hereinafter , characteristics of a crystal growth sige according to the present invention will be explained in detail and in comparison with prior art shown in reference to fig6 - fig1 . in the present specification , a crystallo - graphically equivalent crystal orientation group such as crystal orientations ( 110 ), ( 101 ) , and ( 011 ) are summarized and are represented as { 111 }. fig6 shows prior art of a surface sem ( scanning electron microscope ) image of a poly - crystalline si thin film formed by eximer laser annealing for a base material of the tft . in this poly - crystalline si thin film , a film is formed on a glass substrate with a thickness of 50 nm by a well - known plasma cvd method , and the film is then annealed by an excimer laser under the conditions of an energy density of 340 mj / cm 2 . although an example having a relatively small size of 50 - 100 nm is described as an average grain size of low - temperature poly - si , the maximum grain size that can be achieved at present is 200 - 300 nm . however , the greater the grain size , the more increase the dispersion of the grain size . as a result , there is a drawback that a large dispersion is generated in tft mobility . therefore , as a practical grain size , the size of 50 - 100 nm is a typical example . although grain boundaries of respective crystal grains show dark contrasts , adjacent portions thereto can sporadically observed as a plurality of bright contrast regions . a difference in the contrast such as this corresponds to surface roughness . a heat treatment method such as the excimer laser annealing involves volume expansion of a si crystal in processes from melting to solidifying . therefore , in the vicinity of grain boundaries where respective crystal grains bump against each other , a force uplift of the film in an upper direction perpendicular to a substrate is created in order to expand the volume portions . this force is further enlarged in the vicinity of a triple point in grain boundaries of crystals and constitutes a cause of surface roughness . an average surface roughness reaches 50 nm relative to a si - poly crystal with a film thickness of 50 nm . fig7 shows a surface sem image ( left figure ) and a plane tem ( transmission electron microscope ) image of a low - temperature poly - crystalline si 1 - x ge x thin film according to the present invention . the film is formed by 30 shots of pulsed laser beam under conditions that the ge concentration x is x = 0 . 3 , and an energy density of krf excimer laser is 240 mj / cm 2 . in this case also , the film having a thickness of 50 nm is formed on a glass substrate by a well known plasma cvd method . at that time , 30 mol % of ge is introduced as a source relative to si into cvd gas , and a si 0 . 7 ge 0 . 3 thin film ( hereinafter simply refer to sige thin film ) is formed . that film is annealed by the excimer laser having an energy density of 240 mj / cm 2 . when the left - side figure in fig7 is observed , it will be understood that although crystal grain size is substantially similar to crystal grain size of a poly - crystalline si thin film in fig6 a contrast relationship between an interior grain and a grain boundary is reversed . in contrast to fig6 this is because a portion of the grain boundary is projected upward more than a portion of the interior grain . as a result of elementary analysis , a remarkably higher concentration of ge is detected in the grain boundary as compared with the interior grain . the high concentration region approximately coincides with the bright contrast region in fig7 . when a dark field image ( right figure in fig7 ) of plane ten of poly - crystalline si 0 . 7 ge 0 . 3 thin film is observed , details of a crystal structure can be determined . in this figure ( right figure in fig7 ), measurements are conducted under the condition that a { 110 } surface in parallel with a surface of substrate is brightly displayed . from the figure it will be understood that most of the crystal grains are similar in brightness to each other , and several black grains exist between the crystal grains . in an interior grain of the crystal , rectilinear patterns are observed at several places . these patterns may be considered stacking faults or twin crystals . the other portions thereof are constituted of substantially beautiful single crystals . fig8 shows a view illustrating a crystal structure of a poly - crystalline sige thin film of the present invention illustrated in fig7 . most of the crystal grains have { 110 } surfaces in parallel to the substrate and trued up one another . several number of grains having different crystal orientations exist between the crystal grains . these grains having different crystal orientations may have the { 110 } surfaces inclined at an angle of 1 - 10 ° from a surface in parallel to the substrate . thereby , it will be understood that the poly - crystalline sige thin film of the present invention is the poly - crystal having basically a { 110 } surface orientation . the interior grain is more si - rich than a ge concentration which has been introduced before annealing , and the grain boundaries are constituted of crystals having larger ge concentrations . the cause for occurrence of a phase separation ( a ge concentration is different between crystal interior grain and grain boundary ) like this results from a diffusion coefficient of ge in si and bonding energy of si versus ge . the diffusion coefficient of ge in amorphous si is comparatively large and d = 8 . 0 × 10 20 cm 2 / s even at temperature of 600 ° c . see s . m . prokes and f . spaepen , appl . phys . lett ., vol 47 , p 234 ( 1985 ). under a mobility condition like this , in order that a crystal assemble a stable lattice , it is better to minimize the bonding energy between respective atoms . the bonding energy between si - si , si - ge , and ge - ge are respectively 3 . 73 ev , 3 . 65 ev , and 3 . 56 ev . see k . nakagawa , n . sugii , s . yamaguchi , and m . miyao , j . cryst , growth , vol . 210 , p560 ( 1999 ). therefore , ge is energetically stable bonded together to ge rather than bonded to si . when a condition is set that there is more si than ge before annealing , a si crystal nucleus is produced in a certain optional position at the initial stage of crystallization . in a growth process thereof , a crystal grain involves many si performing a growth while expelling ge to a periphery thereof . it is believed that a poly - crystalline sige having such a crystal structure is formed by attaining a growth everywhere of the crystal grains like this . the phase separation between elements composed of such a plurality of sorts thereof is known . there is an example ( for example , japanese unexamined patent publication h2000 - 261043 ) that a poly - crystalline thin film is utilized as a thermo - electric conversion material by cutting and separating phase separated elements respectively to p type / n type . however , the poly - crystalline sige thin film in which structures in every portions of the grain boundaries thereof are constituted of their perfectly ge - rich state such as a poly - crystalline si thin film of the present invention , the surface roughness in the grain boundary thereof can be restrained as described below , and which can be applied to a tft . this has not been previously known . further , when the phase of ge - rich like this can be produced , in particular , the perfect state thereof constitutes an advantageous structure to positive hole mobility . a single crystal ge ( electron mobility ˜ 3000 cm 2 ns , positive fault mobility ˜ 1500 cm 2 ns ) as a property of a material itself has a larger mobility than a single crystal si ( electron mobility ˜ 1500 cm 2 ns and positive hole mobility ˜ 500 cm 2 ns ). see m . v . fischetti and s . e . laux , j . apple . phys . vol 80 , p2234 , ( 1996 ). a problem of interface stability of ge - oxidation film is not so much a problem if a thermal oxidation film is not used but rather a deposit oxidation film is used . one reason why ge having such a high potential has not been utilized to a tft is that ge cannot be practically applied since the grain size of poly - crystalline ge capable of being formed is remarkably small and the current scattering in a grain boundary is large . however , if the material has a poly - crystalline sige thin film structure like the present invention , there is such an advantage that , as a whole , high mobility can be realized by making grain size thereof equivalent to poly - crystalline thin film , and by existing ge - rich phases of high mobility in the vicinity of grain boundary having large current scattering . fig9 shows prior art of a surface sem image ( left figure ) and an afm ( atomic force microscope ) image ( right figure ) for a squarely enclosed region in the left figure of a poly - crystalline si thin film . the afm image displays the surface roughness directly with a ratio of contrast as it is . bright projection parts are observed everywhere in the vicinity of the triple points of crystal grains in a poly - crystalline si thin film . a difference of elevation between a top - most point of these projection parts and a bottom - most point of recess parts is about 50 nm as described above and is remarkably large . this means that the force facing upward operated by volume expansion is remarkably large at the triple point . on the other hand , fig1 shows a sem image ( left figure ) and an afm image ( right figure ) for a squarely enclosed region in the left figure of a poly - crystalline sige thin film of the present invention . as clearly understood from the afm image , portions corresponding to grain boundaries are bright , and the projection parts are formed in those portions . the left figure in fig1 is an afm image similar to the right figure of fig1 . the right figure in fig1 shows a view illustrating a distribution of elevations sectioned at a straight line portion drawn in the left figure . from this figure it will be clearly understood that bright portions correspond to the projection parts and dark portions correspond to the recess parts . differences of elevations between the top - most point of the projection parts and the bottom - most point of recessed parts are a maximum of 20 nm or so and are remarkably restrained as will be understood by comparing it with 50 nm of the poly - crystalline si thin film illustrated in fig7 . differences in coefficients of volume expansion or moduli of elasticity between si and ge are considered to be the main cause of the remarkable difference in the elevation . that is , a thin film is formed by a lattice constant ( larger than amorphous si ) as mixed crystals of amorphous sige before annealing . however , since a soft ge - rich phase is formed around a comparatively hard si crystal by a phase separation at the time of solidification , the grain boundary causes a relaxation of volume expansion portion . as a result , the surface roughness can be restrained . anyway , a poly - crystalline sige thin film of the present invention provides unusually smaller surface roughness as compared with a conventional poly - crystalline si thin film . fig1 shows views illustrating laser annealing conditions required for forming a poly - crystalline sige thin film of the present invention having a ge concentration x of x = 0 . 3 . an abscissa shows an energy density [ mj / cm 2 ] of excimer ( krf ) laser , an ordinate shows a film thickness of a poly - crystalline sige thin film , and frequencies of all laser beam annealing of 30 times . when the energy density is gradually increased from the minimum of 140 of mj / cm 2 , bright contrast regions showing surface projection parts are gradually increased . only in the case of the film thickness being 50 nm and 30 nm , and the energy densities of 240 mj / cm 2 , and 220 mj / cm 2 , respectively , are projection parts peculiarly coincided with the structure of the crystal grain boundaries . structures like this can be observed in other ge concentrations ( for example x = 0 . 1 or the like ). it has been clear that only under very narrow annealing conditions can the coincidence be realized . this results from a condition under which ge concentration introduced before annealing become timely in a segregable condition in the solidification process is not so much wide . however , in the present invention , a poly - crystalline sige thin film which has been realized under condition of these peculiar annealing treatment is effectively utilized . hereinafter , embodiments of the present invention will now be explained . embodiments of the present invention will be specifically explained with reference to fig1 to fig5 . fig1 shows a thin film transistor device relating to a first embodiment of the present invention . in the drawing , a figure in an upper part of fig1 shows a longitudinal sectional view , a figure in a lower part thereof shows a plan view transversely ( taken on line x - x ′) cross sectioning a channel portion . a poly - crystalline si 1 - x ge x thin film is formed on the insulator substrate 1 composed of a glass plate under a condition of forming the film by plasma cvd as described below , and under a laser annealing condition . that is , silane and germane are utilized as raw material gas , while a gas volume is adjusted for obtaining a flow ratio between si versus ge of 0 . 7 versus 0 . 3 . an amorphous si 1 - x ge x thin film is formed by the plasma cvd to obtain the total film thickness of 50 nm . next , a poly - crystalline si 1 - x ge x thin film 2 is formed by irradiating an excimer laser with respect to a surface of the substrate 1 . the laser annealing may be provided under conditions of an energy density of 240 mj / cm 2 , the number of pulsed laser beam of 30 shots , and a pulse frequency of 100 hz . a source 3 and a drain 4 are formed on this poly - crystalline si 1 - x ge x thin film , and a gate insulation film 5 and a gate 6 are formed on a channel . the region directly below the gate insulation film 5 is an active region of an electric field effect transistor , so that a current density is the largest . a plan view of that portion is shown in the lower part of fig1 . in the present embodiment , the ge concentration x in an interior of a crystal grain 7 of the poly - crystalline si 1 - x ge x thin film on this plane is set to be 0 & lt ; x ≦ 0 . 1 where a ge concentration x in a grain boundary of the crystal 8 is set to be 0 . 3 ≦ x & lt ; 1 . with such a lattice structure , a difference in elevations between surfaces ( projection parts ) of grain boundaries 8 and surfaces ( recessed parts ) of crystal grains 7 is about 20 nm and the difference is remarkably restrained so that a gate insulation film can be made comparatively thin (˜ 50 nm ). therefore , high mobility can be realized since a number of carriers can be induced to the channel by a relatively small gate voltage . further , since most of the crystal grains 7 are trued up to a { 110 } surface in parallel to the substrate 1 , a lattice conformity in crystal grain boundaries is relatively tidy , so that it has an effect that current scattering in grain boundaries can be restrained . the present embodiment further improves mobility of entire films by forming a ge - rich phase of high mobility in the grain boundaries 8 . measurement of a ge concentration x with respect to si in a poly - crystalline si 1 - x ge x thin film is conducted by the following methods . concentrations of si and ge are measured by using a small ( about 100 nm ) electron beam for a probe of an x - ray micro - analyzer equipped in an interior of a transmission electron microscope ( tem ), irradiating surfaces of a sample , and by measuring a wave length and intensity of a characteristic x - ray emitted from a laser irradiation region . next , a ge concentration x relative to si is found by calculation using the results of measurement for the concentrations of si and ge . further , the measurement of a concentration of composition for crystal grain is conducted so that a laser beam irradiation region is contained in an interior of a crystal grain . measurement of a concentration of composition at a grain boundary is conducted so that a laser beam irradiation region includes a grain boundary . here , the laser beam irradiation region may protrude from the grain boundary and may stride over the crystal grains . fig2 - fig4 show views illustrating a thin film semiconductor device and production process thereof relating to a second embodiment of the present invention . in the present embodiment , poly - crystalline si 1 - x ge x thin films are partially introduced and a transistor is formed of a cmos ( complementary nos ) type . firstly , as illustrated in fig2 an amorphous si thin film 9 is formed on an insulator substrate ( glass plate ) 1 . a part of the thin film 9 is formed by etching and removing using a photo process and is provided with an increased region 10 of a ratio of an embedded type ge composition . a laser beam irradiation region 11 of the thus obtained thin film surface is scanned by sequentially moving a stage retaining the substrate 1 while conducting krf excimer laser beam irradiation . at this time , by program controlling , in advance , a moving region of the stage , selectively crystallize only portions that will later be transistor regions . with such a process , as illustrated in fig3 pure si poly - crystals 12 and poly - crystalline si 1 - x ge x thin films 2 regions are formed only on required regions of the amorphous si thin film 9 . next , as illustrated in fig4 n type regions 14 are formed by implanting as ions on an crystallized thin film , and p type regions 13 are formed by implanting b ions . both of the regions are systematically and selectively formed by utilizing an implanting mask . thereafter , furnace annealing is conducted in a nitrogen atmosphere at a temperature of 600 ° c . for approximately one hour , and the carriers of n - type regions 14 and in p type regions 13 are activated . the gate insulation films 5 and gates 6 are provided on the n type regions . 14 and the p type regions 13 to form transistors . by so doing , there is an advantage that the cmos type transistors in which low consumption power and high mobility being made compatible , are formed by respectively forming an n type transistor ( composed of the poly - crystalline si thin films 12 in the p type region 13 ), and p type transistors ( composed of the poly - crystalline si 1 - x ge x thin films 2 in the n type region 14 ). fig5 shows an example of an image display device used as a thin film semi - conductor device of the present invention . poly - crystalline si thin films and poly - crystalline si 1 - x ge x thin films are selectively formed on an insulator substrate ( glass plate ) 1 . circuits composed of a pixel driver region 17 , a buffer amplifier region 18 , gate driver regions 19 , shift resister regions 20 , gate driver regions 21 and the like are integrated on the poly - crystalline si thin films and the poly - crystalline si 1 - x ge x thin films . these are integrally formed and are connected to an image display panel 15 having pixels 16 . since the required performances to transistors constituting these circuits are respectively different from each other , the first to third embodiments of the present invention are selectively and complexedly combined with one another and utilized . with such a constitution , the main circuit can be integrated on the glass substrate of a large area , and an image display device integrating most of the conventional peripheral circuits can be formed . as such , the image display device can be produced with few processes utilizing the low cost glass substrates .