JPH0444263B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a simplified method for detecting the optimum value of exposure for determining the optimum exposure in a photoresist process.

(b) Conventional technology In recent years, with the improvement in performance and integration of semiconductor devices, for example, Japanese Patent Application No. 145525/1983
As described in Japanese Patent Laid-open No. 299969 (Japanese Unexamined Patent Publication No. 62-299969), the resists used in their manufacture are also shifting from conventional negative resists to positive resists, which are more suitable for miniaturization. Conventional negative resists have exposed areas that remain, so the photomask used for this resist has an overall white (transparent) pattern with most areas being white (transparent) and areas corresponding to the diffusion windows being black. On the other hand, since the exposed portion of a positive type resist is removed, the photomask for it has an overall black pattern with most of the area being black and the area corresponding to the diffusion window being white (transparent).

On the other hand, in order to accurately transfer a pattern from a reticle to a master mask, from a master mask to a work mask, or from a work mask to a semiconductor wafer using an optical exposure device, it is necessary to optimize the exposure conditions. Even after setting appropriate conditions, it is necessary to re-optimize the exposure amount, which is easier to control, when changing resist lots, developer lots, or replacing optical lamps. In particular, when using the above-mentioned positive resist, stricter control is required than with a negative resist due to the unique property of a positive resist that exposed areas are removed.

When optimizing the exposure amount mentioned above, it is possible to easily adjust the exposure amount for one substrate by changing the exposure amount for each step with step-and-repeat type exposure equipment, but it is possible to easily adjust the exposure amount for one substrate by changing the exposure amount for each step. 1
In a contact type exposure apparatus that exposes at a time, multiple substrates are wasted in order to do the same thing.

As a method to improve this problem, there has conventionally been a method of using a pattern called a step tablet.

FIG. 4 shows a pattern used in such a method, in which a plurality of rectangular detection patterns 2 are provided on a glass substrate 1 using vapor-deposited metal such as chromium, similar to a normal photomask. Detection pattern 2 is one in which the film thickness of vapor-deposited chromium is made different and the transmittance is changed stepwise. After exposure and development at a predetermined exposure amount, the minimum exposure amount at which the resist is removed from detection pattern 2 is determined. The optimum exposure amount is calculated from the minimum exposure amount.

(c) Problems to be Solved by the Invention However, in order to manufacture the detection pattern 2 using a step tablet, it is necessary to repeat the chromium film deposition process multiple times, which increases the cost.
Furthermore, since it is very difficult to control the film thickness to a value corresponding to the transmittance, it is not possible to arrange a large number of detection patterns 2 with densely arranged steps on the same substrate 1.
Therefore, there was a drawback that the minimum exposure amount could not be detected more precisely.

(d) Means for solving the problems The present invention was made in view of the above-mentioned drawbacks.
A plurality of detection patterns 2 were prepared in which the ratio of the area of the black background part 3 and the white part 4 to a predetermined unit area was changed, and the patterns were exposed under conditions such that the shape of the black background part 3 was not imaged. It is characterized by

(e) Effect According to the present invention, since the exposure is performed under conditions in which the shape of the detection pattern 2 is not imaged, the exposure light 5 is applied to the resist so that it has a uniform intensity distribution over the whole due to the light diffraction effect. 6. Therefore, changing the overall amount of transmitted light by changing the area ratio of the white portion 4 is equivalent to changing the transmittance of the detection pattern 2.

(f) Examples Hereinafter, the present invention will be explained in detail with reference to the drawings.

In FIG. 1, 1 to C indicate the pattern shapes of detection patterns 2 used in the present invention, in which a plurality of square black background portions 3 are arranged in a tile-like manner within a unit area of, for example, about 10×10 mm. Other examples of the shape and arrangement method include a mesh shape and a lattice shape. In the pattern shown in FIG. 1A, sides A and B of the white portion 4 are set to 5 μm each using CAD, and the patterns are arranged with a pitch of 10 μm in the X direction and the Y direction. The ratio (T ₁ ) of the area of the white portion 4 to the unit area of ×10 mm is set to 50%. Therefore, the amount of light transmitted through the entire detection pattern 2 shown in FIG. In the pattern shown in Fig. 1B, sides A and B of the white part 4 are each set to 5.063 μm and 10 μm.
The area ratio (T ₂ ) of the white portion 4 is set to 51.25%. As a result of increasing the area of the white portion 4, the area of the black background portion 3 decreases, and one pattern thereof becomes smaller than 5×5 μm. Figure 1C
The sides A and B of the white portion 4 are each set to 5.127 μm, and the area ratio (T ₃ ) of the white portion 4 is thereby set to 52.50%.

FIG. 2 shows a photomask in which a plurality of detection patterns 2 described above are arranged. In the figure, 1 is a glass substrate such as quartz, and 2 is the 10×10 mm detection pattern formed on the surface of the glass substrate 1 with vapor-deposited metal such as chromium in the shape shown in FIGS. 1A to C. The detection pattern 2 is formed by changing the area ratio (T ₁ , T ₂ , T ₃ . . . Tn) of the white portion 4 by the above-mentioned means, and the step is arbitrary within the range of 40 to 80% in practice. It is. The above range is theoretically 0% to 100
%, but it can be limited to some extent based on the relationship between the minimum exposure amount and the optimum exposure amount, which will be described later.

FIG. 3 shows a situation in which the photomask shown in FIG. 2 is exposed using a contact type exposure device. In the figure, 5 is exposure light irradiated from above the glass substrate 1, 6 is a positive resist coated on one plane 7 by, for example, a spin-on method, and 8 is a chromium film deposited on the surface of the glass substrate 1. The region where the chromium film 8 is present corresponds to the black background portion 3, and the region where there is no chromium film corresponds to the white portion 4. Normally, in a contact type exposure apparatus, exposure is performed with the substrate 1 and the resist 6 in close contact with each other. The situation is set such that the shape of portion 3 is not imaged. This takes advantage of the diffraction phenomenon of light, and empirically it has been found that it is sufficient to have a gap of 10 times or more than the pitch, for example, when forming the above-mentioned 5 x 5 μm shape with a 10 μm pitch, it is sufficient to have a gap of about 100 μm. be. Incidentally, in an exposure apparatus of the mirror explosion type, the situation characterized by the present invention can be set by intentionally removing the focus.

Then, a plurality of detection patterns 2 are simultaneously exposed onto the resist 6 by irradiating the exposure light 5 with a predetermined intensity and a predetermined time from above the substrate 1 . At this time, in order to simplify the explanation, it is assumed that an amount of exposure light 5 of, for example, 100 is irradiated per unit area of 10×10 mm. Then, only the amount of exposure light 5 corresponding to the area ratio (T ₁ , T ₂ , T ₃ . . . Tn) of the white portion 4 reaches the resist 6, and the rest is blocked by the black portion 3. I end up. In other words, when an amount of exposure light 5 of 100 passes through the detection pattern 2 as shown in FIG.
It is only irradiated. Furthermore, as is clear from the intensity distribution characteristics shown in FIG. 3, the irradiated exposure light 5 with an amount of 48.75 has an almost uniform intensity distribution over the entire detection pattern 2 due to the light diffraction effect. It becomes like this.

This point is the most important part of the present invention. In other words, by changing the area ratio of the white portion 4, the amount of transmitted light is changed for each detection pattern 2, and the changed amount of transmitted light is distributed uniformly. By exposing to light, the transmittance of the detection pattern 2 can be controlled in a practical manner equivalent to the conventional means of changing the thickness of the chromium film 8.

The minimum exposure amount can be determined from the detection pattern 2 thus exposed by visually inspecting the detection pattern 2 after a predetermined development process has been performed. In other words, since the positive resist 6 is not removed unless a certain amount of exposure is reached, among the two arrays of detection patterns in which the amount of transmitted light is varied stepwise, there are patterns in which the resist 6 remains somewhere and those that are removed. There should be a boundary between the pattern group and the pattern group. Detection pattern 2 with high transmittance
The resist 6 is completely removed, and the detection pattern 2 having a lower transmittance remains with the resist 6 having a thinner film thickness. Then, the detection pattern 2 with the lowest transmittance is identified among the patterns from which the resist 6 has been removed, and the product of the transmittance and the given exposure amount is the minimum exposure amount. for example,
Area ratio of the identified detection pattern 2 (T _x )
If is 51.25%, then 51.25% of the given exposure amount of 100 is the minimum exposure amount.

Then, the optimum exposure amount for the exposure apparatus shown in FIG. 3 is obtained by multiplying the minimum exposure amount determined as described above by a certain magnification. Since the minimum exposure amount is the minimum exposure amount necessary to remove the resist 6, it is completely impossible to control the line width, etc. if pattern transfer is performed using this value. Therefore, as a means for determining the exposure amount that can be easily controlled, a method is used that uses the fact that the exposure amount and the resist film thickness have a certain correlation and applies the above-mentioned fixed magnification. This fixed magnification is selected in advance based on various conditions such as the line width controllability of the resist film thickness used, and is generally
There is no change in the range of 1.5 to 4.0.

Therefore, if the constant magnification is, for example, 2.0 and the minimum exposure amount is 51.25 as mentioned above, the optimal exposure amount is 102.5 for the 100 exposure amount given during exposure.
Therefore, by adding a correction of 2.5, this exposure device can perform pattern transfer in a state completely equal to the previous state. Incidentally, the area ratio (T ₁ , T ₂ , T _{3 .} . . Tn) of the white portion 4 of the detection pattern 2 created on one substrate 1 may be determined in the range in view of the above-mentioned constant magnification. , the constant magnification is 2
If it's 3, it's in the range of 45-65%, and if it's 3, it's 30-50.
It may be formed in an arbitrary step within a range of about 30%.

(g) Effects of the Invention As explained above, according to the present invention, by changing the area ratio (T ₁ , T ₂ , T ₃ ...Tn) of the white portion 4, the transmittance of the detection pattern 2 can be substantially reduced. Since the detection pattern 2 can be easily and inexpensively formed in denser steps on one substrate 1, the minimum exposure amount of the positive resist can be easily determined with high precision. It has the advantage of being able to Since the minimum exposure amount can be detected with high precision, the exposure apparatus can always be set in the best condition, which has the advantage of providing high-quality semiconductor devices.

[Brief explanation of drawings]

1 to 3 are an enlarged plan view, a plan view, and a schematic sectional view for explaining the present invention, respectively, and FIG. 4 is a plan view for explaining a conventional example. 1 is a glass substrate, 2 is a detection pattern, 4 is a white part, 5 is an exposure light, and 6 is a positive resist.

Claims (1)

[Claims] 1. In the method for detecting the optimum value of the exposure amount, the optimum exposure amount is obtained by coating a resist on one substrate and simultaneously exposing and developing a plurality of detection patterns having mutually different transmittances. Using a detection pattern in which the transmittance is substantially controlled by changing the ratio of the area of the white part per unit area, and exposing under conditions such that the intensity distribution of the exposure amount after exposure is approximately uniform. A method for detecting an optimum value of exposure, which is characterized by the following.