LU82779A1 - PROCESS FOR CRYSTALLIZATION OF FILMS AND FILMS THUS OBTAINED - Google Patents

Description

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The present invention relates to a process for crystallizing films chosen from the group comprising amorphous elementary semiconductor films and polymetallic films composed of two elements belonging respectively to Groups III and V or to Groups II and VI of the Table. Periodical, as well as to the semiconductor polycrystalline films thus obtained.

The miniaturization of electronic circuits is one of the major objectives of the electronics and IT industry.

i: ’Current techniques use selective doping methods I:‘ tif monocrystalline silicon wafers by various masks whose precision determines the limits of development of these circuits. These processes are expensive, very delicate to set up and only a few systems have been developed which are reliable and of large capacity. These systems are made from monocrystalline silicon, which implies the discontinuity of disj | install this material in sufficient quality and quantity to produce the circuits. All the processes were broken down into several stages, each of which is characterized by a large number of parameters which must be controlled with precision: crystal preparation, masking, doping. These parameters render the; "realization of miniaturized circuits a very complex undertaking which cannot be generalized to other base materials! · · than silicon, for example, without a general modification | j of all the parameters. The lack of flexibility of these techniques i ·; and their complexity underline the need for a new technique which is simpler and easily adaptable to other supports than Si - 3 -! monocrystalline.

The object of the present invention is to remedy the aforementioned drawbacks, and to provide methods for crystallizing amorphous elementary semiconductor films or polymetallic films composed of two elements belonging respectively to Groups III and V or to Groups II and VI of the Periodic Table. , which have a reliability at least identical to the methods used so far, and which also allow more advanced miniaturization and simultaneous large-scale multiplication of the products obtained.

To this end, according to the invention, the surface of the film to be crystallized is irradiated by a laser beam guided by an assembly of optical fibers arranged parallel to each other, each fiber having a diameter not exceeding 50fJ->, the irradiation causing crystallization into regularly distributed and tightly confined crystallites.

According to a particularly advantageous embodiment of the invention, the optical fibers have a diameter equal to 50 ^ and preferably a diameter between 4 and 25jij /, the assembly of parallel optical fibers having a diameter substantially equal to that of the bundle laser, this assembly of fibers comprising a very large number of fibers, preferably between 300 and 15000 fibers, the number of fibers varying according to the useful diameter of these fibers and the useful diameter of the laser beam.

According to another particular embodiment of the method of the invention, the laser beam is homogenized before being guided by the assembly of fibers, by passage through - 4 - I (i of a cylindrical bar of quartz of diameter substantially equal to the diameter of the laser beam, bent twice at right angles in opposite directions, covered with a metal layer, the entry and exit ends of the bar being polished, mutually parallel and perpendicular to its axis .

Advantageously, one obtains an ordered network or circuit II of crystallites on the film which one irradiates, by displacing | this in a plane perpendicular to the axis of the fibers, the fine impression of the network or circuit of crystallites being controlled; . The object of the present invention is also to carry out a process allowing the printing of an ordered network or circuit of crystallites to be multiplied on a single film or on a assembly of elementary or polymetallic semiconductor films included in the category of the aforementioned films.

The aims mentioned above are achieved by using the radiation produced by a medium-energy laser, that is to say with an energy of between 50 and 100 mj / cm. The energy of this beam is taken up by an assembly of fibers; 1 optics with a diameter less than or equal to 50JM, preferably: ^ between 4 and 25JM, and directed towards a target consisting of an amorphous elementary semiconductor film or a polymetallic film composed of two elements belonging respectively in Groups III and V or in Groups II and VI of the Periodic Table.

^ Under the impact of the beam, the amorphous elementary film crystallizes; in an orderly manner and confined to very reduced volumes determined; by the diameter of the fibers and the distance between the end of | | fiber exit and target. On identical volumes, the polymetallic film crystallizes in the form of the corresponding semiconductor compound, the rest of the film (not irradiated) remaining metallic. By a programmed displacement of this target in a plane perpendicular to the axis of the fibers, an ordered network of cris-tallites is then "printed" optically on the film whose electronic transport properties (mobility and number of carriers) are thus found strongly modified by several orders of magnitude in irradiated areas compared to non-irradiated areas. The use of a very large number N of identical fibers each transmitting the same energy then makes it possible to reproduce N times the programmed circuit. Targets which have been found to be particularly suitable for this purpose are semiconductor füns formed of Si or Ge, and polymetallic films composed of alternating layers of aluminum and antimony, aluminum and arsenic, galium and arsenic, indium and phosphorus (Groups III and V), or cadmium and sulfur (Groups II and VI).

Other details and particularities of the invention will emerge from the description given below by way of nonlimiting example of some particular forms of the invention. The description given below will relate in particular to the shaping of the laser beam, the scanning of the irradiated surfaces by the displacement of the irradiated film or films and the simultaneous reproduction in a large number of copies of an ordered network or circuit of crystallites on a single film (target) or an assembly of films (different targets).

1. Beam shaping.

Depending on the thickness of the films to be treated, which is at least equal to 0.015 p>, and preferably between 1 and 25 μl /, the laser radiation can have different origins, for example: pulsed laser with medium power dye and low energy for thin films of thickness less than or equal to 0.2JJ / on glass, or pulsed laser with high power ruby but low energy for films of thickness greater than Ψ- also deposited on non-crystalline substrate, example of glass or fused silica.

Whatever the laser beam, it is placed opposite an assembly of parallel quartz fibers, with a diameter less than or equal to assembled on a diameter equal to that of the beam, the laser beam penetrating all the fibers siwant their respective longitudinal axis. The fibers, for example 1000 to 2000, all have an equal diameter, the number of fibers being only limited by the useful diameter of the bundle on which it is homogeneous and by the diameter of the fibers. Each fiber is polished at its ends. This work is carried out by assembling all the fibers in a compact manner, held at each end, by a metal ring with a diameter less than or equal to the useful diameter of the bundle. Thus assembled, all the fibers are polished together, at their two successive ends, by abrasive on a rotary table. The respective ends of the assembled fibers are each located in the same plane arranged perpendicular to the longitudinal axis of each of these fibers. The ends of the fibers facing the laser beam are then held in their assembly ring, the opposite ends being released from their ring.

As already stated, according to a preferred embodiment of the invention, before being guided by the assembly of fibers, the laser beam can be made homogeneous by passage through any means adequate optics known from the state of the art. The homogenizer used is preferably a cylindrical quartz bar, with an inlet diameter equal to the diameter of the laser beam, bent twice at right angles in opposite directions, covered with a metallic layer, for example a film of aluminum, the entry and exit ends of the bar being polished, mutually parallel and perpendicular to its axis. The laser beam can possibly be concentrated by a system of lenses at the entrance of the bar. When a homogenizing bar of this type is used, the ends of the fibers facing the homogenized bundle are held in their assembly ring, which is then brought into contact with the outlet of the bar, the opposite ends being of course freed from their ring, as we just mentioned.

Since each of the fibers receives the same energy (plus or minus 1%), the capacity of each fiber to transmit radiation without losses (either by absorption or by lateral transmission) then makes it possible to have a very large number light sources of identical energy, on identical diameters. Depending on the energy required, the laser radiation can be reduced by one or more calibrated filters placed on the beam path, perpendicular to it, before the fibers enter. After having passed through the assembly of optical fibers, the laser beam can be structured, for example by passing through an optical means arranged to produce interference fringes, this optical means possibly consisting of a optical network in engraved quartz.

2. Crystallization and scanning of films.

If the network is not used, the pulsed beam which leaves the end of a fiber has a granular structure (or "speckle"), that is to say that its impact on a surface is broken down into a set of substantially circular tasks distributed in a homogeneous and stable manner from one pulse to another. The size of these "grains" of light is given by A = ^ where \ tg a is the wavelength of the radiation and at the angle at which} each site of the target or film sees the radius R of the fiber.

|

If tg a = \ d, where d is the distance between target (film) and

| d R

fiber.

We see that for a given fiber and a fixed wavelength, Δ increases with d. On the other hand l \ decreases if R increases, at constant d. An irradiation of this type produces star crystallites in number and dimension identical to those of speckle spots, cou-; covering the entire irradiated surface, the diameter of which is equal to that of the fiber. By acting on the speckle (therefore on, R and d), it is thereafter easy to vary the size of the crystallites, in particular to produce a single star crystallite of diameter equal to that of the fiber.

By interposing an optical network on the beam path, each speckle task is fringed and the stars produced are structured.

Since no alteration of the crystallized zones produced on a pulse is observed when a train of pulses is superimposed on these same zones, the surface of the film to be irradiated is moved opposite a fixed fiber end, that is to say in a plane perpendicular to the axis of this fiber, so as to allow an overlap of the irradiated zones from one pulsation to the next, thus making it possible to obtain an ordered network or circuit of crystallites. This overlap determines the fineness of the printing of the circuit crystallized in the film, finesse which is controlled by varying the speed of movement of the film, that is to say in fact the scanning speed of the surface of the film. by means of the laser radiation transmitted by the optical fibers, and the repetition rate of the laser pulses.

3. Method allowing the multiplication of the printing of an ordered network or circuit of crystallites.

As already mentioned above, the present invention also provides a method for multiplying the impression of an ordered network or circuit of cris-. tallites on a single film or on an assembly of films chosen from the group comprising amorphous elementary semiconductor films and polymetallic films composed of two elements belonging respectively to Groups III and V or to Groups II and VI of the Periodic Table. In this case, the output ends of the fibers mounted in the axis of the shaped bundle as described above, are assembled on a flat frame according to a geometric configuration adapted to the number of fibers and to the extent of the network or circuit. from cris- I.

- 10 - tallites to print. The assembly on the chassis is such that all the fibers are parallel to each other and their ends in the same plane parallel to the plane of the chassis. Next to this frame and parallel to it, another flat frame is mounted on which is mounted either the film to be irradiated, covering the entire surface of the frame, or the assembly of the films to be irradiated, distributed according to an identical geometrical configuration | to that of mounting the fibers on their chassis, so as to accommodate the extent of the network or circuit of crystallites to be made {* 1 - read in a number of copies equal to the number of fibers i |! (each fiber being directly facing a given film). The distance between the frames supporting the film (s) (target) and; that of the fibers is adjusted so that the distance between fiber and film corresponds to the desired impression (refer, in this regard, to chapter 2 above). The fiber frame remains fixed while the frame supporting the film (s) can move in its plane, at a fixed distance from the previous one. A movement! translation jl ment is then provided to the film frame. This movement allows each fiber to optically print an ordered circuit or network of semiconductor crystallites on the single film or on each film mounted on the frame.

It will be noted, taking into account the above, that the size and the distribution of the crystallites on the film or films to be irradiated, whatever the crystallization process used, can be controlled as a function of the diameter of the optical fibers, the fiber-film distance, as well as length! I; | wave, energy and power of the laser beam irradiating the film.

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The shaping of the laser beam being stable in space, it is possible to irradiate successively under the same energy conditions, two superimposed films, allowing an epitaxial crystallization of the second film covering the first, that is to say say an exact superimposition of the cris-tallites belonging to each of these films. One such example of superimposed films is given by the Si / Al-Sb system, obtained by evaporating an amorphous layer of Si on an Al-Sb film, crystallized according to the invertim, in the form of the semiconductor compound AlSb, the film of Si being irradiated by the same 3aser beam in an identical manner.

The examples which follow illustrate the invention without however limiting it.

Example 1.

Germanium film.

The experiments and tests described below were carried out with optical fibers with a diameter equal to 50 µm *, the results obtained being obviously extrapolable to any fiber diameter, in particular to fibers of smaller diameter at 50JM ,. In these tests, only the speckle effect was used, the addition of an optical means (for example an optical network of quartz) for structuring the speckle of course making it possible to improve the crystallization.

For the laser used (dye, power of 6 KW for pulses of 10 ^ sec repeated at a rate of 25 sec, the following results have been recorded: - a homogeneous beam of 2 mm of useful diameter has been produced, which can accommodate 300 fibers with a useful diameter of 50yy;; - 12 - i I- on the irradiated germanium film areas, with a diameter of 50, a homogeneous distribution of star crystallites was obtained, all of the same diameter chosen in the range from 2 i to 25 / ^ depending on the irradiation conditions, this homogeneous distribution being reproducible. A single star with a diameter of 50JA * was obtained by placing the target film 2 mm from the end - 'miter of the fiber and by concentrating the beam slightly, ii I the energy per unit of surface then being reduced · *; |. - with an overlap of 90% between successive irradiated zones,!' the displacement of the target film at a speed of 0.12 mm dry allows definition of the limits of printing to - 0.3%, or 0.13 DD .

Example 2.

Germanium film.

For fibers of useful diameter, the miniaturization of the crystallized zones is as follows; - a single impact crystallite of dimension equal to 7 for a film-fiber distance equal to 40/1; :, - for a 90% overlap between successive irradiated zones, j "a displacement speed of 0.017 mm sec ^ allows a definition of the edges of - 0.25%, ie 0.017 // ,.

j

It will be noted that the advantages of fibers of a very small diameter reside in a better definition of the traces, in a reduction in the intensity of the radiation at its source, in a higher scanning speed, compared to fibers of a diameter of SOJX, and in a much greater multiplication of the circuits produced (of the order of 15,000,

Claims (28)

1. Method for crystallizing a film chosen from the group comprising amorphous elementary semiconductor films and polymetallic films composed of two. elements belonging respectively to Groups III and V or to Groups II and VI of the Periodic Table, characterized in that it consists in irradiating the surface of the film with a laser beam guided by an assembly of optical fibers arranged parallel to each other, each fiber having a diameter not exceeding 50 microns, the irradiation causing crystallization into regularly distributed and closely confined crystallites. 2. Method according to claim 1, characterized in that the optical fibers have a diameter equal to 50 microns. 3. Method according to claim 1, characterized in that the optical fibers have a diameter between 4 and 25 microns. 4. Method according to any one of claims 1 to 3, characterized in that the optical fibers each have an equal diameter. 5. Method according to any one of claims 1 to 4, characterized in that quartz fibers are used as optical fibers. ! 16. Method according to any one of claims 1 to 5, characterized in that the assembly of parallel optical fibers has a diameter substantially equal to that of the laser beam. ! 7. Method according to claim 6, characterized! in that the fiber assembly comprises 300 to 15,000 fibers. 18. A method according to any one of claims 1 to 7f characterized in that the laser beam is placed I opposite the optical fibers assembled so as to penetrate r, the latter along their longitudinal axis. * 1 9. A method according to any one of claims 1 to 8, characterized in that the optical fibers are 'assembled in a compact manner, polished at each of their ends: i mities and held by their end facing the beam by means of a metal ring with a diameter not exceeding the useful diameter of the laser beam. i 10. The method of claim 9, character 1. t; 'j risé in that the respective ends of the assembled fibers I are located in the same plane arranged substantially perpendicular- | Irement stretching to the longitudinal axis of these fibers. 111. Method according to any one of claims 1 to 10, characterized in that the laser beam is | homogenized before being guided by the assembly of fibers. * ΐ ïi 12. The method of claim 11, characterized in that the laser beam is homogenized by passing it through a cylindrical quartz bar with an inlet diameter 1 substantially equal to the diameter of the laser beam, bent i! * - 15 - twice at right angles in opposite directions, covered with a metallic layer, the inlet and outlet ends of the bar being polished, parallel to each other and perpendicular to its axis. 13. The method of claim 12, characterized in that the laser beam is concentrated by a lens system before being homogenized. 14. Method according to any one of claims 1 to 13, characterized in that the radiation of the laser beam is reduced by one or more filters arranged on the path of the beam, perpendicular to it, before it enters assembly of optical fibers. 15. Method according to any one of claims 1 to 14, characterized in that the laser beam is structured after having passed through the assembly of optical fibers. 16. The method of claim 15, characterized in that the laser beam is structured by passage through an optical means arranged to produce interference fringes. 17. The method of claim 16, characterized in that the optical means arranged to produce · interference fringes is constituted by an optical network of etched quartz. 18. Method according to any one of claims 1 to 17, characterized in that the film is deposited on a non-crystalline substrate. ί - 16 -, 19. A method according to any one of claims 1 to 18, characterized in that the film has a thickness at least equal to 0.015 microns. 20. The method of claim 19, character ized in that the thickness of the film is between 1 and 25 microns. 21. Process according to any one of the claims! cations 1 to 20, characterized in that the dimension and the distribution of the crystallites on the film are controlled as a function of the diameter of the optical fibers, of the fiber-film distance as well as of the wavelength, of the energy and power of the laser beam irradiating the film. 22. Method according to claim 21, characterized in that the fiber-film distance is of the order of 0.5 to 5 mm. 23. Method according to either of claims 21 and 22, characterized in that the energy of the laser beam 2 is between 50 and 100 mj / cm. 24. Process according to any one of the claims:. cations 1 to 23, characterized in that the film is moved in a plane perpendicular to the axis of the fibers so as to obtain | an ordered network or circuit of crystallites. 25. The process as claimed in claim 24, characterized in that the fineness of printing of the network i or crystallite circuit is controlled by the speed of movement of the film and the repetition rate of the laser pulses. 26. A method according to any one of claims 1 to 25, characterized in that an amorphous elementary semiconductor film formed from silicon or germanium is used. - 17 - 27. A method according to any one of claims 1 to 25, characterized in that a poly-metallic film is used composed of alternating layers of aluminum and antimony, aluminum and arsenic, of galium and arsenic, indium and phosphorus (Groups III and V), or of cadmium and sulfur (Groups II and VI). 28. A method of multiplying the impression of an ordered network or circuit of crystallites on a single film ”or on an assembly of films chosen from the group comprising amorphous elementary semiconductor films and polymetallic films composed of two elements belonging respectively in Groups III and V or in Groups II and VI of the Periodic Table, characterized in that it consists in irradiating the surface of the semiconductor film (s) with a laser beam guided by the assembly of optical fibers according to one any one of claims 1 to 23, by assembling the outlet ends of the fibers mounted in the axis of the bundle on a fixed flat frame according to a geometrical configuration adapted "to the number of fibers and to the extent of the network or printed circuit, the fibers on the frame being parallel to each other and their ends being arranged in the same plane parallel to the plane of the frame, and arranged parallel to the frame of fibers and opposite this, a movable chassis-plane on which the above-mentioned film is mounted, covering the entire surface of the chassis, or the assembly of the aforementioned films, distributed in a geometric configuration identical to that of the mounting of fibers on their chassis, each fiber facing a given film, and to move the chassis supporting the film or the assembly of films i -18 - In a translational movement relative to the fiber chassis, the film chassis remaining at a fixed distance of the fiber chassis, thus allowing each fiber to print an ordered network or circuit of crystallites on the single film or on each film mounted on the chassis. 29. The method of claim 28, character-ized in that one adjusts the distance between the film j] and fiber frames so that the distance between fiber and film Ij ·; % corresponds to the desired impression. il - Μ * 30. Method for crystallizing two superimposed films chosen from the group comprising semiconductor films i ’j i '; amorphous elementary teurs and polymetallic films composed of two elements belonging respectively to Groups III and V \ j jj or to Groups II and VI of the Periodic Table, characterized in that it consists in crystallizing a first film according to one any one of claims 1 to 27, superimposing on it by evaporation a second film, and irradiating this second film in the same manner as the first so as to obtain a crystallization. # epitaxial tion of this second film on the first. i! 31. Method according to claim 30, characterized in that the first film is a film composed of an alternation of layers of aluminum and antimony and in that the second film is formed of silicon or germanium. 32. Process for the crystallization of films and films P j] thus obtained, as described above, in particular in the examples given. Drawings. floor i .....: a-L. pages of which —A ...... cover page i ..... yiy .. description pages I claim pages ...... Λ— short description Luxembourg, ie U SEr; ί§5 £