JP2005340554A - Manufacturing method of semiconductor memory device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively remove, in a short time, contamination with chalcogenide adhering to a back surface and a bevel portion of a silicon substrate in a manufacturing process of a phase change memory using a chalcogenide material.
After a chalcogenide film is formed and processed into a desired shape, a substrate is first cleaned with a first cleaning liquid containing hydrogen fluoride and nitric acid or hydrogen fluoride, nitric acid and acetic acid. Next, cleaning is performed with a second cleaning liquid containing hydrochloric acid and hydrogen peroxide, hydrogen fluoride and hydrogen peroxide, or ammonia and hydrogen peroxide.
[Selection] Figure 1

Description

  The present invention relates to a semiconductor substrate cleaning technique, and more particularly to a method for manufacturing a semiconductor memory device using a chalcogenide-based material.

Currently, DRAM, SRAM, and flash memory are commonly used as readable and writable memories, but DRAM can be highly integrated, but is volatile and difficult to mix with logic circuits. SRAM The flash memory has high speed but is volatile and difficult to integrate, and the flash memory is non-volatile, but the flash time is slow and the number of times of rewriting is less than 1 million times. If an element having the advantages of these memories can be realized, it is epoch-making in that the current semiconductor memory can be replaced as well as the currently mixed memory can be made into one chip. As one of such memories, Intel proposed a phase change memory in 2001 IEDM (International Electron Device Meeting). Phase change memory uses a material called chalcogenide as a storage node. Chalcogenide has a different resistance depending on whether the bonding state of the elements in the alloy is single crystal or amorphous, and the resistance is low in the single crystal state. It is a nonvolatile memory that records data using the property of high resistance in the state. Chalcogenide is a material used for DVD-RAM and CD-RW media. Ge-Sb-Te system (Ge ₂ Sb ₂ Te _{5 and the} like) containing at least antimony (Sb) and tellurium (Te) is a representative example. It is. A basic memory cell is composed of a transistor and a chalcogenide. This configuration is similar to a so-called DRAM cell, and can be regarded as a capacitor replaced with a chalcogenide. In order to change the crystal state of chalcogenide, Joule heat generated by applying a voltage is used. In order to obtain an amorphous state, chalcogenide is heated to a melting point or higher and dissolved, and then rapidly cooled. In order to crystallize, data can be recorded / erased by heating to a temperature above the crystallization temperature (below the melting point) and then cooling. In order to read data, the word line is turned on, and binary information (0 or 1) is discriminated by the current flowing between the common ground line and the bit line.

On the other hand, conventional cleaning methods for removing metal contamination adhered to a semiconductor substrate are disclosed in acidic chemicals such as hydrofluoric acid, hydrochloric acid, sulfuric acid nitric acid, phosphoric acid, and nitric acid, and JP-A-11-302877. As described above, a mixed acid chemical solution obtained by mixing a plurality of types of the acidic liquid, HPM (HCl / H ₂ O ₂ / H ₂ O mixed liquid) in which hydrogen peroxide water is added to the acidic liquid as an oxidizing agent, and SPM (H ₂ SO _4). / H ₂ O ₂ mixed solution), FPM (HF / H ₂ O ₂ / H ₂ O mixed solution), and DHF (HF / H ₂ O mixed solution) are generally used. As a common chemical solution for etching Ge, Sb, and Te, which are constituent elements of chalcogenide, a mixed solution of hydrofluoric acid / nitric acid / acetic acid is known.

  In each process of semiconductor manufacturing, it is known that metal contamination occurs on the wafer back surface and bevel portion (wafer edge portion and peripheral portion) other than the device surface of the semiconductor substrate. May be diffused to the device surface of other substrates in the process of transporting, storing, and processing the substrate, which may degrade device characteristics. is there. In order to remove metal contamination on the back surface, the peripheral portion, and the edge portion of the wafer, a single wafer spin cleaning method using the above various cleaning liquids is widely employed.

JP-A-11-302877 JP 2002-184751 A New silicon wafer surface cleaning technology (Realize) CRC Handbook of Metal Etchants (CRC Press, Inc)

  However, the single wafer spin cleaning method that cleans and removes the metal on the back surface and the bevel of the wafer described above is known to easily leave metal contamination on the bevel, and in conventional chalcogenide cleaning using a single chemical solution. In particular, there was a problem that Te remained.

  In order to improve the cleaning performance of the bevel portion, as disclosed in Japanese Patent Application Laid-Open No. 2002-184751, a plurality of chemical solution supply nozzles are provided in single-wafer spin cleaning, one for each of the central portion and the bevel portion of the substrate. Although there is a cleaning method arranged, there is a problem in that the cleaning device is enlarged because the mechanism is more complicated than that of a single nozzle cleaning device.

  In single wafer spin cleaning using a single chemical solution supply nozzle, a method of reducing the load in cleaning by using a so-called edge cut wafer having a region where no film is formed several mm inside from the periphery of the substrate is used. ing.

  The present invention is not limited to edge-cut wafers in single-wafer spin cleaning using a single chemical solution supply nozzle that is simple in terms of mechanism of the cleaning apparatus, and even a semiconductor substrate having a chalcogenide film formed on the entire wafer surface An object of the present invention is to provide a method for manufacturing a semiconductor device having a cleaning method for removing chalcogenide from the back surface and the beveled portion.

  As a result of investigations by the inventors, it has been clarified that the chalcogenide wet cleaning in the method of manufacturing a phase change memory is effective to perform cleaning step by step using two types of cleaning liquids.

  As shown in FIG. 1A, in the semiconductor manufacturing process, the first cleaning liquid and the second cleaning liquid are stepped in order to remove the chalcogenide on the back surface and bevel portion of the substrate on which the chalcogenide film serving as the storage node is formed. (Claim 1). Further, as shown in FIG. 1B, after the chalcogenide formed on the substrate is processed into a desired shape by dry etching or the like, the first cleaning liquid and the first cleaning solution and the first cleaning solution are removed in order to remove the chalcogenide on the back surface and bevel portion of the substrate. Two cleaning liquids are used in stages (claim 2).

  The first cleaning liquid has one of the following compositions. The first cleaning liquid 1 is composed of hydrogen fluoride and nitric acid, contains hydrogen fluoride at a concentration of 0.05 wt% to 1.00 wt%, and nitric acid of 60.0 wt% to 69.9 wt%. Containing in a concentration (Claim 3). The first cleaning liquid 2 is composed of hydrogen fluoride, nitric acid and acetic acid, contains hydrogen fluoride at a concentration of 0.1 wt% or more and 5.0 wt% or less, and nitric acid 25.0 wt% or more and 40.0 wt%. The acetic acid is contained at a concentration of 40.0 wt% or more and 55.0 wt% or less (Claim 4).

  The second cleaning liquid has any one of the following compositions. The second cleaning liquid 1 contains hydrochloric acid at a concentration of 0.1% by weight to 12.0% by weight and hydrogen peroxide at a concentration of 0.1% by weight to 10.0% by weight. ). The second cleaning liquid 2 contains hydrogen fluoride at a concentration of 0.5 wt% to 15.0 wt% and hydrogen peroxide at a concentration of 0.1 wt% to 15.0 wt%. (Claim 6). The second cleaning liquid 3 contains ammonia at a concentration of 0.1 wt% to 10.0 wt%, and hydrogen peroxide at a concentration of 0.1 wt% to 15.0 wt%. It is characterized (claim 7).

The initial concentration of each element of the chalcogenide (Ge ₂ Sb ₂ Te ₅ ) on the back surface of the substrate and the bevel portion after film formation is about 1.0 × 10 ¹⁴ atoms / cm ² at the maximum. When the back surface of the substrate and the bevel portion are cleaned using this, Ge, Sb, and Te on the back surface of the substrate can be removed to 1.0 × 10 ¹⁰ atoms / cm ² or less in a cleaning time of at least 1 minute. Regarding the bevel portion, Ge and Sb can be removed to 1.0 × 10 ¹⁰ atoms / cm ² or less, but Te of about 5.0 × 10 ¹² atoms / cm ² remains. The remaining Te can be removed to 1.0 × 10 ¹⁰ atoms / cm ² or less in a cleaning time of less than 1 minute by using the second cleaning liquid according to the present invention.

In the method for manufacturing a semiconductor memory device of the present invention, contamination by chalcogenide on the back surface of the substrate and the bevel portion is removed to 1.0 × 10 ¹⁰ atoms / cm ² or less in a short time by using two types of cleaning liquids in stages. it can. Therefore, a semiconductor memory device can be obtained with a high yield without contaminating the device surface of another substrate with chalcogenide in the steps of substrate transport, storage, and processing.

  Of the first cleaning liquid according to the present invention, the first cleaning liquid 1 is composed of hydrogen fluoride and nitric acid, contains hydrogen fluoride at a concentration of 0.05% by weight or more and 1.00% by weight or less, and nitric acid at 60.0%. It is contained at a concentration of not less than 6% and not more than 69.9% by weight. The concentration of hydrogen fluoride is preferably 0.05% by weight or more and 0.5% by weight or less, and the concentration of nitric acid is 69.0% by weight or more and 69.9% by weight or less. The chemical solution is obtained, for example, by mixing 50% by weight hydrogen fluoride and 70% by weight nitric acid. A preferable mixing ratio is 50% by weight hydrogen fluoride to 1 in volume ratio, and 70% by weight nitric acid is 100-600. Become. When the volume ratio of nitric acid is less than 100, the concentration of hydrogen fluoride is relatively high, so that the surface roughness of the silicon wafer increases due to etching. When the volume ratio of nitric acid exceeds 600, the etching rate of chalcogenide is slow and there is a problem that it takes time for cleaning.

  The first cleaning liquid 2 is composed of hydrogen fluoride, nitric acid and acetic acid, contains hydrogen fluoride at a concentration of 0.1 wt% or more and 5.0 wt% or less, and nitric acid 25.0 wt% or more and 40.0 wt%. It is contained at a concentration of not more than wt%, and acetic acid is contained at a concentration of not less than 40.0 wt% and not more than 55.0 wt%. The preferred hydrogen fluoride concentration is 0.25 wt% or more and 0.5 wt% or less, the nitric acid concentration is 30.0 wt% or more and 35.0 wt% or less, and the acetic acid concentration is 40.0 wt% or more and 50.0 wt% or less. % By weight or less. The chemical solution is obtained, for example, by mixing 50% by weight hydrogen fluoride, 70% by weight nitric acid, and 99.9% by weight acetic acid. The preferred mixing ratio is 70% by weight nitric acid and 99.9% by weight acetic acid. 50% by weight of hydrogen fluoride is 50 to 50%. When the mixing ratio of hydrogen fluoride exceeds 10, there is a problem that the surface roughness of the silicon wafer is increased by etching. When the mixing ratio is less than 0.5, there is a problem that the etching rate of chalcogenide is slow and time is required for cleaning.

  Of the second cleaning liquid according to the present invention, the second cleaning liquid 1 contains hydrochloric acid at a concentration of 0.1 wt% or more and 12.0 wt% or less, and hydrogen peroxide is 0.1 wt% or more and 10.0 wt%. Contains at the following concentrations. A preferable concentration of hydrochloric acid is 0.5 wt% or more and 10.0 wt% or less. If the concentration of hydrochloric acid exceeds 12.0% by weight, the Te ionization tendency is smaller than that of hydrogen, so that precipitation is likely to occur and the substrate may be recontaminated. If it is less than 0.5% by weight, the etching rate with respect to Te is slow, and there is a problem that it takes time for cleaning.

  The second cleaning liquid 2 contains hydrogen fluoride at a concentration of 0.5 wt% to 15.0 wt% and hydrogen peroxide at a concentration of 0.1 wt% to 15.0 wt%. . A preferable concentration of hydrogen fluoride is 0.5 wt% or more and 10.0 wt% or less, and a preferable concentration of hydrogen peroxide is 0.5 wt% or more and 5.0 wt% or less. When the concentration of hydrogen fluoride and hydrogen peroxide exceeds 15.0% by weight, there is a problem that the surface roughness of the silicon wafer is increased by etching, and the concentration of hydrogen fluoride is less than 0.5% by weight and hydrogen peroxide. If the concentration is less than 0.1% by weight, the etching rate with respect to Te is slow, and there is a problem that time is required for cleaning.

  The second cleaning liquid 3 contains ammonia at a concentration of 0.1% by weight to 10.0% by weight and hydrogen peroxide at a concentration of 0.1% by weight to 15.0% by weight. A preferable ammonia concentration is 1.0 wt% or more and 5.0 wt% or less, and a hydrogen peroxide concentration is 1.0 wt% or more and 10.0 wt% or less. If the ammonia concentration exceeds 10.0% by weight and the hydrogen peroxide concentration exceeds 15.0% by weight, the etching rate for silicon increases and the surface roughness of the substrate surface increases. When the concentration of ammonia is 0.1% by weight and the concentration of hydrogen peroxide is less than 0.1% by weight, the etching rate with respect to Te is slow, and there is a problem that it takes time for cleaning.

  Examples of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto.

  FIGS. 1A and 1B are diagrams showing a manufacturing process of a memory cell of a semiconductor memory device using chalcogenide as a storage node. After a transistor (not shown) for controlling writing and reading to the storage node is formed on the silicon substrate (1), an insulating film (2) is deposited, and a cell wiring (3) is formed by a normal method. In this embodiment, tungsten is used as the wiring material. At this time, for the purpose of preventing diffusion of tungsten into the insulating film, a diffusion preventing layer made of an alloy with a metal nitride such as Ti / TiN is interposed between the insulating film and the insulating film. (4) may be formed.

Next, after chalcogenide (Ge ₂ Sb ₂ Te ₅ ) (5) is deposited on the entire surface of the substrate, the back surface and the bevel portion of the substrate are cleaned using the first cleaning solution and the second cleaning solution by the single wafer spin cleaning method. Here, the single wafer spin cleaning method is controlled to a certain flow rate and temperature from a nozzle located above the center of a silicon wafer held on a stage rotating at a certain rotational speed with the back surface of the substrate facing up. This is a cleaning method in which the cleaned cleaning liquid is dropped onto the center of the wafer. The cleaning solution that has come into contact with the wafer spreads to the periphery and reaches several millimeters on the back side of the wafer to clean the bevel.

  FIG. 2 and FIG. 3 show the transition of the chalcogenide contamination concentration remaining in the bevel portion with respect to the cleaning time when the first cleaning solution is used for cleaning at a chemical temperature of 25 ° C. The residual contamination concentration was measured by inductively coupled plasma-mass spectrometry (ICP-MS; Inductively Coupled Plasma-Mass Spectrometry).

In FIG. 2, the first cleaning liquid 1 containing hydrogen fluoride and nitric acid was used, but the cleaning liquid was prepared by mixing commercially available 50 wt% hydrogen fluoride and 70 wt% nitric acid at a volume ratio of 1: 300. did. Precleaning According to FIG. 2 was (washing time 0 seconds) 1.0 × ¹⁰ 14 atoms / cm ² of about Ge, Sb contamination concentration in the wash of 10 seconds or more 1.0 × ¹⁰ 10 atoms / cm ² The following are shown to be reduced. Regarding Te, contamination of about 1.0 × 10 ¹⁴ atoms / cm ² remains about 5.0 × 10 ¹² atoms / cm ² before cleaning. The remaining Te is removed using a second cleaning liquid described later. The above results can be obtained even when 50 wt% hydrogen fluoride and 70 wt% nitric acid are mixed at a volume ratio of 1: 150 and 1: 600.

In FIG. 3, the first cleaning liquid 2 containing hydrogen fluoride, nitric acid and acetic acid was used. The cleaning liquid was prepared by mixing commercially available 50 wt% hydrogen fluoride, 70 wt% nitric acid and 99.9 wt% acetic acid in a volume ratio of 1:10:10. According to FIG. 3, the Ge and Sb contamination concentration, which was about 1.0 × 10 ¹⁴ atoms / cm ² before the cleaning, is reduced to 1.0 × 10 ¹⁰ atoms / cm ² or less by cleaning for 10 seconds or more. Is shown. Regarding Te, contamination of about 1.0 × 10 ¹⁴ atoms / cm ² remains about 5.0 × 10 ¹² atoms / cm ² before cleaning. The remaining Te is removed using a second cleaning liquid described later. The above results are the same when 50% by weight hydrogen fluoride, 70% by weight nitric acid and 99.9% by weight acetic acid are mixed at a volume ratio of 1:50:50 and 1: 5: 5. can get.

  The transition of the Te concentration remaining in the bevel portion with respect to the cleaning time when the second cleaning solution is used and the chemical solution temperature is 25 ° C. after the cleaning with the first cleaning solution is shown in FIGS.

In FIG. 4, the second cleaning liquid 1 containing hydrochloric acid and hydrogen peroxide was used, but the hydrochloric acid concentration was 5.0% by weight, the hydrogen peroxide concentration was 4.0% by weight (6), and the hydrochloric acid concentration was 0.5%. The results are obtained by using two kinds of cleaning solutions each having a weight% and hydrogen peroxide concentration of 0.5% by weight (7). According to FIG. 4, Te of about 5.0 × 10 ¹² atoms / cm ² remaining after cleaning with the first cleaning liquid is reduced to 1.0 × 10 ¹⁰ atoms / cm ² or less by cleaning within at least one minute. Which indicates that.

In FIG. 5, the second cleaning liquid 2 containing hydrogen fluoride and hydrogen peroxide was used. At this time, both the hydrogen fluoride concentration and the hydrogen peroxide concentration are 5.0% by weight. According to FIG. 5, Te of about 5.0 × 10 ¹² atoms / cm ² remaining after cleaning with the first cleaning liquid is reduced to 1.0 × 10 ¹⁰ atoms / cm ² or less by cleaning within at least one minute. Which indicates that. Note that the above results are similar to those obtained when the hydrogen fluoride concentration is 0.5 wt% to 15.0 wt% and the hydrogen peroxide concentration is 0.1 wt% to 15.0 wt%. It is done.

In FIG. 6, the second cleaning liquid 3 containing ammonia and hydrogen peroxide is used. At this time, the ammonia concentration is 3.0% by weight and the hydrogen peroxide concentration is 6.0% by weight. According to FIG. 6, Te of about 5.0 × 10 ¹² atoms / cm ² remaining after cleaning with the first cleaning liquid is reduced to 1.0 × 10 ¹⁰ atoms / cm ² or less after cleaning within at least one minute. Which indicates that. Note that the above results are similar to those obtained when the ammonia concentration is 0.1 wt% to 10.0 wt% and the hydrogen peroxide concentration is 1.0 wt% to 15.0 wt%.

  Next, after depositing a metal (8) such as tungsten serving as the upper electrode on the chalcogenide film, a sacrificial film (9) such as a silicon oxide film for forming the chalcogenide serving as the storage node and the upper electrode is deposited, It is processed into a desired shape by a normal method such as dry etching. At this time, the chalcogenide again adheres to the back surface and bevel portion of the substrate, but it is clear that the amount of adhesion is much smaller than when chalcogenide is deposited, so the above-described first and second cleaning liquids were used. Needless to say, it can be removed by a cleaning method. After this cleaning step, necessary wiring that can be conducted to the upper electrode is formed, and a desired semiconductor memory device can be obtained.

  The present invention relates to a method for manufacturing a semiconductor memory device using chalcogenide as a storage node, but the disclosed cleaning liquid can be applied to manufacturing an engineering member using chalcogenide.

FIG. 6 is a process diagram showing a manufacturing process of the semiconductor memory device of the present invention. The figure which shows transition of the contamination density | concentration with respect to the washing | cleaning time at the time of wash | cleaning using the 1st washing | cleaning liquid 1 of this invention. The figure which shows transition of the contamination density | concentration with respect to the washing | cleaning time at the time of wash | cleaning using the 1st washing | cleaning liquid 2 of this invention. The figure which shows transition of the contamination density | concentration with respect to the washing | cleaning time at the time of wash | cleaning using the 2nd washing | cleaning liquid 1 of this invention. The figure which shows transition of the contamination density | concentration with respect to the washing | cleaning time at the time of wash | cleaning using the 2nd washing | cleaning liquid 2 of this invention. The figure which shows transition of the contamination density | concentration with respect to the washing | cleaning time at the time of wash | cleaning using the 2nd washing | cleaning liquid 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Silicon substrate, 2 ... Insulating film, 3 ... Cell wiring, 4 ... Diffusion prevention layer, 5 ... Garcogenide, 6 ... 2nd washing | cleaning liquid containing hydrochloric acid concentration 5.0 weight% and hydrogen peroxide concentration 4.0 weight% Transition of residual Te concentration with respect to cleaning time when 2 is used, 7 with respect to cleaning time when second cleaning liquid 2 containing 0.5% by weight of hydrochloric acid and 0.5% by weight of hydrogen peroxide is used Transition of residual Te concentration.

Claims (8)

  A method of manufacturing a semiconductor memory device using a chalcogenide-based material as a storage node, wherein two kinds of chalcogenides are removed when depositing the chalcogenide on a semiconductor substrate and then removing excess chalcogenide adhering to the back and end surfaces of the semiconductor substrate. A method of manufacturing a semiconductor memory device, wherein a cleaning liquid is used stepwise.   A method of manufacturing a semiconductor memory device using a chalcogenide-based material as a storage node, wherein after the chalcogenide deposited on a semiconductor substrate is processed into a desired shape, excess chalcogenide adhering to the back and end surfaces of the semiconductor substrate is removed. In this case, a method of manufacturing a semiconductor memory device is characterized in that two types of cleaning liquids are used step by step.   3. The method of manufacturing a semiconductor memory device according to claim 1, wherein the first cleaning liquid is composed of hydrogen fluoride and nitric acid, and contains hydrogen fluoride at a concentration of 0.05 wt% to 1.00 wt%. A method for manufacturing a semiconductor memory device, comprising using a chemical solution containing 60.0 wt% or more and 69.9 wt% or less.   3. The method of manufacturing a semiconductor memory device according to claim 1, wherein the first cleaning liquid is composed of hydrogen fluoride, nitric acid, and acetic acid, and contains hydrogen fluoride at a concentration of 0.1 wt% to 5.0 wt%. A semiconductor memory characterized by using a chemical solution containing nitric acid at a concentration of 25.0 wt% to 40.0 wt% and acetic acid at a concentration of 40.0 wt% to 55.0 wt%. Device manufacturing method.   5. The method of manufacturing a semiconductor memory device according to claim 1, wherein the second cleaning liquid contains hydrochloric acid at a concentration of 0.1 wt% or more and 12.0 wt% or less, and hydrogen peroxide is 0.1 wt% or more and 10 wt% or less. A method of manufacturing a semiconductor memory device, comprising using a chemical solution contained at a concentration of 0.0% by weight or less.   5. The method of manufacturing a semiconductor memory device according to claim 1, wherein the second cleaning liquid contains hydrogen fluoride at a concentration of 0.5 wt% or more and 15.0 wt% or less, and hydrogen peroxide is 0.1 wt%. A manufacturing method of a semiconductor memory device, characterized by using a chemical solution characterized by containing at a concentration of 15.0% by weight or less.   5. The method of manufacturing a semiconductor memory device according to claim 1, wherein the second cleaning liquid contains ammonia in a concentration of 0.1 wt% to 10.0 wt% and hydrogen peroxide is 0.1 wt% to 15 wt%. A method of manufacturing a semiconductor memory device, characterized by using a chemical solution characterized by containing at a concentration of 0.0% by weight or less. A semiconductor memory device using a chalcogenide-based material manufactured by the method for manufacturing a semiconductor memory device according to claim 1 as a storage node.

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