Patent Application
20080245305
The present invention relates to a metal evaporation heating element and a method for evaporating a metal.
Heretofore, as a metal evaporation heating element (hereinafter sometimes referred to as “boat”), for example, an electrically conductive ceramic sintered body comprising boron nitride (EN), aluminum nitride (AlN) and titanium diboride (TiB2) as the main components and having a cavity formed on the upper surface thereof has been known (JP-B-53-20256). As one example of commercial products, “BN COMPOSITE EC”, tradename, manufactured by Denki Kagaku Kogyo Kabushiki Kaisha may be mentioned.
As a method of using the boat, each end of the boat is connected to an electrode by a clamp, a voltage is applied to generate heat, and a metal such as an Al wire rod put in the cavity is melted and evaporated to obtain a deposited film, followed by cooling. Such an operation is repeatedly carried out, during which the boat undergoes temperature cycles and erosion by the molten metal, and it will reach the end of its usefulness.
The boat life greatly relates to wettability of the boat to the molten metal, and if the wettability is poor, not only the molten metal is localized and no evaporation efficiency inherent in the boat will be obtained, but also the progress of erosion of the boat by the molten metal will be accelerated, whereby the boat life will be shortened. Accordingly, in order to secure the wettability of the boat, various attempts have been made such as irradiation with laser (JP-A-2000-93788), but no sufficient prolongation of life has been achieved. Further, extensive apparatus and facility will be required for irradiation with laser.
It is an object of the present invention to provide a metal evaporation heating element (boat) which has improved wettability to a molten metal and which has a prolonged life, and a method for evaporating a metal using it.
As the composition of the ceramic sintered body to be used in the present invention, it contains at least an electrically conductive substance titanium diboride and/or zirconium diboride and an insulating substance boron nitride as essential components. An electrically conductive substance such as titanium nitride, silicon carbide or chromium carbide and an insulating substance such as aluminum nitride, silicon nitride, alumina, silica or titanium oxide may suitably be incorporated. Among them, preferred is one containing as the main components titanium diboride and/or zirconium diboride, and boron nitride, or one containing as the main components titanium diboride and/or zirconium diboride, and boron nitride and aluminum nitride. Particularly preferred is one containing from 30 to 60% (hereinafter % means mass % unless otherwise specified) of titanium diboride and/or zirconium diboride and from 70 to 40% of boron nitride, or one containing from 35 to 55% of titanium diboride and/or zirconium diboride, from 25 to 40% of boron nitride and from 5 to 40% of aluminum nitride. When the ceramic sintered body has such a composition, it will very easily be processed.
Further, the ceramic sintered body has a relative density of preferably at least 90%, particularly preferably at least 93%. If the relative density is less than 90%, the molten metal will erode the pores of the ceramic sintered body, whereby erosion will be accelerated. A relative density of at least 90% will be easily realized by incorporating a sintering aid as described hereinafter to the above composition within a range not exceeding 10%. The relative density of the ceramic sintered body is determined by processing the sintered body into a rectangular solid having predetermined dimensions and dividing the actually measured density obtained from the outer dimensions and the mass by the theoretical density.
The ceramic sintered body to be used in the present invention can be produced by forming a material powder mixture containing an electrically conductive substance titanium diboride and/or zirconium diboride and an insulating substance boron nitride and sintering the mixture.
A material titanium diboride powder may be produced by any production method such as a method of utilizing a direct reaction with metal titanium or a reduction of an oxide such as titania. The powder preferably has an average particle size of from 5 to 25 μm.
A boron nitride powder is preferably hexagonal boron nitride or amorphous boron nitride or a mixture thereof. The powder may be produced, for example, by a method of heating a mixture of borax with urea in an ammonia atmosphere at 800° C. or higher, or a method of heating a mixture of boric acid or boron oxide with calcium phosphate and a nitrogen-containing compound such as ammonium or dicyandiamide at 1,300° C. or higher. Further, the boron nitride powder may be heated at high temperature in a nitrogen atmosphere thereby to increase crystallinity. The boron nitride powder has an average particle size of preferably at most 10 μm, particularly preferably at most 5 μm.
An aluminum nitride powder may be produced by a direct nitriding method or an alumina reduction method, and it has an average particle size of preferably at most 10 μm, particularly preferably at most 7 μm.
As a sintering aid, one or more powders selected from the group consisting of an alkaline earth metal oxide, an oxide of a rare earth element and a compound to be converted to such an oxide by heating. Specifically, it may, for example, be CaO, MgO, SrO, BaO, Y2O3, La2O3, Ce2O3, Pr2O3, Nd2O3, Pm2O3, Sm2O3, Eu2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3 or Lu2O3, or a compound to be converted to such an oxide by heating, such as a hydroxide such as Ca(OH)2 or a carbonate such as MgCO3. The sintering aid has an average particle size of preferably at most 5 μm, particularly preferably at most 1 μm.
The material powder mixture containing the above components is preferably granulated, and then formed and sintered. As one example of the forming and sintering conditions, uniaxial pressing or cold isostatic pressing under from 0.5 to 200 MPa is carried out, and then normal pressure sintering or low pressure sintering under 1 MPa or below is carried out at a temperature of from 1,800 to 2,200° C. As an example of more preferred conditions, hot pressing or hot isostatic pressure under from 1 to 100 MPa is carried out at from 1,800 to 2,200° C.
Sintering is carried out preferably in a state where is the mixture is accommodated in a container made of graphite, a container made of boron nitride, a container lined with boron nitride, or the like. In the case of hot pressing, sintering is carried out preferably by using a sleeve made of graphite or boron nitride, a sleeve lined with boron nitride, or the like.
Production of a boat from the ceramic sintered product can be carried out, for example, by forming the sintered body into a suitable shape by means of e.g. mechanical processing. Further, in the boat of the present invention, a cavity may be formed on a substantially center portion on the upper surface of the ceramic sintered body. As one example of the boat shape, the boat has a plate shape having a whole dimension with a length of from 100 to 200 mm, a width of from 25 to 35 mm and a thickness of from 8 to 12 mm. In a case where a cavity is formed, the cavity may, for example, have a rectangular shape having a length of from 90 to 120 mm, a width of from 20 to 32 mm and a depth of from 0.5 to 2 mm.
The boat of the present invention has, on the upper surface of the ceramic sintered body, or with respect to one having a cavity, on the bottom surface of the cavity and/or on the upper surface of the ceramic sintered body, one or more grooves in a direction not in parallel with a current direction (i.e. a direction connecting electrodes), i.e. with a predetermined angle α with the current direction which is the longitudinal direction of the ceramic sintered body as shown in
A suitable angle a in a direction not in parallel with the current direction is, as shown in
Particularly, it is preferred that the grooves are crossed so as to form at least one intersection, preferably intersections in the same or more number of the grooves, or on the upper portion of the ceramic sintered body and/or on the bottom of the cavity, a pattern (planar pattern) such as a circular, elliptic, rhomboidal, rectangular, mooned, lattice or radial pattern is drawn by the grooves. The area ratio occupied by the pattern is preferably at least 30%, particularly preferably at least 50%, more preferably at least 80% to the bottom surface area of the cavity with respect to one having a cavity, or to the upper surface area of the ceramic sintered body with respect to one having no cavity. The area ratio occupied by the pattern is defined as a percentage of a value obtained by dividing the area formed by connecting outermost grooves forming the pattern by the upper surface area of the ceramic sintered body or the bottom surface area of the cavity. When the area ratio occupied by the groove is employed instead of the area ratio occupied by the pattern, the area ratio occupied by the groove to the upper surface area of the ceramic sintered body or the bottom surface area of the cavity is preferably at least 10%, particularly preferably at least 30%, more preferably at least 50%.
Further, in the present invention, in one groove or between different grooves to be formed on the ceramic sintered body, a significant difference is preferably provided in the depth of the groove. By the significant difference, wettability to a molten metal will further be accelerated. In the present invention, the significant difference (%) in the depth of the groove is represented by the following formula. A groove to be used to measure the depth of the deepest portion of the groove and a groove to be used to measure the depth of the shallowest portion of a groove for the following formula may be the same or different.
{(depth of the deepest portion of the groove)−(depth of the shallowest portion of the groove)}×100/(depth of the deepest portion of the groove)
In the present invention, the significant difference of the groove by the above formula is preferably at least 10%, more preferably at least 20%, particularly preferably at least 30%. Further, regardless of the above formula or in relation to the above formula, the depth of the groove is suitably such that {(depth of the deepest portion of the groove)−(depth of the shallowest portion of the groove)} is preferably at least 0.005 mm, particularly preferably at least 0.1 mm.
In the present invention, the significant difference in the depth of the groove may be provided by (i) providing a significant difference in the depth of the groove in at least one groove among a plurality of grooves, (ii) providing a significant difference in the depth of the groove between two or more grooves, or (iii) a combination thereof.
In the case of the above method (i), the deepest portion in one groove is suitably provided preferably at a center portion with a length of from 10 to 80%, particular preferably at a center portion with a length of from 40 to 60% in the longitudinal direction of the groove, and the shallowest portion is suitably provided at the other end portion in the longitudinal direction.
In the case of the above method (ii), the groove employed to determine “the deepest portion of the groove” and the groove employed to determine “the shallowest portion of the groove” may be the same or different. Further, a plurality of grooves having different depths, each having a uniform depth, may be provided, or at least one groove among the plurality of grooves may be a groove having a non-uniform depth as in (i). Further, in the case of the above (iii), a groove having a uniform depth and a groove having a non-uniform depth are combined.
Further, in the case of the above (ii) or (iii), a deep groove (including a groove having the deepest portion) and a shallow groove (including a groove having the shallowest portion) are freely arranged, such that they are alternately provided, two or more grooves and two or more of the other types of grooves are alternately provided, or they are randomly provided. However, a deep groove (including a groove having the deepest portion) is preferably provided at a center portion in the longitudinal direction of the ceramic sintered body or in the vicinity thereof. The center portion in the longitudinal direction of the ceramic sintered body or in the vicinity thereof, is preferably a center region with a length of preferably from 20 to 80%, more preferably from 30 to 70%, particularly preferably from 40 to 60%, of the total length of the ceramic sintered body. Further, it is preferred to provide a groove shallower than the deep groove (including a groove having the deepest portion) at an end region other than such a center region. Particularly, in one or each end region in the longitudinal direction of the ceramic sintered body, the outermost groove preferably has the shallowest portion.
In the present invention, it is particularly preferred that a plurality of grooves having a width of from 0.1 to 1.5 mm, a length of at least 1 mm and a depth of from 0.03 to 1.0 mm are provided, the significant difference in the depth of the groove is at least 10%, and {(depth of the deepest portion of the groove)−(depth of the shallowest portion of the groove)} is at least 0.005 mm.
Processing of the groove on the ceramic sintered body of the present invention may be carried out, for example, by mechanical processing, sandblasting or water jet.
The boat of the present invention has suppressed wettability to a molten metal in a direction in parallel with a current direction, by formation of the groove. Thus, arrival of a molten metal to electrodes can be remarkably reduced as compared with a conventional boat having no groove, whereby the metal can be evaporated stably with high efficiency.
On a conventional boat, a cavity is formed so as to prevent the molten metal such as aluminum being dripping from the side surface. However, in the present invention, a cavity is one having grooves with different size or function provided thereon. Therefore, the cavity is not necessarily required in the present invention. However, with respect to one having a cavity, the groove or a pattern by the groove is formed preferably on at least the bottom surface of the cavity. Perspective views illustrating one example of the boat of the present invention are shown in
Boats in
In the boat shown in
In the boat shown in
In the boat shown in
In the boat shown in
In the boat shown in
In the boat shown in
The method for evaporating a metal of the present invention comprises supplying a metal such as an Al wire rod so that it is in contact with part or all of the groove portion on the boat of the present invention (in a case where one groove is formed, it may be in contact with a part of the groove), heating and carrying on heating while the molten metal and the groove are in contact. In such a manner, a metal deposited film is formed on an object substance. As one example of vacuum heating conditions, the degree of vacuum is preferably from 1×10−1 to 1×10−3 Pa and the temperature is preferably from 1,400 to 1,600° C.
A material powder mixture comprising 45 mass % of a titanium diboride powder (average particle size: 12 μm), 30 mass % of a boron nitride powder (average particle size: 0.7 μm) and 25 mass % of an aluminum nitride powder (average particle size: 10 μm) was put in a die made of graphite, followed by hot pressing at 1,750° C. to produce a ceramic sintered body (relative density: 94.5%, diameter 200 mm ×height 20 mm). From this ceramic sintered body, a rectangular column having a length of 150 mm, a width of 30 mm and a thickness of 10 mm was cut out, and at a center portion on the upper surface thereof, a cavity having a width of 26 mm, a depth of 1 mm and a length of 120 mm was formed by mechanical processing. On the bottom surface of the cavity, 50 grooves having a width of 1 mm, a depth of 0.15 mm and a length of 20 mm were formed with a distance of 1 mm at an angle of 90° to a current direction by mechanical processing to produce a boat. Its perspective schematic view is shown in
A boat was produced in the same manner as in Example 1 except that the grooves had a width of 0.5 mm, a depth of 0.1 mm and a length of 20 mm.
A boat was produced in the same manner as in Example 1 except that on the bottom surface of the cavity of the boat, 35 grooves having a width of 1 mm, a depth of 0.15 mm and a length of 28 mm were formed with a distance of 1 mm at an angle of 45° to a current direction by mechanical processing, and 35 grooves having the same dimensions were formed at an angle of 135° to the current direction, at right angles to the above grooves by mechanical processing. Its perspective schematic view is shown in
A boat was produced in the same manner as in Example 1 except that on a center portion of the upper surface of the rectangular column, one linear continuous groove having a width of 1.5 mm, a depth of 0.2 mm and a length of 645 mm was formed at an angle of 90° to a current direction in a stripe pattern directly without forming a cavity. Its perspective schematic view is shown in
A boat was produced in the same manner as in Example 1 except that on a center portion of the upper surface of the rectangular column, 50 grooves having a width of 1.0 mm, a depth of 0.15 mm and a length of 25 mm were formed with a distance of 1 mm at an angle of 90° to a current direction by mechanical processing, directly without forming a cavity. Its perspective schematic view is is shown in
A boat was produced in the same manner as in Example 1 except that the grooves were formed by sandblasting.
A boat was produced in the same manner as in Example 1 except that the grooves were formed by water jet and that the boat was dried by a vacuum dryer.
A boat was produced in the same manner as in Example 1 except that no groove was formed on the rectangular column.
A boat was produced in the same manner as in Example 1 except that the grooves had a width of 2.0 mm.
A boat was produced in the same manner as in Example 1 except that the grooves had a depth of 2.0 mm.
A boat was produced in the same manner as in Example 1 except that the grooves were formed with a distance of 3.0 mm.
In order to evaluate wettability of the boats in the above Examples and Comparative Examples to a molten metal, each end portion of the boat was connected to an electrode by a clamp, and a voltage to be applied was set so that the temperature at a center portion of the boat would be 1,550° C. Then, a voltage was applied to the boat for heating, an aluminum wire was supplied to the groove portion at a rate of 6.5 g/min for 5 minutes in vacuum at a degree of vacuum of 2×10−2 Pa and heating was continued. 5 Minutes after initiation of aluminum supply, the upper surface of the boat was photographed, and the wet area was obtained from a comparison between the glowing portion and the molten metal portion. Then, the wet area was divided by the bottom surface area of the cavity with respect to a boat having a cavity or by the upper surface area of the ceramic sintered body with respect to a boat having no cavity to calculate the wet area ratio (%). The results are shown in Table 1.
Further, the boat life was evaluated. Namely, an evaporative test was carried out at a temperature at a boat center portion of 1,500° C. in vacuum at a degree of vacuum of 2×10−2 Pa while an aluminum wire was supplied at a rate of 6.5 g/min for 40 minutes as a unit cycle, and this operation was repeatedly carried out. The number of repetition when the maximum erosion depth on a surface of the boat on which aluminum was evaporated reached 3 mm, was taken as the boat life. The results are shown in Table 1.
A boat was produced in the same manner as in Example 1 except that instead of the uniform grooves (totally 50 grooves) in Example 1, 50 grooves among which predetermined number of grooves had different depths, as identified in Table 2, were formed from one end to the other end in a longitudinal direction of the boat so that grooves at a center region would be deepest.
A boat was produced in the same manner as in Example 8, 9 or 10 except that no cavity was formed on the boat.
A boat was produced in the same manner as in Example 1 except that each of the 50 grooves had a groove depth of 0.15 mm at a portion of ⅓ from the center in a longitudinal direction of the groove and a groove depth of 0.10 mm at each end portion.
With respect to the boats in Examples 8 to 14, in the same manner as in Examples 1 to 7, the number of repetition when the maximum erosion depth on a surface of the boat on which aluminum was evaporated reached 3 mm, was measured as the boat life. Further, the wettability to a molten metal was measured in accordance with the following method. The results are shown in Table 2.
Test on Wettability to Molten Metal end portion of the boat was connected to an electrode by a clamp, and a voltage to be applied was determined and set so that the temperature at a center portion of the boat would be 1,600° C. Then, a voltage was applied to the boat for heating, an aluminum wire was supplied to the groove portion at a rate of 6.5 g/min for 5 minutes in vacuum at a degree of vacuum of 1×10−2 Pa, and heating was continued. 5 Minutes after initiation of aluminum supply, the upper surface of the boat was photographed, and with respect to the expansion of a molten metal portion, the width (mm) and the maximum length (mm) at a center portion were measured. The results are shown in Table 2.
The boat and the method for evaporating a metal of the present invention are useful for deposition of various metals on e.g. a film.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-390344 | Nov 2003 | JP | national |
| 2004-008217 | Jan 2004 | JP | national |
| 2004/010568 | Jul 2004 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2004/017023 | 11/16/2004 | WO | 00 | 6/11/2008 |
