JP3044843B2 - Charged particle beam exposure method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charged particle beam exposure apparatus, and more particularly to a method for determining a beam deflection position before exposure for improving thermal stability of beam irradiation.

In recent years, charged particle beam exposure apparatuses have been used for pattern formation of LSIs, but high precision and high resolution have been demanded as the densities and sizes of LSIs have increased. The present invention can be used as a method corresponding to this demand.

[0003]

2. Description of the Related Art FIG. 9 is a schematic illustration of beam deflection.
In the figure, 1 is a charged particle beam, 2 is a deflection coil, 3
And the main deflection area on the object to be exposed (wafer or mask substrate), 4
Is an auxiliary deflection area (exposure field), and 5 is an arrow indicating the order of deflection.

In an actual apparatus, the deflection coil 2 has an X-direction deflection coil and a Y-direction deflection coil arranged in a plurality of stages. The beam is supplied to the main deflection area 3 by changing the current value supplied to the deflection coil 2.
And deflects the beam to the position of each sub-deflection area 4 according to the deflection order 5.

The beam deflected to the respective sub-deflection areas 4 by the deflection coil 2 performs pattern exposure in the sub-deflection areas 4 by an electrostatic deflector (not shown). Here, the deflection coil 2 is usually called a main deflection coil because it determines a deflection position in the main deflection area.

The deflection position of the main deflection area 3 is set by scanning MD marks provided at the four corners of the main deflection area 3 on the surface of the exposure object with a beam to obtain a field correction coefficient for connecting exposure fields.

[0007] The deflection coil of the charged particle beam exposure apparatus is arranged in a narrow space (in the last lens) below the column, and when a beam is deflected, a current flows through the deflection coil to generate heat.

[0008] The coil itself undergoes thermal deformation due to the temperature rise due to this heat generation, resulting in a difference in the deflection position. Also,
In the worst case, the bobbin and the pole piece of the final lens are deformed, causing the lens to be misaligned.

At the time of actual exposure, a basic beam correction coefficient is obtained in advance, and a field correction coefficient for superimposing on the object to be exposed by the MD mark is calculated.
Exposure is repeated for each unit field.

At this time, the amount of heat generation (thermal state) of the deflection coil is, of course, different between the exposure and the beam deflection for calculating the field correction coefficient because the beam is deflected differently. As a result, a deviation occurs in the deflection position with the correction coefficient obtained initially, and high-precision exposure cannot be performed. Further, if the axial displacement of the final lens occurs, high resolution of exposure cannot be maintained.

For this reason, it is necessary that the deflection coil be in a thermally stable state at any time during exposure, during beam deflection for correction coefficient calculation, during beam adjustment, or during non-exposure such as during exposure. There is.

In the conventional method, the beam is deflected in the same manner as in the exposure, even when the exposure is not performed, so that the deflection coil is always in a thermally stable state.

[0013]

In an exposure apparatus, a beam is used at the time of exposure and scanning of an MD mark for beam adjustment and calculation of a correction coefficient, but such a beam is not used for a long time. In this case, the conventional method is effective, but it is impossible to perform the same beam deflection as in the exposure (long time) within a short time such as the moving time of the stage on which the object is placed or the waiting time between the exposures.

For this purpose, it is necessary to find a thermally stable position as a deflection position in a non-exposure state for a short time. Further, in an actual device, the deflection coils for the X direction and the Y direction are independent, and the shape, resistance value, cooling state, and the like of each coil are different. Therefore, there is a slight difference in the deflection ability.

The deflection ability also differs depending on the axis orthogonality and the axis rotation of the X coil and the Y coil. That is, the thermally stable position obtained assuming that the X coil and the Y coil are equivalent is insufficient in accuracy.

Therefore, it is necessary to determine a more strict stable position in consideration of the thermal stability ratio in the X direction and the Y direction based on the thermal stable position determined that the X coil and the Y coil are equivalent. is there.

The present invention provides a high-precision, high-resolution exposure method in which a deflection coil is always in a thermally stable state, prevents a rapid thermal change, and does not cause a positional shift with a beam correction coefficient obtained in advance. Aim.

[0018]

Resolving the Problems [Means for Solving the Problems] is 1) the pattern density of the exposure field assuming equal, as the current flowing through the deflection coils during unexposed, the maximum current I _max flowing in the deflection coils during exposure A current value of 3 ^-1/2 times is set, a beam deflection position corresponding to the current value is set as a thermally stable position, and a point on the thermally stable position is set as a beam deflection position when not exposed. Charged particle beam exposure method, or 2) The average value of the amount of power supplied to the beam deflection coil at the time of exposure is gradually obtained for each time interval having a superposition period, and the average value of the final time interval at the time of exposure is maintained. The value of the current flowing through the deflection coil during non-exposure
3. A charged particle beam exposure method according to claim 1, wherein a deflection position of the beam corresponding to the current value is a thermally stable position, and a point on the thermally stable position is a deflection position of the beam when not exposed. One point on the obtained thermally stable position is the reference point A
As (x ₀ , y ₀ ); (x ₀ = y ₀ ), two points B and C are set at an arbitrary distance from the reference point. As a beam deflection position, a change amount of the field correction amount after repeating the exposure for a certain period is calculated, a direction having a smaller change amount is found from points B and C, and two points are newly set in this direction. The same processing is repeated, and the position where the amount of change is the least is set as the corrected thermal stable point Z (x ₁ , y ₁ ), and the charged particle beam is set as the deflection position of the beam when not exposed. Exposure method. Or 4) Instead of the thermally stable position determined in 1) above, 2)
The above 3) using one point on the thermally stable position obtained in step 3 as a reference point
The charged particle beam exposure method according to the above. 5) above) to correct the coordinates of the thermal stability point obtained in 2 in a ratio which is obtained from the 3), that is, the X direction in the coordinate x ₁
/ X ₀ , the charged particle beam exposure method in which the Y direction is corrected by multiplying by the ratio of y ₁ / y ₀ , or 6) the beam deflection position at the time of non-exposure is closest to the beam deflection position at which the next exposure starts This is achieved by the charged particle beam exposure method according to any one of 1) to 5) above.

[0019]

According to the present invention, the average value of the electric power supplied to the deflection coil at the time of exposure is gradually obtained for each time interval (having a mutually overlapping period), and the average value of the final time interval is maintained. Since the current flowing through the deflection coil during exposure is set, the deflection coil is always thermally stable.

Since the beam is deflected by this current to a fixed point on the thermally stable position, the beam can be easily moved to that position regardless of whether the processing time during non-exposure such as stage movement is short or long. It is possible to transfer to

Although a plurality of thermally stable positions can be provided (see FIG. 6), by setting them near the next deflection position, the deflection amount can be reduced and the beam stabilization time can be shortened.

Further, the ratio of the thermal stability of the X coil and the Y coil is determined, and the value of the current flowing through each coil is set based on the ratio. A stable state can be obtained.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Invention 1): Referring now to FIG.
Consider only directional deflection.

FIG. 2 is a diagram showing the relationship between the current I flowing through the deflection coil and the time t when the pattern density of the sub deflection area is the same. Assuming that the pattern density in the sub-deflection region 4 is the same, the current flowing through the deflection coil 2 is as shown in FIG. The average power when deflected by one column in the X direction is expressed by the following equation.

∫ (I _max t / T) ² Rdt / 2T = I _max ² R / 3 (1) Here, integration is performed from time −T to T, and I _max is a value obtained when deflection is maximized. The current value of the deflection coil, R is the resistance of the deflection coil.

That is, I _max
If a current of 3 ^-1/2 times the current is applied, the same amount of power as during exposure is obtained. In other words, since the deflection position and the current are in a linear relationship, the deflection position is 3 ^-1/2 of the maximum deflection position,
This position is the thermally stable position.

The same applies to the deflection in the Y direction. One point of the thermal stable position thus obtained is set as a beam deflection point at the time of non-exposure. (Inventions 2 and 6) However, actually, the current flowing through the deflection coil does not become as shown in FIG. 2 because the pattern density in the sub-deflection area is different or there is a place where deflection is not performed.

Therefore, the average electric energy is obtained by constantly monitoring and integrating the deflection position (or the current value flowing through the deflection coil) at a certain time interval. In the exposure apparatus, monitoring can be easily performed since the deflection position or the current value required to flow through the deflection coil to deflect the beam to the deflection position is known.

The average value of the amount of power supplied to the deflection coil at the time of exposure is gradually obtained at each time interval, and the current flowing through the deflection coil at the time of non-exposure is set so that the final average value is maintained.

One point of the thus obtained thermally stable position is defined as a beam deflection point at the time of non-exposure. FIG. 1 is an explanatory diagram of Embodiment 1 of the present invention. Figure shows the time course of the current flowing through the deflection coil, the current is always being monitored, reading the current value of the time interval T _n, and calculates the average value calculated amount of power in the time by integrating interval .

As shown in the figure _, T _n sequentially moves in small increments _,
The old data is deleted and the new data is imported to calculate the average power. The stage moving time of FIG calculates the average amount of electric power based on the current value during the time interval T _5, the average power of the time average power of interval T ₆ next time is calculated interval T ₅ The current value to be passed through the deflection coil is set so as to be equal to

Although the current flowing in the deflection coil has been considered here, the deflection position may be set by monitoring the deflection position. Since the time interval can be freely set, the time interval may be one chip exposure time or one wafer exposure time.

When processing such as stage movement is not performed, the value of the previous exposure is set. In the first embodiment,
Since the deflection position of the respective time stage moved by T _n immediately before is set, the deflection position at the unexposed (thermally stable position) changes for each of the exposure process.

FIGS. 3A to 3C are plan views showing examples of deflection positions when the stage is moved. Each drawing shows an example of the deflection position when the stage moves after the exposure processing.

FIG. 4 is a block diagram for explaining the deflection function.
In the figure, 11 is a column, 12 is a stage, 13 is a sample (object to be exposed), 14 is a CPU, 15 is a control system, 16 is a main deflection DAC (D / A
A converter and an AMP (amplifier) for both X and Y directions, 17 is a current monitor that monitors the deflection position, and 18 is a deflection position determination circuit that determines the set current of the deflection position.

FIGS. 5A and 5B are plan views showing the deflection order in the normal case and the embodiment, respectively. In FIG. 5A, in the normal case, the exposure in the main deflection area is completed, and when moving to the next main deflection area, the light beam immediately moves from the deflection end position to the deflection start position.

FIG. 5B shows the case of the embodiment, in which the exposure in the main deflection area is completed, and when moving to the next main deflection area, it is once deflected to a thermally stable position, and from this point the next main deflection area is deflected. Move to the deflection start position. At this time, by selecting a thermally stable position close to the deflection start position as shown in the figure, the amount of deflection is small, so that the beam stabilization time can be shortened. (Invention 3): FIGS. 6A and 6B are explanatory diagrams of Embodiment 2 of the present invention.

The coordinates in the figure are the currents (positions) of the X coil and the Y coil. In FIG. 6A, if the density of the pattern in the exposure field (sub-deflection area) is the same, the thermally stable position of the deflecting coil becomes a radius of 3 ^{-1 / 2} × I with the center O of the sub-deflection area as the center. Any point on the circumference of _max .

In this example, assuming that the next exposure start position is at the lower left of the figure, the beam deflection position at the time of non-exposure is determined to be point A on the thermally stable position. In this case, since the deflection characteristics of the X coil and the Y coil are the same, the deflection distance of both coils is the same. That is, A (x ₀ , y ₀ );
x ₀ = y ₀ .

In the second embodiment, a stricter thermal stability point Z (x ₁ , y
₁ ); x ₁ ≠ y ₁ is obtained as follows. First, the above point A is set as a reference point. In this case, the line segment OI _max is, X coils, deflection characteristic of the Y coil is a straight line of 45 ° to the origin with respect to street axes by the condition that is the same.

Next, in FIG. 6B, two points B and C, which are at an arbitrary distance L1 from the point A, are set as measurement reference points. The measurement reference points B and C are combined with the four points around each of them to give a total of 2 ×
The thermal stability point Z is determined using the measurement points of No. 5.

Here, the measurement point is a position to be a beam deflection position at the time of non-exposure, and the amount of change of the field correction amount for each measurement point is calculated as described later. Hereinafter, a method of obtaining the thermally stable position Z using the measurement points will be described.

Points B and C and four points around them, a total of 10 points
Assuming that the points are the beam deflection positions at the time of non-exposure, the amount of change in the field correction amount for each point is calculated, and the most thermally stable point exists in the direction in which the amount of change decreases.

Now, assuming that the direction of the arrow is this direction, it can be expected that the point Z exists in the hatched portion in the figure. Next, the same processing is performed for two points in which the distance from the reference point A in the direction of the oblique line is smaller than L1. If the direction of the stable point is changed by sequentially performing the same processing, there should be a thermal stable point Z to be found between that point and the previous measurement point.

Therefore, the pitch of the measurement is made finer, and the processing is continued down to, for example, the LSB on hardware (the smallest unit that can be realized on hardware), and the processing is continued.

Next, a description will be given of a method of evaluating the thermal stability point for each measurement point based on the amount of change in the field correction amount. First, it is assumed that the measurement point is the initial position of the beam, and the beam returns to this position (deflection position at the time of non-exposure) at the end of processing such as exposure and beam adjustment. In other words, the current that deflects to this position continues to flow through the deflection coil.

As a method for judging a change in the characteristics of the deflecting coil in this state, the second embodiment uses the above-mentioned change amount of the field correction coefficient (or the field correction amount).
As described above, the beam position given from the CPU is controlled by controlling the current flowing through the deflection coil by the correction register of the control unit to perform the field correction.

Therefore, the effect of the current flowing through the coil at the measurement point, that is, the thermal effect can be determined by investigating the amount of change in the correction coefficient depending on the measurement point for an arbitrary time or number of days. That is, the thermal stability point is a point where the variation of the field correction coefficient is the smallest.

Using the above method, the thermal stable point moves from the reference point A (x ₀ , y ₀ ) to the point Z (x ₁ , y ₁ ).
Next, a method of obtaining the field correction coefficient will be described below.

[0050] Now, the input position of the beam X, Y, the output position X ', Y' _{When, X '= G x · X} + R x · Y + H x · X · Y + O x ····· (2) _{Y '= G y · Y +} R y · X + H y · X · Y + O y ····· (3) where, G _x, G _y is the amplification factor, R _x, R _y is turnover, H
_x, H _y parallel rate, O _x, is O _y is the shift amount (offset).

[0051] Figure 7 is field a point of the four corners of the exposure field is a plan view of the exposure field describing the correction factor, b, c, d (MD mark) positional deviation amount of each [Delta] X in _{a, ΔY a;} ΔX _b , ΔY _b ; ΔX _c , Δ
Y _c; and [Delta] X _d, [Delta] Y _d, these (2), (3) are substituted into equation is _as follows seek field correction factor.

G _x = (ΔX _b −ΔX _a + ΔX _c −ΔY _d ) / 4 · xx G _y = (ΔY _d −ΔY _a + ΔY _c −ΔY _b ) / 4 · yy R _x = (ΔX _d −ΔX _a + ΔX _c −ΔX _b ) / 4 · yy R _y = (ΔY _b −ΔY _a + ΔY _c −ΔY _d ) / 4 · xx H _x = (ΔX _a −ΔX _b + ΔX _c −ΔX _d ) / 4 · xx · yy _{H x = (ΔY a -ΔY b} + ΔY c -ΔY d) / 4 · xx · yy O x = (ΔX a + ΔX b + ΔX c + ΔX d) / 4 O y = (ΔY a + ΔY b + ΔY c + ΔY d) / 4. Next, a process for obtaining a thermally stable position will be described with reference to a flowchart.

FIG. 8 is a flowchart of the processing of the second embodiment. First, the reference point A is set at 1. In step 2, measurement reference points B and C are set.

At 3, the measurement reference points B and C are
Add points and acquire data for a total of 10 points. In the processing after data acquisition, the amount of change in the field correction value is calculated according to the flows 31 to 36 on the right.

Based on this result, it is determined at 4 whether or not the position is the optimum position. If the judgment of _No. 4 is YES, the ratio x ₁ / x ₀ for correcting the X, Y coordinates of the reference point A (x ₀ , y ₀ ) of ₅ ,
to calculate the y ₁ / y _0.

If the determination in 4 is NO, the process returns to 2 and the process is repeated. Next, the flow of processing after data acquisition will be described. 31 determines the number of data acquisitions and the data acquisition cycle (hours or days).

At 32, each measurement point is set to the beam initial position. A field correction is performed in step 33, and the result is stored in a memory. At 34, it is determined whether or not all the data has been completed.

If the determination at 34 is YES, then at 36, the amount of change in the field correction amount is calculated. If the determination at 34 is NO, data is acquired at 35 and the process returns to 33. (Invention 4): In the second embodiment, a point on the thermally stable position when the pattern density of the exposure field is assumed to be equal is used as a reference point. Instead of this, the thermal point obtained in the first embodiment is used. One point on the stable position may be used. (Invention 5): In the second embodiment, the coordinate of the corrected thermal stable point Z is a value obtained by multiplying the ratio of x ₁ / x _{0 in} the X direction and the ratio of y ₁ / y _{0 in} the Y direction.

In actual operation, the beam may be corrected by correcting the thermally stable position obtained in the first embodiment by this ratio. According to each of the above embodiments, it is possible to always supply a current that makes the deflection coil thermally stable.

[0060]

According to the present invention, a high-precision, high-resolution exposure method can be obtained in which the deflection coil is always in a thermally stable state and a rapid thermal change is prevented, and no positional displacement occurs with a beam correction coefficient obtained in advance.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a current I flowing through a deflection coil and a time t when the pattern density of a sub-deflection region is the same.

FIG. 3 is a plan view showing an example of a deflection position when the stage is moved.

FIG. 4 is a configuration diagram illustrating a deflection function.

FIG. 5 is a plan view showing a deflection order in a normal case and an embodiment.

FIG. 6 is an explanatory view of Embodiment 2 of the present invention.

FIG. 7 is a plan view of a field for explaining a field correction coefficient.

FIG. 8 is a flowchart of a process according to a second embodiment.

FIG. 9 is a schematic illustration of beam deflection.

[Explanation of symbols]

 Reference Signs List 1 charged particle beam 2 deflection coil 3 main deflection area on exposure target (wafer or mask substrate) 4 sub deflection area (exposure field) 5 arrow indicating deflection order 11 column 12 stage 13 sample (exposure target) 14 CPU 15 Control system 16 Main deflection DAC (D / A converter), AMP (amplifier) 17 Current monitor that monitors deflection position 18 Deflection position determination circuit that determines deflection current setting current

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Junko Hatta 1015 Uedanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Hiroshi Yasuda 1015 Kamikodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited ( 58) Surveyed field (Int.Cl. ⁷ , DB name) H01L 21/027

Claims (6)

(57) [Claims] Assuming that the pattern densities of an exposure field are equal, a current flowing through a deflection coil at the time of non-exposure is:
3 sets the current value of ^-1/2 times, a deflection position of the beam corresponding to the current value and thermal stable position, a point on the thermal stability the position of the maximum current I _max flowing in the deflection coils during exposure Is the beam deflection position at the time of non-exposure. 2. An average value of the amount of power supplied to the beam deflection coil at the time of exposure is gradually obtained for each time interval having a superposition period, so that the average value of the final time interval at the time of exposure is maintained. A current value to be supplied to the deflection coil at the time of exposure is set, a beam deflection position corresponding to the current value is set as a thermally stable position, and a point on the thermally stable position is set as a beam deflection position at the time of non-exposure. A charged particle beam exposure method, comprising: 3. A point on the thermally stable position obtained in claim 1 as a reference point A (x ₀ , y ₀ ); (x ₀ = y ₀ ), and two points separated by an arbitrary distance from the reference point. B and C are set, the points B and C and points around them are set as beam deflection positions at the time of non-exposure, and the amount of change in the field correction amount after repeating the exposure for a certain period is calculated. The direction in which the amount of change is smaller is found, two points are newly set in this direction, and the same processing is repeated, and the position in which the amount of change is the least is corrected to the corrected thermal stable point Z (x ₁ , y ₁₎ ), Wherein the thermally stable point is a beam deflection position at the time of non-exposure. 4. The charged particle beam according to claim 3, wherein a point on the thermally stable position determined in claim 2 is used as a reference point instead of the thermally stable position determined in claim 1. Exposure method. 5. The coordinates of the thermally stable point determined in claim 2 are corrected at a ratio determined from claim 3, ie, X is added to the coordinates.
A charged particle beam exposure method, wherein the direction is corrected by multiplying the ratio by x ₁ / x ₀ and the Y direction is multiplied by a ratio of y ₁ / y ₀ . 6. The charged particle beam exposure according to claim 1, wherein the beam deflection position at the time of non-exposure is a position closest to the beam deflection position at which the next exposure starts. Method.