JP2002013922A - Misalignment inspecting method and charged beam irradiation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure misalignment with high accuracy by avoiding the formation of asymmetric potential distribution when measuring the misalignment by scanning an area including misalignment inspection marks with an electron beam. SOLUTION: During a period Tb from the finishing time t1 of one cycle of electron beam scanning to the scanning starting time t2 of the next cycle, a blanking operation is performed to the electron beam to prevent a sample from being irradiated with the electron beam. At the same time as the next cycle of scanning starts or after the starting, the blanking is terminated to perform electron beam scanning in the main scanning direction for a period Ti. Electron beam scanning is performed by rotating the blanking and the electron beam irradiation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting fine patterns, and more particularly to a method for inspecting misalignment of a semiconductor device pattern and a charged beam irradiation apparatus.

[0002]

2. Description of the Related Art There has been proposed a method using a scanning electron microscope (SEM) for a misalignment inspection in a lithography process in manufacturing a fine semiconductor device. In particular, a mark whose surface is flattened is charged, and the mark position can be measured by obtaining a potential contrast image of the base mark. Also, in this case, by setting the beam current high and strongly charging the sample surface, it is possible to quickly obtain a potential contrast image of the base mark. This is an essential element for improving the throughput of misalignment measurement. However, performing excessive electron beam irradiation on the sample surface causes a large potential difference between the beam irradiation region and other portions.

Further, in the case of a general scanning electron microscope in which electron beam irradiation is repeated based on a waveform as shown in FIG. 10, a further problem occurs. That is, the electron beam scanning is repeatedly performed in one direction, the beam position is moved in a period T from the time t ₁ when one cycle of scanning is completed to the scanning start time t _{2 in the} next cycle, and the beam irradiation is further performed. Start. For a short period from the start of beam irradiation to the start of beam scanning, beam irradiation is performed in a stopped state. Therefore, electron beam irradiation is excessively performed at this beam scanning start position. This is commonly done to avoid the presence of distortion due to the transient characteristics of the circuit.

As described above, the difference in the residence time of the electron beam between the beginning and the end of the electron beam irradiation region causes an asymmetric potential distribution in the electron beam irradiation region. This causes a difference in the measurement result depending on where in the electron beam irradiation area the mark position is detected.

FIG. 11 shows the result of measurement in the x direction using the above-described measurement method, with the arrangement of the marks slightly changed in the measurement direction on the CRT display screen. In FIG. 11, the horizontal axis is the distance from the left end of the electron beam scanning area to the mark, and the vertical axis is the misalignment measurement result.

As shown in FIG. 11, when a mark is placed on the left side of the CRT and measurement is performed under the influence of local beam irradiation due to the stay of the electron beam at the electron beam scanning start position, the misalignment measurement value Has undergone a sudden change. In this case, highly accurate measurement is impossible.

Further, in this case, even if a measurement is performed with a mark placed at the center in the electron beam irradiation area, there is a problem that accurate measurement cannot be performed because the potential distribution is different from the left and right.

[0008]

As described above, when measuring the misalignment of two marks formed on a sample,
By causing the electron beam to stay at the scanning start point during electron beam scanning, an asymmetric potential distribution is generated in the electron beam irradiation region. As a result, there is a problem in that the measurement result differs depending on where in the electron beam irradiation area the mark position is detected.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for inspecting misalignment which suppresses the formation of an asymmetric potential distribution and reduces errors in measurement results due to the position of marks when misalignment of two marks formed on a sample is performed. An object of the present invention is to provide a charged beam irradiation device.

[0010]

Means for Solving the Problems [Configuration] The present invention is configured as follows to achieve the above object.

(1) The present invention (claim 1) provides at least a first mark and a second mark of a sample having a first mark formed on the sample and a second mark formed on a layer above the first mark. Repeating the scanning of the charged beam in the main scanning direction on an area including a part of the mark 2, detecting charged particles from the sample, and acquiring a signal waveform as a function of position, Obtaining a representative position of each of the first and second marks based on the signal waveform;
Calculating a positional shift amount of the first and second marks based on the representative position of the mark, when the charged beam is repeatedly scanned in the main scanning direction, each of the charged beams has a periodicity. In scanning, the charged beam stay time at the scanning start position and the scanning stop position are equalized.

Preferred embodiments of the present invention are described below.
The scanning of the charged beam in the main scanning direction includes scanning the electron beam in one direction from a scanning start point to a scanning end point, moving the irradiation position of the electron beam to a scanning start point in the next cycle, and scanning. Blanking the electron beam moved to the start point until scanning is performed, and stopping the irradiation of the charged beam on the sample.

The scanning of the charged beam in the main scanning direction is as follows.
Scanning the electron beam in one direction from a scanning start point to a scanning end point; irradiating the charged beam at the scanning end point for a predetermined time; and moving the irradiation position of the charged beam to a scanning start point in the next cycle. And irradiating at the scanning start point the same time as the irradiation time at the scanning end point.

The scanning of the charged beam in the main scanning direction is as follows.
Scanning the electron beam in one direction from a first scanning start point to a first scanning end point;
Irradiating for a fixed time at the scanning end point, and in a direction opposite to the one direction from a second scanning start point to a second scanning end point with the first scanning end point as a scanning start point in the next cycle. Scanning the charged beam, and at a second scan end point,
Irradiating the sample with a charged beam for the same time as the irradiation time at the first scanning end point.

The first and second marks for the misalignment inspection are arranged at the center with respect to the misalignment measurement direction within the charged beam irradiation area. (2) According to the present invention (claim 6), the first and second marks formed on the sample are aligned by scanning the sample with a charged beam and detecting secondary electrons from the sample. Displacement measurement, a charged beam irradiation apparatus capable of observing the sample surface, characterized in that it comprises a control unit that switches the method of operating the charged beam between the misalignment measurement and observation of the sample surface image. I do.

[Operation] The present invention has the following operation and effects by the above configuration. When the charged beam is repeatedly scanned in the main scanning direction, the charged beam scanning in each cycle is performed by equalizing the charged beam stay time at the scanning start position and the scanning stop position at the charged beam irradiation region boundary. Since the charged beam is uniformly irradiated to avoid formation of an asymmetric potential distribution, highly accurate misalignment measurement can be performed.

Furthermore, since the charged beam scanning is performed in a reciprocating manner, the offset depending on the scanning direction can be offset, so that a more accurate misalignment measurement can be performed.

By arranging the misalignment mark at the center with respect to the measurement direction, the influence from the boundary of the charged beam irradiation area is uniformly received, so that more accurate misalignment measurement can be performed. By switching the charged beam irradiation method according to the application, the cost of the apparatus can be reduced.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] First, a misalignment inspection mark used for misalignment will be described.

FIG. 1 is a diagram showing a schematic configuration of a base mark according to the first embodiment of the present invention. FIG. 1A is a plan view showing the configuration of a misalignment inspection mark, and FIG. 1B is a cross-sectional view taken along the line AA ′ in FIG.

As shown in FIG. 1, a silicon nitride film 12 is formed on a Si substrate 11. The Si substrate 11 and the silicon nitride film 12 have a width of 0.3
Two μm grooves (first marks) 13 are formed. The groove 13 is usually arranged in a dicing area around the chip. A silicon oxide film 14 having a flat surface is formed so as to fill groove 13.

A photoresist pattern (second mark) 16 is formed on the silicon oxide film 14 via an antireflection film 15.
a and b are formed. Photoresist pattern 16
a and b are arranged so as to sandwich the groove 13 and in a direction perpendicular to the longitudinal direction of the groove 13.

Next, the formation of the mark structure will be described. This mark structure is formed at the same time in the step of forming a device structure in a chip. In addition, the illustration of the process cross-sectional view is omitted, and description will be made using the reference numerals shown in FIG. After forming the silicon nitride film 12 on the Si substrate 11, a groove 13 having a depth of 250 nm is formed in the Si substrate 11 and the silicon nitride film 12. After depositing the silicon oxide film 14 on the entire surface, the surface of the silicon oxide film 14 is flattened. At this time, the thickness of the silicon oxide film 14 in the region other than the groove 13 is 300 nm. Next, after forming an anti-reflection film 15 on the silicon oxide film 14, a photoresist pattern 16 (16a, b) as a second mark is formed by photolithography.

Next, the configuration of the length measuring SEM for performing the alignment inspection will be described.

In FIG. 2, 21 is an electron gun, 22 is a primary electron beam, 23a and 23b are condenser lenses, 24
Is a deflector, 25 is an objective lens, 26 is secondary electrons, 32 is an amplifier, 33 is an A / D converter, 34 is an image storage unit, 31
Is a deflector control unit for controlling the deflector 24, and 35 is a misalignment measurement control switching unit.

In this apparatus, the method of scanning the electron beam on the sample is switched between the normal observation of the surface image of the sample and the measurement of the misalignment by the misalignment measurement control switching unit.

Next, a method of measuring misalignment using the misalignment inspection mark will be described. The following description is of the operation after the electron beam scanning method is switched by the misalignment measurement control unit. First, the silicon wafer on which the misalignment inspection mark is formed is carried into the sample chamber of the length measuring SEM, and the position of the second mark of the misalignment inspection mark is detected by the same method as that for normal pattern observation and length measurement. Then, the wafer is moved so that the mark is located on the optical axis of the electron beam optical system.

Next, an area of the sample including the misalignment inspection mark was irradiated with an electron beam based on the scanning waveform shown in FIG. In FIG. 3, the horizontal axis represents time, and the vertical axis represents the distance of the beam irradiation position from the reference line.
The irradiation conditions were an acceleration voltage of 1900 V, a sample current of 6.
0 pA and a scan frequency of 6.4 kHz.

The scanning waveform shown in FIG. 3 will be described below. As shown in FIG. 3, a period T _b from the end time t _{1 of} one cycle of electron beam scanning to the scanning start time t ₂ of the next cycle.
During this time, a blanking operation is performed on the electron beam so that the sample is not irradiated with the electron beam. And
Scanning start simultaneously the next period or to release after the blanking start, during the period T _i, scans the electron beam in the main scanning direction. The electron beam scanning is performed by repeating the blanking and the electron beam irradiation. FIG. 4 shows an SEM photograph obtained by electron beam scanning based on the scanning waveform shown in FIG.

Next, a signal waveform is obtained using the obtained image (FIG. 4). An area 31 including the groove and the photoresist pattern is selected, and a signal waveform of the selected area 31 is obtained. FIG. 5 shows the obtained signal waveform.

Then, the representative positions of the groove and the photoresist pattern were determined by the following procedure from the signal waveform shown in FIG. As shown in a portion 42 in FIG. 5, the secondary electron signal waveform due to the groove is approximated by a higher-order function, and the mark center position X ₁ is calculated from the extreme value of the approximate function. To determine.

On the other hand, the secondary electron signal waveform resulting from the photoresist pattern has a structure having a steep peak in the pattern edge portion reflecting the three-dimensional shape of the pattern, as shown by a portion 43 in FIG. Accordingly, we determined on either side of the mark the peak position, the representative position in pixel coordinates x _2L1, x _2LR, and x _2R1, x _2Rr.

Next, the center position X _2c of the second mark is calculated as follows.

X _2c = (x _2Ll + x _2Lr + x _2Rl + x _2Rr ) / 4 Next, the amount of displacement δX between the groove and the photoresist pattern in the x direction is _calculated by _calculating the difference between the center position of the photoresist pattern and the center position of the groove. It is calculated as (x _2c −x _1c ). Furthermore, by comparing the design value the value of x _2RL -x _2LL or x _2Rr -x _2LR, determining the coefficients R for magnification correction. Finally, by multiplying the magnification correction coefficient R by the positional deviation amount δx in the X direction, the value of the positional deviation amount is represented by the dimension of distance. The displacement was measured in the y direction in the same manner.

FIG. 6 shows the results of measurement in the x direction using the above-described measurement method, with the arrangement of the marks slightly changed in the measurement direction on the CRT display screen. In FIG. 6, the horizontal axis represents the distance from the left end of the electron beam scanning area to the mark, and the vertical axis represents the misalignment measurement result.

The misalignment measurement result shows a substantially constant value regardless of the measurement position. In addition, this observation was 15 ×
10 is performed ^three times, in this case, the electron beam irradiation region is approximately 16μm along the measuring line. Therefore, a constant measurement result is shown near the center (8 μm) of the scanning area.

In this embodiment, the beam is blanked at the start of electron beam scanning to avoid biased beam irradiation. However, an aperture is provided at the start position of electron beam irradiation to block the beam, and the beam irradiation is started. It is clear that a similar effect can be obtained by avoiding this.

According to this embodiment, the electron beam is blanked during the standby time of the electron beam,
The electron beam is not irradiated on the sample surface, and the potential distribution becomes symmetric in the electron beam irradiation area. By avoiding the electron beam irradiation that is deviated in the inspection direction, highly accurate misalignment measurement can be performed.

[Second Embodiment] First, a silicon wafer having a misalignment inspection mark having the same structure as that of the first embodiment is loaded into a sample chamber of a length measuring SEM, and normal pattern observation and length measurement are performed. In the same manner as in the above, the position of the second mark of the misalignment mark was detected, and the mark was moved on the axis of the electron beam optical system.

Next, the sample was irradiated with an electron beam based on the scanning waveform shown in FIG. In FIG. 7, the horizontal axis represents time, and the vertical axis represents the distance of the beam irradiation position from the reference line. Note that the irradiation conditions are as follows:
0V, sample current 6.0pA, scan frequency 6.4kHz
z.

[0042] As shown in FIG. 7, at the end position x _e of the electron beam scanning of one cycle, during the time T ₁ of the from time t ₁ to time t _2, the in the end position x _e of the electron beam scanning,
Irradiation is performed for a while with the electron beam stopped. In this case, time T ₁ for performing electron beam irradiation was equal to the beam irradiation time T ₂ in the electron beam scan start position x _s. Thereafter, the same electron beam scanning was repeatedly performed based on this scanning waveform.

In FIG. 7, T ₁ and T ₂ are shown with different time intervals. In practice, however, between the between the time t ₃ from the time t _2, the electron beam end position x
because it includes the time to move to the start position x _s of _e,
It is equal to the residence time T ₂ of the electron beam in the stay time T ₁ and the start position x _s of the electron beam at the end position x _e. Next, misalignment measurement was performed on the image obtained by this scanning by the same method as in the first embodiment.

FIG. 8 shows the result of the misalignment measurement by using the above-described measurement method and changing the arrangement of the marks slightly in the measurement direction in the CRT screen. FIG.
In the graph, the horizontal axis represents the distance from the left end of the electron beam scanning area to the mark, and the vertical axis represents the misalignment measurement result. As shown in FIG. 8, the measured value tends to increase as approaching both ends of the irradiation area of the electron beam. This is the effect of local beam irradiation due to the stay of the electron beam at the boundary of the electron beam irradiation area. This tendency becomes more remarkable as it approaches the boundary. However, the measurement result near the center (8 μm) of the irradiation area can obtain a substantially constant value. Therefore, it is possible to obtain a constant measurement result, so that it is preferable to perform the measurement substantially at the center except for the periphery of the electron beam irradiation area.

As shown in the present embodiment, when the electron beam scans the irradiation area in one direction, the electron beam stays at both ends of the irradiation area, and the staying time is made the same so that the inspection direction can be improved. Biased electron beam irradiation can be avoided, and highly accurate misalignment measurement can be performed.

Further, by measuring the positional deviation near the center of the electron beam irradiation area, the potential distribution becomes symmetric, so that the measurement can be performed with higher accuracy.

[Third Embodiment] First, a silicon wafer having a misalignment inspection mark having the same structure as that of the first embodiment is loaded into a sample chamber of a length measuring SEM, and normal pattern observation and length measurement are performed. The position of the second mark of the misalignment mark was detected in the same manner as described above, and the mark was moved on the axis of the electron beam optical system.

Next, the region of the sample including the misalignment mark was irradiated with an electron beam based on the scanning waveform shown in FIG. The irradiation conditions were as follows: an acceleration voltage of 1900 V,
The irradiation conditions were a sample current of 6.0 pA and a scan frequency of 6.4 kHz.

The electron beam scanning based on the scanning waveform shown in FIG. 9 will be described. As shown in FIG. 9, by scanning the electron beam in one direction, the electron beam at time t ₁ comes to the position x ₁ is the left end of the scanning area (one end), to stay electron beam until time t _2. After staying at one end, the electron beam is scanned in one direction and the other direction. When the electron beam comes to the position x ₂ is the other end of the scanning area at time t _3, after allowed to stay electron beam until time t _4, also scans the electron beam in one direction. Thereafter, electron beam irradiation was performed by triangular wave scanning that repeated the scanning. However, here, the time T ₁ (t ₂₎ from the end of the beam scanning to the start of the next beam scanning.
−t ₁ ) and T ₂ (t ₄ −t ₃ ) are the same.

Next, misalignment measurement was performed on the image obtained by this scanning in the same manner as in the first embodiment.

When the misalignment is measured using this scanning method, the same result as that shown in FIG. 6 can be obtained.

As described above, the electron beam is scanned in the left and right direction with respect to the irradiation area, and the electron beam stays at both ends of the irradiation area, and the staying time is the same. Beam irradiation can be avoided, and highly accurate misalignment measurement can be performed.

It is apparent that the same effect can be obtained even when the measurement is performed in a state where the time from the end of the beam scanning to the start of the next beam scanning is eliminated.

The present invention is not limited to the above embodiment. For example, in the above embodiment, an ion beam may be used as the charged beam.

In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0056]

As described above, according to the present invention, when the charged beam is repeatedly scanned in the main scanning direction, the charged beam stay time at the scanning start position and the scanning stop position in the periodic charged beam scanning is determined. By making them equal, the charged beam is uniformly irradiated on the boundary of the charged beam irradiation area, and the formation of an asymmetric potential distribution is avoided, so that highly accurate misalignment measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a positioning mark according to a first embodiment.

FIG. 2 is a diagram showing a schematic configuration of a length measurement SEM used for alignment measurement.

FIG. 3 is a scanning waveform diagram used for electron beam scanning of a region including a misalignment inspection mark according to the first embodiment.

FIG. 4 is an SEM photograph obtained by scanning an area including a misalignment inspection mark with an electron beam.

FIG. 5 is a waveform diagram of secondary electrons obtained when the SEM photograph shown in FIG. 4 is obtained.

FIG. 6 is a diagram illustrating a result of measurement performed by changing the arrangement of marks in a measurement direction.

FIG. 7 is a scanning waveform chart used when an area including a misalignment inspection mark according to the second embodiment is scanned with an electron beam.

FIG. 8 is a diagram showing a result of measurement performed by changing the arrangement of marks in a measurement direction.

FIG. 9 is a scanning waveform chart used when an area including a misalignment inspection mark according to the third embodiment is scanned with an electron beam.

FIG. 10 is a scanning waveform diagram used when a region including a misalignment inspection mark according to the related art is scanned with an electron beam.

FIG. 11 is a diagram illustrating a result of measurement performed by changing the arrangement of marks in a measurement direction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Si substrate 12 ... Silicon nitride film 13 ... Groove 14 ... Silicon oxide film 15 ... Anti-reflection film 16a, b ... Photoresist pattern

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F067 AA13 AA15 AA54 BB01 BB04 BB21 CC17 EE04 HH06 JJ05 KK04 LL00 NN05 QQ02 QQ14 SS13 TT01 2G001 AA03 BA07 CA03 GA01 GA06 HA01 HA07 HA13 JA02 JA03 JA03 JA03 KA03 LA03

Claims (6)

[Claims] A first mark formed on the sample and a region including a part of the second mark formed on the first mark; Repeating the steps, detecting charged particles from the sample, obtaining a signal waveform as a function of position, and obtaining a representative position of the first and second marks based on the signal waveform, respectively, Calculating a positional shift amount of the first and second marks based on a representative position of the first and second marks, when the charged beam is repeatedly scanned in the main scanning direction, A misalignment inspection method characterized by equalizing a charged beam residence time at a scanning start position and a scanning beam stop position in each periodic charged beam scanning. 2. The method according to claim 1, wherein the scanning of the charged beam in the main scanning direction includes: moving an irradiation position of the electron beam, which scans the electron beam in one direction from a scanning start point to a scanning end point, to a scanning start point in the next cycle. 2. The misalignment inspection method according to claim 1, further comprising: blanking the electron beam moved to the scanning start point until scanning is performed, and stopping irradiation of the charged beam to the sample. 3. The scanning of the charged beam in the main scanning direction includes a step of scanning the electron beam in one direction from a scanning start point to a scanning end point, and a step of irradiating the charged beam at the scanning end point for a predetermined time. 2. The method according to claim 1, further comprising: moving an irradiation position of the charged beam to a scanning start point in a next cycle; and performing irradiation at the scanning start point for the same time as the irradiation time at the scanning end point. Inspection method for misalignment described in 2. 4. The scanning of the charged beam in the main scanning direction includes: a step of scanning the electron beam in one direction from a first scanning start point to a first scanning end point; Irradiating for a fixed time at an end point, and charging a beam in a direction opposite to the one direction from a second scan start point to a second scan end point with the first scan end point as a scan start point in the next cycle. 2. The method according to claim 1, further comprising the step of: scanning the sample with a charged beam at the second scanning end point at the same time as the irradiation time at the first scanning end point. Misalignment inspection method. 5. The misalignment inspection according to claim 1, wherein the first and second marks for misalignment inspection are arranged at the center in the misalignment measurement direction within the charged beam irradiation area. Method. 6. A sample is scanned with a charged beam to detect secondary electrons from the sample, thereby measuring the misalignment of the first and second marks formed on the sample and measuring the misalignment of the sample surface. A charged beam irradiation apparatus capable of observing, comprising: a control unit that switches an operation method of the charged beam between the misalignment measurement and the observation of a sample surface image.