Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2002-02-28
2003-02-11
Paik, Sang (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C118S725000
Reexamination Certificate
active
06518548
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a technique for heating or cooling a substrate; more specifically, the present invention relates to a substrate temperature control system and a method for controlling the temperature of a substrate, preferably applicable to the lithography process of producing semiconductor devices and the like.
The process of producing semiconductor devices includes a process of heating and cooling substrates; at the lithography process, in particular, heating is conducted several times in repetition. The substrate heating system includes for example a spin-coater wherein a vacuum chuck mechanism is arranged on a hot plate to which is put a substrate in close contact (for example, see Japanese Patent Laid-open No. Sho 62-53773). Additionally, as the substrate heating system, there are many examples of a system of proximity mode, by which a substrate is heated while the substrate floats slightly above a hot plate (see “Electronics Parts and Materials”, published by Kogyochosakai Publishing Co. Ltd., extra number, 1994, pp. 77-83); the substrate heating system is for example a resist baking oven for a semiconductor wafer (proximity bake unit) as shown in FIG.
13
. The system is used at a process after resist coating process of the substrate (semiconductor wafer), and the figure schematically shows the system. In the figure,
1
represents a semiconductor wafer with resist coated thereon; wafer
1
is transferred on an elevator mechanism composed of lift pin
8
and actuator
9
operable of moving the lift pin upward and downward and is then mounted on small block
52
arranged on the surface of hot plate
51
. The hot plate
51
inside which heater element
4
is arranged is controlled to a predetermined temperature by means of thermocouple
6
and thermoregulator
7
. Through the block
52
, the wafer
1
is arranged in a floating fashion by about 0.1 mm apart from the hot plate
51
.
Where the substrate heating system is used for post-exposure bake (referred to as “PEB”) process of, for example, chemical amplified resist with the exposed part extremely temperature sensitive after lithography, the temperature variation can be controlled at about ±0.8° C.; by such proximity mode with an additional control mode of the gas stream above substrates, the temperature variation can be controlled at about ±0.3° C.
Following the high integration tendency of semiconductor devices in recent years, however, it is demanded that the temperature variation at the PEB process should be controlled to a further stricter value. However, the conventional substrate heating system cannot satisfy such demand, disadvantageously. Furthermore, the increase of semiconductor wafer size is now under way, so that the suppression of the temperature variation is more difficult than ever.
The increase of semiconductor wafer size induces the increase of thermal capacity, so that a longer time is required for the wafer to reach a desired temperature. In other words, a new problem of the prolongation of temperature elevation time occurs. A time of about 60 seconds is required to elevate the temperature of a wafer of an 8-inch size to the objective temperature of 60° C. to 150° C. The increase of temperature elevation time deteriorates the through put (production efficiency) of the production process.
Where the float distance of the substrate from the hot plate is slight as described above, gaseous heat conduction according to Fourier law of heat conduction from the hot plate to the substrate is predominant while the heat transfer through gaseous convection is negligible. As will be described below in the case of such heat conduction, the temperature difference between the substrate and the hot plate is in proportion to the float distance. Thus, the local variation of the float distance of the substrate causes the temperature variation of the substrate.
The variation of the float distance is primarily caused by substrate deformation. The deformation of semiconductor wafer increases through various processes, and the resulting shape is so complex that the shape cannot be estimated. Additionally, the deformation is unavoidably enlarged as the wafer size is increased. Therefore, it is suggested that the deformation should be corrected.
The process of putting the substrate in close contact to the hot plate as described in the aforementioned reference is one of processes of correcting the deformation of substrates, but particles deposited on the back face of the substrate and the surface of the hot plate inevitably influence the process so that the variation can hardly be suppressed routinely in a stable manner.
What has been described above is focused only on the heating system, but in a cooling system, a cooling plate is simply replaced with the hot plate, wherein the direction of heat conduction is adverse to the direction thereof in case of the hot plate. Therefore, the advantages and problems are the same as described above. Hereinbelow, heating and cooling are collectively referred to as “temperature control”, and also hot plate and cooling plate are collectively referred to as “temperature control plate”.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the problems of the prior art and provide a novel substrate temperature control system capable of unifying the temperature of the substrate and capable of shortening the temperature elevation time (temperature lowering time).
The problems of the present invention can be effectively solved by placing a temperature control plate (hot plate or cooling plate) with co-planar projections on the surface thereof as well as a substrate chuck mechanism fixing the substrate on the projections by pressing the substrate along the direction of the temperature control plate.
Through the projections arranged, heat conduction through the contact surface to the projections and heat conduction through non-contact surface in a gas phase are formed between the substrate and the temperature control plate, but the heat conduction through the projections is prominent because the heat conduction through the projections is high compared with the conduction in gas. Therefore, the substrate temperature can be unified by unifying the heat transfer at the contact surface on the whole surface of the substrate. Because the efficiency of heat transfer then can be distinctively increased compared with the conventional efficiency thereof through a gas phase, furthermore, the temperature elevation time (temperature lowering time) can be shortened. Because the float distance of the substrate is regulated and aligned through the co-planar projections, the deformation of the substrate is corrected so that the substrate turns flat.
Additionally, a proposition to fix substrates by means of projections has been known as disclosed in Japanese Patent Laid-open No. Sho 62-45378. The system of the publication is a simple spin-coater for the purpose of separating a substrate from the gap for vacuum on a turn table thereby suppressing the temperature variation on the substrate, which variation develops in case that the substrate is put in close contact to a turn table with such gap. No reference is made therein about substrate heating (cooling) by utilizing temperature transfer from a temperature control plate, so that the system cannot suppress the temperature variation on a substrate to be heated.
In accordance with the present invention, furthermore, the efficiency of heat transfer is elevated as the contact surface is larger, but particles deposited on the back face of a substrate and the surface of a hot plate influence the contact surface, with the resulting higher probability of temperature variation. Experimental results suggest that the upper limit of the ratio of the contact surface to the area of the whole back face is about 60%. Alternatively, the efficiency of heat transfer is decreased as the-area of the contact surface is decreased, which induces the increase of the temperature elevation time (temperature lo
Hirasawa Shigeki
Kaneko Yutaka
Kanetomo Masafumi
Kuroda Katsuhiro
Murai Fumio
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Paik Sang
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