Patent Application
20060177949
1. Field of the Invention
The present invention relates to a method for monitoring oxide film deposition, and more particularly to a method for monitoring high temperature oxide (HTO) film deposition in a vertical HTO furnace.
2. Description of the Related Art
Present oxide film deposition processes performed in a vertical furnace have several native issues to be solved. For example, in the oxide deposition process used to form the silicon oxide layers of an oxide-nitride-oxide (ONO) stack layer of a semiconductor device, the electrical thickness of the ONO stack layers formed on wafers on different location of the vertical furnace would vary due to the characteristics of the vertical furnace. The variation of electrical thickness of the ONO stack layer results from the loading of wafer that causes the temperature at the bottom lower than the temperature at the top inside the vertical furnace. To solve this problem, a temperature gradient with high temperature at bottom decreasing toward the top inside the furnace is established in the vertical furnace. Furthermore, the wafer loading sequence between the depositions of the top oxide film and the bottom oxide film of an ONO stack layer is reversed to balance the variation of electrical thickness of the ONO stack layer.
Since the electrical thickness of the ONO stack layer for a semiconductor device such as a flash memory device is a crucial dimension, monitoring of the growth or deposition of the ONO stack layer is inevitable. In order to monitor the deposition of the ONO stack layer, monitor wafers are utilized to find or measure the growth rate of the top and bottom oxide films of the ONO stack layer. However, conventional monitoring ways have a troubling drawback. As shown in
In view of the drawbacks mentioned with the prior art, there is a continued need to develop new and improved method for monitoring oxide film deposition that overcomes the disadvantages associated with prior art. The requirements of this invention are that it solves the problems mentioned above.
It is therefore an object of the invention to provide a method for monitoring oxide film deposition to improve the process stability and enhance the yield performance.
It is another object of this invention to provide a method for monitoring oxide film deposition to simplify the production flow.
It is a further object of this invention to provide a method for monitoring oxide film deposition to obtain an actual electrical thickness of the oxide film on a process wafer.
It is a further object of this invention to provide a method for monitoring oxide film deposition to get a constant electrical thickness of the oxide film at different location inside a furnace.
To achieve these objects, and in accordance with the purpose of the invention, the invention provides a method for monitoring oxide film deposition. The method comprises the following steps. At least one silicon monitor wafer having a silicon nitride film thereon is provided. Then the silicon monitor wafer together with at least one silicon process wafer is loaded into a furnace to monitor the growth of an oxide film on the silicon process wafer.
In another embodiment of the invention, the method comprises the following steps. First of all, at least one first silicon monitor wafer having a first silicon nitride film thereon is provided. Then the silicon monitor wafer together with at least one silicon process wafer are loaded into a furnace to monitor the growth of a first oxide film on the silicon process wafer. Next the silicon process wafer and the silicon monitor wafer are removed from the furnace. Then second silicon nitride films are formed on the silicon process wafer. Finally, at least one second silicon monitor wafer together with the silicon process wafer are loaded into the furnace to monitor the growth of a second oxide film on the silicon process wafer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The present invention is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings.
Common reference numerals are used throughout the drawings and detailed description to indicate like elements.
It is to be understood and appreciated that the structures described below do not cover a complete structure. The present invention can be practiced in conjunction with various fabrication techniques that are used in the art, and only so much of the commonly elements are included herein as are necessary to provide an understanding of the present invention.
As shown in
In a process of non-volatile memory devices such as flash memory devices, monitor wafers are usually used to monitor the growth rate of oxide films of a silicon oxide-silicon nitride-silicon oxide/oxide-nitride-oxide (ONO) stack. The thickness variation of the native oxide films on the monitor wafer resulting from the loading process of the wafer boat and the nature characteristics of the furnace disturbs and misleads the measurement of the electrical thicknesses of the oxide films formed on process wafers. Since the thickness variation of the native oxide films results from those causes which are hard to avoid, a new way to monitor and control the growth rate of oxide films is provided. According to the characteristics of the silicon oxide/dioxide process, native oxide films are hardly formed on the surface of a nitride film at a temperature over 800° C., and wafers with nitride films instead of bare silicon wafers are used to control and monitor the growth of oxide films on process wafers in a furnace.
As shown in
When the silicon wafers having silicon nitride films thereon are used to monitor the growth/deposition of oxide films of a non-volatile memory device such as a flash memory device, the method for monitoring oxide film deposition comprises the following steps. First silicon monitor wafers having first silicon nitride films thereon are loaded together with silicon process wafers into a furnace to deposit first silicon oxide films on the first silicon monitor wafers and the silicon process wafers, and the thickness of the first oxide films are controlled substantially equally on the silicon monitor wafers and the silicon process wafers. After the first silicon oxide films are formed on the silicon process wafers and the silicon monitor wafers, the silicon process wafers and the first silicon monitor wafers are removed from the furnace. Then the thickness of the first oxide films is measured. Then second silicon nitride films are formed on the silicon process wafers. The second silicon nitride films can be formed by chemical vapor deposition processes. Next second silicon monitor wafers having third silicon nitride films thereon together with the silicon process wafers are loaded into the furnace to deposit second silicon oxide films on the silicon process wafers, and the thickness of the second oxide films are controlled substantially equally on the second silicon monitor wafers and the silicon process wafers. Then the thickness of the second silicon oxide films is measured. The first silicon oxide films, second silicon nitride films and the second silicon oxide films on the silicon process wafers are oxide-nitride-oxide stack of the non-volatile memory device such as a flash memory device.
The advantages of the invention includes the followings. First of all, in the process of non-volatile memory devices, the wafer loading sequence between the depositions of the top oxide film and the bottom oxide film of an ONO stack layer is not necessary to be reversed to balance the variation of electrical thickness of the ONO stack layer. The production arrangement involving oxide film deposition can be improved. Moreover, the thicknesses of silicon oxide/dioxide films on the process wafers are equal to the thicknesses of silicon oxide/dioxide films formed on the monitor wafers disregarding the loading process of wafer and the characteristics of a furnace.
Other embodiments of the invention will appear to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples to be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
