JP2559512B2 - Metal film thickness measurement method - Google Patents

Description

The present invention relates to a method for measuring the thickness of a metal film, which is capable of non-destructive, non-contact and highly accurate measurement of the thickness of a metal film embedded in an opening. For the purpose of providing a film thickness measuring method, an insulating layer having an opening is formed on a base film, and the film thickness of a metal film embedded by selective growth on the base film in the opening is measured. In the method, a step of forming an insulating layer on a base film, a step of forming an opening and an opening pattern for measuring a sheet resistance of a metal film having an area larger than the opening in the insulating layer; Part of the metal film embedded in the opening pattern and the step of simultaneously embedding the metal film in the opening pattern, the sheet resistance of the metal film embedded in the opening pattern is measured, and the metal film embedded in the opening pattern is calculated based on the measured value. And the film thickness of The step of obtaining the film thickness of the metal film embedded in the opening according to the relationship with the film thickness of the metal film embedded in the opening.

[Industrial applications]

The present invention relates to a method for measuring a film thickness of a metal film, and more specifically, an insulating layer having an opening is formed on a wafer, and the wafer in the opening is filled with a selective CVD method such as tungsten (W). The present invention relates to a method for measuring the film thickness of a metal film.

In recent years, the aspect ratio of contact holes tends to increase with the miniaturization of semiconductor devices.Therefore, a so-called selective CVD method for growing a metal film such as tungsten in a contact hole with a large aspect ratio is used. Buried formation has become a very useful technique. In particular, the buried formation by the selective CVD method is a very excellent technique for flattening the surface of the metal wiring, and it is important to precisely control and monitor the film thickness of the tungsten buried in the contact hole. Is being watched. Therefore, there is a need for a method that simplifies the measurement of the film thickness of embedded tungsten.

[Conventional technology]

In the conventional method of burying a metal film such as tungsten in a contact hole by selective growth, as a method of measuring the thickness of the buried metal film, a cross-section SEM (scanning electron microscope) is used after the wafer is broken. Method to measure the film thickness of tungsten, or using an alpha step device, etc., a needle with a diameter of several hundred μm is brought into contact with the device pattern and scanned to obtain a relatively large pattern of several hundred μm or more such as a scribe line. A method of mechanically measuring a step difference with an insulating layer such as PSG having a contact hole has been used.

[Problems to be Solved by the Invention]

However, in the method of measuring the film thickness of the metal film embedded by the cross-section SEM, the wafer must be broken before measuring the film thickness of the metal film embedded by the cross-section SEM, and the product must be destroyed. Not only that, but there is also a problem that a lot of man-hours and time are required for measurement. Further, in the method of measuring with a stylus type step difference measuring device such as an alpha step device, since the film thickness of the embedded metal film is measured by bringing the needle into contact with the wafer, mechanical contact However, there are some measurement errors. Specifically, there is a measurement error of 6 to 7% in the measurement of the film thickness of the metal film embedded by the alpha step device with respect to the film thickness of the actually embedded metal film, and accurate measurement can be performed. There was a problem that it was difficult.

Therefore, the present invention is capable of accurately and easily measuring the thickness of a metal film embedded in an opening by a method that does not contact the device pattern and does not damage the wafer. It is intended to provide a way.

[Means for solving the problem]

In order to achieve the above object, the method for measuring the film thickness of a metal film according to the present invention has an insulating layer having an opening formed on a base film and a metal film embedded in the opening by selective growth on the base film. In the method of measuring the film thickness of, the step of forming an insulating layer on the underlying film, and forming an opening in the insulating layer and an opening pattern for measuring the sheet resistance of a metal film having an area larger than the opening And the step of simultaneously embedding a metal film in the opening and the opening pattern, and measuring the sheet resistance of the metal film embedded in the opening pattern, and the opening obtained in advance based on the measured value. The step of obtaining the film thickness of the metal film embedded in the opening from the relationship between the film thickness of the metal film embedded in the pattern and the film thickness of the metal film embedded in the opening.

[Action]

In the present invention, an opening pattern for sheet resistance measurement of a metal film having an area larger than the opening of the insulating layer is formed in the insulating layer formed on the underlying film, and the metal film embedded in the pattern by selective growth. The film thickness of the metal film embedded in the opening is obtained based on the sheet resistance value of. This principle will be described.

When the specific resistance when the metal film is selectively grown in the opening under a certain constant condition is set to ρ and the sheet resistance of the sheet resistance measurement pad pattern is set to ρs, the film thickness t of the metal film in the pattern is set. But Is represented by The formula (1) is multiplied by the change in the specific resistance, the film formation rate, etc., which is caused by the difference in the surface area of the opening and the pad obtained empirically, and is multiplied by the equation (1) to obtain the film thickness of the metal film in the opening. T is If a curve for correcting the film thickness T and the sheet resistance ρs is empirically obtained, the metal embedded in the opening is calculated from the sheet resistance of the metal film embedded in the pad pattern for measuring the sheet resistance. The film thickness T of the film can be easily obtained.

Then, as described above, by using the sheet resistance value of the opening pattern and the relationship between the film thickness of the metal film in the opening and the film thickness of the metal film in the opening pattern, which is obtained in advance by experiments, the metal in the opening pattern is used. By obtaining the film thickness T of the film, it is possible to accurately obtain the film thickness T in the opening that is actually desired.

That is, in the selective growth method for forming a metal film in the opening, the metal film formed in the opening is controlled by the growth conditions such as the size (area) of the opening and the growth rate (supply amount of growth gas). The film thickness is different. Therefore, when the sheet resistance of the metal film in the opening pattern for sheet resistance measurement is simply measured and the film thickness of the metal film in the opening is obtained from the sheet resistance value (the sheet resistance value itself is If the film thickness is set to 1), the film thickness in the opening cannot be accurately obtained.

In the present invention, paying attention to the phenomenon peculiar to selective growth, the correlation of the film thickness in the opening is obtained in advance, and the film thickness in the opening is obtained based on the correlation to obtain the film thickness in the opening actually desired. It is possible to accurately obtain T.

〔Example〕

 Hereinafter, the present invention will be described with reference to the drawings.

1 and 2 are diagrams showing an embodiment of the method for measuring the film thickness of a metal film according to the present invention, and FIG. 1 is a configuration diagram of a semiconductor device to which the film thickness measuring method of the embodiment is applied. FIG. 2 is a graph showing the correlation between the sheet resistance of the metal film embedded in the sheet resistance measurement pad pattern and the film thickness of the metal film embedded in the opening (Via), and the solid line is empirically determined. It is the calibration curve obtained.

First, the configuration will be described. In FIG. 1, 1 is a Si wafer having a diameter of 4 inches which is a base film, and a PSG film 2 as an insulating film is grown on the wafer 1. A plurality of contact patterns 4 are stacked on the PSG film 2 via scribe lines 3, and a plurality of contact holes as openings (not shown) are formed in the contact pattern 4, and the inside of the holes is a Si wafer. 1 is exposed as a base film. Further, nine sheet resistance measurement pad patterns (opening patterns) 5 are formed on the PSG film 2 by four-probe, and the pattern 5 has an area of about 10 mm × 6 mm. Si
The wafer 1 is exposed as a base film.

In this embodiment, a metal film of tungsten or the like is embedded in the contact pattern 4 on the Si wafer 1 by the selective CVD method, and at the same time, a metal film of tungsten or the like is also grown and embedded in the pad pattern 5 for sheet resistance measurement. The sheet resistance on the pad pattern 5 was measured for each of the Si wafers 1, and the film thickness of tungsten in the contact hole was measured by a cross-sectional SEM photograph. In addition,
The sheet resistance on the contact pattern 4 is measured by the well-known 4-probe method. Specifically, a current is passed from a predetermined input terminal provided on the contact pattern 4 to measure a voltage output from a predetermined output terminal provided on the contact pattern 4, and a resistance between both terminals is measured. Measure the sheet resistance of tungsten by. Then, the actual measured film thickness of tungsten in the contact hole and the pad pattern 5 for sheet resistance measurement
FIG. 2 shows the correlation between the measured values of the sheet resistance of the upper tungsten. As a result, assuming that the real curve of the graph of FIG. 2 is a calibration curve for the sheet resistance value of the film thickness of tungsten in the contact hole, the film thickness of tungsten in the contact hole obtained by this curve,
It was confirmed that the error with the film thickness of tungsten measured by the cross-section SEM photograph was about ± 3% in the vicinity of the film thickness of 300 nm and ± 4% in the vicinity of 500 nm, and the measurement error by the conventional alpha step device was 6 to 6%. Since it is 7%, the film thickness can be obtained with extremely high accuracy. Therefore, in this embodiment, the film thickness of tungsten in the contact hole can be accurately and easily obtained without contacting the device pattern and without damaging the Si wafer 1. In particular, since the film thickness of tungsten in the contact hole is obtained from the sheet resistance value of tungsten on the pad pattern 5, it is possible to accurately obtain the film thickness of tungsten in the contact hole that is actually desired.

That is, in the selective growth method of forming a metal film in the contact hole, the metal film formed in the contact hole is changed depending on the growth conditions such as the size (area) of the contact hole and the growth rate (supply amount of growth gas). The film thickness is different. Therefore, when the sheet resistance of tungsten in the pad pattern 5 for sheet resistance measurement is simply measured and the film thickness of the metal film in the contact hole is obtained from the sheet resistance value (the sheet resistance value itself is If the film thickness of tungsten is used), the film thickness in the contact hole cannot be accurately obtained.

In this embodiment, focusing on the phenomenon peculiar to selective growth, the correlation between the contact hole and the tungsten in the pad pattern 5 is calculated in advance, and the film thickness in the contact hole is calculated based on the correlation, so that it is actually calculated. It is possible to accurately obtain the film thickness of tungsten in the desired contact hole.

In this embodiment, nine sheet resistance measurement pad patterns 5 are provided, but the present invention is not limited to this, and when the film thickness distribution in the contact hole is good when tungsten is filled by the selective CVD method, the sheet resistance measurement is performed. The number of pad patterns 5 for use may be reduced. This has the effect that the occupancy of the sheet resistance measuring pad pattern 5 to the contact pattern 4 can be reduced and more chips can be commercialized.

〔The invention's effect〕

According to the present invention, the sheet resistance of the opening pattern and the relationship between the film thickness of the metal film in the opening and the film thickness of the metal film in the opening pattern, which are obtained in advance by experiments, are used to determine the metal in the opening pattern. Since the film thickness is obtained, the film pressure of the metal film embedded in the opening can be measured without contacting the device and the wafer is not destroyed, and the size (area) of the opening can be measured. Even if the film thickness of the metal film formed in the openings and the opening pattern varies depending on the growth conditions such as the growth rate (growth gas supply amount), the film thickness of the metal film embedded in the openings actually desired is determined. It can be measured accurately and easily.

[Brief description of drawings]

FIGS. 1 and 2 are views showing an embodiment of a semiconductor device to which the method for measuring the film thickness of a metal film according to the present invention is applied. FIG. 1 is its configuration diagram and FIG. 2 is embedded in a pad pattern. 7 is a graph showing the correlation between the sheet resistance of the metal film and the film thickness of the metal film embedded in the opening (Via). 1 ... Si wafer (base film), 2 ... PSG film (insulating layer), 5 ... Sheet resistance measurement pad pattern (opening pattern).

Claims (1)

(57) [Claims] 1. A method for measuring a film thickness of a metal film in which an insulating layer having an opening is formed on a base film, and the metal film embedded by selective growth on the base film in the opening is measured. Forming an insulating layer on the insulating layer, forming an opening in the insulating layer and an opening pattern for measuring sheet resistance of a metal film having an area larger than the opening, and forming a metal in the opening and the opening pattern. The step of simultaneously filling the film, the sheet resistance of the metal film embedded in the opening pattern is measured, and the film thickness of the metal film to be embedded in the opening pattern and the opening portion are calculated in advance based on the measured value. And a step of obtaining the film thickness of the metal film embedded in the opening according to the relationship with the film thickness of the metal film embedded in the opening.