JP2002367950A - Isopropyl alcohol vapor dryer and method for drying silicon wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an isopropyl alcohol(IPA) vapor dryer in which generation of watermarks is reduced furthermore. SOLUTION: The IPA vapor dryer 200 of silicon wafer 11 comprises an IPA tank 9 for containing liquid IPA, a sidewall 15 provided around the IPA tank 9, a cooling pipe 7 provided in the vicinity of the sidewall 15 at a specified interval upward from the IPA tank 9, a heating means 8 disposed at least under the IPA tank 9, an IPA supply means including a preliminary heating means 17 for supplying preliminarily heated liquid IPA to the liquid IPA in the IPA tank 9, a carrying means (elevator) 12 for carrying a silicon wafer 11 into/from a space defined by the liquid level of IPA in the IPA tank 9, the sidewall 15 and the cooling pipe 7, and means (drain pipe) 5 for collecting mixture of IPA and water on the silicon wafer 11 and discharging to the outside of the space.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an isopropyl alcohol (IPA) vapor drying apparatus used for drying a cleaned silicon wafer in a semiconductor manufacturing process, and a method for drying a silicon wafer using IPA vapor.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, a wafer drying process is performed at the end of a wet cleaning process of a wafer, and is performed for the purpose of completely removing water on a wafer surface. That is, water droplets having a diameter of from micron to sub-micron or less remaining on the wafer promote natural oxidation of the wafer and cause a defective portion called a so-called watermark. It is known that a chip obtained from a portion including a watermark becomes a defective semiconductor element with a high probability of about 80%, depending on the structure of the element to be manufactured.
Further, even if the wafer surface is cleaned with various cleaning solutions, if the impurities are reattached in this drying step, the cleaning steps performed before that are wasted. Therefore, in the semiconductor manufacturing process, the drying process is very important as in the wet cleaning process which is the preceding process.

Conventionally, a spin drying method has been widely used as a general method for drying a wafer because it can be performed relatively easily. However, this method involves problems such as re-contamination of the wafer due to dust generation and generation of static electricity, destruction of elements (dielectric breakdown), and a problem in which the diameter of the wafer is from micron to sub-micron or less. There is a problem that it is difficult to remove water droplets. For this reason, at present, drying of a wafer is mainly performed by an isopropyl alcohol (IPA) vapor drying method described below.

In the IPA vapor drying method, an IPA vapor drying apparatus 100 as shown in FIG. 1 is generally used. The apparatus 100 is roughly composed of a tank-shaped structure having a wafer holding space in the center of the inside capable of accommodating a plurality of wafers, and a drying space around the holding space filled with IPA vapor. An IPA tank 9 for supplying IPA vapor and a heater 8 for heating IPA provided at least under the IPA tank 9 are provided at a lower portion of the apparatus 100. The side wall 15 of the apparatus 100 is provided with a plurality of cooling water pipes 7 for stopping the rise of the IPA vapor in the drying space and filling the drying space with the IPA vapor. Immediately below the wafer holding space, a drain receiver 13 and a drain 5 extending from the drain receiver 13 to the outside of the apparatus are provided.

[0005] The wafer holding space in the center of the apparatus 100 has I
From the PA tank toward the upper part of the apparatus, it is roughly divided into three sections: a lower standby position 2, an intermediate standby position 3, and an upper standby position 4.
The lower standby position 2 is a space from the IPA tank to the cooling water pipe 7, which is filled with IPA vapor, and is a space in which the wafer is replaced by IPA vapor (that is, water is removed). The intermediate standby position 3 is a space from the cooling water pipe 7 to the top of the device and is a space in the device, but is not filled with the IPA vapor. At this position, the wafer is left or heated and IP
IPA remaining on the wafer after A drying is evaporated. The upper standby position 4 is a space outside the apparatus, and in this space,
The wafer is carried between the previous step and the next step. An elevator 12 is installed in the wafer holding space, and the wafer moves on the elevator 12 in these three spaces.

[0006] The IPA vapor drying method will be described as follows with reference to FIG. That is, the IPA steam drying apparatus 100
The IPA tank 9 provided at the lower part of is heated by the heater 8,
The IPA vapor is filled in the device 100 (where IPA
Since the boiling point of IPA is 82.4 ° C.,
Not heated above ℃). The wafer 11 that has gone through the cleaning process and the like is placed on the elevator 12 at the upper standby position 4,
The wafer is lowered to the lower standby position 2 in the apparatus. IPA
The vapor condenses on the wafer surface and mixes with the moisture on the wafer. The mixture of IPA and water on the wafer thus generated falls from the surface of the wafer onto the drain receiver 13 by its own weight, and is discharged out of the apparatus through the drain 5. The wafer from which the water has been removed in this manner is pulled up to the intermediate standby position 3 where the IPA remaining on the wafer is evaporated by standing, infrared heating, hot air blowing, or the like.

As described above, since the IPA vapor drying method is drying in IPA vapor, it is less likely to cause contamination from the atmosphere and less likely to generate static electricity than the spin drying method.
Since water droplets from micron to submicron can be removed, there is an advantage that generation of watermark is relatively small.

[0008]

However, in the IPA vapor drying method, if the amount of water in the IPA is controlled and the heating system of the IPA, the flow rate of the liquid IPA, and the IPA vapor density are not optimized, the water on the wafer may be reduced. However, there remains a problem that it cannot be sufficiently and reproducibly removed. This problem becomes particularly remarkable as the diameter of the wafer increases to 200 mm or more. That is, when the diameter of the wafer is increased, a temperature gradient occurs in the wafer surface, so that it is difficult to perform a uniform drying process, and a product of the same quality cannot be obtained within one wafer or between wafers.

In order to prevent the occurrence of watermarks sufficiently and with good reproducibility, it is necessary to further increase the rate at which moisture on the wafer surface is replaced with IPA liquefied on the wafer. That is, the processing time of the IPA vapor drying is limited, and it is necessary that the wafer be efficiently contacted with as much IPA vapor as possible within the limited time. Conversely, if the rate of replacement of water with IPA is temporarily reduced for some reason, the removal of water will not be sufficient and a watermark will be generated. This replacement speed largely depends on the amount and concentration of IPA vapor generated. The amount and concentration of the IPA vapor are greatly affected by a change in the temperature of the IPA tank 9. Therefore, in order to keep the replacement rate high and constant, it is necessary to keep the temperature of the IPA tank constant (keep the boiling point at 82.4 ° C. and keep the boiling state) and keep the amount of generated IPA vapor constant.

The above-described conventional IPA steam drying apparatus 100
In order to make up for the IPA evaporated through the drain 5 or at the intermediate standby position 3 and discharged out of the apparatus, the replenishing I
IPA is supplied from the PA supply line 6 at any time. Since the temperature of the IPA replenished at this time is close to room temperature (around 20 ° C.), the IPA in the IPA tank is
The temperature of A decreases every time IPA is supplied.

That is, when the wafer to be dried arrives at the lower standby position, the IPA vapor comes into contact with the wafer, rapidly liquefies, and is discharged from the drain 5. At this time, to compensate for the rapid liquefaction of the IPA vapor, the heater is rapidly heated to
Although the supply amount of the vapor can be increased, the density of the IPA vapor suddenly decreases and rapidly increases from the start of drying the wafer to the increase in the supply amount of the IPA vapor.

Further, in order to keep the amount of liquid in the IPA tank constant, it is necessary to supply IPA each time the wafer is dried. According to the investigation by the present inventors, IPA at room temperature was used in order to compensate for the amount of IPA sharply reduced by the condensation of IPA.
Is supplied, it takes about 2 to 3 minutes for the temperature of the IPA to return to its boiling point temperature. Usually, the moisture is I
The processing time (time for holding the wafer at the lower standby position) set for replacing with PA is about 4 minutes.
The time required for restoring the temperature of the PA for a few minutes is almost equal to the above processing time, and significantly reduces the drying efficiency of the wafer. Therefore, in order to sufficiently reduce the watermark, a processing time exceeding 8 minutes may be required.

Further, in the conventional IPA drying apparatus 100,
Since the IPA liquefied by the cooling water pipe 7 is also collected in the IPA tank 9 through the liquid receiver 14,
The IPA collected in this manner also causes a decrease in the temperature of the IPA tank. That is, even if the heating temperature of the heater 8 is increased to increase the density of the IPA vapor, the cooling water pipe 7
The temperature of the liquid IPA temporarily increases and decreases the IPA vapor density without sufficiently reflecting the rise in the temperature of the heater 8 because the amount of the IPA that is cooled by the liquid and recovered in the IPA tank 9 through the liquid receiver 14 also increases. Happens.

Accordingly, an object of the present invention is to provide a drying process after cleaning (particularly, pre-furnace cleaning performed before a furnace process for forming an oxide film and a nitride film), in which a wafer having a diameter of micron to sub-micron or less is formed. An object of the present invention is to remove water droplets efficiently and with good reproducibility to prevent formation of a watermark on a wafer.

[0015]

According to the present invention, (1)
I containing liquid isopropyl alcohol (IPA)
A PA tank, (2) a side wall provided around the IPA tank,
(3) a cooling pipe provided at a predetermined interval above the IPA tank and near the side wall; (4) a heating means provided at least at a lower portion of the IPA tank; (5) a cooling pipe provided in the IPA tank. IPA supply means including preheating means for supplying the liquid IPA with preheated liquid IPA;
A conveying means for taking a silicon wafer into and out of the space defined by the liquid level of the IPA in the PA tank, the side wall and the cooling pipe, and (7) collecting a mixture of IPA and water on the silicon wafer to collect the space. There is provided an apparatus for IPA vapor drying of a silicon wafer, comprising a discharge means for discharging to the outside.

In the above IPA steam drying apparatus, 1. The preheating means comprises an in-line heater and a heating tank (particularly, a heater including a quartz tank containing IPA and a heater disposed at least under the quartz tank); 2. the discharge means includes a drain receiver and a drain extending from the drain receiver to the outside of the space; 3. A liquid receiver and an IPA recovery pipe extending from the liquid receiver toward the preheating means are provided immediately below the cooling pipe; It is preferable that the IPA supply means further includes a supply port provided near or in contact with the liquid IPA in the IPA tank.

According to the present invention, there are also provided (1) a liquid surface of liquid IPA contained in an isopropyl alcohol (IPA) tank, (2) a side wall provided around the IPA tank, and (3) the IPA. A step of heating the liquid IPA to fill the space defined by the cooling pipe provided at a predetermined interval above the side wall and near the side wall from the tank, and filling the space with the IPA vapor; Mixing the water and IPA on the surface of the silicon wafer while holding the silicon wafer on the surface of the silicon wafer, discharging the mixture of the water and the IPA out of the space to replace the water on the silicon wafer with IPA, Moving the silicon wafer replaced with IPA out of the space, evaporating the IPA from the silicon wafer, discharging the mixture of water and IPA out of the space and out of the space; I from the definitive silicon wafer
A step of supplying IPA to the IPA tank in order to replenish the loss of IPA in the IPA tank due to the evaporation of PA, wherein the IPA supplying step comprises the steps of: There is provided a method for drying a silicon wafer, wherein the method is supplied to a tank.

In the above drying method: 1. The method further includes a step of collecting the IPA liquefied by the cooling pipe, reheating the IPA, and supplying the IPA to the IPA tank as the preheated liquid IPA. When the temperature of the preheated liquid IPA is 50 to 8
Preferably, it is 2.4 ° C.

In the present invention, the preheated liquid IPA
Is replenished to the IPA tank in the apparatus. That is, the replenishing liquid IPA is preliminarily heated by the pre-heating unit, and the temperature difference between the replenished IPA and the IPA bath is reduced, thereby preventing the temperature of the IPA bath from being lowered by the replenishment of the IPA. . As a result, even if IPA is replenished during the drying process, it is possible to suppress a decrease in the generation amount and concentration of IPA vapor. Therefore, always constant IP
Since the drying process can be performed in the atmosphere of the vapor A, the moisture on the wafer can be efficiently removed in a limited processing time. Further, there is no need to wait for the recovery of the temperature of the IPA bath, and the drying efficiency is improved.

See the examples below. Example 1
Means that only preheated liquid IPA (75 ° C) is IPA
This is an example in which the wafer is dried using the IPA vapor drying apparatus of the present invention shown in FIG. 2 configured to be supplied to the tank. According to this example, the temperature of the IPA bath hardly changes during the drying time of the wafer (see FIG. 6), and stable steam supply is possible. It is clear that the number is very low, ie, pieces / wafer. In contrast, Comparative Example 1 uses a conventional IPA vapor drying apparatus shown in FIG. 1 in which only liquid IPA (20 ° C.) that is not preheated is supplied to the IPA tank, and the wafer is dried. This is an example of drying. According to this example, it is clear that the temperature of the IPA bath is significantly reduced by the replenishment of the IPA during the drying time of the wafer (see FIG. 7), and the supply of the IPA vapor is not stable. Therefore, in Comparative Example 1, the watermark generation rate after drying is as high as 20 pieces / wafer. Here, the reason why the generation of the watermark is concentrated on the upper part of the wafer is that the time until the upper part of the wafer comes into contact with the IPA vapor after cleaning is the longest,
This is because a water mark may be formed by air drying before contact with the A vapor.

As described above, according to the present invention, the generation of the watermark can be significantly reduced by supplying the IPA heated from the preheating unit. In the present invention, since the preheated liquid IPA is supplied, the IPA supply port extending from the IPA supply means is provided with the IA supply port.
It is preferable to be provided near or in contact with the liquid IPA in the PA tank.

If the IPA supply port is provided away from the liquid IPA, the liquid level of the IPA bath tends to be wavy due to the falling IPA during the supply of the IPA, which tends to make the supply of the IPA vapor unstable. In this case, the supply port is preferably close to the IPA liquid surface at an interval equal to or less than the size (for example, diameter) of the supply port.

The IPA supply port is preferably provided in liquid IPA in order to stably maintain the IPA liquid level. In this case, a pipe extending from the preheating means for supplying IPA from the upper part of the IPA bath is connected with liquid IP.
A or a supply port may be provided in the bottom or side wall of the IPA bath.

A pipe extending from the preheating means is connected to a liquid IP.
When introducing into A, it is more preferable that the supply port is provided near the bottom wall in order to stabilize the liquid level. In particular, if the supplied IPA is caused to flow along the heater on the bottom wall, not only the disturbance of the liquid surface but also the temperature decrease of the liquid surface can be sufficiently prevented.

When a supply port is provided on the bottom wall or side wall of the IPA bath, a valve is provided on the supply line or on a supply line between the supply port and the preheating section in order to prevent the IPA from flowing backward during non-supply. Preferably, it is provided.

[0026]

FIG. 2 is a schematic view showing an example of an IPA steam drying apparatus 200 of the present invention provided with an IPA preheating section. Unlike the conventional IPA vapor drying apparatus shown in FIG. 1, a preheating unit 17 is provided outside the apparatus 200 and between the IPA tank 9 and the replenishment IPA supply line 6. By providing such a pre-heating unit, the pre-heated IPA (liquid) is transferred to the IP in the apparatus.
A tank 9 can be refilled. Further, since the supply port 19 at the end of the IPA supply line is located in the IPA bath, the IPA liquid level is hardly disturbed by the supply of IPA.

In the preliminary heating section 17, a heating tank (FIG. 3) or an in-line heater (FIG. 4) can be used as a means for heating the IPA. In order to supply the heated IPA each time the drying of the wafer is completed (for each batch), it is preferable to use a heating tank configuration. In order to continuously supply the heated IPA, it is preferable to use an in-line heater.

The temperature of the IPA is set to 5 by the preheating unit 17.
Although it is possible to heat from 0 ° C. to 82.4 ° C., it is optimal to set the temperature from 70 ° C. to 80 ° C. This minimizes the temperature drop during replenishment, ensures the safety of the IPA supply line, and reduces the IPA loss due to evaporation and minimizes consumption when preheating IPA in an open system. It is.

In the present invention, as shown in FIG. 2, the IPA returned to the liquid in the cooling water pipe 7 may be collected by the liquid receiver 14 and returned to the preheating unit 17 through the IPA recovery line 18. it can. With this configuration, the IPA returned to the liquid in the cooling water pipe 7 is
It is possible to prevent the temperature of the IPA tank from dropping due to falling into the tank A.

Quartz or electrolytically polished stainless steel can be used for the steam drying tank 16 filled with IPA vapor. The cooling water pipe 7 is usually made of quartz, and usually uses city water or pure water as a cooling medium.

Further, in order to reduce the evaporation loss of IPA, an IPA vapor recovery device may be provided in the intermediate standby position 3, or an automatic opening / closing lid may be attached above the intermediate standby position 3.

The waste liquid receiver 13 is usually made of SUS (stainless steel) or quartz. Wafer IPA
For steam drying, it usually takes 8 to 10 minutes, more preferably 6 to 8 minutes. According to the present invention, it is possible to supply a uniform IPA vapor. For example, in the conventional apparatus, the drying time (for example, the time during which the wafer is left at the lower standby position in FIG. 1) is reduced to 8 minutes or less. Even if it is difficult to do so, it is possible to reduce the time to 6 minutes or less, particularly to about 4 minutes by using the apparatus of the present invention.

[0033]

The present invention will be further described with reference to the following examples, but the present invention is not limited to these examples.

Example 1 The wafer after the RCA cleaning step was dried using the IPA vapor drying apparatus shown in FIG. 2 having the heating tank shown in FIG. 3 as a preheating unit. In addition,
In FIG. 2, the shape of the supply port 19 was a circle having a diameter of 10 mm, and was located in the IPA bath.

The temperature of the IPA supplied from the preheating section is 75 ° C., and one supply is performed at 200 mL / min. For 30 seconds. Fifty 6-inch silicon wafers were lined up on a carrier with the wafer surface vertical, transported at one time by the elevator 12, and dried. The silicon wafer was left at the lower standby position for 4 minutes, and the wafer was brought into contact with the IPA vapor. Thereafter, the elevator 12 is raised, and the wafer is left at the intermediate standby position for 4 minutes, and the IPA on the wafer is
Was evaporated.

As a result, the number of watermarks on the wafer was 3 / wafer (see FIG. 5B). FIG. 6 shows the temperature change of the IPA tank during the drying time. In FIG. 6, the time when the wafer is started to be loaded into the apparatus is set to 0 minute, and the idle time at the lower standby position: 4 minutes, the idle time at the intermediate standby position: 4 minutes, and the vertical movement time within the apparatus: 30 seconds. After a total of 8 minutes and 30 seconds, the wafer was carried out of the apparatus.

Comparative Example 1 The wafer after the RCA cleaning step was dried using the conventional IPA vapor drying apparatus shown in FIG. 1 having no preheating unit.

I supplied from the replenishment IPA supply line
The temperature of PA is 20 ° C.
/ Min. For 30 seconds. The number and size of the silicon wafers to be dried were the same as in Example 1.
The drying time at the lower standby position and the leaving time at the intermediate standby position were the same as in Example 1.

As a result, the number of watermarks on the wafer was 20 / wafer (see FIG. 5A). FIG. 7 shows the temperature change of the IPA tank during the drying time. In addition,
In FIG. 7, the time when the wafer is started to be loaded into the apparatus is set to 0 minute, and the idle time at the lower standby position: 4 minutes, the idle time at the intermediate standby position: 4 minutes, the vertical movement time within the apparatus: 30 seconds, After a total of 8 minutes and 30 seconds, the wafer was carried out of the apparatus.

[0040]

According to the present invention, the replenishing IPA is preliminarily heated by the preheating section, and the replenished IPA is heated.
By reducing the temperature difference between the temperature of the IPA bath and the temperature of the IPA bath, it is possible to suppress a decrease in the generation amount and concentration of IPA vapor even when IPA is replenished during the drying process. Therefore, it is possible to perform the drying process while the IPA bath is always in a constant state, so that the water on the wafer is sufficiently removed, and a water mark is not easily generated. Further, since there is no need to wait for the temperature of the IPA bath to recover when replenishing the IPA, the efficiency of the wafer drying process is improved.

According to the present invention, the apparatus and method of the present invention can be applied to a large-scale production line because the apparatus is based on an improvement of a relatively easy apparatus in which a preheating section is attached to a part of an IPA supply line. It can be easily incorporated,
In addition, the effect is enormous and extremely practical.

[Brief description of the drawings]

FIG. 1 is a schematic view of a conventional IPA steam drying apparatus.

FIG. 2 shows an IP of the present invention equipped with an IPA preheating unit.
It is the schematic which shows an example of A steam drying apparatus.

3 is a diagram showing an example of a heating tank that can be used as a heating means for IPA in a preliminary heating section 17 in FIG.

FIG. 4 is a diagram showing an example of an in-line heater that can be used as a heating unit for IPA in a preliminary heating unit 17 of FIG.

FIG. 5 is a diagram showing a watermark generation site on a wafer. (A) shows a wafer after drying by the conventional IPA vapor drying apparatus of FIG. 1, and (b) shows a wafer after drying by the IPA vapor drying apparatus of the present invention of FIG. 2. A portion surrounded by an ellipse in the drawing is a watermark generation site.

FIG. 6 is a graph showing a time change of the temperature of the IPA bath in Example 1.

FIG. 7 is a graph showing the time change of the temperature of the IPA bath in Comparative Example 1.

Continued on the front page (72) Inventor Hideaki Seto 10 Kitahara, Tsukuba-shi, Ibaraki RSII Logic Japan Semiconductor Inside

Claims (10)

[Claims] (1) Liquid isopropyl alcohol (I)
(2) a side wall provided around the IPA tank, (3) a cooling pipe provided at a predetermined distance above the IPA tank and near the side wall, (4) ) A heating means provided at least at a lower part of the IPA tank; (5) an IPA supply means including a preheating means for supplying a preheated liquid IPA to the liquid IPA in the IPA tank; Conveying means for taking in and out the silicon wafer into and out of the space defined by the liquid level of the IPA in the IPA tank, the side walls and the cooling pipe; and (7) a space for collecting a mixture of IPA and moisture on the silicon wafer. An IPA vapor drying device for a silicon wafer, comprising: a discharge means for discharging to the outside. 2. The IPA steam drying apparatus according to claim 1, wherein said preheating means is an in-line heater. 3. The IPA steam drying apparatus according to claim 1, wherein said preheating means is a heating tank. 4. The IPA steam drying apparatus according to claim 3, wherein the heating tank includes a quartz tank containing IPA and a heater disposed at least below the quartz tank. 5. The IPA vapor drying apparatus according to claim 1, wherein said discharging means includes a drain receiver and a drain extending from said drain receiver to said outside of said space. 6. The IPA vapor drying apparatus according to claim 1, wherein a liquid receiver and an IPA recovery pipe extending from the liquid receiver toward the preheating means are provided immediately below the cooling pipe. 7. The IPA vapor drying apparatus according to claim 1, wherein the IPA supply means further includes a supply port provided near or in contact with the liquid IPA in the IPA tank. (1) Isopropyl alcohol (IP)
A) the level of the liquid IPA contained in the tank, (2) the IP
The liquid IPA is heated in a space defined by a side wall provided around the A-tank and (3) a cooling pipe provided at a predetermined interval above the IPA tank and near the side wall. Filling the IPA vapor with IPA vapor, holding the silicon wafer in the IPA vapor-filled space, and mixing the water and IPA on the surface of the silicon wafer, and discharging the mixture of water and IPA out of the space. Replacing the water on the silicon wafer with IPA, moving the silicon wafer having the water replaced with IPA out of the space, and evaporating IPA from the silicon wafer, and removing the mixture of water and IPA. Discharge outside the space and IP from the silicon wafer outside the space
A step of supplying IPA to the IPA tank in order to replenish the loss of IPA in the IPA tank due to evaporation of A. The method of drying a silicon wafer, comprising: A method for drying a silicon wafer, comprising supplying the silicon wafer to a tank. 9. The method for drying a silicon wafer according to claim 8, further comprising a step of collecting the IPA liquefied by the cooling pipe, reheating the IPA, and supplying the IPA to the IPA tank as the preheated liquid IPA. . 10. The method for drying a silicon wafer according to claim 8, wherein the temperature of the preheated liquid IPA is 50 to 82.4 ° C.