Low-loss polysilicon waveguides fabricated in an emulated high-volume electronics process

Abstract

We measure end-of-line polysilicon waveguide propagation losses of ~6-15 dB/cm across the telecommunication O-, E-, S-, C- and L-bands in a process representative of high-volume product integration. The lowest loss of 6.2 dB/cm is measured at 1550 nm in a polysilicon waveguide with a 120 nm x 350 nm core geometry. The reported waveguide characteristics are measured after the thermal cycling of the full CMOS electronics process that results in a 32% increase in the extracted material loss relative to the as-crystallized waveguide samples. The measured loss spectra are fit to an absorption model using defect state parameters to identify the dominant loss mechanism in the end-of-line and as-crystallized polysilicon waveguides.

Hot-wire polysilicon waveguides with low deposition temperature

“…A. Woollam spectroscopic ellipsometry system (192-1700 nm) and a multilayer model to calculate the extinction coefficient from which the material-induced loss was found to be approximately 5.1 dB∕cm. Provided the scattering loss is completely eliminated, the material-induced loss is similar to those of previously reported polysilicon waveguides [7,10]. The loss can be further reduced by surface planarization by means of chemical mechanical polishing or similar methods.…”

“…Multilayered integration is desirable due to several advantages such as reduced chip size and improved thermal isolation. Recently, there has been an increased interest in polysilicon waveguides due to their low cost and added design flexibility [3][4][5][6][7][8][9][10]. However, most of the reported polysilicon films were deposited or posttreated at high temperatures (≥900°C), e.g., [3,[6][7][8][9][10].…”

“…However, earlier reported optical propagation losses (35-77 dB∕cm) abated the interest for using polysilicon in photonics applications [5]. Engineering the waveguide structure and deposition processes has recently resulted in reducing the optical propagation loss to ∼6 dB∕cm for transverse electric (TE) mode [7]. However, annealing polysilicon at temperatures ≥900°C has been widely used to improve the crystallinity of as-deposited polysilicon films.…”

Deposited low temperature silicon GHz modulator

“…Since the groundbreaking work on polysilicon photonics 13 , much progress has been made, including active devices. Various works using high temperature annealed polysilicon have demonstrated low loss on the order of 10 dB / cm 14 , and electro-optic modulation 15,16 has also been shown. However, these works are not compatible with CMOS backend integration due to their high thermal budget fundamental to furnace annealed polysilicon, constraining them to frontend integration in CMOS and DRAM.…”

Low temperature hot-wire polysilicon waveguides

“…However, it is constrained by the need for integration of multi-layered silicon photonics to the more established CMOS technology. Recently, there has been an increasing interest in polysilicon waveguides due to their low cost and added design flexibility [2]. However, most of the reported polysilicon films were deposited or post-treated at high temperatures (≥ 900 o C) which may not be compatible with the CMOS fabrication process.…”