JP2000091288A - Cleaning method of semiconductor substrate with high temperature mist sulfuric acid and cleaning equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable eliminating organic contamination and metal contamination of Cu, Fe, etc., of a silicon wafer with a short time treatment for several minutes, by holding a semiconductor substrate in an atmosphere containing mist sulfuric acid at a high temperature, and keeping the surface of the substrate in the state wetted with sulfuric acid. SOLUTION: Sulfuric acid 2 is accommodated at the bottom of a cleaning vessel 1 composed of quartz glass, a lid 3 composed of quartz glass is capped, and heating is performed with a heater 4. The liquid temperature of the sulfuric acid 2 and the temperature of an atmosphere 1a can be measured with a thermocouple arranged in a quartz glass tube. When the liquid temperature reaches 250 deg.C, a wafer 7 accommodated in a carrier 6 composed of quartz glass is put in the vessel and held above the liquid. In this step, the inside of the vessel is filled with white smoke of mist sulfuric acid. When slight exhaust is performed through a sulfuric acid gathering tube 9 which is filled with quartz wool 8, a small amount of air invades from a gap between the cleaning vessel 1 and the lid 3, and white smoke becomes more dense.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a semiconductor substrate having an active region of silicon and a cleaning apparatus for performing the method.

[0002]

2. Description of the Related Art The most typical cleaning process in a semiconductor process is cleaning of a substrate surface whose active region is silicon. Currently, in various devices utilizing the properties of semiconductors, the semiconductor to be cleaned is silicon in most cases. Generally, the object to be cleaned is a silicon surface and an oxide film, a nitride film, and a polysilicon film formed on the silicon surface. Contaminations to be removed are particles, metal elements, and organic substances. A powerful and proven cleaning method for removing such contamination is wet cleaning combining chemical treatment and rinsing with ultrapure water. As treatment chemicals, SC-1 (aqueous cleaning solution containing ammonium hydroxide and hydrogen peroxide) and SC-2 (aqueous cleaning solution containing hydrochloric acid and hydrogen peroxide) called RCA cleaning, sulfuric acid and peroxide Representative examples include a mixed solution of hydrogen and diluted hydrofluoric acid.

In the generation of the 1M DRAM, the allowable amounts of heavy metals such as Fe and Cu and alkali metals such as Na, which were substantially to be cleaned, were about 5 × 10 ¹⁰ atoms / cm ² . Although the importance of removal of organic matter was recognized to some extent, the relationship between device performance and manufacturing yield was not as clear as particles and metals, and setting of allowable values was not required. The roadmap published by the American Semiconductor Industry Association in December 1997
Metal contamination allowed in the 256M DRAM process in 2009 is 5 × 10 ⁹ atoms / cm ² ,
In the DRAM process, it is set to 1 × 10 ⁹ atoms / cm ² or less. Regarding organic substances, the allowable amount in 1997 was 1 × 10 ¹⁴ atoms / cm ² in terms of carbon concentration, and the allowable amount in 2009 was 1.8.
It was shown by a numerical value of × 10 ¹³ atoms / cm ² .

[0004] Many studies have revealed the adverse effects of organic contamination in the process of manufacturing ultra-fine devices, and the fact that organic contamination reduces the effect of removing metal and particle contamination in the cleaning step. This is because substantial damage has been identified. Conventionally, organic contamination is removed by washing at about 130 ° C. with a mixture of sulfuric acid and hydrogen peroxide (about 3: 1 volume) or SC-1 (aqueous ammonia: hydrogen peroxide: water = 1 volume: Approximately 80 ° C by 1 volume: about 5 volumes)
Cleaning is considered to be effective, and the above-mentioned 1 × 10
A cleaning level up to about ¹⁴ atoms / cm ² has been obtained. For more efficient removal of organic substances, washing with ozone water having a high concentration of several tens of ppm has been proposed.

[0005]

[Problems to be Solved by the Invention] One of the inventors will present ¹² C at the 59th JSAP Lecture 18a-ZD-2.
According to charged particle activation analysis using nuclear reaction of (d, n) ¹³ N, carbon of organic matter on the wafer surface is 2 × 10 ¹² a
It became clear that detection was possible up to toms / cm ² . SC
In the case of -1 cleaning, t-butyl-p-cresol (BHT), dioctyl phthalate (DOP) have many chances of contamination in the semiconductor manufacturing process even if the treatment is performed for about 10 minutes even with the optimum composition.
In addition, it can be cleaned only up to about 1 × 10 ¹⁴ atoms / cm ² against the adhesion of hexamethyldisilazane (HMDS) and the like. Although this level can be satisfied at the 256M DRAM level for the time being, it cannot be used for ULSI which will be advanced in the future. In addition, the SC-1 cleaning has a weak cleaning power against the contamination of Fe and Al on the surface, and conversely, there is a high risk of contamination from the cleaning liquid.

[0006] Sulfuric acid / hydrogen peroxide cleaning at about 130 ° C is superior to SC-1 cleaning in removing organic substances.
In the treatment for about 0 minutes, the carbon concentration is reduced only to about 5 × 10 ¹³ atoms / cm ² against the above-mentioned contamination, and the concentration of 10 ¹² to 1 which can occur from the process equipment in the semiconductor manufacturing process.
Regarding metal contamination such as 0 ¹³ atoms / cm ² of Cu and Fe,
It is often difficult to reduce it to 5 × 10 ⁹ atoms / cm ² or less. In addition, since this treatment is immersion treatment, a large amount of chemical solution is used per wafer, and a large amount of sulfuric acid heated together with the oxidizing agent is extremely dangerous. In addition, when it becomes a waste liquid, the amount added as the aqueous hydrogen peroxide becomes water and is diluted and sulphated. Therefore, advanced technology and special equipment are required for the recovery and recovery of sulfuric acid.

Although washing with high-concentration ozone water has a considerably strong ability to remove BHT and DOP contamination, strong HMDS contamination cannot be removed even by immersion treatment for 20 minutes.

Accordingly, the present invention is to reduce the organic contamination of a silicon wafer generated in a normal semiconductor manufacturing process by a carbon concentration of 2 × 1.
It is an object of the present invention to provide a cleaning method and a cleaning apparatus capable of removing metal contamination such as Cu or Fe to 0 ¹³ atoms / cm ² or less and 1 × 10 ⁹ atoms / cm ² or less by a short-time treatment for several minutes. I do.

[0009]

In order to achieve this object, the present invention provides a semiconductor device, comprising: holding a semiconductor substrate in an atmosphere containing high-temperature atomized sulfuric acid; A method for cleaning a semiconductor substrate, the method including a step of keeping the substrate wet. Further, according to the present invention, as a device for carrying out this method, a cleaning tank for bringing a semiconductor substrate into contact with high-temperature mist sulfuric acid and a mist-containing sulfuric acid in the cleaning tank are provided. And a means for forming an atmosphere containing atomized sulfuric acid in a space in the cleaning tank.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention has various preferred embodiments as described below. First, as for the cleaning method, as described in claim 3, the semiconductor substrate to be subjected to the above-mentioned step has at least a surface made of silicon, and a natural oxide film on the silicon surface is removed in advance by hydrofluoric acid treatment. The method for cleaning a semiconductor substrate according to claim 1, wherein:

After the step of holding the semiconductor substrate in an atmosphere containing atomized sulfuric acid, all or part of the chemical oxide film formed in the step on the silicon surface is hydrofluoric acid. 2. The method according to claim 1, further comprising a step of removing by processing.
3. The method for cleaning a semiconductor substrate according to any one of 3.

As set forth in claim 5, before the step of maintaining the semiconductor substrate in an atmosphere containing atomized sulfuric acid, the method further comprises a step of wetting a part of the substrate with liquid sulfuric acid.
4. The method for cleaning a semiconductor substrate according to any one of items above.

According to an embodiment of the above-mentioned cleaning apparatus, the means for forming the atmosphere containing the atomized sulfuric acid may include a cleaning tank bottom containing liquid sulfuric acid and a bottom. The cleaning apparatus according to claim 6, further comprising a heating unit, wherein the heating unit heats the liquid sulfuric acid to form an atmosphere containing atomized sulfuric acid in the cleaning tank.

According to another aspect of the present invention, the means for forming the atmosphere containing the atomized sulfuric acid is formed in an impinger-shaped container having a heating means for atomizing liquid sulfuric acid, and formed in the container. The cleaning apparatus according to claim 6, further comprising: an introduction pipe configured to introduce an atmosphere containing atomized sulfuric acid into the cleaning tank.

According to a ninth aspect of the present invention, the carrier means has a holding means for holding the substrate to be cleaned and a support shaft capable of moving the holding means up and down. The cleaning device according to any one of claims 6 to 8, wherein the cleaning device is capable of freely moving in a space formed by a lid that is covered by the device and that has a space in which the holding means can be stored.

According to a tenth aspect of the present invention, the apparatus further comprises an impinger-like container for creating a hydrofluoric acid-containing atmosphere, and an introduction pipe for introducing the atmosphere into the lid.
The cleaning device according to any one of claims 9 to 13.

According to an eleventh aspect of the present invention, the apparatus further comprises a sulfuric acid collector filled with quartz wool, and the atmosphere in the cleaning tank and the lid is exhausted through the collector. The cleaning device according to any one of -10.

As set forth in claim 12, the cleaning tank has an opening opening upward; the lid has an opening opening downward, and the opening of the lid is It can be opened and closed by sliding laterally with respect to the opening of the cleaning tank; when cleaning the semiconductor substrate, the opening of the cleaning tank and the opening of the bell-shaped lid are in close contact with each other. A space is created in the space, and an atmosphere containing atomized sulfuric acid is formed in the space, the substrate to be cleaned is held above the liquid sulfuric acid in the cleaning tank by the carrier means, and the surface of the substrate is wet with sulfuric acid. And at the time of recovery of the semiconductor substrate, the carrier means moves upward while holding the washed substrate and is accommodated in the lid, and then slides with the carrier means in the lateral direction, Next processing of the cleaned substrate Subjected to extent, cleaning apparatus according to any one of claims 6-11, characterized in that. Hereinafter, the present invention will be described in more detail including these embodiments.

The silicon wafer and the like in the first as the semiconductor substrate to be cleaned cleaned. A film such as a thermal oxide film or a nitride film may be formed on the silicon wafer. The substrate material may be other than silicon. For example, the substrate material may be an SOI wafer, and the substrate may be sapphire and a silicon single crystal film for forming a device may be formed thereon. The region where the device to be cleaned is formed may not be a single crystal, but may be, for example, the surface of a polycrystalline silicon film formed on a glass substrate. In short, the present invention is directed to a substrate for various devices utilizing the property of a semiconductor which is not substantially attacked by high-temperature sulfuric acid of 200 ° C. or more.

Silicon Surface Properties to Hot Sulfuric Acid Silicon surfaces are very well wetted with sulfuric acid at high temperatures, preferably above 200 ° C. The silicon oxide film is more easily wetted with hot sulfuric acid than the silicon surface. Since concentrated sulfuric acid has a strong oxidizing power at high temperatures, the bare silicon surface immediately after being treated with hydrofluoric acid forms a chemical oxide film of several tens of angstroms immediately upon contact with these high-temperature sulfuric acid droplets. Immediately spread to form a thin wetting layer of sulfuric acid. This high temperature wet layer has a strong cleaning effect on organic substances and heavy metals such as Cu and Fe. If the temperature is too low, sulfuric acid does not have a strong cleaning effect on metal elements. However, at a high temperature, a strong oxidizing power is generated, and even a metal element having a low ionization tendency such as Cu is well dissolved. This oxidizing power further enhances the strong decomposition effect of sulfuric acid on organic substances. This property has been used for a long time as a decomposition means for organic matter analysis.

The temperature of the atomized sulfuric mist sulphate is preferably at least 200 ° C., more preferably from 230 ° C. to 300 ° C., more preferably 2
50 ° C to 290 ° C. The cleaning time by contact with the atomized sulfuric acid is usually 1 minute or more, and in many cases, 3 to 30 minutes.

For example, an azeotropic mixture consisting of 98.5% of H ₂ SO ₄ and the remaining H ₂ O has a boiling point of 317 ° C., but 290 ° C.
In this case, considerable SO ₃ is generated and reacts with the water in the air to generate hot sulfuric acid white smoke. The vapor pressure of sulfuric acid is about 200 mmHg at 280 ° C., about 100 mmHg at 250 ° C., and 200 mmHg.
Since the temperature is about 30 mmHg, when sulfuric acid is put into the bottom of a quartz glass container with a lid at a depth of about 1 cm and heated, if there is moisture in the atmospheric air, mist-like sulfuric acid is generated in the container from the liquid temperature of about 200 ° C and white smoke Become Atomized sulfuric acid has aggressive Brownian motion due to its aerosol properties, and its liquid particles tend to condense. The sulfuric acid concentration is desirably 96% or more. When the liquid temperature exceeds 250 ° C., the inside of the container becomes invisible. If the degree of white smoke formation is small, a small amount of humid air is blown into the white smoke.
In such a state, the container is H
_{The 2} SO ₄ concentration becomes much higher, and when a silicon wafer or a wafer with an oxide film is put in this, the entire surface of the wafer is immediately wetted with the sulfuric acid solution film due to the above-described properties. The wet sulfuric acid is dropped from the substrate surface and collected as a liquid when the thickness of the wet layer increases as in the case of ordinary steam cleaning. Therefore, the wet liquid level is always generated by collecting sulfuric acid mist of high purity generated through the gas phase, and the cleaning effect is further enhanced.

The basic mechanism Figure 1 of the cleaning device is a vertical sectional view showing the concept of the apparatus of the present invention. Sulfuric acid 2 having a purity of 96% or more is put in the bottom of a quartz glass washing tank 1, and a quartz glass lid 3 is placed on the washing tank 1 and heated by a heater 4.
The temperature of the sulfuric acid 2 and the temperature of the atmosphere 1a can be measured by a thermocouple (not shown) placed in a quartz glass tube. When the liquid temperature reaches 250 ° C., the wafer 7 placed in the carrier 6 made of quartz glass is put into a tank and held on the liquid. At this stage, the inside of the tank is filled with fume sulfuric acid white smoke. When the air is slightly exhausted through the sulfuric acid collecting cylinder 9 filled with quartz wool 8, a small amount of air enters from the gap between the cleaning tank 1 and the lid 3, and the white smoke further increases.

In the case of a silicon wafer, the temperature of the sulfuric acid 2 is set to 280 ° C., the temperature of the atmosphere 1a is set to 250 ° C., and left for 3 minutes. , HMDS wafer
Even with a strong organic contaminated sample that has been immersed in the solution and dried as it is, the surface carbon concentration can be reduced to 2 × 10 ¹³ atoms / cm ² or less. In addition, add 2 × Cu on the silicon surface in advance.
10 ¹² atoms / cm ² contaminated, and on the other hand, the HMD
S is removed and the surface concentration of Cu is reduced to 1 × 10 ⁹ atoms / cm.
^It can be reduced to ² or less.

In the case of a normal mirror-finished wafer made of a silicon-pulled single crystal, Cu
Impurities with a fast diffusion like 10 ¹⁴ to 10 ¹⁵ ato on average
Even if it has penetrated about ms / cc, it is not immersed in high-temperature sulfuric acid as disclosed in Japanese Patent Application No. 9-7893, but a very thin surface due to contact with atomized high-temperature sulfuric acid having a high sulfuric acid concentration in the atmosphere. With only wet sulfuric acid, the internal Cu is sucked out and
Can be reduced to 1/100. This is thought to be due to the fact that the distilled and purified high-purity sulfuric acid mist always liquefies on the surface more efficiently than the mere vapor-phase steam cleaning action and flows down the silicon surface, so that a good suction effect, that is, a cleaning effect on the bulk is produced. .

In addition, a mechanism capable of raising and lowering the wafer carrier in the cleaning tank is provided, and at the beginning of cleaning, only the lower end of the silicon wafer is immersed in sulfuric acid for several tens seconds to several minutes (the larger the substrate diameter, the larger the substrate diameter). Long) leave and then pull up,
After that, when the wafer is held in the sulfuric acid mist, the wetting by sulfuric acid spreads over the entire surface of the silicon wafer due to immersion, so that the temperature of the entire wafer rises quickly and the processing time for obtaining the same cleaning effect can be shortened.

FIG. 2 is a longitudinal sectional view showing another embodiment of the cleaning apparatus according to the present invention. Elements in common with FIG. 1 are indicated by the same numbers as in FIG. This shows a method in which atomized sulfuric acid is fed into the same tank 17 as in FIG. 1 without preparing a sulfuric acid solution in the cleaning tank 17 in advance. Impinger-shaped quartz glass container 1
Sulfuric acid 11 having a purity of 96% or more can be put in 0. A quartz glass tube 14 extends outward from the top of the quartz glass container 10 and is hermetically introduced into a cleaning tank 17. A plurality of holes 15 are formed in the quartz glass tube 14 at positions substantially below the wafer 7. When the sulfuric acid 11 in the quartz glass container 10 is heated to about 300 ° C. by the heater 12 and moist air is introduced through the quartz glass tube 13 as indicated by an arrow, a white smoke-like sulfuric acid mist generated at a high concentration in the container 10 is formed. It is supplied into the cleaning tank through the hole 15 of the quartz glass tube 14. The wafer 7 in the tank 17 is heated in advance by a heater 16 surrounding the tank so that the temperature is maintained at 200 ° C. or higher. The sulfuric acid that has sufficiently wet the wafer falls to the bottom in the tank 17. In this method, the same cleaning as in the case of FIG. 1 can be performed, and the required amount of sulfuric acid is small, but the cleaning time is slightly longer to obtain the same cleaning effect as in the case of FIG.

The cleaning bath must be made of a high-purity material that can withstand the use of hot sulfuric acid. In addition to quartz glass, silicon carbide and amorphous carbon are suitable. The wafer carrier is desirably made of quartz glass, but may be made of a fluororesin that is resistant to high-temperature sulfuric acid, such as PTFE. Quartz wool is most desirable as a sulfuric acid mist collector. Because of the strong wettability of the quartz surface, sulfuric acid contamination outside the system can be substantially prevented.

Since high-temperature sulfuric acid is an oxidizing cleaning agent, if a thick natural oxide film is formed on the silicon surface, the removal of metal ions may be incomplete if metal ions are incorporated therein. Therefore, it is preferable to remove the natural oxide film by contacting with diluted hydrofluoric acid or a gas containing hydrofluoric acid in advance.

The high temperature sulfuric acid cleaning of the silicon surface produces a chemical oxide film of about 20 angstroms. In the pretreatment for performing the epitaxial growth, it is necessary to remove the natural oxide film and sufficiently remove the organic matter. An azeotropic hydrofluoric acid from which organic substances have been removed is placed in an impinger hydrofluoric acid evaporator made of a high-purity fluororesin (for example, PFA washed with a strong organic alkali), and the hydrofluoric acid is evaporated. When introduced into the cleaning tank with a fluororesin introduction pipe of the same material and reacted with the silicon surface after the sulfuric acid mist treatment, a clean surface with a very small amount of natural oxide film and very little organic matter remaining can be obtained. According to this, the epitaxy growth temperature of monosilane was 7
The temperature can be lowered to about 00 ° C., and the occurrence of slip can be suppressed even in the case of a large diameter wafer. If only a part of the surface layer of the chemical oxide film is removed by immersion cleaning in dilute hydrofluoric acid or by single-wafer spin cleaning in which dilute hydrofluoric acid is incident, it is effective in reducing the concentration of fine particles on the surface.

[0031]

EXAMPLES The present invention will be described below in more detail with reference to Examples, but it should not be construed that the invention is limited thereto. The sample substrate used was a mirror-finished wafer made of p-type pulled silicon single crystal having an oxygen concentration of 1.4 × 10 ¹⁸ atoms / cc, which had not been subjected to any gettering treatment. It is Cu that is relatively difficult to remove by washing heavy metals contaminating the surface. In this case, p-type wafers are generally more difficult to clean than n-type wafers.

The evaluation of the cleaning effect is as follows:
According to the I tracer method. That is, metal contamination labeled with a radioisotope was performed on the wafer surface and inside the wafer, the radioactivity before and after cleaning was monitored, and the ratio, that is, the residual ratio of the contaminated element after cleaning was determined.

The surface contamination was measured by immersing the test wafer in a hydrofluoric acid buffer solution (abbreviated to BHF: NH ₄ F + HF) to which ⁶⁴ Cu was added, so that the average concentration of ⁶⁴ Cu on the surface was 5 × 10 ¹² atoms /
It was prepared by an adsorption treatment so as to obtain cm ² . Also, ⁵⁹ Fe
A test wafer having an average concentration of ⁵⁹ Fe on its surface of 5 × 10 ¹² atoms / cm ² was also prepared by immersion in the SC-1 solution to which was added.

Separately, a sample in which ⁶⁴ Cu was penetrated and contaminated inside the wafer was also prepared. That is, ⁶⁴ Cu is converted to BHF as described above.
From the test wafer, and 90
Heated at 0 ° C for 30 minutes, the average concentration of ⁶⁴ Cu in the wafer was 5
Diffusion processing of ⁶⁴ Cu was performed so as to be × 10 ¹⁴ atoms / cc.

The evaluation of the carbon content of the organic substance on the wafer surface was based on the above-described charged particle activation analysis. According to experience, HMDS is the most difficult organic contaminant to clean in a semiconductor clean room process, and it is particularly difficult to remove the contaminated state of the wafer after it has been immersed in the HMDS solution and dried as it is. Therefore, the wafer subjected to the test was thus organically contaminated. Also, when the sample is organically contaminated during Cu cleaning, Cu
Was found to be more difficult to remove,
A sample obtained by further treating the ⁶⁴ Cu-contaminated wafer with HMDS was prepared.

The sulfuric acid used in the following examples is of semiconductor grade and has a concentration indication of 96%. [Example 1] Fig. 3 shows a series of cleaning apparatuses for subjecting a sample wafer contained in a plurality of carriers to the sulfuric acid mist cleaning of the present invention, rinsing with pure water, and drying with heated clean air. And used in this example. (1) is a part for charging and recovering a carrier into a sulfuric acid mist cleaning tank, (2) is a sulfuric acid mist cleaning part, and (3) is a pure water rinsing and drying part. Numeral 1 denotes a quartz glass cleaning tank into which sulfuric acid 2 enters only at the bottom. The upper edge 17 of the tank 1 has a flange-like flat contact surface. If this surface is directly covered with a fluororesin plate,
When the sulfuric acid is heated by the heater 4, the sulfuric acid wets the quartz glass very well. To contaminate. Therefore, an auxiliary cylinder 18 made of quartz glass having a flange-shaped mating surface at the lower end is provided. Since the oozing of sulfuric acid still cannot be reliably prevented, the leaching sulfuric acid having a lowered temperature is recovered by circling the edge groove 19 outside the cleaning tank.

The quartz glass bell 20 is a lid of a washing tank at the time of washing, and stores the quartz glass carrier 6 accommodating the wafer 7, and moves from (1) to (2) and (2).
To (1). This bell is connected to the hole of the flat plate 21 made of fluororesin PTFE which moves horizontally to open and close the washing tank. The movement of the bell is caused by the movement of the flat plate 21. This flat plate moves on a mounting base plate 22 made of a fixed fluororesin PTFE. The auxiliary cylinder and the cleaning tank are arranged such that the upper flat surface of the auxiliary cylinder is in close contact with the lower surface around the hole of the mounting plate.
A heater 4 is arranged below the washing tank, and a quartz wool heat insulating zone 16 is arranged on the side of the washing tank. The bell 20 is provided with a sulfuric acid collecting tube 9 filled with quartz wool 8. Although not shown, a sulfuric acid collecting cylinder filled with quartz wool is also attached to the auxiliary cylinder.

The carrier 6 containing the wafer is hooked on a hook attached to a quartz glass cap 24 joined to the lower end of a carrier support shaft 23 made of a thick quartz glass tube. Near the upper end of the carrier support shaft, there is a support 25 that is linked to a vertical movement mechanism (not shown) connected to the flat plate 21. Support shaft 23
Has a structure capable of moving up and down through a quartz glass bearing 26 at the top of the bell. A mechanism for slightly rotating this shaft is attached to the vertical movement mechanism. The reason why the support shaft is formed in a tubular shape is that when the atomization of sulfuric acid is insufficient, the sulfuric acid is exhausted by a sulfuric acid collecting cylinder to introduce humid air if necessary.

Prior to the sulfuric acid mist cleaning, the carrier 6 is (1)
In this state, the washing tank is located at the position inside the bell 20 indicated by the imaginary line (dotted line). Sulfuric acid can be reciprocated between the sulfuric acid basin 28 and the sulfuric acid reservoir 28 by the quartz tube 27 passing through the side surface of the auxiliary cylinder.
The sulfuric acid was moved to the bottom of the washing tank during the state of and the mixture was heated to 280 ° C. When this temperature is reached, the inside of the tank is filled with sulfuric acid fog white smoke. Then, the carrier was moved to the state (2), the carrier was lowered on the sulfuric acid by lowering the support shaft, and sulfuric acid mist cleaning was performed for 3 minutes. After the washing is completed, the sulfuric acid is first moved to the sulfuric acid reservoir, and the sulfuric acid atmosphere in the bell 20 and the washing tank is rapidly exhausted through the two sulfuric acid collecting tubes.

Here, the carrier is raised, and the bell body is (1)
To the position indicated by the virtual line (dotted line). Bell 20 (1)
The ultrapure water rinsing tank 30 is located below the auxiliary cylinder 29 fixed to the base plate 22 at the position (3), and the mechanism including this tank can reciprocate with the position (3). The carrier is lowered into the rinsing tank and is inserted into the bottom frame 31. When the support shaft is slightly rotated, the carrier comes off the hook. Only the support columns are raised. The rinsing mechanism consists of a rinsing tank and an outer tank 32 outside the rinsing tank.
Consisting of The rinsing mechanism containing the carrier is moved to the position (3), and ultrapure water is introduced from the ultrapure water inlet 33,
Perform overflow rinsing.

At this time, the carrier support shaft 23 is lowered again, a carrier (not shown) on which a wafer to be next cleaned is set is hooked on a hook, the support shaft is raised, and the next cleaning operation is started. At the position (3), there is a drying mechanism above.
The lower end 37 of the second support shaft 36 that penetrates from the upper part of the drying bell 34 and moves up and down by the support 35 by an up-and-down mechanism (not shown) catches the carrier that has been rinsed with ultrapure water. Has the function of pulling in. After the carrier is pulled up, the rinsing mechanism drains and returns to the position (1). The wafer in the carrier pulled up is dried by clean hot air heated to 200 ° C. after passing through the chemical filter and the HEPA filter supplied from the hot air introduction pipe 38. The carrier of the dried wafer can be taken out by lowering the second support shaft. The first embodiment with this device is HM
It is an examination of the ability to remove organic contamination from a sample contaminated with DS. After performing the washing operation as described above, the surface carbon concentration was determined by charged particle activation analysis by deuteron irradiation.
The analysis result for three samples was 1.7 × 10 ¹³ atoms /
cm ² , 1.2 × 10 ¹³ atoms / cm ² , 1.4 × 10 ¹³ ato
ms / cm ² , high cleanliness target value 2 × 10 ¹³ atoms / cm ²
The following has been achieved:

Example 2 ⁶⁴ Cu 2 × 10 ¹² atoms /
The sample that had been immersed in HMDS for one minute and air-dried with respect to the cm ² contaminated sample was subjected to sulfuric acid mist cleaning using the same apparatus and under the same conditions as in Example 1. The residual ratio of ⁶⁴ Cu after washing is 0.04%.
The residual amount of ⁶⁴ Cu is 8 × 10 ⁸ atoms / cm ² , achieving a high cleanliness target value of 1 × 10 ⁹ atoms / cm ² or less. On the other hand, the same sample was used at 70 ° C. and 10 ° C. by SC-1 (aqueous ammonia: hydrogen peroxide: water = 1 volume: 1 volume: 5 volumes).
Washing with SC-2 (hydrochloric acid: hydrogen peroxide solution: water = 1)
(1 volume: 6 volumes), the same washing was performed at 70 ° C. for 10 minutes. The remaining rate of the former was 3.1%, and that of the latter was 1%.
It was 5.3%.

[Example 3] The three kinds of washed samples of Example 2 were treated with hydrofluoric acid distilled with particular attention to removing organic substances, and their respective chemical oxide films were removed. Each of the wafers was rinsed with ultrapure water using a single-wafer spin dryer and then spin-dried at 2,000 rpm. As a result, no water mark was formed at the center of the sulfuric acid mist cleaning wafer. However, SC-
Watermarks are observed in both the 1-cleaned wafer and the SC-2 cleaned wafer, and it can be seen that organic contamination remains in these. The results of charged particle activation analysis of the sulfuric acid mist-washed hydrofluoric acid-treated wafer show that the carbon concentration is 2.8 × 10 ¹³ atoms / cm ² , and defect-free growth at 700 ° C. can be expected in monosilane epitaxy. Value.

Example 4 Using the apparatus of Example 1, the sulfuric acid mist generator of FIG. 2 was connected to the quartz tube 27, and sulfuric acid mist cleaning was performed without putting a sulfuric acid solution in the cleaning tank. The sample used ⁶⁴ Cu contaminated product and ⁵⁹ Fe contaminated product, sulfuric acid was heated to 305 ° C,
After the wafer carrier was placed in the cleaning premises, sulfuric acid white smoke was introduced while exhausting the two sulfuric acid collecting cylinders. Heating was performed by the heater 4 so that the bottom of the washing tank was at 280 ° C., but the atmosphere around the shade was about 200 ° C. ⁶⁴ Cu
The contaminated sample had a residual rate of 0.12% after 3 minutes washing and 0.05% after 5 minutes washing. ^{The 59} Fe-contaminated sample was washed for 3 minutes to obtain 0.1%.
03%.

Example 5 A sample in which ⁶⁴ Cu was diffused into a wafer by heat treatment at 900 ° C. was pre-treated with hydrofluoric acid.
Using the apparatus of Example 1, cleaning was performed in the same manner as in Example 1 except for the following processing. The wafer carrier was first immersed in a sulfuric acid solution at the lower end of the wafer, and after confirming that the entire surface of the wafer was wet in about one minute, the carrier was lifted to the position shown in FIG. 3 and left for 15 minutes. The radioactivity of the wafer after cleaning was 0.9% before cleaning, and it was found that even such a thin high-temperature sulfuric acid liquid film could suck and clean Cu inside the wafer similarly to high-temperature sulfuric acid immersion cleaning. However, in the sample in which the natural oxide film was not removed in advance by the hydrofluoric acid treatment, the ⁶⁴ C
u residual rate reached 27%.

[0046]

According to the sulfuric acid mist cleaning of the present invention, the sulfuric acid mist atmosphere is pure sulfuric acid vapor. Since the sulfuric acid density is higher than the atmosphere and the sulfuric acid fog is generated by the exothermic reaction between sulfuric acid and water, the substrate wafer can be kept at a high temperature, and the cleaning effect is significantly enhanced. The greatest feature of the present invention is that the sulfuric acid arriving at the wafer surface from the sulfuric acid mist spreads uniformly over the entire surface by utilizing the fact that high-temperature sulfuric acid wets the silicon surface very well.
Sliding down the wafer surface smoothly. Therefore, the property of high-temperature sulfuric acid to decompose organic substances well and the property of well dissolving metals such as Cu and Fe are enhanced by the present invention, and the carbon concentration level and metal element concentration level of the silicon wafer surface in 2009 It can be cleaned to satisfy the estimated tolerance.

The above effect is so strong that even though the sulfuric acid solution film is extremely thin, an element which diffuses rapidly in silicon such as Cu is sucked out from the inside of the wafer and cleaned. The sulfuric acid mist cleaning of the present invention is advantageous in terms of safety management because the amount of sulfuric acid used is much smaller than that of the immersion type sulfuric acid cleaning. Naturally, it is economically excellent, and the concentration of waste liquid sulfuric acid is high, so that purification and recovery by distillation can be easily performed.

[0048]

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of one embodiment of the device of the present invention.

FIG. 2 is a longitudinal sectional view of another embodiment of the device of the present invention.

FIG. 3 is a view for explaining an embodiment of the cleaning method and apparatus of the present invention.

 ──────────────────────────────────────────────────続 き Continuing from the front page (71) Applicant 000221122 Toshiba Ceramics Co., Ltd. 7-25-25 Nishi-Shinjuku, Shinjuku-ku, Tokyo (72) Inventor Hisashi Muraoka 735 Nippacho, Kohoku-ku, Yokohama-shi, Kanagawa Pref. Inside Rex (72) Inventor Kaji Ota 2-98-9 Okada, Atsugi-shi, Kanagawa Nomura Micro-Science Co., Ltd. (72) Inventor Hiroshi Tomita 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Toshiba Yokohama Business Co., Ltd. In-house (72) Inventor Ryuji Takeda 6-865-15 Higashiko, Seiro-cho, Kitakanbara-gun, Niigata Pref. Niigata Toshiba Ceramics Co., Ltd.

Claims (12)

[Claims] 1. A method for cleaning a semiconductor substrate, comprising: maintaining a semiconductor substrate in an atmosphere containing high-temperature atomized sulfuric acid, and keeping a substrate surface wet with sulfuric acid. 2. An atmosphere containing said atomized sulfuric acid at a temperature of 20.
The method for cleaning a semiconductor substrate according to claim 1, wherein the temperature is 0 ° C. or higher. 3. The method for cleaning a semiconductor substrate according to claim 1, wherein at least the surface of the semiconductor substrate is made of silicon, and a natural oxide film on the silicon surface is removed in advance by a hydrofluoric acid treatment. 4. The method according to claim 1, further comprising, after the step of holding the semiconductor substrate in an atmosphere containing atomized sulfuric acid, removing all or part of the chemical oxide film formed on the silicon surface by the hydrofluoric acid treatment. The method for cleaning a semiconductor substrate according to any one of 1-3. 5. The semiconductor substrate according to claim 1, further comprising a step of wetting a part of the substrate with liquid sulfuric acid before the step of holding the semiconductor substrate in an atmosphere containing atomized sulfuric acid. Cleaning method. 6. A cleaning tank for bringing a semiconductor substrate into contact with high-temperature atomized sulfuric acid, carrier means for holding a substrate to be cleaned in an atmosphere containing atomized sulfuric acid in the cleaning tank, and a space in the cleaning tank. Means for forming an atmosphere containing atomized sulfuric acid. 7. The means for forming an atmosphere containing mist of sulfuric acid comprises a bottom of a washing tank containing liquid sulfuric acid and a means for heating the bottom, wherein the heating means heats the liquid sulfuric acid to clean the washing. The cleaning device according to claim 6, wherein an atmosphere containing atomized sulfuric acid is formed in the tank. 8. An impinger-like container having a heating means for atomizing liquid sulfuric acid, wherein the means for forming the atomized sulfuric acid-containing atmosphere includes an atomized sulfuric acid atmosphere formed in the container. The cleaning device according to claim 6, further comprising: an introduction pipe that is introduced into the cleaning tank. 9. The cleaning device according to claim 1, wherein the carrier unit includes a holding unit for holding the substrate to be cleaned and a support shaft capable of moving the holding unit up and down. 7. A space that can be freely moved by a space having a space in which the holding means can be stored.
The cleaning device according to any one of -8. 10. The cleaning apparatus according to claim 6, further comprising an impinger-like container for creating a hydrofluoric acid-containing atmosphere, and an introduction pipe for introducing the atmosphere into the lid. 11. The apparatus according to claim 6, further comprising a sulfuric acid collector filled with quartz wool, and evacuating the atmosphere in the cleaning tank and the lid via the collector. Cleaning equipment. 12. The cleaning tank has an opening that opens upward; the lid has an opening that opens downward, and the opening of the lid is connected to the opening of the cleaning tank. On the other hand, when the semiconductor substrate is washed, the opening of the cleaning tank and the opening of the bell-shaped lid are in close contact with each other to form a space inside the semiconductor substrate. An atmosphere containing atomized sulfuric acid is formed in the space, the carrier means holds the substrate to be cleaned above the liquid sulfuric acid in the cleaning tank, and keeps the substrate surface wet with sulfuric acid; and At the time of collecting the substrate, the carrier means moves upward while holding the washed substrate and is housed in the lid, and then the lid slides along with the carrier means in the lateral direction, and the cleaned substrate is moved to the next. Provided for processing process Cleaning apparatus according to any one of claims 6-11 to.