Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
1998-07-13
2001-05-01
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C392S416000, C118S724000, C118S725000
Reexamination Certificate
active
06225601
ABSTRACT:
BACKGROUND
The present invention relates generally to substrate handling and processing chambers, and, in particular, to heating a substrate support in such chambers.
Glass substrates are being used for applications such as active matrix television and computer displays, among others. Each glass substrate can form multiple display monitors each of which contains more than a million thin film transistors.
The glass substrates can have dimensions, for example, of 550 mm by 650 mm. The trend, however, is toward even larger substrate sizes, such as 650 mm by 830 mm and larger, to allow more displays to be formed on the substrate or to allow larger displays to be produced. The larger sizes place even greater demands on the capabilities of the processing systems.
The processing of large glass substrates often involves the performance of multiple sequential steps, including, for example, the performance of chemical vapor deposition (CVD) processes, physical vapor deposition (PVD) processes, or etch processes. Systems for processing glass substrates can include one or more process chambers for performing those processes.
Plasma-enhanced chemical vapor deposition (PECVD) is another process widely used in the processing of glass substrates for depositing layers of electronic materials on the substrates. In a PECVD process, a substrate is placed in a vacuum deposition chamber equipped with a pair of parallel plate electrodes. The substrate generally is mounted on a susceptor which also serves as the lower electrode. A flow of a reactant gas is provided in the deposition chamber through a gas inlet manifold which also serves as the upper electrode. A radio frequency (RF) voltage is applied between the two electrodes which generates an RF power sufficient to cause a plasma to be formed in the reactant gas. The plasma causes the reactant gas to decompose and deposit a layer of the desired material on the surface of the substrate body. Additional layers of other electronic materials can be deposited on the first layer by flowing another reactant gas into the chamber. Each reactant gas is subjected to a plasma which results in the deposition of a layer of the desired material.
Some problems associated with the processing of large glass substrates arise due to their unique thermal properties. For example, the relatively low thermal conductivity of glass makes it more difficult to heat or cool the substrate uniformly. In particular, thermal losses near the edges of any large-area, thin substrate tend to be greater than near the center of the substrate, resulting in a non-uniform temperature gradient across the substrate. The thermal properties of the glass substrate combined with its size, therefore, makes it more difficult to obtain uniform characteristics for the electronic components formed on different portions of the surface of a processed substrate. Moreover, heating or cooling the substrates quickly and uniformly is more difficult as a consequence of its poor thermal conductivity, thereby posing special challenges to achieving a high throughput.
To help obtain a more uniform temperature across large substrates, susceptors having multiple heating elements have been used. For example, some susceptors include inner and outer heating elements. The use of multiple heating elements, however, occasionally results in the susceptor becoming deformed as it is heated. One cause of the deformation is a temperature differential that can occur between the inner and outer heating elements. If the temperature differential, or gap, becomes too large, the thermal stresses in the susceptor can result in deformation of the susceptor and, in some instances, even breakage.
SUMMARY
In general, in one aspect, a method of heating a substrate support includes establishing respective final temperature setpoints for first and second heating elements of the substrate support. The difference in temperatures of the first and second heating elements is caused to be less than a predetermined value &Dgr;T, if the difference initially exceeds the predetermined value. The temperatures of the heating elements then are raised to their respective final temperature setpoints T
F1
, T
F2
based on a predetermined heating rate R. Furthermore, the temperatures of the first and second heating elements are controlled so that the difference between the temperatures of the first and second heating elements does not exceed the predetermined value &Dgr;T while the temperatures of the heating elements are raised to their respective final temperature setpoints.
In general, the final temperature setpoints of the heating elements need not be the same. Controlling the temperatures of the heating elements can include setting a first interim temperature setpoint for the first heating element and setting a second interim temperature setpoint for the second heating element. The second interim setpoint depends on the current value of the first interim setpoint and the predetermined value &Dgr;T. The temperatures of the first and second heating elements then are raised toward their respective interim temperature setpoints for a predetermined delay period. At the end of the delay period, new interim setpoints can be established and the process repeated until the temperature of at least one of the first and second heating elements is within a predetermined amount of its respective final setpoint.
In some implementations, the second interim value used for the second heating element is set equal to the current value of the first interim setpoint plus the predetermined value &Dgr;T. The value of the first interim setpoint can depend on the current temperature of the first heating element and the predetermined heating rate R. For example, the first interim setpoint can be set equal to the sum of the current temperature of the first heating element and the value of the predetermined heating rate R.
In another aspect, a substrate handling apparatus includes a substrate processing chamber and a substrate support disposed in the chamber. The substrate support includes first and second heating elements for heating the substrate support and a controller for controlling the temperature of the heating elements according to the foregoing techniques.
In some implementations, the first and second heating elements are inner and outer heating elements embedded within the substrate, respectively. In addition, the heating elements can have different heating capacities. For example, according to one implementation, the second heating element has a heating capacity greater than the heating capacity of the first heating element.
The techniques described herein are not limited to a substrate support having only two heating elements. Rather, the techniques are applicable to the heating of substrate supports with more than two heating elements or more than two heating zones.
In addition, in various implementations, one or more of the final temperature setpoints for the heating elements, the predetermined heating rate R, and the predetermined value &Dgr;T can be selected by the user, thereby providing a flexible technique which easily can be modified for different systems or configurations.
Various implementations include one or more of the following advantages. The rate at which the interim temperature setpoints for each of the heating elements is increased is designed to be as high as the predetermined heating rate R, within the limitations, for example, of the capabilities of the heating elements. Each time the heating elements approach the current interim setpoints, the interim setpoints can be increased, thereby maintaining a relatively high duty cycle. Maintaining a limited temperature gap between the heating elements and increasing the interim temperature setpoints toward the final setpoints causes heat transfer from the heating element with the greater heating capacity to the heating element with the lower heating capacity. The heating element with the greater heating capacity, therefore, works at a duty cycle that is higher than the duty cycle it would have used s
Beer Emanuel
Kollrack Marc M.
Shen Duoyan
Zohar Eitan
Applied Komatsu Technology Inc.
Fish & Richardson
Fuqua Shawntina
Stern Robert J.
Walberg Teresa
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