JP2690381B2 - Dummy wafer and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a dummy wafer used in an apparatus for manufacturing a semiconductor element such as an IC or an LSI and a manufacturing method thereof.

[Conventional technology]

2. Description of the Related Art Conventionally, in an exposure apparatus for manufacturing a semiconductor element such as an IC or an LSI, two basic performance improvements, namely resolution performance and overlay performance, have been required. The former is the ability to form a fine pattern on the photoresist surface applied on the semiconductor substrate (hereinafter referred to as “wafer”) surface, and the latter is the ability to form the pattern formed on the wafer surface in the previous process. On the other hand, it is the ability to accurately align and transfer the pattern on the photomask.

The exposure apparatus is, for example, a contact,
It is roughly classified into proximity, mirror 1: 1 projection, stepper, X-ray aligner, etc. Among them, the optimum superposition method is devised and implemented.

In general, an exposure method in which both resolution and superposition performance are balanced is preferable for semiconductor device manufacturing, and therefore, a reduction projection type exposure apparatus, so-called stepper, is widely used at present.

The resolution required for future exposure equipment is 0.5
There are three exposure methods that can achieve this performance, such as a stepper using an excimer laser as a light source, a proximity type aligner using an X-ray as an exposure source, and an EB direct writing method. There is. From the viewpoint of productivity, the former two methods are preferable.

On the other hand, overlay accuracy is generally 1/3 to 1
A value of / 5 is required, and achieving this accuracy is generally as difficult or even more difficult as achieving resolution.

Generally, there are the following error factors in the relative alignment between the pattern on the reticle surface and the pattern on the wafer surface, that is, the alignment.

(1-1) The cross-sectional shape, physical properties or optical characteristics of the pattern (or mark) on the wafer surface may be changed in various ways depending on the type or process of the device.

(1-2) The alignment detection system (optical system, signal processing system) must have a degree of freedom in order to ensure accurate alignment with respect to various processes with a predetermined accuracy.

(1-3) In order to give the alignment optical system 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.

Generally, it is important to reduce these error factors as much as possible and maintain them in good balance.

 Next, a specific example of the above-mentioned error factor will be described.

(2-1) A TTL on-axis alignment system can be configured by setting the alignment light to the same wavelength as the exposure wavelength. In such an alignment system, since the projection lens is well corrected for aberrations with respect to this wavelength, for example, the alignment optical system can be arranged above the reticle, and the projection image of the wafer pattern and the pattern on the reticle surface can be formed. Both can be aligned while simultaneously observing in the same visual field. Further, exposure can be performed at the position where the alignment is completed. Therefore, there are no system error factors in this method.

However, in this method, there is no room for selection of the alignment wavelength, and in the process such as the absorption resist, there are drawbacks in the process such that the signal light from the wafer is extremely attenuated.

(2-2) In the off-axis type stepper, the alignment optical system of the wafer can be freely designed without any restriction of the projection lens, and the degree of freedom can enhance the adaptability to the process. However,
With this method, simultaneous observation of the reticle and the wafer is not possible, the reticle is pre-aligned with a reticle alignment microscope to a predetermined reference, and the wafer is a wafer alignment microscope (hereinafter referred to as "wafer microscope").
Aligns with the reference in the microscope. Therefore, there is an error factor between the reticle and the wafer. Further, after the wafer alignment, the wafer must be moved by a predetermined distance (this is referred to as "reference length" or "Base Line") in order to overlap the wafer pattern with the projected image of the reticle. Therefore, this method results in increased system error factors.

As described above, in an apparatus using an alignment method including system errors, it is necessary to make efforts to stably maintain these error factors, and at the same time, to 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 a value of several tens of mm. Generally, even if strict temperature control is performed to suppress the thermal expansion of the substance that binds between these, 0.1 μm
It changes with time in the unit of 0.01 μm. In addition to the reference length described above, factors that cause such a change over time include the projection magnification of the lens, the alignment position of the reticle, and the array coordinate system of the wafer stage.

Therefore, when overlaying the reticle as the first object and the wafer as the second object, various overlay error factors, such as a change in magnification of the projection optical system over time, a change in the reference length over time, and To obtain a system error by using a so-called dummy wafer for the purpose of providing an exposure apparatus that can correct a system error such as a change with time in the arrangement coordinates of the wafer X and Y stages and can always perform high-precision overlay. Is being carried out. This is, for example, in an exposure device that exposes and transfers a pattern on the first object plane illuminated by an illumination system onto a second object plane disposed on a movable stage, by irradiating the alignment pattern provided on the first object plane. A third object surface having a reversible light-sensitive material capable of writing and erasing, which has an image of the alignment pattern on the movable stage instead of the second object and is sensitive to irradiation light of the alignment pattern When the pattern on the first object plane is exposed and transferred onto the second object plane by detecting the image formation state of the image of the alignment pattern formed on the third object plane. The system error is obtained. That is, first, for example, the pattern on the reticle surface as the first object is exposed and transferred onto the dummy wafer surface as the third object, and the image formation state of the transferred image at that time is used for alignment of the wafer as the second object. A wafer alignment microscope is used for detection, and the system error of the entire apparatus is automatically or semi-automatically corrected within the apparatus itself based on the detection error at this time.

[Problems to be solved by the invention]

The dummy wafer photosensitive material is required to have the following characteristics.

Excellent coloring sensitivity with ultraviolet light for high-speed processing.

In order to automatically correct the system error by the machine,
The colored object should have a certain level of contrast or higher while shining visible light and capturing data.

Must have sufficient repeatability.

As a photosensitive material candidate satisfying these conditions, a photosensitive resist, an inorganic photochromic material and an organic photochromic material can be mentioned.

However, since the photosensitive resist must be subjected to post-exposure development processing, it cannot be automated and cannot be used repeatedly.

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

Further, the organic photochromic material is excellent in coloring sensitivity but is rapidly faded, so that the contrast becomes less than a necessary contrast while shining visible light and capturing data. In addition, there is a drawback that the durability is not improved because the decomposition is severe.

As described above, even if the conventional materials are used, they have different drawbacks, and a photosensitive material suitable for the purpose has not been obtained.

The present inventor has conducted various studies on the defects of the organic photochromic material, which is one of the light-sensitive materials, and the overcoat member thereof, and has clarified the cause of the defects as follows.

If even a small amount of the organic solvent remains in the layer containing the organic photochromic material, the stability of the colored product may be deteriorated and the fading may be accelerated.

Baking is required to remove the organic solvent and bring the layer of the organic photochromic material into close contact with the wafer. However, if this is performed in air, the organic photochromic material is decomposed by oxygen in the air and the color density is reduced.

Oxygen in the air decomposes the organic photochromic material, resulting in repeated deterioration of durability.

Moisture in the air decomposes the organic photochromic material, resulting in repeated deterioration of durability.

In view of the above-mentioned problems, an object of the present invention is a dummy wafer using an organic photochromic material having excellent coloring sensitivity as a photosensitive material, and the colored material has a certain or more contrast during automatic correction of system error. However, it is an object of the present invention to provide a dummy wafer having sufficient repeated durability and a manufacturing method thereof.

[Means for solving the problem]

The present invention comprises a step of forming on a substrate a first layer consisting essentially of a resin containing 30 to 80% by weight of an organic photochromic material, a first vacuum for vacuum heating the substrate provided with the first layer. Dummy wafer having a heating step, a step of forming a second layer consisting essentially of polyvinyl alcohol on the first layer, and a second vacuum heating step of vacuum heating the substrate provided with the first layer and the second layer Is a manufacturing method.

Further, according to the present invention, a first layer (organic photochromic material layer) substantially made of a resin containing 30 to 80% by weight of an organic photochromic material on a substrate, and an oxygen permeability of 1 ×.
10 ^-10 cm ³ · cm / cm ² · s · cmHg or less and substantially H ₂
It is a dummy wafer having a second layer (overcoat layer) consisting essentially of O-free polyvinyl alcohol in this order.

When forming the first layer, a coating solution obtained by dissolving a resin and an organic photochromic material in an organic solvent is coated on a substrate such as bare silicon or a silicon wafer that has been subjected to a treatment such as vapor deposition, and then heat treatment in vacuum. To do. As a result, the solvent contained in the binder can be removed without decomposition of the organic photochromic material, the color density can be increased, and the time until fading can be lengthened.

When laminating the second layer on the first layer, a coating liquid in which polyvinyl alcohol (hereinafter referred to as PVA) is dissolved in a solvent that does not dissolve the first layer is coated on the substrate on which the first layer is formed. A known coating technique may be appropriately applied as a coating method. After coating, the substrate is heat treated in vacuum. As a result, the adhesion between the first layer and the second layer is increased, and oxygen and moisture (H ₂ O and OH ⁻ ) in the air contained in the material of the second layer can be removed. By removing these, the decomposition of the photochromic material due to oxygen or moisture can be suppressed.

In both of the first layer and the second layer, it is more preferable to mix the surface active agent in the material, because oxygen and water can be removed early in the heat treatment. As the surfactant, alcohols such as methanol and ethanol and commercially available surfactants can be used. The amount added may be such that the generation of bubbles in each layer can be suppressed, for example, several% by weight.
To about several tens of weight% is sufficient. The surfactant can also be removed by heat treatment.

Preferred examples of the organic photochromic material that can be used in the present invention include (I) spironaphthooxidine, (II) benzopyrrillospirane, and (III) fulgide.

(However, R ₁ = H, alkyl, alkoxy, R ₂ = H, halogen, alkyl, nitro, nitroalkoxy, R ₃ = H, alkyl, alkoxycarbonylalkyl) The resin used for the first layer is in the ultraviolet and visible regions. Polymer resins having high transparency, such as polymethylmethacrylate, polycarbonate, polystyrene and the like are preferable. As the solvent, a solvent having a low volatility such as toluene, xylene, ethyl cellosolve acetate, and diethyl glycol monomethyl acetate having a boiling point of 100 ° C. or higher is preferable.

Further, the concentration of the solid content of the resin and the organic photochromic material in the solution is preferably 40% or less.

The ratio of the organic photochromic material to the resin in the first layer is preferably 30 to 80% by weight, and more preferably 80 to 200 parts by weight with respect to 100 parts by weight of the resin.
The coating method is preferably a spin coating method because it is applied to a silicon wafer.

The polymer used for the second layer has an oxygen permeability of 1.0 × 10 ^-10
Those having a high light transmittance in the visible ultraviolet region of not more than cm ³ · cm / cm ² · s · cmHg are preferable, and polyvinyl alcohol which satisfies this condition and is soluble in a polar solvent such as water or alcohol is preferably used. Further, in order to improve the durability, polyvinyl alcohol can be acetalized to improve the hardenability and the repeating durability. The acetalization can be carried out, for example, by reacting with formalin or HCHO in a solution at 40 to 50 ° C. and substituting it with the OH group of PVA.

Also, the film thickness of the second layer is the first due to refraction in the second layer.
0.1 to 2μ so that there is no error in the position of the layer mark
It is desirable to be within the range of m. After coating the second layer, vacuum baking is performed at a high temperature in order to enhance adhesion with the first layer, but at that time, the organic photochromic material in the first layer is not decomposed, and the acetalized polyvinyl of the second layer is not decomposed. Does not decompose alcohol.

The vacuum heating conditions for the first layer and the second layer are 10 ⁻³ to 10 ⁻⁴ To.
rr, 90 to 100 ° C., preferably about 30 minutes.

By making the atmosphere of the heat treatment a vacuum instead of an inert gas, not only oxygen and the organic solvent in each layer but also a very small amount of residual water can be removed.

The organic solvent is immediately removed from the coating film, carbon dioxide,
Gases such as oxygen and nitrogen are removed relatively early, but water adsorbed on the surface of the coating film is the most difficult to remove and tends to remain. In the present invention, not only vacuum but also heating is used together so that even water can be removed.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 100 parts by weight of spironaphthoxazine having R ₁ = Me, R ₂ = R ₃ = H in the above chemical formula (I), and 100 parts by weight of polymethylmethacrylate having a molecular weight of 2,000,000, and 3 parts by weight. % Methanol was added to prepare an ethyl cellosolve acetate solution having a total concentration of these solid contents of 18% by weight.

3 g of this solution was coated on a silicon wafer at 25 ° C. using a spinner under the conditions of the first 300 rpm × 10 sec and the second 2000 rpm × 60 sec. Then, the first layer was formed by heat treatment for 20 minutes in a vacuum evaporator (vacuum degree 5 × 10 ⁻¹⁰ Torr, output 0.2 kW) set at 98 ± 2 ° C. The thickness of this first layer (coat film) was 0.93 μm, and the unevenness thereof was 30 to 50 nm.

Next, the silicon wafer on which the first layer was generated was set on a spinner without exposing it to ultraviolet rays, and polyvinyl alcohol (manufactured by Kishida Chemical Co., polymerization degree 1000, saponification degree 99 mol) was used.
%) 10% aqueous solution, the first 300 rpm × 30 sec, the second 600
Coating was performed under the conditions of 0 rpm x 60 sec. After that, heat treatment was performed for 40 minutes in the vacuum evaporator set at 98 ± 2 ° C. under the same conditions as for the first layer to obtain a dummy wafer having the first layer and the second layer.

Further, the dummy wafer was treated with 20.6 g of sulfuric acid and 2% of sodium sulfate.
15 g in the treatment liquid consisting of 5.3 g, formalin 9.5 g, and water 44.6 g
The dummy wafer of Example 1 was obtained by immersing it for a minute for acetalization and heating and drying.

The film thickness of the second layer of this dummy wafer was 1.0 μm, and the unevenness thereof was 80 to 100 nm. The oxygen permeability of polymethylmethacrylate used for the first layer was 1.15 × 10 ^-10 cm ³
・ Cm / cm ²・ s ・ cmHg, and the oxygen permeability of polyvinyl alcohol used in the second layer is 0.0089 × 10 ^-10 cm ³・ cm / cm ²
・ S ・ cmHg or less. The moisture permeability of the second layer was several months for one month at a relative humidity of 80%.

When the dummy wafer obtained by irradiating it with an ultraviolet light source of 800 mJ to the saturation amount was colored, the saturation absorbance was 5.0.
The decay time to saturation absorbance of 1.0 with light of 00 nm was 20 seconds. Moreover, the saturation absorbance decreased to 1.0 after repeating 150 times by the color fading.

Although the ratio of the organic photochromic material in the first layer was 50% in this example, there was no difference in the absorbance and the number of repetitions even when the ratio was 80%.

The hardening effect of the present invention not only improved water resistance, but also improved acid resistance and oil resistance, and increased the surface strength of the overcoat member (second layer).

Example 2 Instead of the compound of formula (I), R _{1 of} formula (II)
= Me, R ₂ = H, except for using 1,3,3'- trimethyl-indolino-6'-nitro benzopyrylium loss pyran was R ₃ = NO _2, before further vacuum heating of the second layer A dummy wafer of Example 2 was prepared in the same manner as in Example 1 except that acetalization was performed.

By performing vacuum heat treatment after acetalization,
It is preferable since the solvent and water in each layer are removed more thoroughly.

The saturated absorbance of the obtained dummy wafer was 7.0, and the decay time by the 600 nm light to the saturated absorbance of 1.0 was 2000 seconds.

In addition, the saturation absorbance decreased to 1.0 after repeating 50 times by the color fading.

As described above, it was confirmed that the dummy wafer of the example had a durability success of 50 to 200% as compared with the dummy wafer manufactured by the conventional manufacturing method. Also, by combining vacuum heat treatment and polyvinyl alcohol acetalization, the mechanical strength and environment resistance of the dummy wafer can be increased, and the optical characteristics are maintained without deteriorating the spectral transmittance characteristics of the overcoat member. can do.

Further, the durability can be sufficiently improved without repeating the conversion of polyvinyl alcohol to acetal.

〔The invention's effect〕

According to the present invention, a dummy wafer having a photochromic material layer having excellent stability and high absorbance was obtained.
This makes alignment work extremely easy,
High-precision alignment has become possible.

Claims (4)

(57) [Claims] 1. A step of forming a first layer consisting essentially of a resin containing 30 to 80% by weight of an organic photochromic material on a substrate, and a step of heating the substrate provided with the first layer under vacuum. A vacuum heating step, a step of forming a second layer substantially made of polyvinyl alcohol on the first layer, and a second vacuum heating step of vacuum heating the substrate provided with the first layer and the second layer. Dummy wafer manufacturing method. 2. The method according to claim 1, further comprising a step of acetalizing the polyvinyl alcohol between the step of forming the second layer and the second vacuum heating step. 3. A first layer consisting essentially of a resin containing 30 to 80% by weight of an organic photochromic material on a substrate, and an oxygen permeability of 1 × 10 ⁻¹⁰ cm ³ · cm / cm ² · s ·. A dummy wafer having, in this order, a second layer consisting essentially of polyvinyl alcohol having a cmHg or less and containing substantially no H ₂ O. 4. The dummy wafer according to claim 3, wherein the polyvinyl alcohol is acetalized polyvinyl alcohol.