Work holders – Work-underlying support – Gapped support
Reexamination Certificate
1998-10-01
2001-12-11
Hail, III, Joseph J. (Department: 3723)
Work holders
Work-underlying support
Gapped support
C269S903000, C269S902000, C269S287000
Reexamination Certificate
active
06328296
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a holder for a semiconductor substrate, often referred to as substrate hereinafter for short, comprising a main body which is provided with three or more projections between which the substrate can be fixed in the holder and of which at least a first and a second projection are fixedly connected to the main body, while a third projection which is present opposite the first and the second projection is movably connected to the holder and can be moved in a direction away from the first and the second projection, while the holder is provided with means by which the third projection is urged towards the first and the second projection. The invention also relates to a method of manufacturing a semiconductor device in which such a holder is used.
Such a holder, fitted with a substrate which is usually round, is used for providing the surface of this substrate with a (semi)conducting or insulating region or for removing such a region. To achieve this, the holder is usually placed in a device in which gases or liquids are present by means of which the above operation can be carried out. The holder may also form part of said device.
Such a holder is known from a U.S. patent document published under U.S. Pat. No. 4,971,676 on Nov. 20, 1990. The holder shown in FIG. 1 thereof comprises a main body in the form of a flat carrier plate which is provided with four projections arranged in a circle by means of which the substrate can be fixed in the holder. Three of the projections each comprise a cylinder segment which lies in a different quadrant of the carrier plate each time and whose upper side is covered with a plate in the form of a circle sector which extends over the substrate to be inserted and over the carrier plate. A fourth projection is present in a fourth quadrant, has the shape of a cylinder, and is capable of movement in a direction away from the other projections and is urged towards the fixed projections - and thus towards the substrate to be inserted - by means of a spring. The fourth projection can be recessed into the carrier plate, so that the substrate can be passed over the carrier plate to below the other three projections.
It is a disadvantage of the known holder that it covers part of the substrate. As a result of this, the substrate is not exposed in its entirety to the materials with which the surface of the substrate is treated during a processing operation on the substrate. Moreover, the known holder is comparatively expensive owing to its complexity.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a holder for a substrate which does not have the above disadvantage, which renders it possible to process a portion of the substrate present in the holder which is as large as possible, and which is at the same time simple and inexpensive.
According to the invention, a holder of the kind mentioned in the opening paragraph is for this purpose characterized in that a lateral side of each projection facing towards the substrate to be inserted is provided with a concave recess whose geometry is such that exclusively the outermost edges of the both the upper surface and the lower surface of the substrate to be inserted come into contact therewith. The concave shape of the recess in the portion of a projection facing the substrate achieves that a substrate can be clamped in securely and fixedly in the holder. The entire surface area - both the upper surface and the lower surface - of the substrate is accessible to those substances with which a treatment of the substrate is carried out thanks to a suitable choice of the geometry of the concave recess, which is such that the substrate is in contact with the recess only at the edges of both the upper surface and the lower surface of the substrate. The portion of the projection comprising the concave recess does cause some shadow effect, but this is considerably less than in the known holder thanks to the invention. A very suitable shape for the recess is, for example, the shape of a triangle or a trapezium (=truncated triangle). Preferably, the recess has a cross-section in radial direction which is triangular. The advantages of this will be explained further below. The shadow effect is still further reduced by a suitable choice of the three-dimensional shape of the projection, which will also be discussed further below.
In a preferred embodiment of a holder according to the invention, the first and the second projection lie within two mutually adjoining quadrants of the main body, when viewed in projection, and the third projection lies outside said quadrants, when viewed in projection, and preferably at a distance to the first and the second projection which is as great as possible. A holder suitable for, for example, round substrates, can accommodate a spread in the diameters of these substrates as a result of this placement of the projections. That is to say, substrates having a diameter which is somewhat smaller or somewhat greater than the nominal diameter can still be well retained in the holder. An important advantage of the present invention is a spread in the thickness of the substrates can also be accommodated in such a placement, thanks to the concave recess and the manner in which this makes contact with the substrate. Thus substrate having a thickness greater or smaller than the nominal thickness can still be satisfactorily clamped in in the holder. Preferably, the holder.comprises a total of exactly three projections which are present approximately in the corner points of an equilateral triangle. Such a holder is particularly suitable for round substrates.
In a very important and advantageous modification of a holder according to the invention, the projections each have the shape of a diabolo. This means that a substrate to be placed in the holder makes contact with a projection in one point only at the edge of its upper surface and in one point only at the edge of its lower surface. The already comparatively small shadow effect of the projections in a holder according to the invention is considerably reduced thereby. This shape, where the recess has the shape of a triangle or trapezium, also provides an excellent contribution to the accommodation of fluctuations in thickness and diameter of the substrate.
Preferably, the shape of the projections is that of a diabolo which comprises two truncated cones placed on top of one another. So this is a diabolo which does not have a cylindrical central portion, unlike, for example, a yarn reel. The recess is triangular in shape then. The advantage of such a diabolo shape may be elucidated as follows. It is favorable to choose the apex angle of at least the upper cone of the diabolo to be as small as possible in order to achieve a minimum shadow effect. If the diabolo has no cylindrical central portion in that case, it is easier to achieve, also in the case of a thin substrate, that the latter will make contact with the projection at the edges only. It is favorable in practice to choose different values for the apex angles of the two cones of the diabolo. The cone which is present above the substrate and which causes the shadow effect mentioned above is preferably given an apex angle which is as small as possible, for example an apex angle of between 36 and 44°, and preferably approximately
40°. A somewhat greater apex angle is preferably chosen for the cone which lies below the substrate. A substrate placed in the holder is moved more easily into its end position as a result of this, which is movement involves a displacement over the slope formed by the lower cone. A suitable apex angle for this lies between
116 and 124° and is preferably approximately
120°. The height of the upper cone 31 is chosen to be as possible, again to reduce the shadow effect.
An important additional advantage of a holder according to the invention is that a substrate placed in the holder will always lie parallel to the main body, provided the projections have the same dimensions. This also contributes
Biren Steven R.
Hail III Joseph J.
U.S. Philips Corporation
Wilson Lee
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