JPS6246058B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to an electron beam exposure method, and more particularly to a method for forming a highly accurate electron beam exposure pattern by correcting the so-called proximity effect.

[Conventional technology]

In pattern forming technology using electron beam exposure, correction of so-called proximity effect is essential to improve pattern accuracy.

As is well known, the proximity effect is caused by electron beam scattering (forward scattering) in the resist layer coated on the exposed object and electron beam scattering (backward scattering) from the substrate, which is the exposed object. This is a phenomenon in which the resist pattern after drawing expands to a greater extent than the electron beam irradiation pattern. Especially when the distance between the patterns becomes 2 μm or less, this results in significant distortion of the pattern shape and has a significant negative effect of reducing accuracy. Become.

The electron beam scattering intensity distribution in the resist due to this scattering is calculated by the following equation as a function of the distance r from the center of the beam irradiated from the outside. It is known that the first term is given by forward scattering and the second term is given by backscatter. Note that in formula (1), A, B, and C are constants determined by conditions such as the thickness of the resist and the material of the substrate.

The spread of a pattern due to the proximity effect includes spread caused by the influence of other patterns (inter-pattern proximity effect) and spread caused by drawing the own pattern (intra-pattern proximity effect).

Conventionally, as a method of correcting the spread caused by drawing one's own pattern, the spread is corrected by drawing with a corrected pattern size that is uniformly reduced in pattern size regardless of the size of the unit rectangular pattern.

[Problem that the invention seeks to solve]

FIG. 1 is a graph showing the relationship between the size (area) of a drawing rectangle and the spread of a pattern, using the resist film thickness as a parameter.

A problem arises because, as described above, drawing is performed using a corrected pattern size that is uniformly reduced in pattern size regardless of the size of the unit rectangular pattern. When the initial film thickness of a negative resist becomes large, as shown in Figure 1, when the rectangular size is large, self-spreading becomes particularly noticeable, and this tendency becomes more pronounced as the film thickness increases. . Therefore, it is difficult to make sufficient correction just by uniformly reducing the drawing dimensions.

Furthermore, when creating a photomask using electron beam exposure, the resist film thickness may be thin, but when forming a pattern by directly writing onto the resist on the wafer with an electron beam (direct exposure), the processing process It is necessary to keep the resist film thick after exposure and development. In this case, when the electron beam irradiation density is corrected to ensure a predetermined resist remaining film, the spread of the pattern due to the intra-pattern proximity effect changes depending on the electron beam irradiation density.

Therefore, especially in the case of the direct exposure method, it is practically impossible to obtain high-precision patterns with the conventional uniform size reduction correction, and electron beam irradiation density correction and size correction according to the pattern size are essential. .

The above problem will be explained in more detail with reference to FIG. In Figure 2, the size of the drawing rectangle (length of one side of the square: μm) is used as a parameter, and the electron beam irradiation amount per unit area during drawing (vertical axis), that is, the electron beam irradiation density (C/cm ² ) It is a graph showing the relationship between the pattern width and the residual film pattern width (horizontal axis) of the negative resist after development processing. Curves a, b, and c each have an electron beam drawn rectangular pattern with a side length of 1 μm and 2
It shows the relationship between the electron beam irradiation density and the width of the generated pattern during drawing when the pattern is a square of μm and 5 μm.

Referring to FIG. 2, it can be seen that when each drawing rectangle is drawn at a specific electron beam irradiation density, a resist remaining film pattern of the same size as the drawn pattern is obtained. For example, when drawing a rectangle with a side of 1 μm, a residual film pattern of the same size as the drawing rectangle can be obtained when drawing is performed at the electron beam irradiation density QAo at point Ao, and when the sides of the drawing rectangle are 2 μm and 5 μm. In the case of , each point
Electron beam irradiation density QBo, QCo in Bo, Co
This is when drawing is performed with electron beam irradiation densities QBo and QCo at (QAo>QBo>QCo). That is, FIG. 2 shows that in order to obtain a residual film pattern of the same size as the drawing rectangle, the smaller the drawing rectangle, the higher the electron beam irradiation density is required. In this way, when the electron beam irradiation density is set so that the drawing rectangle size and the remaining film pattern size are the same, the resist remaining film thickness is generally insufficient and the required remaining film rate (for example, the initial 90% of the resist film thickness) requires a higher electron beam irradiation density. In Figure 2, the electron beam irradiation density required to obtain the required constant film remaining rate (for example, 90% of the initial resist film thickness) is plotted on curves a, b, and c corresponding to each drawing rectangle. The point plotted is A ₁ ,
B ₁ and C ₁ , and a curve d connects them. When drawing rectangles of each size at the above electron beam irradiation densities QA ₁ , QB ₁ , and QC ₁ to ensure the required residual film rate, the size of the resist residual film pattern will be as shown in Figure 2. The size of the pattern will be larger than the drawing pattern.

Therefore, from the relationship shown in Figure 2, in electron beam exposure of a negative resist, it is possible to achieve high accuracy by correlating the dimension correction and the dose correction according to the required size of the remaining film rectangular pattern. It turns out that this is necessary for pattern creation.

The relationship shown in FIG. 2 is uniquely determined if the type of resist, the thickness of the resist coated film (initial film thickness), or the conditions of the development process are held constant. Conventionally, it has been common practice to set these conditions, write rectangles of various sizes at various electron beam irradiation densities, develop them, and create experimental resist layer patterns to obtain the relationships shown in Figure 2 for all sizes. An empirical method is adopted in which the size correction amount and the electron beam irradiation density correction amount are determined for each unit rectangular pattern in the actual exposure pattern. However, this method requires a huge number of man-hours for experiments to determine the above relationship, and it takes a great deal of time and effort to carry out this process every time the resist coating thickness or development conditions are changed.

In view of the above points, the present invention easily determines both the dimension-corrected drawing pattern dimensions and the electron beam irradiation density necessary to obtain the required residual film thickness for the resist layer pattern to be formed, and achieves high accuracy. The purpose is to provide a method by which patterns can be formed.

[Means for solving problems]

In the electron beam exposure method according to the present invention, a predetermined pattern is drawn by irradiating an electron beam onto a substrate coated with a negative resist layer, and the desired negative resist layer pattern is left behind after the development process. A method for forming an exposure pattern on the negative resist layer, the method comprising: forming an exposure pattern on the negative resist layer with an electron beam irradiation density and a required amount of radiation so that a resist layer pattern having the same dimensions as the drawing pattern remains after development for any one drawing pattern; Find in advance the ratio to the electron beam irradiation density that will give you the resist residual film thickness.
In determining the drawing pattern and the electron beam irradiation density for the resist layer pattern to be left, the electron beam irradiation density is such that the required resist remaining film thickness can be obtained based on the dimensions of the pattern to be left and the ratio. This method is characterized in that the electron beam irradiation density and the drawing pattern size are determined, and the electron beam drawing is performed using the electron beam irradiation density and the drawing pattern size thus determined.

[Effect]

That is, the present invention provides an electron beam irradiation density that can leave a resist layer pattern with exactly the same dimensions as the drawn pattern after development for any rectangular drawn pattern, and a method to obtain a required constant residual film thickness in the rectangular drawn pattern. It has been experimentally proven that the ratio of the electron beam irradiation density required for the irradiation to the electron beam irradiation density is almost constant, independent of the dimensions of the rectangular pattern, once the surrounding conditions such as the type of resist, coating film thickness, and development conditions are determined. This heading was made based on the knowledge that the correction dimension and the electron beam irradiation density can be determined for a pattern of any size from this constant ratio relationship.

〔Example〕

First, the above-mentioned relationship of constant ratio will be explained.

In the present invention, after repeating many experiments to obtain the relationship shown in FIG. 2, the electron beam irradiation density (point A ₀ in FIG. 2, electron beam irradiation density (electron beam irradiation density at B ₀ or C ₀ ) and electron beam irradiation density that produces a constant film residual rate (points in Figure 2).
It has been found that there is a relationship in which the ratio of electron beam irradiation density at A ₁ , B ₁ , or C ₁ is constant. That is, in Fig. 2, let the electron beam irradiation densities at points A ₀ , B ₀ , and C ₀ be QA ₀ , QB ₀ , and QC _{0 ,} respectively.
The electron beam irradiation density at points A ₁ , B ₁ , C ₁ is QA ₁ ,
Assuming QB ₁ and QC ₁ , there is the following relationship: QA ₁ /QA ₀ =QB ₁ /QB ₀ =QC ₁ /QC ₀ =D (2) (where D is a constant). The value of the constant D is determined by determining the type and thickness of the resist, the development conditions, and the required residual film rate (residual film thickness). Electron beam irradiation density for all patterns −
Compared to experiments to determine pattern width relationships, much fewer man-hours are required. Therefore, if it is possible to numerically determine the dimensions and electron beam irradiation density correction values for a rectangular pattern of any size by using this constant D, the number of experimental man-hours required in advance can be significantly reduced. The present invention provides a method for doing so.

As shown in Fig. 3, a drawing pattern P' with a width of 2M (L>M), which has been corrected by S with respect to the required dimension of the residual film pattern (width 2L), is irradiated with an electron beam at an electron beam irradiation density of Q ₁ . Let us consider a case where a residual film pattern with a width of 2L and a residual film ratio of 90% can be obtained by drawing. It is assumed that the type of resist, coating thickness, and development conditions are fixed in consideration of the actual manufacturing process, and that the constant D has already been determined in advance through an experiment using one rectangular drawing pattern. These relationships are expressed on a graph representing the relationship between electron beam irradiation density and pattern width as shown in FIG. That is, curves l and m show the relationship between the electron beam irradiation density and the resist remaining film pattern width when square patterns of widths 2L and 2M are drawn with the electron beam, respectively. Note that here, the curve l is a known curve, but since S is unknown, the curve m is an unknown curve. Looking at Figure 4, when a pattern with a width of 2M is drawn with an electron beam at an electron beam irradiation density _Q1 , a point _M1 has a width of 2L with the required residual film thickness.
This shows that a residual film pattern of That is, in the present invention, the reduced dimension S (in other words, M) and the electron beam irradiation density are determined using a constant D determined in advance.
Find Q ₁ .

Now, paying attention to the curve m in Fig. 4, the electron beam irradiation density is such that a resist remaining film pattern with the same dimensions (width 2M) as the drawing pattern is obtained, as indicated by point _M0 .
Considering Q ₀ , since there is a relationship in which the above-mentioned ratio is equal to the constant D, the following equation holds true.

Q ₁ /Q ₀ = D ...(3) Next, when drawing a square pattern P' with a side length of 2M, the distance R from the center of the square pattern P'
The exposure intensity F(R) in the resist film at the point is the scattering intensity distribution f(r) expressed by equation (1) in the drawing pattern.
It is obtained by integrating over the entire surface of P' as shown in the following equation. Here, r is the distance between a point separated by a distance R from pattern P' and the center of the electron beam spot within pattern P'.

F(R)=∫ ^M _−M ∫ ^M _−M f(r)dx dy ...(4) The product of the exposure intensity F(R) obtained from this and the electron beam irradiation density Q (C/cm ² ) is This gives the exposure amount E on the pattern side in the actual resist film, and this relationship is expressed as in the following equation.

Q・F(R)=E ……(5) Now, referring to Fig. 4 again and focusing on points M ₀ and M ₁ , we can see that the electron beam intensity distribution has a peak within the drawing pattern and is directed outward. When the electron beam irradiation density is Q ₀ and Q ₁ , the points M ₀ and M at distances M and L from the center of the rectangular pattern P′ gradually decrease.
The curve m means that the actual exposure amount in the resist at L ₀ is equal to the exposure amount threshold E ₀ that determines whether the resist remains after development.

Therefore, this relationship can be expressed as follows.

Q ₀・F(M)=Q ₁・F(L)=E ₀ ……(6) Q ₁ /Q ₀ =F(M)/F(L) ……(6)′ Equation (3) and ( 6) From the equation, the following equation is derived.

F(M)=D・F(L)...(7) Here, L is a known value, and based on equation (4), the right side of in equation (7) is a constant, so equation (7) can be written as Establish M
is uniquely determined as the solution to the integral equation. Since this calculation itself can be performed at high speed using an electronic computer, solutions M for various dimensions L can be obtained quickly.

The dimension value M thus obtained indicates a pattern width of 2M after dimension correction (dimensional correction amount S = L - M), and if a pattern with a width of 2M is written with an electron beam at an electron beam irradiation density _Q1 , After development, a negative resist layer pattern (width 2
L) can be obtained. Note that the exposure amount E ₀ is constant and can be easily determined experimentally by determining the development conditions, etc., so the exposure amount Q ₁ is determined as described above.
It goes without saying that it can be determined from equation (6).

In the above explanation, for the sake of brevity, we have described the case where the correction amount is determined for a square pattern as shown in Figure 3, but it is clear that even in the case of a rectangular pattern, the correction amount can be determined for each of the two orthogonal sides using the above procedure. Dew.

In addition, when applying a huge amount of pattern data to an electronic computer and applying it to a practical electron beam exposure apparatus that performs electron beam writing under computer control, the correction amount calculated as described above is determined at the time of creating the pattern data. If the device is as shown in Fig. 5, the data is stored in the electronic computer 6, and the computer 6 drives the X and Y deflectors 4 to advance the beam spot and irradiate it so as to fill in a predetermined pattern. and draw. FIG. 5 is a conceptual diagram of the basic configuration of a typical electron beam exposure apparatus. The electron beam exposure apparatus main body 1 includes an electron gun 2, a convergent electron lens system 3,
It has an XY deflector 4 and irradiates a thinly focused electron beam onto a substrate coated with resist and a sample 5. The position of the electron beam spot on the sample 5 is determined by pattern data from an electronic calculator 6. It is controlled by driving the XY deflector 4 via the DA converter 7 and amplifier 8. The electron beam is computer 6
Irradiation onto the sample 5 is controlled by a blanking device in accordance with signals from the blanking device.

〔Effect of the invention〕

As described above, according to the present invention, when forming a pattern by electron beam exposure using a negative resist, drawing pattern dimensions are required to ensure a required residual film thickness and create a required negative resist residual film pattern. Correction and dose correction can be achieved by relatively simple operations, and highly accurate fine pattern formation can be achieved with fewer man-hours, so the practical effect is great.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the area of the rectangle drawn by the electron beam and the pattern spread due to intra-pattern proximity effect, Figure 2 is a graph showing the relationship between electron beam irradiation density and pattern width, and Figure 3 is the graph showing the relationship between the electron beam irradiation density and pattern width. FIG. 4 is a graph showing the relationship between electron beam irradiation density and pattern width. FIG. 5 is a diagram showing a basic configuration example of an electron beam exposure system.

Claims (1)

[Claims] 1. A predetermined pattern is drawn by irradiating an electron beam onto a substrate on which a negative resist layer is coated, and an exposure pattern is applied to the negative resist layer so that the desired negative resist layer pattern remains after the development process. It is a method of forming a resist layer in such a way that, for any one drawing pattern, the electron beam irradiation density and the required resist residual film thickness are obtained such that a resist layer pattern having the same dimensions as the drawing pattern remains after development. The ratio to the electron beam irradiation density is determined in advance, and when determining the drawing pattern and the electron beam irradiation density for the required resist layer pattern to be left, based on the dimensions of the pattern to be left and the ratio. An electron beam exposure method characterized in that the electron beam irradiation density and the drawing pattern dimensions that provide the required resist residual film thickness are determined, and electron beam writing is performed using the electron beam irradiation density and the drawing pattern dimensions thus determined.