JPS6145771B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for evaluating the film quality of an insulating film, and particularly to a method for evaluating the film quality of a two-layer insulating film that applies the dynamic scattering phenomenon of liquid crystal.

The film quality of an insulating film on a semiconductor substrate has an extremely large effect on the manufacturing yield and reliability of semiconductor devices. For example, if an insulating film of poor quality with pinhole defects is used, it is impossible to manufacture a semiconductor device with high manufacturing yield and high reliability. Therefore, in the semiconductor industry, there is a need for a film formation technology that is free from pinhole defects, but in order to improve the film formation technology, it is necessary to evaluate the film quality in detail.

One of the methods for evaluating the film quality of insulating films is an evaluation method that applies the dynamic scattering phenomenon of nematic liquid crystals, and this has the advantage of being highly sensitive to pinhole defects that exist in insulating films, and allowing direct visualization of the defect locations. be.

Below is silicon dioxide on a silicon (Si) substrate.
A conventional method for evaluating the film quality of an insulating film using dynamic scattering of liquid crystals will be explained using a two-layer film of a (SiO ₂ ) film and a silicon nitride (Si ₃ N ₄ ) film as an example.

FIG. 1 is a cross-sectional view of a sample to be evaluated having a two-layer insulating film. The sample to be evaluated 100 is a Si substrate 1,
It is composed of a SiO ₂ film 2 and a Si ₃ N ₄ film 3 _.
Film 2 has SiO ₂ film pinhole defect 42, Si ₃ N ₄ film 3
It is assumed that a Si ₃ N ₄ film pinhole defect 43 is included in the Si 3 N 4 film.

In the method for evaluating the quality of insulating films using liquid crystals, a nematic liquid crystal film is formed on the insulating film, a transparent conductive film is placed in contact with the nematic liquid crystal film, and a transparent conductive film is placed between the semiconductor substrate such as a Si substrate and the transparent conductive film. While applying a DC voltage to the area, the dynamic scattering phenomenon that occurs in the liquid crystal film at locations such as pinhole defects is observed.

FIG. 2 is a sectional view and a power supply circuit diagram for explaining the conventional liquid crystal method.

In the figure, reference sample 200 without Si ₃ N ₄ film is shown.
A nematic liquid crystal film 5 is formed on the SiO ₂ film 2, and a transparent conductive film 6 is placed in contact with the nematic liquid crystal film 5. Since the transparent conductive film 6 is a thin film, it is formed on the surface of a glass plate 7 serving as a support.

A DC voltage V ₀ is applied between the transparent conductive film 6 and the Si substrate 1 by a DC power supply 8 . This DC voltage V ₀ is formed from the sum of the potential difference V ₁ of the nematic liquid crystal film 5 and the potential difference V ₂ of the SiO ₂ film 2.

Here, if V ₀ is the threshold voltage V _th that brings the _nematic liquid crystal film 5 into the dynamic scattering _mode , V Since ₂ = 0, V ₁ = V ₀
=V _th and a local dynamic scattering mode is generated as shown in FIG. Since this dynamic scattering mode generation region 9 is larger than the size of the SiO ₂ film pinhole defect 42, by observing the dynamic scattering mode generation region 9, the minute SiO ₂ film pinhole defect 4 can be detected.
2 can be detected, and its location can also be known.

However, conventionally, when applying a method for evaluating an insulating film using liquid crystal, the target insulating film is usually limited to a single type of monolayer film. this is,
If a liquid crystal evaluation method is applied to a two-layer film consisting of two types of insulating films, it can be evaluated as a two-layer film, but it is difficult to evaluate each type of insulating film from the evaluation results as a two-layer film. This was because it was difficult to judge. Improving film formation technology to improve film quality requires evaluation of each type of insulating film, but evaluating each type of single-layer film individually has the disadvantage of decreasing evaluation work efficiency. However, there is a risk of doubts as to whether the evaluation results for each single-layer film can be combined to form the evaluation results for a two-layer film. For example, on a Si substrate
In the case of evaluation of a two-layer insulating film in which a SiO ₂ film is formed and a Si ₃ N ₄ film is further formed on top of it, the pinhole defects detected by the conventional method are due to the fact that the pinhole defects present in the SiO ₂ film are
It is difficult to determine whether it exists in the Si ₃ N ₄ film. Furthermore, if the SiO ₂ film on the Si substrate and the Si ₃ N ₄ film on the Si substrate are evaluated individually, two types of evaluation samples are required, which deteriorates the efficiency of the evaluation work. Also, SiO ₂ on Si substrate
A simple arithmetic sum of the pinhole defect density obtained for the film sample and the pinhole defect density obtained for the Si ₃ N ₄ film sample on _the Si substrate,
It cannot be determined that this is the pinhole defect density of the two-layer Si ₃ N ₄ film. Since the formation of a Si ₃ N ₄ film usually involves heat treatment, new defects may occur in the SiO ₂ film underlying the Si ₃ N ₄ film, or defects may occur on the Si substrate.
This is because new defects may occur in the Si ₃ N ₄ film on the SiO ₂ film, which are different from defects in the Si ₃ N ₄ film.

The present invention has been made in view of the above points, and provides a film quality of an insulating film that makes it possible to evaluate the film quality of each insulating film forming a two-layer insulating film using dynamic scattering of liquid crystal. The purpose is to provide an evaluation method.

FIG. 3 is an auxiliary cross-sectional view and a power supply circuit diagram for explaining the film quality evaluation method according to the present invention.
In the figure, V ₀ is set as V ₀ >V _th +V ₂ . In this case, regardless of the presence or absence of the SiO ₂ film pinhole defect 42, the potential difference V ₁ of the nematic liquid crystal film 5 at all positions on the SiO ₂ film 2 is V ₁ >V _th , so the nematic liquid crystal film 5 is The entire liquid crystal film 5 is in dynamic scattering mode. Here, the entire nematic liquid crystal film 5 is in the dynamic scattering mode.
The value of V ₀ is set to V ₀₂ for the SiO ₂ film 2.

The state where the entire nematic liquid crystal film 5 is in the dynamic scattering mode as explained in _FIG .
It can also be created when replacing with a Si ₃ N ₄ film. In the case of this Si ₃ N ₄ film, the lowest value of V ₀ at which the entire nematic liquid crystal film 5 is in dynamic scattering mode is determined.
Set it as V ₀₃ . However, even in the case of this Si ₃ N ₄ film, the film thickness of the nematic liquid crystal film 5 is the same as that of the SiO ₂ film 2.
The film thickness is set to be the same as in the case of .

The magnitude relationship of V ₀₂ and V ₀₃ differs depending on the thickness of each film, but it is generally used in the semiconductor industry.
In the case of the SiO ₂ film 2 and the Si ₃ N ₄ film 3, V ₀₂ ≠V ₁₃ .

Here, V ₀₂ is set smaller than V ₀₃ .

FIG. 4 is a cross-sectional view and a power supply circuit diagram for explaining the film quality evaluation method of the present invention for a two-layer insulating film. The thickness of the liquid crystal film is set to be the same as the thickness of the liquid crystal film used in the case of FIG. The two-layer insulating film 23 includes a SiO ₂ film pinhole defect 42 and a Si ₃ N ₄ film pinhole defect 43, respectively. In the film quality evaluation method of the present invention, first, a DC voltage V ₀₂ is applied between the transparent conductive film 6 and the Si substrate 1. At this time, as shown in FIG. 4a, only the nematic liquid crystal film 5 at the Si ₃ N ₄ film pinhole defect 43 becomes a dynamic scattering mode generating region 9 because the Si ₃ N ₄ film is missing. Subsequently, a DC voltage V ₀₃ is applied between the transparent conductive film 6 and the Si substrate 1. At this time, as shown in FIG. 4b, not only the nematic liquid crystal film 5 at the Si ₃ N ₄ film pinhole defect 43 but also the nematic liquid crystal film 5 at the SiO ₂ film pinhole defect 42 are affected by SiO ₂ deficiency. Therefore, it becomes a dynamic scattering mode generation region 9. Therefore, the DC voltage applied between the transparent conductive film 6 and the Si substrate 1 is
By observing the dynamic scattering mode generation region 9 that appears as V ₀₂ or V ₀₃ and comparing the observation results, it is possible to detect the Si ₃ N ₄ film pinhole defect 43 or the SiO ₂ film pinhole defect 42, Moreover, the locations of these defects can also be known. It is extremely rare for the Si ₃ N ₄ film pinhole defect 43 and the SiO ₂ film pinhole defect 42 to coincide in location.

The above example shows a two-layer insulating film consisting of an SiO ₂ film and a Si ₃ N ₄ film.
It can also be applied to two-layer insulating films such as SiO ₂ films of various types, and also to alumina (Al ₂ O ₃ ) films as insulating films. Further, although a Si substrate has been exemplified as a semiconductor substrate, it is also applicable to semiconductor substrates such as gallium arsenide (GaAs) substrates, germanium (Ge) substrates, or conductive substrates such as gold (Au) and molybdenum (Mo). Although we did not specify the polarity of the applied DC voltage, in order to reliably detect pinhole defects where the insulating film is missing, it is extremely accurate to set the potential on the semiconductor substrate or conductive substrate and the potential on the transparent conductive film. This is a film quality evaluation method for insulating films that can detect pinhole defects.

As described above in detail, the method for evaluating the film quality of a two-layer insulating film of the present invention is a simple method that allows the film quality of each insulating film to be evaluated independently and also allows the location of defects to be known. For example, the above-mentioned V ₀₂ and V ₀₃ for each insulating film can be easily calculated if the specific electrical resistance, film thickness, and threshold voltage of each insulating film, nematic liquid crystal, and nematic liquid crystal are known. Therefore, it is suitable for evaluating the film quality of two-layer insulating films, which often have different types and thicknesses, such as insulating films in the semiconductor industry. Therefore, by using the film quality evaluation method of the present invention, it can be expected that film forming technology will be improved and that semiconductor devices with high manufacturing yield and high reliability will be manufactured.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of an example of a sample to be evaluated having a two-layer insulating film, Fig. 2 is a cross-sectional view and power supply circuit diagram for explaining the conventional liquid crystal method, and Fig. 3 is a film quality evaluation method according to the present invention. FIGS. 4a and 4b are auxiliary cross-sectional views and power supply circuit diagrams for explaining the film quality evaluation method according to the present invention. In the figure, 1 is a Si substrate (semiconductor substrate), 2 is a
SiO ₂ film (first insulating film), 23 is a double-layer insulating film, 3
is a Si ₃ N ₄ film (second insulating film), 42 is a pinhole defect in the SiO ₂ film, 43 is a pinhole defect in the Si ₃ N ₄ film, 5 is a nematic liquid crystal film, 6 is a transparent conductive film, and 7 is a glass plate. , 8 is a DC power supply, 9 is a dynamic scattering mode generation region, and 100 is a sample to be evaluated. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A nematic liquid crystal film is formed on the second insulating film of a two-layer insulating film in which a first insulating film and a second insulating film are sequentially formed on a semiconductor substrate or a conductive substrate. After bringing the transparent conductive film into contact with the transparent conductive film, the first of the first and second insulating films is
When only an insulating film exists, the nematic liquid crystal film becomes in a dynamic scattering mode over the entire surface.
or a second DC voltage at which the nematic liquid crystal film enters the dynamic scattering mode over the entire surface when only the second insulating film is present, is applied to the semiconductor substrate or the conductive substrate and the transparent conductive film. Observe the locations where the nematic liquid crystal film on the two-layer insulating film enters the dynamic scattering mode with respect to each of the first DC voltage and the second DC voltage applied during A method for evaluating the film quality of an insulating film, which is characterized by comparing.