JPH0318851A - Photomask and inspecting method thereof - Google Patents

Abstract

PURPOSE:To inspect the photomask with high accuracy at a high speed by forming patterns of the size at which the patterns are not resolved by a mask aligner on a mask dry plate and using the patterns as the patterns for alignment at the time of the mask inspection. CONSTITUTION:The patterns 1 having the resolution smaller than the resolution of the mask aligner are plotted by the pattern data of the same chip and exist together with the patterns in the other mask at the same points in a chip. The information relating to the position of the patterns 1 is obtd. from the pattern data and a stage is moved to bring the photomask 3 to the position of the substrates 1. After the spacing between right and left lenses 5 is set at a normal spacing, the alignment is executed while viewing the image on a monitor CRT 7 and a waveform monitor 9 displaying a differential signal. The photomask inspection which can make the high-speed alignment with a high accuracy is executed in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a photomask used in the manufacture of semiconductor integrated circuits and a method for inspecting the same.

BACKGROUND ART Conventionally, automatic defect inspection equipment using a chip comparison method (hereinafter abbreviated as chip comparison type inspection equipment) has been widely used for defect inspection of photomask patterns in which multiple identical chip patterns are arranged. ing. A conventional photomask and its inspection method will be explained below.

Figure 2 shows the configuration of a typical chip comparison type inspection device, where 3 is a photomask to be tested, 4 is illumination light that irradiates the photomask, and 5 is an enlarged image of the pattern of the left and right chips. 6 is a detector, 7 is a monitor CRT for the left and right chip patterns, 8 is a differential amplifier, 9 is a monitor CRT for displaying the difference signal from the left and right detectors, 10
is a control unit that controls the entire device.

The operation of the chip comparison type inspection device configured as described above will be described below. First, the distance between the left and right lenses 5 is set to an integral multiple of the distance between the same chips on the photomask,
The patterns of the inward-chip locations are superimposed so that the difference signals from the left and right detectors are minimized. This operation is called alignment. This situation is shown in FIG. In FIG. 3, 11 is an image on the left monitor CRT, 12 is an image on the right monitor CRT, and 13 is an image on the monitor CRT that displays the difference signal. In this state, the stage is moved to scan the entire photomask, and if a difference signal is detected from the left and right detectors, this is detected as a defect signal.

Alignment before stage scanning is performed manually while viewing an image on a monitor CRT or a waveform monitor (not shown) that displays a difference signal, or is performed automatically. The higher the density of the pattern used for this alignment (hereinafter referred to as alignment pattern), the higher the accuracy of alignment can be.

Problems to be Solved by the Invention However, in conventional photomasks, it is necessary to use turns with a high density as an alignment pattern (if there are no turns, as shown in Figure 3). . When a turn is used for alignment, the alignment accuracy is poor because the signal for alignment is small, and even though there are no defects on the photomask during stage scanning, there is a slight defect in the photomask. There is a drawback that misalignment is detected as a false defect.The present invention solves the above-mentioned conventional problems and provides a photomask that can be aligned with high precision and a method for inspecting the same.

Means for Solving the Problems To achieve this object, the photomask of the present invention has a pattern in the chip that is large enough not to be resolved by a mask aligner.

Function: With this photomask, by using a pattern with a size that cannot be resolved by a mask aligner as an alignment pattern, highly accurate alignment without detecting pattern shift is possible.

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

FIG. 1 shows a pattern of a photomask in one embodiment of the present invention. In Figure 1, 1 is a pattern (turn) that is smaller than the resolution of the mask aligner. This pattern is drawn as a turn data of the same chip, so it exists at the same location in the chip. 2 is the other pattern. This is the pattern in the mask.The operation of the photomask of this embodiment in which the above-mentioned pattern exists will be described below.

First, pattern data or information regarding the position of pattern 1 in FIG. 1 is obtained, and the stage is moved to bring the photomask to the position of pattern 1.

After setting the distance between the left and right lenses to the specified distance,
Precise alignment is performed while looking at the image on the monitor CRT and the waveform monitor that displays the difference signal. Figure ff14 shows an image of the monitor CRT of pattern 1. In Fig. 4, 14 is an image of the left monitor CRT, 16 is an image of the right monitor CRT, and 1e is an image of the monitor CRT that displays the difference signal. Since the alignment signal is high and the alignment signal is large, highly accurate alignment is possible.

When forming a pattern that can be resolved by a mask aligner as an alignment pattern, there are very large restrictions on its size and position. The constraints are small. Furthermore, since it is possible to form patterns at the same position on all layers of masks of the same type, alignment time can be shortened.

As described above, according to this embodiment, by using a pattern that cannot be resolved by a mask aligner as an alignment pattern for chip comparison inspection, the size and position can be freely determined, and extremely high accuracy can be achieved. This enables high-speed alignment.

Note that in this example, a pattern with a size that cannot be resolved by a mask aligner was used as an alignment pattern for chip comparison inspection, but the above pattern can also be used as an alignment pattern for inspection using a data matching method. be.

Effects of the Invention The present invention forms a pattern on a mask dry plate with a size that cannot be resolved by a mask aligner, and uses this pattern as an alignment notch during mask inspection, thereby achieving high-accuracy and high-speed photomask inspection. It is possible to achieve this.

[Brief explanation of the drawing]

FIG. 1 is a front view showing a photomask pattern in an embodiment of the present invention, FIG. 2 is a configuration diagram of an automatic defect inspection device using a chip comparison method, and FIG. 3 is a monitor of an alignment pattern in a conventional example. Front view showing the image, 4th
The figure is a front view showing a monitor image of the alignment pattern in this embodiment. 1...Pattern smaller than the resolution of the mask aligner, 2...Mask pattern, 3...
...Test photomask, 4...Illumination light, 6...
...Lens, 6...Detector, 7...
・Monitor CRT, 8...Differential amplifier, 9...
... Difference signal monitor CRT, 10... Control unit, 11.14... Image of left monitor CRT, 12.15... Image of right monitor CRT, 13.16... Image of difference signal monitor CRT.

Claims (2)

[Claims] (1) A photomask characterized in that a pattern of a size that cannot be resolved by a mask aligner is formed on a mask dry plate. (2) A photomask inspection method characterized in that a pattern of a size that cannot be resolved by the mask aligner according to claim 1 is used as an alignment pattern.