Evaporation boat and use of an evaporation boat

Abstract

An evaporation boat comprising an evaporator body has an evaporator surface which extends along a longitudinal direction of the evaporator body from a first end face toward a second end face of the evaporator body. The evaporator body comprises at least one recess on an underside (20) opposite to the evaporator surface, so that the evaporator body has a thickness between the evaporator surface and the underside in the region of the at least one recess along its longitudinal direction which decreases from the center of the evaporator body in the longitudinal direction toward one of the end faces associated with the recess. The use of such an evaporation boat is specified as well.

Claims

1. An evaporation boat comprising an evaporator body, wherein the evaporator body comprises an evaporator surface which extends along a longitudinal direction of the evaporator body from a first end face toward a second end face of the evaporator body and wherein the evaporator body comprises at least one recess on an underside opposite to the evaporator surface, so that the evaporator body has a thickness between the evaporator surface and the underside in the region of the at least one recess along its longitudinal direction which decreases from the center of the evaporator body in the longitudinal direction toward one of the end faces associated with the recess.

2. The evaporation boat of claim 1, wherein the thickness of the evaporator body decreases substantially continuously in the region of the at least one recess along the longitudinal direction.

3. The evaporation boat of claim 1, wherein the evaporator body comprises an end region on the first end face and/or on the second end face and the at least one recess extends from the center of the evaporator body to the end region of the associated end face, wherein the end region has a thickness which is equal to or greater than that of the center of the evaporator body.

4. The evaporation boat of claim 1, wherein the minimum of the thickness of the evaporator body along the longitudinal direction of the evaporator body is 75 % or less of the maximum of the thickness of the evaporator body.

5. The evaporation boat of claim 1, wherein the evaporator body comprises a mirror plane which extends perpendicular to the longitudinal direction along a transverse direction through the center of the evaporator body.

6. The evaporation boat of claim 1, wherein the evaporator body has a trapezoidal cross-section along the transverse direction and the at least one recess has a rectangular cross-section.

7. The evaporation boat of claim 1, wherein the recess is created in the evaporator body by milling or grinding.

8. Use of an evaporation boat of claim 1 for evaporating metal in a PVD metallization system.

9. The use according to claim 8, wherein, when evaporating metal, the evaporation boat is heated to an operating temperature which exhibits a deviation of at most 10 % along the longitudinal direction of the evaporator body in the region of the at least one recess.

10. The use according to claim 9, wherein the operating temperature is 1500° C. or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The figures show:

[0034] FIG. 1 a perspective view of an evaporation boat according to the invention from above at an angle,

[0035] FIG. 2 the evaporation boat of FIG. 1 in a perspective view from below at an angle,

[0036] FIG. 3 a bottom view of the evaporation boat of FIG. 1,

[0037] FIG. 4 a sectional view through the evaporation boat along the plane A-A of FIG. 1,

[0038] FIG. 5 a sectional view through the evaporation boat of FIG. 1 along a longitudinal direction,

[0039] FIG. 6 the sectional view of FIG. 5 during operation of the evaporation boat,

[0040] FIG. 7 a schematic illustration of temperature profiles of evaporation boats and

[0041] FIG. 8 a sectional view through an example of an evaporation boat as known in the prior art.

DETAILED DESCRIPTION

[0042] FIG. 1 shows an evaporation boat 10 according to the invention comprising an evaporator body 12.

[0043] The evaporator bodies 12 are made of a ceramic material, for example, the main constituents of which are titanium diboride (TiB.sub.2) and boron nitride (BN), as well as optionally aluminum nitride (AIN). Titanium diboride acts as an electrically conductive component and boron nitride as an electrically insulating component, so that the electrical conductivity of the evaporator body 12 and thus of the evaporation boat 10 can be adjusted via the selected composition.

[0044] The evaporator body 12 extends along a longitudinal direction L from a first end face 14 toward an opposite second end face 16.

[0045] The evaporator body 12 further comprises an evaporator surface 18 and an underside 20 opposite to the evaporator surface 18.

[0046] FIG. 2 shows a perspective view of the evaporation boat 10 from below at an angle, in which it can be seen that the evaporator body 12 comprises two recesses 22 and 24 on its underside 20.

[0047] The recesses 22 and 24 extend from a center of the evaporator body 12, configured here as a central ridge 26, along the longitudinal direction toward one of the end faces 14 and 16, respectively, wherein the recess 22 is associated with the first end face 14 and the recess 24 is associated with the second end face 16.

[0048] From FIG. 3, which is a bottom view of the evaporation boat 10, it can be seen that the evaporation boat 10 comprises a mirror plane S along the central ridge 26, which is perpendicular to the longitudinal direction L and parallel to the transverse direction Q.

[0049] In other words, the evaporation boat 10 in the shown embodiment is mirror-symmetrical.

[0050] The evaporator body 12 also comprises a respective end region 28 on both the first end face 14 and the second end face 16, wherein the recesses 22 and 24 extend only to the respective end region 28.

[0051] FIG. 4 shows a cross-section through the evaporator body 12 along the plane A-A of FIG. 1.

[0052] In this illustration, it becomes clear that the evaporator body 12 has a trapezoidal cross-section along the transverse direction Q, which is perpendicular to the longitudinal direction L and to a vertical direction H.

[0053] The recess 22, on the other hand, has a rectangular cross-section, which creates an edge portion 30 on the underside side 20 of the evaporator body 12 that contributes to the mechanical stability of the evaporator body 12.

[0054] The edge portion 30 has a width b.sub.1 of up to 1 mm, for example, while the evaporator body 12 has a thickness h.sub.1 of about 10 mm.

[0055] It goes without saying that the size and dimensions of the evaporation boat 10 can be adapted to the requirements of the metallization system in which the evaporation boat 10 is to be used.

[0056] FIG. 5 shows a sectional view of the evaporation boat 10 along the longitudinal direction L.

[0057] From this illustration, it can be seen that, in the region of the respective recess 22 or 24, a thickness of the evaporator body 12 along the vertical direction H decreases continuously from the central ridge 26, i.e., from the center of the evaporator body 12, in the direction of the associated end face 14 or 16 to the respective end region 28.

[0058] The thickness of the evaporator body is thus reduced continuously, so that a minimum of the thickness of the evaporator body 12, which is shown in FIG. 5 as the thickness h.sub.2, is reached at the transition of the recess into the respective end region 28.

[0059] In the shown embodiment, the thickness h.sub.2 ranges from 5 to 7 mm, which results in a ratio h.sub.2/h.sub.1 of about 0.5 to 0.7. In other words, the minimum of the thickness of the evaporator body 12 along the longitudinal direction L is about 50 to 70 % of the maximum of the thickness of the evaporator body 12.

[0060] The end regions 28 have a width b.sub.2 along the longitudinal direction L of about 3 to 10 mm.

[0061] The mode of operation of the evaporation boat 10 according to the invention is explained in the following.

[0062] The evaporation boat 10 is in particular used for evaporating metal in a (not depicted) PVD metallization system.

[0063] For this purpose, the evaporation boat 10 is inserted via the end regions 28 into a (not depicted) bracket, for example made of copper, which provides electrical contact to the evaporation boat 10, so that the evaporator body 12 can be heated to an operating temperature by direct current flow. The bracket further comprises cooling, for example water cooling.

[0064] A metal wire, for example made of aluminum, is then brought into contact with the evaporator surface 18 and is melted on the evaporator surface 18 because the evaporator body 12 is heated. The formed molten metal is subsequently evaporated, for example to coat a (not depicted) substrate being passed over the evaporator surface 18.

[0065] The molten metal results in corrosion of the evaporator surface 18, as indicated in FIG. 6 in the form of a corroded volume 32 shown with hatching, whereby the extent of corrosion, i.e., the rate of corrosion, increases as the operating temperature increases.

[0066] FIG. 7 schematically shows the progression of the temperature along the lengthwise direction L, i.e., the temperature profile of the evaporation boat 10, whereby the solid line 34 shows the temperature progression of the evaporation boat 10 according to the invention.

[0067] It can be seen that the temperature increases all the way across the end regions 28, i.e., all the way across their width b.sub.2, to a plateau value T.sub.1, which corresponds to the operating temperature.

[0068] The plateau value T.sub.1 remains substantially unchanged over the region of the evaporator body 12 in which the recesses 22 and 24 extend. In this region, the operating temperature of the evaporator body 12 preferably deviates by no more than 10 %.

[0069] The plateau value T.sub.1 is preferably 1500° C. or less.

[0070] This results in the most uniform possible corrosion along the lengthwise direction L of the evaporator body 12, so that the tool life or service life of the evaporation boat 10 increases.

[0071] The dashed line 36 in FIG. 7, on the other hand, schematically shows a temperature profile as would be expected for evaporation boats 38 known from the prior art (see FIG. 8), which have a constant thickness h.sub.3 along their longitudinal direction L.

[0072] In this case, the cooling provided by the bracket disposed near the end regions 28 results in a temperature profile that increases toward the center of the evaporator body of the evaporation boat 38 to a peak temperature T.sub.2 and then decreases again. In order to be able to ensure a sufficient operating temperature of the evaporation boat 38 over its entire length, the peak temperature T.sub.2 is typically around 1700° C.

[0073] There are therefore significant differences in the rate of corrosion along the longitudinal direction L of the evaporation boat 38, whereby more severe corrosion is observed near the center of the evaporation boat 38 than in the end regions 28. This results in a shorter service life of the evaporation boat 38 than that of the evaporation boat 10 according to the invention.