Optics: measuring and testing – By polarized light examination – Of surface reflection
Reexamination Certificate
1998-08-10
2001-10-30
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
By polarized light examination
Of surface reflection
C356S600000
Reexamination Certificate
active
06310688
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for measuring the parameter of a rough film, and more particularly, to a method of monitoring the manufacturing process of rough film by using a measuring light with wavelength in a certain range and a spectroscopic ellipsometer (SEM) as the measuring instrument.
2. Description of the Prior Art
Currently, with the giant advancement in semiconductor technology, the integration density of the integrated circuits has been tremendously increased. Generally speaking, the enhancement in the integration density of the integrated circuits requires a corresponding improvement in their manufacturing process. For example, the capacitor in a dynamic random access memory (DRAM) has to provide a higher capacitance without reducing the integration density. However, the diminution of capacitance will result from the decrease of capacitor surface area when the device area gets smaller. Therefore, other ways of manufacturing DRAM are necessary to increase the capacitance efficiently but still meet the requirements of a smaller device area. This will result in a few obvious benefits, such as the efficient increase of DRAM refresh time and, power saving due to the lowering of memory consuming power. On the contrary, if the capacitance fails to be increased, the refresh time of memory can't be increased efficiently either, then data access will be degraded.
In general, a roughening technique, that is, increasing the capacitor surface-area is used to enhance the capacitance of a capacitor in the integrated circuits, which is the main technology to make stack DRAMs and is called hemispherical grain silicon (HSG). The cross-sectional view of the process diagram is shown in
FIG. 1
, in which amorphous silicon
10
in a device is fonned as a rough film
15
(hemispherical grain) after annealing according to the prior art. However, though the HSG technique can enhance capacitance effectively, monitoring the process is difficult and controlling roughness with good quality control of HSG stability in manufacturing process is almost impossible.
In another aspect, although the technique of selective HSG has dominated the methods of fonning stack DRAM, due to the special structure of hemi-spherical grain, there is a need to provide a cheap in-line control method when applying this technique. If in-line scanning electron microscopy (SEM) is used as the inspecting tool, the problems are high cost, limited throughput, and the biggest-good control of process stability. Because it is very subjective and hard to make a judgment whether the manufacturing process is good or bad under scanning electron microscopy, thus SPC control will be very difficult. Besides, general optical methods have the following restrictions:
1. Microscopic roughness and non-homogeneous make it inefficient to get the optical property of films by optical measurement.
2. Because HSG, that is, a rough film is fonned by crystal growth, the properties of amorphous silicon, such as the refractive coefficient, the extinction coefficient, and the thickness of bottom layer will directly disturb the correct measurement. So, all the disturbances have to be removed first to make the measurement indicative of the property of a rough film.
Therefore, a convenient and simple way to measure the parameter of a rough film is necessary to be developed that the influence from the bottom layer can be got rid of and moreover, the property of the rough film can be accurately measured.
SUMMARY OF THE INVENTION
A convenient method is therefore presented in this invention to improve the former problems and further, measure the parameter of a rough film. This method is particularly suitable for the technology used in enhancing capacitance of a capacitor by HSG, so that the property of a rough film and whether or not it is stable can be assessed efficiently for further treatment.
It is therefore the main object of this invention to provide an available method for measuring the parameter of a rough film that engineers can get a handy way to measure the parameter of a rough film, especially relating to the manufacturing process of a capacitor.
It is therefore another object of this invention to correctly measure the property of a rough film, in which the influence from the bottom layer has been eliminated, so that the property of the rough film can be detected accurately.
The method for measuring the parameter of a rough film has the following steps. At first, a chip with an uneven film is prepared, then a measuring light with wavelength in a certain range is chosen to detect the optical property for assessing how good or bad the manufacturing process is. An uneven film just mentioned is a rough film and the optical instrument used for measuring is a spectroscopic ellipsometer (SEM).
Preferably, the method for measuring the parameter of a rough film includes the following steps. At first, the value of a first standard is taken as a base, and the values of a second standard and a measured one are subsequently taken, then a controlled value is derived from one formula. The formula is stated as:
Measured value=[(1−controlled value) ×the first standard]+[controlled value×the second standard]
In a preferred manner, the method for measuring the parameter of a rough film is completed according to the following steps. Firstly, an object with an uneven film, that is, a rough film is prepared, in which both a concave-convex layer and a bottom layer are included. Afterwards, the concave-convex layer can be macroscopically treated as a smooth virtual layer, in (which the thickness of the virtual layer is exactly the height difference of the concave-convex layer. Therefore, the mentioned rough film can be viewed as a smooth compound film comprising the mentioned virtual layer and bottom layer. Then, a measuring light is selected with wavelength in a certain range and also with the characteristic of being not swayed by the bottom layer. At last, the measuring light with the optical instrument works together to detect the mentioned compound film. It is exactly because the measuring light chosen is free from the influence of the bottom layer, the current object ready to be detected can be taken just as the virtual layer. So the result can precisely represent the parameter of the virtual layer, also the concave-convex layer, and the goal of measuring the parameter of a rough film is thus obtained.
REFERENCES:
patent: 5796484 (1998-08-01), Honma et al.
patent: 5825498 (1998-10-01), Thakur et al.
patent: 5835225 (1998-11-01), Thakur
patent: 5850288 (1998-12-01), Honma et al.
patent: 6034778 (2000-03-01), Shin et al.
Chu Jason C. S.
Kao Ming-Kuan
Bacon & Thomas
Mosel Vitelic Inc.
Pham Hoa Q.
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