JP4487367B2 - Defect inspection method for transfer mask - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a defect inspection method and a defect inspection apparatus for a transfer mask using silicon or the like used for transferring a circuit pattern by electron beam exposure in semiconductor manufacturing as a mask base material.
[0002]
[Prior art]
In recent years, semiconductor devices have been miniaturized, and an electron beam exposure method using a transfer mask has been developed as a technique for forming a fine circuit pattern on the semiconductor substrate. The transfer mask is used by being mounted on an electron beam exposure apparatus, but the transfer mask has a large number of various pattern openings for circuit pattern transfer. When a fine circuit pattern is drawn with an electron beam on the semiconductor substrate through the pattern opening, if there is a defect such as a foreign object or protrusion at or near the pattern opening, the shape is transferred to the semiconductor substrate. In other words, the electron beam is scattered, causing trouble in normal circuit pattern formation, and the function as a semiconductor device is not satisfied.
Therefore, in the manufacture of a transfer mask, there is a demand for a technique for inspecting foreign matters and defects in these pattern openings or in the vicinity thereof and side surfaces of the openings. Furthermore, a technique for efficiently inspecting a large number of masks is required.
[0003]
However, in the past, the pattern opening and its vicinity were inspected in detail using an optical microscope, a scanning electron microscope, or the like. However, the optical microscope has insufficient resolution, and the scanning electron microscope has a mask base material. For example, since it has a thickness of 10 μm to 20 μm, there is a problem that the entire side surface of the pattern opening is not focused.
In addition, it is very time consuming because the operator must use a means such as partially copying the pattern openings one by one on the monitor and then confirming by visual inspection.
In addition, it is difficult to determine whether the detected defects such as foreign matter or protrusions in the pattern opening of the transfer mask are actually defective when transferred, and it is determined that a good transfer mask is defective or not. There is a problem that it is very difficult to determine whether or not a defect is good, for example, by determining that a good transfer mask is good.
[0004]
[Problems to be solved by the invention]
The present invention has been devised in view of the above problems, and provides a defect inspection method and defect inspection apparatus for a transfer mask for inspecting defects such as foreign matter and protrusions in a pattern opening of a transfer mask with good accuracy and reproducibility. The purpose is to do.
[0005]
One embodiment of the present invention is an electron beam irradiation condition for exposing a plurality of non- defective transfer masks in a defect inspection method for a transfer mask used for electron beam exposure in which a pattern opening is formed on a mask substrate. A reference signal setting step for irradiating an electron beam under the same conditions and setting a passing electron signal and a secondary electron signal at the time of the electron beam irradiation as a reference signal, and an electron beam irradiation condition for exposing a transfer mask to be inspected The electron beam irradiation under the same conditions as the above, the inspection step of obtaining the passing electron signal and the secondary electron signal at the time of the electron beam irradiation, the passing electron signal and the secondary electron signal obtained in the inspection step, the reference A first determination step for individually comparing with a signal; a second determination step for forming an inspection signal by superimposing a passing electron signal and a secondary electron signal obtained in the inspection step, and comparing the inspection signal with the reference signal; Judgment worker A defect inspection method for a transfer mask, comprising:
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a configuration of an embodiment of a transfer mask defect inspection apparatus according to the present invention.
In the transfer mask inspection method of the present invention, in claim 1, the transfer mask 50 for electron beam exposure to be inspected is irradiated with the electron beam 11 and passes through various pattern openings formed in the transfer mask 50. Electrons and secondary electrons emitted from the surface of the mask substrate near various pattern openings are detected by the passing electron detector 20 and the secondary electron detector 30, and the passing electron signal and the secondary electron signal are detected. can get. Further, the passing electron signal and the secondary electron signal are taken into the defect extraction unit 70 and compared with the respective reference signals to extract the defect.
[0012]
According to a second aspect of the present invention, an inspection signal is created by superimposing the passing electron signal and the secondary electron signal, and a defect is extracted by comparing with an inspection signal.
[0013]
When the transfer mask is irradiated with an electron beam, secondary electrons are obtained as information in the vicinity of the pattern opening, and a secondary electron signal is obtained by detecting it with the secondary electron detector 30. As the intensity of the electronic signal, the electrons pass through the pattern opening itself, so that the secondary electrons are hardly detected and become large on the surface of the mask base material in other portions.
On the contrary, the intensity of the passing electron signal is large because all the electron beams pass through the pattern opening and are detected, and the mask base material, which is a shielding part, shields the electron beam. Is 0.
[0014]
An inspection signal is obtained by superimposing the secondary electron signal and the passing electron signal. When signals are superimposed in this way, the signal is weak as a whole detection range, but either a secondary electron signal or a passing electron signal is used, such as when there is a foreign object near the pattern opening or a projection in the pattern opening. If there is a characteristic part on one side, the inspection signal intensity of that part can be obtained greatly. At this time, if the threshold value is set so that a specific signal intensity or more can be detected, the characteristic part can be extracted as a defect.
[0015]
When obtaining the reference signal and the inspection signal by superimposing the secondary electron signal and the passing electron signal, superimposing after adjusting the intensity of one of the secondary electron signal or the passing electron signal to be increased or decreased. Therefore, the inspection signal intensity of the characteristic part becomes clearer and preferable. Further, it is preferable to perform signal noise removal processing before superimposing the secondary electron signal and the passing electron signal.
When performing defect inspection of the transfer mask, the processing time is shortened by simultaneously capturing the secondary electron signal that captures the surface of the pattern opening and the passing electron signal obtained through the pattern opening as an image. Sequential overlay processing can be performed.
[0016]
Further, in claim 3, the electron beam irradiation conditions for irradiating the transfer mask with the electron beam are the same as the electron beam irradiation conditions used for the electron beam exposure at the time of producing the transfer mask, and a passing electron signal and a secondary electron signal are obtained. It is intended to be.
Thus, by making the electron beam irradiation conditions at the time of inspection the same as the electron beam irradiation conditions for exposing the circuit pattern on the semiconductor substrate, the defect level extracted by this inspection method is transferred to the circuit transfer at the time of electron beam drawing. It is possible to determine whether or not the defect level is affected.
[0017]
For the reference signal used to compare the passing electron signal of the transfer mask with the secondary electron signal, prepare a plurality of non-defective transfer masks in advance and use the apparatus and method of the present invention to transfer the non-defective transfer mask. Electron beam irradiation is performed under the electron beam irradiation conditions described in claim 3 and the obtained plurality of passing electron signals and secondary electron signals are compared, and the transfer mask passes within a tolerance within the allowable range. The average values of the electronic signal and the secondary electron signal are used as reference signals for the passing electron signal and the secondary electron signal, respectively.
Further, the transfer mask to be inspected is irradiated with the electron beam under the electron beam irradiation conditions described in claim 3, the obtained secondary electron signal and the passing electron signal are compared with the respective reference signals, and a preset allowable range is obtained. If it is inside, it is judged as a good product.
[0018]
As shown in FIG. 1, the defect inspection apparatus for a transfer mask according to the present invention includes an electron gun 10 that irradiates an electron beam, a stage 40 on which the transfer mask 50 is placed and driven, and a passage that detects electrons passing through the transfer mask 50. The electron detector 20, the secondary electron detector 30 for detecting the secondary electrons of the transfer mask 50, and the passing electron signal and the secondary electron signal obtained by the passing electron detector 20 and the secondary electron detector 30 are captured. A defect extraction unit 70 that performs a process of determining whether or not the defect is compared with the reference signal, a display unit 80 that displays the defect as an image, and an apparatus control unit 60 that drives and controls the entire inspection apparatus and individual units. , And a display terminal 90.
[0019]
The transfer mask 50 is placed on the stage 40, the position of the transfer mask 50 is controlled by the apparatus control unit 60, and the inspection is performed while changing the irradiation position of the electron beam.
Further, the apparatus control unit 60 controls the operation of the program, such as input / output control of the detection signal to the defect extraction unit 70, management of image data, display of inspection results to the operator, input and management of control parameters, and the like. An operation is performed.
[0020]
The display terminal 90 includes a television monitor and a keyboard, and displays an inspection status to the worker, inputs various parameters, inputs an instruction to start and end the inspection, and the like.
[0021]
The passing electron signal and the secondary electron signal obtained by the passing electron detector 20 and the secondary electron detector 30 are taken into the defect extraction unit 70, and image processing and defect determination processing are performed. In the defect extraction unit 70, an algorithm for performing image processing and defect determination processing on the passing electron signal and the secondary electron signal is incorporated as a program. The input passing electron signal and secondary electron signal are processed by this algorithm, and if a defect is extracted, the information is displayed on the display unit 80 and output.
[0022]
【Example】
The defect inspection method for the transfer mask of the present invention will be described below with reference to examples.
First, information such as the inspection area of the transfer mask 50 and setting information such as the size and color of foreign matter and defects to be detected by inspection are input to the apparatus control unit 60 using the display terminal 90.
[0023]
Next, the transfer mask 50 to be inspected is placed on the stage 50. It is preferable to use a holder to facilitate continuous inspection.
Next, an inspection start signal is input from the display terminal 90. A control signal is sent from the apparatus control unit 60 to the stage 40 to control the position of the stage 40. On the other hand, an electron beam 11 is irradiated from the electron gun 10 onto the transfer mask 50, a predetermined range of the transfer mask 50 is scanned with the electron beam 11, and the passing electron signal and the secondary electron beam are detected by the passing electron detector 20 and the secondary electron detector 30. It is converted into an electronic signal.
[0024]
The passing electron signal and the secondary electron signal are taken into the defect extraction unit 70, subjected to image processing, compared with the respective reference signals, and subjected to determination processing as to whether or not it is a defect. And check the contents of the defect.
FIG. 2 shows a transfer mask 50 in which a pattern opening 52 is formed in a mask base 51, and schematically shows a state in which foreign matter or protrusion-like defects 53 exist on the opening side wall surface of the pattern opening 52. It is a thing. 3A shows a pattern opening image 81 and a defect image 83a of passing electrons obtained by irradiating the transfer mask 50 with an electron beam, and FIG. 3B shows an electron beam applied to the transfer mask 50. The obtained secondary electron pattern image 82 and secondary electron defect portion image 83b are shown.
[0025]
The passing electron defect image and the secondary electron defect image obtained by irradiating the foreign matter and the protrusion-like defect 53 shown in FIG. 2 with the electron beam are based on the shape and content of the defect and the appearance of the defect (shape, contrast, density). Etc.) is different. Therefore, the defect determination process for the foreign matter or the protrusion-like defect 53 is performed by comparing the passing electron signal and the secondary electron signal with the reference signal as in claim 1 to determine whether the protrusion-like defect is a defect. And a case where an inspection signal is produced by superimposing a passing electron signal and a secondary electron signal as in claim 2 and a process for determining whether or not a protruding defect is a defect as compared with a reference signal; There is.
For this reason, in order to accurately perform the defect determination process for the foreign matter or the protrusion-like defect 53, it is preferable to perform both determination processes and extract the defect.
[0026]
Hereinafter, similarly, the defect determination process by image processing is performed while moving the stage 40 to the coordinates to be inspected one after another, and when the entire measurement range is inspected, the apparatus control unit 60 displays the end of the inspection to the operator on the display terminal 90. And exit.
[0027]
【The invention's effect】
According to the present invention, it is possible to accurately and efficiently inspect foreign matters and protrusion-like defects on various pattern openings and pattern opening side wall surfaces of an electron beam exposure transfer mask.
In addition, automatic inspection is possible, and the conventional inspection time which has been enormous can be shortened, and it becomes possible to quantitatively manage foreign matter and protrusion-like defects. This demonstrates an excellent practical effect in the field of semiconductor device photofabrication processes.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a configuration of an embodiment of a defect inspection apparatus for a transfer mask according to the present invention.
FIG. 2 is a partial plan view schematically showing a state in which a defect 53 is present on the side wall surface of the opening of the pattern opening 52 of the transfer mask 50 in which the pattern opening 52 is formed in the substrate 51. FIG.
FIG. 3A is an explanatory diagram showing a passing electron pattern opening image 81 and a defect image 83a obtained by irradiating the transfer mask 50 with an electron beam.
(B) is explanatory drawing which shows the secondary electron pattern opening part image 82 and the secondary electron defect part image 83b which were obtained by irradiating the transfer mask 50 with an electron beam.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Electron gun 11 ... Electron beam 12 ... Passing electron 13 ... Secondary electron 20 ... Passing electron detector 30 ... Secondary electron detector 40 ... Stage 50 ... Transfer mask 51 ... Mask base Material 52 ... Pattern opening 53 ... Defect 60 ... Device control unit 70 ... Defect extraction unit 80 ... Display unit 81 ... Passed electron image 82 in pattern opening ... Secondary electron image on mask substrate surface 83a …… Defect portion image 83b …… Defect secondary electron image 100 …… Defect inspection apparatus

Claims (1)

In a defect inspection method for a transfer mask used for electron beam exposure in which a pattern opening is formed in a mask substrate,
A reference signal setting step of irradiating an electron beam under the same condition as the electron beam irradiation condition when exposing a plurality of non-defective transfer masks, and setting a passing electron signal and a secondary electron signal at the time of the electron beam irradiation as reference signals When,
An inspection step of irradiating an electron beam under the same conditions as the electron beam irradiation conditions when exposing the transfer mask to be inspected, and obtaining a passing electron signal and a secondary electron signal at the time of the electron beam irradiation;
A first determination step of individually comparing the passing electron signal and the secondary electron signal obtained in the inspection step with the reference signal;
A second determination step in which the passing electron signal obtained in the inspection step and the secondary electron signal are superimposed to form an inspection signal, and the inspection signal and the reference signal are compared;
A defect inspection method for a transfer mask, comprising:

Images