JP3337895B2 - Semiconductor substrate cleaning method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for cleaning a semiconductor substrate.

[0002]

2. Description of the Related Art As is well known, a semiconductor substrate on which a semiconductor device is to be formed is processed by cutting a silicon single crystal into a predetermined thickness and subjecting it to mirror polishing or the like, and then cleaning including the substrate surface on which the semiconductor device is to be formed. . Conventionally, the semiconductor substrate is cleaned by purifying pure water after treating the semiconductor substrate with sulfuric acid and hydrogen peroxide with a mixed chemical solution of sulfuric acid and hydrogen peroxide in the order of arrows as in the first conventional example shown in FIG. A method in which each step is carried out so as to be washed and dried in an overflowing washing container, or in the direction of the arrow as in the second conventional example shown in FIG.
After the semiconductor substrate is treated with sulfuric acid and hydrogen peroxide with a mixed chemical solution of sulfuric acid and hydrogen peroxide, the semiconductor substrate is placed in pure water stored in a cleaning container, washed by irradiating ultrasonic waves, and then dried. A method of performing each step to perform the method, a method of performing a buffered hydrofluoric acid treatment using hydrofluoric acid on a semiconductor substrate, and then cleaning the semiconductor substrate by placing the semiconductor substrate in a cleaning container in which pure water overflows have been performed.

However, in the above-mentioned prior art,
Sulfur component, such as there is a possibility that remaining ^- after the sulfuric acid hydrogen peroxide treatment, SO ₄ on a semiconductor substrate be irradiated with ultrasonic waves while washing or rinsing. For this reason, when the semiconductor substrate after cleaning is left in the air, the remaining sulfur components combine with water to form sulfides as impurities on the substrate surface, causing an increase in dust. I was Further, when a film for forming a semiconductor device is formed on the substrate surface after the generation of impurities, a thin and flat film cannot be grown.

Further, sulfuric acid hydrogen peroxide treatment is carried out at 70 ° C. to 1 ° C.
Since the process is performed at a high temperature of 70 ° C., the temperature of the semiconductor substrate rapidly rises from room temperature. In a semiconductor substrate in which the hydrophobic Si surface is exposed due to the rapid temperature rise, dust easily adheres to the substrate surface.

In the case of irradiating ultrasonic waves while rinsing with water or rinsing with water after the sulfuric acid-hydrogen peroxide treatment, mixing of sulfuric acid and hydrogen peroxide water by the flow rate of pure water at the time of rinsing and the ultrasonic irradiation method. Dust adsorbed in the liquid cannot be removed,
There is a possibility that it will remain on the substrate surface.

In addition, during the buffered hydrofluoric acid treatment, when a plurality of semiconductor substrates are arranged side by side so that the front and back sides of the adjacent semiconductor substrates face each other and the cleaning process is performed, the back surfaces of the adjacent semiconductor substrates are attracted to dust and become dirty. In such a case, dirt is transferred to the surface of the semiconductor substrate opposed thereto.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to keep a semiconductor substrate in air without leaving sulfur components or the like depending on a chemical solution used for cleaning. Sulfides are not generated even if left unattended, there is no danger of dust increase, and a thin flat film can be formed on the substrate surface, and the adsorption of dust to the substrate surface caused by a rapid temperature rise can be suppressed. Another object of the present invention is to provide a method for cleaning a semiconductor substrate, which can sufficiently remove dust adsorbed in a cleaning liquid or the like, and furthermore, does not cause a risk of transferring dirt to an adjacent substrate surface.

[0008]

According to the method of cleaning a semiconductor substrate of the present invention, a semiconductor substrate is immersed in buffered hydrofluoric acid and treated, followed by rinsing with pure water. After the rinsing, the semiconductor substrate is rinsed with ozone water. The method is characterized in that the semiconductor substrate is irradiated with ultrasonic waves while immersed in ozone water, and the concentration of ozone water is further reduced. Is 0.
Characterized in that the concentration is 1 ppm or more and 20 ppm or less, and a treatment with buffered hydrofluoric acid is further performed.
The semiconductor device is characterized in that a pretreatment is performed by immersing the semiconductor substrate in ozone water before.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

First, a first embodiment will be described with reference to FIGS. FIG. 1 is a diagram for explaining a cleaning process, and FIG. 2 is a graph showing a state of adhesion of dirt to a substrate surface when the substrate is left in the air after cleaning.

A semiconductor substrate for forming a semiconductor device is formed, for example, by grinding a single crystal ingot of silicon into an outer shape so as to have a predetermined diameter, dividing the block into pieces, performing orientation flat processing on the block, and cutting the block into a predetermined thickness with a cutting device. After removing the distortion at the time of cutting by lapping, performing edge processing, etching and the like, and then performing chemical mechanical mirror polishing, cleaning including the substrate surface on which the semiconductor device is formed is performed. The semiconductor substrate after being cleaned is immediately put into a manufacturing process of a semiconductor device after a predetermined inspection or the like, or is put after being stocked.

In the above process, cleaning of the semiconductor substrate is performed as follows. That is, in FIG. 1, a mixed chemical solution 2 of sulfuric acid and hydrogen peroxide having a temperature maintained at 70 ° C. to 170 ° C. was stored on the semiconductor substrate 1 subjected to mirror polishing in the first step A ₁ . It is immersed in the first cleaning tank 3 for 2 to 10 minutes, and subjected to sulfuric acid and hydrogen peroxide treatment.

Thereafter, the semiconductor substrate 1 which has been treated with sulfuric acid and hydrogen peroxide in the second step A ₂ is placed in a second cleaning tank 5 to which pure water 4 is supplied so as to overflow.
Washing is performed for a predetermined time in pure water 4 irradiated with ultrasonic waves of 6 MHz to 1.2 MHz.

The semiconductor substrate 1 which has been subjected to the pure water cleaning treatment in the subsequent third step A ₃ is supplied with ozone water 6 having a concentration of 2 ppm to 3 ppm at normal temperature to the third cleaning tank 7 for 4 minutes. Then, ozone water cleaning treatment is performed.

[0015] and further dried semiconductor substrate 1 which is ozone water washing treatment in the fourth step A _4, and terminates the washing.

[0016] Then among the step of cleaning the semiconductor substrate 1 to perform as described above, by cleaning with ozone water 6 in the third step A _3, the semiconductor in the first sulfuric acid hydrogen peroxide treatment step A ₁ attached to the substrate 1, the sulfur component after pure water cleaning process in the second step a ₂ also remains are removed becomes stable.

That is, H ₂ S + O ₃ → H ₂ O + SO ₂ 3H ₂ S + O ₃ → 3H ₂ O + 3S As a result, the semiconductor substrate 1 is left in the atmosphere, for example, after being cleaned and then stored until it is put into a semiconductor device manufacturing process. In addition, sulfide as an impurity is less likely to be generated on the substrate surface by binding of moisture in the atmosphere to the remaining sulfur component, and an increase in dust on the substrate surface is suppressed. Since no sulfide is generated, a thin flat film for manufacturing a semiconductor device can be formed on the substrate surface of the semiconductor substrate 1.

Regarding the suppression of the increase of dust on the substrate surface of the semiconductor substrate 1, the 6-inch semiconductor substrate 1 after performing the above-described cleaning steps in the present embodiment is used.
When the number of dusts on the substrate surface when left in the air for 5 days was counted, the number of days elapsed on the horizontal axis and the number of dusts on the vertical axis were as shown by a polygonal line X in FIG. The broken line Y in the figure indicates the number of dust on the substrate surface when the semiconductor substrate cleaned by the conventional cleaning method is similarly left in the air for 5 days.

According to FIG. 2, when left after the conventional cleaning method, the number of dust increases rapidly after one day, and thereafter increases as the number of days elapses. On the other hand, when left after the cleaning method of the present embodiment, the number of dusts after one day and after five days is almost the same as that immediately after the treatment, and the increase in dust on the substrate surface is greatly suppressed. Become.

Next, a second embodiment will be described with reference to FIG. FIG. 3 is a diagram for explaining the cleaning process.

[0021] In FIG. 3, it is cut into a predetermined thickness, cleaning the semiconductor substrate 1 which is mirror-polished, first, in a first step B _1, similarly to the first step A ₁ in the first embodiment The semiconductor substrate 1 is immersed in a first cleaning tank 3 in which a mixed chemical solution 2 of sulfuric acid and hydrogen peroxide solution is stored for 2 minutes to 10 minutes, and a sulfuric acid hydrogen peroxide treatment is performed.

Thereafter, in a second step B ₂ , the semiconductor substrate 1 which has been treated with sulfuric acid and hydrogen peroxide in the same manner as in the second step A ₂ in the first embodiment is supplied so that pure water 4 overflows. Into the second washing tank 5 and a frequency of 0.6 M
The substrate is cleaned for a predetermined time in pure water 4 irradiated with ultrasonic waves of Hz to 1.2 MHz.

The semiconductor substrate 1 which has been subjected to the pure water cleaning treatment in the subsequent third step B ₃ is supplied with ozone water 6 having a concentration of 2 ppm to 3 ppm at room temperature to the third cleaning tank 8 for 4 minutes. Then, while immersed in ozone water 6, ultrasonic waves having a frequency of 0.6 MHz to 1.2 MHz are irradiated to perform ozone water cleaning treatment.

Further, the semiconductor substrate 1 which has been subjected to the ozone water cleaning treatment in the fourth step B ₄ is dried, and the cleaning is completed.

[0025] The semiconductor substrate 1 as described above, the third immersed in ozone water 6 in Step B _3, by ozone water washing treatment to further ultrasonic irradiation, the first step B ₁ sulfuric acid hydrogen peroxide In the second step B
_The sulfur component remaining after the pure water cleaning treatment of ₂ becomes stable as in the first embodiment by the treatment with ozone water 6,
Furthermore during the first step B ₁ of sulfuric acid hydrogen peroxide treatment by irradiation with ultrasonic waves, dust adsorbed on the substrate surface in mixture 2 is also more securely removed. Since no sulfide is generated, a thin flat film for manufacturing a semiconductor device can be formed on the substrate surface of the semiconductor substrate 1.

Next, a third embodiment will be described with reference to FIG. FIG. 4 is a diagram for explaining the cleaning process.

[0027] In FIG. 4, is cut into a predetermined thickness, cleaning the semiconductor substrate 1 which is mirror-polished, first, a semiconductor substrate 1 which mirror polishing is applied in the first step C _1, concentration 2
1 to 3 ppm of normal temperature ozone water 9 in the first cleaning tank 1
Then, the substrate is immersed in water at 0 for a predetermined time to perform an ozone water pre-cleaning process.

Next, the semiconductor substrate 1 which ozone water pre-wash process is performed in the second step C _2, similarly to the first step A ₁ in the first embodiment, the mixing of sulfuric acid and hydrogen peroxide It is immersed in the second cleaning tank 11 in which the chemical solution 2 is stored for 2 to 10 minutes, and subjected to sulfuric acid and hydrogen peroxide treatment.

Thereafter, the semiconductor substrate 1 subjected to the sulfuric acid / hydrogen peroxide treatment in the third step C ₃ is put into a third cleaning tank 12 to which pure water 4 is supplied so as to overflow, and the frequency is set to 0.6 MHz to 1 MHz. Cleaning is performed in pure water 4 irradiated with 2 MHz ultrasonic wave for a predetermined time.

The semiconductor substrate 1 which has been subjected to the pure water cleaning treatment in the subsequent fourth step C ₄ is supplied with ozone water 6 having a concentration of 2 ppm to 3 ppm at room temperature to the fourth cleaning tank 13 for 4 minutes. Then, ozone water cleaning treatment is performed.

Furthermore ozone water cleaning process is drying the semiconductor substrate 1 which has been made in the fifth step C _5, and terminates the washing.

The semiconductor substrate 1 which has been mirror-polished as described above is first subjected to a pre-cleaning process with ozone water 9 and then cleaned in the same process as in the first embodiment. A natural oxide film (SiO ₂
A film) is formed and is protected by the natural oxide film, thereby suppressing the adsorption of dust. Further, since the same cleaning as in the first embodiment is performed, the same operation and effect as in the first embodiment can be obtained. Obtained more reliably.

In each of the above embodiments, the cleaning is carried out by using a mixed chemical solution 2 of sulfuric acid and hydrogen peroxide solution as a chemical solution, but instead of this, buffered hydrofluoric acid or ammonia is used as a chemical solution. Using a mixed chemical solution of hydrogen water or a mixed solution of hydrochloric acid and hydrogen peroxide solution, wash the chemical solution, irradiate ultrasonic waves in pure water and then wash with ozone water, or immerse in ozone water and irradiate ultrasonic waves The same effect can be obtained by performing an ozone water cleaning process. When buffered hydrofluoric acid is used as the chemical, the ozone water cleaning treatment makes it difficult for the dust to be adsorbed on the back surface of the semiconductor substrate, and prevents the dust from being transferred to the substrate surface of the opposing adjacent semiconductor substrate. If the ozone water treatment is performed before the cleaning, a natural oxide film is formed on the substrate surface as in the third embodiment, and a more reliable cleaning effect can be obtained.

Further, in each of the above embodiments, the cleaning treatment or the pre-cleaning treatment with ozone water having a concentration of 2 to 3 ppm is performed. The same effect as in each embodiment can be obtained. If the concentration of ozone water is lower than 0.1 ppm, the cleaning process takes a long time and is not practical. As the concentration becomes higher, the processing can be performed in a shorter time and the throughput is improved. However, when the concentration is higher than 20 ppm, the processing time becomes too short to obtain a uniform thickness, and the properties of the film are also reduced. Not good. The frequency of the ultrasonic wave applied in ozone water or pure water needs to be 0.5 MHz or more so that cleaning can be performed practically.

[0035]

As is apparent from the above description, the present invention is characterized in that a semiconductor substrate treated by immersion in a chemical solution is rinsed with pure water and further treated by immersion in ozone water, thereby reducing the surface of the substrate. It is possible to sufficiently remove the adsorbed dust and to suppress the adsorption of dust to the substrate surface after cleaning.

[Brief description of the drawings]

FIG. 1 is a view for explaining a cleaning process according to a first embodiment of the present invention.

FIG. 2 is a graph showing a situation in which dirt adheres to the substrate surface when the semiconductor substrate after cleaning according to the first embodiment of the present invention is left in the air.

FIG. 3 is a view for explaining a cleaning process according to a second embodiment of the present invention.

FIG. 4 is a view for explaining a cleaning process according to a third embodiment of the present invention.

FIG. 5 is a diagram for explaining a cleaning process of the first conventional example.

FIG. 6 is a diagram for explaining a cleaning process of a second conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate 2 ... Mixed chemical solution 4 ... Pure water 6, 9 ... Ozone water

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/304

Claims (4)

(57) [Claims] 1. A semiconductor substrate, wherein the semiconductor substrate is immersed in buffered hydrofluoric acid and treated, followed by rinsing with pure water, and after the rinsing, the semiconductor substrate is immersed in ozone water for a predetermined time to be treated. Semiconductor substrate cleaning method. 2. A supersonic wave on a semiconductor substrate while being immersed in ozone water.
2. The method for cleaning a semiconductor substrate according to claim 1, wherein a wave is irradiated . 3. The concentration of ozone water is 0.1 ppm or more.
2. The method for cleaning a semiconductor substrate according to claim 1, wherein the concentration is 0 ppm or less . 4. Prior to performing treatment with buffered hydrofluoric acid
The method for cleaning a semiconductor substrate according to claim 1, wherein the pretreatment is performed by immersing the semiconductor substrate in ozone water .