CN1295138C - Thin film minibridge structure and its mfg. method - Google Patents

Abstract

The present invention discloses a thin film minibridge structure and the manufacture method thereof. Bridge legs and the bridge floor of the thin film minibridge structure are made of composite films of silicon oxide and silicon nitride, and are positioned in the same plane; one end of each bridge leg is connected with the bridge floor, and the other end is erected on metal bridge piers; the bridge floor is supported by the bridge legs and the bridge piers to suspend on a backing, and a cavity is formed between the bridge floor and the backing. The method comprises the following steps: a light-sensitive polyimide film is coated on the surface of the backing, photolithography treatment is carried out then to form solitary islands and bridge pier holes, and then imidization treatment is carried out; the bridge pier holes are filled with metal; silicon oxide and silicon nitride films are successively deposited on the solitary islands and the metal bridge piers to form a composite film layer; a minibridge structure pattern is photo-etched on the composite film layer to the polyimide film layer to form patterns of bridge floor and bridge legs; in addition, the polyimide film at the bottom of the patterns of the bridge floor and the bridge legs are removed to form a minibridge structure. The present invention solves the problem of stress concentration caused by the bending of bridge legs, and obtains a composite film with less stress.

Description

A kind of preparation method of film micro-bridge structure

Technical field

The invention belongs to micro-electromechanical system field, be specifically related to a kind of preparation method of film micro-bridge structure.

Background technology

After the conspicuous Xu Er of Britain physicist in 1800 had found infrared ray, because infrared ray has and can penetrate that night, spissatus and dense smoke etc. are surveyed and the special ability of imaging, infrared acquisition just became an important research content of researcher.Infrared Detectors is divided into two classes: photon detector and thermal detector.Photon detector has very high sensitivity, but need could operate as normal under all relatively large refrigerator of volume and power consumption is assisted.And thermal detector operate as normal at room temperature, need not refrigerator assists, compare with the photon type Infrared Detectors, have that volume is little, in light weight, price is low and lot of advantages such as simple to operate, can be used for military field and civil areas such as public security fire-fighting, vehicle night vision, anti-stealing safety and medical diagnosis under many non-harsh sensitivity requirements, be with a wide range of applications and market prospects.

Micro-metering bolometer is the size of reacting the incident infra-red radiation by variation that measurement is integrated in the thermistor on the detector.The temperature rise of detector is to be directly proportional with thermal resistance between substrate with detector.Because the energy of infra-red radiation is very little, in order to obtain bigger detectable signal, improve the detector signal to noise ratio, often utilize the high thermal resistance between micro-bridge structure realization detector and substrate.U.S. Honeywell research center is through after studying for many years, reported the non-refrigeration micro-metering bolometer of the multiple model that they develop the nineties at twentieth century, wherein noise equivalent temperature difference reaches 0.039 ℃ at the 8-12 mu m waveband, can realize medium wave and LONG WAVE INFRARED imaging (Wood, R.A., " High-performance Infrared ThermalImaging with monolithic silicon Focal planes operating at Room Temperature ", IEEE onIEDM, pp.175-177,1993.).The core texture of this detector is exactly the film micro-bridge structure with high heat resistance characteristic, and this structure utilizes a kind of polymer as sacrificial layer material, utilizes the low stress nitride silicon thin film as structure sheaf, and the thermal conductance after the Vacuum Package and between substrate is 2 * 10 ^-7W/K, has good heat insulation characteristics (Cole, B.E., etc, " Monolithic two-dimensional arrays of micromachined microstructures forinfrared applications " Proceedings of the IEEE, 86 (8), pp.1679-1686,1998).But the micro-bridge structure of Honeywell center development does not have the integrated bridge pier structure, but utilizes the bridge leg of two inclinations that bridge floor is supported on the silicon substrate, and the bridge leg of this bending is easy to generate stress and concentrates, and causes the damaged and device yield decline of micro-bridge structure.

Summary of the invention

The objective of the invention is to overcome above-mentioned micro-bridge structure weak point, a kind of preparation method of film micro-bridge structure is provided, this method has solved because the stress that the bending of bridge leg causes is concentrated the problem of the detector decrease in yield that causes.

The preparation method of film micro-bridge structure provided by the invention, its step comprises:

1., clean substrate surface, and carry out surface active;

2., at the thick photosensitive polyimide film of substrate surface spin coating one deck 1-5 μ m;

3., Kapton is carried out photoetching treatment, form Kapton isolated island and bridge pier hole, carry out imidization again and handle;

4., with metal filled bridge pier hole;

5., on Kapton isolated island and metal bridge pier cvd silicon oxide and silicon nitride film successively, form the THIN COMPOSITE rete, silicon oxide thickness is 0.1-1 μ m, silicon nitride thickness 0.1-1 μ m;

6., carve the micro-bridge structure figure, this THIN COMPOSITE rete of etching forms bridge floor and bridge leg figure to polyimide film layer, and removes the Kapton of bridge floor and bridge leg figure bottom with oxygen plasma, forms micro-bridge structure at above-mentioned THIN COMPOSITE rete glazing.

What the inclination bridge leg structure that adopts with the Honeywell research center was different is, bridge leg structure among the present invention and bridge deck structure are in same horizontal plane, article two, bridge leg one end links to each other with bridge floor, and other end frame has solved owing to the crooked problem of stress concentration that causes of bridge leg on two metal bridge piers.

When the stress level in microbridge bridge floor and the bridge leg structure is too high, can causes the micro-bridge structure buckling deformation, and then cause the detector decrease in yield.In order to improve the detector yield rate, the micro-bridge structure of Honeywell research center development has adopted a kind of low stress nitride silicon thin film as bridge leg and bridge deck structure thin-film material, but, be difficult to strict control because the stress and the preparation technology of silicon nitride film are closely related.In order to address this problem, the present invention has adopted the stress equilibrium technology, utilizes the compression of silica membrane to come the tensile stress of balance silicon nitride film, can obtain to have the laminated film than low stress.Compare with silicon nitride film, the laminated film that silicon nitride and silica are formed has lower thermal capacitance and thermal conductivity coefficient, is more suitable for being used for the making of film micro-bridge structure.

Description of drawings:

Fig. 1 is the structural representation of film micro-bridge structure.

Fig. 2 is the vertical view of Fig. 1.

Fig. 3 is the manufacture craft flow chart of micro-bridge structure.

The specific embodiment

As shown in Figure 1, 2, bridge leg 2,3 and bridge floor 1 adopt silica and silicon nitride laminated film to make, the two is positioned at same plane, one end of bridge leg 2,3 links to each other with bridge floor 1, other end frame is on metal bridge pier 4,5, bridge floor 1 is supported and suspended on the substrate 7 by two bridge legs and two bridge piers, between bridge floor 1 and substrate 7, constitutes cavity 6.

Bridge floor 1 is by bridge leg 2,3 and metal bridge pier 4,5 and 7 formation of substrate heat passage, utilize this micro-bridge structure can obtain low thermal conductance near the infra-red radiation limit, therefore the heat that only needs to absorb seldom just can detect small thermal radiation signal easily so that whole micro-bridge structure obtains bigger temperature rise.Bridge leg 2,3 and bridge floor 1 are in same horizontal plane, have avoided owing to the crooked stress that causes of bridge leg is concentrated.The bridge floor of design is made of film, and the thermal capacitance of whole micro-bridge structure is also very little, so just can reduce the thermal time constant of this structure.The thermal time constant of micro-bridge structure is generally several milliseconds to tens milliseconds, can with the frame frequency compatibility of reading circuit.This structure also is applicable to the occasion that needs high thermal resistance structure in the fields such as infrared image generator and Detection of Weak Signals.

Example 1

32 * 32 battle array micro-bridge structures on silicon and quartz substrate, have been designed and produced.The micro-bridge structure parameter is as shown in table 1.

Table 1 micro-bridge structure parameter list

Structural parameters	Numerical value
		Array scale micro-bridge structure size bridge floor thickness activity coefficient microbridge height	32×32 100×100μm 2 0.6μm 0.25 2μm

The technological process that utilizes surperficial sacrifice layer process to manufacture micro-bridge structure also can be described below as shown in Figure 3:

A) as Fig. 3 (A): substrate 7 surface clean and activation.Clean substrate 7 surfaces, remove the surface and stain.In order to improve the adhesiveness of Kapton, before spin-on polyimide, activation processing is carried out on substrate 7 surfaces with oxygen plasma to substrate 7.

B) as Fig. 3 (B): spin coating photosensitive polyimide film 8.Spin coating photosensitive polyimide film 8 on the standard sol evenning machine can be selected the rotating speed of different sol evenning machines according to thickness requirement.

C) as Fig. 3 (C): light-sensitive polyimide photoetching and imidization.Utilize ultraviolet photolithographic machine photoetching Kapton, form Kapton isolated island 9 and bridge pier hole 10.Subsequently Kapton is placed on and carries out imidization in the annealing device of blanketing with inert gas and handle.The imidization representative temperature is 200-400 ℃, and the imidization time is 30-120 minute.

D) as Fig. 3 (D), fill bridge pier hole 10, form metal bridge pier 4,5.Utilize corrosion, peel off or chemical plating process with metal filled bridge pier hole 10, formation metal bridge pier 4,5.

E) as Fig. 3 (E): preparation structure sheaf laminated film 11.The laminated film that the structure sheaf film selects for use silica and silicon nitride to form.At first utilize CVD or magnetic control film coating equipment to plate the silica membrane of a layer thickness for 100-500nm on Kapton isolated island 9 and metal bridge pier 4,5, preparation one layer thickness is the silicon nitride film of 100-500nm on silica membrane then.

F) as Fig. 3 (F): photolithographic structures layer silica and silicon nitride laminated film 11, remove the polyimide sacrificial layer isolated island 9 of bridge floor 1 and bridge leg 2,3 bottoms.Utilize standard photolithography process to make the micro-bridge structure figure by lithography, and utilize reactive ion etching process etching oxidation silicon and silicon nitride film, expose polyimide sacrificial layer figure isolated island 9.Utilize removing of photoresist by plasma equipment to remove the polyimide sacrificial layer film isolated island layer 9 of bridge floor 1 and bridge leg 2,3 bottoms, micro-bridge structure is suspended, between bridge floor 1 and substrate 7, form cavity 6.

Example 2

The silicon of selecting to have made the CMOS reading circuit is made face battle array micro-bridge structure as substrate.The micro-bridge structure parameter is with table 1.

Integrated micro-bridge structure technology is substantially with example 1 on silicon, but should note following point:

In Fig. 3 (A) step, substrate cleans should select organic cleaning fluid (acetone, methyl alcohol, isopropyl alcohol etc.) for use, can not select for use the mordant Acidity of Aikalinity solution of aluminium read-out electrode (as sulfuric acid, hydrochloric acid, hydrogen peroxide, NaOH etc.) as cleaning fluid;

In Fig. 3 (C) step, Kapton sacrifice layer imidization technological temperature should be controlled at below 400 ℃, in order to avoid the reading circuit performance is caused harmful effect;

In Fig. 3 (E) step, should select low temperature process (as PECVD) when selecting the CVD plated film for use for use, coating temperature should be controlled at below 400 ℃;

In Fig. 3 (F) step, when utilizing removing of photoresist by plasma equipment to remove the bottom thin film sacrificial layer, should note controlling the power of degumming equipment and removing photoresist the time, avoid micro-bridge structure and substrate temperature rise too high.

Summary is got up, and the present invention proposes a kind of miniature the high thermal resistance micro-bridge structure of battle array manufacturing technology.This technology adopts standard micromachined technology, utilize photosensitive polyimide film as sacrificial layer material, utilize silica and silicon nitride double-layer compound film as the low-stress structural layer film, utilize the oxygen plasma dry method technology of removing photoresist to remove thin film sacrificial layer at last, obtained to be suspended in the micro-bridge structure on the silicon substrate.Except that infrared thermal detector, this structure also is applicable to the field that needs high thermal resistance structure in infrared image generator and other Detection of Weak Signals.

Claims (1)

1, a kind of preparation method of film micro-bridge structure, its step comprises:

1., clean substrate surface, and carry out surface active;

2., at the thick photosensitive polyimide film of substrate surface spin coating one deck 1-5 μ m;

3., Kapton is carried out photoetching treatment, form Kapton isolated island and bridge pier hole, carry out imidization again and handle;

4., with metal filled bridge pier hole;

5., on Kapton isolated island and metal bridge pier cvd silicon oxide and silicon nitride film successively, form the THIN COMPOSITE rete, silicon oxide thickness is 0.1-1 μ m, silicon nitride thickness 0.1-1 μ m;

6., carve the micro-bridge structure figure, this THIN COMPOSITE rete of etching forms bridge floor and bridge leg figure to polyimide film layer, and removes the Kapton of bridge floor and bridge leg figure bottom with oxygen plasma, forms micro-bridge structure at above-mentioned THIN COMPOSITE rete glazing.

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