in one embodiment of the disclosed invention , laser - assisted etching or laser ablation is used to form back side alignment markers . the disclosed technique is beneficial over the prior art in that it does not require the use of photolithography to form the back side alignment markers , and additionally in some embodiments does not require the provision of a protective layer on the front side of the substrate . it should be noted that both laser - assisted etching and laser ablation are well - known techniques that have been used to etch materials on integrated circuits . accordingly , only basic aspects of these techniques are discussed , with the focus of the discussion centering on aspects relevant to the back side alignment marker issues discussed earlier . in fig4 , a laser - assisted etch / laser ablation chamber 50 is shown , and which is used in this embodiment to form the back side alignment markers . the chamber 50 includes an optical sensor 51 , a laser 52 , a lens or lenses 54 , a computer 56 , motor stages 58 , a gas inlet port 60 coupled to an etchant gas source 62 via a valve 64 , and a purge pump 73 . chambers with these components are well known , and will vary in design depending on whether laser - assisted etching or laser ablation techniques are used . because a gas inlet port 60 , an etchant gas source 62 , and a purge pump 73 are shown , chamber 50 as illustrated more accurately represents a laser assisted - etching chamber . were laser ablation to be used for the application in question , such gas - and etching - specific structures may not be necessary . further details concerning laser - assisted etch / laser ablation chambers 50 are described in above - incorporated u . s . patent application [ attorney docket 102 - 0103us ]. also present is the substrate 70 to be processed , which sits upon a substrate holding mechanism 71 , such as a chuck 72 or a clamp assembly 79 to be described in further detail later . the laser 52 is used to etch or ablate the bulk substrate 70 material on the backside 70 b without the need to practice the photolithography steps of the prior art ( photoresist deposition , exposure , cleaning and removal of the photoresist , etc .). in this regard , the substrate 70 is initially aligned front side 70 a down in the chamber 50 . this alignment can be relatively crude ( e . g ., +/− 20 microns ), and need not be as sophisticated as the alignment schemes used to align the circuit layers in the device . thus , initial alignment need only be +/− 5 microns for example , and can be performed manually , via operator visual inspection through a microscope , or by automated optical detection schemes , such as automated detection of the edges of the substrate 70 via the use of the optical sensor 51 . once aligned , computer 56 executes a program specific for the substrate 70 in question , and armed with knowledge of the x , y coordinates of where the back side alignment markers 27 are to be fabricated on the substrate 70 . accordingly , the computer 56 , moving the substrate holding mechanism 72 via motor stages 58 , brings the desired back side alignment marker areas 75 into alignment ( fig5 a and 5b ) and engages the laser 52 to form laser radiation 53 to etch or ablate the back side 70 b of the substrate 70 , e . g ., of crystalline silicon ( fig5 c and 5d ). thereafter , the substrate 70 can be cleaned if necessary , and as it would be cleaned in any event prior to further processing of active structures on the front side 70 a of the substrate 70 . in short , the back side alignment markers 27 are formed without photolithography and all of the steps entailed therein . as noted earlier , techniques for using laser - assisted etching and laser ablatement of materials on semiconductor substrates are well known , and hence are not reiterated in much detail herein . considerations relevant to such selective area processing can be found in thin film processes ii , ( ed . john l . vossen & amp ; werner kern ), pp . 621 - 670 , 749 - 856 ( academic press 1991 ), which is submitted herewith and which is incorporated herein by reference . laser ablation is preferably accomplished using an excimer , yag , or nd - yag laser which essentially vaporizes the metal layer 30 or other material where it is focused . suitable nd - yag lasers have wavelengths of 355 nm , and suitable excimer lasers have wavelengths of 193 nm or 248 nm . power levels for such lasers are typically in the 1 - watt range . laser ablation is simpler to implement , and will remove material relatively quickly , but is more difficult to control . moreover , the vaporized material may need to be cleaned from the substrate 70 &# 39 ; s surface . this being said however , laser ablatement can be a suitable choice for forming back side alignment markers in the substrate 70 in some applications . exemplary excimer lasers include the pl - 1500a excimer laser manufactured by potomac photonics , inc ., and the xsie200 excimer laser manufactured by xsil ltd .. an exemplary yag laser suitable for ablation comprises that lam 66 manufactured by heidelberg instruments mikrotechnik gmbh . further details regarding considerations for laser ablation can be found at http :// www . me . mtu . edu /˜ microweb / chap4 / ch4 - 2 . htm , http :// www . me . mtu . edu /˜ microweb / graph / laser / fluence . jpg , and http :// www . me . mtu . edu /˜ microweb / graph / laser / specmet . jpg , which are submitted herewith and which are incorporated by reference in their entireties . laser - assisted etching , by contrast , is slower , but better controlled , and hence is preferred for the application in question . in laser - assisted etching , an etchant gas is introduced into the chamber 50 from an etchant gas source 62 through valve 64 and gas inlet port 60 . the etchant gas is preferably introduced into the chamber 50 as shown proximate to and parallel with the substrate 70 &# 39 ; s surface . interaction of the laser light and the etchant gas produces a controlled reaction at the surface of the substrate 70 to remove the material in question . of course , the etchant gas to be used for a particular application , as well as the laser 52 parameters ( wavelength ; power ; spot size ) will depend on the composition of the substrate 70 , but again such laser - assisted processes are well known . if silicon or polysilicon is being etched , sf 6 would be a suitable etchant gas and would be used in conjunction with a laser having approximately a 10 um wavelength . other etchant gases and associated laser wavelengths suitable for etching silicon can be found in the above - referenced thin film processes book incorporated above at page 832 . an exemplary laser - assist etch chamber 50 can comprise the laser etch and deposition chamber published at http :// www . mesofab . com , which is submitted herewith and which is incorporated herein by reference . because the area 75 in which material will be removed will generally be relatively large compared to the spot size of the laser 52 , removal will preferably be accomplished by rastering the area 75 underneath the laser 52 . the laser 52 can either run continuously , or can be turned on and off at each rastered location . alternatively , if the laser spot size is large enough and comparable with the size of area 75 , rastering may not be necessary . as noted earlier , it is important during formation of the back side alignment markers 27 that the front side 70 a of the substrate 70 not be damaged . in the prior art , protection of the front side 70 a surface was provided by a protective layer ( 40 ; fig3 b ). using the laser - assisted etch / laser ablation chamber 50 shown in fig4 , provision of such a protective layer would be preferred , as the front side 70 a of the wafer comes into contact with the chuck 72 . however , in a preferred embodiment , provision of a front side 70 a protective surface is rendered unnecessary by making modifications to the laser - assisted etch / laser ablation chamber 50 . specifically , and as shown in fig6 and 7 , the chamber 50 a has been modified by exchanging a clamp assembly 79 for the chuck 72 of fig4 . the clamp assembly 79 has the same translational capabilities as the chuck 72 , and again is controlled in its movement by the computer 56 via motor stages 58 . however , through the use of the clamp assembly 79 , the substrate 70 is suspended within the modified chamber 50 a such that its front side 70 a does not come into contact with the clamp assembly and does not substantially come into contact with any work surface , except at certain non - critical points 85 along its edge not otherwise suitable for the formation of active circuitry . accordingly , the back side alignment markers 27 can be fabricated in modified chamber 50 a without the need to provide a protective layer 40 on the front side 70 a . this save a process step , and allows for processing of active structures on the substrate 70 essentially immediately after the back side alignment markers 27 are formed . as best shown in fig7 , the clamp assembly 79 spans underneath the substrate 70 at cross member 83 and rises along toward the sides of the substrate at risers 82 . clamp arms 84 are coupled to the risers 82 and contain a bottom arms and top arms , which contact the front side 70 a and back side 70 b of the substrate 70 respectively . the clamp arms 84 are coupled to the risers 82 via suitable mechanisms 81 . these mechanisms 81 could comprise the spring mechanism for biasing the top and bottom clamp arms 84 together to pin the substrate 70 therebetween , and additionally can incorporate motors to allow the substrate 70 to be rotated around an axis ( φ ) joining the two mechanisms 81 . this allows the wafers to be loaded front side 70 a up , and then rotated to bring the back side 70 b up , thus providing operational flexibility . rotational capability also allows for front side laser - based processing as well , e . g ., to form alignment markers on the front side 70 a as well as the back side 70 b . such rotation and activation of the motors can be accomplished using the computer 56 and the motor stage controls 58 , with wiring to the motors 81 being routed though the body of the cross member 83 and the risers 82 . in other embodiments , the substrate 70 need not be flipped as in chamber 50 a , but instead can sit flat on its back side 70 b when being written to . in such an embodiment , and as shown in fig9 , a back side alignment chamber 30 a or stepper such as those discussed above ( e . g ., fig2 ), can be retrofitted with a laser or lasers 52 . the laser 52 a will allow the back side alignment marker to be written ( i . e ., by laser ablation or laser - assisted etching ) using the same optical path used to “ see ” the alignment markers once they are formed . the lasers 52 may either appear proximate to the front side 70 a of the substrate ( 52 a ) or proximate to the back side 70 b of the substrate 70 b ( 52 b ). through this modification , the same tool can be used both for writing the back side alignment markers and as a photolithographic stepper that uses those markers for alignment purposes . beneficially , through this modification , a protective layer 40 over the front side 70 a of the substrate need not be used when writing the back side alignment markers with the laser . in an alternative embodiment , the need for the computer 56 to know the precise x , y coordinates of the areas 75 to be removed on the back side 70 b is mitigated by the use of a stencil 90 , as shown in fig8 . according to this alternative , the stencil 90 is aligned with the substrate 70 , and contains holes 92 which correspond to the desired shape of the backside alignment markers 27 . the stencil 90 is raised a distance ‘ d ’ away from the surface of the substrate 70 by spacers 91 , which distance might range from approximately 2 to 10 microns . using this approach , the laser 52 can be rastered over the entire surface of the stencil 90 , yet will only have effect to remove the material exposed on the back side 70 b where it is exposed through the holes 92 . accordingly , once the stencil 90 is appropriately aligned with the substrate 70 , using any of the techniques mentioned earlier , radiation 53 from the laser 52 can be appropriately directed to form the back side alignment markers 27 into the desired shape . thus , the stencil 90 ensures good alignment of the radiation 53 with the desired area 75 , making laser alignment and spot size considerations less critical . ( indeed , the use of a laser in conjunction with a stencil overlying the wafer has utility to clearing materials over and above clearing the alignment markers , and can be used for patterning active circuits as well ). because the back side alignment markers are relatively large , diffractive effects occurring at the edges of the holes 92 of the stencil 90 should not cause a problem , although optical proximity corrective measures could be incorporated into the stencil 90 if necessary . if used in a laser - assisted etch application , a material should be chosen for the stencil that will not react to the etchant gases in question . for example , for a silicon etchant , quartz ( silicon dioxide ) would be a good choice for material for the stencil 90 . likewise , in a laser ablation application , a material should be chosen which will remain impervious to the laser radiation in question . although the stencil 90 is disclosed in the figures in conjunction with chuck 72 , it should be understood that the stencil 90 can also be used with the clamp assembly 79 disclosed earlier ( fig6 and 7 ). if so used , the stencil 90 and spacers 91 would also be clamped between the top and bottom clamp arms 84 of the clamp assembly 79 . although the disclosed laser - assisted / laser ablation techniques have been disclosed as useful in the context of forming back side alignment markers , it should be understood that the disclosed techniques can be used to form front side alignment markers , and / or to remove circuit layers from the front side . moreover , while particularly useful to the clearing of materials on semiconductor integrated circuit substrates , the disclosed techniques can have application to other types of substrates and other types of processes . while it is preferred to use radiation , and specifically laser radiation , to etch the substrate to form the back side alignment markers , this is not strictly necessary . one skilled in the art will realize that other techniques for selectively removing discrete areas of materials without the use of a photoresist exist in the art , and these could be used as well . for example , an electron or other particle beam ( e . g ., an ion beam ) could be used in much the same way as the disclosed laser radiation 53 is used to remove the substrate material by the use of a rastered beam to directly remove the material without the need for photoresist or photolithography . the use of such alternative beams can also be accompanied by the use of a stencil as disclosed herein . again , processes for using electron or particle beams to remove materials from semiconductor integrated circuits are well known , and can be found in the thin film processes book incorporated above . “ circuit layer ” as used herein can comprise any layer used in the formation of integrated circuits on the front side of the substrate , including conductive layers , semiconductive layers , or insulating layers , doped regions of the silicon , etc . it should be understood that the inventive concepts disclosed herein are capable of many modifications . to the extent such modifications fall within the scope of the appended claims and their equivalents , they are intended to be covered by this patent .