JP2008311257A - Photoresist removing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively peel resist made of phenol resin remaining sticking on a substrate top surface at a fast peeling speed without damaging the substrate itself. <P>SOLUTION: High-density ozone water is applied over the top surface of the substrate where novolak-resin based photoresist remains and sticks and irradiated with ultraviolet light (for example, excimer laser light), which produces an OH radical from part of ozone of the high-density ozone water. Then the produced OH radical makes the photoresist polyphenolic and the remaining ozone of the high-density ozone water reacts on the photoresist having been made polyphenolic to fragmentate and peel the photoresist off the substrate surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a removal method for removing an organic compound or the like having a benzene ring by irradiating ultraviolet light while pouring high-concentration ozone water, and in particular, remains on a semiconductor substrate surface in a semiconductor manufacturing process. The present invention relates to a photoresist removal method for removing and removing a photoresist from a substrate surface using high-concentration ozone water and ultraviolet light.

  More specifically, the present invention provides a photo resist that can efficiently and uniformly remove photoresist remaining on the surface of a substrate that has been subjected to dry etching or high current ion implantation in a semiconductor manufacturing process. The present invention relates to a resist removal method.

  Conventionally, in a semiconductor manufacturing process, in a resist removing process for removing unnecessary photoresist remaining on the surface of a silicon substrate (in-process silicon wafer) or the like, the photoresist is removed by plasma containing oxygen (ashing means). ) (See Patent Document 1), a method of dissolving a resist using a solvent such as concentrated sulfuric acid, a chemical, or the like.

  A method of removing ozone by supplying ozone water to the surface of a silicon substrate where unnecessary photoresist remains is also known (see Patent Document 2). In particular, a method of pouring ozone water into an ozone water silicon substrate from a cylindrical tube provided with a water inlet facing the surface center of the silicon substrate is also known.

Japanese Patent Publication No.8-021562 JP 2006-295091 A

  However, if an asher is used for removing the resist, the semiconductor substrate may be damaged by plasma, and inorganic impurities cannot be removed. In addition, when resist is removed using a solvent or chemical, a large amount of waste liquid is generated, and this is a major problem both in terms of cost and environment during waste liquid treatment.

  In the method of removing the photoresist by supplying ozone water to the surface of the substrate, removal with only ozone water is not sufficient in removing effect.

  An object of the present invention is to solve the above-mentioned conventional problem in removing the photoresist remaining on the substrate surface, and using the high-concentration ozone water and excimer light, the photoresist remaining on the silicon substrate is removed from the substrate itself. It is an object of the present invention to realize a photoresist removal method in which the reaction efficiency of ozone water per unit volume to a photoresist is increased without causing damage, and the resist is effectively removed and removed.

  In order to solve the above-mentioned problems, the present invention injects high-concentration ozone water onto the surface of the substrate on which the photoresist made of phenol resin remains attached, and irradiates the ultraviolet light, whereby the ultraviolet light is OH radicals are generated from a portion of ozone in the high-concentration ozone water, the generated OH radicals polyphenolize the photoresist, and residual ozone in the high-concentration ozone water reacts with the polyphenolated photoresist. Provided is a method for removing a photoresist, which is fragmented and peeled off from the surface of the substrate.

  The wavelength region of the ultraviolet light is particularly preferably 200 nm to 300 nm, which can generate OH radicals maximum from high-concentration ozone water.

  The photoresist composed of the phenol resin is preferably a novolac resin-based photoresist.

  It is preferable that the speed at which the remaining photoresist is peeled off from the substrate surface can be changed by changing the light intensity of the ultraviolet light and the concentration of high-concentration ozone water.

  The concentration of high-concentration ozone water is characterized by a concentration of ozone water of 80 mg / L or more.

  According to the present invention, an efficiency comparable to the cleaning effect of concentrated sulfuric acid which has been conventionally performed can be realized, and thus high-concentration ozone water cleaning as an alternative technique of cleaning with concentrated sulfuric acid can be put into practical use.

  The best mode for carrying out the photoresist removing method according to the present invention will be described below with reference to the drawings based on the embodiments.

  In a semiconductor manufacturing process or the like, a phenol resin is usually used as a photoresist (eg, novolak resin-based photoresist). The photoresist removing method according to the present invention removes the photoresist from the substrate by irradiating the photoresist remaining on the substrate with high-concentration ozone water and irradiating with ultraviolet light. Is the method. Note that as the ultraviolet light, in this specification, excimer laser light (referred to as “excimer light” in this specification) is described.

  FIG. 1 shows a conceptual diagram of the photoresist removal method of the present invention compared to the prior art. Conventionally, it has been known that the photoresist remaining on the substrate by ozone water (hereinafter, described as a novolak resin-based photoresist) is peeled off. However, this peeling rate is slow, and there is a difficulty that peeling does not occur at a rate that can be said to be sufficient at the production site.

  In order to solve this problem, the present inventors have conducted extensive research and development. As a result, the novolak resin-based photoresist is not directly peeled off from the substrate directly with only ozone water, but once the novolak resin-based photoresist is polyphenolated resin. As a result, a novel finding was obtained that the novolak resin-based photoresist remaining on the substrate (recon wafer, etc.) can be peeled off at a high speed by ozone water.

  As described above, the photoresist removing method according to the present invention was made based on a novel exfoliation mechanism of a novolak resin-based photoresist by irradiating with high-concentration ozone water and ultraviolet light.

In FIG. 1, in the photoresist removing method according to the present invention, high-concentration ozone water is injected onto a substrate on which a novolak resin-based photoresist remains, and excimer light is irradiated. Then, the excimer light, OH radicals from the high concentration ozone water ^(· OH) is quickly generated, the OH radicals acts on the photoresist, to promote the polyphenols of molecules in the surface layer.

  The reaction rate of the polyphenolized photoresist to ozone is dramatically increased compared to the original novolac resin. As a result, the polyphenolated photoresist is easily decomposed and fragmented by causing a chemical reaction with high-concentration ozone water ozone, and is quickly and efficiently peeled off from the substrate surface. In addition, it is preferable that the density | concentration of high concentration ozone water is a density | concentration of ozone water concentration 80 mg / L or more.

(Mechanism of action)
Hereinafter, the action mechanism of the photoresist removal method according to the present invention will be described in detail with reference to the chemical reaction shown in FIG. The photoresist here is a novolak resin-based photoresist.

  When high-concentration ozone water is injected onto the substrate on which the novolak resin-based photoresist remains adhered and irradiated with excimer light, as shown in the following chemical formula 1, a part of the ozone water is decomposed by ultraviolet light to generate OH. Generate radicals.

  When OH radicals come into contact with the surface of the photoresist, the lifetime is short and it is difficult to reach the deep layer portion of the photoresist. However, the phenol polyphenolation reaction (hydroxylation reaction of the benzene ring) of the surface layer portion is efficiently performed.

By reacting phenol with polyphenol, the reactivity to ozone is dramatically increased. The secondary reaction rate constant of phenol and ozone is 1.3 × 10 ³ mol ⁻¹ s ⁻¹ , whereas resorcinol in which one OH group is added to phenol is 3 × 10 ⁵ mol ⁻¹ s ^−1. It has the above value.

  In this way, the introduction of one OH group into phenol increases the reactivity by 300 times or more, so that the polyphenol formed by introducing more OH groups reacts with ozone at a diffusion-controlled rate. Become.

  In this way, when OH radicals generated by the photolysis of ozone change phenol to polyphenol, polyphenol rapidly reacts with undecomposed ozone and breaks the C—C bond of the polymer main chain. This is considered to be a mechanism in which ozone water and excimer light are used in combination, but the photoresist is decomposed at a high speed, but is not oxidized to the deep portion of the photoresist, thereby causing peeling.

  By the way, if excimer light is too strong, all the ozone water injected into the photoresist is photodegraded and only the polyphenol hydroxylation reaction of the resist occurs. Therefore, the peeling speed can be further optimized by skillfully balancing the relationship between the ozone concentration and the light intensity of the excimer light.

(optimisation)
Such optimization is further described below. There are five possible factors affecting the peeling speed: ozone concentration, ozone water pouring speed, excimer light intensity, wafer (substrate) rotation speed, and reaction temperature. The maximum peeling rate can be obtained by adjusting these parameters as appropriate.

  As described above, polyphenolation of a novolak resin-based resist requires generation of OH radicals from ozone of high-concentration ozone water by photolysis of excimer light. However, if all the ozone in the high-concentration ozone water is converted to OH radicals, the polyphenolic photoresist remains as a polyphenol resin and does not come off. An amount of ozone sufficient to react with the polyphenol and break the C—C bond must be secured.

  We examine the relationship between ozone concentration and excimer light intensity. As shown in FIG. 3A, even if the excimer light intensity is kept constant and the ozone concentration is increased, the OH radical concentration does not increase linearly. One of the reasons is that the photon concentration becomes insufficient with respect to the ozone amount.

  However, even if the excimer light intensity is sufficient, the OH radical concentration does not increase linearly in direct proportion to the ozone concentration. The reason for this is that the ozone decomposition reaction proceeds in proportion to the square of the concentration, and therefore, even if the supply ozone concentration is increased, the decomposition consumption is unnecessarily increased. ).

  On the other hand, as shown in FIG. 3B, when the excimer light intensity is raised while supplying a constant concentration of ozone water, the OH radical concentration increases only to a certain extent. This is because when the excimer light is strengthened, ozone is decomposed by the mechanism of Schemes 2 and 3, and thus decreases rapidly.

  OH radicals are essential to polyphenolate novolac resins, and ozone is essential to decompose polyphenols. Therefore, in FIG. 3 (b), the maximum peeling rate can be obtained depending on the amount of ozone and OH radical concentration to be adjusted.

  It has been empirically known that the higher the rotational speed, the higher the peeling speed. In addition, it is advantageous that the reaction temperature is high considering only the chemical reaction rate, but it is also necessary to consider the balance between ozone self-decomposition, which increases in proportion to the temperature rise, and the scattering rate into the air. As described above, the maximum peeling rate is obtained by appropriately selecting the above five parameters.

(Photoresist removal device)
The photoresist removal method according to the present invention can further form a thin liquid film of high-concentration ozone water on the substrate 9 on which the photoresist remains adhered by using the photoresist removal apparatus 1 as shown in FIG. By simultaneously irradiating excimer light, the photoresist remaining on the substrate can be removed more uniformly and effectively.

  This photoresist removal apparatus 1 is driven by a motor 2 to rotate in a horizontal plane, a high-concentration ozone water supply apparatus 4, and a cleaning arm 7 that is mounted on a support arm 5 so as to be adjustable in the vertical direction with screws 6. And an excimer light irradiation source 8.

  The cleaning nozzle 7 includes a cylindrical tube 11 and a transparent disk 13 attached to the lower end of the cylindrical tube 11. The water inlet 12 at the lower end of the cylindrical tube 11 opens downward from the center of the transparent disk 13.

  In the photoresist removing apparatus 1 having such a configuration, the high-concentration ozone water is supplied from the water inlet 12 at the lower end of the cleaning nozzle to a narrow gap having a gap d between the transparent disk 13 and the substrate 9 of about 1 to 3 mm ( The flow of the thin liquid film 15 in the radial direction is formed on the substrate 9 by the centrifugal force generated by flowing into the slit 14 and rotating the rotary support 3, and at the same time, excimer light can be irradiated. It becomes possible. As a result, the cleaning efficiency can be dramatically improved.

(Experimental example)
The present inventors conducted an experiment for removing a photoresist using the photoresist removing apparatus 1 according to the present invention. This experimental example will be described below. In this experimental example, a silicon wafer is placed as a substrate 9 on the rotary support 3, high-concentration ozone water is injected onto the silicon wafer on which the photoresist remains and adhering, and excimer light is applied to the silicon wafer. The removal effect was evaluated by removing the photoresist and measuring the thickness (film thickness) of the remaining photoresist.

  As the excimer light irradiation source 8, an excimer lamp having an output of irradiating excimer light having a wavelength of 222 nm was used. The concentration of the high-concentration ozone water is 104 mg / l, and the ozone water injection time is 40 s. Ozone water is supplied to the center of the silicon wafer by the cleaning nozzle 7. As the photoresist on the silicon wafer, IP-3300-HP (manufactured by Tokyo Ohka Kogyo Co., Ltd.) having an initial film thickness of 10,000 (Å) was used.

Under such experimental conditions, for each of the cases where the silicon wafer was rotated at 300 rpm and 600 rpm,
(1) When ozone water injection and excimer light irradiation are performed simultaneously (in FIG. 5 showing the experimental results, ◇… 300 rpm + Parallel, ◆… 600 rpm + Parallel),
(2) After irradiation with excimer light, measurement and evaluation were performed for the case of pouring ozone water (in FIG. 5, □ ... 300 rpm + Separate, gray □ ... 600 rpm + Separate).
further,
(3) Measurement and evaluation were performed for a case where the rotation number of the silicon wafer was 600 rpm and no excimer light was irradiated (* in FIG. 5, 600 rpm).

  The results of these experiments are shown in FIG. When ozone water and excimer light of (2) above are separately applied, the effect can hardly be confirmed, but the removal amount is slightly improved at the outer edge portion of the silicon wafer. The distribution of the removal amount at this time is almost the same as the case where no excimer light is irradiated.

  On the other hand, when the ozone water and the excimer light of (1) are simultaneously irradiated and the rotation speed of the silicon wafer is 300 rpm, the removal amount at the center of the silicon wafer corresponding to the stagnation point of the water jet increases rapidly. Furthermore, it can be clearly confirmed that the removal speed of the silicon wafer is improved as the rotational speed is increased.

  From this experimental example, it was shown that the removal amount of the photoresist by the high-concentration ozone water becomes the largest in the vicinity of the center of the silicon wafer near the implanted portion. On the other hand, the resist removal rate at the outer edge portion of the silicon wafer was lower than this. It was also shown that the resist removal amount was improved by irradiating excimer light, and that the removal amount at the outer edge of the silicon wafer was improved by rotating the silicon wafer.

  The best mode for carrying out the photoresist removing method according to the present invention has been described based on the embodiments. However, the present invention is not limited to such embodiments, and is described in the claims. It goes without saying that there are various embodiments within the scope of the technical matters stated.

  The photoresist removal method according to the present invention is configured as described above, and is used to remove a photoresist that has been subjected to dry etching treatment and high current ion implantation treatment in a semiconductor manufacturing process. In particular, the environmental load can be reduced by replacing the concentrated sulfuric acid removal process currently used.

It is a conceptual diagram of the photoresist removal method of this invention compared with a prior art. It is a figure explaining the chemical reaction process for demonstrating the action mechanism of the photoresist removal method of this invention. It is a figure for demonstrating the optimization of peeling speed, (a) is a figure explaining the relationship between ozone concentration and H radical concentration when excimer light intensity is made constant, (b) is high concentration ozone. It is a figure explaining the relationship between excimer light intensity and OH radical density | concentration when supply_amount | feed_rate of water is made constant. It is a figure explaining the outline of a photoresist removal apparatus. It is a graph which shows the experimental result of the experiment example of this invention.

Explanation of symbols

1 Photoresist removal device
2 Motor
3 rotation support stand
4 High concentration ozone water supply device
5 Support arm
6 Screw
7 Cleaning nozzle
8 Excimer light irradiation source
9 Board
11 Cylindrical tube
12 Water inlet
13 Transparent disk
13 Transparent disk
14 Clearance (slit)
15 Thin liquid film d Dimension of gap

Claims (5)

By pouring high-concentration ozone water and irradiating ultraviolet light onto the surface of the substrate on which the photoresist made of phenol resin remains attached,
The ultraviolet light generates OH radicals from a part of ozone of high-concentration ozone water,
The generated OH radicals polyphenolize the photoresist,
A method for removing a photoresist, characterized in that the residual phenol of high-concentration ozone water reacts to fragment the polyphenolated photoresist and peels it from the substrate surface.   The photoresist removal method according to claim 1, wherein the ultraviolet light is excimer light.   3. The method of removing a photoresist according to claim 1, wherein the photoresist made of phenol resin is a novolak resin-based photoresist.   4. The speed at which the remaining attached photoresist is peeled off from the substrate surface can be changed by changing the light intensity of the excimer light and the concentration of high-concentration ozone water, respectively. Photoresist removal method.   The photoresist removal method according to claim 1, 2 or 3, wherein the high-concentration ozone water concentration is a concentration of ozone water concentration of 80 mg / L or more.

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