High performance silicon condenser microphone with perforated single crystal silicon backplate

Abstract

A silicon condenser microphone is described. The silicon condenser microphone of the present invention comprises a perforated backplate comprising a portion of a single crystal silicon substrate, a support structure formed on the single crystal silicon substrate, and a floating silicon diaphragm supported at its edge by the support structure and lying parallel to the perforated backplate and separated from the perforated backplate by an air gap.

Description

TECHNICAL FIELD [0001] The invention relates to a method of manufacturing a silicon condenser microphone, and more particularly, to a method of manufacturing a high performance silicon condenser microphone using a silicon micro-machining process. BACKGROUND [0002] Silicon condenser microphones have long been an attractive research and development subject. Various microphone designs have been invented and conceptualized by using silicon micro-machining technology. Despite various structural configurations and materials, the silicon condenser microphone consists of four basic elements: a movable compliant diaphragm, a rigid and fixed backplate (which together form a variable air gap capacitor), a voltage bias source, and a pre-amplifier. These four elements fundamentally determine the performance of the condenser microphone. In pursuit of high performance; i.e., high sensitivity, low bias, low noise, and wide frequency range, the key design considerations are to have a large size of d...

AI Technical Summary

Benefits of technology

[0023] Also in accordance with the objects of this invention a method of fabricating a silicon condenser microphone having high sensitivity and low noise is achieved. A single crystal silicon substrate (P−) is provided. First ions (P+) of a first conductivity type are implanted into the single crystal silicon substrate to form a pattern of acoustic holes in a central portion of the substrate. Second ions (N−) of a second conductivity type opposite the first conductivity type are implanted into the substrate and surrounding the pattern of acoustic holes to form a backplate region. Third ions (P+) of the first conductivity type are implanted overlying the pattern of acoustic holes. Fourth ions (N+) of the second conductivity type are implanted overlying a portion of the backplate region not surrounding the pattern of acoustic holes to form an ohmic contact region. A front side nitride layer is deposited overlying the backplate region. A back side nitride layer is deposited on an opposite surface of the substrate. A front side sacrificial oxide layer is deposited overlying the front side nitride layer. A back side sacrificial oxide layer is deposited overlying the back side nitride layer. First trenches are etched through the front side sacrificial oxide layer to the ohmic contacts, and to the substrate off the backplate region. The first trenches are filled with a first polysilicon layer which is patterned to form polysilicon caps overlying the first trenches and to form polysilicon endplates surrounding the pattern of acoustic holes. A first oxide layer is deposited overlying the patterned first polysilicon layer. The first oxide layer is etched to the polysilicon layer followed by a thin oxide deposition to form the tiny holes for first dimples overlying the endplates. A second polysilicon layer is deposited overlying the first oxide layer and filling the first dimple holes. The second polysilicon layer is etched to form a functional layer of a composite diaphragm and its lead-out to a bond pad. A second oxide layer ...

Problems solved by technology

However, the large diaphragm requires a large span of anchored supports and correspondingly a large backplate.

Also, a large air gap requires a thick sacrificial layer.

These present major difficulties in silicon micro-machining processes.

Due to constraints of material choices and intrinsic stress issues in silicon micro-mac...

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