Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
  • B81B7/00—Microstructural systems; Auxiliary parts of microstructural devices or systems
  • B81B7/0032—Packages or encapsulation
  • B81B7/0035—Packages or encapsulation for maintaining a controlled atmosphere inside of the chamber containing the MEMS
  • B81B7/0038—Packages or encapsulation for maintaining a controlled atmosphere inside of the chamber containing the MEMS using materials for controlling the level of pressure, contaminants or moisture inside of the package, e.g. getters
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L23/00—Details of semiconductor or other solid state devices
  • H01L23/02—Containers; Seals
  • H01L23/10—Containers; Seals characterised by the material or arrangement of seals between parts, e.g. between cap and base of the container or between leads and walls of the container
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L23/00—Details of semiconductor or other solid state devices
  • H01L23/16—Fillings or auxiliary members in containers or encapsulations, e.g. centering rings
  • H01L23/18—Fillings characterised by the material, its physical or chemical properties, or its arrangement within the complete device
  • H01L23/26—Fillings characterised by the material, its physical or chemical properties, or its arrangement within the complete device including materials for absorbing or reacting with moisture or other undesired substances, e.g. getters
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/0001—Technical content checked by a classifier
  • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01079—Gold [Au]

Definitions

• the invention relates to a structure comprising a closed cavity in a controlled atmosphere in which at least one device and a getter comprising at least one getter layer are arranged, the cavity being delimited by a substrate and a closure cap.
• the vacuum integration allows many devices, for example microelectronic, such as microelectromechanical systems (MEMS or "Micro Electro Mechanical Systems” in English) to improve their performance.
• MEMS microelectromechanical systems
• the use of a vacuum encapsulation causes many problems, including the holding in time of the vacuum level and the quality of the encapsulated atmosphere.
• non-evaporable getter materials (NEG or "Non Evaporable Getter” in English) deposited in thin layers have been the subject of numerous publications. These materials react and capture many gases with which they are in contact by formation of an oxide, a hydride or simply by surface adsorption. In this way, the desorption of the materials delimiting a cavity under vacuum is compensated by the getter material layer which adsorbs and / or absorbs the desorbed elements of the other materials.
• the integration of non-evaporable getter materials within an encapsulation structure has in particular been described in patent US6923625. This patent describes the use, on a substrate, of a getter comprising a reactive layer covered by a protective layer.
• the protective layer prevents the reactive layer from reacting with the outside environment at room temperature.
• the reactive layer of the getter acts only from its activation temperature, the temperature at which the atoms of the reactive layer diffuse through the protective layer and absorb some of the gases from the external environment.
• the activation temperature is an intrinsic characteristic of the getter material.
• the known mono or multilayer getters have an absorption or adsorption capacity which is limited to a determined temperature range.
• the stresses can be thermal, it is then necessary to obtain the match between the activation temperature of the getter material and the process of forming a closed cavity by sealing, for example two substrates on a joint.
• the getter material must be able to withstand the gaseous atmospheres that are used during the formation of the device while being reactive when using the device in its closed cavity.
• WO 03/028096 describes the production, on a substrate, of a thin film getter which is constituted by a titanium film deposited on a palladium film.
• the titanium getter film is formed on an electromagnetic shielding layer made of aluminum or copper.
• the object of the invention is to provide a structure in which the getter has optimum pumping capacity in a desired temperature range.
• this object is achieved by the fact that an adjustment sub-layer of the activation temperature of the getter layer is located between the getter layer and the substrate and / or the closure cap on which it is formed and in that the getter layer is constituted by a plurality of elementary getter layers of different compositions disposed above the adjustment sub-layer.
• the invention also relates to a method for producing such a structure.
• FIG. 1 is a diagrammatic sectional view of a structure according to the prior art
• FIGS. 2 and 3 represent, in schematic view, in section, structures according to the invention
• FIG. 4 shows a schematic sectional view, the stack of a multilayer getter of a structure according to the invention.
• a structure 1 that can be a microelectronic chip conventionally comprises at least one device 3, for example of the microelectronic type, arranged in a sealed cavity delimited by two substrates 2 and 4 and by a closed peripheral sealing gasket 5. .
• the sealing of the cavity is ensured by the seal between the substrates and surrounding the device 3.
• the microelectronic device 3 is, for example, formed on the first substrate 2.
• the cavity is generally in depression with respect to the outside atmosphere, preferably under vacuum or under a controlled pressure of nitrogen or argon.
• the height of the cavity is defined by the height of the seal 5 surrounding the device 3 ( Figure 1).
• the second substrate 4 may be structured so as to form a cover having a thinner central portion, so as to increase the volume of the cavity.
• the second substrate 4 is, for example, silicon, oxidized silicon or nitride or glass.
• the first substrate 2 is, for example, silicon or any other semiconductor material, with the exception of gallium arsenide (GaAs), or else another material on which a device already formed can be integrated.
• GaAs gallium arsenide
• the structure 1 comprises a closed and sealed cavity which is delimited by the substrate 3 and by an encapsulation layer 11.
• the tightness of the structure is then ensured by the adhesion between the encapsulation layer 11 and the substrate 2.
• the encapsulation layer then plays the role of a closure cap as the substrate 4 of Figure 1.
• the closure cap may comprise other layers in addition to the encapsulation layer.
• the height of the cavity is defined by the thickness of a sacrificial material 12 deposited on the substrate.
• the cavity comprises at least one getter 6, on at least one of its internal walls.
• the getter 6 is of multilayer type and comprises at least one adjustment sub-layer 8 located between one of the substrates 2 or 4 and a getter layer 7 which conventionally constitutes the adsorbent and / or absorbent layer.
• the getter layer 7 is, for example, a metal material chosen, preferably, so as to have a high nitrogen pumping capacity, this gas is commonly used during the encapsulation of the devices. If the getters 6 have, between them, different activation temperatures, it is advantageous to distinguish them for example in getters 6a and additional getters 6b ( Figures 3 and 4) or first 6a and second 6b getters.
• the getter 6 is formed on the substrate 2.
• a hanging underlayer 9 is advantageously deposited on the substrate 2 before the adjustment sub-layer 8.
• the underlayer 9 is intended to allow better adhesion of the adjustment sub-layer 8 on the substrate 2.
• the hooked underlayer 9 is typically made by any suitable technique, for example in titanium or zirconium and has a thickness advantageously between 20 and 100 nm.
• the adjustment sub-layer 8, located beneath and in contact with the getter layer 7, is intended to make it possible to modulate the activation temperature of the getter layer, that is to say to modulate the temperature at which the getter layer reacts with the atmosphere present inside the cavity.
• the adjustment sub-layer 8 is preferably Cu, Ni, Pt, Ag, Ru, Cr, Au, Al and has a thickness of preferably between 50 and 500 nm when the thickness of the getter layer 7a is of the order of several hundred nanometers, typically between 100 and 2000 nm.
• the thickness of the adjustment sub-layer can be reduced to a few tens of nanometers, typically between 10 and 90 nm, when the getter layer 7a is a few hundred nanometers, typically between 100 and 900 nm.
• an adjustment sub-layer 8 of 30 nm is sufficient for a getter layer 7a of 300 nm.
• the minimum thickness of the adjustment sub-layer 8 is approximately between 5% and 10% of the thickness of the getter layer 7a, for example equal to 8%.
• the adjustment sub-layer 8 is, for example, made of a metallic material, with the exception of palladium, deposited in the form of a pure body which, like platinum, for example, is chemically neutral vis-à-vis -vis the getter layer 7 in the desired activation domain.
• the adjustment sub-layer 8 may also be made of a material that becomes neutral or becomes a trap for certain chemical species, for example oxygen, after interaction with the getter layer 7.
• the adjustment sub-layer 8 may also be of a material which has a high chemical affinity for one or more chemical elements among carbon, oxygen and nitrogen.
• the underlayer may, for example, be chromium or aluminum. In the latter case, the aluminum underlayer 8 serves to protect the getter layer 7 when it is exposed to the ambient air, thus increasing the storage time of the getter without altering its properties, because the underlayment 8 avoids the growth of an oxide layer.
• This architecture is particularly advantageous for obtaining constant pumping capacities after exposure to ambient air for several months.
• Activation temperature gettering stack constituted by a sub-layer 8 of aluminum and a titanium getter layer 7a is about 400 0 C.
• a protective layer 10 may be disposed on the getter layer 7 to protect the getter.
• the getter 6 can maintain its pumping capacity after prolonged exposure to the ambient air or be protected from aggressive technological processes that could degrade it.
• a thin layer of chromium acting as a protective layer 10 can be used on the getter layer 7.
• thickness of the protective layer 10, for example chromium may be between 10 and 50nm, and preferably equal to 20nm.
• the addition of a protective layer 10 contributes to slightly increase the activation temperature of the getter, typically about twenty degrees Celsius for a layer of 20nm in Chrome.
• a regeneration pre-treatment can easily be implemented.
• the regeneration pretreatment consists in exposing the getter under a secondary vacuum, advantageously at a pressure of the order of 10 7 mbar or under a partial pressure of a neutral gas not absorbed by the getter and at a temperature close to its activation temperature for a period that allows it to absorb the layer that degrades its pumping capacity.
• the getter is then cooled to room temperature, typically a temperature close to 20 ° C.
• room temperature typically a temperature close to 20 ° C.
• the getter is exposed to a known gas, preferably nitrogen, which will adsorb to the surface and thus temporarily protect the getter vis-à-vis the ambient air.
• a temperature of 35 ° C. is applied for a few hours to regenerate all the getters 6a described in the present invention.
• sacrificial getters deposited on the entire surface of a substrate.
• the sacrificial getter is chosen to have an activation temperature lower than that of the getter 6 (or getters 6a, 6b) which must be processed during the regeneration pre-treatment.
• the sacrificial getter is then used to improve the quality of the vacuum in the enclosure.
• the getters can thus be subjected to oxidizing atmospheres with which they react and then be regenerated as described above.
• these oxidizing atmospheres are generated during technological steps, in particular the steps of removing a sacrificial layer of polymer resin.
• the getter material 7 is subjected to such oxidizing atmospheres.
• the getter 6a and the device 3 are encapsulated by a sacrificial resin 12 and then by an encapsulation layer 11.
• the sacrificial resin is shaped, for example, by heating before the deposition of the encapsulation layer 11.
• the device and the getter are released from the sacrificial resin layer 12 from orifices made in the encapsulation layer 11.
• the sacrificial resin 12 may be a standard resin of positive polarity used in photolithography and or a resin of negative polarity of polyimide type. These resins can both be destroyed with a heat treatment in an oxidizing atmosphere. It is therefore particularly interesting to choose a getter 6 composed of at least one underlayer 8 and at least one getter layer 7 such that the activation temperature is greater than the baking temperature of the sacrificial resin. In this way, it avoids polluting the getter by the contaminants from the polymer and thus reduce or even cancel its pumping capacity.
• This embodiment is particularly advantageous for the manufacture of MEMS and Infra-Red detectors for burning the resin layers on which are built elements of the microdevice and its encapsulation layer.
• the getter materials are generally exposed to a generally oxidizing dry process in order to improve the propensity of the substrate on which the getter is deposited at the direct sealing. This treatment thus contributes to increasing the adhesion energy between the two substrates which delimit the cavity when they come into contact.
• a protective layer 10 made of chromium is then recommended.
• the sub-layer 8 preferably has a coefficient of thermal expansion substantially comprised between 5.10 "6 Z 0 C and 20.10" 6 / ° C or 23.10 "6 / ° C for aluminum and a ratio its production temperature Te and its melting temperature Tf (in kelvin) substantially between 0.1 and 0.3
• the activation temperature of the associated getter layer 7 is then an increasing function of the coefficient of expansion, of the adjustment sub-layer 8 and the Te / Tf ratio and varies in a decreasing manner with the melting temperature of the adjustment sub-layer 8. It is known that the coefficient of expansion of the metals decreases when the temperature of the fusion said metal increases.
• the deposition is carried out at a temperature close to room temperature on a silicon substrate.
• the effect of the adjustment sub-layer 8 on the getter layer 7 can be interpreted as follows.
• the getter effect in a metal material deposited in a thin layer occurs by diffusion of the adsorbed chemical species into the interior of the layer.
• the getter effect is therefore related to the microstructure, that is to say to the size, shape and orientation of the grains that make up the metallic material.
• Absorption of chemical species from the surface into the getter occurs by diffusion along the grain boundaries. This corresponds to a thermally activated phenomenon that occurs at relatively low temperature, compared to a diffusion of species in the grains.
• the structures most likely to have a getter effect are therefore those for which the grains are columnar and small, thus favoring diffusion at the grain boundaries.
• the structure of the deposit depends to a large extent on the ratio between the temperature of the substrate, that is to say the elaboration temperature (Te), on which the metal is deposited and the melting temperature of the latter (Tf), the ratio Te / Tf (in degrees Kelvin).
• Te elaboration temperature
• Tf melting temperature of the latter
• Te / Tf in degrees Kelvin
• a ruthenium sub-layer will therefore have a finer microstructure, and therefore more grain boundaries, than an aluminum under-layer.
• the growth of the getter layer 7 on the underlayer 8 is partly controlled by the mobility of the getter material atoms on the surface of the adjustment sub-layer 8.
• a ruthenium underlayer 8 could by its microstructure ( preferential germination of the getter layer 7 at the grain boundaries, triple nodes or between the domes of the underlying structure) and / or its high melting temperature limit the surface migration of the getter metal and thus lead to a structure of this ci thinner than in the opposite case or the getter layer 7 is deposited on aluminum.
• the getters 6 can be divided into at least getters 6a and additional getters 6b.
• the getter comprises a getter layer 7 constituted by at least two elementary layers 7a and 7b.
• the getter adjustment sub-layer 6a has, for example, a grain structure greater than the portion of the adjustment sub-layer of the additional getter 6b.
• the grains of the adjustment sub-layer 8 of the getter 6a are larger than the grains of the adjustment sub-layer 8 of the additional getter 6b.
• the adjustment sub-layer 8 being situated between the getter layer and the substrate 2, it also makes it possible to eliminate the chemical interactions between the substrate 2 and the getter layer 7. Thus, the pumping capacity of the getter layer 7 is preserved.
• the getter layer 7 deposited on the adjustment sub-layer 8 is, for example, Ti or Zr and has a thickness between 100 and 2000 nm.
• the activation temperature of the getter layer, without the action of the adjustment sub-layer 8, is greater than 425 ° C. and close to 450 ° C. With the action of the adjustment underlayer 8 , the activation temperature of the getter layer 7 varies according to the nature of this adjustment sub-layer 8.
• the activation temperature of the getter layer 7, made of titanium or zirconium, can vary increasingly substantially between 275 and 425 ° C according to the adjustment sub-layer 8.
• Table 1 gives, by way of example, a few activation temperature values of a getter 6 according to the nature of its adjustment sub-layer 8, for a getter layer 7 made of titanium. All the deposits are produced by evaporation on a silicon substrate at an identical elaboration temperature Te, close to the ambient temperature.
• the microstructure of the zirconium deposit must be finer than that of titanium.
• the activation temperatures presented in Table 1 should therefore be substantially lower with a zirconium getter sublayer than with a titanium getter layer.
• the getter layer 7 is advantageously constituted by the stacking of a plurality of elementary getter layers, preferably two, 7a, 7b, of different chemical compositions.
• the elementary getter layers are deposited one above the other on the adjustment sub-layer 8.
• the first elementary getter layer 7a, in contact with the the adjustment sub-layer 8 has an activation temperature greater than that of the second elementary getter layer 7b which covers it.
• the elementary getter layers 7a, 7b have a decreasing activation temperature as they move away from the underlayer 8.
• the first elementary getter layer 7a in contact with the adjustment sub-layer 8, is preferably of titanium and has a thickness of preferably between 100 and 1000 nm.
• the use of two different elementary getter layers 7a, 7b is particularly advantageous for repackaging the chip during its lifetime by activation of the first layer 7a.
• the adjustment sub-layer 8 of the multilayer getter may be chosen so as to increase the reflectivity of the getter to infrared radiation, typically when the getter is chosen to be reflective to infrared radiation (for certain specific applications).
• This reflective function is advantageously chosen, depending in particular on the nature of the material of the adjustment sub-layer 8 which is advantageously made of copper or aluminum. For example, in a bolometer, this reflectivity is sufficient to place the getter as an IR reflector.
• the getter 6 has another essential function: IR reflector. If the layer is made of titanium, it already has some reflectivity to infrared radiation. The use of a sub Adapted adjustment layer then makes it possible to increase the reflectivity to infrared radiation to the entire getter.
• the multilayer getter 6 comprising at least the adjustment sub-layer 8, the getter layer 7 and possibly the hooked underlayer 9 can be made anywhere in the cavity and for example on the substrate 2 or 4 before or after formation of the microelectronic device 3. Such a getter 6 can also be formed on the two substrates 2 and 4 delimiting the cavity.
• the hooked underlayer 9 is advantageously deposited by any suitable technique, preferably by evaporation on the substrate 2.
• the adjustment sub-layer 8 and then the first and second elementary getter layers (7a, 7b) are then deposited successively. , advantageously by evaporation, on the underlayer hooked 9.
• the deposits of the different layers are made within the same deposition equipment.
• the hooked underlayer 9 can contribute to improving the quality of the vacuum in this deposition chamber, when the material forming this layer (for example Ti or Zr) has getter properties.
• the getter 6 can be structured in a conventional manner, for example by lithography and dry etching, advantageously by a non-reactive plasma and / or wet, so as to precisely locate the areas in which the getter layers 7 are desired.
• the adhesion of the positive resin used for the lithography on the getter layer 7 can be improved, if necessary, by providing an adhesion promoter, advantageously hexamethyldisilazane (HDMS).
• HDMS hexamethyldisilazane
• the layers 7, 8, 9 and 10 are etched from usual liquid chemical reagents and / or by a neutral plasma depending on the materials used.
• the getter 7 and protection layers 10 wet and the rest of the neutral plasma stack when the wet etching of the adjustment sub-layer is not easy, for example for platinum and ruthenium.
• the two etching modes can also be used when there is incompatibility between the etching reagents of the different layers. This incompatibility can lead to phenomena of over-etching or even alteration of certain layers.
• the step of removing the positive resin and optionally all or part of the promoter may be performed by a conventional product used in the microelectronics industry and advantageously followed by cleaning with fuming nitric acid, when the latter does not affect the underlayer 8. Finally, a dry etching with a non-reactive plasma allows, if necessary, to eliminate pollutants or residues from previous technological steps and present on the surface of the getter layer 7.
• the getter can also be structured during the deposit by a lift-off process.
• a photosensitive dry film of negative polarity is laminated to the substrate.
• the dry film having a thickness of between 5 and 50 ⁇ m, advantageously equal to 15 ⁇ m, is insulated and developed according to a conventional photolithography step.
• the assembly is then subjected to secondary vacuum treatment to remove development residues.
• the deposition of the getter is then carried out, for example, by spraying, advantageously by evaporation.
• the removal of the unexposed dry film is carried out by means of a specific product, which does not modify the properties of the getter material.
• the production methods described above it is possible to successively produce several getters 6, having different activation temperatures on the same substrate and / or in the same cavity.
• the structuring of the getter 6 is performed by chemical etching, it is advantageous to deposit and structure the different sub-layers 8 adjustment of different getters.
• the getter layer 7 is then deposited and then structured by chemical etching. Since the adjustment layer 8 and the getter layer 7 are not made immediately afterwards and in the same equipment, it is preferable to use a regeneration pretreatment as described above.
• the structuring of the getter 6 is performed by detachment, it is possible to make successive deposits of getters 6, by rolling a dry film on a getter already formed. It is then possible to adjust, in the same structure, the activation temperature of several different getters.
• the pumping capacity of each getter in terms of the number of moles adsorbed or absorbed can be controlled, which makes it possible to modulate the pressure inside the cavity that contains the getters.

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• 2007
  • 2007-10-15 FR FR0707212A patent/FR2922202B1/fr not_active Expired - Fee Related
• 2008
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