Low drift planar waveguide grating sensor and method for manufacturing same

Abstract

A planar waveguide grating (PWG) sensor is described herein which exhibits a low signal drift and an enhanced sensitivity due to the use of a fully dense silicon-rich nitride surface layer. In the preferred embodiment, the silicon rich silicon nitride surface layer has a composition which includes Si and N, and optionally H, Ge and / or O, where a Si / N atomic ratio is greater than 0.75. In addition, the silicon rich nitride surface layer has a refractive index that is greater than 2.45 and less than 3.2 at a wavelength of operation. A method is also described herein for manufacturing the PWG sensor with acceptable costs and high yields by utilizing well known semiconductor processes and tools.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a planar waveguide grating (PWG) sensor which exhibits a low signal drift and an enhanced sensitivity due to the use of a fully dense silicon rich silicon nitride surface layer. In addition, the present invention relates to a method for manufacturing the PWG sensor with acceptable costs and high yields by utilizing well known semiconductor processes and tools. [0003] 2. Description of Related Art [0004] The following abbreviations are herewith defined, at least some of which are referred to in the ensuing description of the prior art and the preferred embodiments of the present invention. [0005] APCVD Atmospheric Pressure Chemical Vapor Deposition [0006] CVD Chemical Vapor Deposition [0007] FIB Focused Ion Beam [0008] FSG Fluorine Doped Silica Glass [0009] LPCVD Low Pressure Chemical Vapor Deposition [0010] PECVD Plasma Enhanced Chemical Vapor Deposition [0011] PWG Planar Waveguide G...

AI Technical Summary

Benefits of technology

The present invention is about a new type of sensor called a PWG sensor that has improved sensitivity and reduced signal drift. This is achieved by using a fully dense silicon layer with a high amount of silicon and nitrogen, which results in a refractive index greater than 2.45 and less than 3.2. The method for manufacturing this sensor is cost-effective and can produce high yields using standard semiconductor processes.

Problems solved by technology

However, there are problems associated with manufacturing disposable PWG sensors 100 at a high yield and a low cost.

And, there are problems associated with the performance of these disposable PWG sensors 100.

The prior art demonstrates that there has been a struggle to balance the cost and performance in making a disposable PWG sensor 100.

However, the PWG sensor 100 which has a polymeric substrate 102 can suffer from a problematical optical signal loss that is due to absorption in the polymeric substrate 102.

Referring back to FIG. 1, it can be difficult to manufacture the PWG sensor 100 which has a polymeric substrate 102.

In particular, there is a significant manufacturing challenge in keeping the polymeric substrate 102 flat to ensure a uniform coupling angle for the light 116 that is directed into and reflected out-off the PWG sensor 100.

However, the use of a photolithography patterning and etching process to form a smooth and accurately reproduced diffraction grating 104 on the top surface of the glass substrate 102 can be challenging.

Unfortunately, this type of photolithography patterning process can be costly and as such it is not be suitable to manufacture disposable PWG sensors.

Moreover, the etching process which is used to form the diffraction grating 104 within the glass substrate 102 can be a significant challenge itself.

Unfortunately, these plasma etching method are not practical for manufacturing large numbers of glass PWG sensors 100.

This produces a columnar grain growth where the packing of adatoms is not optimal, resulting in porosity (see, D. L. Smith, Thin Film Deposition: Principles and Practice, McGraw-Hill (1995) 159-161).

However, these methods cannot be used in applications where polymer substrates and / or polymer gratings degrade at temperatures below 200° C. and under ion bombardment.

Moreover, since this PVD coating process is a line of sight process, root cracks are often caused by inadequate step coverage over the grating features.

These root cracks may cause signal drift due to infiltration of water during assays.

However, measurements of differential signal drift may only be used if each PWG sensor 500 in the microplate exhibits a similar signal drift when exposed to the same solutions.

Unfortunately, as the plots in FIG. 8 (PRIOR ART) indicate, this is not the case for PWG sensors 500.

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