JP2013064181A - Aluminum material and method for producing the same - Google Patents

Abstract

An aluminum material having a suppressed impurity level and a method for producing (purifying) the same are provided.
SOLUTION: Lithium, beryllium, boron, sodium, magnesium, silicon, potassium, calcium, titanium, vanadium, chromium, manganese, iron, nickel, cobalt, copper, zinc, gallium, germanium, arsenic, selenium, zirconium, molybdenum, The total content of silver, cadmium, indium, tin, antimony, barium, lanthanum, cerium, platinum, mercury, lead, and bismuth is 0.45 ppm or less in atomic ratio, and the size effect correction value of the residual resistance ratio is 70,000 to 100,000. It is an aluminum material characterized by being.
[Selection] Figure 3

Description

  The present invention relates to an aluminum material, in particular, an aluminum material with a small amount of impurities and a method for producing the same.

High-purity aluminum is used in many fields including vapor phase growth of semiconductors such as MBE. As such high-purity aluminum, for example, a high-purity aluminum material produced by a segregation method or a three-layer electrolysis method is known. These high-purity aluminum materials are generally known to have a purity of about 99.99% to 99.999%.
In addition, for example, an ultra-high purity aluminum material having a purity level of 99.9999% as disclosed in Patent Document 1 shows an impurity analysis result.
However, as shown below, the impurity levels of these conventional high-purity and ultra-high-purity aluminum materials may not be sufficient, and there is an increasing demand for aluminum materials with further reduced impurities.

  Light emitting diodes and semiconductor lasers emitting deep ultraviolet rays (wavelength: 200 to 360 nm), which are considered to be applied in a wide range of fields such as high-density optical recording applications, high color rendering illumination and displays, sterilization, and various medical fields, are conventionally known as gases. There were only light sources for large devices such as lasers, but by using AlN and AlGaN semiconductors, light-emitting diodes (LEDs) and semiconductor lasers (LDs) with small size, high efficiency, and long life can be produced.

  However, unlike nitride semiconductors containing In, such as InGaN, which have high quantum efficiency despite having a relatively high threading dislocation density, recombination centers that do not contribute to light emission in AlN and AlGaN semiconductors that do not contain In. Therefore, high quality crystal growth is required.

  This is because, in an AlN or AlGaN crystal, many types of elements are easily taken in as impurities, and deep energy levels are easily formed in the energy band by the incorporated impurities, so that the impurities easily affect the light emission characteristics. Moreover, it is because the contained impurity element is the starting point and crystal defects are likely to occur. Therefore, in order to improve crystal quality and light emission characteristics, it is important to suppress the introduction of these impurity elements as much as possible.

For example, Non-Patent Document 1 evaluates defects caused by oxygen (O) and silicon (Si) by cathodoluminescence of an AlN thin film.
Non-Patent Document 2 describes a non-metallic element such as oxygen and carbon and an element that is easily incorporated with impurities such as silicon.
Non-Patent Document 3 describes the effects of Cr and Mn.
Non-Patent Document 4 examines the existence state of Si, Ge, P, As, Sb, and C in an AlN crystal by calculation.

  A plurality of methods for crystal growth of AlN and AlGaN-based semiconductors have been studied. In the case of the MBE method, aluminum is used as a raw material.

  Therefore, in order to suppress the impurity elements of the AlN and AlGaN phases, it is extremely important to suppress the impurities present in the aluminum used for MBE.

  In addition to this, there is a problem such as abnormal discharge due to non-metallic impurities contained in a conventional high-purity aluminum material in the use of wiring materials for integrated circuits such as LSI.

  For example, the segregation method and the three-layer electrolysis, which are conventional high-purity aluminum refining methods described in Patent Document 1, cannot solve the problems caused by these impurities. Therefore, there has been a demand for an aluminum material in which the impurity level is further suppressed.

JP, 2009-242867, A

B. Bastek et. al. , Applied Physics Letters 95 (2009) 032106. Shigehide Chichibu, Akiyoshi Udono, Journal of Crystal Growth Society of Japan vol. 36 (2009) 166. H. X. Liu et. al. , Applied Physics Letters 85 (2004) 4076. L. E. Ramas et. al. , Physical Review B68 (2003) 085209.

  In response to such a demand, the present application aims to provide an aluminum material in which the impurity level is further suppressed and a method for producing (purifying) the same.

  Aspect 1 of the present invention includes lithium (Li), beryllium (Be), boron (B), sodium (Na), magnesium (Mg), silicon (Si), potassium (K), calcium (Ca), and titanium (Ti ), Vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), cobalt (Co), copper (Cu), zinc (Zn), gallium (Ga) and germanium (Ge) ), Arsenic (As), selenium (Se), zirconium (Zr), molybdenum (Mo), silver (Ag), cadmium (Cd), indium (In), tin (Sn), antimony (Sb), and barium (Ba) ), Lanthanum (La), cerium (Ce), platinum (Pt), mercury (Hg), lead (Pb) and bismuth (Bi) in an atomic ratio of 0.45 ppm or less, Size effect correction value of the ratio is an aluminum material, which is a 70,000 to 100,000.

  Aspect 2 of the present invention is the aluminum material according to aspect 1, wherein the titanium (Ti) content is 0.02 ppm or less in terms of atomic ratio.

  Aspect 3 of the present invention is the use of the aluminum material according to either aspect 1 or 2 in a semiconductor film forming process.

  Aspect 4 of the present invention is the use of the aluminum material according to either aspect 1 or 2 in a semiconductor bulk single crystal growth process.

  Aspect 5 of the present invention is an aluminum material manufacturing method including a zone melting step of forming a molten part obtained by melting a part of aluminum and moving the molten part to remove impurities, wherein the molten part is formed. An aluminum material manufacturing method characterized in that aluminum is disposed on an alumina layer, and the moving speed of the molten portion is 40 mm or less per hour.

  A sixth aspect of the present invention is the manufacturing method according to the fifth aspect, wherein the zone melting step is performed under reduced pressure.

A seventh aspect of the present invention is the manufacturing method according to the sixth aspect, wherein the zone melting step is performed under a reduced pressure of 3 × 10 ⁻⁶ Pa to 2 × 10 ⁻⁵ Pa.

  Aspect 8 of the present invention is the manufacturing method according to aspect 5, wherein the zone melting step is performed in an inert gas atmosphere.

  A ninth aspect of the present invention is the manufacturing method according to any one of the fifth to eighth aspects, wherein a length along the moving direction of the melting portion is 30 to 120 mm.

  According to the present invention, metal 35 elements (Li, Be, B, Na, Mg, Si, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Co, Cu, Zn, Ga, Ge, As, Se, Zr, Mo, Ag, Cd, In, Sn, Sb, Ba, La, Ce, Pt, Hg, Pb, Bi) is a total content of 0.45 ppm or less, and the size effect correction value of the residual resistance ratio is It is possible to provide a high-purity aluminum material having a very low impurity level of 70,000 or more and 100,000 or less and a method for producing the same.

It is sectional drawing which shows the zone melting refinement | purification apparatus 100 which is an example of a zone melting refinement | purification apparatus. It is sectional drawing which shows the example which has arrange | positioned the several aluminum raw material 10 to the zone melting refinement apparatus 100. FIG. It is a graph which shows the relationship between the distance from the melt | dissolution start part of band melting, and the size effect correction value of residual resistance ratio. It is a graph which shows the relationship between the distance from the melt | dissolution start part of band melting, and titanium concentration.

The aluminum material in which impurities of the present invention are suppressed is an aluminum material having a metal element component of a predetermined amount or less.
More specifically, the present invention relates to an aluminum material in which the total content of metal 35 elements is 0.45 ppm or less, preferably 0.05 to 0.2 ppm, more preferably 0.05 to 0.15 ppm. It is.
The aluminum material of the present invention has a residual effect ratio size effect correction value of 70,000 to 100,000, which will be described in detail later.

In this specification, the term “peritectic seven elements” means seven elements of Ti, V, Cr, As, Se, Zr, and Mo.
Similarly, in this specification, the term “metal 35 element” means Li, Be, B, Na, Mg, Si, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Co, Cu, Zn, Ga. , Ge, As, Se, Zr, Mo, Ag, Cd, In, Sn, Sb, Ba, La, Ce, Pt, Hg, Pb, Bi.
Further, “ppm” in the present specification is ppm indicated by an atomic ratio.

Next, the term “residual resistance ratio size effect correction value” will be described.
A residual resistance ratio (RRR) is known as an index indicating the purity of a material such as a metal. Residual resistance ratio is the ratio of the measured electrical resistance of the same material (sample) at an absolute temperature of 4.2K to the measured electrical resistance at room temperature (the measured electrical resistance at room temperature is the electrical resistance at 4.2K). The value is divided by the measured value), and high-purity aluminum usually has a value greater than 1 because of its low electrical resistance at low temperatures.
It is known that the residual resistance ratio increases as the purity of aluminum increases.

With high-purity aluminum with an impurity content of 10 ppm or less, the decrease in the measured value of the residual resistance ratio due to electron scattering on the surface of the measurement sample cannot be ignored, and even if the impurity content is the same, it remains depending on the shape of the measurement sample. The resistance ratio value changes.
This phenomenon is called the size effect, and its effect has been calculated theoretically. A calculation method for removing the influence of the size effect from the measured value of the residual resistance ratio, that is, for evaluating the residual resistance ratio in the bulk state independent of the measurement sample size is disclosed in Y.S. Ueda, J .; Sci. Hiroshima Univ. , Ser. A, 47 (1984) p. 305-340.
Therefore, the inventors of the present application obtained a size effect correction value (residual resistance ratio corrected for the size effect) of the residual resistance ratio using this calculation formula. In the present specification, unless otherwise specified, the size effect correction value of the residual resistance ratio obtained using this calculation formula is described as “residual resistance ratio” for simplicity.

  The aluminum material according to the present invention preferably has a titanium (Ti) content of 0.02 ppm or less. More preferably, it is 0.01-0.05pm.

  The inventor of the present application, when removing impurities in aluminum by a zone melting process, in order to prevent the impurities from diffusing from the boat into the heated aluminum, the surface of the boat on which the aluminum is disposed In order to ensure the separation of impurities from the molten aluminum in advance, the zone melting refining is carried out by reducing the moving speed of the molten part to 40 mm / hour or less, preferably 30 mm / hour or less. It has been found that an aluminum material according to the present invention can be obtained.

Furthermore, it has been found that zone melting purification is preferably performed in an inert atmosphere such as argon gas or nitrogen gas, and more preferably performed under reduced pressure (in a vacuum).
About pressure reduction, Preferably a pressure shall be 3 * 10 < ^-5 > Pa or less, More preferably, a pressure shall be 3 * 10 < ^-6 > Pa or more and 2 * 10 < ^-5 > Pa or less.

  The detail of the manufacturing method of the aluminum material which concerns on this application is shown below.

Aluminum raw material:
As an aluminum raw material for removing impurities by forming a molten part melted in a part of the zone melt refining described later in detail, purity from 5N (99.999% or more, atomic ratio) to 6N (99.9999% or more, atomic ratio) It is preferable to use aluminum).
This is because zone melting and refining can be performed more efficiently by increasing the purity of the aluminum material in advance.

Such aluminum having a purity of 5N to 6N can be obtained by purifying commercially available aluminum having a relatively low purity (for example, a special grade of JIS-H2102 having a purity of 99.9%).
Although it does not restrict | limit especially as a purification method, Preferably, both the refinement | purification by a three-layer electrolysis method and the refinement | purification by a unidirectional solidification method are used.
The order of performing the purification by the three-layer electrolysis method and the purification by the unidirectional solidification method is not particularly limited, but the purification is usually performed by the three-layer electrolysis method and then the unidirectional solidification method. Further, the purification by the three-layer electrolysis method and the purification by the unidirectional solidification method may be repeated alternately, for example, or either one or both may be repeated.

As specific methods and conditions for purification by the three-layer electrolysis method and purification by the unidirectional solidification method, methods and conditions that are usually performed in the technical field may be adopted as appropriate.
The obtained aluminum raw material can be processed into a shape suitable for pretreatment and vacuum melting described later. The shape of the aluminum raw material is pellets, bars, plates, blocks, and the like.

Preprocessing:
The aluminum raw material is preferably pretreated before being subjected to zone melting purification. This is because, when an oxide film or the like generated on the surface in the air atmosphere and the aluminum raw material are processed, the impurity element adhering to the surface is removed in advance so that the band melting purification can be performed more efficiently.

The pretreatment method is not particularly limited, and various treatments used in the technical field for removing the surface layer of the aluminum raw material can be used.
Examples of the pretreatment include acid treatment and electrolytic polishing.

As an example of a suitable acid treatment, the aluminum raw material may be immersed in an acid under the following conditions.
Acid type and concentration: Approximately 20% aqueous hydrochloric acid solution diluted with pure water Temperature: 20 ° C to 40 ° C
Time: 1-5 hours

Examples of suitable electropolishing include the following conditions.
Electropolishing liquid: Perchloric acid and ethanol 1: 6 liquid mixture Temperature: 19-23 ° C
Voltage: 25V (constant voltage electrolysis)
Time: 1-10 minutes

Zone melt purification:
In order to remove the impurities of the aluminum raw material and obtain an aluminum material that has reached the target impurity level, zone melting purification (zone melting method) is performed.
The zone melting and refining is performed by forming a molten portion in which aluminum is melted in a part of the aluminum raw material disposed on the boat and moving the molten portion in a predetermined direction.
The details of zone melt purification are shown below.

-Formation of alumina layer on boat Various types of boats that can be normally used in the zone melting method can be used. Examples of such boats include boats made of stainless steel, boats made of tungsten (W), titanium (Ti), molybdenum (Mo), tantalum (Ta) or carbides of these metals, and boats made of alumina.
A suitable boat is a graphite boat. This is because a high-purity and large-sized material can be easily obtained, is stable in vacuum and in an inert gas atmosphere such as argon and nitrogen, and does not react with molten aluminum.

Then, alumina may be applied on the boat to form an alumina layer. Although the alumina layer may be formed on the entire surface of the boat, it may be formed only on the raw material placement portion where the aluminum raw material is placed.
The alumina layer may be applied by dispersing alumina powder in a liquid such as an organic solvent, applying a liquid containing the alumina powder to a boat, and then evaporating the liquid. Alternatively, alumina solid powder may be applied directly to the boat surface. The latter is preferred because it can be applied more easily.

The alumina layer has a function of preventing an impurity element from entering the aluminum material from the boat, in addition to the function of a release agent that makes it easy to take out the aluminum material obtained by band melting. The alumina to be applied is preferably high-purity alumina such as high-purity alumina powder AKP series (purity 99.99%) manufactured by Sumitomo Chemical Co., Ltd. so as to prevent impurities from entering from the alumina.
Therefore, it is preferable that the aluminum raw material is disposed so as not to come into contact with portions other than the alumina layer of the boat.

  After forming the alumina layer, the boat is preferably baked in an inert gas or vacuum (under reduced pressure). This is because moisture and impurity components adhering to the boat and the alumina layer are removed at a high temperature in a vacuum or an inert gas atmosphere. For the baking, a vacuum heat treatment furnace or an atmospheric heat treatment furnace can be used. Baking may be performed by high-frequency heating in a chamber used for band melting, and the high-frequency heating coil is preferably moved at a moving speed of about 30 to 200 mm / hour.

-Arrangement | positioning of aluminum raw material An aluminum raw material is arrange | positioned on the alumina layer of the boat mentioned above. One or more aluminum raw materials are arranged depending on the shape. The shape of the aluminum raw material (a combined shape when a plurality of aluminum raw materials are used) is preferably a rod shape, and generally a quadrangular prism or a cylinder is preferable because it is simple, but other shapes may be used.
When the shape of the aluminum raw material is regarded as a quadrangular column whose cross section (cross section perpendicular to the moving direction of the molten portion) is a square column, one side of the square is called w (the cross sectional dimension of the aluminum raw material. Is equivalent to the square root of the cross-sectional area of the aluminum raw material), and when the length of the quadrangular column (the length in the direction parallel to the moving direction of the melted portion) is L, L is w × 30 or more and w × 100 or less. Preferably there is. If L is less than w × 30, a sufficient purification effect may not be obtained, and if L exceeds w × 100, purification takes a long time and is not efficient.

  Further, when a plurality of aluminum raw materials are used, a plurality of aluminum raw materials may be arranged in the longitudinal direction (the direction in which a molten portion described later moves).

-Band melting In this invention, in order to suppress the oxidation of the aluminum surface, Preferably, band melting is performed in inert atmosphere, such as argon gas and nitrogen gas, More preferably, it is performed under reduced pressure (vacuum).
About pressure reduction, Preferably a pressure shall be 3 * 10 < ^-5 > Pa or less, More preferably, a pressure shall be 3 * 10 < ^-6 > Pa or more and 2 * 10 < ^-5 > Pa or less.
This is because the impurity component may not be sufficiently removed when the pressure is high (the degree of vacuum is low). Also, the lower the pressure (the higher the degree of vacuum), the better. However, if the pressure is too low, the equipment becomes excessive and the economy is poor.
Such a high vacuum (reduced pressure to a low pressure) is performed using, for example, both a turbo molecular pump and an oil rotary pump to evacuate the chamber in which the above-described boat in which the aluminum raw material is disposed is disposed. This can be achieved. In addition to this, a method of exhausting an oil diffusion pump, a cryopump, or the like in combination with another vacuum pump is also preferable.

And the molten part which aluminum fuse | melted is formed in a part of aluminum raw material arrange | positioned on a boat. Since it is necessary to heat only a part of the aluminum raw material to form the melted portion, it is preferably performed by high frequency heating (high frequency induction heating). For example, a molten part can be formed inside a high frequency coil by arrange | positioning so that only a part of aluminum raw material may be inside a high frequency coil.
Besides this, it may be heated by resistance heating. This is because the melting part can be easily moved by moving the resistance heating part.

In the zone melting and refining of aluminum, zone melting was sometimes performed in vacuum in order to prevent the formation of an oxide film on the surface. Conventionally, the degree of vacuum was as low as about 10 ⁻⁴ to 10 ⁻² Pa. (For example, “Experimental impurity segregation and numerical analysis based on variable solute distribution coefficients during multi-pass zone refining of aluminum” by Noe'Cheung et al. Journal of Crystal Growth 310 (2008) 1274/1280 and “SiC by S. Hauttmann et al. formation and influence on the morphology of laminated silicon thin films on graphite substrates produced by zone melting recrystallization ").

However, the inventor of the present application has found that a high-purity aluminum material can be obtained by performing in a high vacuum (pressure 3 × 10 ⁻⁵ Pa or less) as described above.
The mechanism considered by the inventors of the present invention, which does not limit the scope of the present invention, is the conventional method of extruding impurities from the melted portion to the liquid phase portion and the solid phase portion by performing zone melting in such a high vacuum. By combining the mechanism of melting of steel and the mechanism of vacuum refining (smelting) under high vacuum at the same time, an unprecedented high purity can be achieved. Accordingly, even if the degree of vacuum is lower than that of the extremely high degree of vacuum used in vacuum purification, it is considered that a high purification effect can be obtained because two actions act simultaneously in combination in zone melting purification.

  The temperature of the melting part is preferably 660 ° C. or higher and 900 ° C. or lower. If the temperature is lower than 660 ° C., the aluminum may solidify and a sufficient purification effect may not be obtained. If the temperature is higher than 900 ° C., the temperature of the peripheral member of the boat or the high-frequency coil rises, and the aluminum vapor or generated gas causes This is because sufficient purification may not be possible. Further, if the temperature is higher than 900 ° C., it may react with the graphite used in the boat.

  Although the temperature rise for heating the melting part to a predetermined temperature depends on the apparatus, it is desirable to carry out in 20 minutes or more. The faster the temperature rises, the higher the productivity will be. However, if the temperature is too fast, the vacuum will deteriorate rapidly due to the components released from the aluminum, causing troubles in the evacuation system, and the melting part will expand rapidly, resulting in a melting region. This is because it may be difficult to control.

Although the melt zone width (length along the moving direction of the melted part) depends on conditions such as the apparatus, it is preferably 30 mm or more and 120 mm or less, and more preferably 50 to 100 mm.
The reason for this will be described.
In order to obtain a wide melting zone width, for example, it is usually performed to increase the output of a means for heating a melting portion such as a high-frequency coil. Therefore, when the output of the heating means is increased so as to obtain a melt zone width exceeding 120 mm, the temperature at the center of the melt zone (melt zone) becomes considerably higher than the melting point, and contamination from the atmosphere and surrounding members is likely to occur. .
In addition, when the melting zone width is narrower than 30 mm, the temporal fluctuation of the melting zone width due to the non-uniformity of the sample shape tends to increase, and in the extreme case, the melting zone is solidified (called freeze) and the purification effect is reduced. To do.
Therefore, in order to form a stable melting portion that does not cause freezing, and to suppress contamination and obtain a good purification result, it is preferable that the melting zone width is in the above-mentioned range.
Moreover, since the optimal melting zone width depends on the dimension of the aluminum material, it is even more preferable that w × 1.5 or more and w × 6 or less are satisfied with respect to the cross-sectional dimension w of the aluminum material. When the melting zone width is larger than 120 mm or w × 6, as described above, the temperature of the central portion of the melting portion becomes considerably higher than the melting point, and contamination from the atmosphere and peripheral members is likely to occur.
On the other hand, if the melt zone width is smaller than 30 mm or w × 1.5, it is difficult to control the melt zone width as described above, and the melted portion may be rapidly reduced or solidified.
When the melting zone is heated by high-frequency induction heating as in the zone melting purification apparatus 100 described later, the melting zone width is set by setting the high-frequency coil output to an appropriate value and when the melting zone is heated by resistance heating. Can be controlled to a desired value by setting the current flowing through the melting portion to an appropriate value.

  Next, after making the width | variety (melting zone width | variety) of an aluminum fusion part into a predetermined value, a fusion | melting part is moved to a predetermined position. When the shape of the aluminum raw material is rod-shaped, the molten part is usually moved from one end to the other end in the longitudinal direction of the aluminum raw material. The melting part can be moved by moving at least one of the aluminum raw material or the high-frequency coil and moving the heated part of the aluminum raw material.

The inventor of the present application has found that a high-purity aluminum material can be obtained by controlling the moving speed of the melting part.
Specifically, it has been found that the residual resistance ratio can be remarkably improved to 70000 or more (70000 to 100,000) by setting the moving speed of the melted portion to 40 mm or less, more preferably 30 mm or less. And the total content of the metal 35 elements can also be controlled to 0.45 ppm or less.
Furthermore, it has been found that the concentration of titanium (Ti), which is an impurity element, can be significantly reduced by setting the moving speed of the melted portion to 40 mm or less, more preferably 30 mm or less.

The mechanism for making the residual resistance ratio more remarkably improved and the concentration of titanium remarkably reduced by making the moving speed of the melted portion 40 mm or less is not clearly understood, but the present invention is not clear. The mechanism that is assumed is as follows.
In other words, the rate at which some elements including titanium are taken into the solid at the solidification interface is related not only to the distribution coefficient determined from the equilibrium diagram but also to the solidification interface movement speed. It is presumed that the effect of improving the ratio is great.
And it is thought that this mechanism functions more reliably by setting the moving speed of the melting part to 30 mm or less per hour.
Considering this mechanism, it is preferable that the moving speed of the melted portion is 10 mm or more per hour.
In other words, if the solidification interface moving speed becomes sufficiently small, the vicinity of the melting part can be explained in an equilibrium state, and the purification efficiency is almost governed by the distribution coefficient determined from the equilibrium diagram. Accordingly, it is considered that the capturing rate is substantially constant in a range where the moving speed is sufficiently small, specifically, a range smaller than about 10 mm per hour. If the moving speed of the molten part is less than 10 mm, the purification time becomes longer, the influence of contamination from surrounding members tends to increase, and the element that has moved (purified) to one end of the aluminum raw material diffuses in the solid phase. It is considered that the purification effect may be reduced.

It should be noted that the mechanism described above is estimated by the present invention based on the knowledge obtained up to now, and is not intended to limit the technical scope of the present invention. .
In addition, when a plurality of passes of band melting are performed, the moving direction of the melting portion is usually the same in all passes.

  Zone melting (zone melting purification) can be performed using, for example, a horizontal high-frequency heating type apparatus. The aluminum raw material is put into a boat disposed inside the zone melting purification apparatus chamber, the inside of the chamber is sealed and the pressure is reduced by the exhaust device, and then the aluminum raw material is heated by high-frequency heating, and one end of the aluminum raw material in the longitudinal direction The vicinity is melted to form a melted part.

FIG. 1 is a cross-sectional view showing a zone melt purification apparatus 100 which is an example of a zone melt purification apparatus.
A vacuum chamber 14 having one end sealed and the other connected to a vacuum pump (exhaust device) 20 is arranged so that its longitudinal direction is horizontal.
The vacuum chamber 14 is preferably made of a transparent material such as quartz so that the inside thereof can be visually recognized.

  A graphite boat 16 is disposed inside the vacuum chamber 14. The raw material placement portion of the graphite boat 16 is covered with an alumina layer 18. The aluminum raw material 10 is arranged in the raw material arrangement portion of the graphite boat 16 through the alumina layer 18.

The high frequency coil 12 is disposed so as to surround the vacuum chamber 14 so as to heat a part of the aluminum raw material 10 and form the melting part 10b. The high frequency coil 12 is connected to a high frequency power source (not shown).
The high-frequency coil 12 moves in the direction of the arrow in the drawing at a moving speed of 40 mm / hour or less, preferably 30 mm / hour or less, thereby melting a part of the aluminum raw material 10 located inside the coil. 10b moves at a moving speed of 40 mm or less, preferably 30 mm or less.
By moving the high frequency coil 12 in this way, the aluminum raw material 10 has an unmelted portion 10c in front of the melting portion 10b (advancing direction of the high frequency coil 12), and a molten and solidified portion (refined) behind the melting portion 10b. Part) 10a.

FIG. 2 is a cross-sectional view showing an example in which a plurality of aluminum raw materials 10 are arranged in the zone melting purification apparatus 100. Several aluminum raw materials 10 are arrange | positioned in the state which mutually contacted the edge part in the longitudinal direction (advance direction of the high frequency coil 12).
In the example shown in FIG. 2, the aluminum raw material 10 has not yet been melted and is all in the unmelted portion 10 c.
By moving the high-frequency coil 12 from the left to the right in FIG. 2 (from the left end to the right end of the four aluminum raw materials 10 in FIG. 2), the molten part moves across the plurality of aluminum raw materials 10. As a result, the plurality of aluminum raw materials 10 are joined together.

  By moving the high-frequency coil for high-frequency heating, the melted part can be moved toward the other end, and the entire sample can be melt-purified. Of the metal element components, peritectic components (peritectic seven elements) tend to concentrate in the melting start portion, and eutectic components (28 elements excluding the peritectic seven elements from the metal 35 elements) tend to concentrate in the dissolution end portion. Therefore, it is possible to obtain high-purity aluminum in a region excluding both ends of the aluminum raw material.

  After the molten part is moved for a predetermined time, for example, from one end to the other end in the longitudinal direction of the aluminum raw material, the high-frequency heating is terminated and the molten part is solidified. After solidification, the aluminum material is cut out (for example, both end portions are cut off) to obtain a purified high-purity aluminum material.

In the case where a plurality of aluminum raw materials are arranged in the longitudinal direction (moving direction of the molten portion), the aluminum raw material in the longitudinal direction is brought into contact with each other as one aluminum raw material in the longitudinal direction (i.e., Among the end portions of the plurality of aluminum raw materials, one of the two end portions having no aluminum raw material adjacent in the longitudinal direction to the other end portion (that is, the aluminum raw material adjacent in the longitudinal direction among the end portions of the plurality of aluminum raw materials is It is preferable to move to the other of the two ends not present.
This is because the end portions of the aluminum raw materials that are in contact with each other are joined at the time of band melting, and a single long aluminum material can be obtained.

In addition, after carrying out zone melting (band melting refinement | purification) from one end of the aluminum raw material to the other end as mentioned above, band melting can be repeated in the same direction from one end to the other end again.
The number of repetitions (number of passes) is usually 1 or more and 20 or less. Even if the number of passes is increased further, the improvement of the purification effect is limited.

In order to effectively purify the peritectic 7 elements, the number of passes is preferably 3 or more, more preferably 5 or more. If the number of passes is less than this, the peritectic 7 elements are difficult to move, and thus a sufficient purification effect may not be obtained.
Also, when a plurality of aluminum raw materials are arranged in contact with each other in the longitudinal direction, if the number of passes is less than 3, the shape (particularly the height dimension) of the refined material (aluminum material) after joining becomes non-uniform and refined. This is because the melt zone width may fluctuate and a uniform purification effect may not be obtained.

In order to reduce the total content of the metal 35 elements, it is preferable to clean the boat, the high-frequency coil, and the inside of the chamber, and perform baking in a vacuum in advance to suppress contamination from peripheral members.
Three elements of iron (Fe), silicon (Si), and copper (Cu) are main impurities in high-purity aluminum, and are easily mixed when preparing a material for purification. In order not to bring these elements into the chamber, it is preferable to pretreat the purified raw material and remove contaminating components on the surface of the purified raw material.

The obtained aluminum material is sufficiently reduced even for peritectic 7 elements that are difficult to reduce by standard purification methods. Therefore, generally available high purity aluminum such as 3N, 4N, 5N, etc. In comparison, the impurity element content is even lower.
Furthermore, a particularly high residual resistance ratio and a low titanium concentration can be obtained by setting the moving speed of the melted portion to 40 mm or less as described above.

The obtained aluminum material can be used as a raw material for semiconductor crystal growth (film forming raw material) by MBE. For example, a high-quality AlN or AlGaN epitaxial layer can be formed (film formation).
The film forming method is not limited to MBE, and any film forming method such as HVPE (hydride vapor phase epitaxy) can be used as long as it is a method for forming a semiconductor material containing aluminum. Therefore, high quality film formation with few impurities is possible.

Further, the present invention is not limited to the formation of a semiconductor layer such as AlN and AlGaN, and can be used in a method for manufacturing a bulk single crystal of a semiconductor containing aluminum, such as AlN and AlGaN.
Specific examples of such a semiconductor bulk single crystal manufacturing method include a flux method, a sublimation recrystallization method, and an HVPE method. In the semiconductor bulk single crystal manufacturing method including these, the aluminum material of the present invention is used. Thus, a semiconductor bulk single crystal containing aluminum can be obtained.

  Furthermore, such high-purity aluminum with few impurities can be used for applications such as a superconducting stabilizer that requires low resistance because of its low electrical resistance at low temperatures. It can also be used for heat transfer materials at low temperatures such as superconducting equipment.

Example 1
Aluminum having a purity of 99.93% (atomic ratio, the same applies hereinafter) was purified by a three-layer electrolytic method to obtain 5N aluminum having a purity of 99.999% or more. The component analysis results of 5N aluminum are as follows: Si = 2.4 ppm, Cu = 0.47 ppm, Fe = 0.30 ppm, Mg = 0.54 ppm, and 31 other elements (ie, Li, Be, B, Na) , K, Ca, Ti, V, Cr, Mn, Ni, Co, Zn, Ga, Ge, As, Se, Zr, Mo, Ag, Cd, In, Sn, Sb, Ba, La, Ce, Pt, Hg , Pb, Bi (hereinafter sometimes referred to simply as “31 elements”) was 0.33 ppm, and the total of these 35 impurities was 4.0 ppm.

This 5N aluminum was used as a raw material and purified by unidirectional solidification to obtain 6N aluminum having a purity of 99.9999%.
More specifically, 1.8 kg of 5N aluminum is disposed as a raw material in a graphite crucible (inner dimensions: width 65 mm × length 400 mm × height 35 mm), and this is used as a core tube of a furnace body moving tubular furnace. The furnace body was housed inside (made of quartz, inner diameter 100 mm × length 1000 mm), and the furnace body was temperature-controlled at 700 ° C. in a reduced pressure atmosphere of 1 × 10 ⁻² Pa to dissolve 5N aluminum. Then, the furnace body was solidified in one direction from one end (solidification start end) to the other end by pulling it out of the core tube at a speed of 30 mm / hour. Then, in the length direction, a portion from 50 mm from the solidification start end to 250 mm from the solidification start end was cut out to obtain massive 6N aluminum having a width of 65 mm × length of 200 mm × thickness of 26 mm.

  The main impurity element content of this 6N aluminum is as follows: Si = 0.33 ppm, Fe = 0.043 ppm, Cu = 0.599 ppm (that is, the total content of Fe, Si and Cu is 0.43 ppm), Mg = 0 .11 ppm, 31 elements = 0.11 ppm, and the total of these 35 elements was 0.65 ppm.

  From the 6N aluminum block obtained above, an aluminum raw material was obtained by cutting into a square column of about 18 mm × 18 mm × 100 mm or a similar shape by cutting and acid cleaning with a 20% aqueous hydrochloric acid solution diluted with pure water for 3 hours.

Zone melt purification:
A graphite boat was placed inside a vacuum chamber (quartz tube having an outer diameter of 50 mm, an inner diameter of 46 mm, and a length of 1400 mm) of the zone melting purification apparatus. A high-purity alumina powder AKP series (purity: 99.99%) manufactured by Sumitomo Chemical Co., Ltd. was applied to the raw material placement portion of the graphite boat while being pressed to form an alumina layer.

The graphite boat was baked by heating at high frequency under vacuum.
Baking is performed in a vacuum of 10 ⁻⁵ to 10 ⁻⁷ Pa using a high-frequency heating coil (heating coil winding number 3, inner diameter 70 mm, frequency about 100 kHz) used for band melting, and from one end of the boat at a speed of 100 mm / hour. It moved to the other end and the whole graphite boat was heated in order.

  Nine aluminum raw materials and a total weight of about 780 g were placed in a 20 × 20 × 1000 mm raw material placement portion provided on a graphite boat. A total of nine aluminum raw materials were arranged so that they could be regarded as square pillars in general, and the cross-sectional dimensions of the aluminum raw material were w = 18 mm, length L = 900 mm, and L = w × 50.

The inside of the chamber was sealed and evacuated by a turbo molecular pump and an oil rotary pump until the pressure became 1 × 10 ⁻⁵ Pa or less. Thereafter, one end in the longitudinal direction of the aluminum raw material was heated and melted by a high-frequency heating coil (high-frequency coil) to form a molten portion.
The output of the high frequency power source (frequency 100 kHz, maximum output 5 kW) was adjusted so that the melt zone width of the melt zone (the length along the moving direction of the melt zone) was about 90 mm. The high-frequency coil was moved at a speed of 30 mm / hour, and the melting part was moved about 900 mm. The pressure in the chamber at this time was 5 × 10 ^{−6 to} 9 × 10 ⁻⁶ Pa. It was 660 degreeC-800 degreeC as a result of measuring the temperature of a fusion | melting part with the radiation thermometer.

Thereafter, the high frequency output was gradually lowered to solidify the melted portion.
Then, the high-frequency coil was moved to the melting start position (the position where the melted portion was first formed), and the aluminum raw material was heated and melted again at the melting start position while the inside of the chamber was maintained at a vacuum to form a melted portion. This melting portion was moved to repeat the zone melting purification. A total of 10 melt melts (10 passes) were performed at a melt zone width of about 90 mm and a moving speed of the melt zone of 30 mm per hour. The melting zone width was w × 2.8 to w × 3.9 with respect to the cross-sectional dimension w of the refined raw material.
After 10 passes, the chamber was opened to the atmosphere, aluminum was taken out, and a purified aluminum material having a length of about 950 mm was obtained.

  Table 1 shows the results of cutting out the obtained aluminum material and analyzing the composition. The composition analysis was performed by glow discharge mass spectrometry (using VG9000 manufactured by Thermo Electron). Samples for composition analysis were collected from seven locations of 90 mm, 210 mm, 330 mm, 450 mm, 570 mm, 690 mm, and 810 mm from the melting start end.

In other samples (six samples of 90 mm, 210 mm, 330 mm, 450 mm, 570 mm and 690 mm from the melting start end of the aluminum material) excluding the sample of 810 mm from the melting start end of the aluminum material, the peritectic system 7 elements (Ti, V , Cr, As, Se, Zr, Mo) was 0.018 to 0.11 ppm, and the total content of 35 metal elements was 0.10 to 0.16 ppm. The total content of Fe, Si and Cu was 0.007 to 0.084 ppm. That is, it was confirmed that impurities were reduced as compared with the above-mentioned 6N aluminum before zone melting purification, and that the total content of metal 35 elements was refined to an extremely high purity of 0.2 ppm or less.
When calculating the total content (concentration) of the seven peritectic elements and the total content (concentration) of the 35 metal elements, 0.001 ppm for an element having a concentration below the detection limit, that is, an element having a content of less than 0.001 ppm As a calculation.
Therefore, when all the metal 35 elements are refined to a detection limit of 0.001 ppm or less, the calculation result of the total content of the metal 35 elements is 0.035 ppm (0.001 ppm × 35). However, it is technically difficult to reduce all the elements below the detection limit. In particular, considering that the peritectic 7 elements are likely to remain, the total content of 35 elements of metal is currently set to 0. It is considered difficult to purify to less than 05 ppm. From this, the preferable lower limit of the total content of the metal 35 elements of the aluminum material according to the present invention is 0.05 ppm as described above.

  In the region of 810 mm from the melting start end of the aluminum material, the total content of the peritectic 7 elements was as extremely low as 0.012 ppm, but the total content of the 35 metal elements was as high as 2.5 ppm. In particular, the total content of Fe, Si, and Cu was as high as 2.4 ppm, and Fe, Si, and Cu were concentrated.

A prismatic sample was cut out, the surface-affected layer was removed by electropolishing, and heat treatment was performed at 500 ° C. to be used for residual resistance measurement. The electrical resistance in the liquid helium immersion state is measured by the four-terminal method, and the ratio of the electrical resistance in the liquid helium immersion state to the electrical resistance measured at room temperature is calculated to obtain the residual resistance ratio without size effect correction. It was. Next, the dimension of the prism sample was measured, and the size effect correction calculation was performed using the dimension value to obtain the residual resistance ratio (residual resistance ratio subjected to the size effect correction). The obtained results are shown in FIG.
Except for the areas of 90 mm and 810 mm from the melting start end, the residual resistance ratio (size effect correction value) was 50000 or more. In particular, in the region of 450 mm to 690 mm from the melting start end, an extremely high value of 70000 or more (in the range of 70000 to 100,000) was shown, and it was confirmed that the product was purified to an extremely high purity.
FIG. 4 shows a system between the distance from the melting start end and the titanium concentration. The titanium concentration was obtained by composition analysis by the glow discharge mass spectrometry described above. In the region excluding the 90 mm and 210 mm regions from the melting start end, the titanium concentration is as low as 0.0006 to 0.0135 ppm.
That is, in the sample of Example 1, the high-purity aluminum material targeted by the present invention can be obtained by removing both end sides (region from the melting start end to 210 mm and region from the melting start end to 810 mm and later). .

Comparative Example 1
A sample of Comparative Example 1 was produced under the same conditions as in Example 1 except that the moving speed of the molten part was set to 60 mm / hour. In the same manner as in Example 1, the aluminum material obtained by performing 10 passes of zone melting and refinement was evaluated.
Samples for impurity analysis were collected from 8 locations of 90 mm, 210 mm, 330 mm, 450 mm, 570 mm, 690 mm, 810 mm, and 930 mm. The results of the composition analysis are shown in Table 1.

  In other samples excluding the 930 mm sample from the melting start end of the aluminum material, the total content of peritectic 7 elements (Ti, V, Cr, As, Se, Zr, Mo) is 0.033 to 0.071 ppm. The total content of 35 metal elements was 0.10 to 0.17 ppm. The total content of Fe, Si and Cu was 0.010 to 0.098 ppm. That is, impurities were reduced as compared with the above-described 6N aluminum before zone melting purification.

The measurement samples of the residual resistance ratio were collected from seven locations of 90 mm, 210 mm, 330 mm, 450 mm, 570 mm, 690 mm, and 810 mm from the melting start position.
Residual resistance ratios (residual resistance ratio size effect correction values) of the samples obtained from these seven locations were obtained in the same manner as in Example 1. The obtained results are shown in FIG.
The residual resistance value was 60000 or less in the entire region in the length direction.
FIG. 4 shows a system between the distance from the melting start end and the titanium concentration obtained by the same method as in Example 1.

Comparative Example 2
The moving speed of the melting part was set to 60 to 100 mm per hour.
Specifically, in the first three passes, the moving speed was 100 mm / hour and the melt zone width was about 70 mm. In the remaining 7 passes, the moving speed was 60 mm per hour and the melt zone width was about 50 mm.
Other purification conditions were the same as in Example 1, and a sample of Comparative Example 2 was produced.

  A measurement sample of the residual resistance ratio and a sample for impurity analysis were collected from seven locations of 30 mm, 150 mm, 270 mm, 390 mm, 510 mm, 630 mm, and 750 mm from the melting start position. Table 2 shows the results of the composition analysis.

  In other samples excluding the sample of 750 mm from the melting start end of the aluminum material, the total content of peritectic 7 elements (Ti, V, Cr, As, Se, Zr, Mo) is 0.042 to 0.093 ppm. The total content of 35 metal elements was 0.097 to 0.18 ppm. The total content of Fe, Si and Cu was 0.009 to 0.042 ppm. That is, it can be seen that there are fewer impurities than the above-mentioned 6N aluminum before zone melting purification.

In the same manner as in Example 1, the residual resistance ratio (residual resistance ratio subjected to size effect correction) of the samples obtained from the seven locations was obtained. The obtained results are shown in FIG.
The residual resistance value (size effect correction value) was 60000 or less in the entire region in the length direction.
FIG. 4 shows a system between the distance from the melting start end and the titanium concentration obtained by the same method as in Example 1.

Comparative Example 3
The moving speed of the melting part was set to 60 to 100 mm per hour.
Specifically, in the first three passes, the moving speed was 100 mm / hour and the melt zone width was about 100 mm. In the remaining 7 passes, the moving speed was 60 mm / hour and the melt zone width was about 60 mm.
Samples of Comparative Example 2 were prepared under the same conditions as in Example 1 except for the above.

  The measurement sample of the residual resistance ratio and the sample for impurity analysis were collected from three locations of 30 mm, 270 mm, and 570 mm from the melting start position. Table 2 shows the results of the composition analysis.

  The total content of peritectic 7 elements (Ti, V, Cr, As, Se, Zr, Mo) was 0.050 to 0.076 ppm, and the total content of 35 metals was 0.11 to 0.14 ppm. It was. The total content of Fe, Si and Cu was 0.013 to 0.017 ppm. That is, it can be seen that there are fewer impurities than the above-mentioned 6N aluminum before zone melting purification.

In the same manner as in Example 1, the residual resistance ratio (residual resistance ratio subjected to size effect correction) of the samples obtained from the seven locations was obtained. The obtained results are shown in FIG.
The residual resistance value (size effect correction value) was 60000 or less in the entire region in the length direction.
FIG. 4 shows a system between the distance from the melting start end and the titanium concentration obtained by the same method as in Example 1.

-Residual resistance ratio and titanium concentration The samples of Example 1 and Comparative Examples 1 to 3 are all compared with those before the zone melting refining, the total content of peritectic 7 elements, the total content of 35 metals, Fe and It can be seen that there is a region where the total content of Si and Cu is lower than that of the 6N aluminum material before the zone melting refining, and that a high-purity aluminum material can be obtained by removing this portion.

Furthermore, as shown in FIGS. 3 and 4, it can be seen that the sample of Example 1 is remarkably superior to the other samples in terms of the residual resistance ratio and the titanium concentration.
That is, with respect to the residual resistance ratio, the samples of Comparative Examples 1 to 3 remained below 60,000 in any region, whereas in Example 1, 450 to 690 mm from the melting start end. In the region, it shows an extremely high value of 70,000 or more (in the range of 70,000 to 100,000), and it can be seen that it can be purified to an extremely high purity.

Moreover, about the titanium density | concentration, Example 1 is a value lower than Comparative Examples 1-3 in the area | region of 330 mm-810 mm from a melting start end.
That is, in the region of 450 mm to 690 mm from the melting start end, it can be seen that the sample of Example 1 has a higher residual resistance ratio and a lower titanium concentration than the samples of Comparative Examples 1 to 3.

  According to the present invention, for example, an aluminum material that can be used for various applications such as use in a film forming method such as MBE that performs high-quality crystal growth, and a purification method thereof are provided.

Zone melt refiner 100
Aluminum raw material 10
Melt solidification part (refining part) 10a
Melting part 10b
Unmelted part 10c
High frequency coil 12
Vacuum chamber 14
Graphite boat 16
Alumina layer 18
Vacuum pump 20

Claims (9)

  Lithium (Li), beryllium (Be), boron (B), sodium (Na), magnesium (Mg), silicon (Si), potassium (K), calcium (Ca), titanium (Ti), and vanadium (V) Chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), cobalt (Co), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), and arsenic (As) Selenium (Se), Zirconium (Zr), Molybdenum (Mo), Silver (Ag), Cadmium (Cd), Indium (In), Tin (Sn), Antimony (Sb), Barium (Ba), and Lanthanum (La) The total content of cerium (Ce), platinum (Pt), mercury (Hg), lead (Pb), and bismuth (Bi) is 0.45 ppm or less in terms of atomic ratio. Aluminum product value is equal to or is 70,000 to 100,000.   The aluminum material according to claim 1, wherein the content of titanium (Ti) is 0.02 ppm or less by atomic ratio.   Use of the aluminum material according to claim 1 or 2 in a semiconductor film forming process.   Use of the aluminum material according to any one of claims 1 and 2 in a semiconductor bulk single crystal growth process. A method for producing an aluminum material comprising a zone melting step of forming a melted portion obtained by melting a part of aluminum and moving the melted portion to remove impurities,
A method for producing an aluminum material, characterized in that the aluminum forming the molten part is disposed on the alumina layer, and the moving speed of the molten part is 40 mm or less per hour.   The manufacturing method according to claim 5, wherein the band melting step is performed under reduced pressure. The manufacturing method according to claim 6, wherein the band melting step is performed under a reduced pressure of 3 × 10 ⁻⁶ Pa to 2 × 10 ⁻⁵ Pa.   The manufacturing method according to claim 5, wherein the zone melting step is performed in an inert gas atmosphere.   The manufacturing method according to any one of claims 5 to 8, wherein a length along a moving direction of the melting portion is 30 to 120 mm.

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