APPARATUS FOR FORMING FILM BY ION BEAM

Abstract: An ion beam apparatus comprises a chamber of high vacuum, a heated crucible (4) for producing vapor of a material (3), ionizing means (46, 47, 49), ion accelerating means (6b, 5). A substrate (5) to be coated with the vaporized material is disposed within the chamber. An accelerating voltage (-V₁, 57) is applied across the crucible (4) and the accelerating means (6b, 5) such that the crucible (4) is of positive polarity while the accelerating means is of negative polarity. The crucible is provided with a small hole (7b) for ejecting the vapor of the material into the vacuum chamber to thereby form atom clouds referred to as clusters under adiabatic expansion and supercooling, a part of the clusters being ionized through irradiation of electrons by the ionizing means and accelerated by the accelerating means so that the ionized and accelerated clusters deposit on the substrate (5) to form a thin film (23) thereon. An electrostatic optical system (13, 36, 43) is interposed between the cluster ionizing region (49) and the substrate (5) wherein the electrostatic optical system serves to focus the ionized clusters onto the element to form the thin film (23) thereon through deposition of the ionized clusters.

Description: The present invention relates to an apparatus for forming a film by using an ion beam. More particular, the invention concerns an apparatus which is suited for selectively forming a film or films at a preselected region or regions of a substrate by focussing the ion beam by making use of electric charge carried by ions. Fig. 1 of the accompanying drawings shows a typical example of ion-plating process known heretofore. Referring to the figure, a vacuum container 2 adapted to be evacuated by means of a vacuum pump (not shown) through an evacuation pipe 1 accommodates therein a crucible 4 which contains material to be evaporated or vaporized for vacuum deposition of a substrate 5. A voltage is applied across the crucible 4 and a substrate holder 6a which supports the substrate 5. In carrying out the vapor deposition, the material 3 to be evaporated is heated up by a heating device 7a to be vaporized. Since a voltage is applied across the material 3 and the substrate 5 by way of the crucible 4 and the substrate holder 6a, respectively, vaporized particles 8a of the material 3 are electrically charged, resulting in that ions thus produced are caused to impinge onto the substrate 5 to be deposited thereon. This process is what is referred to as the ion-plating process in which ions of vaporized material having corresponding thermal energy are caused to impinge on the substrate with acceleration energy to be deposited thereon. In this case, it is however noted that the substrate 5 is deposited with the film forming material 3 uniformly over the whole surface. Accordingly, if a film is to be formed at predetermined regions or areas of the substrate through the ion-plating process, a uniform film has to be first formed over the whole surface of the substrate, which must then be followed by selective removal of the film at the unwanted regions through photographical patterning and etching or the like process to thereby allow the deposited film material to be left only at the desired predetermined regions. This procedure is apparently very complicate and time-consuming. Fig. 2 of the accompanying drawings shows a typical example of a cluster beam vacuum-deposition technique known heretofore. Referring to the figure, a vacuum container 2 adapted to be evacuated by means of a vacuum pump (not shown) through an evacuation pipe 1 contains a crucible 4 in which a material 3 to be evaporated for vacuum deposition of a substrate 5 is placed. A holder 6b supporting the substrate 5 can be maintained at a high temperature through electrical heating. On the other hand, the substrate 5 is held at a high voltage level relative to the ground by applying a high voltage thereacross. The crucible 4 is adapted to be heated by heating means such as electron beam irradiation means (not shown) so that the material 3 contained in the crucible 4 can be molten and vaporized. The crucible 4 is further provided with a nozzle 7b for blowing off or ejecting the vapors of the material 4. The vapor of the material 4 ejected through the nozzle 7b under pressure determined by nozzle design factors and the pressure within the crucible 4 which is higher than the pressure within the vacuum chamber 2 by several orders of magnitude form atom clouds or clusters 8b each constituted by several tens to several thousands of loosely combined atoms, which clusters run toward the substrate 5. When the atom clusters encounter flux of electrons in the course of travelling toward the substrate 5, a part of the clusters is ionized, as the result of which the ionized clusters are accelerated to impinge with increased energy onto the substrate 5 to be deposited thereon, since the substrate 5 is maintained at the high potential level as mentioned above. In this manner, a major part of the clusters blown off through the nozzle 7b are accumulatively deposited at a relatively low energy level on the order of 1 eV, while the ionized clusters are caused to deposit on the substrate 5 at an increased energy level of several KeV due to the acceleration. Through deposition of the vaporized material or substance 3 on the heated substrate 5 in the manner mentioned above, a film of an improved quality can be formed on the substrate with an enhanced controll-ability. Also in the case of the cluster beam deposition technique mentioned above, deposition takes place uniformly over the whole surface of the substrate as in the case of the first mentioned ion-plating method. Accordingly, when a particular region or regions of the substrate surface are to be selectively formed with a film through deposition of the vaporized material, it is required that the vapor deposition is once performed over the whole surface of the substrate and the material deposited on the substrate surface at the unwanted region or regions is subsequently removed selectively by resorting to the photographic patterning and etching or the like lithography technique. This process is thus very complicate and time-consuming, to a serious drawback. Fig. 3 shows another example of the conventional cluster beam vapor deposition system. There are housed within a vacuum chamber 2 adapted to be evacuated by a vacuum pump (not shown) through an evacuation pipe 1 a plurality of crucibles 4 containing a material or substance to be vaporized and a substrate 5 to be deposited with the evaporated material. The substrate 5 is mounted on a substrate holder 6b arranged to be maintained at a high temperature through electrical heating. A high voltage is applied across the substrate holder 6b and the ground so that the substrate 5 is at a high potential level relative to the ground. The plurality of crucibles 4 are heated by appropriate heating means such as electron beam irradiation means so that the material or substance 3 placed therein is molten to be evaporated. Each of the crucibles 4 is provided with a nozzle 7b to be blow off the vapor of the material 3 therethrough. From the vapors blown off through the nozzles 7b under the pressure which is determined by the nozzle design factors and the pressure in the crucible 4 which is higher than the pressure the vacuum chamber 2 by several orders of magnitude, there are produced clusters 8b each including several thousands of loosely combined atoms, which clusters run towards the substrate 5. In the course of the travelling, a part of the clusters is ionized (i.e. electrically charged) due to flux of electrons as indicated by e ○⁻ and accelerated due to the high potential applied to the substrate 5, whereby the ionized clusters are caused to be deposited on the substrate 5 with increased energy. On the other hand, those clusters which remain unionized are deposited on the substrate with low energy on the order of 1 eV without being accelerated. In this conjunction, when different types of substances to be vaporized are placed in the different crucibles, respectively, e.g. Ga is placed in one crucible while As is in the other crucible, a film of a compound of different substances, e.g. GaAs, can be formed. On the other hand, when same substance is contained in all the crucibles, the speed at which the film is formed can be increased as compared with the process in which only one crucible is employed. It should however be noted that in the case of the cluster beam deposition technique mentioned above, the film is also formed uniformly over the whole surface of the substrate. Consequently, when selective film formation on predetermined regions is desired, a number of the additional processes such as described hereinbefore are required, to a disadvantage. Fig. 4 shows a further example of the hitherto known cluster ion beam deposition technique. Referring to the figure, a vacuum chamber 2 connected to a vacuum source such as a vacuum pump (not shown) through an evacuation pipe 1 accomodates therein a crucible 9 containing a material or substance 3 to be vaporized for deposition. The crucible 9 is provided with a multi-orifice nozzle 10 for guiding and blowing off the vapor from the crucible 9. In opposition to the multi-orifice nozzle 10, there is disposed a substrate holder 6b imparted with electrically heating function, which holder 6b serves for supporting a substrate 5 to be deposited with the vaporized material. The crucible 9 is heated by means of electron beam irradiation apparatus 11, whereby the material 3 to be evaporated is molten and vaporized. The vapor blown off through the multi-orifice nozzle 10 under a pressure which is determined by the configuration factor of the nozzle orifices and the pressure within the crucible 9 which is higher than that of the vacuum chamber by several orders of magnitude form atom clouds or clusters each including several tens to several thousands of loosely combined atoms, the clusters flying toward the substrate 5 to be deposited thereon with relatively low energy on the order of 1 eV. When the clusters encounter flux of electrons in the course of travelling toward the substrate, a part of the clusters is ionized (i.e. electrically charged) and subjected to acceleration by means of an electrode 12 of a high potential, resulting in that the ionized clusters are deposited on the substrate 5 with high energy on the order of several KeV. Also in the case of the above mentioned ionized cluster beam deposition technique, the film is formed over the whole surface of the substrate, requiring thus a number of additional processes for forming selectively the film at desired regions of the substrate, to a great disadvantage. It is therefore an object of the present invention to provide an ion beam apparatus which is evaded from the drawbacks of the hitherto known cluster ion deposition techniques described above and which is capable of forming a film of high quality selectively at desired regions of a substrate by using a focussed cluster beam. According to the present invention this object is accomplished with an ion beam apparatus as claimed in claim 1. Dependent claims are directed on features of preferred embodiments. The present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: Figs. 1 to 4 are views for illustrating the relevant prior art; Figs. 5a to 5c, 6a to 6d and 7a to 7c are views for illustrating structures of various electrostatic lens systems which can be employed in the apparatus according to the invention; Fig. 8 is a view showing an exemplary embodiment of the invention. Now, the invention will be described in detail in conjunction with the preferred embodiment thereof. Fig. 5a to 5c show, by way of example, structures of the electrostatic lens system which can be employed in the apparatus according to the present invention. The lens shown in Fig. 5a is constituted by a disc having a circular aperture formed at a center. Of the clusters ejected through the nozzle 7b of the crucible 4, those clusters which are ionized are forced to follow paths curved or bent under electric field distributed in the vicinity of the circularly apertured disc lens 16, which field is generated by the voltage V₁ applied to the lens disc 16, resulting in that the ionized clusters are focussed on a focal plane 18. Fig. 5b shows a structure of a bi-potential lens system which includes a cylindrical lens 19 and an electrode plate 20 having a circular bore or aperture formed therein, a voltage V₂ being applied to the cylindrical electrode 19 while a voltage V₃ is applied to the electrode 20. Further, Fig. 5c shows a structure of cylindrical accelerator lens system composed of a pair of coaxially arrayed cylindrical electrodes to which voltages +V₄ and -V₄ are applied, respectively. Fig. 6a shows a disc type acceleration lens system which are constituted by a pair of discs having respective circular apertures disposed coaxially and to which voltages +V₅ and -V₅ are applied, respectively. Further, Fig. 6b shows a Butler type twin acceleration lens system composed of lens elements each formed with such a curved surface that an equi-potential plane is realized which minimizes geometrical aberations, both lens elements being applied with voltages +V₆ and -V₆, respectively. Fig. 6 c shows an Einzel type triplet cylindrical lens system composed of three coaxially arrayed cylindrical lens elements to which voltages -V₇, +V₈ and -V₇ are applied, respectively. Fig. 6d shows a triplet asymmetrical cylindrical lens system in which three cylindrical lenses juxtaposed coaxially are coupled to three different voltages V₉, V₁₀ and V₁₁, respectively. Fig. 7a shows an Einzel type triplet disc lens system which comprises a combination of three disc lenses having respective circular apertures coaxially aligned and coupled to voltages -V₁₂, +V₁₃ and -V₁₂, respectively. Further, Fig. 7b shows a disc type triplet asymmetrical lens system constituted by a combination of three discs having respective apertures coaxially aligned and coupled to different voltages V₁₄, V₁₅ and V₁₆, respectively. Finally, Fig. 7c shows a Butler type triplet symmetrical lens system comprising three lens elements to which voltages -V₁₇, +V₁₈ and -V₁₇ are applied, respectively. The various electrostatic lenses mentioned above can be conveniently employed in the apparatus according to the invention. Next, the cluster beam type vapor deposition apparatus according to an embodiment of the present invention will be described in detail by referring to Fig.8. The cluster beam type vapor deposition apparatus comprises a vacuum container 2 in which a crucible 4 containing a material or substance 3 to be vaporized for deposition and a substrate 5 to be deposited with the vaporized material 3. A high voltage denoted by 57 is applied across the crucible 4 and the substrate 5 to accelerate the clusters which are produced and discharged from the crucible 4. The clusters 8b are ionized by flux of electrons emitted from an electron emitting cathode 46 and introduced through grid 47 to deposit on the substrate 5 for forming a film thereon through vapor deposition. Connected to the vacuum container 2 is an evacuation pipe 1 which in turn is connected to a vacuum pump (not shown) for reducing pressure within the vacuum container 2. As mentioned above, the crucible 4 and the substrate 5 are disposed within the vacuum container 2. The crucible 4 contains the material 3 to be vaporized for deposition on the substrate 5 and is provided with an electron beam irradiation means 7 which is disposed around the crucible 4 and constitutes the crucible heating means. The substrate 5 is held in contact with the substrate holder 6b which serves simultaneously as the substrate heating means. A high voltage 57 is applied across the substrate 5 and the crucible 4. Further, there is disposed between the substrate 5 and the crucible 4 the ionizing means which includes the ionizing electron emitting filament 46 and the grid 47 for drawing the electrons. The material 3 for vapor deposition is heated by the electron beam irradiation means 7 to be molten and vaporized, the resultant vapor being ejected through the nozzle 7b formed in the crucible 4 which is held at a high pressure due to vapor pressure. Since the vacuum container 2 is at a very low pressure, the vaporized material 3 undergoes adiabatic expansion to be supercooled, whereby clouds of atoms, i.e. the so-called clusters 8b are formed. The clusters 8b are caused to run toward the substrate 5 under influence of the high voltage 57. On the way to the substrate, the clusters 8b are exposed to fluxes of electrons produced by the ionizing means 46, 47 in the ionizing region 49, whereby a part of the clusters is ionized. The ionized clusters 8b are accelerated under the high voltage 57 and run toward the substrate 5 with increased energy (several eV to several ten eV per atom), while the remaining clusters 8b which are not ionized travel toward the substrate 5 with low energy (e.g. 0.1 to 1 eV per atom). The substrate 5 is separated from the crucible 4 by an interposed intercepting plate 50 which has a small hole 41 formed therein, whereby a substrate chamber 52 and a vapor source chamber 51 are defined. There is disposed between the separating or partition plate 50 and the ionizing electron drawing grid 47 constituting a part of the ionizing means an electrostatic lens system 13 which serves as the focussing lens described hereinbefore. Additionally, the chamber containing the substrate 5, that is the substrate chamber 52, accommodates therein an evacuation pipe 54 connected to a vacuum means 53, a cooling pipe 55 for conducting a coolant and a conduit 56 for introducing a reaction gas, all of which constitute deposition enhancing and/or improving means described later on. Of the clusters 8b, those which are ionized are focussed by means of the electrostatic lens 13 on the small hole 41. Thus, only the ionized clusters 8b are allowed to enter the substrate chamber 52 to deposit on the substrate 5, whereby a film of a high quality is formed through vapor deposition. Improved vapor deposition can be realized by the vapor-deposition enhancing/improving means described hereinafter. Describing in more detail, the interior space of the vacuum container 2 is divided by the partition plate 50 into the substrate chamber 52 and the source chamber 51 as described above. The substrate chamber 52 accommodates therein the substrate 5 and the substrate holder 6b, while the source chamber 51 accommodates therein the crucible 4, the ionizing electron emitting filament 46, and the ionizing electron drawing grid 47. The partition wall 50 has the through-hole (pin hole) 41 of a small size corresponding to that of the spot produced through focussing. The electrostatic lens system 13 is interposed between the partition wall 50 and the ionizing electron drawing grid 47 and so arranged as to focus the ionized clusters 8b onto the small hole 41. Next, operation of the apparatus will be described. A part of the clusters 8b formed upon ejection of the vapor from the crucible 4 is ionized in the ionizing region 49, resulting in the state that the ionized clusters 8b are coexistent with the neutral clusters (i.e. the clusters which are not ionized). Both the ionized clusters and the neutral clusters travel toward the electrostatic lens system 13. The ionized clusters 8b are focussed by the electrostatic lens 13 to a spot of minute size. On the other hand, the neutral clusters fly straight. Because the pin hole 41 is formed in the partition plate 50 at the position which coincides with the focal point of the electrostatic lens 13, the ionized clusters 8b pass through the small hole 41 to enter the substrate chamber 52. On the other hand, the neutral clusters are intercepted by the partition plate 50 and inhibited from entering the substrate chamber 52. In this way, only the ionized clusters 8b are allowed to deposit on the substrate 5. Since the ionized clusters 8b are deposited on the substrate 5 with high energy as described above, there can be formed a deposited film of high quality on the substrate 5. On the other hand, impurity gas produced around the crucible 4 is prevented from flowing into the substrate chamber 52 by means of the partition plate 50, thus contributing to the formation of the film of higher quality. Further, the substrate chamber 52 is provided with the vacuum means 53 which serves as the deposition enhancing/improving means. The vacuum means 53 includes the evacuation pipe 54 and a vacuum source (not shown) to which the pipe 54 is connected and operates to highly evacuate within the substrate chamber 52. By virtue of these evacuating means (53, 54), the quality of the film formed through the vapor deposition can be further improved. Moreover, there is disposed within the substrate chamber 52 the coolant conduit 55 which also serves as the deposition enhancing/improving means. The coolant conduit 55 conducts liquid nitrogen which is a typical one of the coolants. Through the cooling action of the coolant conduit 55, the degree of vacuum within the substrate chamber 52 is increased to thereby assure the formation of the film of an excellent quality. Besides, as the means for improving further the deposition, there is disposed within the substrate chamber 52 the reaction gas introducing conduit 56 which serves to bring a reaction gas generated by an appropriate source (not shown) into contact with the substrate 5 for promoting or activating the deposition reaction, whereby the deposition as well as the film quality is further improved. The reaction gas is prevented from entering the source chamber 51 by means of the partition wall 50, whereby the components located within the source chamber 51 are protected from deterioration due to the reaction gas, increasing the use life of the apparatus, to an advantage. In the illustrated embodiment, the electrostatic lens system is employed as the cluster focussing lens. However, it should be preciated that the invention is not restricted to the use of such lens. Further, the invention is not restricted to the deposition improving means disclosed herein. The impurity gas produced around the crucible 4 is positively prevented from reaching the substrate 5, as the result of which contamination of the film with the impurity gas is excluded, to assure the more improved quality of the film formed through deposition. Further, the neutral clusters are inhibited from being deposited on the surface of the substrate with only the clusters 8b of high energy being allowed to deposit and migrate on the substrate surface to thereby assure the formation of the film having an excellently high quality. Besides, the apparatus can enjoy an increased use life. As will be appreciated from the foregoing description, it is possible according to the teaching of the present invention to form selectively the high quality film on a substrate at desired regions with high accuracy and precision. Further, by providing the spatial filter for suppressing the major part of the neutral clusters, the film quality is more improved, while controllability of the cluster beam can be enhanced, making unnecessary the etching process for removing the pheripheral or extra film portion. Moreover, because the impurity gas produced around the crucible is positively prevented from contacting with the substrate, no contamination of the deposited film occurs, to contribute to further improvement of the film quality.

Claims: An ion beam apparatus comprising: an enclosure (2) defining a chamber, connected to first evacuating means (1) for producing a high vacuum, said chamber accomodating therein a furnace (4) for producing vapor of a material (3) contained therein, a small hole (7b) is provided in the furnace through which the vapor of said material produced by heating with heating means in said furnace is ejected into said vacuum chamber to thereby form clusters under adiabatic expansion and supercooling, a vacuum pressure difference being maintained between vapor pressure within said furnace and said chamber, ionizing means (46, 47) for ionizing a part of said clusters generated from said small hole (7b) of the furnace by a bombardement of the clusters with an electron beam, and ion accelerating means (6b, 5; V₁, 57) for accelerating ionized clusters ionized by said ionizing means to deposit ionized clusters on a substrate (5) to form a thin film by supplying an accelerating voltage (-V₁ , 57) across said furnace (4) and a substrate holder (6b) supporting said substrate (5) such that said furnace is of positive polarity while said substrate holder and said substrate are of negative polarity, said apparatus further comprising a partition plate (50) separating said chamber into a vapor source chamber (51) provided with said furnace (4) and ionizing means (46, 47) and into a deposition chamber (52) in which said substrate (5) is disposed, a small hole (41) formed in said partition plate (50) to prevent a contamination of the thin film formed on the substrate (5), an electrostatic optical system (13) interposed between said ionizing means (46, 47) and said partition plate (50) in said vapor source chamber (51) to control the path to be followed by said ionized clusters (8b) to focus said ionized clusters at said small hole (41) of said partition plate (50) so as to only enable said focused ionized clusters to pass through said partition plate to form an uncontaminated thin film on said substrate by deposition of said ionized clusters, and vapor deposition enhancing/improving means being provided in association with said deposition chamber (52) in which said substrate (5) is disposed, said vapor deposition enhancing/improving means including second evacuating means (53, 54) connected to said deposition chamber (52) for producing a vacuum in said deposition chamber (52), said vapor source chamber (51) being evacuated by said separate first evacuating means (1). An ion beam apparatus according to claim 1, wherein said small hole (51) formed in said partition plate (50) is a pin hole, and said partition plate serves as a spatial filter for enabling only said focused ionized clusters to pass therethrough to be deposited on said substrate. An ion beam apparatus according to claim 1, wherein said apparatus further includes heating means for heating said substrate (5) to be deposited with the vaporized material. An ion beam apparatus according to claim 1, wherein said vapor deposition enhancing/improving means includes cooling means (55) disposed within said deposition chamber (52) for circulating a coolant. An ion beam apparatus according to claim 1, wherein said vapor deposition enhancing/improving means includes reaction gas introducing means for bringing a reaction gas in contact with said substrate to be deposited with the vaporized material.

Inventors: HONGO, MIKIO, MIYAUCHI, TATEOKI, MIZUKOSHI, KATSURO, SATOH, RYOHEI, SHIMASE, AKIRA, YAMAGUCHI, HIROSHI
Applicants: HITACHI, LTD.
Application year: 1984
Main classification: C23C14
IPC codes: C23C14, H01J37