for the manufacturing of a silicon solar cell , generally , it is necessary or advantageous to dope subzones of a surface of a silicon substrate negatively , i . e . in an n - type manner , in order to , e . g . in a p - type substrate , achieve an emitter , or to , in an n - type substrate , keep charge carriers away from a recombination - active surface and therefore better passivate the same . here , it may be of advantage to realize differently heavily doped zones within a substrate , e . g . in order to generate a selective emitter in which heavily doped subzones may be contacted by metal contacts with low resistance and intermediate lightly doped zones may be well surface - passivated . for the manufacturing of a solar cell on the basis of a silicon substrate , it is generally also necessary to dope other subzones of the silicon substrate positively , i . e . in a p - type manner , in order to achieve , for these subzones too , a sufficiently good contact with a contact metallization or in order to keep charge carriers away from the surface or in order to produce an emitter in an n - type substrate . in the concrete example of a back contact solar cell , as a rule , it is necessary to produce both negative and positive doped subzones on a back side surface of the silicon substrate . i . e . on a surface facing away from the sun during operation . furthermore , the front side of the silicon substrate , i . e . the surface facing the sun in operation , too , should , in proximity to the surface , exhibit an increased basic doping concentration , for example in the form of an fsf ( front surface field ) in order to minimize any surface recombination there . for the production of negatively doped subzones in crystalline silicon , phosphorus is generally used as a doping agent , i . e . as a dopant . in an industrial fabrication of solar cells , doped subzones are e . g . produced for example by diffusing phosphorus out of a phosphoric glass layer ( phosphorus silicate glass , psg ) into the silicon substrate . the phosphoric glass layer is first segregated , e . g . by inducing pocl 3 - gas into the pipe of a furnace . for the actual in - diffusion of the phosphorus , high temperatures of typically more than 800 ° c . and long diffusion times of typically more than 20 min are required , wherein higher temperatures tend to shorten the diffusion time . here , mostly batch diffusion furnaces are used in which both the production of the psg layer and the in - diffusion into the substrate are carried out . during the doping process , however , only a small quantity of the phosphorus used enters the substrate , a larger quantity remains in the glass layer on the substrate or a glass layer on an inner wall of the furnace pipe and stays there unused or leaves the furnace via the gas exiting , same . for the production of subzones differently heavily doped with phosphorus , generally one or more diffusion steps combined with suitable masking and / or etching measures have been used so far . as a masking for a phosphorus diffusion , e . g . a silicon nitride ( sin x ) or silicon oxide ( sio x ) layer of sufficient thickness is used . here , a barrier effect of silicon nitride is , as a rule , greater than one of silicon oxide , so that for example reduced layer thicknesses may be applied . for the production of positively doped subzones in crystalline silicon , generally aluminum or boron is used . as boron exhibits a higher solid body solubility in silicon , it is preferably used for the production of heavily doped p - type zones . boron is typically in - diffused at higher temperatures than phosphorus . e . g . at above 900 ° c . conventionally , two or more separate diffusion steps are necessary for the production of both phosphorus - doped subzones and boron - doped subzones . alternatively , one or more doping sources may be applied and dopants may be in - diffused together in one diffusion step . here , additional masking and / or etching steps may be applied in each case . in order to additionally produce differently heavily phosphorus - doped subzones , further masking and / or etching steps must be used on a regular basis . fig1 illustrates a first embodiment of an inventive method with which two differently heavily phosphorus - doped subzones 3 , 5 may be produced in a silicon substrate 1 . on a surface 13 of the silicon substrate 1 , partial surfaces 9 are covered with a borosilicate glass layer 7 ( bsg , here corresponding to sio x ny : b ). other partial surfaces 11 remain uncovered . the bsg 7 typically serves as a solid body doping source . in experiments , is has been found that this bsg layer 7 is able to enhance a phosphorus diffusion process e . g . for certain process atmospheres in an industry - standard phosphorus diffusion furnace . presumably , the bsg layer 7 serves for the absorption of phosphorus from the process atmosphere , i . e . of for example phosphorus from the furnace pipe walls “ provided with a p - containing layer ”, and for the discharge of this phosphorus onto the silicon substrate 1 and therefore for the doping of the substrate 1 . the bsg layer 7 enhances the absorption of phosphorus into the silicon substrate 1 in the partial surfaces 9 covered with bsg in contrast to the case of the partial surfaces 11 without any covering bsg layer 7 . the bsg layer 7 enhances the absorption of phosphorus into the silicon substrate 1 also compared with the case in which the partial surface is covered with a silicon oxide layer not enriched with any doping agents . as illustrated in fig1 , thus , by the local depositing of a bsg layer 7 and subsequent heating to above 800 ° c ., first subzones 3 may be produced below the bsg layer 7 and second subzones 5 may be produced in places where no bsg layer is provided . surprisingly here , the first subzones 3 are more heavily phosphorus - doped , i . e . n ++ - doped , than the second subzones 5 , which are n + - doped . it has particularly been found that , for a silicon substrate 1 with the bsg layer 7 deposited thereon , a high - temperature step of temperatures above 900 ° c . leads to an in - diffusion of phosphorus in a pocl 3 diffusion furnace previously covered with psg without any phosphoric process gases being added . here , a preliminary performance of industry - standard phosphorus diffusions suffices for covering the diffusion pipe of the furnace . a silicon substrate 1 without such a bsg layer 7 is in this process only doped with phosphorus in a much lighter fashion . in the performance of a subsequent typical phosphorus diffusion at temperatures below 900 ° c . with the addition of pocl 3 , the substrate 1 is overall more heavily doped than by the previous phosphorus diffusion alone . thus , with the help of respectively structured bsg layers 7 , phosphorus - doped subzones 3 , 5 may selectively be realized in a silicon substrate 1 . fig2 illustrates a second embodiment of an inventive method with which both two differently heavily phosphorus - doped subzones 3 , 5 and a boron - doped subzone 15 may be produced in a silicon substrate 1 within a high temperature process step . here , heavily n ++ - phosporus - doped subzones 3 are located on the back side of the silicon substrate 1 between neighboring p - boron - doped subzones 15 . a more lightly n + - phosphorus - doped subzone 5 is located on the front side of the silicon substrate 1 . here , the p + - boron - doped subzones 15 may be produced by depositing a layer 17 acting as a diffusion barrier locally onto a previously deposited bsg layer 7 . alternatively , a layer 17 acting as a diffusion barrier may be applied onto the whole surface and subsequently be locally removed in other zones . the layer 17 prevents significant amounts of phosphorus reaching the bsg layer 7 in a subsequent phosphorus diffusion process . thus , in the associated high temperature step , only boron is in significant quantities driven form the bsg layer 7 into the silicon substrate 1 in the subzones masked by the layer 17 , and the subzones 15 undergo a relatively light boron doping . here , a doping concentration in proximity to the surface may for example be greater than 1e19 cm − 3 , or greater than 5e18 cm − 3 for thin bsg layer less than 15 nm thick . here , a profile depth may typically be greater than 0 . 2 or 0 . 1 μm . with high diffusion temperatures and long diffusion times , profile depths of more than 0 . 5 μm are however also possible . generally , the intensity of the doping depends among other things on the bsg layer , the diffusion barrier layer , the diffusion temperature and the diffusion time . intermediate , heavily n ++ - phosphorus - doped subzones 3 are produced , in a similar manner as described above , in areas in which the bsg layer 7 is not masked and may therefore have enhancing effect on an in - diffusion of phosphorus . here , a doping concentration close to the surface may for example be heavier than 1e20 cm − 3 . here , a profile depth may typically be greater than 0 . 3 μm . with high diffusion temperatures , heavy pipe coverage and / or long diffusion times , profile depths of more than 0 . 6 μm are however also possible . with low diffusion temperatures , light pipe coverage and / or short diffusion times , profile depths in the range from 0 . 1 to 0 . 3 μm are also possible . here , the intensity of the doping depends among other things on the bsg layer , the atmosphere in the diffusion furnace , the diffusion temperature and the diffusion time . on the front side , a relatively lightly n + - doped subzone 5 is produced , as there neither a layer 17 as a diffusion barrier nor a bsg layer 7 enhancing an in - diffusion is active . in order to achieve sufficient coverage of psg on the furnace pipe , a surface concentration may typically amount to more than 1e19 cm − 3 , and a profile depth may typically be greater than 0 . 2 μm , wherein possible implementations include no profile for a furnace pipe having no coverage thereon and a more marked profile for a furnace pipe with a heavier deposition thereon . by way of example , in the following , possible parameters in an inventive production of doped subzones 3 , 5 , 15 are given . the silicon substrate 1 may be a crystalline n - type silicon wafer ( c - si ). it may have a thickness of more than 50 μm , typically between 100 and 300 μm . a base concentration may range from 1e14 to 5e16 cm − 3 , which corresponds to a conductivity in a range from 0 . 1 to 50 ohm * cm . the bsg layer 7 may for example be produced by chemical vapor deposition ( cvd ), e . g . by pecvd ( plasma enhanced cvd ). however , other deposition techniques such as sputtering , evaporation deposition , imprinting of thin layers ( possibly repressed / converted ) may also be used . the bsg layer 7 may be formed with a layer thickness of less than 400 nm , preferably less than 100 nm and particularly a thickness in the range from 5 to 100 nm . a concentration of boron in the bsg layer may be effected by e . g . addition of diborane ( b 2 h 6 ) during a deposition process . as an example , boron may be included in a silicon oxide matrix at a concentration of 1e21 to 1e22 cm − 3 . an in - diffusion of phosphorus from a gas atmosphere on the one hand and of boron from the bsg layer 7 on the other hand may be carried out at temperatures of more than 800 ° c ., preferably more than 900 ° c ., for example at 920 ° c ., wherein , with the temperature increasing , a decreased process time may be chosen and may e . g . have a duration between a few minutes and several hours . at 920 ° c ., a process time may e . g . be 100 min . subsequently , after this driving - in step , a pocl 3 diffusion may optionally be performed at lower temperatures , for example below 850 ° c ., particularly for example at 830 ° c . fig3 shows a cross section through an inventively manufactured solar cell 100 in the form of an ibs solar cell . the layers 7 , 17 used in producing differently doped subzones 3 , 5 , 15 , as they are shown in fig2 , were removed after the high temperature step , e . g . by etching . then , on the front side of the silicon substrate 1 , one or more dielectric layers 33 , for example of silicon nitride and / or silicon oxide , which may serve for a surface passivation and / or as an anti - reflex layer were produced . on the back side of the silicon substrate 1 , too , one or more dielectric layers 35 which may particularly serve for a surface passivation were formed . furthermore , metal contacts 37 contacting oppositely doped subzones 3 , 15 on the back side of the silicon substrate 1 through the dielectric layer 35 were formed . the metal contacts may e . g . be imprinted or vapor deposited and , if applicable , subsequently be fired , sintered or alloyed or for example be realized as laser fired contacts ( lfcs ). with respect to fig4 and 5 , doping profiles of in - diffused dopants are described as they typically materialize in inventively produced subzones 3 , 15 . the graphs depicted were measured by sims ( secondary ion mass spectrometry ) and thus reflect the actual concentration of dopants and not only the concentration of electrically active dopants . fig4 shows doping profiles 19 , 21 in a first subzone 3 . the doping profile 19 describes the concentration k of phosphorus as a function of the depth t , i . e . as a function of a distance from a surface of the silicon substrate 1 . the doping profile 21 describes the concentration k of boron as a function of the depth . in subzone 3 , both dopants occur , however , the phosphorus concentration clearly predominates so that subzone 3 is to be regarded as predominantly n - type doped . fig5 shows a doping profile 23 in a third subzone 15 . the doping profile 23 describes the concentration k of boron as a function of the depth t . in subzone 15 , boron is the only dopant occurring as an in - diffusion of phosphorus in any significant amount is prevented by the masking layer 17 so that subzone 15 is to be regarded as p - type doped . interestingly , the two boron doping profiles 21 , 23 greatly differ from each other in terms of quality in subzones 3 , 15 . the doping profile 23 of fig5 corresponds to a typical doping profile as it is known when in - diffusing boron from a solid body doping source such as bsg . close to the surface , the doping concentration at first declines only slightly in the logarithmic plotting depicted , as illustrated by the flat gradient 25 . in the case shown , the exponential decline of the doping concentration only starts to increase when greater depths of more than 0 . 4 μm are reached , as illustrated by the steeper gradient 27 . the in - diffusion of boron at a different temperature or a different duration leads to an extension / compression of the depth scale , the qualitative course remains unchanged . the doping profile 21 of fig4 for boron differs greatly therefrom . close to the surface , the doping concentration at first declines strongly down to a depth of approximately 0 . 1 μm in the logarithmic plotting illustrated , as shown by the steep gradient 29 . at greater depths of more than approximately 0 . 1 μm , the exponential decline of the doping concentration decreases , as illustrated by the flatter gradient 31 . such a doping profile seems unusual and is most likely caused by the specific diffusion conditions as they occur in the above - described in - diffusion of phosphorus at the simultaneous presence of a bsg layer 7 serving as a boron source . conclusively , it is to be noted that the terms “ include ”, “ comprise ”, etc . are not meant to exclude the existence of further additional elements . the term “ one ” does not exclude the existence of a plurality of elements or objects . furthermore , in addition to the method steps named in the claims , further method steps may be necessary or advantageous in order to e . g . ultimately complete the production of a solar cell . the reference signs in the claims only serve to enhance readability and are not meant to in any way limit the scope of the claims . 25 near - surface gradient of the boron doping profile in sub one 15 27 distant - surface gradient of the boron doping profile in subzone 15 29 near - surface gradient of the boron doping profile in subzone 3 31 distant - surface gradient of the boron doping profile in subzone 3