JP2007317863A - Electron beam exposure device, and method for inspecting mask for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic beam exposure device capable of easily inspecting a mask without opening the device to the air, and to provide a method for inspecting the mask for the device. <P>SOLUTION: The electronic beam exposure device includes: a block mask 8 for reshaping an electronic beam EB into the shape of a block pattern 8a; deflectors 13, 14 for deflecting the EB concerning one of the plurality of block patterns 8a; a lens system 21 for forming an image on the surface of a wafer 26 through the use of the EB passing the block pattern 8a; an electric current meter 27a for measuring the electric current value of the EB passing the lens system 21; and a control unit 30 for calculating the current density of the EB by dividing the electric current value by the opening area of the block pattern 8a, inspecting whether the current density exceeds the permission range of a reference value or not, and determining that the block pattern 8a has an abnormality in the case of exceeding. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electron beam exposure apparatus and a mask inspection method for an electron beam exposure apparatus.

  In addition to the optical exposure apparatus, an exposure apparatus used in the manufacturing process of a semiconductor device such as an LSI includes an electron beam exposure apparatus. In particular, in a block electron beam exposure apparatus, a plurality of block patterns made up of repetitive patterns are formed on a block mask, and a repetitive pattern is exposed on a semiconductor wafer in one shot by deflecting the electron beam to a desired block pattern. Is done. Therefore, exposure using a block electron beam exposure apparatus is suitable for manufacturing a semiconductor device having a repetition of a basic pattern, for example, a memory such as a DRAM (Dynamic Random Access Memory) or a FeRAM (Ferroelectric Random Access Memory).

  Here, if there is a pattern defect or foreign matter in the block mask, an abnormality occurs in the pattern transferred to the wafer. Therefore, usually, the pattern of the block mask is visually inspected with a microscope, and after determining that there is no abnormality in the pattern by this inspection, the block mask is mounted on the exposure apparatus.

  However, even if there is no pattern abnormality before being mounted on the exposure apparatus, the pattern of the block mask is lost or the pattern is buried by the irradiation heat of the electron beam, for example, while using the exposure apparatus. Sometimes.

  In order to visually detect a pattern abnormality occurring during use of such an exposure apparatus, the column of the exposure apparatus in a vacuum state must be opened to the atmosphere, and the block mask must be temporarily removed from the exposure apparatus. However, this requires an operation of opening the column to the atmosphere or returning it to a vacuum, which reduces the throughput of the exposure apparatus and is not suitable for mass production of semiconductor devices.

  Therefore, a block electron beam exposure apparatus is desired to detect a block mask pattern abnormality without exposing the apparatus to the atmosphere.

  As such a method, for example, after exposing a photoresist on a wafer with an electron beam transmitted through a block mask, developing the photoresist to form a resist pattern, an SEM (Scanning Electron Microscope) image of this resist pattern There is a method of visually inspecting whether there is a defect in the block pattern.

  However, with this method, if the number of block patterns formed on one block mask increases in the future, it will take a considerable amount of man-hours to visually check the SEM image, so it takes time to inspect. A problem will occur.

  Another method is disclosed in Patent Document 1.

  In the method of Patent Document 1, a pattern abnormality is detected by forming an image of a block mask pattern on a blanking aperture plate and detecting an electron beam that has passed through an opening of the blanking aperture plate.

However, with this method, the electron beam that forms an image on the wafer surface during exposure is imaged on the blanking aperture plate, so the intensity of the magnetic field and electric field generated by the electromagnetic lens must be different from that during exposure. There is a problem that it takes.
JP-A-5-41348

  An object of the present invention is to provide an electron beam exposure apparatus and a mask inspection method for an electron beam exposure apparatus that can easily inspect a mask without opening the apparatus to the atmosphere.

  According to an aspect of the present invention, an electron gun that generates an electron beam, a plurality of block patterns are formed, a mask that shapes the electron beam into the shape of the block pattern, and one of the plurality of block patterns A deflector for deflecting the electron beam; a lens system for forming an image of the electron beam that has passed through the block pattern on a wafer surface; and an ammeter for measuring a current value of the electron beam that has passed through the lens system; When the current value is divided by the opening area at the time of designing the block pattern, the current density of the electron beam is calculated, and it is further checked whether or not the current density exceeds the allowable range of the reference value. An electron beam exposure apparatus having a control unit that determines that the block pattern is abnormal.

  According to another aspect of the present invention, (a) a step of deflecting an electron beam to one of a plurality of block patterns formed on a mask for an electron beam exposure apparatus, and (b) the block pattern Measuring the amount of current of the electron beam that has passed, and (c) calculating the current density of the electron beam that has passed through the block pattern by dividing the amount of current by the opening area at the time of designing the block pattern. And (d) a mask for an electron beam exposure apparatus, comprising: (d) checking whether the current density is outside a permissible range from a reference value, and determining that there is an abnormality in the block pattern if it is outside An inspection method is provided.

  Next, the operation of the present invention will be described.

  The current density of the electron beam generated from the electron gun is substantially uniform on the block mask. However, if the current density calculated in step (c) fluctuates more than the reference value, an abnormality occurs in the block pattern, and the opening area of the block pattern is different from the design value. I can judge.

  Therefore, in the present invention, in step (d), whether or not there is an abnormality in the block pattern by examining whether or not the current density of the electron beam that has passed through one block pattern to be inspected exceeds the allowable range of the reference value. Judging.

  In this method, since it is not necessary to remove the block mask from the electron beam exposure apparatus, the apparatus need not be opened to the atmosphere. Therefore, the product wafer can be exposed immediately after the inspection of the block mask, and the reduction of the throughput of the electron beam exposure apparatus accompanying the inspection can be prevented.

  In addition, when inspecting, the intensity of the magnetic field in the lens system may be the same as that when performing drawing on the wafer. Therefore, as compared with the case of changing the intensity of the magnetic field of the electromagnetic lens as in Patent Document 1, The inspection is not time-consuming.

  Furthermore, since the inspection is performed using the amount of current density that can be calculated in the computer without using information that depends on human vision such as SEM images, the labor required for the inspection compared to the case where human inspection is performed. And time can be significantly reduced.

  As the reference value used in step (d), an average value of current density in all block patterns or a past value of current density can be adopted.

  According to the present invention, since whether or not the block pattern is abnormal is inspected depending on whether or not the current density of the electron beam passing through the block pattern deviates from the reference value beyond the allowable range, It is not necessary to open the atmosphere to the atmosphere, and inspection can be performed easily.

  Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram of an electron beam exposure apparatus according to the present embodiment.

  The electron beam exposure apparatus is a block electron beam exposure apparatus that shapes an electron beam EB with a block pattern and repeatedly exposes a pattern on a wafer in one shot. As shown in the figure, a control unit 30 such as a computer and an electron optical system. 40.

  The electron optical system 40 includes a column 39 whose inside is maintained in a vacuum, and includes a slit 4 in the column 39 for shaping the cross-sectional shape of the electron beam EB generated from the electron gun 1 into a rectangle. The electron beam EB exiting the slit 4 is focused by the first electromagnetic lens 5 and then enters the second electromagnetic lens 7 through the first deflector 6. In the second electromagnetic lens 7, the electron beam EB is converted into a parallel beam.

  Further, second and third deflectors 13 and 14 are provided at the subsequent stage of the second electromagnetic lens 7, and the electron beam EB is deflected to a predetermined block pattern 8 a of the block mask 8 by these deflectors. .

  As will be described later, a plurality of block areas are defined in the block mask 8, and a plurality of block patterns made up of repeated patterns such as lines and holes are formed in each of the block areas.

  The electron beam EB that has passed through the block mask 8 is returned to the optical axis C by the fourth and fifth deflectors 15 and 16 and then focused by the third electromagnetic lens 17.

  A blanking electrode 18 for controlling the passage of the electron beam EB is provided at the subsequent stage of the third electromagnetic lens 17, and the electron beam EB is blanked when the electron beam EB is not drawn on the wafer. Absorbed by the electrode 18.

  The electron beam EB that has passed through the blanking electrode 18 is reduced by the fourth electromagnetic lens 19 and then passed through the diaphragm 20. Thereafter, the electron beam EB is deflected by the main deflector 23 and the sub deflector 24 and is imaged on the surface of the wafer 25 by the lens system 21 including the fifth and sixth electromagnetic lenses 21a and 21b.

  The wafer 25 is placed on a stage 26 provided with a current measuring unit 27. The current measurement unit 27 includes a metal foil 29 that covers the inner surface of the hole 26a of the stage 27, and the amount of current of the electron beam EB irradiated on the metal foil 29 is measured by the ammeter 27a.

  The control unit 30 controls the magnetic field strength in the first to sixth electromagnetic lenses 5, 7, 17, 21, 22, the deflection amount in the deflectors 6, 13-16, 23, 24, and the ammeter 27 a. The

  FIG. 2 is a plan view of the block mask 8 described above.

  As shown in FIG. 2, a plurality of block areas 8b are defined in the block mask 8, and a plurality of (in this example, 100) block patterns 8a are formed in each of the block areas 8b. The block pattern 8a is a repeating pattern such as a line or a hole, but the pattern shape is not particularly limited. Further, the size of the block pattern 8a is not limited, but in the present embodiment, it is a square of 300 μm × 300 μm, for example.

  Further, the block mask 8 is manufactured from a thin plate made of silicon and has a thickness of about 20 μm.

  In the present embodiment, when the electron beam EB is deflected in the same block area 8b, the block mask 8 is kept fixed.

  On the other hand, when the electron beam EB is deflected from one block area 8b to another block area 8b, the mask moving mechanism 28 (FIG. 1) is arranged so that the deflection-destination block area 8b is within the region where the electron beam EB can be deflected. Then, the block mask 8 is moved, and the electron beam EB is deflected to select the target block pattern 8a.

  FIG. 3 is a schematic view showing an exposure method using this exposure apparatus.

  As shown in FIG. 3, the electron beam EB shaped into a rectangle by the slit 4 is deflected to a predetermined block pattern 8a of the block mask 8 to form a repetitive pattern (line in the example shown in the figure). ). Then, the electron beam EB is irradiated onto the wafer 25 in one shot, and the wafer 25 is repeatedly exposed with the pattern. In the present embodiment, by repeating the above operation while deflecting the electron beam EB by the main deflector 23 and the sub deflector 24 described above, a predetermined number of repetitive patterns are exposed on the wafer 25 shot by shot. .

  By the way, when exposure is performed in this manner, the block mask 8 made of a thin silicon plate is melted by the irradiation heat of the electron beam EB, and the block pattern 8a may be lost or buried during use.

  In order to detect such an abnormality of the block pattern 8a, in the present embodiment, the block mask 8 is inspected as follows.

  FIG. 4 is a diagram schematically showing an electron beam exposure apparatus mask inspection method according to the present embodiment, and FIG. 5 is a flowchart thereof. Note that all the following steps are performed under the control of the control unit 40.

  In the first step S1 of FIG. 5, as shown in FIG. 4, the electron beam EB is deflected to one of the plurality of block patterns 8a formed on the block mask 8, and the deflector 23 and the sub deflector 24 are used. Thus, the electron beam EB is deflected so that the current measuring unit 27 is irradiated with the electron beam EB.

  Next, the process proceeds to step S2, and the current amount I of the electron beam EB passing through the block pattern 8a is measured. This measurement is performed in an ammeter 27 a connected to the current measurement unit 27 under the control of the control unit 30. The output value of the ammeter 27 a is stored in a memory (not shown) provided in the control unit 30.

  Next, the process proceeds to step S3, where the current amount I is divided by the opening area S at the time of designing the block pattern 8a, whereby the current density J (= I / S) of the electron beam EB passing through the block pattern 8a. Is calculated. This calculation is performed in the control unit 30. The opening area S is acquired from the design data of the block pattern 8a stored in the memory (not shown) of the control unit 30.

  Next, the process proceeds to step S4, and it is determined whether or not the current density J is calculated for all the block patterns 8a in the block mask 8.

  Here, if it is determined that it has not been calculated (NO), the process proceeds to step S1, the electron beam EB is deflected to the block pattern 8a for which the current density J is not calculated, and then the block according to steps S2 and S3. The current density J of the pattern 8a is calculated.

  On the other hand, if it is determined in step S4 that the current density J has been calculated for all the block patterns 8a (YES), the process proceeds to step S5.

  Here, the current density of the electron beam EB generated from the electron gun 1 is substantially uniform on the block mask 8. However, if the current density J calculated in step S3 fluctuates more than the reference value, an abnormality occurs in the block pattern 8a, and the opening area of the block pattern has a value different from that at the time of design. I can judge.

  Therefore, in step S5, it is checked whether or not the current density J for one block pattern 8a to be inspected exceeds the allowable range of the reference value. If it exceeds (YES), there is an abnormality in the block pattern 8a. Judge that there is.

  There are the following two reference values that can be adopted in this step.

(i) Current density J _mean J _mean
The mean value J _mean refers to the mean value J _mean of the current density J in all of the block pattern 8a, is in each value of the sum obtained is divided by the number of block pattern 8a of the current density J of respective block pattern 8a .

(ii) Past value J _prev of current density J
The past value J _prev is a past current density value of the block pattern 8a to be inspected, for example, a value on the day before the inspection.

In the present embodiment, one of J _mean and J _prev is adopted.

Further, as the allowable range, a range of ± 5% of the reference value is adopted. For example, when the average value J _mean is employed as the reference value, it is determined that there is an abnormality in the block pattern 8a when the current density J is less than 0.95 × J _mean or greater than 1.05 × J _mean . The same applies when the past value J _prev is adopted as the reference value.

  If it is determined in step S5 that there is an abnormality in the block pattern 8a (YES), the process proceeds to step S6, and the block pattern 8a having the same pattern shape as the block pattern 8a in which the abnormality is found is changed to another block. It is determined whether or not the area 8b exists.

  If it is determined (YES), the process proceeds to step S7, and the mask movement mechanism 28 selects another block area 8b. Thereafter, it is confirmed that there is no pattern abnormality in the block pattern 8a according to steps S1 to S5 described above, and the wafer 25 is exposed by deflecting the electron beam EB to the pattern 8a.

  FIG. 6 is a plan view showing an example of the block mask 8 provided with two block patterns 8a having the same pattern shape as described above. In this example, two identical block areas 8b indicated by hatching are defined in the block mask 8, and the same block pattern 8a is formed in these block areas 8b.

  On the other hand, when there is no block pattern 8a having the same pattern shape (NO) in the determination in step S6 and when there is no abnormality in the block pattern 8a (NO) in the determination in step S5, the block mask according to the present embodiment. End inspection.

  According to the present embodiment described above, in step S5, by checking whether or not the current density J for one block pattern 8a to be inspected exceeds the allowable range of the reference value, the abnormality of the block pattern 8a is detected. Judgment is made.

  In this method, since it is not necessary to remove the block mask 8 from the electron beam exposure apparatus, the column 39 (see FIG. 1) need not be opened to the atmosphere. Therefore, the product wafer can be exposed immediately after the inspection of the block mask 8, and a decrease in the throughput of the electron beam exposure apparatus associated with the inspection can be prevented.

  Moreover, when the inspection is performed, the strength of the magnetic field in each of the electromagnetic lenses 5, 7, 17, 19, 21, and 22 may be the same as when drawing on the wafer 25. Compared with the case of changing the intensity, the inspection of the block mask 8 does not take time.

  Furthermore, since the inspection is performed using the amount of current density that can be calculated in the computer without using information that depends on human vision such as SEM images, the inspection is required compared to the case where human inspection is performed. Labor and time can be significantly reduced.

  The features of the present invention are added below.

(Appendix 1) an electron gun that generates an electron beam;
A plurality of block patterns are formed, and a mask for shaping the electron beam into the shape of the block patterns;
A deflector for deflecting the electron beam to one of the plurality of block patterns;
A lens system that images the electron beam that has passed through the block pattern on a wafer surface;
An ammeter that measures the current value of the electron beam that has passed through the lens system;
By dividing the current value by the opening area at the time of designing the block pattern, the current density of the electron beam is calculated, and it is further checked whether the current density exceeds the allowable range of the reference value. A control unit that determines that the block pattern is abnormal;
An electron beam exposure apparatus comprising:

  (Supplementary note 2) The electron beam exposure apparatus according to supplementary note 1, wherein the reference value is an average value of the current densities in all the block patterns.

  (Supplementary note 3) The electron beam exposure apparatus according to supplementary note 1, wherein the reference value is a past value of the current density.

(Supplementary Note 4) The mask has two or more block patterns having the same pattern shape,
The controller, when an abnormality is found in one of the block patterns, deflects the electron beam to another block pattern having the same pattern shape as the block pattern and exposes the wafer. The electron beam exposure apparatus according to appendix 1, which is characterized by the above.

(Additional remark 5) (a) The step which deflects an electron beam to one of the some block patterns formed in the mask for electron beam exposure apparatuses,
(b) measuring the amount of current of the electron beam that has passed through the block pattern;
(c) calculating the current density of the electron beam passing through the block pattern by dividing the amount of current by the opening area at the time of designing the block pattern;
(d) Checking whether the current density exceeds an allowable range of a reference value, and determining that there is an abnormality in the block pattern if it exceeds,
A method for inspecting a mask for an electron beam exposure apparatus.

  (Supplementary note 6) The mask inspection method for an electron beam exposure apparatus according to supplementary note 5, wherein an average value of the current densities in all the block patterns is adopted as the reference value in the step (d).

  (Supplementary note 7) The mask inspection method for an electron beam exposure apparatus according to supplementary note 5, wherein a past value of the current density is adopted as the reference value in the step (d).

(Additional remark 8) Two or more said block patterns of the same pattern shape are provided in the said mask for electron beam exposure apparatuses,
When an abnormality is found in one block pattern in the step (d), the electron beam is deflected to another block pattern having the same pattern shape as the block pattern, and the wafer is exposed. The inspection method of a mask for an electron beam exposure apparatus according to appendix 5.

FIG. 1 is a block diagram of an electron beam exposure apparatus according to an embodiment of the present invention. FIG. 2 is a plan view of a block mask provided in the electron beam exposure apparatus of FIG. FIG. 3 is a schematic diagram showing an exposure method using the electron beam exposure apparatus of FIG. FIG. 4 is a diagram schematically showing a mask inspection method for an electron beam exposure apparatus according to an embodiment of the present invention. FIG. 5 is a flowchart showing a mask inspection method for an electron beam exposure apparatus according to an embodiment of the present invention. FIG. 6 is a plan view showing an example of a block mask provided with two block patterns having the same pattern shape in the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electron gun, 4 ... Slit, 5 ... 1st electromagnetic lens, 6 ... 1st deflector, 7 ... 2nd electromagnetic lens, 8 ... Block mask, 8a ... Block pattern, 8b ... Block area, 13-16 ... 1st 2-5th deflector, 17 ... 3rd electromagnetic lens, 18 ... blanking electrode, 19 ... 4th electromagnetic lens, 20 ... aperture stop, 21 ... lens system, 21a, 21b ... 5th, 6th electromagnetic lens, 23 ... Main deflector 24 ... Sub deflector 25 ... Wafer 26 ... Stage 27 ... Current measuring unit 27a ... Ammeter EB ... Electron beam

Claims (5)

An electron gun that generates an electron beam;
A plurality of block patterns are formed, and a mask for shaping the electron beam into the shape of the block patterns;
A deflector for deflecting the electron beam to one of the plurality of block patterns;
A lens system that images the electron beam that has passed through the block pattern on a wafer surface;
An ammeter that measures the current value of the electron beam that has passed through the lens system;
By dividing the current value by the opening area at the time of designing the block pattern, the current density of the electron beam is calculated, and it is further checked whether the current density exceeds the allowable range of the reference value. A control unit that determines that the block pattern is abnormal;
An electron beam exposure apparatus comprising:   2. The electron beam exposure apparatus according to claim 1, wherein the reference value is an average value of the current density in all the block patterns.   2. The electron beam exposure apparatus according to claim 1, wherein the reference value is a past value of the current density. The mask has two or more block patterns having the same pattern shape,
The controller, when an abnormality is found in one of the block patterns, deflects the electron beam to another block pattern having the same pattern shape as the block pattern and exposes the wafer. The electron beam exposure apparatus according to claim 1. (a) deflecting the electron beam to one of a plurality of block patterns formed on the mask for the electron beam exposure apparatus;
(b) measuring the amount of current of the electron beam that has passed through the block pattern;
(c) calculating the current density of the electron beam passing through the block pattern by dividing the amount of current by the opening area at the time of designing the block pattern;
(d) Checking whether the current density exceeds an allowable range of a reference value, and determining that there is an abnormality in the block pattern if it exceeds,
A method for inspecting a mask for an electron beam exposure apparatus.

Images