CN102963859A - Testing structure for corrosion time of sacrificial layer and preparation method of MEMS (Micro-electromechanical System) device - Google Patents
Testing structure for corrosion time of sacrificial layer and preparation method of MEMS (Micro-electromechanical System) device Download PDFInfo
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- CN102963859A CN102963859A CN2012104517658A CN201210451765A CN102963859A CN 102963859 A CN102963859 A CN 102963859A CN 2012104517658 A CN2012104517658 A CN 2012104517658A CN 201210451765 A CN201210451765 A CN 201210451765A CN 102963859 A CN102963859 A CN 102963859A
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Abstract
The invention discloses a testing structure for determining the corrosion time of a sacrificial layer in real time. The testing structure comprises a sacrificial layer, an MEMS (Micro-electromechanical System) structural layer and a metal layer which are formed from bottom to top, wherein a metal in the metal layer falls off when the sacrificial layer is corroded. In the testing structure, a dual-material beam is taken as a sensitive element, and testing units are arranged preferably in an array way, so that the reliability of an entire online testing result is improved. A method for preparing an MEMS device by using the structure can be compatible with the conventional sacrificial layer process, the method and the conventional sacrificial layer process can be finished simultaneously, and online monitor of the process is realized. Due to the adoption of the testing structure, the corrosion time of the sacrificial layer can be determined in a non-contact and non-breaking way through a naked-eye observation way, the MEMS process quality and yield can be increased, and the process time is greatly shortened.
Description
Technical field
The invention belongs to microelectromechanical systems (MEMS) processing technology field, be applied in especially MEMS surface sacrificial process field, relate to the test structure of the wet etching time of MEMS surface sacrificial process, and adopt this test structure to prepare the method for MEMS device.
Background technology
Since the nineties, microelectromechanical systems (MEMS) technology has entered the high speed development stage, is not only because concept is novel, and is because the MEMS device is compared with traditional devices, has miniaturization, integrated and prospect characteristics that performance is more excellent.Nowadays MEMS has been widely used in the fields such as automobile, Aero-Space, information control, medical science, biology.MEMS technique mainly is divided into three major types: bulk silicon technological, surface sacrificial process, and some special MEMS processing technologys.
Surface sacrificial process is take silicon chip as matrix, and by multilayer film deposit and the three-dimensional movable micro mechanical structure of figure processing preparation, because the selective height of technique, application is very extensive.The surface treatment development time is the longest, and the material that can select is very abundant.Surface sacrificial process mainly comprises the sacrifice layer deposit, microstructured layers deposit, and sacrifice layer corrosion step.Wherein, sacrifice layer corrosion is divided into again wet method and dry method.Because dry release is higher to the requirement of equipment, the gas of some dry release even be toxic gas, wet method discharges the more general of application.
But wet method discharges and also faces a series of problem, and determining of etching time is exactly one of them.Definite general process of etching time is according to etchant solution corrosion rate and the sacrificial layer material thickness gauge of sacrificial layer material to be calculated an etching time, but because process deviation, can cause the thickness of sacrificial layer material and the difference of corrosion rate, the pattern that covers the microstructured layers of sacrificial layer material top also can affect corrosion rate, so the definite of etching time is difficult to by simple calculative determination.Common processing method is by a plurality of different etching times of many experiments, by the destruction micro-structural of probe contact, to observe release conditions, selects at last a suitable etching time to discharge more chip when wet etching is finished.Definite needs of the etching time of common a collection of chip calculate an etching time scope in advance, several time spans in the selection range, attempt, and the chip of each etching time length all can experience the steps such as sacrifice layer corrosion, displacement and cold-trap and could real " release " finish, and be put into microscopically and observe release conditions, check devastatingly very very long of this stage with probe.With the PSG(phosphorosilicate glass) sacrifice layer be released to example, usually need the BHF(buffered hydrofluoric acid) corroded 20 minutes, use afterwards DI water (deionized water) displacement 3 times, each 30 minutes, again with cyclohexane displacement 3 times, each 30 minutes, replace 3 times with isopropyl alcohol afterwards, still be 30 minutes at every turn, changes to be put in the cold-trap, 2 hours cooling and temperature-rise period, the single test time will be above 5 hours.Contrast the release conditions of the chip of different etching time length, could finally determine the suitable sacrifice layer corrosion time.This way can be destroyed certain chip, reduces yield rate, increases the flow time, is not suitable for the streamline processing of MEMS.
Summary of the invention
The objective of the invention is for the problems referred to above, a kind of online test structure of determining the sacrifice layer corrosion time of surface treatment is proposed, and adopt this test structure to prepare the method for MEMS device, to satisfy the non-demand of determining etching time of noncontact, can improve processing quality and yield rate with destroying.
For achieving the above object, the present invention adopts following technical scheme:
A kind of test structure for determining in real time the sacrifice layer corrosion time comprises sacrifice layer, MEMS structure sheaf and the metal level arranged from bottom to top; Metal in the described metal level comes off when described sacrifice layer corrosion is finished.
A kind of method that adopts above-mentioned test structure to prepare the MEMS device, its step comprises:
1) divides basic chips zone and surveyed area at substrate;
2) adopt surface sacrificial process to make the structure sheaf of sacrifice layer and MEMS device at described substrate;
3) deposited metal on the structure sheaf of described surveyed area;
4) the described sacrifice layer of wet etching determines to etch the time by observing in the described metal level coming off of metal, discharges the MEMS device architecture.
Preferably, mark off basic chips zone and surveyed area at substrate, as shown in Figure 4, implement described step 2 at this surveyed area), (being surveyed area zone in addition) do not implement described step 2 in the basic chips zone).Like this, two material tests structures are finished in detection zone, with the basic chips process compatible.If the body region of chip (being the basic chips zone) also needs to use two material structures and has used metal of the same race (i.e. the MEMS device needs of actual preparation preparation metal level itself); for the metal that prevents agent structure comes off; can increase a photoetching; protect with photoresist this regional metal level, this regional metal problem of coming off can be resolved like this.
The described surface sacrificial process of step 1) mainly comprises: deposit sacrifice layer and graphical sacrifice layer; Deposition structure layer and patterned structures layer.Described sacrifice layer preferably adopts the deposit of low-pressure chemical vapor phase deposition (LPCVD) method, and the material of sacrifice layer is preferably phosphorosilicate glass (PSG); Described structure sheaf preferably adopts the deposit of LPCVD method, and material is preferably polysilicon (Poly-Si); Described metal preferably adopts the method deposit of sputter or evaporation, and material is preferably gold (Au), increases chromium (Cr) thin layer and increases metal adhesion.
Step 2) and step 3) adopt the graphical metal of method of dry method or wet method, adopt reactive ion etching (RIE) patterned structures layer.Step 3) can adopt all chips of the disposable wet etching of wet etching sacrifice layer, need not the test of many times etching time.
Principle of the present invention is to use two Material Cantilever Beam as Sensitive Apparatus.Two Material Cantilever Beam structures are commonly used for the infrared imaging field, and principle is the thermal mismatching formation internal stress by bi-material, makes beam produce distortion.The present invention has namely utilized the significant internal stress of two material structures: at first form two material tests structures by structure sheaf and metal level; Then carry out wet etching, when the moment (when also namely etching) that release is finished, should be sacrificed the microstructured layers of layer pulling because the dissolving of sacrifice layer breaks away from institute's Constrained, produce deformation, the deformation meeting makes two materials from interface weak spot generation interfacial fracture, and the metal in the metal level is come off; These metals that come off drop in the etchant solution, are macroscopic reflective particles with metallic luster, judge to discharge with this and finish.Can judge by the dropping situations of observing two material surface metals whether release is finished, judge namely whether wet etching is finished.
In the described pair of material tests structure, metal is in and is difficult for deformation region.In order to guarantee to observe the metal that comes off, this pair material structure can adopt the mode of array, and namely etching forms a plurality of unit with array format on described structure sheaf and metal level, repeats a lot of test structures, with the come off quantity of metal of increase, such as Fig. 4, shown in Figure 5.So also can reduce the metal that uncertain factor causes comes off.Metal impact owing to dust in deposit such as certain local does not have deposit good, and adhesion is poor, causes being easy to come off in advance.After adopting the mode of array to increase the quantity of the metal that comes off, metal is come off become the behavior of a kind of groups, rather than individual behavior, when observing a large amount of metals and come off, be and etch constantly, the namely release of MEMS structure has been finished.Owing to be the MEMS device, its size is in micron dimension, therefore only has when metal is shed to just can be observed when a certain amount of.
The present invention provides a kind of online method of determining the sacrifice layer corrosion time of surface treatment for the technologist in MEMS field, adopt sacrifice layer process to realize the on-line testing of etching time, there are not the problems such as test of many times and destructive testing in this method, has following advantage:
1. the present invention can determine not need extra destructive testing by etching time accurately, uses when being applicable to produce in batches the MEMS chip.
2. the processing step of the inventive method can be compatible with basic surface sacrificial process, can not affect the reliability of technology of chip, can the making of basic chips do not impacted.
3. the technique of the present invention's design comprises rational architectural feature, has reduced the uncertainty that incident causes, has improved controllability and the accuracy of etching time.
4. the present invention is that the body region of chip also needs to use the situation of two material structures to propose relevant solution, adopts photoresist to prevent that the metal of two material chips from coming off, and does not influence each other before the test structure.
5. method for designing of the present invention and structure can not introduced unnecessary residual stress problems, have improved the reliability of technique.
6. the structure of the present invention's design can be used as a normal structure and is placed on test zone, has reduced the complexity of independent design.
7. the technology difficulty of the structure that comprises of technological process of the present invention is lower, easily obtains higher yield rate.
Test structure of the present invention can with the IC process compatible, can be used in the monitoring in the integrated field of IC-MEMS except the MEMS chip.
Description of drawings
Fig. 1 is the process flow diagram in the specific embodiment, and wherein: Fig. 1 (a) is the schematic diagram of the chip substrate after the LPCVD oxide layer; Fig. 1 (b) is the schematic diagram of lpcvd silicon nitride and PSG; Fig. 1 (c) is the schematic diagram of etching anchor point; Fig. 1 (d) is the schematic diagram of LPCVD polysilicon structure layer; The schematic diagram of the graphical polysilicon of Fig. 1 (e); Fig. 1 (f) is the schematic diagram at test structure district depositing metal; The schematic diagram that Fig. 1 (g) discharges for structure.
Fig. 2 is the schematic diagram of method for releasing contrast, and wherein Fig. 2 (a) is normally used release flow process in the prior art, the method for releasing flow process that Fig. 2 (b) uses for the present invention.
Fig. 3 is the schematic diagram of corrosion step among the embodiment.
Fig. 4 is that test zone is divided schematic diagram.
Test structure top view among Fig. 5 embodiment.
Among the figure: the dotted line left side is the detection architecture district, and the right side is the chip body structural area; 1-substrate; 2-silicon oxide layer; 3-silicon nitride layer; 4-PSG sacrifice layer; 5-structure sheaf; 6-metal level; 7-the metal that comes off; 8-BHF corrosive liquid; 9-isopropyl alcohol; 10-cyclohexane; 11-cold-trap; 12-probe test platform; 13-eye-observation; 14-chip unit; 15-test zone array; 16-two testing of materials construction units; A, B, C-etching time pilot chip (small pieces); D-formally discharge chip (sheet).
The specific embodiment
Below by specific embodiment, and cooperate accompanying drawing, the present invention is described in detail.
Etching time detection method of the present invention mainly is applicable to the MEMS device chip of the movable structure of surperficial sacrifice layer integrated technology processing, as: the actuators such as the sensors such as accelerometer, gyro, tunable capacitor structure.Making the comb teeth-shaped resonator as example, the making of the manufacturing resonator of etching time detection architecture is merged, concrete technological process as shown in Figure 1, wherein the dotted line left side is the detection architecture district, the right side is the chip body structural area, and it is described as follows:
1, standby sheet: monocrystalline silicon substrate is as the substrate of chip;
2, deposit substrate protective layer comprises: LPCVD SiO2, thickness is
Namely form silicon oxide layer 2 among Fig. 1 (a); LPCVD Si3N4, thickness is
Namely form silicon nitride layer 3 among Fig. 1 (b);
3, adopt the MEMS surface sacrificial process to make movable structure, comprising:
A) LPCVD PSG sacrifice layer 4, thickness are 2 μ m, shown in Fig. 1 (b); The photoetching salient point; BHF corrodes PSG
The photoetching anchor point; RIE PSG 2 μ m; Shown in Fig. 1 (c);
B) LPCVD poly-Si structure sheaf 5, thickness are 2 μ m, shown in Fig. 1 (d); Inject P+; Fine and close annealing 950 ℃ done the activation of MOS resonator, and 10min is since 650 ℃ of intensifications;
C) lithographic definition resonant body structure; RIE Poly-Si 2 μ m are shown in Fig. 1 (e);
4, make metal level 6, form two material tests structures, comprising: photoetching; Sputter Cr/Au, thickness is
Stripping photoresist; Alloy (even metal A u, Cr phase counterdiffusion under high-temperature technology) is shown in Fig. 1 (f); Wherein Cr is adhesion layer, adopts alloying technology to increase the adhesion of described structure sheaf and described metal level; In other embodiments, the Cr layer thickness also can be selected other value, as
Also direct sputter Au layer.
5, adopt BHF corrosion PSG, releasing structure is shown in Fig. 1 (g).
Among the above-mentioned preparation method, be used for the structural material of resonator except polysilicon, can select other material; Accordingly, the material of sacrifice layer and corrosive liquid also can be with other material and other solution.
Among the above-mentioned preparation technology, after step 4 was finished, the chip of preparation had comprised comb teeth-shaped resonator part (dotted line right side) and etching time detection architecture part (dotted line left side).The main body of etching time detection architecture is the detection architecture of the sensitivity of two materials of being formed by polysilicon and Au.By step 5, chip is placed in the BHF corrosive liquid, the situation that the visual observations metal comes off (seeing the metal 7 that comes off among Fig. 1 (g)) then can be determined to etch constantly.This pair material tests structural requirement metal is above structure sheaf, and is just passable as long as metal does not stretch out the zone of structure sheaf.
Fig. 2 is the schematic diagram of method for releasing contrast, and wherein Fig. 2 (a) is normally used release flow process in the prior art, the method for releasing flow process that Fig. 2 (b) uses for the present invention.The method of Fig. 2 (a) is processed by BHF corrosive liquid 8, isopropyl alcohol 9, cyclohexane 10, cold-trap 11 successively, then carries out destructiveness at probe test platform 12 and penetrates; The method need to be divided into complete chip a plurality of small pieces (seeing A among the figure, B and C), the etching time that test of many times is different after at last definite time, could be finished release to large stretch of chip D, whole test need to repeatedly be carried out, and is consuming time and need the probe destructiveness to penetrate.And the method shown in Fig. 2 (b) that the present invention proposes is the release that only needs once can finish to large stretch of chip D.
Fig. 3 has provided the test procedure of Fig. 2 (b) in corrosive liquid 8, by visually observing metal 7 dropping situations, can judge that sacrifice layer corrosion can stop, and puts into immediately solution 9, continues the step in Fig. 2 (b).
If the body region of chip also needs to use two materials, for the metal that prevents agent structure comes off, can protect with photoresist this zone, this regional metal problem that comes off also can be resolved like this.This discharges detection method can't cause bad impact to the making of the agent structure of chip.The etching time detecting unit that the release detection architecture of the present invention's design can be used as a standard places in the middle of the layout design, only need to open up the test monitoring zone of small size, can nondestructive high efficiency the determining etching time of finishing of noncontact.
MEMS sacrifice layer process in above-described embodiment only is to have selected the individual layer sacrifice layer process, and select to do the example explanation with the broach resonator, those skilled in the art is to be understood that, in the scope that does not break away from essence of the present invention, can make certain variation and modification for the processing step of device architecture, material selection and preparation method among the present invention, the MEMS sacrifice layer process selects more complicated multilayer sacrifice layer process (comprising a plurality of electrodes of deposit, sandwich construction) also still applicable.Protection scope of the present invention should be as the criterion so that claims are described.
Claims (10)
1. a test structure that is used for determining in real time the sacrifice layer corrosion time is characterized in that: comprise sacrifice layer, MEMS structure sheaf and the metal level arranged from bottom to top; Metal in the described metal level comes off when described sacrifice layer corrosion is finished.
2. test structure as claimed in claim 1, it is characterized in that: described structure sheaf and metal level comprise a plurality of test cells with array format.
3. test structure as claimed in claim 1 or 2, it is characterized in that: described structure sheaf is polysilicon, described metal level is Au.
4. test structure as claimed in claim 1 or 2 is characterized in that: comprise an adhesion layer adjacent with described structure sheaf in the described metal level.
5. test structure as claimed in claim 4, it is characterized in that: the material of described adhesion layer is Cr.
6. method that adopts test structure as claimed in claim 1 or 2 to prepare the MEMS device, its step comprises:
1) divides basic chips zone and surveyed area at substrate;
2) adopt surface sacrificial process to make the structure sheaf of sacrifice layer and MEMS device at described substrate;
3) deposited metal on the structure sheaf of described surveyed area;
4) the described sacrifice layer of wet etching determines to etch the time by observing in the described metal level coming off of metal, discharges the MEMS device architecture.
7. method as claimed in claim 6 is characterized in that: step 3) is also in described basic chips zone deposited metal, and makes with photoresist protective layer as described basic chips zone in step 4).
8. such as claim 6 or 7 described methods, it is characterized in that: etching forms a plurality of test cells with array format on the structure sheaf of described surveyed area and metal level.
9. such as claim 6 or 7 described methods, it is characterized in that: comprise an adhesion layer in the described metal level, adopt alloying technology to increase the adhesion of described structure sheaf and described metal level.
10. such as claim 6 or 7 described methods, it is characterized in that: adopt the low-pressure chemical vapor phase deposition described sacrifice layer of method deposit and described structure sheaf; Adopt sputtering method to prepare described metal level.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN109802649A (en) * | 2018-12-29 | 2019-05-24 | 开元通信技术（厦门）有限公司 | A method of monitoring air-gap type bulk acoustic wave resonator cavity discharges process |
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| CN109802649B (en) * | 2018-12-29 | 2023-04-11 | 开元通信技术（厦门）有限公司 | Method for monitoring cavity release process of air-gap type bulk acoustic wave resonator |
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