JPH0621778B2 - Mask defect inspection method - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a mask defect inspection method for inspecting the presence or absence of a defect in a mask used for manufacturing an LSI or the like and the correctness of a pattern.

[Technical background of the invention and its problems]

Conventionally, in a mask defect inspection method for inspecting a pattern formed on a photomask or the like, the main surface of the mask is irradiated with light (usually, its wavelength is 0.4 to 0.7 μm) to form a pattern. The amount of transmitted light corresponding to the presence / absence is detected, and the presence / absence of a defect in the mask and the correctness of the pattern are inspected. Actually, the mask is moved in parallel in the plane orthogonal to the light irradiation direction, and the scanning signal (first scanning signal) detected at this time and the scanning signal obtained based on the design data used in the pattern formation. The above-mentioned inspection is performed by comparing and collating with (the second scanning signal).

By the way, in this type of mask defect inspection method, detection of defects within 1 [μm] is almost limited due to interference and diffraction of light transmitted through the mask. An optical reduction projection exposure apparatus called a so-called stepper exposes the wafer by optically reducing the image of the mask to 1/5 to 1/10. Therefore, it is sufficient to detect such a defect. However, as the development of a VLSI having a line width of 1 [μm] or less is directed, it is expected that a pattern is transferred using X-ray, electron beam or ion beam. With these transfer technologies, reduction transfer is extremely difficult, and therefore inevitably, equal-size transfer is performed. Therefore, considering the conventional defect detection at the same level, the defect detection of 0.1 to 0.2 [μm] is required. However, such detection accuracy is difficult in the conventional method using light.

[Object of the Invention]

An object of the present invention is to provide a mask defect inspection method that can detect even fine defects of 1 [μm] or less and is effective for defect inspection of masks used for X-ray transfer, electron beam transfer, and the like. is there.

[Outline of Invention]

The essence of the present invention is to perform a defect inspection using electrons instead of light to prevent a decrease in detection accuracy due to light diffraction or interference.

That is, the present invention, in a method for inspecting a defect of a mask used for energy beam exposure or the like, after depositing a film such as a photoelectric film that emits electrons by irradiation of light on the pattern forming surface side of the mask, Irradiate a light beam on the side opposite to the pattern forming surface of the mask, and detect the electron beam from the coating film excited by the transmitted beam amount that differs depending on the presence or absence of the pattern, and detect defects in the mask according to the detection result. It is the method that was inspected.

〔The invention's effect〕

According to the present invention, necessary defects can be inspected in a submicron region or less, which is impossible with the conventional method. Therefore, it is extremely effective for defect inspection of masks used for X-ray transfer, electron beam transfer and the like. Further, for an electron beam transfer mask that requires a photoelectric film, a defect inspection including the photoelectric film can be performed.

Example of Invention

FIG. 1 is a schematic configuration diagram showing a mask defect inspection apparatus used in an embodiment method of the present invention. In the figure, reference numeral 1 denotes a sample table on which a mask 2 to be described later is placed. The sample table 1 is a rotatable θ table 1a, an X table 1b movable in the X direction (left and right direction on the paper) and a Y direction (vertical direction on the paper surface). ) Is movable to the Y table 1c. These tables 1a, 1b, 1c are composed of the table drive control circuit 4 and the respective drive circuits 5a, 5 which have received a command from the computer 3.
b and 5c, respectively. The moving position of the sample table 1 is measured by the laser interferometer 6 and the position circuit 7.

On the other hand, a light source 8 for generating X-rays is arranged above the sample table 1, and the X-rays (energy beam) emitted from the light source 8 are applied to the mask 2 placed on the sample table 1. To be done. Here, the mask 2 is used for X-ray transfer, electron beam exposure, etc., and is formed by depositing a pattern 2b of chrome or the like on the lower surface of a glass plate 2a of synthetic quartz or the like as shown in FIG. There is. Then, on the lower surface of the mask 2, a photoelectric film (coating) 9 that emits photoelectrons upon irradiation with a light beam is applied. Therefore, the above X
By the line irradiation, photoelectrons corresponding to the pattern are emitted from the mask 2. Photoelectrons emitted from the photoelectric film 9 of the mask 2 are detected by an electron detector 10 using a scintillator or a P-N junction, a signal detection circuit 11, and the like. Here, by continuously moving the sample stage 1 together with the X-ray irradiation, the signal detection circuit 11 detects the scanning signal (first scanning signal) corresponding to the pattern of the mask 2. Then, this detection signal is supplied to the defect determination section 13 together with the scanning signal (second scanning signal) generated based on the design data when the drawing circuit 12 forms the pattern. The defect determination unit 13 compares and collates the first and second scanning signals based on the position data from the position circuit 7, and determines that there is a defect when they are different.

In FIG. 1, 14 is a deflector for deflecting and scanning X-rays, 15 is a focusing coil for applying a magnetic field in the optical axis direction, 16 is the sample stage 1, the light source 8, the electron detector 10 and the deflector. A vacuum container for housing the container 14 and the like is shown.

Next, a mask defect inspection method using the apparatus having the above configuration will be described. First, a mask 2 to be inspected is prepared, and a photoelectric film 9 made of CsI is deposited on the pattern forming surface side of the mask 2 by a method such as vapor deposition. Then, the mask 2 is placed on the sample table 1 with its pattern forming surface side facing down. If the photoelectric film 9 is unnecessary after the inspection, it can be easily removed by a known method. Next, when the upper surface of the mask 2 is irradiated with spot-shaped focused X-rays, the amount of transmitted beam changes depending on the presence or absence of the pattern on the mask 2, and photoelectrons are emitted from the photoelectric film 9 in accordance with the amount of transmitted beam. It That is, photoelectrons are emitted from the mask 2 depending on the presence or absence of the pattern. The photoelectrons emitted from the photoelectric film 9 of the mask 2 are focused by the magnetic field in the optical axis direction and the electric field in the optical axis direction by the focusing coil 15,
It goes straight along the optical axis and enters the electron detector 10. Here, if the sample table 1 is continuously moved in the X direction and stepwise moved in the Y direction, the signal detection circuit 11 detects the first scanning signal corresponding to the pattern of the mask 2. Then, this scanning signal is compared and collated with the second scanning signal by the defect determining section 13 as in the conventional general mask defect inspecting apparatus, whereby the presence or absence of defects in the mask 2 and the correctness of the pattern are inspected. Become.

In this case, the electrons emitted from the mask 2 for the defect inspection do not cause inconvenience such as interference and diffraction unlike the case of light or the like. Therefore, the accuracy of defect detection can be significantly improved. According to the experiments conducted by the present inventors, it was found that even minute defects of 1 [μm] or less can be sufficiently detected. Therefore, it is extremely effective for defect inspection of masks used for X-ray transfer and electron beam transfer.
Further, for a mask such as an electron beam transfer mask in which a photoelectric film is essential, a defect inspection including the photoelectric film can be performed. Further, the apparatus used in the method of this embodiment has an advantage that it can be easily realized only by improving the detection optical system of the conventional optical mask defect inspection apparatus, that is, the light source and the detector.

The device used in the method of the present invention is not limited to the structure shown in FIG. 1 and may be modified as appropriate. For example, it is possible to add a spot-shaped beam irradiation function, a defect determination function, and the like to an ordinary electron beam transfer device, and use the defect irradiation function of the present invention. In addition, various modifications can be made without departing from the scope of the present invention.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a mask defect inspection apparatus used in an embodiment method of the present invention, and FIG. 2 is a schematic diagram for explaining the embodiment method. 1 ... Sample stage, 2 ... Mask to be inspected, 2a ... Glass plate, 2b ... Mask pattern, 3 ... Computer, 4 ... Table drive control circuit, 5a, 5b, 5c ... Table drive circuit, 6 ...... Laser interferometer, 7 …… Position circuit, 8 ……
Light source (energy beam radiation source), 9 ... Photoelectric film (coating), 10 ... Electron detector, 11 ... Signal detection circuit, 1
2 ... Drawing circuit, 13 ... Defect determination unit, 14 ... Rotating mirror.

Claims (3)

[Claims] 1. A pattern formation surface of a mask is coated with a photoelectric film that emits electrons by irradiation of light, and then a light beam is irradiated on the side opposite to the pattern formation surface of the mask, depending on the presence or absence of the pattern. A method for inspecting a mask defect, which comprises detecting an electron beam from the photoelectric film excited by the amount of a transmitted beam, and inspecting a defect in the mask according to the detection result. 2. The mask defect inspection method according to claim 1, wherein an X-ray is used as a light beam for irradiating the mask. 3. The mask defect inspection method according to claim 1, wherein CsI is used as the photoelectric film.