JPH10172887A - Method of exposure for photolithography process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of photolithography exposure capable of stable size control on a semiconductor substrate having a different reflectivity, without increasing the number of processes. SOLUTION: A correlation coefficient between the reflectivity and the line width, and the exposure and the line width of a semiconductor substrate, are obtained by use of the same semiconductor substrate of a desired process beforehand, and according to the mutual correlation coefficient, the correction rate of exposure is calculated and the exposure control system of the aligner is set so that the same line width can be obtained under various reflection rate of semiconductor substrate. When the exposure is made by step and repeat method, before exposure, the reflection factor of a semiconductor substrate is measured, every exposure shot through or not through the projection lens. The exposure is made by compensating every exposure shot unit using the reflection factor measured above and the correction rate above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus in a photolithography process used in the manufacture of a semiconductor device, and more particularly to an exposure method using a reduced projection exposure apparatus using a step and repeat method.

[0002]

2. Description of the Related Art As a process leading to the formation of a resist pattern by a conventional photolithography technique, a method shown in FIG. 3 is employed. First, in the process, water (H) is desorbed to remove water adsorbed on the wafer substrate.
A bake treatment for dehydration is performed at a temperature setting equal to or higher than the boiling point of ₂ O).

[0003] Next, in the process, in order to improve the adhesion between the resist film to be coated on the wafer substrate and the substrate, a method of exposing the wafer to an HMDS (hexamethylammonium hexadisizaran) atmosphere is generally used. Is adopted. Next, in the process, a resist is dropped on the wafer substrate, and a desired resist film thickness is formed by spin coating.

[0004] Next, in the step, a bake treatment is performed for the purpose of removing unnecessary residual solvent from the resist film formed by applying a pre-bake treatment. Next, in the exposure step in the process, a reduction projection exposure apparatus is used, and (1)
After performing alignment measurement and correction, (2) measurement and correction of a wafer tilt component, and (3) focus measurement and correction are repeatedly performed for each shot to be exposed, and are determined in advance and input at a fixed exposure amount ( 5) Perform exposure.

Next, in the process, a baking process (generally, PEB (Post Expos) is performed for the purpose of eliminating standing waves due to a thermal diffusion effect and improving a resist profile.
ure bake). Next, in the step, in the case of a positive resist using a novolak resin system, a developing treatment is performed using an alkaline aqueous solution of TMAH (tetramethylammonium hydroxide) = 2.38%, and then a pure water cleaning treatment is performed. .

Next, in the process, a resist pattern is formed by performing a post-bake treatment at a temperature equal to or higher than the boiling point of water in the same manner as a pre-bake treatment in order to remove residual water on the wafer substrate surface generated by the pure water washing in the process. A method was adopted.

[0007]

In the recent sub-micron and half-micron regions, miniaturization is not the first step but S
In RAM and DRAM products, etc., the increase in chip size due to the increase in memory capacity and the increase in shot size along with the increase in wafer diameter are steadily increasing. Along with these developments, from the viewpoint of minimizing dimensional variations in chips and shots, a reduction in projection and exposure apparatus using the step-and-repeat method requires higher precision for the image plane tilt and curvature, and for the image plane tilt, the exposure shot unit. (Generally referred to as chip leveling or die-by-die tilt).

However, factors that determine the resist dimensions include variations in the thickness of the silicon oxide film, silicon nitride film, polycrystalline polysilicon film, and the like formed on the semiconductor substrate, and the reflectivity of the semiconductor substrate caused by the assembled state. Has a large effect, but in the current exposure, the exposure amount in each wafer is actually exposed at a constant exposure amount.

[0009] Therefore, the dimensional accuracy of all the exposure shots in the wafer is reduced due to the difference in the reflectivity on the wafer substrate, thereby deviating from the specified size, causing problems such as deterioration of characteristics and a reduction in yield. Was. The present invention has been made based on the above circumstances, and an object of the present invention is to provide a photolithography exposure method which is stable and can be dimensionally controlled even on a semiconductor substrate having a different reflectance without increasing the number of steps. It is assumed that.

[0010]

To achieve the above object, an exposure method for photolithography according to the present invention comprises:
A step-and-repeat method was used as a part of a process of forming a resist pattern having desired dimensions by sequentially performing dehydration bake treatment, HMDS treatment, pre-bake treatment, resist coat treatment, exposure, development, and post-bake treatment on a semiconductor substrate. G-line, i-line, X
Line, a specific single wavelength regardless of the exposure wavelength such as Krf,
Alternatively, in a photolithography exposure method in which exposure is performed in a desired size by transmitting and irradiating a reticle using a wide-band wavelength, a wafer in a semiconductor substrate process in which an exposure is performed in advance through an experiment is performed by reflection. Calculating a correlation coefficient between the rate and the line width, and a correlation coefficient between the exposure amount and the line width, calculating a correction amount at the time of exposure from these correlation coefficients, and inputting the correction amount to the exposure apparatus; When performing exposure by the repeat method, the reflectance of the semiconductor substrate is transmitted through the projection lens (TTL ON LENS) or not transmitted (TTL OFF LENS) for each exposure shot prior to exposure of each exposure shot. And the step of performing exposure by performing exposure correction on each exposure shot unit using the reflectance measured in the above step and the correction amount. It is intended.

[0011]

When a resist pattern having the same dimensions is formed on semiconductor substrates having different reflectivities, the resist pattern can be arbitrarily controlled by increasing or decreasing the amount of exposure. Therefore, if the exposure amount for each of the semiconductor substrates having the same dimensions and different reflectances is obtained, the reflectance measurement is performed before exposure of each exposure shot unit by reduced projection exposure, and the correlation coefficient is converted to the exposure amount. By providing feedback, a resist pattern having the same dimensions can be easily formed uniformly over the entire surface of a semiconductor substrate having different reflectivities.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present embodiment, a case where a step-and-repeat reduction projection exposure apparatus using an i-line wavelength is used as an exposure apparatus is taken as an example, and a global alignment method (overlapping by statistical calculation) is used. A description will be given of an example of an exposure method in the case of performing leveling correction for correcting the tilt of an exposure shot area in units of exposure shots.

The overall process flow is as shown in FIG. In the present embodiment, the resist film thickness is set in consideration of the bulk effect of the resist film itself, a standing wave effect such as an intra-film multiple reflection effect, and a step structure formed on a semiconductor substrate. The case where the film thickness is set to 1.2 microns will be described as an example. The process from step to step and the process from step to step are the same as the conventional one shown in FIG. 3, and thus detailed description thereof will be omitted.

At the time of the exposure in the process, first,
In the step (1), alignment measurement is performed on shots that have been arbitrarily set in the wafer, and then the shrinkage ratio of the wafer and the amounts of displacement in the X and Y directions are calculated and corrected by statistical calculation.
In the step (2), the inclination component of the exposure area is measured for each exposure shot, and the wafer stage holding the wafer substrate is operated to perform the inclination correction so that the flatness is the best.

In the step (3), the optimum focus point of each exposure shot is measured in a state where the measurement is performed in a state where the light is transmitted through the projection lens (TTL ON LENS) or in a state where the light is not transmitted (TTL OFF LENS). And the wafer stage holding the wafer substrate is moved up and down to maintain the best focus state.

The next step is the most characteristic of this embodiment. In the step (4), a reduction projection exposure apparatus is provided with a reflectance measuring mechanism, and the light is transmitted through the projection lens (TTL ON).
LENS), or the reflectance of each exposure shot is measured by any method of not transmitting (TTL OFF LENS). At this time, the measurement is performed using a single wavelength different from the exposure wavelength or a wavelength having a wide bandwidth for the purpose of preventing exposure of the resist film.

Next, an exposure correction coefficient is obtained from the correlation between the reflectance and the line width obtained in advance by experiments and the line width variation rate (correlation between the exposure amount and the line width) due to the change in the exposure amount. Is input to the exposure control system, and an appropriate exposure amount is automatically calculated based on this correction coefficient, and then the exposure step (5) is performed. As an example of the correction method, an example based on experimental results on a semiconductor substrate on which a polycrystalline polysilicon film is formed will be described with reference to FIG.

FIG. 2 shows an exposure at the same exposure dose (exposure at 150 mj / cm ^{2 in} this experiment) on the semiconductor substrate when it is carried out under the process conditions of FIG. 1 conducted in this experiment. Shows the resist dimensions for each reflectance at the time of the exposure. here,
For example, the exposure at which a line width of 1.0 μm can be obtained under the condition of 50% reflectance is 150 mj / cm ² , and the line width variation ΔX = 0.02 μm due to a 5% change in reflectance on the substrate.
m. Incidentally, it is required that the exposure amount necessary for changing the thickness by 0.02 μm is 5 mj / cm ² in advance based on an experimental result using a substrate having a reflectance of 50% (not shown).

Therefore, on a 50% reflectance substrate, 1.
On the basis of obtaining a size of 0 μm, an appropriate exposure amount for each exposure shot due to a change in reflectance can be obtained by the following formula using the correction coefficient obtained as described above. Proper exposure amount for each exposure shot = 150 mj / cm ^2-
[((A−50) / 5) × 5] (where A is the measured reflectivity.) However, this formula is an example in the present embodiment, and the resist film thickness conditions used, baking Since the conditions, development conditions, and the size of the reduction projection exposure apparatus to be used vary depending on the conditions, it is necessary to obtain experimentally various conditions in advance in experiments.

Although the above embodiment has been described taking the case of using global alignment as an example, the alignment may be performed by a die-by-die method for performing alignment measurement and correction for each exposure shot. .
Also, the explanation has been given by taking as an example the correction of the exposure shot unit as the tilt correction of the semiconductor substrate to be exposed. However, the present invention can be applied to any of the global tilt for correcting the tilt of the entire wafer or the case where the tilt correction is not performed. The most characteristic point is that tilt correction is performed in a state immediately before exposure. By performing this, measurement and correction of exposure are performed in a final state in which stage driving is not performed.

[0021]

According to the present invention, even when the film formed on the substrate or the film formed by vapor deposition has a different reflectance in each region in the wafer, the same size is used for each exposure shot unit. Exposure can be performed after performing the obtained exposure correction, and the increase in the diameter of the wafer, from the basis, does not depend on the variation in the reflectance of the lower layer film, the entire wafer, and the resist dimension between the wafers It is possible to achieve stabilization, and it is possible to obtain the effect of improving the reliability and the yield by making the element characteristics uniform among the product chips by improving the dimensional control accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram showing a photolithography process of the present invention.

FIG. 2 is a graph showing a correlation between a reflectance and a line width dimension when exposure is performed at the same exposure amount on a semiconductor substrate.

FIG. 3 is a diagram showing a photolithography process according to a conventional method.

Claims (4)

[Claims] 1. A semiconductor substrate is sequentially subjected to a dehydration bake treatment,
As a part of the process of forming a resist pattern having desired dimensions by performing a DS process, a pre-bake process, a resist coat process, an exposure, a development, and a post-bake process, a g-line is produced by a reduction projection exposure apparatus using a step-and-repeat method. In a photolithography exposure method, a specific single wavelength or a wide bandwidth wavelength is used regardless of the exposure wavelength such as i-line, X-ray, Krf, etc. and the pattern on the reticle is projected onto a semiconductor substrate in a reduced size. In advance, using a semiconductor substrate in a desired process, a correlation coefficient between the reflectance and the line width of the semiconductor substrate and a correlation coefficient between the exposure amount and the line width are obtained, and the correlation coefficient of the semiconductor substrate is obtained from the mutual correlation coefficient. A step of calculating a correction amount for increasing or decreasing the exposure amount to obtain the same dimension when the reflectance changes, and setting the exposure control system of the exposure apparatus; and When performing the exposure by Pete method, transmitted through the projection lens the reflectivity of the semiconductor substrate for each of the exposure shot prior to the exposure of each exposure shot state (TTL O
NLENS) or non-transmitting (TTL
OFF LENS), and using the reflectance measured in the above step and the correction amount,
A step of performing exposure by performing exposure correction for each exposure shot, and an exposure method for photolithography. 2. A reduction projection exposure apparatus for performing exposure for reducing and projecting a pattern on a reticle onto a semiconductor substrate by using a specific single wavelength such as g-line, i-line, X-ray, or Krf or a wide-band wavelength. When performing exposure by an AND repeat method, prior to exposure of each exposure shot, reflectance measurement means for measuring the reflectance of the semiconductor substrate for each exposure shot, and in advance, the reflectance of the semiconductor substrate and the resist A correlation coefficient between the line width and a correlation coefficient between the exposure amount and the line width of the resist is obtained, and using these correlation coefficients, the correction of the exposure amount according to the reflectance measured by the reflectance measuring means. And a correcting means for performing the following. 3. The reduction projection apparatus according to claim 2, wherein said reflectance measuring means measures the reflectance using a single wavelength having a wavelength different from the exposure wavelength or a wavelength having a wide bandwidth. 4. The reduction projection according to claim 2, wherein the correction of the exposure amount corrects an increase or a decrease in a line width of the resist due to a difference in reflectance of the semiconductor substrate. apparatus.