JPH0410409A - Dummy wafer - Google Patents

Abstract

PURPOSE:To obtain a dummy wafer with a photochromic material layer of excellent stability and high absorbance by making a silicon wafer substrate carry the first layer made of a J association element of organic photochromic material and the second layer made of specific polymer in this order. CONSTITUTION:For example, spironaphthoxazine of chemical formula I where R1=Me, R2=R3=H is developed in an LB film deposition apparatus and overlaid with five piles of monomolecular 0.03nm form an organic photochromic material layer of about 0.15nm on a silicon substrate face. Next, this silicon wafer is set on a spinner with no exposure to ultraviolet rays and coated with a 10% aqueous solution of polyvinyl alcohol. Thereafter, the wafer is heat- treated in a clean oven replaced by N2 set at a specified temperature to obtain a dummy after having the first and second layers.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a dummy wafer used in an apparatus for manufacturing semiconductor elements such as ICs or LSIs.

(Prior Art) Conventionally, there has been a demand for improvements in two basic performances, resolution performance and overlay performance, in exposure apparatuses for manufacturing semiconductor devices such as ICs or LSIs. The ability to form fine patterns on the photoresist surface coated on the wafer surface (referred to as wafer J) is the ability to form fine patterns on the photomask surface compared to the pattern formed on the wafer surface in the previous process. It is the ability to accurately align and transfer patterns.

Exposure apparatuses vary depending on their exposure method, such as contact, proximity, mirror 1 projection, stepper, x11!
i! They are broadly classified into aligners, etc., and the optimal overlapping method for each has been devised and implemented.

Generally, for the manufacture of semiconductor devices, an exposure method that has a good balance between resolution performance and overlay performance is preferable, and for this reason, reduction projection type exposure devices, so-called steppers, are often used at present.

The resolution performance required for future exposure equipment is 0.5
In the vicinity of μm, exposure methods that can achieve this performance include, for example, a stepper using an excimer laser as a light source, xIt! There are three types of aligners: a broximity type aligner using No. 11 as an exposure source, and an EB direct writing method. Of these, the former two methods are preferable from the viewpoint of productivity.

On the other hand, the overlapping grain size is generally 1/3 to 1/3 of the minimum line width for printing.
A value of 115 is required, and achieving this granularity is generally as difficult or more difficult than achieving resolution performance.

In general, the following error factors exist in relative positioning, that is, alignment, between a pattern on a reticle surface and a pattern on a wafer surface.

(+-1) The cross-sectional shape, physical properties, or optical characteristics of the pattern (or mark) on the wafer surface vary widely depending on the type of device or process.

(1-2) In order to reliably perform alignment at a predetermined grain size in response to various processes, the alignment detection system (optical system, signal processing system) must have a degree of freedom.

(+-3) In order to provide the alignment optical system with a degree of freedom, it is necessary to configure the projection lens and the alignment optical system independently, and as a result, the alignment between the reticle and the wafer becomes indirect.

In general, it is important to minimize these error factors and maintain a good balance.

Next, specific examples of the above-mentioned error factors will be explained.

(2-1) By setting the alignment light to the same wavelength as the exposure wavelength, a TTL on-axis alignment system can be constructed. In such an alignment system, the projection lens has good aberration correction for this wavelength, so the alignment optical system can be placed above the reticle, for example, and the projected image of the wafer pattern and the pattern on the reticle surface can be It is possible to align both images without simultaneously observing them within the same field of view. Furthermore, exposure can be performed at the position where alignment has been completed. Therefore, there are no systematic error factors in this method.

However, in this method, there is no choice in the alignment wavelength, and in processes such as absorption resist, the signal light from the wafer is extremely attenuated, and this method has disadvantages in terms of the process.

(2-2) In an off-axis type stepper, the wafer alignment optical system can be freely designed without being subject to any restrictions of the projection lens, and this degree of freedom can enhance process adaptability. However, with this method, it is not possible to observe the reticle and wafer at the same time; the reticle must be aligned with a predetermined standard using a reticle alignment microscope, and the wafer must be aligned using a wafer alignment microscope (hereinafter referred to as "wafer microscope"). Alignment is performed to the reference inside the microscope.

For this reason, an error factor exists between the reticle and the wafer. Furthermore, after wafer alignment, in order to overlap the wafer pattern with the projected image of the reticle, a predetermined distance (this is called the "reference length" or rBa5eLine J) is used.
The wafer must be moved.

Therefore, this method results in an increase in system error factors.

In an apparatus using an alignment method that includes such system errors, it is necessary to try to maintain these error factors stably, and at the same time, periodically check and correct the amount. For example, the reference length, which is the distance between the optical axis of the projection lens and the optical axis of the alignment microscope, is usually several tens of mm.
He is a detective.

In general, even if strict temperature control is performed to suppress the thermal expansion of the material that connects this space, the
It changes over time in units of μm. Factors that cause such changes over time include, in addition to the above-mentioned reference length, the projection magnification of the lens, the alignment position of the reticle, and the arrangement coordinate system of the wafer stage.

Therefore, when overlapping a reticle as a first object and a wafer as a second object, there are various error factors in overlay, such as changes in the magnification of the projection optical system over time, changes in the reference length over time, With the aim of providing an exposure apparatus that can satisfactorily correct system errors such as changes in the arrangement coordinates of the wafer X-Y stage over time, and that can always perform highly accurate overlay.
The system error is determined using a so-called tummy wafer. For example, in an exposure device that exposes and transfers a pattern on a first object surface irradiated by an illumination system onto a second object surface placed on a movable stage, an alignment pattern provided on the first object surface is irradiated. ,
An image of the alignment pattern is placed on the movable stage in place of the second object on a third object surface having a reversible photosensitive material that is sensitive to the irradiation light of the alignment pattern and capable of writing and erasing. A system for exposing and transferring a pattern on the first object surface onto the second object surface by detecting the imaging state of the image of the alignment pattern formed on the third object surface. This is to find the error.

That is, first, a pattern on a reticle surface as a first object is exposed and transferred onto a dummy wafer surface as a third object, and the image formation state of the transferred image at that time is used for alignment of a wafer as a second object. Detection is performed using a wafer alignment microscope, and based on the detection results, the system of the entire apparatus (differences are automatically or semi-automatically corrected within the apparatus itself).

[The invention or the problem the invention is trying to solve]

By the way, the following characteristics are required of the photosensitive material for use in the photographic process.

- Excellent coloring sensitivity with ultraviolet light for faster processing.

■In order to automatically correct system errors caused by machines,
Colored objects must have a certain level of contrast while capturing data using visible light.

■Have sufficient durability for turning edges.

Candidates for photosensitive materials that meet these conditions ■～■ are:
Examples include photosensitive resists, inorganic photochromic materials, and organic photochromic materials.

However, since photosensitive resists must be subjected to visual processing after exposure, they cannot be automated and cannot be used repeatedly.

Inorganic photochromic materials have poor coloring sensitivity and cannot be processed at high speeds.

Furthermore, although organic photochromic materials have excellent coloring sensitivity, they fade quickly, and the contrast falls below the required level while data is being captured by exposing it to visible light. In addition, it has the disadvantage that the durability of edge reversing cannot be improved because it decomposes rapidly.

As mentioned above, even if conventional materials are used, each has different drawbacks, and a photosensitive material that meets the purpose cannot be obtained.

The present inventor has studied various drawbacks of the organic photochromic material, which is one of the photosensitive materials, and has clarified the cause of the drawbacks as follows.

■If even a small amount of organic solvent remains in the layer containing the organic photochromic material, the stability of the colored product may decrease and the color may fade more quickly.

■Beta is required to remove the organic solvent and adhere the organic photochromic material layer to the wafer, but if this is done in air, the organic photochromic material will decompose with the oxygen in the air and the coloring density will drop.

■Organic photochromic materials decompose due to oxygen in the air, resulting in poor durability over repeated use.

■Organic photochromic materials decompose due to moisture in the air, resulting in poor durability over repeated use.

The present applicant would like to first propose a dummy wafer that improves the drawbacks of such organic photochromic materials as follows (Japanese Patent Application Laid-Open No. 2-56919).

The dummy wafer includes a resin layer containing 30% to 80% of an organic photochromic material as a first layer on a substrate such as a bare silicon wafer or a silicon wafer that has been subjected to a process such as vapor deposition, and a resin layer containing 30% to 80% of an organic photochromic material as a first layer. Oxygen permeability as two layers?1. OXl0-”c+n3・cm/cm2・5-
It is characterized by comprising a polymer resin layer having a weight of 11 g or less per cm.

When forming such a first layer, a coating solution in which a polymer resin and an organic photochromic material are dissolved in an organic solvent is coated on a substrate such as bare silicon or a silicon wafer that has been subjected to a process such as vapor deposition. Heat treatment in inert gas or vacuum.

As a result, the solvent contained in the binder can be removed without causing decomposition of the organic photochromic material, increasing the color density and lengthening the time until fading.

However, the characteristics of this tummy wafer cannot be said to be fully satisfactory. An object of the present invention is to provide a dummy wafer having an organic photochromic material layer with extremely high stability and high edge-reversal durability in addition to increasing the absorbance of the photochromic layer.

[Means to solve the problem]

The present invention is a dummy wafer having a first layer made of a J-aggregate of an organic photochromic material and a second layer made of a polymer on a silicon wafer substrate in this order.

In organic photochromic materials based on merocyanine or spiropyran, which are sensitizing dyes, the absorption wavelength of the material shifts to longer wavelengths in the range of several nanometers to several tens of nanometers depending on the aggregation state of the molecular structure alone.

For example, when J-aggregates are formed in merocyanine, the number is 10
The absorption maximum shifts to the nm longer wavelength side.

When J-aggregates are formed radiatively, (1) the absorption spectrum becomes sharper and the absorbance (absorption intensity) increases several times.

(2) The colored object becomes stable.

In the case of a spiropyran-based organic photochromic material, the half-width is 25r+m, the absorbance is about 3 times, and the half-life is 104 times that of normal spiropyran. The present invention applies these principles and features to tummy wafers.

Organic photochromic materials that can be used in the present invention include 1. Those that form a J-aggregate through B11Q formation can be used, and preferred examples thereof include (I) spironaphthoxin, (II) benzobirilosbilane, and (III) fulgide.

(I) (II) (In) Tatashi, R, = H, alkyl, alkoxy, R2 = H,
halogen, alkyl, nitro, nitroalkoxy, R3
=H, alkyl, alkoxycarbonylalkyl In the first layer, the organic photochromic material is 0.0
By stacking 5 to IO monomolecular layers in the range of 3nar-0.15nm, a J-aggregate can be formed by repeating a normal LB film removal formation method, such as a pulling method.

The polymer used for the second layer has an oxygen permeability of 1. Ox 1
It is preferable to have a high light transmittance in the visible and ultraviolet region of 0-"cm3-cm/cm2-s-c+nHg or less, and polyvinyl alcohol and polyvinyl acetate that meet this condition and are soluble in polar solvents such as water and alcohol are preferred. Partially saponified materials, cellulose, etc. are preferably used.In order to further improve durability, polyvinyl alcohol is acetalized using a compound containing an aldehyde group such as formaldehyde to improve hardness and edge reversal durability. In addition, the thickness of the second layer is set to 0.1 to prevent errors in the position of the marks on the first layer due to refraction in the second layer.
It is desirable that the thickness be within the range of ~2 μm. After coating the second layer, it is preferable to bake at a high temperature of, for example, about 100°C for 30 to 40 minutes in order to increase the adhesion with the first layer. The acetalized polyvinyl alcohol of the second layer also does not decompose.

There are no particular restrictions on the method of forming the second layer.

According to the present invention, in order to form a laminated film of LB films, there is no need to mix, dissolve, and coat a photochromic material and a resin, and therefore, organic solvents, water, oxygen, etc. are not contained in the coating film. However, the deterioration caused by the chemical reaction with the photochromic material is significantly less.

There is no possibility of their inclusion in the LB film forming process, and only moisture or oxygen adsorbed to the LB film. However, since these can all be removed by heating and drying in nitrogen gas or vacuum in the post-process, an extremely stable and high-quality photochromic material layer can be obtained.

In addition, conventional projection systems require an exposure light source to utilize the maximum sensitivity of the resist, and in order to eliminate error factors with the alignment optical system, an en-axis alignment system is configured to use light sources of the same wavelength. However, it would be advantageous if the degree of alignment could be improved by using another long-wavelength exposure light source for alignment while maintaining off-axis alignment, and this has been achieved by the present invention.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Actually, the spironaphthoxazine with R, = Me, R2 = R, -H in the chemical formula (I) described above is developed in an LB film production device, and one molecule is 0.03r + ll1f! : a Repeatedly stacked 5 times, about 0. A photochromic material layer (first layer) of I5 nm was formed on the silicon substrate surface.

Next, the silicon wafer on which this '7tS1 layer was formed was set on a spinner without being exposed to any ultraviolet light, and a 10% aqueous solution of polyvinyl alcohol (manufactured by Kishida Chemical Co., Ltd., polymerization degree 1000, saponification degree 99 mo1%) was added to the first layer. times 300rp
m x 30sec, 2nd 6000rpm x 60
Coating was performed under conditions of sec. Thereafter, heat treatment was performed for 40 minutes in a clean oven set to 98±2° C. and replaced with N2 to obtain a dummy wafer having a first layer and a second layer.

Instead of the compound of chemical formula (I) in Example 1 above, Rr = C + aH: +t, R2 = N02 with chemical formula (rl)
, R3= CIh0COC2+ l (a. A J-aggregate of closed long-chain spiropyrans was formed.

The spiropyran based on this example is as shown in FIG.
Either the process of spiropyran (a) → photomerocyanine (b) → J-aggregate (C) shifts the absorption wavelength to the longer wavelength side, or the process of spiropyran-photomerocyanine is unstable, and spiropyran #J-aggregate The process is stable. Moreover, the magnitude of the absorbance is several ten times as large. The off-axis alignment system enables alignment at a wavelength different from the conventional exposure wavelength. In other words, the absorption wavelength of conventional spiropyran was the same as that of ultraviolet light exposure, but by using the aggregate, 6328 people's H
Alignment exposure using an e-Ne laser or a semiconductor laser with a longer wavelength is now possible. Absorbance is also 3-5
doubled.

Next, the silicon wafer on which the first layer was formed was coated with a 10% aqueous solution of polyvinyl alcohol in the same manner as in Example 1. Thereafter, this wafer was treated with 20.5 g of sulfuric acid,
Sodium sulfate 25.3g, formalin 9.5g, water 44.
Acetalization was performed by immersing it in a treatment solution containing 6 g for 15 minutes. Thereafter, heat treatment was performed in the same manner as in Example 1 to obtain a dummy wafer of Example 2 having a first layer and a second layer.

The thickness of the second layer on this dummy sea urchin is 1.0 μm, and the difference in unevenness is 80 to 100 r++n.

The saturated absorbance of the obtained dummy wafer was 7.0, which was 600.
The decay time to saturation absorbance 1.0 with nm light is 400
It was 0 seconds.

Furthermore, when the edges were turned over 100 times due to color fading, the saturated absorbance decreased by 1.0.

〔Effect of the invention〕

According to the present invention, a dummy wafer having a photochromic material layer with excellent stability and high absorbance was obtained. This makes alignment work extremely easy and allows high-grain alignment.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the absorption spectrum of spiropyran used in Example 2, (a) is spiropyran, (b)
(C) shows the spectrum of photomerocyanine, and (C) the J-aggregate. Patent applicant Canon Co., Ltd. Representative Patent attorney Tadashi Wakabu

Claims (1)

[Claims] 1. A first layer made of a J-aggregate of an organic photochromic material and a second layer made of a polymer on a silicon wafer substrate.
A dummy wafer with layers in this order. 2. The dummy wafer according to claim 1, wherein the polymer is polyvinyl alcohol or polyvinyl alcohol acetal.