JP2889448B2 - Method and apparatus for measuring grain size of polycrystalline film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for measuring the grain size of a polycrystalline film in an LSI manufacturing process.

[0002]

2. Description of the Related Art Al multilayer wiring of LSI has a problem of disconnection or short circuit failure due to electromigration or stress migration. Electromigration is a phenomenon that when the current density is high, the probability of collision between electrons and atoms at lattice points increases, atoms move in the same direction as electrons travel, and hillocks and voids are generated. Is generated. It is said that the electromigration of the AL wiring is mainly caused by grain boundary diffusion.

Conventionally, in-line management of Al film quality has been mainly performed.
It has been performed by controlling the reflectance of Al. ("VLSI thin film technology" Takashi Ito et al. Maruzen). However, the quantitative relationship between the reflectance of Al and the electromigration resistance is unknown. On the other hand, the electromigration resistance of Al can be evaluated by conducting a direct electromigration evaluation test or examining the grain size distribution and orientation.
It is known that it can be evaluated. (S. Vaidy
a et al ThinSolid Films 7
5 (1981) p253-259) The distribution of “time to failure” (TTF) due to Al electromigration can be predicted very well from the statistical distribution of grain size. However, although various methods for measuring the grain size distribution of the grains of the Al crystal film have been proposed, the work of obtaining the grain size distribution from the obtained grain size is cumbersome, and attempts to automate this work with an image analyzer have not been made. Not being successful, William Baerget
et. al: SolidState Techn
This is reported in "Mayology, Japan Version May, 1991, p. As described above, conventionally, it has been difficult to control the electromigration of Al in-line from the grain size distribution of the crystal film. A conventional example of particle size measurement by an image analyzer is to take an image of a grain, binarize the image, obtain the diameter of a circle having the same area as the area enclosed by the boundary of the grain, and calculate the value of this diameter. This is a means of setting the grain size.

[0004]

As described above, conventionally,
Determining the grain size distribution of Al grains is troublesome, cumbersome, and unsuitable for inline management. Also, when analyzing the particle size distribution by image processing, if small grooves or dirt is present on the Al grains, or if the boundaries of the grains are unclear, the binarization of the captured image will be one in the former. There is a problem that it is frequently considered that two grains are regarded as two, and in the latter, two grains are regarded as one. For this reason, the conventional state cannot correctly evaluate the grain size distribution of the grains.

The present invention has been made in view of such a conventional situation,
Developed a technology to easily determine the grain size distribution of Al grains and a technology to correctly evaluate the boundaries of the target grains in this case. Based on this technology, it is possible to investigate the electromigration resistance of Al wiring in-line. The purpose is to. That is, an object of the present invention is to overcome the difficulty of in-line management of the electromigration resistance of Al wiring and to establish an in-line management technique of Al film quality in an LSI manufacturing process.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention captures an image of a grain of a polycrystalline film,
The image is binarized and displayed, a plurality of straight lines crossing the image are added to the image, and intersections between these straight lines and the boundaries of the grains are fixed by visual correction, and the intersections between the intersections on the straight lines are determined. This is a method for measuring the grain size of a polycrystalline film, wherein a distance is determined, and this distance is regarded as a grain size of the grain, and a median diameter and a shape factor are calculated.

The method of the present invention will be described with reference to the flowchart shown in FIG. (1) An image of the Al crystal film is collected using a microscope, and is binarized. (2) The binarized image and the original image are superimposed and displayed on the display. (3) A rectangular border is provided on this image, and its diagonal line is drawn. (4) A mark is made at the intersection between the diagonal line and the crystal boundary line of the binarized image. The above process is an automation process. (5) The following steps (6) and (7) are performed manually. (6) The intersection of the diagonal line and the crystal boundary line of the binarized image is visually determined, and a mark is added or deleted. That is, a portion where the boundary line is thin and the mark is missing is marked, and an erroneous mark which is not in the crystal grain boundary due to a groove, shadow, or the like is deleted. This determination can be easily and reliably made with high accuracy by visual observation. (7) When addition and deletion of the intersection are completed, the magnification of the image is input. (8) Return to the automatic operation again, and the computer calculates each distance between the intersections of the diagonal lines. (9) The calculated distance is regarded as the particle diameter, and the grain size is calculated. That is, the median value s of the particle diameter, the standard deviation σ in the lognormal distribution, and the shape coefficient μ _e are calculated. (10) Output the calculation result to an output device such as a display or a printer.

An apparatus of the present invention for suitably implementing the above method is an apparatus for measuring the grain size of a polycrystalline film by combining the following technical means. That is, an image input device for taking an image of a crystal film, a binarizing means for binarizing the image, a display device for displaying the binarized image, and a straight line writing means for drawing a straight line in the display image An image correction device that visually corrects a display image, a calculation unit that collects distance data between intersections on a straight line from the image and performs a parameterization calculation of the data, and an output device that outputs the parameter. It is characterized by having.

[0009]

According to the present invention, first, as the grain size of the Al crystal film, the diameter of the circle corresponding to the area of the grain is not used, and the distance between the intersections of a plurality of straight lines crossing the entire image and the boundary of the grain is used as the grain size. I do. This allows
Grain size measurement becomes very simple. Moreover, the value of the grain size distribution obtained by this means corresponds one-to-one with the value of the conventional distribution for obtaining a diameter equivalent to a circle.

In the measurement according to the present invention, the intersection of a plurality of straight lines and the boundary of the grain is marked on the image, and the data is read by the arithmetic means. In this case, the intersection may not be confirmed correctly. That is, blur, dirt, disappearance, and the like of the image are inevitable. This is the same in the conventional method.
Such defects on the image are visually confirmed, and based on this confirmation, intersections are added to points that need intersections using a mouse or a pen, illegal points are corrected, and extra points are corrected. delete. This is easily achievable. In this operation, the burden on the measurer is sufficiently smaller than when a diameter equivalent to a circle is obtained.

Next, the parameters used in the present invention are the median diameter s of the crystal grain size, the standard deviation σ of the lognormal distribution, and the shape factor μ _e calculated from both.
The grain size of the grain is indicated by the median diameter and the standard deviation of the lognormal distribution. It is known that a lognormal distribution can be used as a failure distribution of a semiconductor device.

As described above, the electromigration of Al
MT of "time to failure"
The distribution of F is μ = (s / σ^Two ) Log (I₁₁₁ / I
₂₀₀ ) ^Three And there is a close correlation. Ie log-log
There is a linear relationship on the mound. Where s: median diameter,
σ: standard deviation, I₁₁₁ : X-ray diffraction peak in the 111-axis direction
Value, I₂₀₀ : Peak value in the 200-axis direction of X-ray diffraction
You. Assessing the data provided by Vaidya et al.
(I₁₁₁ / I₂₀₀ ) Is constant, MTF and μ are log-logarithmic
Has a linear relationship on the scale (only one point does not fall on a straight line)
You can see that. Therefore, in the present invention, (I₁₁₁ / I₂₀₀ )
Is assumed to be almost constant, and the shape factor μ_e = (S / σ ^Two Wear on)
In this way, the electromigration of Al
The tolerance was determined.

[0013]

FIG. 2 is a block diagram showing an apparatus for measuring the grain size of a polycrystalline film. The image input device 1 shown in FIG.
1 captures an image of the Al crystal film taken by a microscope, binarizes this image by an image binarizing means 12 and records it on a hard disk, and displays the original image and the binarized image on a display device 13 I do. FIG. 3A shows this.
As shown in FIG. 3 (b), the straight line writing means 14 writes a rectangular outline 22 in the displayed image 21 to determine a grain size measurement area, writes a diagonal 23 in this rectangle 22, and writes the diagonal 23 and the crystal. A mark 24 is provided at the intersection with the boundary line, as shown in FIG. FIG. 3D shows FIG.
(C) shows a partially enlarged view. The measurer visually corrects the display image 21 using the image correction device 15. That is, a necessary mark is input and an unnecessary mark is removed. Next, when the magnification of the image is input, the calculating means 16
Extracts distance data between intersections on a straight line from an image, calculates these data, and outputs them to the output device 17. In this case, as shown in FIG. 4, when a plurality of diagonal lines cross one grain 25, one of the data is deleted.

Using the apparatus for measuring the grain size of the polycrystalline film shown in FIG.
The grain size of the crystal film was measured. The wafer sputtered with Al is subjected to Keller's etch to make the boundaries of the grains visible, and an SEM image is taken with an image input device. SEM
The image is captured to the workstation by Ethernet or removable hard disk. An image is displayed on the screen, a diagonal line is drawn on the image, and a mark is made at the intersection of the diagonal line and the boundary of the grain. The above operations are performed automatically.

Next, a mark is added or deleted by a measurer using a mouse. The measurer looks at the boundary between the diagonal line and the grain on the image and corrects the mark. This step is a manual operation in which the measurer intervenes. Next, the distance between the intersections of the diagonal grain boundaries is calculated, the frequency distribution of the logarithmic value of the distance is calculated, the median value, the standard deviation is calculated, the shape coefficient is further calculated, and these are output. . This step is performed automatically. As a result, the grain size parameter can be easily obtained, and the electromigration evaluation of the Al polycrystalline film can be performed based on the relationship between the parameter and the electromigration resistance of Al. Therefore, it has conventionally been difficult to manage the electromigration of the Al polycrystalline film in-line, but this has now become possible easily.

[0016]

According to the present invention, the grain size of an Al polycrystalline film can be easily measured in-line, and the electromigration control of the Al polycrystalline film can be performed by in-line inspection using the data of the grain size. It is possible to do. Therefore, a lot with a reduced electromigration withstand voltage can be easily selected, a defective product can be prevented from flowing as a product, and quality control can be improved.

[Brief description of the drawings]

FIG. 1 is a flowchart of an embodiment.

FIG. 2 is a block diagram of an embodiment.

FIG. 3 is a diagram of an image showing an image processing step of the embodiment.

FIG. 4 is a diagram of an image of the embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Image input device 12 Image binarization means 13 Image display device 14 Straight line entry means 15 Image correction device 16 Calculation means 17 Output device 21 Image 22 Outline 23 Diagonal line 24 Mark

Claims (2)

(57) [Claims] An image of a grain of a polycrystalline film is captured,
The image is binarized and displayed, a plurality of straight lines crossing the image are added to the image, and the intersection between the straight line and the boundary of the grain is fixed by visual correction, and the distance between each intersection on the straight line is determined. And calculating a median diameter, a standard deviation of a lognormal distribution, and a shape factor by regarding this distance as a grain size of the grain. 2. An image input device for taking an image of a crystal film, a binarizing means for binarizing the image, a display device for displaying the binarized image, and drawing a straight line on the display image. A straight line entry means, an image correction device for visually correcting a display image, a calculation means for collecting distance data between intersections on a straight line from the image and calculating the data, and an output device for outputting the calculated value. An apparatus for measuring the grain size of a polycrystalline film, comprising: