Summary of the invention
The objective of the invention is to overcome the deficiencies in the prior art, a kind of body silicon micro-processing method of the MEMS of formation thermopile detector cavity structure is provided, the cavity structure inner surface rule of formation is smooth, and structural symmetry is good, and technique realizes that controllability is high.The technical solution used in the present invention is:
Step 101 provides silicon base, at the front of silicon base thermal oxide growth silicon dioxide film;
Step 102 forms thermoelectric pile zone and INFRARED ABSORPTION district by deposit, photoetching, etching on silicon dioxide film;
Step 103, deposit structure of composite membrane in silicon dioxide film, thermoelectric pile zone and INFRARED ABSORPTION district; The upper strata of structure of composite membrane is Si
3N
4Passivation layer, lower floor is silicon dioxide layer of protection;
Step 104 is at Si
3N
4Passivation layer surface spin coating photoresist, and form the photoresist opening figure on photoresist by photoetching process, namely corrode opening; Then utilize the material of RIE technology etching corrosion opening below, until reach silicon base, to form the release channel of thermoelectric pile structure;
Step 105 by release channel, adopts isotropic etch method corrosion body silicon face shallow-layer, with the slim cavity of organizator silicon shallow-layer;
Step 106 by release channel and slim cavity, adopts the body silicon deep layer of the slim cavity of anisotropy rot etching method corrosion below, the ladder cavity structure that formation rule is level and smooth.
Advantage of the present invention: the two etching process releasing heat pile detector cavitys that adopt isotropic etch to combine with anisotropic corrosion technique, make the thermopile detector symmetrical configuration, the manufacture process controllability is high, and manufacturability is strong and traditional cmos process is compatible.
The specific embodiment
The invention will be further described below in conjunction with concrete drawings and Examples.
The infrared thermopile detector structure with cavity structure that the present invention proposes as shown in Figure 6, thermal oxide growth silica (SiO2) film 2 on silicon base 1, form thermoelectric pile zone 3 and INFRARED ABSORPTION district 4 on silicon dioxide film 2, wherein the thermoelectric pile structure can take various ways as circle, rectangle etc.Being thermojunction district 31 near the end in INFRARED ABSORPTION district 4 on thermoelectric pile zone 3, is cold junction district 32 away from the other end in INFRARED ABSORPTION district 4.Deposit silicon nitride and silica structure of composite membrane 5 on the thermoelectric pile structure sheaf, photoetching corrosion opening 6 on composite membrane.Form the release channel 61 of thermoelectric pile structure by corrosion window 6, discharge silicon base and form cavity 7, the slim cavity 71 of the body silicon shallow-layer that its cavity 7 is formed by isotropic etch technique and the ladder cavity structure 72 of the body silicon deep layer that the anisotropy rot etching technique forms form.The concrete grammar process is as described below.
Step 101 provides silicon base 1, at the front of silicon base 1 thermal oxide growth silica (SiO
2) film 2; Specifically as shown in Figure 1, the silicon base 1 that adopts can be a kind of at the doped silicon based end of the single silicon base of twin polishing, the doped silicon based end of P type or N-type.This example adopts the single silicon base of twin polishing.In the front of silicon base 1 by the mode of the dry-oxygen oxidation silica (SiO that grows
2) film 2, the thickness of this silicon dioxide film 2 is 5000, and during dry-oxygen oxidation, temperature is 950 ℃, and the content of oxygen is 60%.
Step 102 forms thermoelectric pile zone 3 and INFRARED ABSORPTION district 4 by deposit, photoetching, etching on silicon dioxide film 2;
As shown in Figure 2, be thermojunction district 31 near the end in INFRARED ABSORPTION district 4 on thermoelectric pile zone 3, be cold junction district 32 away from the other end in INFRARED ABSORPTION district 4, the thermoelectric pile composition material can be polysilicon/metal, doped silicon/aluminium, N-type polysilicon/P type polysilicon etc. and CMOS process compatible material.The processing step that forms thermoelectric pile zone 3 and INFRARED ABSORPTION district 4 is the common technique means of this area, and is not the emphasis of this method, does not deeply launch for its detailed technical process at this.The process that focuses on the cavity structure in organizator silicon of the present invention.
Step 103, deposit structure of composite membrane 5 on silicon dioxide film 2, thermoelectric pile zone 3 and INFRARED ABSORPTION zone 4; The upper strata of structure of composite membrane 5 is Si
3N
4Passivation layer, lower floor is silicon dioxide layer of protection;
Specifically as shown in Figure 3, on silicon dioxide film 2, thermoelectric pile zone 3 and INFRARED ABSORPTION zone 4 first by LPCVD technology growth diaphragm material SiO
2, thickness is 4000, to form silicon dioxide layer of protection; Then by LPCVD technology growth passivation material Si
3N
4, thickness is 4000, to form Si
3N
4Passivation layer.During LPCVD technology growth structure of composite membrane 5, the work furnace tube temperature is 800 ℃, and pressure is 200mTorr, deposition rate 10 ~ 20nm/min.
Step 104 is at Si
3N
4Passivation layer surface spin coating photoresist, and form the photoresist opening figure on photoresist by photoetching process, namely corrode opening 6; Then utilize the RIE(reactive ion etching) material of technology etching corrosion opening 6 belows, until reach silicon base 1, to form the release channel 61 of thermoelectric pile structure;
Specifically as shown in Figure 4, at Si
3N
4Then passivation layer surface spin coating photoresist produces the Si of the correspondence of release channel at needs
3N
4The passivation layer surface position forms the photoresist opening figure on photoresist by photoetching process, namely corrode opening 6; Utilize the material of RIE technology etching corrosion opening 6 belows, positions (to comprise Si
3N
4Material in passivation layer, silicon dioxide layer of protection, silicon dioxide film 2), until reach silicon base 1, to form the release channel 61 of thermoelectric pile structure.Utilize at last the oxygen plasma dry method to remove photoresist and remove Si with the remove photoresist method that combines of sulfuric acid/hydrogen peroxide wet method
3N
4The photoresist of passivation layer surface.RF power during above-mentioned RIE etching is 150W, and chamber pressure is 400mTorr, and etching gas is CHF3, He, SF6 mist, and corresponding flow is 7/100/30sccm.Release channel 61 diameters that form are 14um.Distance between each release channel is 15um.
Step 105 by release channel 61, adopts the surperficial shallow-layer of isotropic etch method corrosion body silicon (being silicon base 1), with the slim cavity 71 of organizator silicon shallow-layer;
Specifically as shown in Figure 5, etchant gas or the liquid release channel 61 corrosion body silicon face shallow-layers that can form in step 104 are to form slim cavity 71.This example adopts XeF
2The body silicon face shallow-layer of gas dry etching technology isotropic etch thermoelectric pile zone 3 and 4 belows, INFRARED ABSORPTION district, in step 101, the silica of thermal oxide growth (SiO2) film 2 plays the effect that stops corrosion in the process of corrosion releaser silicon, thereby forms slim cavity 71.Adopt XeF
2The gas dry etching is due to XeF
2It is selectively good to corrode, hardly silica (SiO2) film 2 of thermal oxide growth in corrosion step 101.XeF
2The gas dry etching can be at XeF
2Carry out in etching machine, the etch chamber internal pressure is 533Pa, carries out two etching cycles, each cycle 20s.
Step 106 by release channel 61 and slim cavity 71, adopts the body silicon deep layer of the anisotropy rot etching method slim cavity of corrosion 71 belows, the ladder cavity structure 72 that formation rule is level and smooth;
Specifically as shown in Figure 6, during anisotropic etch, the slim cavity 71 corrosion deep layer body silicon of corrosive liquid by forming in step 105 form ladder cavity structure 72.In step 101, the silica of thermal oxide growth (SiO2) film 2 plays the effect that stops corrosion in the process of corrosion releaser silicon.Anisotropic etch solution adopts potassium hydroxide (KOH) solution or TMAH corrosive liquid.When adopting potassium hydroxide (KOH) corrosive liquid, potassium hydroxide (KOH), isopropyl acetone (IPA), water (H
2O) weight proportion is 23.4%:13.3%:63.3%, 80 ℃ of corrosion temperatures.When adopting TMAH corrosive liquid (TMAH water), in the TMAH corrosive liquid, the TMAH molar concentration is 22%, 90 ℃ of corrosion temperatures.Two kinds of etchant solutions all have higher selective, and for the thermoelectric pile structure that the present invention relates to, two kinds of corrosive liquids all can the level and smooth ladder cavities of formation rule.The ladder cavity structure 72 inner surface rules that adopt the anisotropic etch method to form are smooth, and structural symmetry is good, and its physical dimension can accurately be controlled according to designing requirement, and technique realizes that controllability is high.
In sum, the present invention is directed to existing back side etching process etching time long, to the demanding shortcoming of device corrosion resistance, well-designed positive perforate etching process releasing structure layer shortens etching time, improves yield rate.Uncontrollable for the undercutting of existing isotropic etch technique side direction, corrosion structure smooth interior surfaces degree is low, the shortcomings such as symmetry is poor, the two etching process releasing heat pile detector cavitys that adopt isotropic etch to combine with anisotropic corrosion technique, manufacture process is simple, cavity structure can accurately be controlled according to designing requirement, and technique realizes that controllability is high.The thermopile detector symmetrical configuration that adopts the method to make, excellent performance, manufacturability is strong, and compatible with traditional cmos process, is easy to realize the integrated of sensor and subsequent readout circuit.