JPS6311771B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for automatically inspecting a photomask pattern drawn based on information stored in a recording means such as a magnetic tape, and in particular to a method for automatically inspecting a drawn pattern into an electrical signal. and the signal is
The present invention relates to an inspection method in which original information is compared with a reference signal obtained by electrically converting the original information, and in which the two image signals are compared while feeding back information regarding the amount of time difference existing between the two image signals.

The procedure for creating a pattern for a photomask, etc. based on information stored on magnetic tape is as follows: A photographic plate for a photomask on which a pattern is to be drawn is set on a stage movable in the X-Y directions, and then it is moved in the X and Y directions. Scanning is performed with the light beam while moving.

At this time, the light flux passes through a slit called an aperture that opens and closes based on the information on the magnetic tape.
Draw the desired pattern on the photomask.

The following method has conventionally been used to check whether the pattern created in this way is correctly drawn.

That is, first, the obtained pattern is imaged with a video camera, and as shown in FIG. 1, the pattern is converted into an electrical image signal 1'.

On the other hand, the information stored on the magnetic tape is converted to obtain image signal 1 as a reference, these two image signals are compared, and those whose difference is within an allowable range are accepted.

FIG. 1 schematically shows the process from pattern drawing to inspection.

In this case, the start time difference Δt due to the accuracy of setting the photomask on the inspection equipment
Even if this problem could be solved by some means, there would be a time lag that would occur in the middle of the image signal because the stage is moved and the opening is opened and closed by mechanical means during the drawing process. The problem remains that it cannot be addressed.

These time lags increase the number of errors that are counted when the drawing is actually correct or there is a slight positional shift within the allowable range.

Therefore, it is necessary to determine the tolerance including the deviation of the starting position, and it is extremely difficult to inspect the pattern with an accuracy within 2 to 3 mm.

As one solution to this problem, a method has been proposed in which the stage is driven by a pulse motor in accordance with the pixel divisions, but it is unavoidable that the device becomes large and expensive.

The present invention solves these conventional drawbacks and is a method for inspecting patterns drawn by ordinary equipment,
The purpose of the present invention is to provide a method that can perform inspection regardless of deviations caused by mechanical precision of the inspection device.

The present invention will be explained below.

FIG. 2 illustrates an embodiment of the present invention.

It is similar to the conventional technology in that the reference image signal 1 created from the magnetic tape and the image signal 1' obtained from the photomask are compared, but in the present invention, if a difference is found between the two, it is immediately detected. Rather than treating this as a defective point, the two signals are compared over a certain time range and detected as a time lag.

That is, the amount corresponding to Δt in FIG. 1 is obtained.

As shown in FIG. 2, the two image signals pass through delay circuits 2 and 2' and enter the comparison detection section 3, which feeds back a signal for controlling the delay time based on the detected time difference. By delaying one signal by the necessary time, signals at equal positions can be easily compared.

In the method of the present invention, since the image signal is processed and then fed back, the control is performed intermittently, but in reality, this is sufficient, and deviations due to lack of mechanical precision occur in the middle of the pattern. It can also be dealt with when it occurs.

In Figure 2, the route of the control signal to delay circuit 2 is shown by a broken line, but this means that the delay amount in delay circuit 2 is kept constant, and only the delay amount in the other delay circuit 2' is This indicates that it is possible to arbitrarily select a method of eliminating the time difference between the two signals, or a method of eliminating the time difference by sending a control signal to each of 2 and 2'.

One of the conditions necessary for carrying out the method of the present invention is that the starting positions on the patterns be the same.

That is, when comparing image signals at completely different positions, it is impossible to calculate the time difference, and correction by passing the signal through a delay circuit becomes impossible.

It is obvious that the most convenient place to align the positions is the starting position of drawing, so
When trying to obtain an image signal from a drawn pattern, the scanning start position must be the same as the drawing start position, or must be very close to the drawing start position.

To achieve this, it is possible to align the stage visually and manually, but if you want to do it automatically, scan in the same direction as when drawing, and first check the signal level. An appropriate method is to set the position where is displaced as the start position.

In addition to such alignment, it is also necessary to correct rotational deviations around the Z-axis when setting the photomask in the inspection equipment. It can be determined by whether it is longer (or shorter) than the period, so
Modifications can be made based on that.

Since the comparison of the image signals is usually performed by a computer, in that case, functions such as position alignment and rotation correction can be built into the apparatus using software.

The present invention takes advantage of the fact that the image signal obtained from the drawn pattern can be processed as a digital signal as it is, and the delay of the image signal can also be done inside the computer, so the required hardware is other than ordinary inspection equipment. It is only a device for matching the time axes of an image signal obtained from a magnetic tape and an image signal obtained from a drawn pattern,
All other features can be processed by software.

Although the case where drawing is performed based on information stored on a magnetic tape has been described above, the present invention also applies when processing is performed based on information stored on a magnetic recording device other than a magnetic tape or an optical recording device. It can be implemented similarly.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining a conventional pattern inspection method, and FIG. 2 is a diagram for explaining an embodiment of the pattern inspection method according to the present invention. In the figure, 1 is an image signal obtained from a magnetic tape.
1' is an image signal obtained from a pattern drawn by a drawing device, 2 and 2' are delay circuits, and 3 is a device for comparing the two types of image signals and detecting defective points in the pattern.

Claims (1)

[Claims] 1 An image signal obtained by scanning a pattern of the object to be inspected drawn based on drawing information stored in an information storage device via a photoelectric conversion device and information stored in the information storage device In a pattern inspection method for determining the quality of a pattern of an object to be inspected by comparing it with a reference image signal obtained by converting the image signal, the scanning is performed in the same direction as when drawing the object to be inspected; The amount of time axis deviation between the two image signals is detected using the position where the signal level first changes as a starting position, and one or both of the two image signals is delayed according to the amount of time deviation. A pattern inspection method characterized in that the time axes of both image signals are made to coincide with each other, and then the quality of the pattern is determined by comparing the two image signals.