Abstract:
In various embodiments, an integrated circuit die is provided. The integrated circuit die may include a circuit on a surface of a semiconductor substrate that has a peripheral sidewall extending substantially perpendicular to and away from the surface. A first protective layer may cover the sidewall of the semiconductor substrate and peripheral edges of the circuit to provide protection from contaminant diffusion. In some embodiments, a semiconductor substrate is provided that has a plurality of dice contained thereon. Each of the dice may have an integrated circuit region and a peripheral sidewall etched into the semiconductor substrate. A first protective layer may be used to cover the peripheral sidewall of the semiconductor substrate to provide protection from contaminant diffusion. Additional apparatuses, systems, and methods are disclosed.

Description:
PRIORITY APPLICATION 
     This application is a divisional of U.S. application Ser. No. 12/577,602, filed Oct. 12, 2009, now U.S. Pat. No. 8,093,090 which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present invention relate to the field of integrated circuits and especially of semiconductor integrated circuits. These embodiments also relate to a method to fabricate a semiconductor integrated circuit. 
     BACKGROUND OF THE INVENTION 
     Semiconductor integrated circuits (IC) are widely used in a large variety of applications. The impressive progress in technology has allowed the integration of many functions, i.e. logical, data storage, parameter and/or motion sensors, etc. Correspondingly a wide variety of semiconductor ICs are produced, such as micro-processors, volatile and non-volatile memories, micro-electro-mechanical devices, embedded products, and others. 
     Typically many (from a few hundred to some thousands of) IC chips are realized on a wafer, such as a silicon wafer. The improved control on processing technology has lead to a miniaturization of the elementary electronic components, so that current ICs including more than 1 billion transistors are available, the maximum number being essentially limited by the chip size on the wafer and economic considerations based on a corresponding achievable yield. However, in many other cases ICs are much smaller, so that typical chip size may range from about 1 mm 2  to about 2 cm 2  (these figures are not absolute limits). 
     In all cases both cost and reliability are fundamental parameters to be considered together with functionality and performance. Reliability is affected by several variables such as contaminants entering the IC device. To limit such an occurrence, a top passivation layer is usually formed on the IC chip, however the finishing at the chip&#39;s edge sidewalls is a potential source of contaminants. This problem is particularly severe in those applications in which the IC is directly assembled on a board without additional assembly or package to further protect the semiconductor chip (this often occurs when space and/or weight constraints are important, such as in mobile phone apparatuses). Overall cost is not only affected by chip area but also by wafer area not useful in the final product, such as inter-dice separation scribe lanes that, despite necessary, can be viewed as wasted wafer area; which is more important in the case of small sized IC chips. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of the present invention will be made apparent by the following detailed description of some embodiments thereof, illustrated merely by way of non-limiting examples in the annexed drawings, wherein: 
         FIG. 1  illustrates a fabrication method according to one embodiment of the invention. 
         FIG. 2  illustrates a fabrication method according to another embodiment of the invention. 
         FIG. 3  illustrates a detail of a separation step in a fabrication method according to an embodiment of the invention. 
         FIG. 4  illustrates a detail of a separation step in a fabrication method according to another embodiment of the invention. 
         FIG. 5  illustrates a non-rectangular IC obtained from a wafer according to one embodiment of the invention. 
         FIG. 6  illustrates a flow chart of a method according to an embodiment of the invention. 
         FIG. 7  illustrates an edge portion of an IC according to one embodiment of the invention. 
         FIG. 8  illustrates an edge portion of an IC according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An IC comprises a plurality of electronic components that are coupled to each other so that when in operation the desired electronic functions are performed (a circuit). The circuit typically comprises transistors, diodes, resistors, capacitors, interconnections, and/or other electronic elements. 
     Typically many ICs are fabricated on one side of a semiconductor wafer with each IC made in an area called a die. An example of such a wafer is a circular substrate of crystalline silicon material. The processing steps are carried out on the whole wafer (and often in batches of several wafers) at the same time. The dice are separated from each other to form separate ICs. 
     As it will be clear from the description of the different embodiments, the specific processing steps used to fabricate the electronic components and the circuit may vary according to the specific IC. The processing steps may comprise oxidation, doping (i.e. by ion implantation), deposition, patterning, etching, thermal treatments and the like. Different materials are used to form the electronic components and the IC, exploiting their respective properties. 
     For the purposes of the embodiments of the invention, the description is limited to the distinguishing steps for obtaining an IC featuring an improved edge finishing and correspondingly a better immunity to contaminant diffusion. Moreover a better exploitation of wafer area is also obtained. When possible, in the description and in the figures the same numerals are used to refer to the same objects, structures, or materials. 
     Trenches are formed in the wafer substrate at the periphery of each IC so that the peripheral trenches substantially define a perimeter of the ICs on the silicon wafer. As it will be described in detail in the following embodiments, dice separation is obtained just at the location of trenches after back-lapping of the silicon wafer down to a thickness less than the trench depth. The separation trenches may be filled or partially filled with a protective material to minimize possible contaminant diffusion into the IC from the sidewall at the edge of the IC. 
     Moreover, since it is possible to define a very narrow trench width and to tightly control its dimension and alignment, the area between adjacent dice is considerably reduced, therefore minimizing the “wasted” area on the silicon wafer (i.e. the inter-dice separation area not useful for hosting the electronic components and the circuit of the IC but necessary to separate them from one-another). 
       FIG. 1  illustrates a fabrication method of an IC  100  according to one embodiment of the invention. A semiconductor substrate  110 , typically in the shape of a circular wafer, is used to host the electronic components  115  of the IC ( FIG. 1   a ). The wafer  110  has a front-side  104  and a back-side  106 . More precisely several die  100  (each one including the same electronic components) are fabricated simultaneously, i.e. following a sequence of processing steps to define the IC, on the front-side side or surface  104  of a semiconductor wafer, such as silicon wafer  110 . Only relevant processing steps are described in detail in the following paragraphs, the others being IC-specific and therefore depend on which electronic components are to be fabricated. 
     In  FIG. 1  layer  115  represents the whole of the electronic components fabricated on the entire wafer surface  104  (the same components are present in each die), including the dielectric layers placed in between and/or on top. The electronic components are realized by a plurality of patterned and/or un-patterned layers on the entire wafer  110 . After dice separation the ICs  100  are obtained from the wafer  110 , each one with its own substrate  110   a  and its own set of electronic components  115   a  (the latter are also referred to as the circuit  715   a  and  815   a  in subsequent  FIGS. 7 and 8 , respectively). 
     Trenches  125  are formed in the wafer substrate  110  at the periphery of each IC to be formed so that the peripheral trenches  125  substantially define a perimeter of the ICs on the silicon wafer  110  (see  FIG. 1   b ). Correspondingly the electronic components  115  are physically subdivided into sets  115   a , corresponding to the many ICs on the wafer. 
     The trenches&#39; pattern is obtained by depositing a photo-resist layer  120 , selectively exposing it in the desired regions, developing it, and removing it from the area where the trenches are to be formed by etching, while leaving it on regions to be protected from the etch (see  FIG. 1   b ). In one embodiment a hard mask process is used; and the photo-resist material  120  is used to transfer the pattern to a different material (not shown in  FIG. 1   b ) that is more resistant to the trench etch. 
     In one embodiment, dry etching is used. This technique allows for better control on the lateral profile of the trench. If multiple layers are present on the wafer (as may be the case if the trench formation occurs at a late stage of the fabrication process) different reactants may be used in sequence to adapt the etching step to the exposed layer. A combination of dry etching and wet etching is used in another embodiment. 
     The width (W) of trenches  125  is controlled by a photolithographic process and it is kept within a very small range, for example between 3 and 50 the minimum size being essentially limited by the aspect ratio depth/width (D/W) of the trenches to be formed. In one embodiment the trench width W is 10 μm. 
     The trench depth (D) is larger than the active depth of the electronic components  115 . The latter depth is the depth into the silicon wafer  110  that is considered to be important for the correct functionality of electronic components  115 . For example, the depth of trenches  125  is in the range 30 to 300 μm; in one embodiment it is 60 μm. It is important that the separation trench depth is larger than the final wafer thickness after back-lapping to enable dice separation (see below for the detailed description). 
     Adjacent dice (not yet separated from each other but with already independent circuits  115   a ) are divided by a inter-dice separation trench  125  of width. Separation trenches  125  define sidewalls  127 , each one associated with respective die at its periphery. 
     A protective layer  130  is formed on the sidewalls  127  ( FIG. 1   c ) so that a uniform layer is exposed at the edge of each IC  100  after dice separation. This feature is a considerable advantage with respect to conventional dice separation techniques that results in a plurality of materials being exposed on the sidewall of the IC. As such a configuration has weak points at the interfaces between different layers used to fabricate the circuit (i.e. the electronic components) because contaminants may effectively migrate along such interfaces. For example, contaminants may diffuse into the IC chip at the silicon/silicon dioxide interface, or at the interface between superimposed inter-metal dielectric layers, or the like. On the contrary, with the present solution the protective layer is a uniform layer without exposed interfaces. 
     In one embodiment, the protective layer  130  is formed by thermal oxidation of silicon in the substrate  110 . Thermal silicon oxide is a high quality layer and is an effective material to prevent contaminant diffusion. Thermal oxidation of silicon is especially suited for trench sidewall  127  protection if the trench  125  is formed at an early stage of the manufacturing process. In this case the high temperature treatment necessary to oxidize silicon does not affect other structures or materials because they have not been formed at this stage. Alternatively layer  130  is deposited, for example by Chemical Vapor Deposition. This is better suited if the trench  125  formation is carried out at a later stage of the manufacturing process. Layer  130  comprises a dielectric layer. In one embodiment, the dielectric layer comprises silicon nitride. During the formation of protective layer  130  on sidewalls  127 , the bottom of trenches  125  are also covered by layer  130 , however this portion of the wafer will be removed at a later time. 
     An additional layer  135  of a different material, i.e. silicon nitride, is formed in one embodiment on top of protection layers (see  FIG. 1   c ). A dual- or multi-layer configuration results in even better immunity to contaminant diffusion because the different materials have different diffusion coefficients for different contaminant species. 
     In the example depicted in  FIG. 1 , the trenches  125  are completely full with filling material  140 . The filling material  140  is deposited on the whole wafer surface  104  and it is etched back, for example by chemical etch or by Chemical Mechanical Polishing. The filling material  140  is therefore removed from the surface  104 , while it remains into the trenches  125 . In one embodiment the filling material  140  is a metal or a metallic compound. The filling material may include for example tungsten, titanium, cobalt, aluminum, copper, their alloys, or other conducting material. 
     The choice of the filling material depends at least in part on other process steps possibly necessary for the manufacturing of the IC. For example Through Silicon Vias (TSV) are sometime used in ICs. TSVs are electrical contacts extending through the entire thickness of the IC and multiple ICs are piled on top of each other to obtain a more compact package. If Through Silicon Vias are formed (in the circuit portion of each chip—not shown in  FIG. 1 ) during the manufacturing process, the same process steps and process materials are also used to form the separation trenches  125  at the periphery of the dice in order to achieve process optimization and overall cost reduction—for this purpose a simple mask pattern modification will be necessary to simultaneously open the inter-dice separation trenches  125  in the scribe lane and the TSV trenches in the circuit. 
     The substrate  110  is back-lapped to a thickness less than the depth D of trenches  125  ( FIG. 1   d ), so that the bottom portion of the trenches  125  is also removed and the periphery of each die is defined by the separation trench for all the ICs thickness. The substrate&#39;s back-side surface  106  is moved from its original position closer to front-side surface  104  at new back-side surface  108 . For example the final thickness of the wafer is in the range 25 to 270 μm (when the original trench depth is in the range 30 to 300 μm and final thickness of the wafer&lt;original trench depth). In one embodiment, it is 50 μm (when the original trench depth is 60 μm). 
     As shown in the inset of  FIG. 1   d , the silicon wafer is now divided into a plurality of IC substrates  110   a  with corresponding circuits  115   a , separated from each other by trenches  125  full with layers  130 ,  135  and  140 . Note that not all the layers shown in  FIG. 1   d  are necessary present. Furthermore, other additional layers not shown in  FIG. 1   d  may be present, such as a barrier layer surrounding the metallic layer or a sealing/passivation layer also deposited on top of the surface  104 , or other layers formed after trench filling and etch back. 
     To separate the dice from each other, the silicon wafer is mounted on a support  185 , such as an adhesive foil, for keeping the ICs in place after physical separation. In the embodiment depicted in  FIG. 1   e  a laser source  195  is used for dice separation. The focused laser beam is directed to and scanned on the separation regions (i.e. at the separation trenches  125 ), i.e. by a x-y stage  190 . The filling material is cut or evaporated and the dice separate form each other, as illustrated in  FIG. 1   f  (the die  100  are removed from support  185  and assembled in the package, if necessary). However, different separation techniques may be used; for example in one embodiment a selective etch of the filling material  140  removes it from the central portion of the trench  125  portions at the periphery of the dice, therefore separating adjacent ICs  100  from each other. 
     The photo lithographically-defined inter-die spacing is considerably reduced with respect to the conventional techniques. In the typical approach dice separation is carried out by a sawing process. In view of the wafer cut, both the space for the cut width and for the mechanical alignment of the cutting tool with respect to the dice must be allowed for. With the photolithographic process no space is necessary for the tool; moreover the process is intrinsically more precise, both in terms of dimension control and alignment tolerances. 
     To quantify the cost saving in terms of silicon wafer area it is noted that each IC effectively needs the area for the circuit and the surrounding area defining its perimeter (the scribe lane where the saw cuts the wafer, or where the trenches  125  are formed—one scribe lane is shared by two adjacent dice, but each die has two opposite sides, so that one scribe lane area must be added to each IC in each direction). Considering an active chip size of 1.5×1.5 mm 2  the effective area on wafer is reduced from approximately 1.6×1.6 mm 2  (considering a typical scribe lane of 100 μm for the saw-cut process) to about 1.51×1.51 mm 2 , (considering a typical scribe lane of 10 μm for the separation trench process), or about 11%. Therefore the “wasted” area on the silicon wafer may be minimized. The improvement may be even better, at its edge some otherwise specially designed dummy structures in the peripheral region of the IC and the so called chip-outline-band may be avoided. 
     It is noted that the processing sequence described above may vary, especially with regard to the moment during the manufacturing process when the step of etching trenches in the wafer is carried out. More precisely the trenches may be formed before the structures of the electronic components are defined, when they have only partially been defined, or even after they have been completely defined. Clearly the choice depends on the optimum manufacturing sequence for the specific IC, and minor modifications to the teaching described above may be necessary without departing from the scope of the invention. 
       FIG. 2  illustrates a fabrication method according to another embodiment of the invention. On a front side  104  of a substrate  110 , such as a substantially circular silicon wafer, circuits  115  are formed (see  FIG. 2   a ). Numeral  115  in  FIG. 2  generally refers to all the electronic components in the IC as already described with reference to the embodiments in  FIG. 1 . The specific processing steps to form electronic components  115  may vary with the kind of IC to be fabricated, and will not be discussed here. 
     As depicted in  FIG. 2   b , trenches  125  of depth D are formed in the silicon wafer  110  at the periphery of IC chips, therefore defining their perimeter. Trenches  125  involve any layer possibly present in circuit  115  at the time of the trench formation. Since the trenches  125  define the chip&#39;s perimeter, a minimum acceptable distance is present between any active structure of circuit  115  and trench  125  to avoid the risk of destroying or damaging the circuits during trench etch. 
     A photo-resist material  120  is exposed through a photo-mask, developed and selectively etched according to a photolithographic patterning technique. A hard mask formation to define the trench position and width W on silicon wafer  110  is possibly used. Electronic components  115  are therefore separated from each other into a plurality of circuits  115   a , each one in a distinct IC chip (all project from the same silicon wafer  110  and therefore not mechanically independent, yet). 
     Trench depth D is in the range 25 to 250 μm. It is important that the depth D is larger than the final wafer thickness after back-lapping to enable dice separation (see below for the detailed description). In one embodiment, the depth D is 110 μm. Trench width W is in the range 4 to 60 μm, the minimum size being essentially limited by the capability of etching trenches with high aspect ratio (D/W). In one embodiment, the trench width W is 14 μm. 
     A sealing or passivation layer  150  is formed on the wafer surface, to protect the circuits  115   a  from possible contaminant diffusion into the chip. The passivation layer is also deposited in the trenches  125 , and especially on its sidewalls  127 —it is also deposited on the bottom of the trench, but this is less relevant because this portion will be later removed. In one embodiment the passivation material only partially fills the trench  125 , i.e. the deposited thickness is less than half the trench width W, so that a void is present in the central portion of trenches  125 , as shown in the inset of  FIG. 2   c.    
     The passivation layer  150  includes a material with good contaminant diffusion blocking properties. For example, a doped silicon oxide glass, a nitride layer, or both may be used. Openings (not shown) are formed in the passivation layer  150  at positions where pads are present for wire-bonding and/or electrical contact to the IC. 
     Optionally, before deposition of passivation layer  150 , a further protective layer  130  may be formed on the sidewalls  127  of trenches  125 . The further protective layer  130  includes silicon dioxide (either deposited or thermally grown). In one embodiment, additional protective layers are formed to obtain a multi-layer protective barrier, for example also including silicon nitride. 
     The front-side  104  of silicon wafer  110  is fixed to a support  185  (see  FIG. 2   d ) and the silicon wafer  110  is back-lapped to a final thickness less than the depth D of trenches  125 . During this operation the IC chips (each including semiconductor substrate  110   a  and circuit  115   a ) are mechanically separated from each other along the peripheral trenches  125  that are empty in their central portion. The final thickness of the wafer is in the range 20 to 230 μm (when the original trench depth is in the range 25 to 250 μm and final thickness of the wafer&lt;original trench depth). In one embodiment it is 100 μm (when the original trench depth is 110 μm). 
     ICs obtained according to the edge finishing description above have a uniform protective layer (or a uniform multi-layer structure) to seal the sidewalls  127  and protect the IC from possible contaminant diffusion into the chip; therefore improving device reliability. 
     Wafer area is also saved and production cost reduced with respect to a conventional saw-cutting separation approach because there is no need to allow for cutting tool space. Moreover, the photolithographic alignment and dimensional control in separation trench definition are much higher than even the most sophisticated mechanical techniques. As such a reduced die-to-die space is possible and a corresponding higher number of dice may be placed on the same silicon wafer. 
     It is noted that the separation trench technique may also be applied at very late stages of the manufacturing process, so that the space in the scribe lane is available to host all those structures useful during the processing (such as photolithographic alignment marks, thickness and/or dimensional control structures, or the like). Structures for electrical parameter testing may also be included in the separation trench scribe lane space, although such a space is reduced with respect to previous scribe lanes. According to one embodiment (not depicted in a figure), the parametric testing structures are formed during the manufacturing process simultaneously with the circuit portions  115  ( 715  and  815  in  FIGS. 7 and 8 ); the wafer is then tested to evaluate the parametric compliance with pre-defined targets. If the tested wafer is in line with desired results, the inter-dice separation trenches are formed and during this step the structures present in the etched regions are removed. Finally, the wafer is back-lapped to a final thickness less than the separation trench depth and the dice are separated from each other. 
     Regardless which of the embodiments described above is utilized, the chip edge finishing is achieved by a chemical process and therefore it is very uniform (much more than using a saw-cutting technique). The separation trench technique also has lower defectivity and higher yield. Moreover, the embodiments of the invention have the further advantage of avoiding any scratch on the lateral sidewalls  127  whereas the conventional cutting approach, on the contrary, inevitably produces a mechanical damage of the sidewalls that is a further potential cause of enhanced contaminant diffusion, as scratches may act as impurity getters and preferential diffusion paths. 
     One further advantage of the proposed solutions is that the tensile or compressive stress present on wafer (due to the different materials and layers used in the manufacturing process) is reduced by the trench network at the periphery of the dice when the wafer thickness is reduced. The material in the trench contributes to stress relaxation and the maximum contiguous silicon area is that of a single die or IC (i.e. about 1 to 10 mm in one direction, to be compared to 200 or 300 mm wafer&#39;s diameter), so that wafer warping and bending is minimized. 
       FIG. 3  illustrates a detail of a separation step in a fabrication method according to an embodiment of the invention. Both a top view and the corresponding cross section of a wafer are shown. A production wafer  310  comprises a plurality of ICs  300 . Each IC  300  includes a substrate portion  310   a  and a circuit portion  315   a  and has external sidewalls  327  at the periphery. The manufacturing process includes all processing steps necessary to fabricate the electronic components in circuits  315   a  and the specific steps to separate the ICs from each other. More specifically the dice  300  on the production wafer  310  are spaced one from another by separation trenches  325  that are formed, for example, according to one of the embodiments described above, so that the sidewalls  327  are sealed by a protective layer to minimize contaminant diffusion into the chip. 
     A complementary wafer  320  is fabricated comprising a pattern of IC housing trenches  326  and holding fences  390  at the periphery of each IC housing trench  326 . The pattern is complementary to that of the production wafer  310 , so that the holding fences  390  in the complementary wafer  320  match the separation trenches  325  in the production wafer  310  and the IC housing trenches  326  in the complementary wafer  320  perfectly match the ICs  300  in the production wafer  310 . The depth of IC housing trenches  326  is less than total extension of separation trenches  325  from production wafer&#39; surface on front-side, so that after back-lapping it is possible to grasp the ICs  300 , as better described below. 
     The complementary wafer  320  is used as mechanical support to host the production wafer  310  during the back-lapping step. The production wafer  310  is coupled to the complementary wafer  320  so that the ICs extensions are housed in the IC housing trenches in the complementary wafer  320 , while holding fences  390  are plugged into the separation trenches  325  in the production wafer  310 . To facilitate coupling of production wafer to complementary wafer, holding fences  390  have a sharp termination, as depicted in the cross section in  FIG. 3 . In one embodiment the holding fences  390  in the complementary wafer  320  are protected by a protective layer (not shown in  FIG. 3 ). The protective layer may be chosen so as to produce in the complementary wafer a tensile or compressive stress opposite to the one present in the production wafer at the end of processing. Once back-lapping of production wafer to final thickness the ICs  300  are removed from the IC housing trenches  326  and assembled in the package. 
       FIG. 4  illustrates a detail of a separation step in a fabrication method according to another embodiment of the invention. The wafer  410  comprises a plurality of ICs  400  (see  FIG. 4   a ). Each IC  400  includes a substrate portion  410   a  and a circuit portion  415   a  and has external sidewalls at the periphery. The manufacturing process includes all processing steps necessary to fabricate the electronic components in circuits  415   a  and the specific steps to separate the ICs from each other. More specifically the dice  400  on the production wafer  410  are spaced one from another by separation trenches that are formed, for example, according to one of the embodiments described above, so that the sidewalls are sealed by a protective layer to minimize contaminant diffusion into the chip. 
     The wafer  410  is mounted on a flexible support  485 , i.e. an adhesive foil.  FIG. 4   b  shows the mounting on the back-side of the wafer, which is the preferred embodiment in case the separation trenches are not completely full, however the mounting on the flexible support  485  may also be done on the frontside of wafer  410 . 
     The wafer  410  is then clamped in a vice  490  up-to an inter-dice separation trench line ( FIG. 4   c ), leaving a portion of the wafer unclamped. A lever  492  exercises a force on the unclamped portion of wafer  410  leading to mechanical separation of substrate portions  410   a  along the inter-dice separation trench line. This step is repeated for all inter-dice separation trench lines in both directions, so that all ICs  400  on wafer  410  are mechanically separated from each other. The flexible support  485  is elongated ( FIG. 4   d ) and the chips are removed from it for assembling in the final package. 
     While  FIG. 4  represents an embodiment in which the wafer has been back-lapped, in other embodiments the mechanical separation of ICs is carried out without the back-lapping step, so that adjacent dice are separated by trenches only for a portion of the wafer thickness and the protective sealing layer on sidewalls at ICs edge extends all the way to the separation trench depth (leaving the deepmost portion of the substrate unprotected). 
     It is noted that, while the use of saw-cutting technology limits the shape of any device to a rectangular one, with the proposed perimetric separation trench solution it is possible to produce devices of any shape.  FIG. 5  illustrates a non-rectangular ICs  500 , more precisely hexagonal ICs in the example depicted, obtained from a wafer  510  according to one embodiment of the invention. While  FIG. 5  depicts a regular pattern with complete silicon area coverage on the wafer surface, any desired shape is obtained by appropriate layout and patterning of the IC  500  on wafer  510 , including shapes that do not completely cover the surface (in this case the separation trench width is not constant on the wafer). 
     Such non-rectangular shapes are of interest in some cases because the maximum distance within the device is reduced. Moreover an improved area exploitation may be obtained, for example with an hexagonal shape may improve area usage at border silicon wafer. Additionally, other constraints may benefit from non-rectangular shaped dice, for example for packaging purposes. As a further example, multi-device mask sets with chips of different shapes can be realized. More precisely, sometimes, especially during the process development phase, it is desirable to include several ICs in the same mask set to reduce costs. Typically different ICs (let&#39;s consider all of them are rectangular) have different area and shape factors, so that it is not possible to assemble all of the products on a wafer because during dice separation some IC are inevitably cut for lack of periodicity. With the embodiment discussed above, however, it is possible to mechanically separate all ICs from each other (therefore maintaining the possibility to assemble all of them) independently of their shape and form factor. In one embodiment, a region with parametric testing structures and process control structures is present on the wafer. 
     When implementing the non-rectangular shape embodiments, care should be paid to correctly shield the exposition field during photolithographic steps to avoid superimposition of pattern in device areas. 
       FIG. 6  illustrates a flow chart of a method according to an embodiment of the invention. A circuit of the integrated circuit is formed on one side of a semiconductor wafer at  610 . A trench with a depth in the semiconductor wafer to define a periphery of the integrated circuit is formed at  620 . The semiconductor wafer is thinned to a thickness less than the trench depth to separate. the integrated circuit from a second integrated circuit on the wafer at  630 . 
     Additional method steps (not shown in  FIG. 6 ) may include one or more of forming a protective layer on the trench sidewalls to reduce possible contaminant diffusion into the chip, forming a second protective layer onto said first protective layer to further reduce the possible contamination into the chip; depositing a sealing passivation layer onto the semiconductor wafer and into the trench, and filling the trench with a conductive material. 
       FIG. 7  illustrates an edge portion of an IC according to one embodiment of the invention. The integrated circuit  700  includes a substrate portion  710   a , typically a silicon crystal, and a circuit portion  715   a . The circuit portion  715   a  comprises the electronic components that, coupled to each other, carry out the desired functions when the IC is in operation. The electronic components typically include transistors, diodes, resistors, capacitors, interconnections, etc. The electronic components are formed by several layers of different materials (i.e. dielectric, such as oxide, nitride, low-K dielectrics, etc., conductive materials such as polysilicon, tungsten, titanium, aluminum, copper, etc., and other material such as, ferroelectric, phase-change, magnetic materials) that are appositely shaped to obtain the desired structures (i.e. lines, gates, spacers, contacts, plates, and others). A passivation layer  780  of sealing material is present on top of the IC  700 . 
     Chip  700  has a periphery with a sidewall  727  which is covered at least in part by a sealing protective layer  730  to limit contaminant diffusion into the device. The protective layer is substantially uniform. In one embodiment the protective layer is a dielectric layer, for example silicon dioxide. In another embodiment, the protective layer comprises the same material used as a sealing (passivation) layer  780  on top of the IC. 
     Additional protective layer(s) overlap the first protective layer in another embodiment. For example  FIG. 8  illustrates an edge portion of an IC  800  according to a different embodiment of the invention. The integrated circuit  800  includes a substrate portion  810   a  and a circuit portion  815   a . The circuit portion  815   a  comprises the electronic components that, coupled to each other, carry out the desired functions when the IC is in operation, as described above. 
     Chip  800  has a periphery with a sidewall  827  which is covered at least in part by a sealing protective layer  830  to limit contaminant diffusion into the device. Sidewall  827  is further sealed by second protective layer  835 . Protective layers  830  and  835  are substantially uniform. The second protective layer  835  comprises a layer different from the first protective layer  830 , for example in one embodiment the second protective layer  835  comprises a silicon nitride layer and the first protective layer  830  comprises a silicon dioxide layer. In another embodiment the second protective layer  835  comprises a conductive material and the first protective layer comprises a dielectric material. 
     Many electronic systems which embed an integrated circuit according to those above described embodiments of the invention are possible. These electronic systems, such as a mobile phone, a personal computer, a joy-pad, a measurement instrument, comprise one or more electronic boards with a plurality of integrated circuits assembled on the board(s) and include Input/Output ports coupled to a micro-controller, CPU, or other processor. Depending on the application, the processor is also coupled to other integrated circuits on the same board or on other boards of the electronic system. Such integrated circuits may include, but are not limited to, a memory device (volatile or non-volatile), a micro-electro-mechanical device, a actuator device, a sensor, a digital-analog converter device, or other micro-controllers. Each integrated circuit has one or more circuits to perform a specific function and is on a surface of a semiconductor substrate, for example a Silicon substrate. The substrate of one in the plurality of integrated circuits has sidewalls defining the periphery of the integrated circuit (in a direction substantially perpendicular to the surface hosting the circuit). A protective layer is present on the sidewalls of the substrate to protect the integrated circuit from contaminant diffusion. The reliability of the integrated circuit(s) and of the electronic system is therefore improved. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.