JP2005340618A - Method for cleaning semiconductor substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for cleaning a semiconductor substrate which can solve a problem of a drying failure in a copper wiring forming step using a Low-k film. <P>SOLUTION: The method for cleaning the semiconductor substrate with a copper wiring layer formed therein comprises a first step in which a hydrophilic first film 7, a hydrophobic second film 8 and a hydrophilic third film 9 are laminated on the copper wiring layer in this order, and in a state that a copper layer composed of the copper wiring layer is exposed from an opening 11 provided in these films, the semiconductor substrate is subjected to a liquid medication processing; a second step of cleaning the semiconductor substrate with pure water after this liquid medication processing; and a third step in which, in a state that the semiconductor substrate is rotated, a gas containing vapor of isopropyl alcohol having a concentration of 0.01 volume% to 2.0 volume% is supplied and a drying processing for removing the pure water adhered to the semiconductor substrate is carried out. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for cleaning a semiconductor substrate, and more particularly to a method for cleaning a semiconductor substrate on which a copper wiring layer is formed.

  In recent years, the speed of semiconductor devices has been remarkably increased, and transmission delay due to a decrease in signal propagation speed due to wiring resistance in a multilayer wiring portion and parasitic capacitance between wiring layers has become a problem. Such a problem tends to become more prominent because the wiring resistance increases and the parasitic capacitance increases as the wiring width and the wiring interval become finer due to higher integration of semiconductor devices.

  In order to prevent signal delay due to an increase in wiring resistance and parasitic capacitance, copper wiring has been introduced instead of aluminum wiring, and an insulating film having a low dielectric constant (hereinafter referred to as a low-k film) is used as an interlayer insulating film. Has been attempted.

  As a method for forming a copper wiring using a low-k film, there is a damascene method. This is known as a technique for forming a wiring without etching copper, considering that it is difficult to control the etching rate of copper compared to aluminum.

  Specifically, in the damascene method, an opening is formed by dry etching of a low-k film using a resist film as a mask, and then the resist film is removed by ashing, and then a copper layer is embedded in the opening. This is a method of forming a wiring layer. The copper layer is embedded by forming a copper film so that the opening is embedded by plating and then planarizing the surface using a CMP (Chemical Mechanical Polishing) method so that the copper film remains only in the opening. Can be realized.

  By the way, the substrate cleaning method performed in the manufacturing process of the semiconductor device includes a batch method for cleaning a plurality of substrates at once and a single wafer method for cleaning the substrates one by one. In recent years when the diameter of the substrate is increasing, a cleaning method using a sheet method tends to become mainstream.

  As a sheet-type cleaning device, a spin-type cleaning device is generally used. According to this apparatus, cleaning is performed by sequentially supplying a chemical solution and pure water onto the rotated substrate. In addition, the substrate after cleaning is dried by blowing off the liquid adhering to the substrate by rotation, and the substrate is sprayed with inert gas or clean air, or the adhering liquid is isopropyl alcohol (hereinafter referred to as IPA). It is also performed by substituting with a liquid or its vapor (for example, refer to Patent Document 1).

Japanese Patent Application Laid-Open No. 09-038595

  However, in the copper wiring process by the damascene method, the cleaning performed after forming the opening in the low-k film has the following problems. Hereinafter, this problem will be described in detail with reference to FIG.

  In FIG. 7, a low-k film 23 and a copper wiring layer 24 are formed on the diffusion prevention film 22 provided on the silicon substrate 21. Further, on the low-k film 23, a diffusion preventing film 25, a low-k film 26, and a cap film 27 are further laminated in this order. In these films, an opening 28 reaching the copper wiring layer 24 is provided.

  In general, a hydrophilic material is used for the diffusion prevention film 25 and the cap film 27, whereas a hydrophobic material is used for the low-k film 26. For this reason, the water (pure water) 29 used for the cleaning is repelled by the Low-k film 26 and is divided into upper and lower parts inside the opening 28 as shown in FIG. In this case, since the water 29 at the bottom of the opening 28 is difficult to be removed, it remains in the opening 28 after the drying process and forms a film on the copper wiring layer 24. This film has a problem in that poor connection between wirings is caused, contact resistance is increased, and yield is lowered in a wiring forming process.

  The present invention has been made in view of such problems. That is, an object of the present invention is to provide a semiconductor substrate cleaning method capable of solving the problem of poor drying in a copper wiring forming process using a low-k film.

  Other objects and advantages of the present invention will become apparent from the following description.

  The present invention relates to a method for cleaning a semiconductor substrate on which a copper wiring layer is formed. A hydrophilic first film, a hydrophobic second film, and a hydrophilic third film are formed on the copper wiring layer. Films are laminated in this order, and a first step of performing a chemical treatment on a semiconductor substrate in a state where a copper layer constituting the copper wiring layer is exposed from an opening provided in these films, and the chemical treatment A second step of washing the semiconductor substrate with pure water later, and a vapor of isopropyl alcohol having a concentration of 0.01% by volume to 2.0% by volume while the semiconductor substrate is rotated. And a third step of performing a drying process for removing pure water adhering to the semiconductor substrate.

  In the present invention, the third step is preferably performed continuously to the second step. Alternatively, it is preferable to start the third step just before finishing the second step.

  In the present invention, the third step includes a first step of rotating the semiconductor substrate at a low speed of 200 rpm to 800 rpm, and a second step of rotating the semiconductor substrate at a high speed of 1,000 rpm or more after the first step. It is preferable to consist of. In this case, the first step may further include a plurality of steps having different rotational speeds.

  In the present invention, the first film can be a diffusion preventing film.

In the present invention, the second film can be a low dielectric constant insulating film. Here, the low dielectric constant insulating film refers to an insulating film having a relative dielectric constant lower than that of the SiO ₂ film.

  Furthermore, in the present invention, the third film can be a cap film.

  According to the method for manufacturing a semiconductor device of the present invention, the drying treatment of the semiconductor substrate is performed using the gas containing the vapor of isopropyl alcohol having a concentration of 0.01% by volume to 2.0% by volume. The semiconductor substrate can be cleaned without any trouble.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that a normal LSI manufacturing process such as MOS transistor, diffusion layer, and plug formation will be omitted for the sake of convenience, and the metal wiring forming process will be described.

  1 to 6 and 8 are cross-sectional views showing a method for manufacturing a semiconductor device in the present embodiment. In these drawings, the same reference numerals indicate the same parts.

  First, a lower copper wiring layer 2 is formed on a silicon substrate 1 as a semiconductor substrate (FIG. 1).

  Specifically, the first diffusion barrier film 3 and the first interlayer insulating film 4 are sequentially stacked on the silicon substrate 1, and then the opening reaching the first diffusion barrier film 3 in the first interlayer insulating film 4. The copper wiring layer 2 can be formed by providing a portion and embedding the first copper layer 6 in the opening via the first barrier metal film 5.

  Next, the second diffusion prevention film 7, the second interlayer insulation film 8, and the cap film 9 are laminated in this order on the first interlayer insulation film 4 on which the copper wiring layer 2 is formed (FIG. 2). Here, the second diffusion prevention film 7, the second interlayer insulating film 8 and the cap film 9 are respectively the hydrophilic first film, the hydrophobic second film and the hydrophilic third film in the present invention. Corresponds to the membrane.

In the present embodiment, as the first interlayer insulating film 4 and the second interlayer insulating film 8, an insulating film (Low-k film) having a relative dielectric constant lower than that of the SiO ₂ film is used. In particular, the relative dielectric constant is preferably 3.0 or less. The second interlayer insulating film 8 is made of a hydrophobic material. As long as it is such a film, the first interlayer insulating film 4 and the second interlayer insulating film 8 may be films formed by any method. For example, a porous insulating film having pores (pores) in the film or an insulating film having no pores may be used. Furthermore, there are no particular restrictions on the size of the holes and the density of the holes when the holes are provided. Specifically, in addition to inorganic insulating films such as SiOC, HSQ (hydrogenated silsesquioxane), MSQ (methylsilsesquioxane), porous HSQ, and porous MSQ, organic polymers containing fluorine A system insulating film or the like can also be used. The first interlayer insulating film 4 and the second interlayer insulating film 8 may be films made of the same material or films made of different materials.

On the other hand, as the first diffusion preventing film 3, the second diffusion preventing film 7 and the cap film 9, for example, a SiO ₂ -based, SiN-based, SiC-based or AlO-based inorganic insulating film can be used. However, in the present invention, the second diffusion prevention film 7 and the cap film 9 are made of a hydrophilic material. Similarly to the interlayer insulating film, the first diffusion preventing film 3, the second diffusion preventing film 7 and the cap film 9 are preferably insulating films having a relative dielectric constant as low as possible. As long as it has such characteristics, there are no particular restrictions on the film quality, film thickness, formation method, and the like of these films. When a material having a relatively high relative dielectric constant is used, it is preferable that the material be formed as thin as possible without impairing the film characteristics.

  After the cap film 9 is formed, a hard mask 10 having a predetermined pattern is formed by using a photolithography method (FIG. 3). As the hard mask 10, a film made of a material having a high etching selectivity with the cap film 9 is used.

  Next, using the hard mask 10 as a mask, the cap film 9, the second interlayer insulating film 8, and the second diffusion prevention film 7 are sequentially dry etched. Thereby, as shown in FIG. 4, the 2nd opening part 11 which reaches the copper wiring layer 2 can be formed. At this time, along with the formation of the opening 11, the contaminant 12 generated by etching adheres to the copper wiring layer 2 (FIG. 4). The contaminant 12 is mainly composed of a substance generated by a reaction between plasma active species and copper.

  After the opening 11 is formed, the silicon substrate 1 is cleaned. This cleaning process is mainly intended to remove the contaminants 12 formed on the copper wiring layer 2, and includes a chemical solution process, a water washing process, and a drying process.

  The chemical solution used for the chemical treatment needs to be capable of peeling and removing the contaminants 12 and not causing substantial damage to the copper wiring layer 2 and the second interlayer insulating film 8. However, the chemical solution is not particularly limited in its components and composition as long as it has such characteristics. As a chemical solution suitable for the present embodiment, for example, one containing fluorine (F) can be given.

  The chemical treatment can be performed by a sheet type method in which a chemical solution is sprayed onto a substrate in a rotating state to wash the substrates one by one. Moreover, you may perform a washing process by the batch system which immerses a some board | substrate in a chemical | medical solution.

  After the chemical liquid treatment is completed, the chemical liquid is washed away by washing with pure water, and the remaining contaminants 12 are completely removed. The water washing process may be performed by either a single wafer system or a batch system. For example, when performing the cleaning process by a single wafer system, the water washing is rotated with respect to the substrate after chemical treatment. It can be performed by spraying pure water in a state.

  After the chemical solution adhering to the substrate is completely replaced with pure water, a drying process for removing the pure water is performed. In the present invention, the drying process is performed in an atmosphere containing isopropyl alcohol (hereinafter referred to as IPA) at a concentration of 0.01% by volume to 2.0% by volume. Since IPA has low surface tension and high permeability, it can be easily replaced with pure water that has entered the inside of the opening.

  Here, when the concentration of IPA becomes lower than 0.01% by volume, water tends to remain inside the opening 11 in FIG. On the other hand, when the concentration of IPA is higher than 2.0% by volume, although water is removed, IPA remains in the opening 11. The remaining IPA forms a film on the surface of the copper wiring layer 2 to cause a connection failure between the wiring layers, and reduces the yield in the wiring forming process. Moreover, since the explosion limit of IPA is 2.0 vol% to 12.7 vol%, the concentration of IPA in the drying treatment is preferably 2.0 vol% or less.

  In the case of performing a drying process using IPA, strictly speaking, an IPA film is formed on the surface of the copper wiring layer 2 after the drying process regardless of the concentration of IPA. This IPA film becomes thicker as the concentration of IPA used increases. However, it is possible to remove the IPA film formed on the surface by physically cleaning the surface of the copper wiring layer 2 by sputtering before forming the wiring layer inside the opening 11. . Therefore, conversely, the concentration of IPA may be in a range where the remaining IPA can be removed by this cleaning.

  Specifically, the drying process using IPA can be performed as follows.

First, liquid IPA is heated to a temperature equal to or higher than its boiling point (83 ° C. or higher) to form gaseous IPA (IPA vapor). Next, nitrogen (N ₂ ) gas is used as a diluent gas, and a mixed gas having an IPA concentration of 0.01% by volume to 2.0% by volume is generated. In order to prevent the IPA from condensing from the mixed gas, the mixed gas is supplied onto the rotating substrate while keeping the temperature of the mixed gas at a certain temperature or higher.

  When the IPA vapor is supplied onto the substrate, the temperature of pure water is lower than that of the IPA vapor, so that the IPA vapor is cooled and condensed by the contact of both, and changes from IPA vapor to liquid IPA. The liquefied IPA is gradually replaced with pure water while being mixed with pure water, thereby drying the surface of the substrate. That is, since the substrate is in a rotating state while the IPA vapor is supplied, the IPA replaced with pure water evaporates while being pushed out of the substrate. Thereby, the pure water adhering to the substrate can be removed.

  In the present invention, it is preferable not to leave time between the washing process and the drying process. That is, it is preferable to perform the drying process continuously with the water washing process. Specifically, the mixed gas containing IPA can be continuously supplied after completion of the supply of pure water in the water washing treatment. In the present invention, the water washing treatment and the drying treatment can be partially overlapped. That is, you may start a drying process just before finishing a water washing process. Specifically, the supply of IPA is started just before the end of the pure water supply process, and only the supply of IPA is performed after the end of the supply of pure water. As described above, it is possible to perform the drying process without leaving moisture in the opening.

  In the present invention, it is preferable to set the rotation state of the substrate during the drying process in at least two stages. This is because the supply of IPA is dominant when the substrate is rotated at a low speed, whereas the evaporation of IPA is dominant when the substrate is rotated at a high speed.

  When the IPA is supplied only in a high-speed rotation state, the IPA evaporates before the pure water is sufficiently replaced with the IPA, so that the pure water may remain in the opening even after the drying process. . Since the first stage (first step) of the drying process is a stage in which the replacement of pure water with IPA is advanced, it is preferable to supply IPA with the substrate rotated at a low speed. Specifically, the rotation of the substrate is preferably 1,000 rpm or less, and more preferably 200 rpm to 800 rpm. By doing so, pure water and IPA can be sufficiently replaced even in the opening provided on the substrate.

  In the present invention, the low-speed rotation is not limited to one-stage rotation, and may be two-stage or more. That is, the first step of rotating at a low speed may further comprise a plurality of steps having different rotational speeds.

  After the replacement of pure water and IPA is completed, it is preferable to change the rotation of the semiconductor substrate at a high speed in order to advance the evaporation of IPA, which is the second stage (second step). This is because the IPA evaporation is slow and the throughput is reduced in the low speed state. Specifically, the rotation of the semiconductor substrate is preferably set to 1,000 rpm or more. By doing so, evaporation of IPA can be promoted and the drying process time can be shortened.

  As one example, the rotation state of the substrate during the drying process may be changed to 150 rpm for 5 seconds (Step 1), 500 rpm for 10 seconds (Step 2), and 4,000 rpm for 15 seconds (Step 3). it can. In this case, Step 1 and Step 2 are low-speed rotation stages, and Step 3 is a high-speed rotation stage.

  After finishing the cleaning process, the water washing process, and the drying process, the second barrier metal film 13 such as a tantalum nitride (TaN) film is formed on the inner surface of the opening 11 in FIG. . Thereafter, the copper layer 14 is embedded in the opening 11 via the second barrier metal film 13. Thereby, the copper wiring layer 15 can be formed in the upper layer of the lower copper wiring layer 2 (FIG. 5). Specifically, after forming a copper film (not shown) as seed copper by a sputtering method, the second copper layer 14 is formed so as to bury the opening 11 using a plating method. Next, the surface is planarized using a CMP (Chemical Mechanical Polishing) method so that the second copper layer 14 remains only in the opening 11. Thereby, the copper wiring layer 15 electrically connected to the copper wiring layer 2 can be formed.

  FIG. 6 shows an example of product yield when the drying treatment according to the present invention is performed. Specifically, after the water washing treatment, the substrate is dried in three steps by rotating the substrate in three steps of 150 rpm for 5 seconds, 500 rpm for 10 seconds, and 4,000 rpm for 15 seconds. For comparison, the drying process was performed by rotating the substrate only after the washing process (Comparative Example 1), and the drying process was performed by supplying the IPA vapor after rotating the substrate for 30 seconds after the washing process. The product yield in each case (Comparative Example 2) is also shown. Note that the product yield in FIG. 6 indicates the yield of contact resistance between the lower copper wiring layer and the upper copper wiring layer.

  From FIG. 6, the yield of Comparative Example 1 is about 70%, which indicates that drying is not sufficient only by rotating the substrate. On the other hand, it can be seen that the yield can be improved to some extent by the supply of IPA vapor (Comparative Example 2) as compared with Comparative Example 1. However, the yield of Comparative Example 2 is about 90%, and even this method cannot sufficiently eliminate the drying defect. On the other hand, according to the present invention, a yield of 99% or more can be achieved. This indicates that the present invention can solve the problem of poor drying in the copper wiring forming process using the low-k film and can manufacture a semiconductor device having excellent electrical characteristics with a high yield.

It is sectional drawing which shows the manufacturing process of the semiconductor device in this Embodiment. It is sectional drawing which shows the manufacturing process of the semiconductor device in this Embodiment. It is sectional drawing which shows the manufacturing process of the semiconductor device in this Embodiment. It is sectional drawing which shows the manufacturing process of the semiconductor device in this Embodiment. It is sectional drawing which shows the manufacturing process of the semiconductor device in this Embodiment. It is a figure which shows the yield at the time of applying this invention. It is sectional drawing which shows the manufacturing process of the conventional semiconductor device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,21 Silicon substrate 2,15,24 Copper wiring layer 3 1st diffusion prevention film 4 1st interlayer insulation film 5 1st barrier metal film 6 1st copper layer 7 2nd diffusion prevention film 8 2nd Interlayer insulating film 9, 27 Cap film 10 Hard mask 11, 28 Opening 12 Contaminant 13 Second barrier metal film 14 Second copper layer 22, 25 Diffusion prevention film 23, 26 Low-k film 29 Water

Claims (6)

A method for cleaning a semiconductor substrate on which a copper wiring layer is formed,
On the copper wiring layer, a hydrophilic first film, a hydrophobic second film, and a hydrophilic third film are laminated in this order, and from the opening provided in these films A first step of performing a chemical treatment on the semiconductor substrate with the copper layer constituting the copper wiring layer exposed;
A second step of performing a washing process using pure water on the semiconductor substrate after the chemical treatment;
A drying process for removing the pure water adhering to the semiconductor substrate by supplying a gas containing vapor of isopropyl alcohol having a concentration of 0.01% by volume to 2.0% by volume with the semiconductor substrate rotated. And a third step of performing a semiconductor substrate cleaning method.   The method for cleaning a semiconductor substrate according to claim 1, wherein the third step is performed continuously with the second step.   The method for cleaning a semiconductor substrate according to claim 1, wherein the third step is started just before the second step is finished.   The third step includes a first step of rotating the semiconductor substrate at a low speed of 200 rpm to 800 rpm, and a second step of rotating the semiconductor substrate at a high speed of 1,000 rpm or more after the first step. The method for cleaning a semiconductor substrate according to claim 1, comprising:   The semiconductor substrate cleaning method according to claim 4, wherein the first step further includes a plurality of steps having different rotational speeds. The first film is a diffusion barrier film;
The second film is a low dielectric constant insulating film;
The method for cleaning a semiconductor substrate according to claim 1, wherein the third film is a cap film.

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