Coating processes – Measuring – testing – or indicating – Thickness or uniformity of thickness determined
Reissue Patent
2000-09-28
2002-02-12
Bueker, Richard (Department: 1763)
Coating processes
Measuring, testing, or indicating
Thickness or uniformity of thickness determined
C427S248100, C118S666000, C118S708000, C118S712000, C118S715000, C118S725000, C118S730000, C374S131000, C374S141000
Reissue Patent
active
RE037546
ABSTRACT:
BACKGROUND AND TECHNICAL FIELD OF THE INVENTION
The present invention relates to a processing reactor and, more particularly to a processing reactor for the thermal processing and chemical deposition of thin film applications on a substrate, such as semiconductor wafer, in which the temperature of the substrate can be accurately monitored and the injection of gas into the chamber can be controlled to provide better control of the substrate processing.
In semiconductor fabrication, semiconductor substrates are heated during various temperature activated processes for example, during film deposition, oxide growth, etching, and thermal annealing. The control of deposition and annealing processes depends on the control of the gas flow and pressure and the wafer temperature. When heating a substrate, it is desirable to heat the substrate in a uniform manner so that all the regions of the substrate are heated to the same temperature. Uniform temperatures in the substrate provide uniform process variables on the substrate; for instance in film deposition, if the temperature in one region of the substrate varies from another region, the thickness of the deposition in these regions may not be equal. Moreover, the adhesion of the deposition to the substrate may vary as well. Furthermore, if the temperature in one region of the substrate is higher or lower than the temperature in another region of the substrate, a temperature gradient within the substrate material is formed. This temperature gradient produces thermal moments in the substrates which in turn induce radial local thermal stresses in the substrate. These local thermal stresses can reduce the substrate's strength and, furthermore, damage the substrate. Therefore, knowing the temperature of the wafer is important in determining the thermal diffusion depths of surface implanted dopants, the deposited film thickness, and the material constitution quality and annealed or reflowed characteristics.
Various methods have been developed for measuring the temperature of a substrate during processing in order to improve the control of the various processes. Direct methods, which include the use of contact probes, such as thermocouples or resistance wire thermometers, are generally not suitable for substrate processing because direct contact between the probes and the substrate contaminates the device structure. More typically, indirect measuring methods are used, such as the use of preheated platforms that are calibrated prior to processing. However, this method is not typically accurate. In some applications, the temperature of the back side of the substrate is calibrated or monitored, but such methods also lead to significant errors due to the large variances between the back side and device side surface characteristics that lead to different substrate temperatures. The patterns of the specific devices being processed, the type of material being deposited or annealed, the degree of the roughness of the surface, and the operating temperature all affect the characteristics of the substrate surface and define what is known as the surface emissivity of the substrate.
In U.S. Pat. No. 5,310,260 to Schietinger et al. a non-contact temperature measuring device is disclosed. The device includes two sapphire optical fibre probes, with one of the probes directed to the lamp source providing the heat to the wafer and the other probe directed to the wafer itself. Each fiber probe sends its respective signal to a measuring instrument which converts the photon density measured by the probe to an electrical current. The ratio of the two signals provides a measure of the surface reflectivity, which approximates the total hemispherical reflectivity. However, this method can only be used with an AC source lamp and when the lamp shines directly on the wafer. Since two optical fiber probes must be used in order to implement this technique, the characteristics of each probe must be accurately detailed in order to obtain accurate emissivity measurements. In the event that one of the probes must be replaced, a total system re-calibration is required. Furthermore, this method cannot be used in chambers in which thin films are deposited, etched, or sputtered since the thin films will also deposit on the optical fiber photon density sensors and drastically alter the results and render the measurement method inoperative. Moreover, the optical fiber sensors are always directed at one fixed area of the wafer. Since different parts of the wafer may have different device patterns and, therefore, may have different local emissivities, the temperature measurement and control would be limited in value as it would represent the emissivity information only for that specific area rather than the average surface topology of the substrate.
In addition to temperature uniformity, the uniformity of film deposition is affected by uniformity of the delivery of the process gas. Good process uniformity usually requires adjustments and optimizations for both the wafer temperature uniformity and the gas flow pattern of the process gas. In most conventional chambers or reactors, the reactant gas is delivered through a single port, which injects gas into the chamber above the wafer. Due to the geometry of the wafer, the resulting deposition of the gas onto the wafer is not uniform.
More recently, shower-like gas injection systems have been developed in which separate gases are injected in a shower-like pattern over the entire substrate area. However, such gas delivery systems fill the entire chamber volume and, thus, deposit films on the substrate as well as the chamber walls. Consequently, these gas delivery systems preclude the use of any optical instruments for non-contact temperature measurement and in-situ film methodology.
Consequently, there is a need for a processing reactor which can deliver heat to a substrate in a uniform manner and can accurately monitor the temperature of the substrate during processing and adjust the profile of the applied heat as needed to achieve optimal processing of the substrate. Furthermore, there is a need for a processing reactor which can deliver and direct the flow of gas to the substrate during processing so that the substrate receives a uniform deposition of thin film of the process gas or gases in a discrete area on the substrate.
SUMMARY OF THE INVENTION
One form of the invention provides a reactor having a processing chamber with an emissivity measuring device and improved gas injection system. The emissivity measuring device measures the photon density from a light source, which is housed in the processing chamber, and the reflected photon density off a substrate, which is processed in the processing chamber. These measurements are then used to determine the emissivity and, ultimately, the temperature of the substrate with a high degree of accuracy. The emissivity measuring device includes a communications cable which includes a photon or emissivity sensor that is positioned in the processing chamber. The photon density sensor is adapted to move between a first position wherein the photon density sensor is directed to the light source for measuring the incident photon density of the light and a second position wherein the photon density sensor is directed toward the substrate for measuring the reflected photon density off the substrate. The gas injection system is adapted to inject and direct at least one gas onto a discrete area of the substrate. The reactor is, therefore, particularly suitable for use in a semiconductor fabrication environment where the control of heating and injection of gas must be maintained in order to produce uniform process variables during the fabrication of semiconductor devices.
In one aspect, the emissivity measuring device comprises first and second communication cables. The first communication cable includes the photon density sensor and is in communication with the second cable for sending signals from the photon density sensor to a processor. Preferably, the first and second communication cables comp
Bueker Richard
Micro C Technologies, Inc.
Van Dyke Gardner, Linn & Burkhart, LLP
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