Abstract:
A silicon-on-insulator integrated circuit comprises a handle die, a substantially continuous and unbroken silicide layer over the handle die, and a substantially continuous and unbroken first dielectric layer overlying one side of the silicide layer. A device silicon layer having an upper surface overlies the first dielectric layer, and a second dielectric layer on the handle die underlies the opposite side of the silicide layer. Interconnected transistors are disposed in and at the upper surface of the device silicon layer. A silicon-on insulator integrated circuit includes a handle die and a first dielectric layer formed on the handle die. A substantially continuous and unbroken silicide layer is formed on the first dielectric layer; the silicide layer has a controlled resistance and provides a diffusion barrier to impurities. A substantially continuous and unbroken second dielectric layer is disposed between the silicide layer and a device silicon layer, and trenches extend through the device silicon layer and silicide layer and separate the device silicon layer into islands, each having an underlying continuous silicide area. Interconnected transistors are disposed in and at an upper surface of the device silicon layer. A bonded wafer integrated circuit comprised a handle die and a homogeneous silicide layer bonded to the handle die. A device layer is bonded to the silicide layer, and interconnected transistors are disposed in and at a surface of device layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 08/915,841, filed Aug. 21, 1997, now abandoned; which is a continuation of U.S. application Ser. No. 08/681,038, filed Jul. 22, 1996, now abandoned; which is a division of U.S. application Ser. No. 08/351,933, filed Dec. 8, 1994, now U.S. Pat. No. 5,569,620; which is a continuation of U.S. application Ser. No. 07/939,786, filed Sep. 3, 1992, now U.S. Pat. No. 5,387,555, the disclosures of which are incorporated herein by reference. 
     This application is also a continuation of U.S. application Ser. No. 07/834,439, filed Feb. 12, 1992, now U.S. Pat. No. 5,266,135; U.S. application Ser. No. 07/921,197, filed Jul. 28, 1992, now U.S. Pat. No. 5,362,667; and U.S. application Ser. No. 08/430,312, filed Apr. 28, 1995, now U.S. Pat. No. 5,849,627, the disclosures of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to electronic integrated circuits and methods of fabrication, and, more particularly, to dielectrically isolated semiconductor integrated circuits and related fabrication methods. 
     BACKGROUND OF THE INVENTION 
     Integrated circuits fabricated in silicon-on-insulator substrates offer performance advantages including freedom from latchup for CMOS structures, high packing density, low parasitic capacitance, low power consumption, radiation hardness, high voltage operation, and the possibility of three dimensional integration. Indeed, isolation trenches extending through the silicon layer down to the insulation provide a simple approach to dielectric isolation of integrated circuit devices. The sidewalls of such trenches are coated with an insulator, usually silicon dioxide, and the remaining portion of trench opening, if any, is filled with a filler, usually polycrystalline silicon. Diffused PN junctions can also be used for lateral isolation. 
     Additionally, silicon-on-insulator technology using very thin films offers special advantages for submicron devices. Scaling bulk devices tends to degrade their characteristics because of small-geometry effects such as punch-through, threshold voltage shift, and subthreshold-slope degradation. The use of silicon-on-insulator devices suppresses these small-geometry effects. Therefore, even in the submicron VLSI domain, silicon-on-insulator technology can offer even higher device performance over bulk technology, along with the inherent advantages of silicon-on-insulator. 
     Silicon-on-insulator substrates may be fabricated in various ways: a crystalline silicon layer may be formed over an existing oxide layer either by laser or strip heater recrystallization of polysilicon deposited on the oxide, or by selective epitaxial silicon growth over the oxide. However, the quality of such a silicon layer is generally inferior to that normally associated with bulk silicon. Other approaches entail forming an oxide layer beneath an existing high quality silicon layer, either by oxidizing a buried porous silicon layer or by oxygen ion implantation; however, such oxide is low quality, and the silicon top layer may be damaged during the oxide layer formation. 
     Another approach to silicon-on-insulator is wafer bonding, as described by J. Lasky et al., “Silicon-On-Insulator (SOI) by Bonding and Etch-Back,” 1985, IEDM Tech. Deg., 684. This wafer bonding process proceeds as follows: a lightly doped epitaxial layer of silicon is grown on a heavily doped silicon substrate, oxide is thermally grown on the epitaxial layer, a second lightly doped silicon substrate is thermally oxidized, and the two oxidized surfaces are pressed together. See  FIG. 1   a . The pressed together wafers are inserted into an oxidizing atmosphere at 1100° C. to bond them, as illustrated in  FIG. 1   b . Lastly, a preferential etch is used to remove the heavily doped substrate, leaving the thin, lightly doped epitaxial layer above the bonded thermally grown oxides, which are now on the second substrate, as shown in  FIG. 1   c . The resulting thin silicon layer above the thermally grown oxide is of high quality; the oxide also retains its quality and may be either thick, as might be desired for CMOS or high voltage devices, or thin, as might be desired for shared element applications.  FIG. 1   d  heuristically illustrates trench isolation with polysilicon-filled trenches isolating MOSFET and bipolar devices. 
     Conceptually, this process may meet all the desired goals for the ultimate silicon-on-insulator material: a specular finished crystalline silicon layer without dislocations and a back interface with the insulator of quality equal to the interface of thermally grown silicon dioxide on silicon, both the crystalline silicon layer and the insulator being of variable thickness. 
     Another wafer bonding method, illustrated in  FIGS. 2   a-c  and described in U.S. Pat. No. 5,362,667, proceeds as follows: Beginning with a device wafer having a lightly doped epitaxial layer on a heavily doped substrate and a handle wafer with a thick (4,000 A) oxide layer, activate the device wafer surface with an acid or peroxide wash to enhance hydroxyl group formation. Place a drop of oxidant such as water plus hydrogen peroxide on the oxide, and squeeze the wafers together. See  FIG. 2   a . The drop of oxidant has a volume in the range of 0.8 to 8.0 microliters per square inch of wafer surface. After drying the squeezed wafers at room temperature for a day, heat them to 1150° C. for two hours, which causes oxidation of the device wafer and formation of silicon-oxygen bonds to fuse the wafers. See  FIG. 2   b . Lastly, grind and etch the device wafer to expose the epitaxial layer, which completes the silicon-on-insulator substrate, as shown in  FIG. 2   c . For applications that require a thick (10-60 μm) silicon-on-insulator layer and a thicker (e.g., 4 μm) bottom oxide but allow some tolerance in the layer thickness, a slightly simpler process, where a uniformly lightly doped device wafer is thinned by grinding and polishing, can be used. 
     Bonded wafers, however, have problems of high temperature bonding that lead to film stress and delamination. Also, because oxides are poor diffusion barriers to mobile ions such as sodium, bonded wafers with silicon dioxide buried layers are susceptible to contaminant diffusion. Contaminants introduced during the bonding process can easily diffuse to the device layer interface, resulting in electrical instability. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a silicon-on-insulator integrated circuit that comprises a handle die, a substantially continuous and unbroken silicide layer over the handle die, and a substantially continuous and unbroken first dielectric layer overlying one side of the silicide layer. A device silicon layer having an upper surface overlies the first dielectric layer, and a second dielectric layer on the handle die underlies the opposite side of the silicide layer. Interconnected transistors are disposed in and at the upper surface of the device silicon layer. 
     Also in accordance with the present invention is a silicon-on-insulator integrated circuit that includes a handle die and a first dielectric layer formed on tie handle die. A substantially continuous and unbroken silicide layer is formed on the first dielectric layer; the silicide layer has a controlled resistance and provides a diffusion barrier to impurities. A substantially continuous and unbroken second dielectric layer is disposed between the silicide layer and a device silicon layer, and trenches extend through the device silicon layer and silicon layer and separate the device silicon layer into islands, each having an underlying continuous silicide area. Interconnected transistors are disposed in and at an upper surface of the device silicon layer. 
     The present invention is further directed to a bonded wafer integrated circuit that comprises a handle die and a homogeneous silicide layer bonded to the handle die. A device layer is bonded to the silicide layer, and interconnected transistors are disposed in and at a surface of device layer. 
     The present invention provides silicon-on-insulator bonded wafer processing with the features of (1) relatively low temperature bonding by the use of low temperature, about 500-800° C. metal silicidation reactions for bonding; (2) better stress compensation by providing materials in the bonding zone that will produce silicides with coefficients of thermal expansion closely matched to those of the substrate wafers and buried dielectric layers, thereby reducing warpage; (3) limiting contaminant migration by means of a bonding zone that provides a barrier to diffusion of mobile contaminants; (4) simultaneously producing a buried doped layer in the silicon during the bonding process; (5) a conductive, dielectrically-isolated layer at the bonding zone; and (6) a thermally conductive layer at the bonding zone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1   a-d  illustrate in cross-sectional elevation views known wafer bonding methods. 
         FIGS. 2   a-c  illustrate in cross-sectional elevation views a further wafer bonding method. 
         FIGS. 3   a-g  are cross-sectional elevation views of a first preferred embodiment of a wafer bonding method of the present invention. 
         FIGS. 4   a-d  are cross-sectional elevation views of a second preferred embodiment of a wafer bonding method of the invention. 
         FIGS. 5   a-b  show in cross-sectional elevation views a third preferred embodiment of a wafer bonding method of the invention. 
         FIG. 6  is a cross-sectional elevation view of a bonded wafer with diamond buried dielectric in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Silicidation Bonding 
       FIGS. 3   a-f  illustrate in cross-sectional elevation view a first preferred embodiment method of silicon-on-insulator bonded wafer processing. 
     (a) Begin with a four-inch diameter 500 μm-thick silicon device wafer  302  and a comparable diameter 500-μm thick silicon handle wafer  312 . Device wafer  302  has the doping type and resistivity (e.g., N type and 20 ohm-cm resistivity) desired for eventual device fabrication. Thermally oxidize device wafer  302  to form oxide layer  316 . Oxide  316  will become the bottom oxide, so the oxide is grown to the desired bottom oxide thickness, e.g., about 2-4 μm. Alternatively, diamond or silicon nitride (“nitride”) can be deposited on device wafer  302  to form the buried dielectric layer  316 . A diamond thin film  316  can be deposited by a chemical vapor deposition (CVD) reaction of methane and hydrogen, and a nitride thin film can be deposited by decomposition of silane and ammonia. 
     Deposit a 500-angstrom thick polysilicon layer  317  on oxide (or other dielectric)  316 , or deposit a thicker polysilicon layer and polish it down to 500 angstroms. Then deposit a 500-1000- angstrom thick layer platinum  318  on polysilicon  317 ; see  FIG. 3   a . The polysilicon layer can be deposited by silane decomposition, the platinum layer by sputtering. Handle wafer  312  only has native oxide on its surfaces. 
     (b) Press handle wafer  312  and device wafer  302  together, and heat them to 500° C. in a 2-6 hour furnace cycle with a nitrogen or forming gas ambient. This drives platinum  318  to react with silicon  312  and polysilicon  317  to form platinum silicide, PtSi and thereby bind the wafers together. Native oxide on handle wafer  312  dissolves in the PtSi and does not prevent the silicidation. This low temperature bonding depends upon the silicidation reaction and not on thermal oxidation as in the process depicted in  FIGS. 2   a-c . See  FIG. 3   b  showing PtSi layer  315 . The platinum forms silicon-platinum bonds with both device wafer silicon  312  and polysilicon  317 . The deposition of polysilicon  317  on oxide (or other dielectric)  316  had previously formed silicon-oxygen (or silicon-carbon or silicon-nitrogen) bonds and bound polysilicon  317  to oxide (dielectric)  316 . The silicidation of polysilicon  317  retains these silicon bonds and thus binds device wafer  302  to handle wafer  312  through silicon/silicide and silicide/dielectric interfaces. The silicon-platinum bond-forming reaction basically is:
 
Pt+Si−PtSi+heat (16 kcal/mole)
 
Bonded zone PtSi  315  has a thickness of approximately 600-1000 angstroms.
 
     (c) After bonding, remove the bulk of device wafer  302  by grinding, lapping, and polishing to leave the desired device island thickness, e.g., 35-40 μm. This thinning of device wafer  302  proceeds without any etch stop, so the final thickness of device wafer  302  depends upon process control. See  FIG. 3   c . The use of an etch stop permits much smaller device island thicknesses, e.g., about 1 μm. 
     (d) Deposit mask oxide  326  on device wafer  302  to a thickness of about 4 μm. PtSi is stable up to 550° C., so thermal oxidation cannot be used. However, other refractory metals such as cobalt and nickel form suicides that are stable to above 900° C., so thermal oxidation can be used with bonding by such silicides. Mask oxide  326  is used as a trench etch mask; see  FIG. 3   d . Thermal oxidation will also grow oxide  314  on the backside of handle wafer  312 . 
     (e) Print a trench pattern into photoresist spun onto mask oxide  326 . Note that for thermal oxidation, the bottom oxide (or other dielectric)  316  (4 μm), the mask oxide  326  (4 μm) and the backside oxide  314  (4 μm) are all fairly closely matched in thickness during the photoresist patterning, and bond silicide layer  315  is fairly thin. This provides a rough stress balance and limits warpage of the bonded wafers. Alternatively, with PtSi or other silicide with limited temperature stability and deposited mask oxide, the process temperature cycling has had limited excursions, so warpage is not as great a problem. Use the patterned photoresist as etch mask to wet etch (HF) the trench pattern in oxide  326 ; then strip the photoresist and use the patterned oxide  326  to plasma reactive ion etch (REIF) device wafer  302  to form silicon islands  322 ,  323 , . . . on oxide layer  316 . This etch stops on oxide or other dielectric  316 ; see  FIG. 3   e.    
     (f) Strip patterned oxide  326  with a wet etch, which also removes the remaining backside oxide  314  on the back of handle wafer  312 . Then thermally grow or conformally deposit (depending on silicide thermal stability) oxide to a thickness of 4 μm to form isolation oxide  336  on the sides of islands  322 , 323 , . . . This also forms 4 μm of oxide  338  on the island surfaces and 4 μm of backside oxide  346  on handle wafer  312 . Next, deposit polysilicon  348  to fill the trenches. Lastly, planarize to remove the polysilicon except from the trenches; see  FIG. 3   f . Note that again the island surface oxide  338 , bottom oxide  316 , and backside oxide  346  all have about the same thickness (4 μm), which limits warpage resulting from stress differentials. 
     (g) Fabricate devices in the silicon islands. The particular fabrication steps used will depend on the types of devices, interconnection structure, and insulations desired and can include oxide growth and deposition, photoresist patterning, wet and dry etches, diffusions and implants, various material depositions such as polysilicon and nitride, epitaxial layer growth, deposition of various metals such as aluminum and tungsten, and chemomechanical polishing.  FIG. 3   g  schematically shows in expanded cross-sectional elevation view a partially completed MOSFET in island  322 , which would be just one of thousands of such devices in an integrated circuit fabricated on the bonded wafer. 
     An advantage of silicon-on-insulator integrated circuits with devices overlying bottom oxide (or other dielectric)  316  plus bond PtSi (or other silicide) layer  315  rather than just bottom oxide layer  316  alone includes extra charge dissipation along silicide layer  315 , better thermal dissipation in the case of diamond films  316  along silicide  315 , and a silicide diffusion barrier to prevent contaminants from diffusing upward from the handle wafer or bonding zone. In addition, these integrated circuits can be produced on wafers that have much lower thermal budgets as a result of the low temperature wafer bonding or silicidation. This results in less inherent stress, especially in the case of diamond films  316 , and less dopant and contaminant diffusion. 
     Dielectrically Isolated Silicidation Bonding 
       FIGS. 4   a-c  illustrate in cross-sectional elevation view a second preferred embodiment method of bonded wafer processing. 
     (a) Begin with a six-inch diameter 600-μm thick silicon device wafer  402  and a comparable diameter 600-μm thick silicon handle wafer  412 . Device wafer  402 , which has the doping type and resistivity, including any buried layer doping, desired for eventual device fabrication, has a 500-angstrom thick, substantially continuous thermal oxide layer  406 , a 500-angstrom thick polysilicon layer  417 , and a 1000-angstrom thick cobalt layer  418  on its bonding surface. Thermally oxidize handle wafer  412  to form oxide layers  416  and  413 . Oxide  413  will become the bottom oxide, so the oxide is grown to the desired bottom oxide thickness, e.g., 3 μm. Again, alternative bottom dielectrics can be deposited: diamond, nitride, oxynitride, multiple layers of different dielectrics, and so forth. Oxide  416  provides stress compensation to restrain warpage. Deposit a 500-angstrom thick polysilicon layer  414  on oxide (dielectric)  413 ; see  FIG. 4   a . The deposition of polysilicon can be by silane decomposition, the deposition of cobalt by sputtering. 
     (b) Press handle wafer  412  and device wafer  402  together, and heat them to 800° C. in a 2-6 hour furnace cycle with a nitrogen or other inert ambient. This drives cobalt  418  to react with polysilicon  414  and polysilicon  417  to form a substantially continuous layer of cobalt silicide, CoSi 2  and thereby bind the wafers together. This low temperature bonding depends upon the silicidation reaction and not on thermal oxidation, as in the process represented by  FIGS. 2   a-c . See  FIG. 4   b  showing CoSi 2  layer  315 . The cobalt forms silicon-cobalt bonds with both polysilicon  414  and polysilicon  417 . The deposition of polysilicon  417  on oxide  406  had previously formed silicon-oxygen bonds and bound polysilicon  417  to oxide  406 ; similarly, polysilicon  414  is bound to oxide  413 . The silicidation of polysilicon  414  and  417  retains these silicon/oxygen bonds and thus binds device wafer  402  to handle wafer  412  through silicon/oxide and silicide/oxide interfaces. Bonded zone CoSi 2    415  has a thickness of about 600-1000 angstroms. Note that cobalt forms the silicide in preference to reducing the oxide by SiO 2 +Co−Si+CoO 2 . 
     (c) After bonding, remove the bulk of device wafer  402  by grinding, lapping, and polishing to leave the desired device island thickness, e.g., 20 μm. This thinning of device wafer  402  proceeds as in the first preferred embodiment, as does subsequent device fabrication. Because thermal oxide  406  is quite thin, the trench etch will remove it, and the exposed CoSi 2  can then also be removed. Then a trench sidewall oxidation plus conformal oxide deposition will isolate the substantially continuous CoSi 2  layer under each silicon island between the trenches; see  FIG. 4   c.    
     The structure of the second preferred embodiment has the advantage that CoSi 2  layer  415  can act both as a resistor under each silicon island and as a diffusion barrier for impurities diffusing out of bottom oxide (dielectric)  413  during processing. Thin thermal oxide  406  provides the electrical isolation of CoSi 2    415  from its silicon island. Such buried resistors help in three-dimensional integration by allowing vertical integration, thus providing smaller die geometries.  FIG. 4   d  illustrates the use of CoSi 2  as a resistor stacked directly below the silicon island. In particular, contacts to CoSi 2    415  can be made by another trench etch that stops on the silicide followed by oxidation of trench sidewalls and filling with a metal plug  420  such as tungsten. This resistor contact formation may be most convenient with thin silicon islands; that is, when silicon  402  is about 2 μm or less in thickness. The resistance of such resistors can be adjusted by varying the silicide thickness/composition or silicon island size. The structure illustrated in  FIG. 4   d  shows a single transistor. 
     Silicidation Plus Oxidation Bonding 
       FIGS. 5   a-b  illustrate in cross-sectional elevation view a third preferred embodiment of the bonded wafer processing method of the invention. 
     (a) Begin with a six-inch diameter 600-μm thick silicon device wafer  502  and a comparable diameter 600-μm thick silicon handle wafer  512 . Device wafer  502 , which has the doping type and resistivity desired for eventual device fabrication, has a 500-angstrom thick thermal oxide layer  506 , a 500-angstrom thick polysilicon layer  517 , and a 1000-angstrom thick tungsten layer  518  on its bonding surface. Thermally oxidize handle wafer  512  to form oxide layer  513 . Oxide  513  will become the bottom oxide, so the oxide is grown to the desired bottom oxide thickness, e.g., 2 μm. Deposit a 500-angstrom thick polysilicon layer  514  on oxide  513 . The deposition of polysilicon may be by silane decomposition, the deposition of tungsten by sputtering. Place drop  505  of oxidizing aqueous bonding solution of HNO 3  and H 2 O 2  on polysilicon  514 ; see  FIG. 5   a . Drop  505  consists of 20% by volume of a 67% HNO 3  solution and 80% by volume of a 30% H 2 O 2  solution. Drop  505  has a volume of about 0.05 cc, corresponding to about 4.0 microliters per square inch of wafer surface, and theoretically will spread out to a layer with a thickness (if uniform) of 6 μm on polysilicon  514 . Note that drop  505  wets the surface of polysilicon  514 . A drop volume in the range of 4 to 10 microliters per square inch of wafer surface leads to good bonding. 
     (b) Press handle wafer  512  and device wafer  502  together with drop  505  of first preferred embodiment oxidizer on the surface of polysilicon  514 . The pressed together wafers, after being allowed to dry for 24 hours, are heated to 900° C. in a 2-6 hour furnace cycle with an oxidizing ambient. This drives polysilicon  517  to react with tungsten  518  to form tungsten silicide, WSi 2 , and drives oxidizer  505  to react with polysilicon  514  to form silicon oxynitrides (“nitrox”). The tungsten also reacts with the nitrox, thereby binding the wafers if polysilicon  514  is consumed. See  FIG. 5   b . The tungsten forms tungsten-silicon bonds, the nitrate forms both silicon-oxygen and silicon nitrogen bonds, and the water evaporates. The reactions basically are:
 
W+2Si→WSi 2 
 
Si+HNO 3 +H 2 O 2 →Si w O x N y +H 2 O+O 2 
 
The oxidize in drop  505  oxidizes the portion of polysilicon  514  not consumed by the silicidation. This creates a bonded zone with a mixture of nitrox  519  connecting bottom oxide  513  plus handle wafer  512  to silicide  515  plus oxide  506  and device wafer  502 . Bonded zone nitrox  519  has a thickness of about 500-860 angstroms, and silicide layer  515  has a thickness of about 800-1000 angstroms. Of course, increasing the ratio of HNO 3  to H 2 O 2  in oxidizer drop  505  will increase x and decrease y and somewhat increase the thickness of bonded zone nitrox  315 ; decreasing the ratio has a converse effect. If there is a shortage of polysilicon, then the oxidizer oxidizes the silicide:
 
WSi 2 +HNO 3 +H 2 O 2 →Si w O x N y +W z O u N v +H 2 O+O 2 
 
     (c) After bonding, remove the bulk of device wafer  502  by grinding, lapping, and polishing to leave the desired device island thickness and fabricated devices, as with the first preferred embodiment. As with the second preferred embodiment, the silicide layer can be isolated under each silicon island and thereby form a buried resistor. The resistance of such resistors can be adjusted by varying the thickness of the polysilicon and tungsten (or other metal) layers in the initial wafers and/or the size of each of the device islands. 
     Method with Silicides 
     The fourth preferred embodiment method of bonded wafer processing follows the steps of any of the first three preferred embodiments but replaces the metal (platinum, cobalt, and tungsten) with a silicide (or metal plus silicide mixture) that can further react with silicon, for example, the reaction of TiSi and Si to form TiSi 2 . Again, the buried dielectric can be, for example, diamond, nitride, nitrox, and multilayered. 
     Diamond Buried Dielectric 
       FIG. 6  shows a cross-sectional elevation view of a buried diamond structure in which device wafer  602  has diamond film  613  grown, polysilicon then deposited on the diamond, and platinum deposited on the polysilicon. The polysilicon and the handle wafer silicon both react with the platinum to form PtSi  615  to bind the wafers at 500° C., as in the first preferred embodiment. Diamond  613  requires low temperature bonding in order to avoid warpage, and the lack of any oxide layers provides high thermal conductivity from devices in device wafer  602  through diamond insulator  613  and bonding silicide  615  and into handle wafer  612 . Diamond  613  and silicide  615  also provide lateral spreading of heat and limit hot spots in device wafer  602 . The trench isolation in  FIG. 6  includes deposited oxide, again to avoid high temperature processing of diamond film  613 , and polysilicon filling the trench. Devices such as the illustrative field effect transistor can be situated over buried layers that are formed simply by introducing dopants prior to the growth of diamond film  613 ; these dopants do not excessively diffuse during processing because of the small thermal budget used with diamond films. As shown in  FIG. 6 , the buried layer of device wafer  602  abuts the diamond first dielectric layer  613 . 
     Further Modifications and Variations 
     The preferred embodiments can be varied in many ways while retaining the feature of a silicidation reaction for bonding wafers. For example, metal and silicon, or other silicide precursors, can be on one of or both of the device and handle wafers that are brought together to be bonded. In addition, many different refractory metals form various silicides at various temperatures and with various temperature stability ranges. Thus, the type of dielectric and other materials involved and the processing steps to be used in device fabrication will determine thermal budgets and the choice of available silicides. For example, platinum is good for low temperature processing, whereas nickel and tungsten permit higher temperature processing. Also, some metals such as titanium, tantalum, and platinum easily dissolve or penetrate native oxides on wafer surfaces to form suicides, whereas cobalt is notorious for its resistance to silicidation in the presence of native oxides. Note that for many metals the metal migrates in the silicon to form silicides, but for tungsten the silicon migrates in the metal; this difference permits differing bonding zone reaction systems. Lastly, the metal can be chosen to minimize the differences between thermal coefficients of expansion of the silicide, dielectric, and wafers. 
     Device Characteristics 
     Devices and integrated circuits fabricated in silicon-on-insulator of the bonded wafers in accordance with the preferred embodiments of the present invention and then diced have the following beneficial properties: 
     (a) stress compensation due to incorporation of buried layers with closely matched thermal coefficients of expansion substrates and buried films 
     (b) layers that can function as diffusion barriers to limit the diffusion of mobile contaminants 
     (c) low temperature bonding that allows (i) dopants profiles in the device wafer from pre-bonding processing due to low thermal budgets of the silicidation bonding, and (ii) stress reduction and less warpage, especially for diamond dielectric 
     (d) buried layers that are dielectrically isolated and able to function as resistor films 
     (e) buried layers that can better dissipate thermal energy transferred through thermally conductive diamond films 
     The invention has been described in detail for the purpose of illustration, but it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the following claims.