CN1596035B - An amendment process for chemical surface of silicon minisize electret acoustic sensor electricity storage membrane - Google Patents

Abstract

The invention is a chemical surface decoration process for silicon micro type electret voice sensor electricity storing film. It uses glass container with air extracting valve, its bottom is arrangedwith solution HMDS or DCDMS, the top is arranged with pile film Si plate containing SiO2 or Si3N4/SiO2, under the pure saturate steam of the solution, carries on air phase reaction, avoids the film from being contaminated by water or other active substance, the invention can improve electret state of SiO2, Si3O4/SiO2, guarantees the stability of charge storage.

Description

A kind of chemical surface modification method of micro-silicon electret acoustic sensor accumulate film

Technical field

The invention belongs to sensor technical field, be specifically related to a kind of chemical surface modification method of micro-silicon electret acoustic sensor accumulate film.

Background technology

The silicon-base miniature electret acoustic sensor, because its microminiaturization, processing technology and planar technique and micromachining technology compatibility, may realize full-automatic large-scale production, again because the advantages such as long-life of substrate electret, be the miniature acoustic-electric and the electroacoustic transducer of the integrability of new generation of generally acknowledging, be expected to be used for national defence, security personnel, Aero-Space, and field such as civilian sound information system.For example can be widely used in miniature tapping device, Mini-otophone, mobile phone, battlefield phone, naval vessel commander's sound information system etc.Though begin this sonic transducer to be set about research not commercialization as yet at home and abroad over year surplus in the of 20 so far from early eighties.One of the main reasons is because the used Si base of the accumulate layer of this class transducer SiO ₂Monofilm or Si ₃N ₄/ SiO ₂Duplicature presents hydrophily.

Work as SiO ₂When in air, storing, owing to be exposed to SiO ₂The ≡ Si-O-Si ≡ of film surface and the chemical reaction of water, and physical absorption form respectively and contain the hydrophilic surface layer of first silanol ≡ SiOH, thereby present high surface conductance, that is:

And under the electret outer field action, ≡ SiOH also will with water generation physical absorption (Van der Waals for effect), cause conducting electricity the formation of water layer:

Thereby greatly increased SiO ₂Surface conductance.

And on the other hand, because the major part of corona charging iunjected charge all is deposited on SiO ₂Film or Si ₃N ₄/ SiO ₂The surface of duplicature or nearly surface, the formation of above-mentioned high surface electrical conducting shell will cause the decay of electric charge, jeopardize the Charge Storage life-span of electret.

To Si base Si ₃N ₄/ SiO ₂Though duplicature is Si ₃N ₄As the surface coating of this assembly of thin films, and and SiO ₂Compare Si ₃N ₄Present hydrophobicity, but because the Si in the Si base electret acoustic sensor substrate ₃N ₄Layer needs to form with the APCVD method:

Its reaction reagent is except SiH ₄And NH ₃In addition, in reaction tube, still contain a certain amount of O ₂, therefore, in above-mentioned course of reaction, except forming Si ₃N ₄In addition, SiH ₄And O ₂In the time of 900 ℃, may react the SiO that generates certain content simultaneously ₂:

Therefore, no matter be SiO ₂Monofilm or Si ₃N ₄/ SiO ₂Duplicature, the number that reduces the film surface hydrophilic radical are to reduce surface conductance, improve the Basic Ways of electret Charge Storage Stability.

In order to improve its Charge Storage life-span, must carry out the chemical surface correction to them. people utilize HMDS (HMDS) and DCDMS chemistry such as (dichlorodimethylsilane) correction reagent that it is carried out surface treatment, make it become hydrophobic layer from hydrophilic layer.

Use HMDS that the accumulate film surface that forms first silanol (≡ SiOH) is carried out chemical treatment, then the nonpolar methyl group (CH among the HMDS ₃) will replace the semipolar oh group of first silanol and (OH), form the hydrophobic protective layer of one deck densification on the surface, may prevent the continuation absorption of sealing, played the formation of the conduction water layer of the generation that stops the proton conduction phenomenon.This has just improved SiO greatly ₂The stability of Charge Storage in the electret body, that is:

2≡SiOH+(CH ₃) ₃SiNHSi(CH ₃) ₃＝2≡SiOSi(CH ₃) ₃+NH ₃ (5)

DCDMS also can replace SiO ₂Hydroxyl in the first silanol of surface hydrophilic.Obtain similar chemical surface treatment effect.Below be the chemical equation of DCDMS and first silanol:

2≡SiOH+Cl ₂Si(CH ₃) ₂＝(≡SiO) ₂Si(CH ₃) ₂Cl+2HCl (6)

But, in course of reaction, can produce reaction by-product respectively---HCl and NH _3.These byproducts may form hydrochloric acid and NH respectively with water reaction in air ₄OH, this class acid-base material very easily is deposited on film surface, causes the SiO as the accumulate layer ₂Or Si ₃N ₄/ SiO ₂The surface contamination of film causes the acceleration decay of electric charge and device sensitivity to descend.

The P.Guenther of Germany etc. are to utilize the gas-phase reaction of the mist of the saturated vapor of above-mentioned chemical reagent and the air composition that contains the steam sky to film in the atmospheric environment in the glassware of a sealing; Or in atmospheric environment at Si base SiO ₂Or Si ₃N ₄/ SiO ₂HMDS or DCDMS reagent are dripped in the surface of film, the spin coating by certain rotating speed reagent is contacted with film surface and react a period of time (Holland, W.Olthuis); Or the Si sheet directly immersed in the mentioned reagent finish.Yet owing to moisture in the atmosphere and other harmful active gases and impurity, therefore in glassware that contains steam or environment, react the NH of generation through HMDS in the course of reaction ₃(seeing reactional equation (5)), react with steam again:

Or, react with steam again through DCDMS reaction generation HCl (seeing reactional equation (6)):

Byproduct alkali NH ₄OH and moisture HCl (hydrochloric acid) etc. are to SiO ₂Or Si ₃N ₄/ SiO ₂The erosion of accumulate superficial layer and pollution cause the decay aggravation of electret deposited charge, influence the stability of accumulate layer charge, and then the useful life of reducing transducer.

Summary of the invention

The objective of the invention is to propose a kind of chemical surface modification method of the micro-silicon electret acoustic sensor accumulate film of avoiding the accumulate superficial layer to be etched and polluting, to form more perfect hydrophobic layer, improve the electret properties of accumulate film, guarantee the useful life of transducer.

The chemical surface modification method of the micro-silicon electret acoustic sensor accumulate film that the present invention proposes, concrete steps are as follows:

Utilize the glass container (Fig. 1) of band evacuating valve, place uncovered vessel that fill reagent HMDS or DCDMS in its bottom, place the pending SiO that contains above ₂Or Si ₃N ₄/ SiO ₂At this moment and SiO the Si sheet of electret film pumps the HMDS of air moisture in the container and volatilization or DCDMS mixed air or gas with vacuum pump, and valve-off makes the inherent later stages in chamber evaporate the pure saturated steam that only comprises HMDS or DCDMS, ₂Or Si ₃N ₄/ SiO ₂Gas-phase reaction can avoid water and other active dusty gas and impurity that film surface is polluted.Improved SiO significantly ₂, Si ₃N ₄/ SiO ₂The electret state of film type electret has been guaranteed the stability of Charge Storage. the above-mentioned gas-phase reaction time is 12-240 hour, and reaction temperature is a room temperature.

The safe handling temperature that gas-phase reaction finishes the hydrophobic layer of back formation should be controlled at below 200～260 ℃, and promptly charging process or charging back must be limited in below 200～260 ℃ the heat treatment temperature T of this class Si base functional membrane.

For example, when the T=250 ℃ of left and right sides, its charge stability is similar to without heat treated sample (when being the RT storage), and Charge Storage presents high stability, when explanation was lower than about 250 ℃ in heat treatment temperature, its surface hydrophobicity layer still remained intact (seeing Fig. 3 curve II);

Yet in the time of T=400 ℃, its charge stability presents obvious decay, behind process 80min, and V _sDecayed to about 57% (seeing Fig. 3 curve III) of initial value;

With when T=600 ℃, through same time, V _sAlmost decay to 0 (seeing Fig. 3 curve IV).

Therefore, the present invention determines can not be higher than 200～260 ℃ through the revised film heat treatment temperature of chemical surface.

Description of drawings

Fig. 1 with HMDS or DCDMS to Si base SiO ₂And Si ₃N ₄/ SiO ₂Duplicature carries out the device schematic diagram of chemical surface correction.

Fig. 2 is at the Si that revises under the pure saturated steam of HMDS and under the non-pure steam ₃N ₄/ SiO ₂The current potential V of film behind the normal temperature corona charging _s(t) curve contrast (V _S0=-40V)

Fig. 3 is the Sol-gelSiO after different temperatures is aging after the chemical surface correction ₂Isothermal surface potential attenuation curve.

Embodiment

The invention is further illustrated by the following examples.

Embodiment 1, adopts HMDS reagent, to Si ₃N ₄/ SiO ₂Electret film (thickness d=0.45 μ m) carries out the chemical surface correction, uses the glass container of band evacuating valve as shown in Figure 1.Before HMDS handles, take out the steam in the dereaction chamber and the mixing composition of HMDS volatilization gas, under the pure saturated steam of HMDS, with Si ₃N ₄/ SiO ₂Carry out gas-phase reaction, if the reaction time was respectively 12-24 hour and 180-240 hour.After again the film through revising being carried out the normal temperature corona charging, be 88%, last storage in 7 days at relative humidity RH.Detect its surface potential V respectively _s(t), it the results are shown in shown in Figure 2.The former surface potential is 92.5 (curves 2) of initial value, and the latter's surface potential is initial value 94% (curve 1).And as a comparison, without the same sample of bleeding and handling, its surface potential has decayed to 86% (curve 3) of initial value.The result shows, under pure saturated steam, carry out the importance of this condition of gas-phase reaction.This result also illustrates, extends to 180-200 hour along with the prolongation in reaction time: 12-24 hour, and is constantly perfect by the unimolecule hydrophobic layer that the chemical surface correction forms.

Embodiment 2, adopt DCDMS reagent, to SiO ₂Electret film carries out the chemical surface correction, uses the glass container of band evacuating valve as shown in Figure 1.Before DCDMS handles, take out the steam in the dereaction chamber and the mixing composition of DCDMS volatilization gas, under the pure saturated steam of DCDMS, with SiO ₂Carry out gas-phase reaction, the reaction time was respectively 12-24 hour and 220-240 hour.Again the film through revising is carried out the normal temperature corona charging, (ambient temperature is 32 ℃, and humidity is 99%) stores 25 days under the comparison adverse circumstances, detects its surface potential V then respectively _s(t), its experiment law and embodiment 1 result are similar: revise the reaction time and be 12-24 hour, the current potential of film is 42% of an initial value, revise the reaction time and be 220-240 hour, the current potential of film is 45% of an initial value, and without the same sample of bleeding and handling, its surface potential has decayed to 34% of initial value.

Claims (1)

1. the chemical surface modification method of a micro-silicon electret acoustic sensor accumulate film, it is characterized in that concrete steps are as follows: the glass container that utilizes the band evacuating valve, place uncovered vessel that fill reagent HMDS or DCDMS in its bottom, place the pending SiO that contains above ₂Or Si ₃N ₄/ SiO ₂The Si sheet of electret film pumps with the HMDS or the DCDMS mixed air of vacuum pump with air moisture in the container and volatilization, and valve-off makes the inherent later stages in chamber evaporate the pure saturated steam that only comprises HMDS or DCDMS; At room temperature gas-phase reaction is 12 hours-240 hours.

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