JP2005321312A - Acid diffusion constant measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for determining quantitatively an acid diffusion constant precisely, in lithography using a chemical amplification type resist. <P>SOLUTION: A resist solution added with a photo-acid generating agent in a resin is applied onto two sheets of substrates to prepare resist-applied substrate samples, the plurality of resist-applied substrate samples is irradiated thereafter with a laser beam to expose the resist to the beam, one side of the exposed resist-applied substrate samples is kept in a low temperature, and the other is heated. The each resist in the two resist-applied substrate samples is cut along a diagonal direction by a blade to form a sloped face on a resist layer. Then, the sloped faces of the resist layers in the low-temperature-held sample and the heated sample are component-analyzed by a micro-area quantitative determination means to determine distributions of an acid component, two obtained component distributions are compared each other to determine the acid diffusion constant of an acid existing in the resist. A resist composition in a PAG or a quencher is thereby optimized to enhance lithography performance. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a measurement method for accurately obtaining an acid diffusion constant, which is effective in the development of a lithography process using a chemically amplified resist using an excimer laser beam as exposure light.

In the manufacturing process of a semiconductor element, photolithography is employed to perform fine processing on a semiconductor substrate.
In recent optical lithography, the pattern width of a semiconductor element is required to have an accuracy of 0.15 μm or less. To meet this, the wavelength of exposure light used from KrF exposure to ArF exposure and F2 exposure is different. The wavelength is getting shorter. When such short-wavelength exposure light is used, the light transmittance of the resist is reduced, resulting in insufficient light intensity at the bottom of the resist and reduced sensitivity. Therefore, a photoacid generator is added to the resist material. Chemically amplified resists that generate and sensitize acid by light irradiation have been used.
In this chemically amplified resist, a photoacid generator such as bissulfoniuazomethanes or a nitrobenzyl derivative is added to the resin material, and an acid is generated in the resist by exposure to exposure light. Is to improve.

  By the way, in order to optimize such a resist material and its processing process, it is necessary to grasp the behavior of the acid generated during the exposure process and the subsequent development process. In other words, the acid generated by exposure diffuses in the resist by post-exposure heating (PEB). However, in a resist system having a high diffusion rate, when the PEB treatment is performed for a long time, the acid generated by exposure is reduced. Quantitative understanding of the acid diffusion rate in the resist system is necessary for optimizing the process, because it diffuses to the non-exposed areas and results in distortion of the pattern. .

  Conventionally, the acid diffusion constant of such a chemically amplified resist is derived by (1) a method obtained from PEB temperature dependency and PEB time dependency of transfer pattern dimensions, and (2) from an upper layer containing acid molecules by a multilayer resist. Determining the acid diffusion in the depth direction to the resist thin film by developing the resist thin film after PEB and examining its depth, (3) Measured from the temperature dependence of the electrical conductivity of the resin thin film containing acid molecules The technology to do is known.

  When using the chemically amplified resist itself as a means of observing how far the acid has diffused by PEB treatment, it utilizes the deprotection reaction of the chemically amplified resist by acid and the dissolution reaction in an alkaline developer. In these reactions, the reaction rate changes depending on conditions such as the PEB temperature and the acidity of the acid molecules to diffuse, and the acid diffusion behavior cannot be strictly extracted. In addition, the method of measuring acid diffusion based on the temperature dependence of electrical conductivity derived from the thermal motion of acid molecules in the resist resin is sensitive to the electrical conductivity of additives other than acid molecules in the resist. Relative evaluation when the chemical species of the acid molecule changes between resists with different compositions of the additive, due to the fact that the acid diffusion constant and electrical conductivity are indirectly related by the theoretical formula, There is some difficulty in evaluating the absolute value of the acid diffusion constant.

The present invention has been made to solve the problems that occur in conventional resist development and design, and aims to realize a method capable of quantitatively determining an acid diffusion constant with high accuracy by a simple method. .

The present invention comprises a step of applying a resist solution to which a photoacid generator is added on at least two substrates to prepare a resist-coated substrate sample;
Irradiating the plurality of resist-coated substrate samples with laser light to expose the resist; and
Holding one of the exposed resist-coated substrate samples at a low temperature and heating the other;
Cutting the resist of the two resist-coated substrate samples in an oblique direction with a blade to form an inclined surface on the resist; and
Analyzing the inclined surfaces of the resist of the low temperature holding sample and the heated sample by a component analysis by a micro area quantitative analysis means, and determining the distribution of the acid component;
It is an acid diffusion constant measuring method characterized in that two component distributions obtained by the above steps are compared to determine a diffusion constant of an acid present in the resist.

  In the present invention, a chemically amplified resist can be used as the resist. As the exposure light, a KrF excimer laser can be used. Furthermore, a diamond blade is preferable as the blade.

  According to the present invention, a tool that precisely cuts a resist resin thin film in a slanting direction with a sharp blade to create an inclined surface with a distance of several hundred μm, and a spectroscopic analyzer that can analyze acid molecules in a minute area By using this system, acid molecules in the resist thin film can be observed directly, and the thermal diffusion behavior can be traced directly, so that quantitative acid diffusion constant measurement is possible. is there.

Then, by determining the acid diffusion constant using such a principle, in the lithography using the chemically amplified resist, by providing a highly accurate means for determining the acid diffusion constant, the resist composition of PAG and quencher It is possible to optimize the lithography performance and improve the lithography performance.

[Principle of the Invention]
The principle of the present invention will be described below. In the present invention, by vertically irradiating laser light onto a resist thin film uniformly coated and formed on a reflective substrate such as Si, the resist thin film is formed by optical interference between reflected light from the substrate surface and incident light. A pattern of acid molecule concentration with a period of n / λ (where n is the refractive index of the resist resin and λ is the wavelength of the laser beam) is formed. Quantitative analysis of a sample having this acid molecule concentration distribution pattern and heating the sample with a resist thin film having the same distribution pattern as this distribution pattern to diffuse the acid molecules, the acid in the resist thin film of the sample obtained This is made by paying attention to the fact that the diffusion behavior of acid molecules by heat treatment can be analyzed by quantitatively analyzing the concentration and comparing the acid concentration distributions of the two samples.

  In order to quantitatively analyze the distribution of acid molecules by the above method, it is necessary to analyze the depth direction pattern of the acid concentration according to the standing wave of the exposure light. It is difficult to quantitatively analyze the distributed acid molecules. Therefore, in the present invention, the resist thin film is cut so as to form an inclined surface, and the surface exposed to the inclined surface is used by using an apparatus capable of quantitative component analysis of minute spots such as X-ray fluorescence analysis. This enables analysis of acid molecule distribution in the thickness direction of the resist thin film.

[Measuring method]
Hereinafter, the measuring method of the present invention will be described in detail with reference to FIG.

(First step)
The first step of the measurement method of the present embodiment is a step of creating a resist-coated substrate sample by applying a resist solution in which at least a photoacid generator is added to a resin on at least two substrates (FIG. 1 (a)). In this step, as a substrate to be used, a substrate having a surface that reflects exposure light can be used. Specifically, a silicon substrate whose surface is mirror-polished, a glass substrate having a reflective metal thin film formed on the surface, or the like can be used. One of the two substrates is for measuring the reference concentration of the acid molecules generated according to the intensity of the standing wave generated by exposure, and the other one is heat-treated ( This is for measuring the concentration distribution of acid molecules in a state where acid molecules are diffused by PEB treatment.

  As the resist formed on the surface of the substrate, a conventionally known chemically amplified resist can be used. As this resist, it is possible to use a resist material obtained by adding a known additive such as a photoacid generator and other base to a resist resin which is an object of process design.

  As the resist resin used in this embodiment, a resist that is sensitive to light having a wavelength of KrF light or less is preferable. However, when the wavelength is shorter than F2 light, the photosensitivity of the resist is lowered, so that it is sensitive to light in the DUV region. A resist material is preferable. Specific examples include polyhydroxystyrene having a tertiary butoxycarbonyl group.

  The photoacid generator used in the present embodiment is not particularly limited, but bissulfoniudiazomethanes, nitrobenzyl derivatives, polyhydroxy compounds and aliphatic or aromatic sulfonates, onium salts, sulfonyls Examples include carbonylalkanes, sulfonylcarbonyldiazomethanes, halogen-containing triazine compounds, oxime sulfonate compounds, and phenylsulfonyloxyphthalimides.

  The resist material is prepared by adding a dissolution inhibitor, a crosslinking agent, etc., if necessary, in addition to these resist resin and photoacid generator and dissolving in a solvent.

(Second step)
The second step of the measurement method of the present embodiment is a step of exposing the resist by irradiating the two resist-coated substrate samples with laser light (FIG. 1B). As described above, excimer laser light having a wavelength of KrF or less is preferable as the laser light in this step, and excimer laser light having a longer wavelength than F2 light is more preferable. As an exposure apparatus used for this, a generally used exposure apparatus for photolithography can be used. As described above, in this step, the exposure light applied to the sample is reflected by the substrate and generates a standing wave in the resist layer. As a result, the intensity of the applied light varies in the resist depth direction. This situation will be described with reference to FIG. 2 which is an enlarged sectional view of the substrate and the resist thin film formed on the surface thereof. In FIG. 2, a resist 12 is formed on the surface of a substrate 11, and exposure light is irradiated from the surface vertical direction. This exposure light is reflected between the surface of the substrate 11 and the surface of the resist 12 to generate a standing wave. In the portion 21 where the light intensity of the standing wave is high, the concentration of acid molecules generated from the photoacid generator is high, while in the portion 22 where the light intensity of the standing wave is low, the concentration of acid molecules is low. As a result, the concentration of the acid generated from the photoacid generator by light irradiation varies depending on the position in the depth direction of the resist. In the present invention, the acid diffusion constant of the acid is determined by utilizing the non-uniformity of the acid concentration thus generated. The exposure light irradiation condition for this is preferably a condition in which a standing wave due to the exposure light is stably formed inside the resist layer. It is possible to determine the optimum condition by changing the above and trial and error.

(Third step)
The third step of the measurement method of the present embodiment is a step of PEB processing one of the exposed resist-coated substrate samples. By this step, the acid generated in the resist as a result of the exposure treatment in the above step diffuses. Generally used conditions can be adopted as the conditions for the PEB treatment. Specifically, it is preferable to set it as 70-200 degreeC. In this treatment, a hot plate generally used for PEB treatment can be used as the heating means, but in order to determine a highly accurate acid diffusion constant, a heating device capable of controlling the temperature with high accuracy is preferable. . The accuracy is preferably within a range of ± 0.1 ° C.

  On the other hand, in the present invention, in order to determine the amount of acid transfer due to this diffusion phenomenon, a reference sample is prepared and compared with the sample subjected to the PEB treatment. For this purpose, one of the exposure samples is stored at a low temperature so that the generated acid does not diffuse and move. The storage temperature is preferably 5 ° C. or less and about 100 minutes or less. When the storage conditions exceed the above range, the acid generated by exposure diffuses and cannot be used as a reference sample.

(Fourth process)
The fourth step of the measurement method of the present embodiment is a step of cutting a resist layer of a sample that has been subjected to PEB processing or stored at a low temperature in the above step (FIG. 1C). That is, the resists of the two resist-coated substrate samples are cut in an oblique direction with a blade to form an inclined surface on the resist layer. Specifically, the cutting device used in this step cuts the resist layer in an oblique direction using a cutting tool such as a diamond blade to form an inclined surface. In this step, the angle of the inclined surface to be formed, that is, the angle formed between the substrate surface and the inclined surface is preferably in the range of 10 to 0.1 °. When the angle of the inclined surface is less than the above range, the signal intensity obtained from the contained element is reduced in elemental analysis performed in a subsequent process, and it is difficult to detect a trace amount contained component. On the other hand, if the angle of the inclined surface exceeds the above range, it is necessary to make the spot diameter of the irradiation light of the spectroscopic analyzer used in the element analysis in the subsequent process fine, and the apparatus is large. End up.

  Further, it is preferable that the inclined surface is cut so as to be in a state close to a mirror surface. When the surface is rough, noise during component analysis becomes excessive, which is not preferable.

Such a cutting apparatus includes a sample stage for holding a rough sample, a blade holder for holding a blade for cutting a resist layer on the surface of the sample, and a blade holder for slidably supporting the blade holder and moving it in a predetermined path. Mainly from guides. This apparatus is preferably provided with a temperature control device that can be kept at a low temperature so that the substance contained in the sample resist does not change.
Such a device has been developed by the Toray Research Center and is generally available from the company.

(Fifth step)
The fifth step of the measurement method according to the present embodiment is a step of determining the acid concentration distribution by analyzing the components of the inclined surface of the resist layer by a micro area quantitative analysis means (FIG. 1 (d)). An analyzer that can be used in this step includes an X-ray fluorescence analyzer such as XPS or SIMS. This device irradiates a sample surface with an X-ray spot and, as a result, spectroscopically analyzes the fluorescence emitted from the sample, and detects the contained substance quantitatively from the signal output. Can be determined.
Further, in this step, the amount of acid molecules distributed on the inclined surface of the resist layer can be measured by scanning X-rays irradiated on the sample surface.
In this step, the X-ray spot to be irradiated is preferably as fine as possible in order to accurately measure the acid diffusion constant, but it is generally preferable to set the spot within a range of 10 to 1000 nm. In order to make the X-ray spot diameter smaller than the above range, the apparatus becomes large and uneconomical. On the other hand, when the spot diameter exceeds the above range, acid molecules existing in a wide area are quantified, and the accuracy of the acid concentration distribution to be measured is lowered.

  In FIG. 4, the example of the graph which visualized the acid concentration distribution obtained by the said process is shown. FIG. 4 shows the results of quantitative analysis of acid molecules generated by exposure of the PEB-treated sample and the cryopreserved sample by the above-mentioned means, and the depth from the surface of the sample is plotted on the horizontal axis and the content of acid molecules on the vertical axis. Are plotted. As shown in FIG. 4, a large amount of acid is present in a portion having a large standing wave light intensity generated by exposure light irradiated in the thickness direction of the resist layer, and a small amount of acid is present in a portion having a low standing wave intensity. Indicates that it exists. For samples stored at a low temperature, the concentration of the acid contained in the portion with relatively high light intensity and the portion with low light intensity differ greatly, whereas for the sample heated by PEB treatment, The change in concentration is moderated, which indicates that the acid is thermally diffused by heating. Thus, by comparing the distribution of acid molecules generated by standing waves generated by exposure with a sample that has been heated and diffused, and a reference sample that has not been treated in this way, It becomes possible to calculate the diffusion constant.

(Sixth step)
In the sixth step of the present embodiment, based on the acid content distribution data of the two samples obtained by the step, the component distributions of the two samples obtained by the step are compared, and The acid diffusion constant of the acid present in Specifically, by starting the distribution of the reference acid molecules that have not been heat-treated, the result of simulating the diffusion equation by varying the acid diffusion constant on the computer, and checking the measured data, It becomes possible to determine the acid diffusion constant in the measured data. As a computer used in this step, a general-purpose personal computer, a workstation, or the like can be employed.

Sectional drawing for demonstrating the process of the acid diffusion constant determination method of this invention. The conceptual diagram for demonstrating the state which irradiates exposure light to a resist and has produced the standing wave. Sectional drawing of the sample which cut the resist layer diagonally. The graph for showing the process of the acid diffusion constant determination of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Board | substrate 12 ... Resist layer 13 ... Exposure light 14 ... Inclined surface formed by cutting 15 ... X-ray for component analysis 21 ... The part with strong light intensity of standing wave 22 ... The light intensity of standing wave is weak portion

Claims (4)

Applying a resist solution to which a photoacid generator has been added on at least two substrates to create a resist-coated substrate sample;
Irradiating the plurality of resist-coated substrate samples with laser light to expose the resist; and
Holding one of the exposed resist-coated substrate samples at a low temperature and heating the other;
Cutting the resist of the two resist-coated substrate samples in an oblique direction with a blade to form an inclined surface on the resist; and
Analyzing the inclined surfaces of the resist of the low temperature holding sample and the heated sample by a component analysis by a micro area quantitative analysis means, and determining the distribution of acid components
A method for measuring an acid diffusion constant, comprising: comparing two acid component distributions obtained by the step to determine a diffusion constant of an acid present in the resist.   The acid diffusion constant measuring method according to claim 1, wherein the resist is a chemically amplified resist.   The acid diffusion constant measuring method according to claim 1, wherein the exposure light is a KrF excimer laser. The acid diffusion constant measuring method according to any one of claims 1 to 3, wherein the blade is a diamond blade.

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