JP3318847B2 - Repair method of residual defect of shifter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a correction of residual defects of the shifter in the phase shift photomask, in particular, the correction of residual defects of the shifter of the phase shift mask using a shifter material SiO ₂ system Regarding effective correction method.

[0002]

2. Description of the Related Art In recent years, as semiconductor integrated circuits have become more highly integrated, further miniaturization of a reticle used for fabricating the circuit has been required. Currently 1
The line width of the device pattern transferred from the 5 × reticle for a 6M DRAM is as small as 0.6 μm. 6
For a 4M DRAM device pattern, 0.3
A resolution of 5 μm line width is required, and the light exposure method using a conventional stepper has reached the limit.
For this reason, the resolution of a device pattern transferred from a reticle in light exposure can be improved, and a phase shift mask of a type that can be used in a current stepper has been attracting attention. The basic idea and principle of the phase shift mask have already been described in JP-A-58-17344 and JP-B-62-59296.
Given the merit that the existing light exposure system can be used as it is, the development of various types of phase shift masks has been actively studied.

As shown in FIG. 1, a phase shift mask called an upper shifter type having a structure in which a shifter layer is formed by patterning on a glass substrate provided with a light-shielding layer pattern,
A phase shift mask called a lower shifter type in which a shifter is provided under a light shielding layer pattern is one of them. As a shifter material, PMMA, SiO ₂ -based materials, oxides, nitrides, oxynitrides of chromium containing chromium as a main component, and compounds of Mo and Si have been studied. However, the phase shift photomask has a complicated structure and requires many steps as compared with a normal photomask not using a shifter layer. In some cases, the mask manufacturing process is completed while the shifter material remains.
(Hereinafter, such a residue of the shifter material is referred to as a residual defect of the shifter.)
When used as a mask as it is, it does not contribute to improving the resolution of the mask, but rather causes defects in device patterns and the like during mask transfer. Therefore, for practical use, it is necessary to correct the shifter, and an appropriate correction method is being studied.
Various types are in parallel, and there is no suitable method for correcting a shifter, particularly, for removing excess shifter material. In order to correct the residual defect of the shifter, it is conceivable to use a laser beam such as a YAG laser which has been conventionally used to correct the residual defect of the light-shielding layer containing chromium as a main component. In the case of using a SiO ₂ system, some method for absorbing the laser beam without absorbing the laser beam is required. When the SiO ₂ material is used as a shifter material, a focused ion beam device (FIB device) such as Ga or Ar is used to correct by milling, or a predetermined gas is excited by an ion beam and etched. Correction by gas-assisted etching has also been proposed, but there is a problem that damage due to the ion beam around the residual defect is unavoidable, and it is difficult to detect the end point of the residual defect removal and correction, and it is difficult to detect the ion on the base of the residual defect. The problem of beam damage remains. Generally, as a method of detecting the end point of the residual defect removal and correction, a method of monitoring the increase or decrease of Cr ions (a main component of a light shielding pattern) and Si ions (a main component of a glass substrate), or a method of monitoring the amount of secondary electrons Therefore, it has been considered that it is difficult to detect an etching end point in removing a residual defective portion of the shifter. This is because when an SiO ₂ -based material is used for the shifter material and only the residual defects of the shifter are to be corrected by milling or gas-assisted etching using a FIB apparatus, the etching stopper layer is This is because, in the case of a mask that does not have an end point, the end point cannot be confirmed on the glass substrate under the shifter of the residual defect, and etching or milling is performed up to the glass substrate. In practice, it is difficult to determine the method of correcting the residual defect depending on the presence or absence of the etching stopper layer. Regardless of the presence or absence of the etching stopper layer, any of the above conventional endpoint monitoring methods can be used. In the repair of the residual defect of the shifter used, a reliable method of confirming the end point by gas assisted etching correction and milling correction has been required.

[0004]

[0008] The present invention is based on such circumstances, but to provide a residual defect correction method of the shifter material of the phase shift photomask, in particular, the shifter portion of material of the SiO ₂ system In the method for repairing residual defects of a phase shift photomask, even with the conventional endpoint monitoring method for etching used in the FIB apparatus, the endpoint is reliably monitored regardless of the presence or absence of the etching stopper layer of the shifter. It is an object of the present invention to provide a correction method that can be performed, can be corrected, and the corrected one can sufficiently cope with quality in practical use.

[0005]

SUMMARY OF THE INVENTION According to the present invention, there is provided a method for repairing a residual defect of a shifter of a phase shift photomask, wherein a residual defect portion of a shifter material in the phase shift photomask is milled by using a focused ion beam (FIB). A method of repairing a shifter, or a method of repairing by a gas-assisted etching method in which a predetermined gas is excited by an ion beam to etch the shifter, and at least a FIB is provided on the entire outer periphery or a part of the outer periphery of the residual defect portion. A carbon film, which is a film that can be removed by laser beam irradiation, is formed by assisted CVD, and the entire region of the residual defect portion surrounded by the film and a partial region of the film are collectively milled or gas-assisted etched. Then, after performing the process of removing the defective portion of the shifter and the process of removing the defective portion of the shifter,
This is a method of correcting a residual defect of a shifter, including a step of removing a carbon film remaining by laser beam irradiation. FIB assist C is applied to the entire outer periphery or a part of the outer periphery of the residual defect.
The reason for forming a carbon film, which is a film that can be removed by laser beam irradiation by VD, is that the residual defect is not a regular shape but an irregular shape, and the beam itself has a distribution. This is because irradiation with an ion beam cannot be performed, and this is to prevent damage to the periphery of the defective portion due to the ion beam. Then, using a focused ion beam (FIB) capable of removing a shifter material, after removing a shifter defect portion, the carbon film formed earlier is removed by a laser beam. Therefore, as shown in FIG. 1A, in the case of removing and correcting the residual defect 6 which leads to the shifter material portion on the chrome light-shielding pattern 2, ions It is not necessary to provide a carbon film that can be removed by laser beam irradiation to prevent damage due to the beam. However, in the case where a defective portion is isolated or a defect as shown in FIG. ,
In order to prevent damage around the defect due to the repair, it is necessary to provide a carbon film on the entire outer periphery of the defect. In the case where the shifter material is of SiO2 type, in the above-described step of removing the defective portion of the shifter, the end point of the removal processing is determined as follows.
This is performed by monitoring the increase / decrease of Si ions and / or the change of the amount of secondary electrons. In this case, if the phase shift mask is not provided with a shifter etching stopper layer, the base of the shifter material becomes a glass substrate and contains Si.
If the increase / decrease of ions and the change in the amount of secondary electrons are performed together with monitoring, the end point of the etching can be determined with higher accuracy. In particular, when the shifter material is SiO2 based and the phase shift mask has a shifter etching stopper layer, it is effective, and the thickness of the carbon film provided around the residual defect portion is completely eliminated by the residual defect. Even if it is performed, the remaining thickness is determined, and the process of removing the defective portion is monitored by S
The time point at which the i-ion has disappeared or the time point at which the amount of secondary electrons has significantly changed (increased) is determined as an endpoint, and can be accurately determined. This is due to the fact that the etcher is etched and the point where the etching stopper layer of the shifter is exposed is used as an end point. At the time when the etchin ヂ stopper layer is exposed, the Si ions disappear and the secondary electron intensity changes. It is. As the etching stopper layer of the shifter, a film mainly composed of tin oxide, a film mainly composed of magnesium fluoride, and the like are generally used. In the case where the phase shift mask is of a type in which a recess is formed in the substrate itself and used as a shifter, the thickness of the carbon film, which can be removed by laser beam irradiation, is reduced by the ion beam so that the remaining amount of the shifter is reduced. By making the thickness to be removed almost simultaneously with the defect portion, and by simultaneously removing the entire region of the residual defect portion surrounded by the film and a part of the film, the removal is performed at the same time. The time point when the Si ions rapidly increase or the time point when the amount of secondary electrons largely changes (increases) is defined as an endpoint, and can be reliably determined. FIG. 5 is a schematic diagram of a defect repair apparatus using FIB, wherein 15 is an ion beam, 18 is an ion source,
19 is an ion detector, 23 is a correction phase shift mask,
Reference numeral 21 denotes a correction phase shift mask 23, and an X, Y stage that moves X and Y while controlling the position thereof. Reference numeral 22 denotes a gas gun, which performs correction while evacuating.

[0006]

According to the present invention, there is provided a method for repairing a residual defect of a shifter in a phase shift photomask, wherein the residual defect of the shifter material is corrected by milling using a focused ion beam (FIB) or a predetermined gas. Is excited by an ion beam and the shifter is etched by a gas-assisted etching method to correct the shifter, thereby removing the shifter and forming a carbon film that can be removed by laser beam irradiation over the entire circumference of the residual defect. Then, the entire region of the residual defect portion surrounded by the film and a partial region of the film are collectively subjected to milling or gas-assisted etching to remove the defect portion of the shifter. To prevent damage to the surroundings by the ion beam, and after removing the defective part of the shifter,
The remaining unnecessary film is removed by removing the remaining carbon film by laser beam irradiation. If the shifter material is of the SiO2 type, in the process of removing the defective portion of the shifter,
The end point of the removal process is determined by monitoring the increase / decrease of Si ions and / or the change of the amount of secondary electrons, thereby preventing damage to the base of the defective portion due to the ion beam and preventing the influence upon transfer to the device pattern on the wafer. It does not appear. In the case where the shifter material is SiO2 based and the phase shift mask has a shifter etching stopper layer, the thickness of the carbon film which can be removed by laser beam irradiation is reduced to a level where residual defects are completely eliminated. The thickness that remains even after the removal, and the time when the Si ions disappear or the time when the amount of secondary electrons greatly changes (increases) in the monitoring of the Si ions is set as the end point of the shifter removal processing, and the removal processing is finished. As a result, the influence on the base of the shifter material is surely eliminated. When the phase shift mask is of a type in which a recess is formed in the substrate itself and is used as a shifter, the thickness of the carbon film, which is a film that can be removed by laser beam irradiation, is reduced by the ion beam. By removing the entire area of the residual defect surrounded by the film and a part of the film at the same time and simultaneously removing the defect, it is possible to detect end-fin by Si ions. It is possible.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 and FIG. 2 show a process for correcting a residual defect of a shifter according to the present invention.
a Gas assisted etching method using an ion focused ion beam device (FIB device) was used. The acceleration voltage of Ga ions is 20 KV, the current value is 140 PA, and the beam diameter is 0.
Xenon fluoride was used as the etching gas. 4A to 4E are a plan view of a mask including a repair portion in each step and a cross-sectional view over a defect portion.
1A and 1B are plan views, and FIGS. 1A and 1B are cross-sectional views taken along line a1-a2 of FIGS.
2 (C) to 2 (E) are cross-sectional views corresponding to the portions shown in FIGS. 1 (A) and 1 (B). First, a pattern formation of the shifter 3 under the shifter 3 is performed by using an upper shifter type phase shift mask in which the shifter 3 is disposed on the chrome light-shielding pattern 2 having the convex defect portion 6 of the shifter as described in (A). A mask 1 having an etching stopper layer 4 which is an etching resistant film for repair and correction was prepared. Residual defective portion of the mask shifter Around the defective portion on the glass substrate, as shown in FIG.
The carbon film 7 is formed by IB assisted CVD so as to have a thickness that can suppress the occurrence of the riverbed, and a thickness that remains even when the residual defect is completely removed in the following residual defect removing process using an ion beam; A film was formed. (B) Next, the entire region of the residual defect surrounded by the carbon film 7 and a partial region of the carbon film 7 are collectively subjected to gas-assisted etching using the ion beam 14 to remove the defective portion of the shifter. Performed (C). Accompanying the process of removing the defective portion, detection of increase / decrease of Si ions and monitoring of the amount of secondary electrons were performed. Several seconds after the removal process was continued, the Si ions disappeared and the secondary electron intensity increased sharply. This point was determined as the etching end point where the etching stopper layer 4 was exposed, and the removal process of the defective portion was stopped. . (D)
Next, the remaining carbon film 7 is
, Irradiation was performed several times at once, removed (E), and the correction was completed. (F) The device pattern was formed by transfer using this mask, but the portion corresponding to the defective portion A was not transferred, and there was no problem.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIGS. 3 and 4 show a step of repairing the residual defect of the shifter of the second embodiment. As a method of removing the residual defect, a gas assisted etching method using FIB was used as in the first embodiment. 4A to 4E are a plan view of a mask including a repair portion in each step and a cross-sectional view over a defect portion. 3A and 3B are plan views, and FIG.
4A and 4B are cross-sectional views taken along the line b1-b2 in FIGS. 3A and 3A, and FIGS. 4C to 4E are FIGS.
It is sectional drawing corresponding to the part of (b). The photomask in the second embodiment is a halftone type phase shift mask of a type in which a concave portion is formed on a quartz substrate by etching and used as a shifter.
If a concave portion is not formed in a place where the shifter material is not originally required, this place is called a residual defect. First,
As shown in (A), a concave portion is formed in the substrate itself, and a type in which a phase difference is made between light passing through a portion having a concave portion and light passing through a portion having no concave portion during transfer, and is usually a concave portion. Was used as a shifter, and a mask 9 having a residual defect portion 12 was prepared. FIB assist CV is applied to the entire periphery of the residual defect portion of the shifter of this mask.
By D, the carbon film 13 was formed to a thickness enough to suppress the occurrence of the riverbed, and to a thickness such that the residual defects were removed almost at the same time as the residual defects were removed in the following ion beam 14 removal processing. . (B) Next, the entire region of the residual defect portion 12 surrounded by the film and a part of the carbon film 13 are collectively subjected to gas-assisted etching using the ion beam 14 to remove the defective portion of the shifter. Performed (C). Accompanying the process of removing the defective portion, detection of increase / decrease of Si ions and monitoring of the amount of secondary electrons were performed. A few seconds after the removal process was continued, the Si ions rapidly increased and the secondary electron intensity changed suddenly. Therefore, this point was determined as the etching end point where the glass substrate under the carbon film was exposed, and the removal process of the defective portion was performed. Stopped. (D) Then, the remaining carbon film 13 was collectively irradiated several times using the laser beam 15 and removed (E), and the modification was completed. (F)
This mask was also transferred to form a device pattern, but the portion corresponding to the defective portion B was not transferred, and there was no problem.

[0009]

According to the present invention, in the correction of the residual defect of the shifter in the phase shift photomask, the above-mentioned configuration has an effect on the transfer and fabrication of a device pattern which has been considered difficult. It is possible to remove the residual defect of the shifter using the FIB device, which eliminates the damage due to the repair around the defect region and the repair due to the repair of the base of the defect region, and is stable in a range where the quality can be sufficiently guaranteed. It is possible to provide a correction method that can be worked on.

[Brief description of the drawings]

FIG. 1 is a process diagram of a method for correcting a residual defect of a shifter according to a first embodiment of the present invention.

FIG. 2 is a process drawing following FIG. 1 of Example 1 of the present invention.

FIG. 3 is a process diagram of a method for correcting a residual defect of a shifter according to a second embodiment of the present invention.

FIG. 4 is a process drawing following FIG. 3 of Example 2 of the present invention.

FIG. 5 is a schematic diagram of a FIB device for correcting a residual defect of a shifter.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 upper shifter type phase shift photomask 2 chrome light shielding film pattern 3 shifter material 4 etching stopper layer 5 glass substrate 6 residual defect A 7 carbon film 7 ^, carbon film after ion beam correction 8 residual defect portion after correction 9 substrate itself Phase shift mask of the type forming a concave portion 10 Shifter portion 11 Glass substrate 12 Residual defect portion B 13 Carbon film 13 ^, Carbon film after ion beam correction 14 Ion beam 15 Laser beam 16 Residual defect portion after correction 17 Focused ion beam device ( FI
B) 18 ion source 19 ion detector 20 Si ion 21 XY stage 22 gas gun 23 photomask for correction

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-115842 (JP, A) JP-A-5-142756 (JP, A) JP-A-4-128758 (JP, A) JP-A-6-142 347997 (JP, A) JP-A-6-118627 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03F 1/00-1/16

Claims (4)

(57) [Claims] 1. A method of repairing a residual defect portion of a shifter material in a phase shift photomask by milling or gas assist etching using a focused ion beam (FIB), wherein at least the residual defect portion is completely repaired. A carbon film that is a film that can be removed by laser beam irradiation by FIB assisted CVD is formed on the outer periphery or a part of the outer periphery, and the entire region of the residual defect portion surrounded by the film and a partial region of the film are formed. Collectively, milling or gas-assisted etching, a process of removing the defective portion of the shifter, and after the process of removing the defective portion of the shifter, including a process of removing the remaining carbon film by laser beam irradiation, A method for correcting a residual defect of a shifter, comprising: 2. The method according to claim 1, wherein the shifter material is SiO2.
In the system, the judgment of the end point of the removal process of the defective portion of the shifter is performed by S
A method for correcting a residual defect of a shifter, characterized by monitoring increase / decrease of i-ion and / or change of secondary electron quantity. 3. The method according to claim 1, wherein the shifter material is SiO2.
The phase shift mask has a shifter etching stopper layer, and the thickness of the carbon film, which is a film that can be removed by laser beam irradiation, is set to a thickness that remains even when the residual defects are completely removed. A method of repairing a residual defect in a shifter, characterized in that the removal of the part is completed when the Si ions disappear or the amount of secondary electrons changes significantly by monitoring the Si ions. 4. The phase shift mask according to claim 1, wherein the phase shift mask is of a type in which a recess is formed in the substrate itself and is used as a shifter, and the thickness of the carbon film which can be removed by laser beam irradiation is adjusted by an ion beam. To a thickness that can be removed almost simultaneously with the residual defect portion of the shifter, and the entire region of the residual defect portion surrounded by the film and a part of the film are collectively removed at the same time to monitor Si ions. A method of correcting residual defects in a shifter, wherein the irradiation of the ion beam is terminated at the time when the number of Si ions rapidly increases or when the amount of secondary electrons greatly changes.