Miniature integrated grating spectrometer and method for making based on blazed grating and thermopile detector
Technical field
The present invention relates to a kind of miniature integrated grating spectrometer based on blazed grating and thermopile detector and preparation method thereof, belong to the grating spectrograph field.
Background technology
The microminiaturized trend of sensor makes the integrated possibility that becomes of a plurality of sensors or dependency structure.Along with manufacturing and production technology develop to the scale level, existing that a plurality of sensors are integrated to finish the report of sophisticated functions in the world.Research centre, IBM Zurich is with biochemical Intelligent Recognition of the non-sign of the integrated realization of a plurality of gas sensors and artificial electric nasus system.ETH Zurich Univ. adopts then that four sensors such as quality, heat, electric capacity, temperature and treatment circuit are carried out monolithic is integrated with compatible mutually MEMS (MEMS (micro electro mechanical system)) technology of complementary metal oxide semiconductor (CMOS) (CMOS) technology, realizes intelligent gas sensor.But a series of problems such as complex structural designs, processing compatibility are poor, information processing difficulty that these sensors often all are faced with.
Miniature grating spectrograph is to be subjected to a kind of device that people note at present.Adopt the grating spectrograph of the integrated infrared sensor of MEMS technology will have microminiaturization, integrated, easy to use flexibly, characteristics such as ratio of performance to price height, its application can contain space flight such as remote sensing remote measurement, mineral exploration, gas detection, constituent analysis, environmental monitoring, geology, chemistry, biology, medicine and field of metallurgy etc., has important economic value and social value.
Traditional grating spectrograph comprises a plurality of discrete parts such as entrance slit, collimation lens, spectro-grating, condenser lens and detector.Have optical path length (being several meters), resolution height (can reach nanometer scale) is analyzed advantage accurately, but complex structure, bulky, cost an arm and a leg, limited its range of application greatly.And in some occasions, spectrometer does not need too high resolution, small size, light weight, low price and to be easy to carry be its an urgent demand.In order to reach this purpose, people have adopted certain methods to make the spectrometer microminaturization.As employing slab guides such as Datskos Panagiotis George that concave grating is mutually integrated with pyroelectric detector, developed incorporate micro spectrometer.Concave grating wherein adopts reactive ion etching (RIE) or deep reaction ion etching (DRIE) fabrication techniques, photoetching, requirement on machining accuracy are high, otherwise will cause grating of low quality, coupling efficiency, branch light quality all are affected, and waveguide difficulty of processing wherein is bigger, and manufacturing cost is still very expensive.
D.P.Poenar proposed to adopt MEMS fabrication techniques grating and detector in 1999, with the imagination of both fully-integrated realization spectrometers.On the basis that possible spectrometer architecture and performance are comparatively analysed in depth, Poenar points out: the integration spectrum instrument that adopts microelectric technique to make can provide simply at some chemical substance fully, fast, cheapness, test easily, differentiate and analyze.Calendar year 2001 S.H.Kong etc. adopts the MEMS technology first with black and white diffraction grating and the integrated integration grating spectrometer of having made of thermopile detector first.In their research, utilize two silicon chips to make black-white grating and thermopile detector respectively, then two silicon chips are carried out Si-Si aligning, bonding, realized integrated encapsulation, in the technology of microelectronics compatibility, finished the making of miniature grating spectrograph.Though this design has as much as possible utilized the MEMS technology, still exist some problems in its design.Because what its structure adopted is black-white grating, interfere factor main pole overlapping by force between the unit diffraction factor and unit, the zero level main pole is convertd the overwhelming majority of total luminous energy, and the zero level main pole does not have the beam split ability by force, therefore, most incident light has all been wasted, and this performance to device has great influence.
Summary of the invention
The object of the invention is to utilize the MEMS technology, proposes a kind of miniature integrated grating spectrometer and method for making based on blazed grating and thermopile detector.Its advantage is: volume is small, Stability Analysis of Structures, good reproducibility, with low cost etc., all has wide practical use in fields such as modern science experiment, biological study, medical science and medical research, industrial and agricultural production, national defence, astronomical predictions.
The principle of work of grating spectrograph of the present invention is as follows: incident light enters spectrometer through optical window, impinges perpendicularly on blazed grating, through the blazed grating beam split, diffraction on infrared eye, thereby the photodetection of different wave length is come out.
According to Fig. 1 (b) thus shown in, the miniature integrated grating spectrometer of made of the present invention is by with the integrated in order device that forms specific function of combining of cover plate, thermal reactor array chip and grid chip.Incident light enters spectrometer through the light hole 4 of cover plate 1, the angle that the slit that is formed by the light hole 8 on light hole on the cover plate 14 and the thermal reactor chip 2 limits incident light at one more among a small circle; Incident light is by after blazed grating 9 beam split, arrive thermal reactor chip 2, the relative position between thermal reactor chip 2 and the grid chip 3 need be through well-designed, thereby guarantee to have only the infrared light reflection arrival thermopile detector of certain or certain several specific wavelength, produce voltage signal, read through amplification.
Described cover plate 1 comprises light hole 4 and the shallow slot 6 that a two sides erodes away, thereby reaches the restriction light path, the purpose that shielding is disturbed.For fear of the influence of parasitic light, surface sputtering has the high-reflectivity metal film thereon, as Au, Ag or Al etc.Guaranteed like this thermal reactor 5 received have only from back surface incident through the quasi-monochromatic light after the beam split.The shallow slot 6 of cover plate 1 lower surface is for fear of the contacting of cover plate 1 and thermal reactor 5, and forms electrical short or hot short circuit.Cover plate 1 size makes that than hot core sheet 2 undersized the stem 11 on the thermal reactor chip 2 can be exposed, and the convenient gold wire of making realizes that electricity is interconnected; Cylindrical microlenses or diffraction microlens can be laid in light hole position on the cover plate.
Dielectric film 7 on the described thermal reactor chip 2 is in order to realize that heat isolates, and reduces the heat interchange of heat energy on the thermal reactor 5 and surrounding environment and designs; Thermal reactor 5 is positioned at above the dielectric film 7; 12 of support frames play the effect of supporting the light path between whole membrane structure and control blazed grating 9 and the thermal reactor 5 simultaneously; High-reflectivity metal film 13 is positioned on the dielectric film 7, has reduced to have improved the antijamming capability of device from the influence to film temperature of all band light source of light hole 4 incidents; Light hole 4 corresponding control incident light incident angles on light hole 8 on the thermal reactor chip 2 and the cover plate 1; Thermal reactor 5 is as infrared eye, and its structure is positioned on the dielectric film fully, and 11 of its stems are positioned on the support frame, and the convenient gold wire of making is drawn detectable signal.Both constitute for monox, silicon nitride or they for dielectric film 7.
Described blazed grating 9 proposes " a kind of based on { infrared blazed grating structure and method that 100} crystal face silicon ingot is made " patent (ZL200410025197.0 by the inventor, 2004.6.16) make, specifically, adopt the particular crystal orientation silicon wafer to manufacture, its structure must take into account manufacture difficulty simultaneously and function designs, corresponding mutually with the horizontal range and the vertical range of thermal reactor 5, thereby the peak power of the infrared light of specific wavelength just in time can be reflected on the film surface in thermal reactor 5 hot junctions, for improving reflectivity, its surface sputtering has golden reflectance coating 10.But the blacking of infrared eye surface is to improve ir-absorbance.
The miniature integrated grating spectrometer of made of the present invention, the thermal reactor 5 on the thermal reactor chip 2 can be made single or hundreds of according to using the needed number of channel.The determining positions of the required wavelength that its position is obtained by grating beam splitting.Should calculate the spectroscopic distance of grating in advance, thermal reactor (5) is placed certain location,, wherein also will consider the distance between thermal reactor, to reduce the signal cross-talk of each interchannel to accept the radiation luminous energy of specific wavelength.
The miniature integrated grating spectrometer of made of the present invention, three chip blocks adopt the wafer level packaging mode to encapsulate earlier after completing respectively, are diced into device one by one afterwards, carry out the encapsulation of device level again.The employing of two-stage packaged type had both helped improving alignment precision very much, thereby guaranteed product quality, can protect easily impaired film portion again, improved yield rate.In wafer level packaging, can adopt point gum machine point glue to aim at bonding, perhaps adopt photoetching type BCB glue lithography alignment bonding, to guarantee the precision of the critical size in the design.
Concrete processing step of the present invention is:
A. cover plate is made
Adopt the corrosion of one or many double-sided alignment photoetching and KOH or Tetramethylammonium hydroxide anisotropic etchant, obtain a reach through hole and a shallow slot, the alignment mark when photoetching alignment mark gives over to follow-up wafer level packaging;
B. thermal reactor chip manufacturing
1) silicon chip surface chemical vapor deposition silicon dioxide and silicon nitride and polysilicon, and in polysilicon, inject the boron ion, to form P type polycrystalline silicon material;
2) utilize the silicon dioxide of polysilicon surface to make mask, the photoetching post-etching goes out the pattern of polysilicon, as the right part of thermocouple;
3) oxidation protection polysilicon layer, and etch fairlead;
4) adopt stripping technology to make the metal film of titanium platinum, form thermal reactor structure and reflectance coating part;
5) alloying;
6) protect front shaped structures, the monox at the photoetching and the etching back side, silicon nitride or the film that they are combined to form form pattern;
7) the silicon nitride pattern that utilizes the back side is as mask, and KOH or Tetramethylammonium hydroxide anisotropic etchant corrosion body silicon materials until removal fully, thereby discharge film, form film and supporting construction;
C. grid chip is made
1) customizes the silicon chip that special crystal orientation single or double polishes according to designing requirement;
2) photoetching utilizes the KOH anisotropic etch to go out smooth groove as grating;
3) utilize repeatedly oxidation technology that the connecting portion between groove is fined away;
4) sputter obtains the golden film of high reflectance, increases efficient;
D. wafer level packaging
1) the above-mentioned chip that has prepared is arranged in order, utilizes point gum machine programmed point glue; Perhaps successively at cover plate lower surface and grid chip upper surface spin coating photoetching type BCB glue, and photoetching development;
2) move on on the litho machine, utilize the alignment mark that stays in the cover plate manufacture craft to aim at, and clamping;
3) send into the bonding stove bonding that is heating and curing;
E. scribing
The disk that bonding is good is scratched one by one, after the device isolation, along this groove switch out, takes out redundance, exposes stem, so that make gold wire.
F. device level encapsulation
Single device is installed in the standard shell one by one, fixing, and beat gold wire signal is guided on the pin.Level Hermetic Package.
The miniature integrated grating spectrometer of made of the present invention is realized the high-level efficiency beam split of infrared light by utilizing blazed grating, and infrared thermopile detector is finished the detection of different wave length infrared light, utilizes microelectronic technique that both are integrated, realizes the spectrometer characteristic.Characteristics such as the spectrometer of making has that volume is small, Stability Analysis of Structures, good reproducibility, cost are low all have important economy and social value in fields such as space flight, geology, chemistry, biology, medicine and metallurgy.
Description of drawings
Fig. 1 is the schematic diagram and the assembly structure figure of system.
Fig. 1 (a) is a systematic schematic diagram, after the perforate on incident light process cover plate and the film, is reflected by optical grating diffraction, finally arrives thermal reactor, thereby is absorbed, the output electric signal.
Fig. 1 (b) is the wiring layout of three chip blocks, and it is installed according to order among the figure, and relative position is got by calculated in advance, and realizes by the alignment mark on the silicon chip is auxiliary.
Fig. 2 is the synoptic diagram of each ingredient of device. Comprising cover plate 1,3 three parts of thermal reactor chip 2 and grid chip.
Fig. 2 (a) is the composition structure of cover plate 1, mainly is made of light hole 4 and shallow slot 6.
Fig. 2 (b) is the composition structural drawing of thermal reactor chip 2, and it mainly comprises thermal reactor 5, film 7, light hole 8, support frame 12, reflectance coating 13, polysilicon strip 14, gold thread 15 and stem 11 compositions.
Fig. 2 c is the composition structural drawing of grid chip 3, and it mainly comprises blazed grating 9 and reflectance coating 10.
Fig. 3 has increased the lenticular cover plate synoptic diagram of refractive, and its upper surface hot melt circumfluence method etching has with photoresist been made a refractive cylindrical microlenses 16, is used for incident light is assembled.
Embodiment
Carry out the making of cover plate 1, thermal reactor chip 2 and grid chip 3 according to the structure of the provided by the invention miniature integrated grating spectrometer shown in Fig. 1 b, then assemble.
(A) making of cover plate
1) get<100〉two throwing silicon chips, oxidation forms the 2000nm silicon dioxide layer.
2) the photoetching development oven dry is aimed in front gluing photoetching development oven dry, reverse side gluing.
3) normal temperature BOE corrosion is 25 minutes, and cleaning is removed photoresist.
4) 50 ℃ of KOH corrosion is 25 hours, connects fully to light hole.
5) at front sputtering sedimentation titanium 20nm, platinum 100nm and golden 200nm, to improve reflectivity.
(B) making of thermal reactor chip
1) take N type<100〉the two silicon chips of throwing in crystal orientation, adopt standard cleaning program clean surface, remove organic and inorganic and metal pollutant.Two surfaces at silicon chip deposit 250nm silicon dioxide, 150nm silicon nitride and 3500nm polysilicon in order successively with LPCVD (low-pressure vapor phase chemogenic deposit).
2) the boron ion of injection energy 50kev dosage 9E15 in the polysilicon forms P type polycrystalline silicon material, dried oxygen annealing in 40 minutes, and when the injection ion was distributed again, the oxide layer of the about 160nm of growth one deck also eliminated stress.
3) BOE corrosion 120 seconds after the photoetching obtains the silicon dioxide pattern as mask, and the back 50 ℃ of KOH solution corrosions 20 minutes of removing photoresist are produced polysilicon strip, as the right part of thermocouple.BOE corrosive liquid proportioning is HF:NH
4F:DI=3ml:6ml:9ml, DI are deionized water.
4) take out remaining silica, the oxide layer of thermal oxide 350nm is as the dielectric protection layer polysilicon layer.
5) photoetching and with BOE corrosion 280 seconds obtains fairlead, and removes photoresist.
6) photoetching forms thick glue pattern, and ion beam sputtering is titanium deposition 20nm, platinum 100nm and golden 200nm successively, and acetone soaked 4 hours, ultrasonic removal photoresist with and top metal film, absolute ethyl alcohol is replaced acetone, deionized water rinsing.Final thermal reactor structure and the reflectance coating part of forming.
7) 400 ℃ of alloyings of nitrogen protection stove are 30 minutes, form alloy to reduce resistance.
8) back side photoetching, the front gluing is protected shaped structures, and the silicon nitride film at the 15 minutes back side of ion beam etching is opened corrosion window.
9) the silicon nitride pattern that utilizes the back side is as mask, and the body silicon materials are removed in 80 ℃ of corrosion of 20%TMAH solution 23 hours fully from the back side, thereby discharge film, form film and supporting construction.
(C) making of grid chip
1) the preparation surface is the silicon chip of special crystal face, as to depart from silicon<111〉29.49 ° of crystal faces<113〉crystal face as the surface, twin polishing.
2) with silicon chip 350nm, in its front gluing photoetching, the backsizing protection, normal temperature BOE corrosion surface silicon dioxide 300 seconds, and remove photoresist.
3) utilize KOH solution anisotropic etch characteristic, corrode after 30 minutes, obtain some and stop to corrode the triangular form groove of formation automatically along two<111〉crystal face, be blazed grating; The remaining silica layer was removed in the BOE corrosion in 400 seconds.
4) silicon dioxide layer of oxidation 800nm thickness again, and most oxide layer was gone in the BOE corrosion in 10 minutes.
5) repeat above-mentioned 4) step 2 to three time, the junction between adjacent two grooves of grating becomes the pinnacle by the plane.
6) surface sputtering titanium deposition 20nm, platinum 100nm and the golden 200nm of grating are arranged at silicon chip, to improve reflectivity.
(D) encapsulation
1) the grid chip upper surface that has prepared is spin coating tackifier AP3000 and photoetching type BCB glue 10 μ m successively, and photoetching development, remove the glue-line on the blazed grating, 80 ℃ of drying glues 5 minutes.
2) grid chip and thermal reactor array chip are arranged in order move on on the litho machine, utilize the alignment mark that stays in the IC technology to aim at, and clamping.
3) send into the bonding stove and be heated to 250 ℃ of curing bondings 0.5 hour.
4) at cover plate chip lower surface spin coating tackifier AP3000 successively and photoetching type BCB glue 5 μ m, and photoetching development, remove the glue-line on the blazed grating, 80 ℃ of drying glues 5 minutes.
5) the grating of part bonding-thermal reactor chipset and cover plate are arranged in order, and put into litho machine and aim at and clamping.
6) send into the bonding stove and be heated to 250 ℃ of curing bondings 1 hour.
7) bonding is good chipset pastes blue film, section.
8) gluing being affixed in the standard pipe shell of single chip point that will divide, 150 ℃ of drying glues 50 minutes are added a cover after the cooling.