Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
2001-08-22
2002-12-17
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
C219S494000, C219S501000, C219S510000, C392S416000, C118S724000, C118S725000
Reexamination Certificate
active
06495805
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of determining a set temperature trajectory for a heat treatment system for conducting a heat-treating process, such as a film deposition process, to an object to be processed. More particularly, the present invention relates to a method of determining a set temperature trajectory for a heat treatment system to enable the heat treatment system to form a film accurately.
2. Description of the Related Art
A heat treatment step for heat-treating a wafer to form a specific film thereon is one of essential processes for fabricating a semiconductor device or the like. The heat treatment step is carried out by a heat treatment system in a high-temperature environment of a comparatively high temperature in the range of about 750 to 900° C. Chemical vapor deposition processes (CVD processes) and oxidation/diffusion processes are such heat treatment processes.
Generally, the heat treatment system is provided with a wafer holding device (called a wafer boat) for holding a plurality of wafers in a vertically layered (tier-like) arrangement, a tubular reaction tube for containing the wafer holding device therein, a plurality of heaters formed so as to surround the side wall of the reaction tube and arranged at axial intervals, a gas supply line for carrying reactant gases to the reaction tube, and an exhaust line through which gases are discharged from the reaction tube.
Power is supplied at a predetermined rate to the heaters to maintain the wafers at a temperature suitable for film formation. It is practically impossible to measure the temperatures of the wafers during a film forming process. Therefore, usually, the measured temperature of a part other than the wafers is used for controlling the process temperature.
The control of the respective outputs of the heaters is essential to accurately achieving a heat treatment process, such as a process for depositing a film on wafers. A film deposition process will be described as an example of such a heat treatment process.
The thickness and quality of a film deposited on a wafer deviate from set values when the temperature of the wafer differs even slightly from a set wafer temperature. For example, in a certain film deposition process, a temperature difference of 1° C. of the temperature of a wafer from a set wafer temperature causes a thickness difference of 0.1 nm of the thickness of a film from a set thickness. If the thickness of a film is in the range of several nanometers to several tens nanometers, the temperature of the wafer must be controlled in an accuracy of several degrees centigrade when the set temperature of the wafer is several hundreds degrees centigrade.
The distribution of the concentration of the reactant gas in the reaction tube is not uniform when the reactant gas flows in a constant flow from the gas supply side toward the gas discharge side of the reaction tube. If the temperatures of different zones in the reaction tube are controlled in the same way while the distribution of the concentration of the reactant gas in the reaction tube is not uniform, films respectively having different thicknesses are deposited on different wafers, respectively. Therefore, different set temperatures are set for the plurality of heaters arranged in the direction of arrangement of the plurality of wafers, respectively, and the respective temperatures of the plurality of heaters are controlled individually.
Optimum set temperatures must be determined for zones in the reaction tube respectively corresponding to the plurality of heaters through the repetition of correction of forming a film of a thickness in an allowable thickness range, in order to deposit films having accurate and uniform thicknesses on the wafers in the reaction tube.
An optimum set temperature can be determined by, for example, a method including the steps of placing a plurality of test wafers in the reaction tube, depositing films on the wafers at a set temperature, measuring the thicknesses of the deposited films by means of a measurement instrument, adjusting a set temperature condition in the reaction tube corresponding to the outputs of the plurality of heaters on the basis of the differences of the measured thicknesses from a desired thickness, and depositing films on test wafers under the adjusted set temperature condition. These steps are repeated until the differences of the measured thicknesses of the films from the desired thickness are reduced below a predetermined level. The set temperature condition thus determined is used as a set temperature condition in the reaction tube corresponding to the outputs of the plurality of heaters.
In some cases, films of different types are deposited in layers by film deposition processes when fabricating a semiconductor device. In such a case, optimum set temperature condition in the reaction tube corresponding to the outputs of the plurality of heaters is determined for each of the film deposition processes.
Suppose, for example, that a first film is deposited on a wafer and then a second film is deposited on the first film. An optimum set temperature condition in the reaction tube corresponding to the outputs of the plurality of heaters is determined by the aforesaid method for a first film deposition process for forming the first film. Then, an optimum set temperature condition in the reaction tube corresponding to the outputs of the plurality of heaters for a second film deposition process for forming the second film is determined by the aforesaid method using the wafers on which the first films are deposited under the optimum temperature condition as determined above. Thus, the optimum set temperature conditions are determined individually for the films to be deposited on the wafers.
However, in some cases, the semiconductor device fabricating process needs to continuously form the first film and the second film. When forming the first film and the second film continuously, the first film is deposited on wafers loaded to a heat treatment system, and then the second film is deposited on the first film without unloading the wafers from the heat treatment system after the first film has been deposited.
When the first film and the second film are thus formed continuously, only data on the result of film deposition on the wafer on which both the first and the second film are formed can be measured by a measuring instrument, and hence the foregoing method that determines optimum set temperature conditions individually for the first and the second film cannot be used.
There are two different cases of measuring data on the result of the deposition of the first and the second film. In a first case, such as a case where both the first and the second film are nitride films, the respective thicknesses of the first film and the second film cannot be individually measured and only the sum of the respective thicknesses of the first and the second film can be measured. In a second case, such as a case where the first film is an oxide film and the second film is a nitride film, the respective thicknesses of the first and the second film can be individually measured.
In the first case, an optimum set temperature condition can be determined for the film deposition process for depositing either the first or the second film. In this case, the sum of the respective thicknesses of the first and the second film can be managed, but the respective thicknesses of the first and the second film cannot be individually managed. In addition, optimum set temperature conditions may be determined for the film deposition processes respectively for depositing the first and the second film by properly dividing data on the result of film deposition. However, practically, it is unknown whether the division (assignment) is proper. Consequently, such a film thickness management is unable to achieve the film thickness management for the individual films.
In the second case, the optimum set temperature conditions for the film forming processes for forming the f
Sakamoto Koichi
Suzuki Fujio
Suzuki Keisuke
Wang Wenling
Yasuhara Moyuru
Fuqua Shawntina T
Smith , Gambrell & Russell, LLP
Tokyo Electron Limited
Walberg Teresa
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