon photonics, intrinsic stress, amorphous silicon nitride ﬁlms

PACS: 68.35.Gy, 81.15.Gh, 81.70.–q DOI: 10.1088/1674-1056/24/10/106801

1. Introduction

Thin ﬁlms of hydrogenated silicon nitride fabricated by

plasma-enhanced chemical vapor deposition (PECVD) have

been widely used in the semiconductor industry as passivation

layers, diffusion barriers, gate dielectrics, and also as materials

for micro-electro-mechanical systems (MEMS) and antireﬂec-

tion coatings for silicon solar cells.

[1–5]

In the past decade the

applications of silicon nitride thin ﬁlms have been extended to

silicon photonics.

The inﬂuence of strain in the thin ﬁlms on the properties

of devices is a long known effect.

[6]

The strain appears from

different steps in the CMOS (complementary metal–oxide–

semiconductor) process and often is a reason for device degra-

dation. This problem becomes even more signiﬁcant for de-

vices on a nanoscale. However, besides the undesired effects

strain can also be used to enhance the desired physical prop-

erties of nanostructured devices as already done in the ﬁeld of

strained silicon CMOS technology.

[7]

Another ﬁeld of investigations that is still developing is

strained silicon photonics.

[8–10]

The goal of silicon photonics

is to investigate the integration of individual photonic devices

with microelectronic devices that enables high-performance,

cost-effective optical communication, and computing systems.

The inversion symmetry of silicon crystal prohibits the exis-

tence of a linear electro–optic effect. It was shown experimen-

tally and theoretically by Govorkov et al.

[11]

that the symme-

try can be broken by applying inhomogeneous stress in silicon

surface layers. Now this idea helps to realize an all-silicon

electro–optic modulator based on a strain-induced Pockel’s ef-

fect in silicon. A Mach-Zehnder modulator based on a locally

strained waveguide structure is presented in Ref. [12]. The au-

thors used a silicon nitride strain layer deposited directly on

the top of the silicon rib-waveguide.

The silicon nitride thin ﬁlms produced by PECVD tend

to be non-stoichiometric and contain hydrogen due to the gas

precursors (SiH

and NH

) used for deposition. Structures and

properties of SiN

:H ﬁlms depend on the deposition rate, sub-

strate temperature, plasma power, pressure in the deposition

chamber, gas composition, etc. For applications in photonic

devices it is necessary for ﬁlms to have high intrinsic stresses

(above 600 MPa).

Currently, there are only two methods that are described

to obtain strain layers of hydrogenated amorphous silicon ni-

tride ﬁlms. The authors in Ref. [13] presented the measure-

ment results of the intrinsic stresses of silicon nitride ﬁlms de-

posited by PECVD with dual plasma excitation frequencies.

By changing only the duty cycle of the high (13.56 MHz) and

low (380 kHz) plasma excitation frequencies throughout the

deposition it was possible to control the stresses of the ﬁlms,

and stress can vary from tensile (up to 500 MPa) to com-

pressive (−850 MPa). A highly tensile silicon nitride layer

is obtained by using cascaded ultraviolet (UV) irradiation in

Ref. [14]. Successive UV radiation of equal or shorter wave-

lengths with variable intensity and duration selectively breaks

bonds in the Si–N matrix and minimizes shrinkage and ﬁlm re-

laxation. In this case higher tensile stress than a non-cascaded

∗

Project supported by RFBR (Grant No. 14-03-91154 NNSF) and the National Natural Science Foundation of China (Grant No. 61411130212).

†

Corresponding author. E-mail: oisem@isp.nsc.ru

106801-1

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