Abstract:
The specification teaches a device for use in the manufacturing of microelectronic, microoptoelectronic or micromechanical devices (microdevices) in which a contaminant absorption layer improves the life and operation of the microdevice. In a preferred embodiment the invention includes a mechanical supporting base, and a layer of a gas absorbing or purifier material is deposited on the base by a variety of techniques and a layer for temporary protection of the purification material is placed on top of the purification material. The temporary protection material is compatible for use in the microdevice and can be removed during the manufacture of the microdevice.

Description:
REFERENCE TO OTHER RELATED DOCUMENTS 
     This application is a divisional of U.S. patent application Ser. No. 10/211,426, filed Jul. 19, 2002 now U.S. Pat. No. 7,180,163, which claims priority under 35 U.S.C. 119 to two Italian Applications: MI-2001-A-001557, filed Jul. 20, 2001, and MI-2002-A-000689 filed Apr. 2, 2002, both of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present invention relates to a support for manufacturing microelectronic, microoptoelectronic or micromechanical devices with integrated deposit of gas absorbing material. 
     Microelectronic devices (also called integrated electronic circuits, or ICs) are the base of the integrated electronics industry. Microoptoelectronic devices comprise, for example, new generations of infrared radiation (IR) sensors which, unlike traditional ones, do not require cryogenic temperatures for their operation. These IR sensors are formed of an array of semiconductor material deposits, for example silicon, arranged in an evacuated chamber. Micromechanical devices (better known in the field under the definition “micromachines” or referred herein as MMs) are being developed for applications such as miniaturized sensors or actuators. Typical examples of micromachines are microaccelerometers, which are used as sensors to activate automobile airbags; micromotors, having gears and sprocket wheels of the size of a few microns (μm); or optic switches, wherein a mirror surface on the order of a few tens microns can be moved between two different positions, directing a light beam along two different directions, one corresponding to the “on” condition and the other to the “off” condition of an optical circuit. In the following description, these devices will also all be referred to within the general definition of solid-state devices. 
     ICs are manufactured by depositing layers of material with different electric (or magnetic) functionalities on a planar then selectively removing them to create the device. The same techniques of depositions and selective removal create microoptoelectronic or micromechanical device construction as well. These devices are generally contained in housings formed, in their turn, with the same techniques. The support most commonly used in these productions is a silicon “slice” (usually referred to as a “wafer”), about 1 mm thick and with a diameter up to 30 cm. On each of these wafers a very high number of devices may be constructed. At the end of the manufacturing process individual devices, in the case of micromachines, or part, in the IR sensor case, are separated from the slices using mechanical or laser means. 
     The deposition steps are carried out with such techniques as chemical deposition from vapor state, (“Chemical Vapor Deposition” or “CVD”); or physical deposition from vapor state (“PVD”, or “Physical Vapor Deposition”) The latter is commonly known in the art as “sputtering.” Generally, selective removals are carried out through chemical or physical attacks using proper masking techniques, and such techniques are well-known in the field and will not be discussed here except as they relate specifically to the invention. 
     The integrated circuits and the micromachines are then encapsulated in polymeric, metallic or ceramic materials, essentially for mechanical protection, before being put to final use (within a computer, an automobile, etc.). In contrast, IR radiation sensors are generally encapsulated in a chamber, facing one wall thereof”, transparent to the IR radiation and known as a “window.” 
     In certain integrated circuits it is important to be able to control the gas diffusion in solid state devices. For example, in the case of ferroelectric memories, hydrogen diffuses through the device layers and can reach the ferroelectric material, which is generally a ceramic oxide, such as lead titanate-zirconate, strontium-bismuth tantalate or titanate, or bismuth-lanthanum titanate. When the hydrogen reaches the ferroelectric material, it can alter its correct functioning. 
     Still more important is gas control and elimination in IR sensors and in micromachines. In the case of IR sensors, the gases which may be present in the chamber can either absorb part of the radiation or transport heat by convection from the window to the array of silicon deposits, altering the correct measurement. In the case of micromachines, the mechanical friction between gas molecules and the moving part, due to the very small size of the latter, can lead to detectible deviations from the device&#39;s ideal operation. Moreover, polar molecules such as water can cause adhesion between the moving part and other parts, such as the support, thus causing the device&#39;s failure. In the IR sensors with arrays of silicon deposits or in the micromachines, it is therefore fundamental ensure the housing remains in vacuum for the whole device life. 
     In order to minimize the contaminating gas in these devices, their production is usually conducted in vacuum chambers and pumping steps are performed before the packaging. However, the problem is not completely solved by pumping because the same materials which form the devices can release gases, or gases can permeate from outside during the device life. 
     To remove the gases entering in solid state devices during their life the use of materials that can sorb these destructive gases may be helpful. These absorptive materials are commonly referred to as “getters,” and are generally metals such as zirconium, titanium, vanadium, niobium or tantalum, or alloys thereof combined with other transition elements, rare earths or aluminum. Such materials have a strong chemical affinity towards gases such as hydrogen, oxygen, water, carbon oxides and in some cases nitrogen. The aborptive materials also include the drier materials, which are specifically used for moisture absorption, which usually include the oxides of alkali or alkaline-earth metals. The use of materials for absorbing gases, particularly hydrogen, in ICs, is described for instance in U.S. Pat. No. 5,760,433, by Ramer et. al. Ramer teaches that the chemically reactive getter material is formed as part of the process of fabricating the integrated circuit. The use of getters in IR sensors is described in U.S. Pat. No. 5,921,461 by Kennedy et. al. Kennedy teaches that a getter is deposited onto preselected regions of the interior of the package. Finally, the use of gas absorbing materials in micromachines is described in the article “Vacuum packaging for microsensors by glass-silicon anodic bonding” by H. Henmi et al., published in the technical journal Sensors and Actuators A, vol. 43 (1994), at pages 243-248. 
     The above references teach that localized deposits of gas absorbing materials can be obtained by CVD or sputtering during solid-state device production steps. However, this procedure can be costly and time consuming if done during the solid-state manufacturing CVD or sputtering process. This is because gas absorbing material deposition during device production implies the step involved in localized deposition of the gas absorbing or getter material. This is generally carried out through the steps of resin deposition, resin local sensitization through exposure to radiation (generally UV), selective removal of the photosensitized resin, gas absorbing material deposition and subsequent removal of the resin and of the absorbing material thereon deposed, leaving the gas absorbing material deposit in the area in which the photosensitized resin had been removed. Moreover, depositing the gas absorbing material in the production line is disadvantageous because there are an increased number of steps required in the manufacturing process. Increase deposits, in turn, require that more materials be used, which also significantly increases the risk of “cross-contamination” among the different chambers in which the different steps are carried out. Also, there is a possible increase of waste products because of contamination. 
     SUMMARY 
     The present invention solves some of the above-described problems of the prior art and, in particular, simplifies the manufacturing process for solid-state devices. The present invention includes a device for use in manufacturing microelectronic, microoptoelectronic or micromechanical devices (herein also referred to as ‘microdevices’) with an integrated deposit of gas absorbing or purification material. In one embodiment, the invention is formed of a base which includes the function of a mechanical backing, a continuous or discontinuous deposit of a gas absorbing material on a surface of said base, and a layer totally covering said gas absorbing material deposit, made with a material compatible with the production of microelectronic, microoptoelectronic or micromechanical devices or parts thereof. The invention shares many of the same manufacturing properties as standard silicon wafers or other semiconductor materials and therefore can be used in many of the same manufacturing processes as these materials. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described below with reference to the drawings in which: 
         FIG. 1  shows a perspective, partially cut-out view of a first possible embodiment the invention as a support; 
         FIG. 2  shows a perspective, partially cut-out view of a second possible support according to the invention; 
         FIG. 3  shows a cross section of one embodiment of the invention to represent a particular final end product using an embodiment of the invention; 
         FIG. 4  is a single microdevice as cut from the full support; 
         FIG. 5  shows an alternate embodiment of the invention for use with micromechanical devices with a channel to the purification material; 
         FIG. 6  shows the alternate embodiment in  FIG. 5  with a covering layer; 
         FIG. 7  shows a second alternate embodiment of the invention; 
         FIG. 8  is another alternate embodiment of the invention where the manufacturing layer of  FIG. 2  has passages cut into it; 
         FIG. 9  is another alternate embodiment of the invention for use in a micromechanical device; 
         FIG. 10  is the individual microdevice shown from  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     For purposes of clarity, the drawings show supports as represented with an exaggerated height-diameter ratio. Such exaggerations are for illustration purposes only and are not intended to reflect any particular limitations on the actual dimensions of the invention. Moreover, in the drawings supports are always represented with a wafer geometry, that is a low-disk of material, because this is the geometry commonly adopted by the producers of solid state devices, but such geometry could be also different without departing from the scope of the invention, for example square or rectangular. 
     Referring now to  FIG. 1 , a partially cut-out view of a first embodiment of the invention, a support for use in the manufacture of a microdevice, is shown. The support  10  includes a base layer  11 . One of the functions of the base layer  11  includes the function of mechanical backing of the entire support  10  and the devices which are subsequently manufactured on it. The thickness of the support  10  is generally on the order of one millimeter and is nearly comprised entirely from the thickness of the base layer  11 . In one embodiment of the present invention on the surface  12  of the base layer  11  there is a continuous intermediate layer  13  of a gas absorbing or cleansing (also referred to herein as purification) material,  14 , whose upper surface is covered with a manufacturing layer  15 , which is generally a substrate material  16  compatible with an integrated circuit or micromechanical device production process, both embodiments which are produced on the upper surface  17  of the manufacturing layer  15 . The material of the base layer  11  can be a metal, a ceramic, a glass or a semiconductor, and is silicon in a preferred embodiment. 
     The purification material  14  can be any known material chosen among the materials commonly referred to as either: (1) the getters, which are capable of sorbing various gas molecules, and/or (2) the driers (or drier materials), which are used specifically for moisture absorption. Although in an alternate embodiment both materials can be used, in a preferred embodiment only one of these materials is used. 
     In the scenario where the cleansing material  14  is solely a getter material which in one embodiment is either (1) a metal chosen among the group of Zr, Ti, Nb, Ta, V; or an alloy among these metals or (2) among these and one or more elements, chosen from among Cr, Mn, Fe, Co, Ni, Al, Y, La and rare-earths, such as binary alloys Ti—V, Zr—V, Zr—Fe and Zr—Ni, ternary alloys Zr—Mn—Fe or Zr—V—Fe or alloys with more components. Preferred getter materials for this application are titanium, zirconium, the alloy having weight percentage composition Zr 84%-Al 16%, produced and sold by the Applicant under the trade name St 101®, the alloy having weight percentage composition Zr 70%-V 24.6%-Fe 5.4%, produced and sold by the Applicant under the trade name St 707® and the alloy having weight percentage composition Zr 80.8%-Co 14.2%-TR 5% (wherein TR stands for a material that is selected from the following group: rare-earth, yttrium, lanthanum or mixtures thereof), produced and sold by the Applicant under the trade name St 787®. A cleansing or purification layer  13  which is a getter material layer can be obtained on the base material layer  11  by different techniques, such as evaporation, deposition from metallorganic precursors, or by techniques known in the field as “laser ablation” and “e-beam deposition.” However, in a preferred embodiment, the getter material is obtained by sputtering. 
     In an alternate embodiment, the cleansing material  14  is one of the drier materials. These materials are preferably chosen from among the oxides of alkali or alkaline-earth metals, which is preferably calcium oxide, CaO, which is used in a preferred embodiment as it does not pose safety or environmental problems during the phases of production, use or disposal of devices containing it. An intermediate layer  13  of oxide may be obtained for instance through the so-called “reactive sputtering” technique, depositing the alkali or alkaline-earth metal of interest under an atmosphere of a rare gas (generally argon) in which a low percentage of oxygen is present, so that the metal is converted to its oxide during deposition. 
     The intermediate layer  13  can have a thickness within the range of about 0.1 and 5 μm. Thickness values lower than 0.1 μm, result in the gas sorption capacity of the intermediate layer  13  being excessively reduced, while thickness values greater than the preferred embodiment of 5 μm, requires deposition times which are extended without providing any additional sorption properties for the intermediate layer  13 . 
     The manufacturing layer  15  is chosen from one of the materials which are usually used as substrate in solid-state device production. In one embodiment, this material can be a so-called “III-V material” (for example, GaAs, GaN or InP), but is silicon in a preferred embodiment. The manufacturing layer  15  can be obtained on the intermediate layer surface  14  by sputtering, by epitaxy, by CVD or by other techniques which are well-known by those skilled in the art. The thickness of manufacturing layer  15  is generally less than 50 μm and within the range of about 1 to 20 μm in a preferred embodiment. The manufacturing layer  15  performs two functions: (1) it protects the gas absorbing material from the contact with gases until the purification material  14  is exposed by partial and localized removal of manufacturing layer  15 , and (2) acts as an anchorage for the layers which are subsequently deposed it to construct ICs, microoptoelectronic devices or MMs. In one embodiment, the manufacturing layer  15  can be itself the layer in which these microdevices are formed. For example, the moving parts of a micromachine can be obtained in the manufacturing layer  15  by removal of sections of the layer. The upper surface of manufacturing layer  16  can also be treated so as to modify its chemical composition, for example forming an oxide or a nitride. 
       FIG. 2  shows an alternate embodiment of the invention as represented partially in a cut-out view, (like  FIG. 1 , the lateral dimensions of the various deposits on the base of gas absorption material are exaggerated for the sake of clarity and should not be considered limitations of this alternate embodiment). The support  20  comprises a base layer  21 . In areas  22 ,  22 ′, . . . of the base layer surface  23 ) discrete deposits,  24 ,  24 ′, . . . of a gas absorbing material  25  are formed. The discrete deposits  24 ,  24 ′, . . . are then covered with a manufacturing layer  26  of substrate material  27 . Base layer  21  is of the same kind and size of base layer  11  of support  10  in the first embodiment. Analogously, materials  25  and  27  in the alternate embodiment are respectively of the same kind of materials  14  and  16  in the first embodiment, which are described above. 
     Purification material deposits  24 ,  24 ′, . . . are generally as thick as intermediate layer  13  of the support  10  in the first embodiment. These deposits  24 ,  24 ′, . . . are, however, discrete, and have lateral dimensions generally lower than 2000 μm in the length and width dimensions These dimensions are variable within wide ranges depending on the final use of the microdevice. For example, if the device taught by the invention is expected for use in an ICs, the lateral dimensions will be within the range of a few microns or less, while if the invention is used in MMs, these dimensions can be comprised between a few tens and a a couple of thousands of microns. 
     The manufacturing layer  26  has a variable thickness, which is thinner in the areas over purification material deposits  24 ,  24 ′, . . . , and thicker in the areas cleared from these deposits. The manufacturing layer  26  adheres to the base layer surface  23  in these areas which are clear from the purification material deposits. The thickness of the manufacturing layer  26  in the areas over the purification material deposits  24 ,  24 ′, . . . has the same values of manufacturing layer  15  of the support  10  in the first detailed embodiment, while in areas not located over the purification material deposits  24 ,  24 ′, . . . , its thickness will be increased by the thickness of these deposits. To help promote adherence, the manufacturing layer  26  can be made with the same material of base layer  21 . In a preferred embodiment, the preferred combination is silicon (which may include mono- or polycrystalline depending on the manufacturing needs for the microdevice) for base layer  21 , and silicon grown through epitaxy for manufacturing layer  26 . However, those skilled in the art would appreciate that other combinations of appropriate materials can be used for these layers which would adhere to each properly, such as the family of GaAs semiconductors. 
       FIGS. 3 and 4  show an embodiment of the invention for use of the support  10  in IC production. On the upper surface of manufacturing layer  17  of the support  10  as shown in the first embodiment, formed of the manufacturing layer  15  (which is made of silicon in preferred embodiment), solid-state microelectronic circuits, numbered as elements  30 ,  30 ′, . . . are formed. These circuits  30 ,  30 ′, . . . are obtained) techniques which are known to those skilled in the art and do not need to be discussed here. The support  10  of the first embodiment is then cut along dotted lines shown in  FIG. 3 , to obtain single ICs devices, which is illustrated in  FIG. 4 , and shows an integrated circuit  40  obtained on a part of the support  10  of the first embodiment which has integrated, (which may be considered “buried”) under surface  17 , an intermediate layer of gas absorbing material  14 . This intermediate layer  13  is capable of sorbing gases, especially hydrogen, which may diffuse through the different layers of the device, thus preventing or reducing the contamination of the integrated circuit  40 . 
     In a second alternate embodiment the invention is used for micromachine production. On manufacturing layer surface  17  of the support are produced structures, which are listed in  FIG. 5  as micromachine elements  50 ,  50 ′, . . . , which comprise the mobile parts of the micromachine. When the production of the micromachine elements  50 ,  50 ′, . . . (including leads for the electric connection of every single micromachine with the outside, which are not shown in the drawing) is finished, the support is subjected to a localized removal operation of manufacturing layer  15 , in areas of manufacturing layer surface  17  which are cleared from said structures, thus forming passages  51 ,  51 ′, . . . , which expose the gas absorbing material  14 ; then a covering element  60  is placed over the treated support  10 , which is shown in  FIG. 6 . 
     The covering element will be realized, generally, with the same materials of base layer  11  and it should be made easily fixable to manufacturing layer surface  17  (for example silicon is used in a preferred embodiment). The covering element  60  can have hollows,  61 ,  61 ′, . . . , corresponding with areas wherein, on support  10 , structures  50 ,  50 ′, . . . , have been obtained and portions of intermediate purification material layer  13  have been exposed. In particular, each of these hollows will be configured such that when support  10  and covering element  60  are fixed together, a space  62  is obtained wherein a micromachine element like  50 ,  50 ′, . . . , and a passage  51  giving access to purification material  14  are contained, so that this latter is in direct contact with the space  62  and is able to sorb gases which may be present or released during time into the space  62 . Finally, single micromachines are obtained by cutting the assembly made up of support  10  and element  60  along their adhesion areas. 
     In another alternate embodiment of the invention, during the micromachine production process summarized above, the localized removal of manufacturing layer  15  is carried out before the manufacturing steps of the micromachine elements  50 ,  50 ′, 
       FIG. 7  illustrates yet another embodiment of the invention which is made by a variation of the process outlined above. In this embodiment, which is depicted as micromachine  70 , the support of the invention is used as a covering element  60 . In this case, the substrate on which the micromachine is formed in a traditional manner as known by those skilled in the art, without the integrated purification (gas absorbing) layer. The support  10  of the invention is subjected to a localized removal treatment of manufacturing layer  15 , thus forming at the same time a hollow  71  constituting space  72  for housing mobile structure  73 , and the passage giving access to material  14 . 
       FIGS. 8 and 9  illustrates the use of a support  20  in the alternate embodiment of the invention. Although only a micromachine is illustrated in this family of figures, in another alternate embodiment this can clearly be used with an integrated circuit. The alternate support  20  is subjected to a localized removal treatment of manufacturing layer  26  in correspondence to purification material deposits  24 ,  24 ′, . . . , thus obtaining on the support passages  80 ,  80 ′, . . . , as shown in section in  FIG. 8 , ready for the sequence of steps for micromachine production. Moving micromachine structures, elements  90 ,  90 ′, . . . , are then formed on this support. Microdevice assembly  101  is an alternate embodiment of the invention. A covering element  100  is fixed to the support  20 , in the areas cleared from moving micromachine structures  90 ,  90 ′, . . . and from passages  80 ,  80 ′, . . . , finally, by cutting assembly  101  along lines (dotted in figure) comprised in adhesion areas between support  20  and element  100 , the micromachine  110  shown by  FIG. 10  is obtained. 
     In the alternate embodiment of the invention which uses the support of type  20  with the discrete getter deposits  24 ,  24 ′, . . . , the support  20  must be produced with the final application in mind. This is because, in case of the micromachines, it is important to know the lateral size of the moving structures ( 50 ,  50 ′, . . . ,  73  or  90 ,  90 ′ . . . ) as well as the lateral size of the hollows ( 61 ,  61 ′, . . . or  71 ) to be produced next, so the designer will be able to correctly define the lateral size and reciprocal distance of deposits  24 ,  24 ′, . . . . This consideration is important in order to assure that the hollows giving access to the gas absorbing material do not interfere with moving structure, but also that they are contained in the perimeter of space  62  or  72  wherein the micromachine is housed. This correct sizing can be carried out by obtaining, from final circuits producers, drawings, even preliminary, of devices to be produced on support  20 . 
     The invention is applicable to microdevices or solid-state device of any type which can benefit from an internally deposed gettering layer as defined by the invention. A microdevice is described as any of microelectronic, microoptoelectronic, or micromechanical device. However, any small-scale device which requires purification for contaminants which passes through the device substrate or channels cut into the substrate layer, which allow a purification layer to capture these contaminants will benefit from the scope and spirit of the invention and the invention should not be limited to only the three types of applications recited, but rather be defined by the claims below.