JP2016119359A - Washing method for semiconductor substrates - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform, when a semiconductor substrate containing high melting point metal and unnecessary metal is to be washed, washing by which unnecessary metal and the like are effectively removed without damaging the high melting point metal.SOLUTION: In a semiconductor substrate washed by a washing method for semiconductor substrates to remove unnecessary metal from a semiconductor substrate containing high melting point metal, namely the semiconductor substrate cleared of the unnecessary metal by being brought into contact with a sulfuric acid solution having a sulfuric acid concentration of 80 to 98 mass %, an oxidizer concentration of 0.0005 to 1 mol/L and a temperature of 80 to 180°C, the etching rate of the high melting point metal is not more than 10 nm/min, the etching rate of the unnecessary metal is not less than 5 nm/min and the dissolution ratio, which is the unnecessary metal etching rate (nm/min)/high melting point metal etching rate (nm/min), is not less than 8.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a semiconductor substrate cleaning method for removing unnecessary metals from a semiconductor substrate containing a refractory metal.

In semiconductor manufacturing processes, refractory metals such as W (tungsten) are frequently used for contact plugs and the like. In using these metals, a process of removing other metals such as TiN (titanium nitride) which are coexistent on the semiconductor wafer and become unnecessary and leave a metal such as W is required.
The following methods are known as TiN removal and W protection techniques for semiconductor substrates.

In Patent Document 1, TiN is dissolved with high concentration of sulfuric acid while suppressing dissolution of W. Patent Document 2 proposes a treatment method using a solution containing quaternary ammonium hydroxide and hydrogen peroxide.
Patent Document 3 and Patent Document 4 propose a method for treating W and TiN containing a mixed solution of hydrofluoric acid, hydrogen peroxide, a water-soluble organic solvent, and an anticorrosive.

JP 2003-234307 A Japanese Patent No. 5347237 JP 2009-19255 A JP 2009-21516 A

However, in the technique proposed in Patent Document 1, since the etching rate of TiN is low at 1.5 nm / min or less, the actual processing time becomes long and the throughput becomes small.
In the method proposed in Patent Document 2, since the TiN / W selection ratio is as low as 7.8 or less, the treatment time must be shortened in order to suppress the dissolution of W. There is a problem that it does not dissolve sufficiently.
Furthermore, in the methods proposed in Patent Documents 3 and 4, the etching rates of TiN and W are very large at 0.12 mm / min or more for TiN and 0.01 mm / min or more for W, and control on the order of nm is required. It is difficult to apply to the process.
As described above, the above-described prior art has a problem that the TiN / W selection ratio is low, the processing speed of TiN is low, or the processing speed of W and TiN is too high.

  The present invention has been made against the background of the above circumstances, and provides a semiconductor substrate cleaning method capable of effectively cleaning and removing unnecessary metals and avoiding the necessary removal of refractory metals as much as possible. For the purpose.

That is, of the semiconductor substrate cleaning methods of the present invention, the first present invention is a semiconductor substrate cleaning method for removing unnecessary metals from a semiconductor substrate containing a refractory metal,
The semiconductor substrate is contacted with a sulfuric acid solution having a sulfuric acid concentration of 80 to 98% by mass, an oxidizing agent concentration of 0.0005 to 1 mol / L, and a temperature of 80 to 180 ° C., thereby removing the unnecessary metal. .

Another method for cleaning a semiconductor substrate according to the present invention is characterized in that, in the present invention, the unnecessary metal includes one or both of Ti and TiN.
Still another semiconductor substrate cleaning method of the present invention is characterized in that, in the present invention, the refractory metal contains W.
Still another semiconductor substrate cleaning method of the present invention is characterized in that, in the present invention, the sulfuric acid solution is electrolytic sulfuric acid.
Still another semiconductor substrate cleaning method of the present invention is characterized in that, in the present invention, the sulfuric acid solution contains sulfuric acid and one or both of ozone and aqueous hydrogen peroxide.
Another method for cleaning a semiconductor substrate of the present invention is characterized in that, in the present invention, peroxidic acid is included as the oxidizing agent.
Still another semiconductor substrate cleaning method of the present invention is characterized in that the semiconductor substrate is immersed in the sulfuric acid solution for cleaning.
Still another method for cleaning a semiconductor substrate according to the present invention is characterized in that the semiconductor substrate is cleaned by bringing the sulfuric acid solution into contact therewith and flowing down.
Still another method for cleaning a semiconductor substrate of the present invention is such that, in the cleaning, the etching rate of the refractory metal is 10 nm / min or less, the etching rate of the unnecessary metal is 5 nm / min or more, and the etching rate of the unnecessary metal ( (nm / min) / melting ratio of refractory metal etching rate (nm / min) is 8 or more.

  Below, the conditions etc. which are prescribed | regulated by this invention are demonstrated.

Sulfuric acid concentration: 80-98 mass%
By using sulfuric acid, unnecessary metals such as Ti and TiN can be removed and washed while suppressing dissolution of refractory metals such as W and Mo. When the sulfuric acid concentration is less than 80% by mass, the effect of suppressing the dissolution of the refractory metal cannot be sufficiently obtained. Concentrated sulfuric acid easily dissolves a very small amount of water in the air, so the upper limit of sulfuric acid concentration is 98% by mass. The sulfuric acid concentration indicates the concentration when used for cleaning.

Oxidant concentration: 0.0005 to 1 mol / L
Due to the action of the oxidizing agent, the action of dissolving unnecessary metals can be obtained. However, if the concentration of the oxidizing agent is less than 0.0005 mol / L, the detergency is insufficient. On the other hand, if the concentration exceeds 1 mol / L, damage to the refractory metal increases. For this reason, an oxidizing agent density | concentration is set to 0.0005-1 mol / L. For the same reason, the lower limit of the oxidant concentration is desirably 0.005 mol / L, and the upper limit of the oxidant concentration is desirably 0.1 mol / L. The oxidant concentration indicates the concentration when used for cleaning.
Examples of the oxidizing agent include peroxodisulfuric acid, peroxomonosulfuric acid (collectively referred to as persulfuric acid), ozone, active oxygen, and the like.

Temperature: 80-180 ° C
The sulfuric acid solution increases the cleaning effect of unnecessary metals by increasing the temperature. If the temperature is low, the cleaning ability is insufficient. On the other hand, if the temperature is too high, the refractory metal is damaged. For this reason, the temperature of a solution shall be 80-180 degreeC. The lower limit of the solution temperature is desirably 90 ° C., and the upper limit is desirably 130 ° C. In addition, when adjusting liquid temperature, it shall have the said temperature when a solution is made to contact a semiconductor substrate.

  ADVANTAGE OF THE INVENTION According to this invention, the washing | cleaning which removes unnecessary metals, such as Ti and TiN which coexist in the semiconductor substrate from a semiconductor substrate, can be performed, suppressing the damage of refractory metals, such as tungsten.

It is a figure which shows the sulfuric acid recycle type washing | cleaning system used for one Embodiment of this invention. Similarly, it is a figure which shows the sulfuric acid recycle type cleaning system used for other embodiments. Similarly, it is a figure which shows the sulfuric acid recycle type washing | cleaning system used for other embodiment.

Example 1
Below, one Embodiment of this invention is described based on FIG.
The sulfuric acid recycling type cleaning system used in this embodiment includes a cleaning tank 1 and an electrolytic reaction tank 10. The washing tank 1 is connected to the electrolytic reaction tank 10 by a circulation path including a return pipe 4 and a feed pipe 5. The return pipe 4 and the feed pipe 5 each have at least an inner surface made of a fluororesin such as tetrafluoroethylene, and the return pipe 4 is provided with a liquid feed pump 6 for feeding the sulfuric acid solution 2. Yes.

  A heat exchanger 7 is interposed between the return pipe 4 and the feed pipe 5 so that the solution flowing through the return pipe 4 and the solution flowing through the feed pipe 5 can exchange heat with each other. It has become. Note that at least the inner surface of a flow path (not shown) in the heat exchanger 7 is also made of a fluororesin. By configuring the flow paths of the return pipe 4, the feed pipe 5, and the heat exchanger 7 with a fluororesin resistant to persulfuric acid, wear due to persulfuric acid can be avoided. In this embodiment, the heat exchange of the solution is performed between the return pipe 4 and the feed pipe 5. However, in the present invention, the solution is preferably supplied to the return pipe 4 at 10 to 90 ° C. (during electrolysis). It is also possible to provide a cooling means for cooling to (temperature) and a heating means for heating the solution to 80 to 180 ° C. (temperature during washing) in the feed pipe 5. Further, a heater or the like may be provided in the cleaning tank 1.

  In the electrolytic reaction tank 10, an anode 11 and a cathode 12 are arranged, and a plurality of bipolar electrodes 13... 13 are arranged between the anode 11 and the cathode 12 at a predetermined interval. The number of bipolar electrodes is not particularly limited. Further, instead of the bipolar type, only an anode and a cathode may be provided as electrodes. A DC power source 14 is connected to the anode 11 and the cathode 12, thereby enabling DC electrolysis in the electrolytic reaction tank 10.

  In this embodiment, the anode 11, the cathode 12, and the bipolar electrode 13 are constituted by diamond electrodes. The diamond electrode is manufactured by forming a diamond thin film on a substrate and doping boron in a range of preferably 50 to 20,000 ppm with respect to the carbon content of the diamond thin film. Further, it may be a self-supporting type by removing the substrate after forming the thin film.

  Moreover, the washing tank 1 is connected to the thermal decomposition tank 20 by thermal decomposition circulation pipes 22 and 24 in a separate system from the circulation line. A liquid feed pump 23 is interposed in the thermal decomposition circulation pipe 22, and the cleaning liquid can be circulated between the washing tank 1 and the thermal decomposition tank 20 by the heat decomposition circulation pipes 22 and 24 and the liquid feed pump 23. It has become. The thermolysis tank 20 is provided with a heater 21 for heating the liquid in the tank.

Next, the operation of the sulfuric acid recycling type cleaning system having the above configuration will be described.
In the washing tank 1, sulfuric acid is accommodated, and ultrapure water is mixed therein to obtain a sulfuric acid solution having a sulfuric acid concentration of 80 to 98% by mass. This is sequentially fed to the electrolytic reaction tank 10 by the liquid feed pump 6. In the electrolytic reaction tank 10, when the anode 11 and the cathode 12 are energized by the DC power source 14, the bipolar electrodes 13 ... 13 are polarized, and the anode and the cathode appear at predetermined intervals. The solution sent to the electrolytic reaction tank 10 is passed between these electrodes. At this time, it is desirable to set the output of the liquid feed pump 6 so that the liquid flow rate is 1 to 10,000 m / hr. In the above energization, it is desirable to control the energization so that the current density on the diamond electrode surface is 10 to 100,000 A / m ² .

When electricity is supplied to the solution in the electrolytic reaction tank 10, the sulfuric acid ions in the solution undergo an oxidation reaction to generate persulfuric acid. The sulfuric acid solution 2 containing persulfuric acid is fed from the feed pipe 5 to the washing tank 1, and in the washing tank 1, the sulfuric acid concentration is 80 to 98 mass% and the oxidizing agent concentration is 0.0005 to 1 mol / L. Become. It is desirable to measure the oxidizing agent concentration in the cleaning tank 1 and perform cleaning within the above range.
In the washing tank 1, although the persulfate ion concentration gradually decreases due to autolysis, the solution circulates between the electrolytic reaction tank 10 and is electrolyzed in the electrolytic reaction tank 10 to generate persulfate ions. Sulfate ion concentration is maintained. In this embodiment, the process of changing from sulfuric acid to sulfuric acid solution containing persulfuric acid at the time of start-up has been described. However, as the present invention, persulfuric acid may be prepared from the beginning. However, in terms of producing persulfuric acid on-site, it is advantageous to produce persulfuric acid using an electrolytic reactor.

  Further, the sulfuric acid solution 2 in the cleaning tank 1 is circulated between the thermal decomposition tank 20 by the thermal decomposition circulation pipes 22 and 24 and the liquid feed pump 23, and further the solution in the thermal decomposition tank 20 by the heater 21. Is heated to raise the temperature of the sulfuric acid solution 2 in the washing tank 1. The circulation by the thermal decomposition circulation pipes 22 and 24 and the liquid feed pump 23 may be performed after the persulfuric acid concentration in the cleaning tank 1 becomes sufficiently high.

Cleaning of the semiconductor wafer 100, which is the material to be cleaned, is started in the state where the temperature of the sulfuric acid solution 2 serving as the cleaning liquid becomes 80 to 180 ° C. in the cleaning tank 1 due to the temperature increase. The semiconductor wafer 100 corresponds to the semiconductor substrate of the present invention. In this example, tungsten is used as the refractory metal in the semiconductor wafer 100, and TiN remains as an unnecessary metal.
In cleaning, the semiconductor wafer 100 is immersed in the cleaning tank 1. Then, in the cleaning tank 1, a high oxidation action is obtained by the self-decomposition of persulfuric acid and the action of sulfuric acid, and contaminants and unnecessary metals on the semiconductor wafer 100 are effectively removed and transferred into the sulfuric acid solution 2. To do. Of the removed matter transferred into the sulfuric acid solution 2, organic compounds such as resist are decomposed by the action of persulfuric acid. The sulfuric acid solution in the washing tank 1 is sent to the electrolytic reaction tank 10 by the return pipe 4 and the liquid feed pump 6, and the persulfate concentration is reduced by self-decomposition as persulfate ions are generated from the sulfate ions as described above. Is increased to regenerate the sulfuric acid solution 2.

  Further, when the sulfuric acid solution 2 moves from the washing tank 1 toward the electrolytic reaction tank 10, the sulfuric acid solution 2 is moved in the electrolytic reaction tank 10 and moved through the feed pipe 5 when the return pipe 4 is moved. In the heat exchanger 7, heat exchange is performed. The sulfuric acid solution 2 fed from the washing tank 1 is heated so as to be suitable for washing. On the other hand, the temperature of the sulfuric acid solution 2 fed from the electrolytic reaction tank 10 is lowered. As the sulfuric acid solution 2 is heat-exchanged, the temperature of the sulfuric acid solution 2 moving through the return pipe 4 is lowered, while the sulfuric acid solution 2 moving through the feed pipe 5 is heated to a high temperature. The sulfuric acid solution 2 that is heat-exchanged by the heat exchanger 7 and moves through the return pipe 4 is then gradually cooled by natural cooling to a temperature (10 to 90 ° C.) suitable for the electrolytic reaction. In order to reliably lower the temperature, a cooling unit that forcibly cools the sulfuric acid solution reaching the electrolytic reaction tank 10 by water cooling or air cooling may be provided.

The sulfuric acid solution 2 that is heat-exchanged by the heat exchanger 7 and moves through the feed pipe 5 is sent to the washing tank 1 and mixed with the sulfuric acid solution 2 remaining in the washing tank 1.
The sulfuric acid solution 2 in which the removed substance is taken in the washing tank 1 is sent to the thermal decomposition tank 20 through the thermal decomposition circulation pipe 24, where it is heated to a sufficient temperature by the heater 21, thereby resist in the removed substance. Organic compounds such as these are decomposed by heating, and the cleanliness of the sulfuric acid solution 2 is increased. In addition, insoluble SS can be removed by an SS removal filter interposed in the circulation path. However, since metal ions are difficult to remove and are concentrated over time, it is necessary to periodically replace the liquid. By returning the sulfuric acid solution 2 to the electrolytic reaction tank 10 by the thermal decomposition circulation pipe 22 and the liquid feed pump 23, the cleaning can be continued with the sulfuric acid solution 2 whose cleaning effect has been recovered.

(Embodiment 2)
Next, another embodiment will be described with reference to FIG.
The sulfuric acid recycling type single wafer cleaning system used in this embodiment includes a single wafer cleaning device 30, an electrolytic reaction device including electrolytic reaction tanks 50 and 55, return pipes 40a and 40b, and feed pipes 41a and 41b. The circulation line is the main component.
In the single wafer cleaning device 30, a liquid spray nozzle 32 is provided as a droplet jet forming device, and a tip side ejection portion of the liquid spray nozzle 32 is located in the cleaning tank 31. The liquid spray nozzle 32 is connected to a return pipe 40b of a circulation line for circulating a sulfuric acid solution containing persulfuric acid between the electrolytic reaction apparatus and a supply pipe 33 for N ₂ gas. The liquid spray nozzle 32 mixes the sulfuric acid solution supplied from the return pipe 40b with the high-pressure N ₂ gas supplied from the N ₂ gas supply pipe 33, and drops droplets of the sulfuric acid solution containing persulfuric acid downward. It is comprised so that it may eject toward. In the single wafer cleaning apparatus, the sulfuric acid solution may be ejected, or the semiconductor wafer may be brought into contact with the semiconductor wafer in the form of foam, sprayed, or dropped.
The return pipe 40b is provided with a heating device 49 immediately before the connection portion of the liquid spray nozzle 32 so that the sulfuric acid solution supplied to the liquid spray nozzle 32 has a temperature of 80 to 180 ° C. during cleaning. Heat.

  A substrate mounting table 34 is installed in the cleaning tank 31 in the ejection direction of the liquid spray nozzle 32. The semiconductor wafer 100 is placed on the substrate platform 34. The substrate mounting table 34 or the liquid spray nozzle 32 can be relatively movable so that the liquid droplets uniformly hit the surface of the semiconductor wafer 100.

  A feed pipe 41a is connected to the drainage section of the cleaning tank 31, and a feed pump 42 for feeding a sulfuric acid solution is interposed in the feed pipe 41a. A heat exchanger 43 that performs heat exchange is disposed between the return pipe 40b and the feed pipe 41a on the downstream side of the liquid feed pump 42, and is connected to the solution storage tank 44 on the downstream side thereof. The solution storage tank 44 is connected to an ultrapure water supply line 45 for supplying ultrapure water, and further includes a TOC measuring device 48 for measuring the TOC of the stored solution. A feed pipe 41 b further extends from the solution storage tank 44, and is connected to the liquid inlet side of the electrolytic reaction tank 50 via a liquid feed pump 47.

  In the electrolytic reaction tank 50, an anode 51a and a cathode 51b are arranged, and a plurality of bipolar electrodes 51c... 51c are arranged at a predetermined interval between the anode 51a and the cathode 51b. The number of bipolar electrodes is not particularly limited. Moreover, in an electrolytic reaction tank, you may provide only an anode and a cathode as an electrode. A DC power supply 52 is connected to the anode 51a and the cathode 51b.

  In the electrolytic reaction tank 50, a connecting pipe 53 is connected to the liquid discharge side, and the other end is connected to the liquid inlet side of the electrolytic reaction tank 55. The electrolytic reaction tank 55 has the same configuration as that of the electrolytic reaction tank 50, and an anode 56a and a cathode 56b are arranged, and a plurality of bipolar electrodes 56c are arranged at a predetermined interval between the anode 56a and the cathode 56b. ... 56c is arranged. A DC power source 57 is connected to the anode 56a and the cathode 56b. A return pipe 40 a is connected to the liquid discharge side of the electrolytic reaction tank 55.

  In this embodiment, each anode and each cathode is constituted by a diamond electrode. The diamond electrode is manufactured by forming a diamond thin film on a substrate and doping boron in a range of preferably 50 to 20,000 ppm with respect to the carbon content of the diamond thin film. Alternatively, a self-stand type may be used by removing the substrate after forming the thin film.

  A return pipe 40 a connected to the electrolytic reaction tank 55 is connected to the solution storage tank 44, and a return pipe 40 b connected to the solution storage tank 44 is connected to the heat exchanger 43 through the liquid feed pump 48. Furthermore, it is connected to the liquid spray nozzle 32 via a heating device 49.

Next, the operation of the sulfuric acid recycling type single wafer cleaning system configured as described above will be described.
Sulfuric acid is accommodated in the solution storage tank 44, and ultrapure water is mixed into the solution storage tank 44 at a predetermined volume ratio from the ultrapure water supply line 45 to obtain a sulfuric acid solution having a sulfuric acid concentration of 80 to 98% by mass. This is sequentially sent to the electrolytic reaction tank 50 by the liquid feed pump 47. In the electrolytic reaction tank 50, when the anode 51a and the cathode 51b are energized by the DC power source 52, the bipolar electrodes 51c... 51c are polarized and the anode and cathode appear at predetermined intervals. The sulfuric acid solution sent to the electrolytic reaction tank 50 is passed between these electrodes. At this time, it is desirable to set the output of the liquid feed pump 47 so that the liquid flow linear velocity is 1 to 10,000 m / hr. In the above energization, it is desirable to control the energization so that the current density on the diamond electrode surface is 10 to 100,000 A / m ² .

  When the sulfuric acid solution is energized in the electrolytic reaction tank 50, the sulfate ions in the solution undergo an oxidation reaction to generate persulfate ions, thereby obtaining a sulfuric acid solution containing a high concentration of persulfuric acid. The sulfuric acid solution is further sent from the connecting pipe 53 to the electrolytic reaction tank 55 and is energized by the DC power source 57 in the same manner as the electrolytic reaction tank 50 to generate persulfate ions. In this way, the sulfuric acid solution containing a high concentration of persulfuric acid is temporarily stored in the solution storage tank 44 through the return pipe 40a. The sulfuric acid solution stored in the solution storage tank 44 is fed to the cleaning device 30 side by the liquid feed pump 48 through the return pipe 40b. The sulfuric acid solution passes through the heat exchanger 43, where it heat-exchanges with the solution in the feed pipe 41a fed from the washing tank 31 toward the solution storage tank 44, and the temperature rises. The sulfuric acid solution is further fed to the cleaning device 30 side, heated to 80 to 180 ° C. by the heating device 49, and supplied to the liquid spray nozzle 32.

In the washing tank 30, the heated sulfuric acid solution and N ₂ gas are mixed in the liquid spray nozzle 32, and high-temperature sulfuric acid droplets are ejected for a certain period of time. In this case, the sulfuric acid solution has a sulfuric acid concentration of 80 to 98% by mass and an oxidizing agent concentration of 0.0005 to 1 mol / L.
A semiconductor wafer 100 is placed on the substrate mounting table 34, the semiconductor wafer 100 is rotated by the substrate mounting table 34, the surface of the semiconductor wafer 100 is cleaned by droplets of sulfuric acid solution, an organic compound such as a resist, Unnecessary metal is removed. The ejected sulfuric acid solution scatters and drops after the semiconductor wafer 100 is cleaned, and is discharged to the feed pipe 41a together with unnecessary metals, resist dissolved matter, and the like. In the feed pipe 41a, the sulfuric acid solution is fed to the solution storage tank 44 side by the liquid feed pump. At this time, the heat exchanger 43 exchanges heat with the return pipe 40b to lower the temperature of the sulfuric acid solution. Further, the temperature is gradually lowered by natural cooling, and is 10 ° C. to 90 ° C. suitable for the electrolytic reaction. The temperature is within the range. Thereafter, the solution is temporarily stored in the solution storage tank 44. If it is desired to reliably lower the temperature, a cooling unit that forcibly cools the solution storage tank 44 by water cooling or air cooling may be provided. When the liquid is fed through the feed pipe 41a, the dissolved resist material peeled and removed in the cleaning tank 31 is decomposed. Moreover, in the solution storage tank 44, the temperature of the solution is lowered by the heat exchange, and self-decomposition is suppressed. Further, when the solution is temporarily stored in the solution storage tank 44, the decomposition of the resist melt proceeds, and the inflow of the resist melt into the electrolytic reaction apparatus is effectively prevented.

In the solution storage tank 44, TOC is generated as the resist and other contaminants are peeled and dissolved in the single wafer cleaning apparatus. The TOC is measured by the TOC measuring device 58, and the TOC increase rate can be calculated based on the temporal change of the measurement result. In addition, insoluble SS can be removed by an SS removal filter interposed in the circulation path. However, the metal ions dissolved in the liquid are difficult to remove and are concentrated over time, so it is necessary to periodically replace the liquid.
The sulfuric acid solution stored in the solution storage tank 44 is then sent to the electrolytic reaction apparatus in the same manner as described above, and the persulfate ion concentration is reduced by autolysis to generate persulfate ions from the sulfate ions. Then, the sulfuric acid solution is regenerated and stored again in the solution storage tank 44, and then returned to the cleaning device 30 and used as a cleaning liquid in the same manner as described above.

(Embodiment 3)
In each of the above embodiments, electrolytic sulfuric acid is used as a cleaning liquid containing an oxidizing agent other than persulfuric acid in sulfuric acid. However, another embodiment using a sulfuric acid solution of another aspect may be used.
A sulfuric acid recycling type single wafer cleaning system used in this embodiment will be described with reference to FIG. In this embodiment, the same components as those in the above embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified.
The sulfuric acid recycle type single wafer cleaning system has a cleaning device 30 and a solution storage tank 60, and a feed pipe 61 connected to the solution storage tank 60 is connected to the liquid spray nozzle 32 of the cleaning tank 30. . A liquid feed pump 61 and a heating device 49 are interposed in the feed pipe 61.
In the washing tank 31, a drain pipe 35 for draining the sulfuric acid solution used for washing is connected. It is also possible to configure the washed sulfuric acid solution to circulate to the storage tank 60 side.
In the storage tank 60, a supply pipe 64 for supplying ozone or hydrogen peroxide water into the tank is connected.

Next, the operation of the sulfuric acid recycling type single wafer cleaning system configured as described above will be described.
Sulfuric acid is accommodated in the storage tank 60, ultrapure water is mixed at a predetermined volume ratio, and a predetermined amount of ozone or hydrogen peroxide solution is supplied into the storage tank 60 through a supply pipe 64. In the storage tank 60, at the time of washing | cleaning, adjustment is performed so that a sulfuric acid density | concentration may be 80-98 mass%, and an oxidizing agent density | concentration may be 0.0005-1 mol / L. Accordingly, the mixing ratio of hydrogen peroxide is limited to sulfuric acid: hydrogen peroxide = 50: 1 to 200: 1 by volume ratio.
The sulfuric acid solution in the storage tank 60 is fed to the cleaning device 30 side by the liquid feed pump 61 via the feed pipe 62. The sulfuric acid solution is heated by the heating device 49 so as to have a temperature of 80 to 180 ° C. during cleaning and is supplied to the liquid spray nozzle 32.

In the washing tank 30, the heated sulfuric acid solution and N ₂ gas are mixed in the liquid spray nozzle 32, and high-temperature sulfuric acid droplets are ejected for a certain period of time. The oxidant concentration at this time is 0.0005 to 1 mol / L.
A semiconductor wafer 100 is placed on the substrate mounting table 34, the semiconductor wafer 100 is rotated by the substrate mounting table 34, the surface of the semiconductor wafer 100 is cleaned by the droplets of the sulfuric acid solution, and an organic compound such as a resist is unnecessary. The metal is removed. The ejected sulfuric acid solution scatters and drops after the semiconductor wafer 100 is cleaned, and is discharged from the drain line 35 together with unnecessary metals, dissolved resist, and the like.

Examples of the present invention and comparative examples are shown below. In the examples and comparative examples, the cleaning system of the above embodiment was used.
(Examples 1-7 and Comparative Examples 1-5)
Fill the washing tank of the batch type cleaning device with the electrolytic sulfuric acid solution (sulfuric acid concentration, oxidizing agent concentration in the table),
(1) A solid wafer in which a TiN layer was laminated to 200 nm on a silicon wafer and (2) a solid wafer in which a W layer was laminated to 200 nm on a silicon wafer were cleaned at a temperature shown in the table for 120 seconds. The processed solution was subjected to component analysis using an ICP-MS (inductively coupled plasma mass spectrometer, hereinafter simply referred to as ICP-MS), and the wafer etching rate (E / R) was determined from the TiN concentration and W concentration in the solution. The TiN / W dissolution ratio was calculated from the etching rate.
The results are shown in the table.

(Examples 8 and 9, Comparative Example 6)
Supply the hydrogen peroxide solution or sulfuric acid solution with ozone added (sulfuric acid concentration, oxidizing agent concentration, mixing ratio of sulfuric acid and hydrogen peroxide water in the table) into the cleaning machine of the single wafer cleaning device,
(1) A solid wafer in which a TiN layer was laminated to 200 nm on a silicon wafer and (2) a solid wafer in which a W layer was laminated to 200 nm on a silicon wafer were cleaned at a temperature shown in the table for 120 seconds. The components after the treatment were analyzed using ICP-MS (inductively coupled plasma mass spectrometer, hereinafter simply referred to as ICP-MS), and the wafer etching rate was confirmed from the TiN concentration and W concentration in the solution. The TiN / W dissolution ratio was calculated from the etching rate.
The results are shown in the table.

As shown in the table, in the examples, by bringing a sulfuric acid solution having a sulfuric acid concentration of 80 to 98% by mass, an oxidizing agent concentration of 0.0005 to 1 mol / L, and a temperature of 80 to 180 ° C. into contact with a semiconductor substrate, silicon In the wafer, E / R (TiN) was 5 nm / min or more and the E / R ratio was 8 or more, and TiN could be effectively removed while reducing damage to tungsten.
On the other hand, in the comparative example, since at least one of sulfuric acid concentration, oxidant concentration, and temperature is inappropriate, the silicon wafer is effectively damaged due to damage to tungsten or insufficient TiN removal effect. Cleansing could not be performed.

  As mentioned above, although this invention was demonstrated based on the said embodiment and Example, this invention is not limited to the content of the said embodiment and Example, and unless it deviates from the range of this invention, it is suitably. Can be changed.

DESCRIPTION OF SYMBOLS 1 Washing tank 2 Sulfuric acid solution 4 Return pipe 5 Feeding pipe 6 Liquid feeding pump 7 Heat exchanger 10, 10a, 10b Electrolytic reaction tank 11, 11a, 11b Anode 12, 12a, 12b Cathode 13 Bipolar electrode 14 DC power supply 20 Thermal decomposition tank DESCRIPTION OF SYMBOLS 21 Heater 25 Ultrapure water supply line 30 Cleaning apparatus 31 Cleaning tank 32 Liquid spray nozzle 34 Substrate mounting table 40a Return pipe 40b Return pipe 41a Feed pipe 41b Feed pipe 42 Liquid feed pump 47 Liquid feed pump 48 Liquid feed pump 49 Heating apparatus 50 Electrolytic reaction tank 51a Anode 51b Cathode 51c Bipolar electrode 52 DC power supply 55 Electrolytic reaction tank 56a Anode 56b Cathode 56c Bipolar electrode 57 DC power supply 100 Substrate

Claims (9)

A method of cleaning a semiconductor substrate that removes unnecessary metals from a semiconductor substrate containing a refractory metal,
The semiconductor substrate is contacted with a sulfuric acid solution having a sulfuric acid concentration of 80 to 98% by mass, an oxidizing agent concentration of 0.0005 to 1 mol / L, and a temperature of 80 to 180 ° C., thereby removing the unnecessary metal. A method for cleaning a semiconductor substrate.   The method for cleaning a semiconductor substrate according to claim 1, wherein the unnecessary metal includes one or both of Ti and TiN.   The method for cleaning a semiconductor substrate according to claim 1, wherein the refractory metal contains W.   The method for cleaning a semiconductor substrate according to claim 1, wherein the sulfuric acid solution is electrolytic sulfuric acid.   The method for cleaning a semiconductor substrate according to claim 1, wherein the sulfuric acid solution contains sulfuric acid and one or both of ozone and hydrogen peroxide water.   The method for cleaning a semiconductor substrate according to claim 1, wherein the oxidizing agent contains persulfuric acid.   The method for cleaning a semiconductor substrate according to claim 1, wherein the semiconductor substrate is immersed in the sulfuric acid solution for cleaning.   The method for cleaning a semiconductor substrate according to claim 1, wherein the sulfuric acid solution is brought into contact with and flowed down to the semiconductor substrate for cleaning.   In the cleaning, the etching rate of the refractory metal is 10 nm / min or less, the etching rate of the unnecessary metal is 5 nm / min or more, and the etching rate of the unnecessary metal (nm / min) / etching rate of the refractory metal (nm). 9. The method for cleaning a semiconductor substrate according to claim 1, wherein the dissolution ratio is 8 or more.

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