JP2002131887A - Mask inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a good image generation without drift and contrast fluctuation by carrying a mask to a chamber after removing static electricity by generating a plasma in a subchamber before carrying the mask to the chamber. SOLUTION: This mask inspection device comprises a subchamber which carries the mask from the atmosphere and exhausts preliminarily, a plasma generator which is installed in the subchamber, generates a plasma and neutralizes the charge on the mask carried into the pre-exhausted subchamber and a carrying method set the mask at the observation position, carrying the mask to the chamber from the subchamber after neutralizing the charge on the mask.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mask inspection apparatus for inspecting a mask.

[0002]

2. Description of the Related Art Conventionally, inspection of a defect of a photomask has been performed by observing the defect using an optical microscope. As the integration and miniaturization of wafers have progressed, patterns on photomasks have become increasingly finer, and optical microscopes have exceeded their resolution, making it impossible to observe defects. For this reason, inspection of the photomask for defects by a scanning electron microscope using an electron beam having a shorter wavelength has come to be performed.

[0003]

However, as a material of the photomask, an electrically insulating quartz glass is usually used, and has a property of easily being charged with static electricity. Therefore, in a scanning electron microscope, the generation rate of secondary electrons is reduced by using an accelerating voltage close to 1 to suppress charging by an electron beam.
Perform image observation. However, at the time of etching or the like in the previous step, charges are attached to the photomask surface and become charged.

[0004] Such charging is partially alleviated by removing the photomask to the atmosphere, but a part remains. When observing such a photomask with a scanning electron microscope at a high resolution (driving the photomask), drift and changes in contrast occur, making it difficult to accurately inspect and measure the length. was there.

[0005] The present invention solves these problems,
Plasma is generated in the sub-chamber just before the mask is transferred to the chamber to remove static electricity, then carried into the chamber, and the static electricity from the mask is removed to produce a high-quality image with no drift and no contrast fluctuation. It is intended to realize.

[0006]

Means for solving the problem will be described with reference to FIG. In FIG. 1, a sub-chamber 1 is a container for carrying a mask 13 and preliminarily evacuating it. Here, a bell jar 2 is connected in a vacuum.

The bell jar 2 is a non-conductive vacuum vessel for supplying high-frequency power to the inside from a coil or an electrode provided outside to turn residual gas into plasma. The main chamber 11 is a container for carrying in the mask 13 and scanning the surface while irradiating an electron beam to generate an enlarged image thereof.

Next, the operation will be described. Photo mask 13
A sub-chamber 1 is provided for transferring and pre-evacuating air from the atmosphere, and a coil or an electrode is provided outside a bell jar 2 vacuum-connected to the sub-chamber 1 to radiate high-frequency power inside to convert residual gas into plasma. After neutralizing the electric charge on the mask 13 being transferred to the sub-chamber 1, the mask 13 is loaded from the sub-chamber 1 into the main chamber 11 and set at the observation position.

At this time, the bell jar 2 which is a vessel for generating plasma has a structure made of a non-conductive vacuum vessel and connected to the sub-chamber 1 in a vacuum, and a coil or a coil provided outside the vacuum vessel is provided. High-frequency power is radiated from the electrodes into the inside of the vacuum vessel to excite residual gas into a plasma state.

[0010] Therefore, the mask 13 is
Plasma is generated in the sub-chamber 1 immediately before the main chamber 11 is carried into the main chamber 11 to remove static electricity.
In this case, it is possible to remove static electricity from the mask 13 and to generate a high-quality image (scanning electron microscope image) without drift and without fluctuation in contrast.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment and operation of the present invention will be sequentially described in detail with reference to FIGS. FIG.
1 shows a system configuration diagram of the present invention.

In FIG. 1, a sub-chamber 1 is a container for carrying a mask 13 and preliminarily evacuating it. In this case, the bell jar 2 is vacuum-connected. The bell jar 2 is a non-conductive vacuum vessel for supplying high frequency power to the inside from an electrode 4 provided outside to turn residual gas into plasma. The electrode 4 is a coil or an electrode on a flat plate, and is a coil or an electrode for radiating high-frequency power from the outside to the inside of a non-conductive vacuum container (for example, a glass container).

The high-frequency power supply 3 is a power supply for supplying high-frequency current to the electrode 4 to radiate high-frequency power into the bell jar 2 to convert residual gas into plasma. The valve 5 is a vacuum gate valve between the atmosphere and the sub-chamber 1. The valve 6 is a valve that introduces or shuts off the atmosphere into the sub-chamber 1.

The valve 7 is provided between the rotary pump 15 and the sub-chamber 1 and connects the sub-chamber 1 and the rotary pump 15 for preliminary exhaust. The valve 8 includes a turbo pump 9 and a rotary pump 15
To exhaust the gas compressed by the turbo pump 9.

The turbo pump 9 is a pump for evacuating the sub-chamber 1 to a high vacuum. The valve 10 is provided between the sub-chamber 1 and the turbo pump 9 to exhaust the sub-chamber 1 to a high vacuum. The main chamber 11 carries the mask 13 to the observation position, scans the surface with the reduced electron beam emitted from an electron gun (not shown), detects the secondary electrons emitted at that time, and detects the secondary electrons. This is a container for displaying an image.

The valve 12 is a gate valve between the sub-chamber 11 and the main chamber 11. Plasma 1
Reference numeral 3 denotes a plasma in which the residual gas is converted into plasma by the high-frequency electrode, and is used to neutralize the charge on the mask 13 (see FIG. 2).

The transfer arm 14 transfers the mask 13. The rotary pump 15 is a pump for preliminary exhaust. Next, the operation will be described. (1) After the atmosphere is introduced into the sub-chamber 1 by opening the valve 12 and the valve 10 and the valve 6 is opened (after the atmospheric state), the valve 5 is opened and the mask 13 is opened.
Is mounted on the transfer arm 14 and transferred to the position shown in the sub-chamber 1.

(2) The valves 5 and 6 are closed, the valve 7 is opened, and the sub-chamber 1 and the bell jar 2 are pre-evacuated by the rotary pump 15. (3) When the pressure becomes 1 Torr or less, the valve 7 is closed, and the valves 8 and 10 are opened.
The inside of the sub-chamber 1 is further evacuated by the turbo pump 9.

(4) A pressure of 20 mmT in the state of (3)
When the power reaches the orr level, the high-frequency power source 3 is turned on, high-frequency power is radiated from the electrode 4 into the bell jar 2, and the residual gas is turned into plasma to generate plasma 18. (5) The plasma 18 generated in (4) spreads in the sub-chamber 1 after a while. When the pressure reaches about 5 mmTorr for about 1 second, the high-frequency power supply 3 is turned off.
Change to F. As a result, the surface of the mask 13 is covered with the plasma to neutralize the charge on the mask 13 and erase the charge (see the description of FIG. 2).

(6) Next, the valve 12 is opened,
Mask 13 after erasing charges in main chamber 11
Is transported, fixed to a sample moving table (not shown), and arranged at the observation position, the transfer arm 14 is returned to the sub-chamber 1 and the valve 12 is closed. (7) While the main chamber 11 is evacuated to a high vacuum in the state of (6), the mask 13 is plane-scanned with an electron beam narrowed down and secondary electrons emitted at that time are detected, and the high resolution of the mask 13 is detected. Is displayed, and the mask 13 is displayed.
Inspection for defects.

As described above, when the pressure of the mask 13 reaches a pressure suitable for forming plasma while the mask 13 is being pre-evacuated in the sub-chamber 1, the high-frequency power source 3 is turned on and the plasma 1 is turned on.
8 to cover the surface of the mask 13 and
After neutralizing and erasing the charge on the surface of No. 3, the mask 12 after neutralizing the charge is loaded into the main chamber 11 and fixed to the sample transfer table to observe the enlarged secondary electron image. The mask 1 is automatically replaced during the replacement operation of the mask 13.
Immediately after neutralizing the charge of 3 with the plasma 18 and erasing it, the charge is carried into the main chamber to form a secondary electron image.
The charge of the mask 13 can be reliably neutralized and erased immediately before the observation, and the drift of the secondary electron image and the fluctuation of the contrast during the secondary electron observation due to the conventional charge of the mask 13 can be removed.

FIG. 2 is an explanatory view of static electricity removal by plasma according to the present invention. In FIG. 2, the static electricity 16 on the mask 13 is a secondary electron which is displayed by detecting a secondary electron emitted from the surface of the mask 13 by scanning the electron beam narrowly focused on the mask 13 at that time. This causes drift and contrast fluctuation of the image.

The charged particles 17 are plasmas 18 generated by converting the residual gas described above into plasma. In this case, positively charged ○ + (for example, positive ions) and negatively charged ○-( (For example, electron). As described above, when the static electricity 16 is present on the surface of the mask 13, the positively charged ○ + (eg, positive ions) or the negatively charged ○ − (eg, electrons) constituting the charged particles 17 converted into plasma are generated. Among them, those having a polarity opposite to that of the static electricity 16 are combined as shown by the arrow in the drawing, neutralized, and the static electricity 16 is erased. Although only positive electricity is shown as static electricity 16 on the mask 13 in the drawing, when negative electricity is charged, it is neutralized by the positive electricity in the charged particles 17. Accordingly, regardless of whether the static electricity 16 having a positive charge or a negative charge is charged on the surface of the mask 13, the charge is neutralized by the charged particles 17 and erased.

The high-frequency power supply 3 is turned on only when the sub-chamber 11 is evacuated and passes through a certain vacuum area. During this time, plasma is generated and the charge on the mask 13 is neutralized (medium). Does not affect the throughput at all (there is no need to take any special time for charge elimination and no effect on the throughput).

The electrode 4 is provided in the atmosphere,
Since the low-pressure residual gas in the bell jar 2 is excited by high-frequency power to generate plasma, no contamination is generated from the electrode 4, and the mask 1 is short-time at low pressure.
Since the static electricity on 3 is removed, damage to the mask 13 can be avoided.

FIG. 3 shows an explanatory diagram of the present invention. FIG. 3A shows a secondary electron image of static electricity removal (with) by plasma, and FIG. 3B shows a secondary electron image of static electricity removal (without) by plasma. The sample is a photomask, and “H” is a chrome pattern on quartz. The secondary electron image in FIG. 3B is a photograph having a drift caused by static electricity, and it is difficult to measure the length of the “H” shape. FIG.
The secondary electron image (a) is an image from which static electricity has been removed, and is a normal image in which sharp and uniform edges are visible. As can be seen from both photographs, by removing (neutralizing) static electricity on the mask 13 according to the present invention,
As shown in FIG. 3A, it is possible to reliably obtain a sharp and uniform edge secondary electron image without drift and contrast fluctuation due to charging.

[0027]

As described above, according to the present invention,
Since a configuration is employed in which plasma is generated in the sub-chamber 1 immediately before the mask 13 is carried into the main chamber 11 to remove static electricity, and then carried into the main chamber 11 and observed, the static electricity of the mask 13 is discharged. It is possible to reliably generate a high-quality image with no drift and no fluctuation in contrast. As a result, the static electricity on the mask 13 is reliably removed (neutralized) in the sub-chamber 1 immediately before the observation without any influence on the throughput, and a sharp and sharp edge-free image is generated without drift or contrast fluctuation. The length measurement can be performed accurately.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of the present invention.

FIG. 2 is an explanatory view of static electricity removal by plasma of the present invention.

FIG. 3 is an explanatory diagram of the present invention.

[Explanation of symbols]

 1: Subchamber 2: Bell jar 3: High frequency power supply 4: Electrode 5, 6, 7, 8, 10, 12: Valve 9: Turbo pump 11: Main chamber 13: Mask (photomask) 14: Transfer arm 15: Rotary pump 16: Static electricity 17: Charged particles

Claims (2)

[Claims] 1. A mask inspection apparatus for inspecting a mask, comprising: a sub-chamber for transporting a mask from the atmosphere and preliminarily evacuating; and providing a plasma in the pre-evacuated sub-chamber to generate plasma and transport the plasma to the sub-chamber. A plasma generator for neutralizing the charge on the mask, and a transfer means for setting the observation position by transferring the mask from the sub-chamber to the chamber after neutralizing the charge on the mask. A mask inspection apparatus characterized by the above-mentioned. 2. The plasma generator has a structure made of a non-conductive vacuum vessel and connected to the sub-chamber in a vacuum, and applies high frequency power from a coil or an electrode provided outside the vacuum vessel. 2. The mask inspection apparatus according to claim 1, wherein the residual gas is radiated into a vacuum vessel to excite the residual gas into a plasma state.