JP2512131B2 - Electronic beam exposure method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electron beam exposure method.

Conventional technology When performing electron beam exposure, in the resist,
The irradiated electrons are scattered. Therefore, the exposure area becomes wider than the irradiation area, and when the drawn figure becomes smaller than the electron scattering length, or when multiple drawn figures become closer than the electron scattering length, the influence of scattering becomes remarkable, and the pattern of the desired size is obtained. Will not be obtained. This is conventionally known as the proximity effect. Generally, in order to form a fine pattern using an electron beam exposure method, exposure is performed with proximity effect correction taking into consideration the scattering intensity distribution of electrons and the shape of the pattern and the distance between another pattern existing around a certain pattern. Law is needed.

Generally, the scattering intensity distribution of electrons is expressed by a double Gaussian distribution as shown below, where X ₁ is the coordinate of the center of the beam to be irradiated and E (r) is the scattering intensity at the coordinate.

Here, α represents the spread of forward scattering generated in the resist, β represents the spread of backscattering caused by reflection from the substrate, and η represents the reflection coefficient of the backscattering.
When the pattern represented by the area S ₁ is actually exposed with the irradiation amount Q _E , the absorption amount Q (r) at the coordinate r is Q (r) = _{S 1} Q _E · E (r−X ₁ ) d ² X It is represented by ₁ (2). Next, when the resist at coordinate r is removed for the first time after development when the exposure dose Q _E1 is exposed to this pattern, the dissolution absorption amount Q _C of the resist is Q _C = _S1 Q _E1 · E (r−X ₁ ) d ² X ₁ (3) In the case of correcting the proximity effect, in order to form a target pattern, the absorption amount Q (r) in the equation (2)
There greater than the dissolution absorption Q _C is a region existing in the desired pattern, in regions where there is no pattern of interest seeking dissolved absorption Q _C is smaller than the irradiation area S ₁ and the irradiation amount Q _E1, this irradiation area S ₁ And exposure with a dose Q _E1 corrects the proximity effect. The above is a description of the case where a positive resist is used, but for a negative resist, the proximity effect can be corrected by a completely similar method if the resist remains in a portion where the resist is considered to be removed in the above. .

Generally, in order to perform proximity effect correction, a large number of evaluation points are set on the contour line of a target pattern, an equation is set up so that equation (3) is satisfied on all the evaluation points, and the above condition is set as a solution of the equation. Determine the irradiation area to be satisfied and the irradiation amount. At this time, the forward scattering spread α and the backward scattering spread β of the electron beam scattering intensity distribution used in the equation (3),
Reflection coefficient η The dissolved absorption Q _C of the resist is a process-dependent parameter. However, these parameters depend on the resist material, the resist film thickness, the resist development condition, the substrate material, the electron beam acceleration voltage, etc., and if any one of these conditions is different, it is recalculated according to the condition. There is a need. Here, of the above parameters, the dissolution absorption amount Q _C of the resist can be easily defined because it can be defined as the irradiation amount when the film thickness of the resist becomes zero for the first time when a parameter that is much wider than the electron scattering length is irradiated. You can ask. Therefore, a method for easily obtaining α, β, η among the parameters is required. Further, in the equation (3), it is generally known that α is about 0.1 to 0.3 μm, and even if it is approximated to α = 0, the correction effect can be obtained. Therefore, α, β, and η need not be obtained at the same time. Alternatively, only β and η may be obtained. Conventionally, the following method has been performed to obtain the parameters α, β, η.

(Conventional example 1) n smallest irradiation patterns that can be exposed by the exposure apparatus used are separated by a distance that is not affected by electron scattering, and the irradiation amount is Q ₁ <Q ₂ <Q ₃ <... <Q _n . Expose. After development,
Each dose _{Q 1, Q 2, Q 3} , ..., the radius of the circular portion where the resist is removed with respect to _{Q n r 1, r 2,} r 3, ..., to measuring the r _n. Next, the dose Q _E is plotted against the resist removal dimension r to obtain the scattering intensity distribution curve shown in FIG. Then, assuming that the scattering intensity distribution curve satisfies the condition shown in the equation (3), the parameters α, β, η of the electron scattering intensity distribution equation are obtained by using the least square method. In the above method, the irradiation pattern may have any shape and size in principle, but the irradiation pattern having the minimum dimension that can be exposed is generally used for the following reason. For one, it is generally known that α is 0.1 to 0.3 μm and β is 2 to 4 μm. In order to accurately measure the portion due to the influence of forward scattering, a length of 0.1 μm or less is required. This is because it is necessary to measure the length. Second, the least-squares method is used to finally obtain the parameters α, β, and η from the observed data. However, if equation (3) is used as it is, then a system of nonlinear equations must be solved. Is very difficult. Therefore, under the condition that the irradiation pattern is very small, the irradiation pattern having the minimum dimension that can be exposed is used in order to simplify the equation by ignoring the integral of the expression (3).

(Conventional Example 2) A curve satisfying the condition of the expression (3) can be obtained without performing length measurement. As shown in FIG. 11, when irradiation patterns L ₁ and L ₂ composed of exactly the same two line patterns are exposed with the same irradiation amount at a distance d, the absorption at the midpoint O between the two line patterns. The quantity is expressed as a function of the distance d. At this time, when the amount of dissolution and absorption is realized at the middle point O, the resist shape after development has the resist between the two lines removed.
Therefore, _{assuming that} the dose when the resist between the _two line patterns L ₁ and L ₂ is first removed is a critical dose, some distances d ₁ <d ₂ <d ₃ <... <d _n Dose E ₁ for removing the resist between the _two line patterns L ₁ and L ₂ having
E _2, E _3, ..., by determining the E _n, such as Fig. 12 (3) can be obtained a characteristic curve that satisfies the equation, each parameter by using a least-squares method with respect to this curve Desired. Here, it is considered that the resist between the _two line patterns L ₁ and L ₂ is removed, but it is considered that the resist between the line patterns is simultaneously removed when a plurality of lines having the same size are arranged at regular intervals. However, it is exactly the same, and the phenomenon of the same condition is simultaneously observed by the easier observation by this method, so that the statistically reliable effect can be obtained. This conventional example is the journal Vacuum Science Technology J.Vac.Sci.Technol.Vo119.No4.1286-1290 (198
It is described in 1). Although the positive type resist has been described above, the same applies to the negative type resist if the resist removed portion is defined as the resist residual portion and the dissolved absorption amount is defined as the insoluble absorption amount.

However, in the method shown in Conventional Example 1, it is necessary to accurately measure a large number of sub-micron patterns or less in order to obtain the scattering intensity distribution curve shown in FIG. Since the boundary between the resist and the substrate with such a fine pattern cannot be clearly identified, accurate length measurement cannot be performed. As described above, the conventional method requires a great deal of labor and has a problem that an accurate result cannot be obtained.

Further, the method shown in Conventional Example 2 can eliminate the labor of length measurement for obtaining the characteristic curve shown in FIG. 12, but the resist between the line patterns is not completely dissolved, so that the linear resist is not formed. It is not easy to judge whether or not it is separated from the substrate. In addition, since all irradiation patterns have areas where the integral of equation (3) cannot be ignored,
Equation (3) that satisfies the characteristic curve shown in Fig. 12 is a very complicated equation, and the nonlinear least squares method must be used to obtain each parameter α, β, η from the curve in Fig. 12, and the numerical calculation There was a problem that the labor required for it would be enormous.

The present invention has been tried in view of the above-mentioned problems, and an electron beam exposure method capable of realizing shortening of measuring time and eliminating labor by complicated numerical calculation for obtaining each parameter from observation data. The purpose is to provide.

Means for Solving the Problems According to the present invention, a two-dimensional periodic pattern in which a non-irradiation part is surrounded by a linear irradiation part is formed as a block having a size much larger than a scattering length of an electron beam, and the block is irradiated. As the pattern, a line width of the irradiation part is smaller than the length of backscattering length in electron beam exposure, and a plurality of irradiation patterns having different sizes of the non-irradiation part or the irradiation part are respectively provided with different irradiation doses. After exposure and development using a positive resist, the minimum irradiation dose at which the resist in the center of the non-irradiated part is removed is set as the critical irradiation amount, and the irradiation pattern with different dimensions of the non-irradiated part or irradiated part is used. On the other hand, an electron beam exposure method in which the distribution of the scattered intensity of the electron beam is obtained by obtaining the critical irradiation amount.

In addition, a two-dimensional periodic pattern in which the non-irradiated portion is surrounded by linear irradiation portions is formed as a block having a size much larger than the scattering length of the electron beam, and the block is set as the irradiation pattern. Is smaller than twice the backscattering length in electron beam exposure, and a plurality of irradiation patterns with different dimensions of the non-irradiated part or the irradiated part are exposed with different irradiation doses and developed. After that, in the case of the positive type resist, the critical dose is determined for each irradiation pattern having different dimensions of the non-irradiated part or the irradiated part, with the minimum irradiation amount for removing the resist at the center of the non-irradiated part as the critical irradiation amount. This is an electron beam exposure method for obtaining the scattered intensity distribution of the electron beam.

Action The present invention has the above-described configuration, and the critical irradiation amount that simultaneously realizes the dissolved absorption amount or the insoluble absorption amount of the resist at a plurality of positions with respect to the irradiation pattern of a predetermined size by only confirming the presence or absence of the resist in a relatively large area. Therefore, the characteristic curve of the critical dose and the size of the irradiation pattern or the resist removal size can be obtained without using length measurement.

Further, according to the present invention, the irradiation pattern of 2
If the length of the dimensional period is shorter than the electron backscattering length, the absorption distribution due to backscattering of the electron beam in the resist will be uniform regardless of the irradiation part or non-irradiation part, and the value of the absorption amount will be On the other hand, it can be determined only by the ratio of the irradiated portion and the non-irradiated portion. Therefore, by subtracting the amount of backscattered absorption from the total amount of electron beam absorption,
Since the amount of absorption due to only forward scattering can be evaluated, the value of each parameter can be obtained by a simple analysis.

Example (Example 1) FIG. 1 is a diagram showing a mesh-like irradiation pattern in a first example of the present invention. In the present invention, a two-dimensional periodic pattern from a mesh pattern is used as the irradiation pattern 1 as shown in FIG. The irradiation portion 2 is a mesh pattern area having a line width u, and the non-irradiation portion 3 is a square area having one side w. This mesh-like pattern is much larger than the electron scattering length, and can be easily recognized with an optical microscope.
For example, it is created with a size of about 100 μm square, and this is regarded as one block. When this one block pattern is exposed, the scattering of electrons reaches only a few microns.
The absorption amount at the center of the non-irradiated part 3 existing in the block is equal in all non-irradiated parts 3 except the non-irradiated part 3 existing within several microns from the end of the block. Therefore,
When the irradiation pattern 1 was exposed at an irradiation amount such that the absorption amount at the center of the non-irradiated portion 3 became a dissolution absorption amount, the resist of the entire block was simultaneously removed after development, and the exposure was performed at a lower irradiation amount. In some cases, a mesh pattern can be seen.

FIG. 2 is a diagram showing the arrangement of blocks in the first embodiment of the present invention. Block 4 is the two-dimensional periodic pattern shown in FIG. The line width of the irradiation part 2 of each block 4
u ₁ ≤u ₂ ≤u ₃ ≤ ... ≤u _n , the size of the non-irradiated portion 3 is w ₁ ≤w ₂ ≤w ₃
≦ ... ≦ w _n , and n pieces are arranged in the horizontal direction. The same components are arranged in m rows in the vertical direction and arranged as shown in FIG. In addition, in the arrangement shown in FIG.
Exposure is performed with a dose of Q ₁ ≤Q ₂ ≤Q ₃ ≤ ... ≤Q _m . After developing the sample exposed to each block 4 shown in FIG. 2 under predetermined conditions, the blocks 4 in each column are sequentially observed from the first row, and the resist of the entire block 4 is removed from the mesh pattern to form a large hole. Find the critical dose Q _E that gives the desired shape for u or w in each column. That is, the irradiation unit 2 and the non-irradiation unit 3
The irradiation dose at which the amount of absorption at the center of the non-irradiation part 3 of the mesh-shaped irradiation pattern having is equal to the dissolution absorption amount Q _C is the critical irradiation amount Q _E for the dimensions u and w. Using the critical irradiation dose Q _E obtained by the above operation, each parameter can be obtained by setting equation (3) with respect to the center point of the non-irradiated portion 3.

(Example 2) In Example 2, the absorption distribution by backscattering can be made uniform irrespective of the irradiation part and the non-irradiation part by utilizing the two-dimensional periodicity, and the equation (3) can be simplified. . Below, STEP
As (1), the absorption amount distribution due to backscatter becomes uniform 2
A method of obtaining the period of the dimensional periodic pattern will be described.

STEP (1) Arrange the blocks composed of a mesh pattern in the same arrangement as shown in FIG. In the horizontal direction, the ratio of the area of the irradiated portion to the area of the non-irradiated portion within one block having a mesh pattern is made equal. Ie At, u and w are simultaneously changed so that ξ becomes 1/2. In this way, w and u are simultaneously increased so that the ratio of the irradiation area to the non-irradiation area of each block becomes constant in the lateral direction,
Exposure is performed by increasing the irradiation amount in the vertical direction. FIG. 3 is a characteristic curve diagram showing the relationship between the critical irradiation dose and the non-irradiated portion in the second embodiment of the present invention. The critical dose Q _E is obtained for each w and the plot of 1 / Q _E vs. w / 2 is performed to obtain a curve as shown in FIG. Further, FIG. 4 shows several absorption distributions u, w on the line AA ′ of the irradiation pattern 1 shown in FIG.
On the other hand, the absorption distribution due to forward scattering and the absorption distribution due to back scattering are shown separately. The curve in FIG. 3 and the absorption distribution diagram in FIG. 4 show that the electron scattering intensity distribution is a square Gaussian distribution, and w is α << w + u << β
The critical dose Q _E does not change with respect to the value of. That is, when the size w of the non-irradiated portion 3 is w ≧ wα with respect to wα shown in FIG. 3 when a pattern on the mesh is irradiated, the contribution of the forward scattering of the absorption distribution of electrons is completely ignored. And w + u ≦ 2Wβ with respect to wβ shown in FIG.
, The contribution due to backscattering of the electron absorption distribution is w +
Independent of u, it is uniform regardless of the irradiation portion 2 and the non-irradiation portion 3, and depends only on the ratio of the irradiation area to the non-irradiation area.
The value of Qβ shown in the figure is Becomes An example of obtaining α, β, η by a very simple method using wα, wβ obtained in STEP (1) will be described below.

Method for obtaining η (1) w + u for the values wα and wβ obtained in STEP (1)
Using the conditions of ≦ 2wβ and wα ≦ w, w of each block of the first embodiment is fixed, u is changed, and the critical irradiation dose Q _E is obtained for each u. 1 / Q _E vs. ξ = u Plotting ² + 2uw / (u + w) ² gives the straight line shown in FIG. At this time, the right side of the equation (3) representing this straight line is wα ≦ w, w
The absorption due to forward scattering becomes zero under the condition of + u ≦ 2wβ, and the absorption due to back scattering is determined by the areas of the irradiated and non-irradiated parts. Becomes Therefore, equation (3) is Therefore, 1 / Q _C · η / η + 1 can be obtained from the slope of the straight line in FIG. 5, and thus η can be obtained from Q _C.

Method for obtaining η (2) w + u for the values wα and wβ obtained in STEP (1)
Using the conditions of ≦ 2wβ and wα ≦ w, u of each block of Example 1 is fixed and w is changed, and the critical dose Q _E is determined for each value of w, and 1 / Q _E pair ξ ＝ u ² ＋ 2uw / (u ＋
When w) ² is blotted, the straight line shown in FIG. 5 is obtained in the same manner as in the determination method (1). Therefore, η is obtained from this inclination.

Method for obtaining α wα ≤ wα and wβ obtained in STEP (1)
Under the condition of u and u + w ≦ 2wβ, u of each block of Example 1 is fixed, w is changed, critical irradiation dose Q _E is determined for each w, and 1 / Q _E vs. w / 2 is plotted. Then, a curve as shown in FIG. 6 is obtained. At this time, if the right side of the equation (3) is expressed as (irradiation dose Q _E ) − (absorption amount when the non-irradiated part is irradiated with the irradiation dose Q _E ), the absorption amount due to forward scattering is Becomes This is because each non-irradiated portion can be regarded as an isolated pattern when considering the contribution of forward scattering under the above conditions. The backscattering absorption is Represented by Therefore, equation (3) is Next to Becomes Therefore, the QE in Fig. 6 By plotting and converting W / 2 vs. QE ', the straight line shown in FIG. 7 is obtained. 1 / α is obtained from the slope of this straight line.

Method of obtaining β (1) Wβ <with respect to the values Wα and Wβ obtained in STEP (1)
Under the conditions of <u, W α ≦ W, u of each block of Example 1 is fixed, W is changed, and the critical dose QE for each W is changed.
In the same way as for how to obtain α Then, when a blot of w / 2 vs. Q _E 'was converted, a straight line similar to that in FIG. 7 is obtained, and 1 / β can be obtained from the slope. This is because the amount of absorption due to forward scattering is zero under the condition of wα ≦ W, and because of wα << u, the back side of the non-irradiated portion can be regarded as an isolated pattern. And thus This is because

Method for obtaining β (2) u << for the values Wα and Wβ obtained in STEP (1)
Under the conditions of wβ and Wα ≦ W, u of each block of Example 1 is fixed, W is changed, and the critical irradiation dose for each W is changed.
Seeking Q _E, to obtain a straight line as shown in FIG. 8 is plotted (w / ²⁾ 2 pairs lnQ _E. Here, according to the condition of Wα ≦ W,
The amount of absorption due to forward scattering becomes zero, and u << wβ
From the condition of, the integral for the backscattering can be ignored in the equation (3), Next Therefore, 1 / β ² can be obtained from the slope of the straight line in FIG.
Therefore, in the present embodiment, when performing the proximity effect correction, the important parameters η and β can be easily evaluated by different methods.
The validity of the Bodel function of the electron beam scattering intensity distribution can also be evaluated by comparing As described above, w (α) obtained in STEP (1) is used to obtain η (1), η is obtained (2), α is obtained, β is obtained (1), and β is obtained (2). ) Has been mentioned, the dependency of these methods is shown in FIG. That is, in the method for obtaining α and the method (1) for obtaining β, it is necessary to obtain the value first, but in the method (2) for obtaining β, wα and w
It can be implemented if only the value of β is known. Further, in order to obtain η, either the method for obtaining η (1) or the method for obtaining η (2) may be performed.

Although all of the above examples have been performed on the positive type resist, it is assumed that the resist remains on the negative type resist even when the resist is removed. These embodiments can be done in the same way. According to the present embodiment, as the irradiation pattern, a very large change in the entire pattern that can be easily confirmed by an optical microscope is used as the observation data. Since the change of the entire pattern is a change that occurs at the same time for a large number of resists under the same condition, the results obtained in this example are the same as those obtained by repeatedly measuring and averaging the same phenomenon. Have meaning. Further, since all the parameters are obtained from the slopes of the straight lines obtained from the observation data, it is possible to evaluate the respective parameters as those in which variations in the irradiation size and the irradiation amount of the exposure apparatus are averaged and removed.

EFFECTS OF THE INVENTION As can be seen from the above description, according to the present invention, in order to obtain the parameters α, β, and η necessary for performing the proximity effect correction, the resist dimensions after development are not measured, The characteristic curve of the irradiation pattern size and the irradiation dose can be drawn only by observing the resist shape pattern, which is a very easy operation. Furthermore, by making the period of the two-dimensional periodic pattern of the irradiation pattern shorter than the backscattering length of the electron beam, the absorption amount of the electron beam in the resist due to backscattering can be easily obtained from the size of the irradiation pattern. In the required analysis method,
Since the absorption amount of only forward scattering and the absorption amount of only back scattering can be easily evaluated, each parameter can be obtained by a simple analysis method.

[Brief description of drawings]

FIG. 1 is a diagram showing a mesh-like irradiation pattern in the first embodiment of the present invention, and FIG. 2 is a diagram showing an arrangement of blocks formed in the mesh-like pattern in the first embodiment of the present invention. FIG. 3 is a characteristic curve diagram showing the relationship between the critical irradiation dose and the non-irradiated portion in the second embodiment of the present invention, and FIG. 4 is a diagram showing the absorption amount distribution in the second embodiment of the present invention. FIG. 5 is a characteristic curve diagram showing the relationship between the area ratio of the irradiation part and the critical irradiation amount in the second embodiment of the present invention, and FIG. 6 is the critical irradiation amount and non-irradiation part in the second embodiment of the present invention. FIG. 7 is a characteristic curve diagram showing the relationship with FIG. 7, and FIG. 7 is a characteristic curve diagram showing the relationship between the critical irradiation dose and the non-irradiation area in the second embodiment of the present invention.
FIG. 9 is a characteristic curve diagram showing the relationship between the critical irradiation dose and the non-irradiated portion in the second embodiment of the present invention, and FIG. 9 is a subordinate of the method for obtaining α, β, η in the second embodiment of the present invention. FIG. 10 is a diagram showing the relationship, FIG. 10 is a characteristic curve diagram showing the relationship between the conventional irradiation amount and the resist removal dimension, FIG. 11 is a layout diagram of irradiation patterns consisting of conventional line patterns, and FIG. 12 is conventional irradiation. It is a characteristic curve figure which shows the relationship between quantity and a line space. 1 ... Irradiation pattern, 2 ... Irradiation part, 3 ... Non-irradiation part,
4 ... Block

Front page continuation (72) Inventor Yoko Hamaguchi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP 57-83029 (JP, A) JP 58-10825 (JP) , A)

Claims (2)

(57) [Claims] 1. A block composed of a two-dimensional periodic pattern in which a non-irradiation part is surrounded by a linear irradiation part and having a size much larger than a scattering length of an electron beam, and the block is an irradiation pattern, and the irradiation part is provided. The line width of is smaller than the length of the backscattering length in electron beam exposure, and a plurality of irradiation patterns with different sizes of the non-irradiated part or the irradiated part are exposed with a plurality of different irradiation doses, respectively. After development, in the positive type resist, the minimum irradiation dose at which the resist in the center of the non-irradiated part is removed is taken as the critical irradiation amount, and the critical irradiation amount for each irradiation pattern with different dimensions of the non-irradiated part or the irradiated part is set. An electron beam exposure method characterized in that a scattering intensity distribution of an electron beam is obtained by obtaining the distribution. 2. A two-dimensional periodic pattern in which a non-irradiated portion is surrounded by a linear irradiated portion is formed into a block having a size much larger than a scattering length of an electron beam, and the block is used as an irradiation pattern, and the periodic pattern is used. In which the period is smaller than double the backscattering length in electron beam exposure, a plurality of irradiation patterns with different sizes of the non-irradiated part or the irradiated part are exposed using different irradiation doses. After the development, in the positive type resist, the minimum irradiation dose at which the resist in the center of the non-irradiated part is removed is set as the critical irradiation amount, and the critical irradiation is performed for each irradiation pattern having different dimensions of the non-irradiated part or the irradiated part. An electron beam exposure method characterized in that a scattering intensity distribution of an electron beam is obtained by obtaining a quantity.