Patent Application: US-90896401-A

Abstract:
the present invention discloses a semiconductor film having a reduced dislocation density . the film comprises at least one interlayer structure , including a group iii - nitride layer , a passivation interlayer disposed on the group iii - nitride layer , interrupting the group iii - nitride layer , and an island growth interlayer disposed on the passivation interlayer , and interrupting the group iii - nitride layer . a method of making a semiconductor film of the present invention comprises producing a semiconductor film including at least one interlayer structure , each interlayer structure produced by the substeps of growing a group iii - nitride layer , depositing a passivation interlayer on the group iii - nitride layer , depositing an island growth interlayer on the passivation interlayer and continuing growing the group iii - nitride layer .

Description:
in a preferred embodiment ingan inter - layers are grown in a selective island growth mode after partially passivating the gan surface with silicon nitride , on the structural properties of gan films grown on silicon and sapphire substrates . the growth of ingan has shown that ingan films have a high tendency to grow in a spiral growth mode around threading dislocations with a screw component . ingan spiral islands were obtained , when the gan surface was partially passivated with disilane under formation of a submonolayer of silicon nitride ( henceforth referred to as “ si x n y ”) prior to deposition of the ingan layer . [ 8 , 9 ] it should be understood , however , that the present invention is not limited to embodiments using partial passivation or selective island growth modes . in the present invention , the selective island growth of ingan can be utilized to reduce the dislocation density in gan films . in particular , the effect of the thickness of the silicon nitride layer and the number of si x n y / ingan interlayers improves the structural quality of the films . this may be evaluated by high resolution x - ray diffraction . [ 0020 ] fig1 illustrates a typical semiconductor film of the invention . the invention is generally directed to a semiconductor film 100 including at least one interlayer structure 102 including a group iii - nitride ( such as gan ) layer 104 , a passivation interlayer 106 disposed on the group iii - nitride layer 104 and an island growth interlayer 108 ( such as ingan ) disposed on the passivation layer 106 . the passivation layer 106 is typically composed of silicon nitride or silicon dioxide , however other passivating materials may also be used . a continued growth of the group iii - nitride layer 104 ( which is also the beginning of second interlayer structure 102 ) completes the first interlayer structure 102 . two such interlayer structures 102 are preferred . in addition , the invention is typically formed on a substrate 110 having a nucleation layer 112 disposed thereon and a cap layer 114 ( which is also the continued growth of the final group iii - nitride layer 104 ) is deposited on the uppermost interlayer structure 102 . it should be noted that , in addition to si 3 n 4 and sio 2 , the passivation layer may be formed of any material which will produce a group iii - nitride growth perturbation which can be initiated by the deposition of at least one layer to stop the dislocation propagation . any inorganic dielectric passivating material known to those skilled in the art may be used [ 0022 ] fig2 a and 2b are flowcharts illustrating methods of making semiconductor films 100 of the invention . fig2 a is a flowchart of the steps of making an interlayer structure 102 of the invention . beginning at block 200 , a group iii - nitride layer 104 is grown . next , a passivation layer is deposited on the group iii - nitride layer at block 202 . then , an island growth layer is deposited on the passivation layer at block 204 . finally , growing the group iii - nitride layer 104 is continued at block 206 . fig2 b is a flowchart of the steps of making a semiconductor film of the invention . beginning at block 208 , a nucleation layer 112 is formed on a substrate 110 . next , at least one interlayer structure 102 is formed by the substeps 200 - 204 of fig2 a . substeps 200 - 204 are repeated for each interlayer structure 102 at block 210 . finally , a cap layer 114 is grown on the last interlayer structure 102 at block 212 . further details of the steps will be described hereafter . all epitaxial layers in the present invention may be grown by metal - organic chemical vapor deposition using the precursors trimethylgallium ( tmga ), trimethyaluminum ( tmal ), trimethylindium ( tmin ), ammonia , and disilane . typical embodiments of the invention are grown with two si x n y / ingan layers 106 , 108 , separated by 0 . 1 - 5 μm gan layers 104 to form the interlayer structures 102 . the passivation layers may range from 0 . 05 - 5 å in thickness . for samples grown on silicon substrate 110 ( procedure a ), the growth may be initiated with the deposition of a 100 - nm - thick aln nucleation layer 112 at 900 ° c ., followed by the growth of a 1 . 7 μm of gan layer 104 at a temperature of 1080 ° c . following this , the tmga injection is stopped and 2 - 10 nmol / min disilane is added for 16 - 48 seconds to form the passivation layer 106 . the 12 - nm - thick in 0 . 1 ga 0 . 9 n layer 108 which follows is deposited at 790 ° c . using a tmga and tmin flow of ƒ tmga = 0 . 6 μmol / min and ƒ tmin = 12 μmol / min and an ammonia flow of ƒ nh 3 = 0 . 32 mol / min . after deposition of the ingan layer 108 , the wafer temperature is raised to 1070 ° c . and a 0 . 5 μm gan layer 104 is deposited . next , the gan growth is interrupted again and a second passivation layer 106 , a submonolayer of silicon nitride , is grown , followed again by an ingan layer 108 under the same conditions as the previous one . the structure is completed with the deposition of a 0 . 8 μm thick gan cap layer 114 . for the first set of samples grown on c - plane sapphire substrate 110 ( procedure b 1 ), the growth is initiated with a 20 - nm - thick gan nucleation layer 112 , followed by the growth of a 0 . 5 μm gan layer 104 at 1070 ° c . afterwards 0 . 15 å passivation layer 106 of silicon nitride followed by a 12 nm ingan layer 108 is deposited in the same manner as described for the growth on silicon substrates 110 . the growth is continued with the deposition of a 0 . 5 μm gan layer 104 , a second 0 . 15 - å - thick passivation layer 106 of silicon nitride , a 12 nm ingan layer 108 , and completed with 2 μm cap layer 114 of gan . the effect of the number of si x n y / ingan interlayers is shown in a second set of samples with four si x n y / ingan interlayers , all separated by 0 . 5 μm gan to form interlayer structures 102 . the thickness of the cap layer 114 may be reduced to 1 μm to keep the total thickness of the epitaxial layer constant . in the case of the second set of samples grown on sapphire substrate 110 ( procedure b 2 ), the thickness of the gan layer 102 prior to deposition of each of the two ingan layers 108 of the interlayer structure 102 is increased to 3 μm , and the thickness of the gan cap layer 114 to 2 . 5 μm . the average thickness of the passivation layers 106 , the si 3 n 4 submonolayers ( si x n y ), may be calculated from the results obtained for the deposition of thick si 3 n 4 layers on silicon under similar conditions , and assuming a homogeneous distribution of silicon over the surface . [ 10 ] the structural quality of the invention may be evaluated by high resolution x - ray diffraction using a philips materials research diffractometer equipped with a four crystal [ ga ( 220 )] monochromator utilizing the cu k / α line of λ = 0 . 15406 nm . all rocking curves may be obtained in the symmetric geometry ( ω = θ ). for the off - axis scans , the wafer is tilted about the ψ axis ( commonly referred to as χ on many four - circle diffractometers ) by the appropriate angle . the full width at half maximums ( fwhms ) of the on - and off - axis diffraction peaks are a measure of the mosaic in the epitaxial layer and can each be related to specific types of threading dislocations ( tds ). the fwhm of the symmetric ( 0002 ) diffraction peak is related to the tilt of the subgrains with respect to the substrate , and thus to the density of pure screw and mixed tds . the off - axis ( 10 { overscore ( 1 )} 2 ) and ( 20 { overscore ( 2 )} 1 ) fwhms result from a combination of the tilt and the twist of the subgrains and are related to the density of mixed and pure edge tds . thereby , the sensitivity toward pure edge tds increases with increasing asymmetry ( increasing ψ ). [ 11 ] [ 0029 ] fig3 shows the dependence of the fwhm of the ( 0002 ) and ( 10 { overscore ( 1 )} 2 ) rocking curves on the average thickness of the silicon nitride passivation layers 106 found for samples grown on silicon substrates 110 following procedure a and samples grown on sapphire substrates 110 via procedure b 2 . since the island growth of ingan layer 108 depends on the predeposition of silicon nitride , first the influence of the silicon nitride layer 106 thickness was investigated . in the case of the samples grown on silicon 110 , the films grown in a regular manner without si x n y / ingan interlayers were of poor crystalline quality ( td density ˜ 10 11 cm − 2 ), as visible in the wide fwhm of the ( 0002 ) diffraction peak of about 1300 arcsec . ( the poor quality was mainly related to the fact that the growth conditions of the aln nucleation layer 112 had not been fully optimized .) however , the crystalline quality of the gan - on - silicon layers 104 is significantly improved by inserting the two si x n y / ingan interlayer structures 102 . the fwhm of the ( 0002 ) diffraction peak decreased from 1280 to 795 arcsec for a silicon nitride layer 106 thickness of 0 . 14 å . a further increase in the silicon nitride layer 106 thickness causes the layer quality to degrade again , and the fwhm increases to 920 arcsec . [ 0030 ] fig4 is a table of the ( 0002 ) and ( 10 { overscore ( 1 )} 2 ) diffraction peak for gan films 100 of the present invention . for the samples grown on sapphire substrates 110 , which were of higher crystalline quality when grown in a regular manner ( td density & lt ; 10 9 cm − 2 ) the insertion of the si x n y / ingan interlayers results in a decrease of the fwhm of the asymmetric ( 10 { overscore ( 1 )} 2 ) diffraction peak but did not affect the fwhm of the symmetric ( 0002 ) diffraction . samples with different numbers of si x n y / ingan interlayers may be grown on sapphire substrates 110 following procedure b 1 , using the optimum si x n y layer 106 thickness of 0 . 14 å , as determined in experiments . the lower crystalline quality of these samples [ td density ˜( 5 - 8 )× 10 9 cm − 2 ] compared to those grown following procedure b 2 is related to the low thickness of the gan layer 104 prior to deposition of the first si x n y / ingan layer . for samples without , with two , and with four interlayers ( 10 { overscore ( 1 )} 2 ) fwhm , values of 870 , 720 and 795 arcsec , respectively , have been measured ( not shown ). the corresponding values of the ( 0002 ) fwhms were 390 , 390 and 420 arcsec . the results demonstrate that the increase of the number of si x n y / ingan interlayers from two to four caused the crystalline quality to degrade again . obviously , the si x n y / ingan interlayers can also create new defects if too high in number . for this reason , embodiments using two si x n y / ingan interlayers may be preferred , however the invention is not limited to two interlayer structures . [ 0032 ] fig5 displays the dependence of the fwhm of the x - ray diffraction peak on increasing inclination angle ψ during the measurement for three different gan film 100 samples . since the sensitivity of the diffraction measurement with respect to pure edge tds increases with increasing ψ , the fwhm of the ( 20 { overscore ( 2 )} 1 ) diffraction peak reflects their density even more strongly than the ( 10 { overscore ( 1 )} 2 ) diffraction peak . furthermore , the mosaic due to pure edge dislocations may be estimated through extrapolation of the data toward ψ = 90 °. [ 11 ] the graph illustrates the improved crystalline quality of the sample with two si x n y / ingan interlayers using the optimum silicon nitride layer 106 thickness of 0 . 14 å , exhibiting a fwhm of the ( 20 { overscore ( 2 )} 1 ) diffraction peak of 500 arcsec in comparison to the standard gan film ( 720 arcsec ). the highly dislocated gan film ( td density of 5 × 10 9 cm − 2 ), which was grown under growth conditions not fully optimized , shows an even broader ( 20 { overscore ( 2 )} 1 ) fwhm of 910 arcsec . the results demonstrate that the crystalline quality of gan films 100 can be significantly improved through the insertion of the si x n y / ingan interlayers . although a homogeneous distribution of si atoms on the gan surface may be assumed in calculating the si x n y layer 106 thickness , the si atoms accumulate in surface areas with a high density of n - dangling bonds and specifically at the surface sites created by the intersection of the edge dislocations with the gan layer 104 surface . the thin silicon nitride layer 106 masks the dislocation , preventing the adsorption of ga and n species . in contrast , the intersections of threading dislocations with screw character , which create an additional surface step , act as nucleation sites for the ingan layer 108 growth resulting in the formation of the ingan islands . the islands then overgrow the passivated areas of the gan layer 104 surface . this mechanism is more effective the higher the td density in the starting layer due to the closer dislocation distance . in conclusion , dislocation reduction in gan films grown on silicon and sapphire substrates may be observed through a passivation of the gan surface with silicon nitride . the subsequently grown ingan islands overgrow areas with pure edge dislocations . the present invention is most effective at reducing the pure edge dislocation density when it is high , i . e ., & gt ; 10 10 cm − 2 . for highly dislocated gan on silicon films ( td density 10 11 cm − 2 ), the fwhm of the ( 0002 ) diffraction peak decreases from approximately 1300 to 800 arcsec after insertion of two silicon nitride / ingan interlayers . in the case of gan layers grown on sapphire ( dislocation density ˜ 10 9 cm − 2 ), the method results mainly in a reduction of the fwhm of the ( 10 { overscore ( 2 )} 2 ) and ( 20 { overscore ( 2 )} 1 ) diffraction peaks . the described method is most effective for applications which do not require a complete elimination of dislocations . although the present invention has been detailed with respect to gan , equivalently , the present invention may be extended to apply to all group iii - nitrides , aluminum -, gallium -, indium - and boron - ( aln , gan , inn , bn ) and their alloys with phosphorous ( p ), arsenic ( as ) and antimony ( sb ). in addition , as previously discussed , the passivation layer may be any material which produces a growth perturbation in the group iii - nitride and thereby halts the dislocation propagation . the invention may also be applied to the growth of group - iii nitrides on any compatible simple or complex oxide substrate known to those skilled in the art . some examples include silicon , sapphire , silicon carbide , zinc oxide , lithium gallate , lithium aluminate and aluminum nitride . this concludes the description including the preferred embodiments of the present invention . the foregoing description of the preferred embodiment of the invention has been presented for the purposes of illustration and description . it is not intended to be exhaustive or to limit the invention to the precise form disclosed . many modifications and variations are possible in light of the above teaching . it is intended that the scope of the invention be limited not by this detailed description , but rather by the claims appended hereto . the above specification , examples and data provide a complete description of the use of the invention . since many embodiments of the invention can be made without departing from the spirit and scope of the invention , the invention resides in the claims hereinafter appended . 1 . h . amano , n . sawaki , i . akasaki , and y . toyoda , appl . phys . lett . 48 , 353 ( 1986 ). 2 . a . usui , h . sunakawa , a . sakai , and a . yamaguchi , jpn . j . appl . phys ., part 2 36 , l899 ( 1997 ). 3 . t . gehrke , k . j . linthicum , d . b . thomson , p . rajagopal , a . d . batch - elor , and r . f . davis , mrs internet j . nitride semicond . res . 4s1 , ( 1999 ). 4 . s . nakamura , m . senoh , s . nagahama , n . iwasa , t . yamada , t . matsus - hita , h . kiyoku , y . sugimoto , t . kozaki , h . umemoto , m . sano , and k . chocho , appl . phys . lett . 72 , 211 ( 1998 ). 5 . p . kozodoy , j . p . ibbetson , h . marchant , p . t . fini , s . keller , j . s . speck , s . p . denbaars , and u . k . mishra , appl . phys . lett . 73 , 975 ( 1998 ). 6 . g . parish , s . keller , p . kozodoy , j . p . ibbetson , h . marchand , p . t . fini , s . b . fleischer , s . p . denbaars , u . k . mishra , and e . j . tarsa , appl . phys . lett . 75 , 247 ( 1999 ). 7 . m . iwaya , t . takeuchi , s . yamaguchi , c . wetzel , h . amano , and i . akasaki , jpn . j . appl . phys ., part 2 37 , l316 ( 1998 ). 8 . s . keller , u . k . mishra , s . p . denbaars , and w . seifert , jpn . j . appl . phys ., part 2 37 , l431 ( 1998 ). 9 . s . tanaka , s . iwai , and y . aoyagi , appl . phys . lett . 69 , 4096 ( 1996 ). 10 . a . c . abare , ph . d . thesis , ece technical report no . 00 - 04 , department of electrical and computer engineering , university of california at santa barbara , march 2000 . 11 . v . srikant , j . s . speck , and d . r . clarke , j . appl . phys . 82 , 4286 ( 1997 ). 12 . tanaka , s . ; 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