Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
1999-01-08
2001-02-06
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
C118S728000, C118S724000
Reexamination Certificate
active
06183565
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for contactless treatment of a substrate such as a semiconductor wafer, comprising enclosing the wafer in an apparatus and applying two gas streams, in opposing directions, from first and second side sections located opposite on another, to the two opposing planar sides or surfaces of the wafers.
A method of this general type is disclosed in Netherlands Laid Open Application 8402410, in which furthermore, reference is made to Netherlands laid Open Applications 8103979, 8200753 and 8203318.
From these publications it is known to position a wafer such that it is floating between the two side sections. If the gas flow is suitably chosen, it has been found that a highly accurate definition of the position of the wafer with respect to the side sections is possible and this position is relatively fixed, that is to say little variation occurs in the position of the wafer with respect to the side sections. In the patent publications concerned it is described that the wafer is subjected to a wet treatment and is then possibly dried. For the purposes of drying, the gas which holds the wafer in place is heated to about 100° C. and is moved over the surface of the wafer, as a result of which the moisture present is automatically removed.
Heating to much higher temperatures in the range of 200°-1200° C. is frequently necessary when treating semiconductor substrates. Heating can involve annealing or raising the temperature to make deposition or other processes possible. In the prior art, wafers are to this end placed in furnaces and then heated. Although this method is adequate, it has at least two disadvantages. Firstly, a method of this type is usually not completely contactless, that is to say certain points of the wafer are supported. Secondly, it takes a relatively long time to heat a wafer. This is due not so much to the thermal capacity of the wafer itself as to the relatively slow heat transfer between the furnace and the wafers and to the fact that in order to achieve a controlled, deformation free heating of the wafers, the wafers need to be heated inside the furnace together with the furnace itself.
In order to solve this problem single wafer systems have been disclosed with which rapid heating was achieved with the aid of high power lamps (50-80 Kw). Such a method is particularly expensive and difficult to control.
U.S. Pat. No. 4,622,918 discloses an apparatus wherein a wafer is fed through between a number of columns located some distance apart. Sets of columns located opposite one another, between which the wafer moves, are likewise some distance apart. In the gap between the sets of columns, heating is effected by means of a lamp some distance away. This apparatus has the drawback that due to the presence of many metal parts with complicated constructions in close proximity to the wafer, only heating to limited temperatures is possible. Furthermore, in this apparatus a wafer is supported by a plurality of columns of air streams with gaps in between the columns. Due to the succession of columns, where the wafer is supported, and gaps between the columns where the wafer is exposed to the heat radiation of the lamps, both the support of the wafer and the heating are not homogeneous.
It has been found that only limited heating can take place effectively by heating the gases, as is described in the above-mentioned Netherlands applications.
SUMMARY OF THE INVENTION
The aim of the present invention is to provide a method with which contactless heating of semiconductor substrates to relatively high temperature within a relatively short time is possible.
This aim is achieved by enclosing a wafer between relatively massive side sections of an apparatus and applying gas streams to opposite planar sides of a wafer. Preferably the side sections include plates having a minimum thickness of about 10 mm with the spacing between each of the side sections and the wafer to be at most about 1.0 mm. Further, at least one of the side sections is heated to a temperature higher than 200° C.
Surprisingly, it has been found that if the spacing between the side sections, or between side section and wafer, is set to be relatively small, particularly rapid heat transfer can take place. It is possible to achieve heating to far above 1000° C. within a few seconds. Because with this arrangement the wafer, in principle, does not have to be supported, but is held accurately and definitively in its place by the gas streams, the wafer will also not be subjected to stresses generated by local temperature differences and distortion will be prevented as far as possible. Incidentally, it is pointed out that if a slight degree of distortion does take place, the stabilizing effect of the gas streams in opposing directions is such that the wafer is pressed straight in a ‘gentle’ manner without damage.
Therefore, it is now possible to keep the apparatus at the process temperature and load the wafer while the side sections are at process temperature without damage to the wafer. As a consequence, a particularly small peak power is needed to achieve such rapid heating of wafer because the energy required to heat the wafer is withdrawn from the side sections. It will be understood that the method described above is outstandingly suitable for processes in which wafers are treated one-by-one (‘single wafer processing’). However, it is also possible to treat large numbers of wafers one after the other or parallel to one another in the manner described above.
Introduction of the wafer into the enclosing apparatus described above can be effected in any way known from the prior art. A particularly simple method is that in which the side sections can be moved apart. The wafer can be placed between the side sections when the latter have been apart. Supporting means can optionally be present to fix the wafer in such a position. The side sections then move towards one another and the function of the supporting means can be taken over by the gas stream moving out of the side sections concerned. As a result, the wafer moves away from the supporting means.
Apart from heating the semiconductor substrate in this way it is also possible to carry out treatments on the substrate, such as oxidation, etching or the deposition of layers. To this end it is possible to mix a gaseous medium with the gas which holds the wafer in its place. Of course, it is also possible to position the wafer using process gas only. This is in contrast to what is described and suggested in the above-mentioned Netherlands Applications, where only wet treatment of the related substrate takes place. This process gas can be supplied, uniformly distributed, from one of the side sections, such that a uniform distribution over the related wafer surface takes place.
One of the problems encountered in the prior art when supplying process gas at elevated temperature and more particularly when depositing layers is that the apparatus and more particularly when depositing layers is that the apparatus used to supply the process gas becomes contaminated by deposition of the material concerned from the process gas. This means that apparatuses of this type have to be cleaned regularly and that major problems arise with regard to clogging.
With the method according to the invention it is possible to prevent these problems. This is because, according to a further embodiment of this method, a temperature difference is applied over the wafer. One of the side sections is heated to a relatively high temperature, whilst the other of the side sections is heated to a relatively low temperature. It has been found that, as a result of the thermal behavior of the enclosing apparatus, the wafer will assume a temperature which is dependent on the position of the wafer with respect to the two heated side sections. If the two side sections are equidistant from the wafer and the same gas is present on both sides, the temperature will fairly accurately be the average of the values of the temperatures of each of the side sections
Granneman Ernst Hendrik August
Huussen Frank
ASM International N.V
Hassanzadeh P.
Knobbe Martens Olson & Bear LLP
Mills Gregory
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