JPH04255847A - Exposing method - Google Patents

Abstract

PURPOSE:To shorten the process time for exposure conditioning and to easily and accurately expose the upper and lower parts of a step by varying an exposure quantity and a focus value completely independently. CONSTITUTION:Initial values and arithmetical quantities (or geometric constant) are given as exposure conditions of an optional shot SrL (r row and L column) under 2XM conditions of SrL=(F1r and E1L (once), F2r and E2L (twice), F3r and E3L (three times)...FMr and EML (M times)). Then when multiple exposure is performed plural times, the exposure quantity and focus value of each of the exposing operations are varied completely independently to form patterns on the same wafer under the various multiple exposure conditions. Further, the optimum conditions of the exposure quantity and focus value are found by pattern inspection and the multiple exposure is performed plural times according to the found exposure quantity and focus value to form a resist pattern on the wafer.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an exposure method, and more specifically, it can be applied to photolithography technology in the manufacture of semiconductor integrated circuits, and in particular, it is possible to obtain optimal exposure conditions for multiple exposures on a single wafer. The present invention relates to an exposure method that can be used.

[0002] In recent years, there has been a demand for higher integration of LSIs, and there is a demand for larger LSI chips while miniaturizing circuit patterns.

0003

2. Description of the Related Art In conventional exposure methods, each exposure shot is completed in a single exposure using a stepper, and then developed to form a resist pattern. there were. However, as the pattern becomes finer, the depth of focus decreases, so it is difficult to effectively increase the depth of focus or create the same pattern above and below the steps caused by the IC pattern already partially formed on the wafer surface. As shown in FIG. 8, multiple exposures are performed by changing each exposure amount and each focus value by multiple exposures (M times), as shown in FIG. Exposure of one chip is completed.

0004

[Problems to be Solved by the Invention] However, in the above-mentioned conventional exposure method, in order to obtain the optimal conditions for multiple exposure, the exposure distribution is limited to (a) the number of exposures M on the same wafer;
is fixed, (b) focus step ΔF (=F(i)-F
(j), i, j=1, 2..., M) are fixed, (c) exposure ratio (=E(i)/E(i), i, j=1, 2...,
M, ratio of exposure amount each time) is fixed, (d) total exposure amount (=
ΣE(i)) is variable, (e) center focus value (=ΣF
There is a restriction that (i)/M) is variable, and it is extremely difficult to determine the relationship between multiple exposures (particularly the optimal conditions of (b) and (c) above).

In particular, it is a practical problem that it is not possible to change the ratio between the focus increments and the exposure amount in (b) and (c). It is not possible to reduce the amount of light, and this problem becomes particularly noticeable when exposing the upper and lower parts of a step.

[0006] Therefore, it is not possible to determine the optimal conditions for multiple exposure using a single wafer, and the exposure conditions must be determined using multiple product wafers, which is troublesome.
A long process time is required to set the exposure conditions, resulting in a problem of reduced throughput.

Therefore, in order to change the exposure conditions for the same wafer, first, change the conditions for the first exposure, expose the wafer once, and then chuck the wafer again and change the conditions for the second exposure. I had to repeat the process by changing the exposure conditions.

[0008] Accordingly, the present invention makes it possible to easily determine optimal exposure conditions for multiple exposure using as few wafers as possible (even one wafer) than before, and to shorten the process time for determining exposure conditions. It is an object of the present invention to provide an exposure method that can improve throughput, and can easily and accurately expose the upper and lower parts of a step.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the exposure method according to the present invention uses a sequentially movable reduction projection type exposure device and changes the focus value and exposure amount of the distance between the imaging plane and the wafer surface at the same location. to achieve the desired I by multiple exposures.
In the exposure method of multiple exposure of the C pattern, prior to the exposure, the exposure amount and focus value for each exposure are changed independently, and the same wafer is exposed under various multiple exposure conditions,
Thereafter, development and pattern inspection are performed to determine the optimal conditions for the exposure amount and focus value, and a resist pattern is formed on the wafer based on the determined exposure amount and focus value.

[0010] In the present invention, a plurality of exposures may be performed consecutively at the same location on the wafer, and in this case, positional deviation can be reduced, which is preferable. In the present invention, when changing the exposure amount or each focus value in M-times multiple exposure, the n-th exposure condition is set to A.
1(n) +ΔA2(n) ・R+ΔA3(n) ・L
(However, A1 is the initial value of exposure amount or focus value, Δ
A2 and ΔA3 are the exposure amount or focus value increments, R,
When multiple exposure is performed by changing L and n according to the formula expressed as integers (1≦n≦M), and changing R and L in accordance with the order of the row direction and column direction on the wafer. It may be.

[0011]

[Operation] According to the present invention, patterns formed under various multiple exposure conditions can be created on the same wafer by independently changing the exposure amount and focus value for each exposure in multiple multiple exposures. Then, optimum conditions for the exposure amount and focus value are determined through pattern inspection, and multiple exposures are performed a plurality of times based on the determined exposure amount and focus value to form a resist pattern on the wafer.

As described above, in the present invention, since the exposure amount and the focus value are all changed independently, the optimal exposure conditions for multiple exposure can be achieved by using as few wafers as possible (even one wafer). This can be easily performed on a wafer, and the process time for setting exposure conditions can be shortened. Below, the exposure method of the present invention is shown in FIG.
This will be specifically explained using 2.

In FIG. 1, the exposure conditions for an arbitrary shot SrL (r row, L column) are as follows. SrL=(F1r,
E1L (1 time), F2r, E2L (2 times), F3r,
E3L (3 times),,,,,,, FMr, EML (M
)) For each of these 2×M conditions, an initial value and an arithmetic difference amount (or a geometric constant) are given.

Generalizing, the Nth (1≦N≦M) exposure condition for an arbitrary (r row, L column) shot can be given by the following equation. In the case of arithmetic difference...Focus value FNr=FN1+(r-1
)・ΔFN Exposure amount EN1=EN1+(L-1)・ΔEN In the case of equal ratio...Focus value FNr=FN1・PFN r-1
Exposure amount EN1=EN1・PEN L-1 where, ΔFN: Arithmetic change in focus value of N-th exposure during multiple exposures ΔEN: Arithmetic change in exposure amount for N-th exposure during multiple exposures Amount PFN: Amount of geometric change in focus value for the Nth exposure during multiple exposures PEN: Amount of geometric change in the exposure amount for the Nth exposure during multiple exposures In Figure 1, the conditions for the exposure amount and focus value Although the case where the sheets are arranged in a matrix has been described, they may also be arranged in a zigzag pattern as shown in FIG. 2, and this layout method will be explained below.

[0015] This is useful when, for example, you want to set a condition for only the exposure amount by fixing each focus value of multiple exposures, or conversely, when you want to fix the exposure amount and set a condition for only the focus value. This is especially effective when you want to swing. FIG. 2 shows a case where the focus value is fixed and only the exposure amount is changed, and the same is true when it is desired to change only the focus value. In this case, more conditions can be changed, which is preferable.

In this way, in the present invention, as shown in FIG. 1, in order to independently set each exposure condition (=2) of the exposure amount and focus value for multiple exposures (=M), the initial value It is possible to expose the same wafer under various conditions with a total of 1+3M+3M=1+6M designations of geometric ratio or arithmetic difference (=2) and amount of change (=1).

[0017] Exposure number M designation 1 exposure condition 2 (initial value, ratio/difference designation) x M + M (change amount) = 3M focus value
2 (initial value, ratio/difference specification) x M + M (change amount) =
3M Therefore, the relationship between each exposure within one shot can also vary indirectly.

[0018]

[Embodiment] The following describes a procedure for specifying exposure conditions for determining optimal conditions for multiple exposure. ■ Specify the number of rows R and the number of columns L.

■ Specify the number of multiple exposures M. ■ Specify zigzag or grid pattern.

[0020] In the case of a lattice shape, specify exposure change or focus change for each row and column. ■ Specify each initial value, specify the difference/ratio, and specify the amount of change. E11, ΔE1, F11, ΔF1 E21
, ΔE2 , F21 , ΔF3 EM1, Δ
EM, FM1, ΔFM ■ Start of exposure Expose according to the conditions of ■ to ■.

(1) Move the wafer stage under the projection lens (R row, L column). (2) Multiple exposure is performed under the exposure conditions of (R row, L column).

Exposure under the first exposure conditions (E1L, F1
r) Exposure under the second exposure condition (E2L, F1r) Exposure under the M-th exposure condition (EML, FMr) (For arithmetic difference, as shown below) Focus value FNr=FN1+(r-1)・ΔFN Exposure amount ENL=EN1+(L-1)·ΔEN (3) Move to another row or column and perform multiple exposure under the conditions of that location.

(4) Repeat the following. ■ End the exposure. Next, an exposure method applicable to the present invention will be explained using FIG. 3.

For example, if you want to widen the interval between focus values each time with the center of the focus value fixed,
As shown in , the focus increment during the first exposure is increased, the focus increment during the second exposure is set to zero, and 3
The focus increments at the time of the second exposure are reduced. Here, the case is three-time multiple exposure, and for the sake of simplicity, the exposure amount is not mentioned here.

[0025] In this way, by varying the focus conditions, the optimum focus interval can be detected for one wafer. Next, the present invention can also be applied to the case where the overall focus average value is changed, as shown in FIG. Here, for example, the relative relationship between the focus at the first exposure, the focus at the second exposure, and the focus at the third exposure is constant, and in this case, the overall focus center value can be obtained. This is a case in which a conventional exposure method can also be applied and is therefore included in the scope of the present invention.

It is clear that the embodiments shown in FIGS. 3 and 4 are also effective for two exposures and four or more exposures. Next, in the present invention, as shown in FIG.
For example, if you don't know the exposure amount for the first exposure and shake it up a lot,
This is a case where the exposure amount at the time of the second exposure is known, so it is fixed, but in this case, the focus value is a relative value, whereas the exposure amount (mJ/cm2) is an absolute amount, so it is It is also an effective method to set conditions to increase the exposure amount at the first exposure in a geometric ratio. This is particularly effective since the properties of the resist vary logarithmically.

Next, in the present invention, as shown in FIG. 6, it is also possible to fix the ratio of each exposure amount and make the relative value of each exposure amount the same, thereby making the total exposure amount variable. next,
An exposure method applicable to the present invention will be explained using FIG. 7.

The exposure method here is used when it is desired to change the focus interval and also to change the center focus.

For example, a case of three times multiple exposure will be shown. Note that the exposure amount is fixed. F1rL = F1r+(L-1)・ΔF1,
F1r=F10+(r-1)・ΔF F2rL
=F2r+(L-1)・ΔF2, F2r=F20+(
r-1)・ΔF F3rL =F3r+(L-1
)・ΔF3, F3r=F30+(r−1)・ΔF, and unlike the above embodiments shown in FIGS. 2 to 6, the initial value is also allowed to fluctuate. To summarize, the exposure shot conditions for (R row, L row) are: F1rL = F10 + (r-1) ΔF + (L-1) ΔF
1 F2rL =F20+(r-1)ΔF+(L-1)
ΔF2 F3rL =F30+(r-1)ΔF+(L-
1) It can be expressed as ΔF3, and can be shaken in a matrix on one wafer, as shown in FIG. 7(a). An example of an actual swing is shown in FIG. 7(b).

Next, in the present invention, following the embodiment shown in FIG. 7, the present invention can be similarly applied to cases where it is desired to fix the focus value and change the exposure amount ratio, and also to vary the total exposure amount. Needless to say, it can be done. Note that in this case, in order to change the initial value, it is also necessary to specify the step size of the initial value. The flowchart of the specification procedure is as follows.

■ Specify the number of rows R and the number of columns L. ■
Specify the number of multiple exposures M. ■ Specify zigzag or grid pattern.

[0032] In the case of a lattice shape, specify exposure change or focus change in each row and column. Here, if there is an exposure change or focus change in both rows and columns, ■
Specify parameters.

(a) Specify whether to assign the initial value depending on whether the row or column is young. (b) Specify true initial values for each exposure (M values). (c) Specify how the initial value changes (difference, ratio) (one for each, M total).

(d) Specify the amount of change in the initial value (M pieces).

(E) Specify (M) the method of change (difference, ratio) in the column (horizontal) direction. (f) Specify (M) the amount of change in the column (horizontal) direction. ■ Expose to light.

It may be done as follows.

[0037]

[Effects of the Invention] According to the present invention, optimal exposure conditions for multiple exposure can be easily determined using as few wafers as possible (even just one wafer) than before, and the process time for determining exposure conditions can be shortened. It is possible to improve throughput.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the principle of the present invention.

FIG. 2 is a diagram explaining the principle of the present invention.

FIG. 3 is a diagram illustrating an exposure method applicable to the present invention.

FIG. 4 is a diagram illustrating an exposure method applicable to the present invention.

FIG. 5 is a diagram illustrating an exposure method applicable to the present invention.

FIG. 6 is a diagram illustrating an exposure method applicable to the present invention.

FIG. 7 is a diagram illustrating an exposure method applicable to the present invention.

FIG. 8 is a diagram illustrating a conventional exposure method.

Claims (2)

[Claims] 1. An exposure method in which a desired IC pattern is exposed multiple times by changing the focus value and exposure amount of the distance between the imaging plane and the wafer surface at the same location using a sequentially moving reduction projection type exposure device. Prior to the exposure, the same wafer is exposed under various multiple exposure conditions by independently changing the exposure amount and focus value for each exposure, and then development and pattern inspection are performed to determine the optimal conditions for the exposure amount and focus value. An exposure method comprising: determining the exposure amount and focus value, and forming a resist pattern on a wafer based on the determined exposure amount and focus value. [Claim 2] When changing the exposure amount or each focus value in M-times multiple exposure, the n-th exposure condition is A.
1(n) +ΔA2(n) ・R+ΔA3(n) ・L
(However, A1 is the initial value of exposure amount or focus value, Δ
A2 and ΔA3 are the exposure amount or focus value increments, R,
A claim characterized in that L and n are integers and are changed according to a formula expressed by 1≦n≦M), and R and L are changed in accordance with the order of the row direction and column direction on the wafer. 1. The exposure method described in 1.