JP2005048286A - Cover assembly for crucible used for evaporation of raw material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent spot errors or pits, resulting in uneven deposit of phosphors or scintillators. <P>SOLUTION: An assembly comprises two plates or covers, one of which being an outermost plate or cover, and both, at least in part having a perforation pattern over a surface area covering an open side of a crucible having a bottom and surrounding sidewalls containing raw materials, wherein the outermost cover is mounted at a distance farther from the crucible than the cover covering the open side of a crucible, and wherein both covers are mounted versus each other, so that, when viewed through an axis in a direction perpendicular to the bottom of the crucible from a distance to the outermost cover of at least 10 times the distance between the two plate or covers, its contents cannot be observed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a solution for the non-uniform deposition of phosphor or scintillator material from the raw material, thereby causing a “spot error” resulting in non-uniform deposition of said phosphor or scintillator due to the discharge of liquefied raw material present in a heated crucible. "Or" pit "is avoided.

  In physical vapor deposition (PVD) and chemical vapor deposition (CVD) techniques, in addition to the use of specially designed electric heated crucibles, the factors that provide uniform phosphor or scintillator coating composition and uniform layer thickness deposition over the entire surface are For example, EP Application No. Related to the distance determining the profile of the vapor cloud at the location of the substrate as described in 03100723 (filed 20 March 2003) and 04101138 (filed 19 March 2004).

  The average value of the shortest distance between the crucible and the substrate is preferably in the range of 5-10 cm. If this distance is too large, it will lead to material loss and reduced process yields, while if this distance is too small it will lead to very high temperatures of the substrate.

  However, care should be taken to avoid “spot errors” or “pits” that result in non-uniform deposition of phosphors or scintillators due to the discharge of liquefied raw materials present in the heated vessel: undesirable non-uniformities at the surface In addition to its physical presence, differences in speed or sensitivity may strain its use as a screen, plate or panel for use in diagnostic imaging. In particular when those phosphors are suitable for use in direct radiographs as scintillators, intensifying screens as prompt phosphors or as stimulating phosphors used in computer radiography (CR) for storage panels. It is.

  The object of the present invention is therefore to evaporate and deposit the scintillator or phosphor material on a support, in particular of the phosphor or scintillator to be produced while applying CVD or PVD technology under vacuum conditions in the deposition chamber. It is to provide a tool for preventing unwanted “spots” or “pits” from reaching the substrate or support.

  The abovementioned advantageous effect is realized by utilizing a special assembly of the cover combined with a heated crucible containing the raw materials as starting material, said assembly having the features set out in claim 1. The features of preferred embodiments of the invention are set out in the dependent claims.

  Further advantages and embodiments of the present invention will become apparent from the following description.

  One way to avoid the spot reaching the web, substrate or support is for a container, tray, boat or crucible supported by the peripheral edge of the crucible and at least partially covering the crucible. Is to give.

  Obviously, the material composition of the cover and crucible should be resistant to physical influences and the material should be a refractory material. The preferred refractory material is selected from the group of materials consisting of Mo, Nb, Ta and W. The ultimate choice of material suitable for use as a refractory cover material is largely dependent on its manu- mentation. This is because the cover should be brought into the desired shape to be suitable for use as a cover on the container of raw material to be evaporated, boat or crucible (eg a so-called “nip area” or roller or other Deformation by bending or bending a plate of a desired thickness in “smoothing means” or “bending means”).

  Furthermore, because only the raw materials contained in the crucible or boat are later evaporated and deposited on the cooled substrate support, the designed high process temperature (at least 300 ° C, more preferably at least 450 ° C, even 700 ° C). It is clear that it should melt at ˜900 ° C.). The formation of raw materials contained in the crucible and for example “mixed melt” crystals of the crucible material should not be clearly recognized. This is because the presence of crucible material in the deposited layer is a source of undesirable contamination. In addition to being physically inert, the cover material as well as the crucible material should be chemically inert and that no chemical reaction between the raw material and the crucible material in contact should be possible. Is obvious, otherwise the composition of the vapor deposition compound on the cooled substrate will not be under control, and in addition to such uncontrollable composition, the uniformity of the deposited layer will also be out of control. .

  Various configurations are available to obtain the most advantageous solution to avoid those spot defects. Even when very small holes are present in the panel covering the crucible according to the invention, "spot errors" or "pits" can still hinder the uniformity of the pattern of the deposited layer. The solution for this is achieved by mounting a second cover (with or without the same hole pattern across its surface) with small holes at a distance farther from the crucible than the first cover, with holes on both surfaces. After mounting both covers with a pattern, they cover each other completely when viewed from the direction perpendicular to the bottom of the crucible from a distance of at least 10 times the distance between the two outermost plates or covers. Positioned so that there is never.

  The assembly according to the invention comprises two plates or covers, one of which is the outermost plate or cover, both covering at least partly the open side of the crucible having a bottom containing the raw material and a peripheral side wall. The outermost cover is mounted at a distance farther from the crucible than the cover covering the open side of the crucible, and both covers are the two plates or covers. Mounted relative to each other such that their contents cannot be observed when viewed through an axis perpendicular to the bottom of the crucible from a distance to the outermost cover of at least 10 times the distance between them. In other words, their perforation or perforation pattern (but not excluding the zigzag refractory metal structure that appears as perforation pattern), and the bottom of the crucible viewed from the direction perpendicular to the plane formed by the bottom of the crucible Sometimes never form a single line. Thus, the raw material in the crucible remains invisible when viewed from a distance from the outermost perforated cover at least 10 times the distance between the two plates or covers.

  In another preferred embodiment of the invention, the covers are in the range of 5 ° to 30 ° when viewed in a direction below a limited viewing angle about each axis perpendicular to the bottom of the crucible. Sometimes again, when viewed from a distance (from the outermost perforated plate or cover) of at least 10 times the distance between the two outermost plates or covers, their contents cannot be observed. Is done.

  According to the present invention, an assembly is provided in which the two plates or covers are mounted in parallel.

  In one example according to the invention, the perforation pattern in the plate or cover has perforations having an average equivalent circle diameter in the range of 1 mm to 5 mm and an average distance between the centers of the equivalent circles in the range of 2 mm to 10 mm. The terms “equivalent circle diameter” and “equivalent circle” were introduced to allow each form of perforation and to define the size and distance between perforations in a manner independent of the shape of the perforations or perforation pattern: The term “equivalent circular diameter” refers to the diameter calculated from any perforation, displaying the surface area of the perforation as the equivalent surface area of the circle. From the same circular equivalent surface area, it is centered to display the average distance between perforations. The shape of the perforation or perforation pattern, even when obtained from or in a zigzag structure, is a circle, triangle, square, hexagon (eg, honeycomb), or another polygon (not limited to them) May be the same size or not. Thus, for a plate that is in closest contact with the crucible, for example, a perforation having a large size in the center of the outermost plate and a small size near the side wall and vice versa, for example, is advantageous in the construction of the assembly of the present invention. It is possible. According to the present invention, the shortest distance between perforated plates or covers in the assembly is in the range of 1 mm to 20 mm, more preferably in the range of 5 mm to 10 mm.

  In one example according to the present invention, the assembly is configured such that the perforations are the same for both of the two plates.

  In another example according to the invention, the assembly is configured such that the perforations are different for both of the two plates and the plate farthest from the crucible has the smallest perforations.

  In yet another example for an assembly according to the invention, the perforation has a large size in the center of the outermost plate and a small size near the crucible sidewalls for the perforated plate that is in closest contact with the crucible. It is preferable.

  According to a further example according to the invention, in the assembly the two covers and the crucible are made of the same or different refractory materials, which are tantalum (Ta), molybdenum (Mo), niobium (Nb), tungsten ( W) and a metal or metal alloy selected from the group consisting of heat-resistant stainless steel. The refractory material is the same or different refractory material as for the crucible and the plate or cover is mounted on the crucible as an assembly according to the invention.

  A cover without any holes or other perforation pattern, also referred to as a “non-perforated cover” as a closure cover or “slot cover”, is preferably present as the outermost cover of the assembly according to the invention, in particular during heating, whereby Cover the hole of the outermost cover of the cover assembly according to the present invention. Thus, the assembly according to the invention is further provided with a non-perforated cover as a closure cover. It is preferable to cover the crucible with such a slot cover before bringing the crucible to an optimal constant high temperature. The temperature is preferably distributed uniformly throughout the crucible to evaporate the raw material in a “steady state flow”.

  Once the “slot cover” is removed, the evaporation of the raw material is performed in such a way as to obtain a continuous and uniform vapor flow in the direction to the substrate, where a guide plate is further provided in the evaporation or evaporation chamber. , Thereby guiding one or more vapor streams toward the substrate in order to more clearly define the region in which the phosphor or scintillator material is to be deposited. Thus, the presence of the deflector advantageously limits the deposition area on the substrate to a small area, thus preventing undesired deposition of scintillators or phosphor materials, such as on the walls of the deposition chamber.

  Especially in the vapor deposition process, the evaporated raw material may escape from the liquefied or molten raw material mixture in an uncontrolled manner at a rate in the range of a few m / s, or km / s.

  A preferred phosphor of the alkali metal storage type deposited from the vapor phase using an assembly as described above is, for example, as described in US Pat. No. 5,736,069.

There are disclosed phosphors having the general formula given below:
M ¹⁺ X. aM ²⁺ X ′ ₂ . bM ³⁺ X ″ ₃ : cZ
^Wherein M ¹⁺ is at least one component selected from the group consisting of Li, Na, K, Cs and Rb,
M ²⁺ is at least one component selected from the group consisting of Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu, Pb and Ni,
M ³⁺ is selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Bi, In, and Ga. At least one component,
Z is at least one component selected from the group consisting of Ga ¹⁺ , Ge ²⁺ , Sn ²⁺ , Sb ³⁺ and As ³⁺ ,
X, X ′ and X ″ may be the same or different and each represents a halogen atom selected from the group consisting of F, Br, Cl, and I, and 0 ≦ a ≦ 1, 0 ≦ b ≦. 1 and 0 <c ≦ 0.2.

  In addition to a screen or panel having a phosphor or scintillator layer having the composition described above, a CsX: Eu stimulable phosphor (X represents a halide selected from the group consisting of Br, Cl and I). A phosphor screen or panel containing is particularly desirable.

  Manufacturing processes for manufacturing such screens or panels are described in WO 01/03156. Acicular Eu-activated alkali metal halide phosphors are preferred for image sharpness, in particular Eu-activated CsBr phosphor screens as described in EP-A 111 13458, and EP-A for improved sensitivity. Annealing of the phosphor, such as 1217633, is advantageously performed, and the annealing step results in a cooled deposited mixture as deposited on the substrate at a temperature of 80-220 ° C., at which temperature 10 Consisting of maintaining for 15 minutes.

High crystallinity is easily analyzed by X-ray diffraction techniques that give specific XRD spectra as shown in EP-A 11113458. Therefore, a mixture of CsBr and EuOBr and / or EuBr ₃ is provided as a raw material mixture in the crucible, where the ratio between the two raw materials is usually about 90% by weight. High crystallinity is easily analyzed by X-ray diffraction techniques that give specific XRD spectra as shown in EP-A 11113458.

Therefore, a mixture of CsBr and EuOBr and / or EuBr ₃ is provided as a raw material mixture in the crucible, with the ratio between both raw materials being about 90% by weight cheap CsBr and about 10% by weight expensive EuOBr.

However, it has been shown that the proportions can be adapted to favor low materials and manufacturing costs without causing a change in composition as a function of coating (evaporation) temperature: 99.5 wt% CsBr and 0.5 wt% The high evaporation temperature for the EuOBr / EuBr ₃ ratio raw material mixture gives the same result (in terms of speed) as before.

  Such a method clearly leads to a more evenly divided phosphor layer and a lower amount of Eu dopant.

At least 500-800 p. p. m. Low amounts (ie in the range of 100-200 pm) of europium dopant relative to (see EP-A 111 13458-a phosphor layer made in the absence of a covered crucible assembly according to the invention) Having a CsBr: Eu ²⁺ phosphor screen thus became available.

  These data suggest that despite the presence of low amounts of europium dopant leads to the same screen speed, it shows a more uniform distribution of dopant and / or more efficient incorporation.

  In contrast, 1000 p. p. m. To 3000 p. p. m. Screens requiring amounts of dopant in the range indicate that the dopant does not appear to be incorporated efficiently.

EP-A 111 13458 Example CsBr: From Eu the screen is made by thermal deposition of CsBr and EuOBr (and / or EuBr ₃ ) and the variables in the deposition process are the substrate temperature and Ar gas pressure, which in the XRD spectrum [ 100] It is recognized that it leads to needle-like crystals with characteristically high strength with respect to the crystal plane.

EXAMPLE Utilizing the assembly according to the present invention not only avoids unwanted spot formation or “spouting” as considered for the purposes of the present invention, but ultimately (trivalent Eu dopants in small non-negligible amounts). Containing acicular CsBr: Eu ²⁺ phosphor) leads to a more uniform distribution of dopants.

In the assembly of the present invention, the crucible is heated to an optimal and constant high temperature (800 ° C.) while covering the assembly with a non-perforated outermost cover to obtain the temperature evenly distributed throughout the crucible, and On the perforated cover far from the crucible when evaporating the raw materials (95: 5 wt.% CsBr and EuOBr / EuBr ₃ ) in a “steady flow” in a uniform vapor cloud after removal of the outermost non-perforated cover Thus, it was experimentally observed that during evaporation, acicular crystals formed as an intermediate “layer” on the perforated cover (mounted at a distance of 5 mm from the cover in contact with the crucible wall).

  The perforations in the cover were in the form of circles with a diameter of 2 mm with a center distance of 10 mm. Said intermediate layer is continuously fed from the evaporation raw material present in the crucible on one side and continuously consumed by evaporation to the deposition chamber on the other side, and the evaporation cloud is just EP application no. It was deposited on an aluminum substrate as described in 03100723 (filed 20 March 2003) and 04101138 (filed 19 March 2004).

  This phenomenon of forming such an intermediate layer is understood as the formation of an intermediate “homogenization layer”, which gives even more uniform incorporation of europium dopant in the cesium bromide base material, thereby reducing the amount of expensive europium dopant during manufacture. Gives the possibility to use raw materials.

  An improved assembly according to the present invention having two parallel plates covering the crucible, wherein the plate is perforated and mounted on the crucible to avoid “spout” or “spout” of the liquefied raw material after heating. In addition to utilizing an assembly that provides a bottom and a peripheral sidewall, and provides an electrode clamp to an exterior portion of the sidewall that is positioned opposite to each other, the portion extending as a lip to the sidewall, A crucible connectable with an electrode for heating the crucible, wherein the cross-sectional area of each of the lips between the crucible wall and the electrode clamp is disclosed in a patent application filed on the same day as this patent application. Utilizing a crucible characterized by at least a 5% reduction, thereby making the crucible more uniform in the vacuum deposition chamber Give the heat capacity.

  While the invention has been described in connection with preferred examples thereof, it is manifestly not intended to limit the invention to those examples, and the scope of the invention as defined in the claims. It will be apparent to those skilled in the art that many changes can be made without departing from the invention.

Claims (4)

  An assembly comprising two plates or covers, one of which is an outermost plate or cover, both covering at least in part the open side of a crucible having a bottom containing material and a peripheral side wall The outermost cover has a perforated pattern on a surface region, and the outermost cover is mounted at a distance farther from the crucible than the cover covering the open side of the crucible, and both covers are between the two plates or covers. Assembly mounted relative to each other such that when viewed through an axis perpendicular to the bottom of the crucible from a distance to the outermost cover of at least 10 times the distance of   Both covers when viewed in a viewing angle direction limited around each axis perpendicular to the bottom of the crucible from a distance to the outermost cover at least 10 times the distance between the two plates or covers. The assembly of claim 1, mounted on each other such that its contents cannot be observed.   The perforations are the same for both of the two plates or different for both of the two plates, the plate farther from the crucible has smaller perforations and the assembly is non-perforated as a closure cover Assembly according to claim 1 or 2, further provided with a cover.   The two covers, the non-perforated closure cover and the crucible are made of the same or different refractory materials, the refractory materials being tantalum (Ta), molybdenum (Mo), niobium (Nb), tungsten (W) and heat resistant stainless steel. 4. The assembly of claim 3, wherein the assembly is a metal or metal alloy selected from the group consisting of steel.