JP4906198B2 - Isopropyl alcohol vapor drying apparatus and silicon wafer drying method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an isopropyl alcohol (IPA) vapor drying apparatus and a method for drying a silicon wafer using IPA vapor used when drying a cleaned silicon wafer in a semiconductor manufacturing process.
[0002]
[Prior art]
In the semiconductor manufacturing process, the wafer drying process is performed at the end of the wafer wet cleaning process for the purpose of completely removing moisture on the wafer surface. That is, water droplets having a diameter of micron to sub-micron or less remaining on the wafer promotes the natural oxidation of the wafer and causes a so-called defect portion called a 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. Even if the wafer surface is cleaned with various cleaning solutions, if the impurities are deposited again in this drying process, the cleaning process performed before that is wasted. Therefore, in the semiconductor manufacturing process, the drying process is extremely important, as is the wet cleaning process that is the previous process.
[0003]
Conventionally, as a general method for drying a wafer, a spin drying method has been widely used because it can be performed relatively easily. However, this method has problems such as re-contamination of the wafer due to dust generation and generation of static electricity, destruction of elements (insulation breakdown), etc. There is a problem that it is difficult to remove water droplets. For this reason, at present, the wafer is mainly dried by the isopropyl alcohol (IPA) vapor drying method described below.
[0004]
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-like structure having a wafer holding space capable of accommodating a plurality of wafers in the center of the inside and a drying space for filling IPA vapor around the holding space. In the lower part of the apparatus 100, an IPA tank 9 for supplying IPA vapor and a heater 8 for heating IPA provided at least in the lower part are provided. The side wall 15 of the apparatus 100 is provided with a plurality of cooling water pipes 7 for stopping the IPA vapor from rising in the drying space and filling the drying space with the IPA vapor. A drain receiver 13 and a drain 5 extending from the drain receiver 13 to the outside of the apparatus are provided immediately below the wafer holding space.
[0005]
The wafer holding space in the center of the apparatus 100 is roughly divided into three sections, a lower standby position 2, an intermediate standby position 3, and an upper standby position 4, from the IPA tank toward the upper part of the apparatus. The lower standby position 2 is a space from the IPA tank to the cooling water pipe 7, and is a space where the IPA vapor is filled and the wafer is replaced by the IPA vapor (that is, moisture is removed). The intermediate standby position 3 is a space from the cooling water pipe 7 to the uppermost part of the apparatus and is a space in the apparatus, but is not filled with IPA vapor. At this position, the wafer is left or heated to evaporate the IPA remaining on the wafer after IPA drying. The upper standby position 4 is a space outside the apparatus, and the wafer is transported between the previous process and the next process in this space. An elevator 12 is installed in the wafer holding space, and the wafer moves on these three spaces on the elevator 12.
[0006]
This IPA vapor drying method will be described with reference to FIG. That is, the IPA tank 9 provided at the lower part of the IPA vapor drying apparatus 100 is heated by the heater 8 to fill the apparatus 100 with the IPA vapor (here, the boiling point of IPA is 92.4 ° C. in the IPA tank 9). And not heated above 82.5 ° C.). The wafer 11 that has undergone the cleaning process or the like is placed on the elevator 12 at the upper standby position 4 and lowered to the lower standby position 2 in the apparatus. The IPA vapor condenses on the wafer surface and mixes with moisture on the wafer. The resulting mixture of IPA and water on the wafer falls from the wafer surface onto the drainage receiver 13 due to its own weight, and is discharged out of the apparatus through the drain 5. The wafer from which moisture 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 being left as it is, by infrared heating, hot air blowing or the like.
[0007]
As described above, since the IPA vapor drying method is drying in IPA vapor, compared to the spin drying method, contamination from the atmosphere is less likely to occur, static electricity is less likely to be generated, and micron to submicron water droplets can be removed. Therefore, there are advantages such as relatively less occurrence of watermarks.
[0008]
[Problems to be solved by the invention]
However, in the IPA vapor drying method, moisture on the wafer cannot be removed sufficiently and reproducibly without controlling the amount of moisture in the IPA and optimizing the IPA heating system, the liquid IPA flow rate, and the IPA vapor density. The problem remains. This problem becomes particularly noticeable 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 is generated in the wafer surface, so that a uniform drying process becomes difficult, and a product of the same quality cannot be obtained within one wafer or between wafers.
[0009]
In order to sufficiently prevent the occurrence of the watermark with good reproducibility, it is necessary to further increase the speed at which the moisture on the wafer surface is replaced with IPA liquefied on the wafer. That is, the processing time of IPA vapor drying is limited, and it is necessary for the wafer to efficiently contact as much IPA vapor as possible within this limited time. Conversely, if the rate of replacement of moisture with IPA is temporarily reduced for some reason, the removal of moisture will not be sufficient and a watermark will be generated. This replacement rate greatly depends on the generation amount and concentration of IPA vapor. The generation amount and concentration of the IPA vapor are greatly influenced by the temperature change 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 82.4 ° C. and maintain the boiling state), and keep the amount of IPA vapor generated constant.
[0010]
In the conventional IPA vapor drying apparatus 100 described above, IPA is replenished as needed from the replenishment IPA supply line 6 in order to supplement the IPA evaporated through the drain 5 or at the intermediate standby position 3 and discharged outside the apparatus. It has become. Since the temperature of the IPA replenished at this time is a temperature close to room temperature (around 20 ° C.), the temperature of the IPA in the IPA tank decreases every time the IPA is supplied.
[0011]
That is, when the wafer to be dried arrives at the lower standby position, the IPA vapor comes into contact with the wafer and rapidly liquefies and is discharged from the drain 5. At this time, in order to compensate for the rapid liquefaction of the IPA vapor, it is possible to increase the supply amount of the IPA vapor by heating the heater rapidly. This results in a rapid decrease and increase in density.
[0012]
Further, in order to keep the liquid amount in the IPA tank constant, IPA must be supplied every time the wafer is dried. According to the investigations of the present inventors, when IPA at room temperature is supplied in order to compensate for the amount of IPA that has rapidly decreased due to condensation of IPA, it takes about 2 to 3 minutes for the temperature of IPA to return to its boiling temperature. Cost. Usually, the processing time (time for holding the wafer in the lower standby position) set to replace moisture with IPA is around 4 minutes, so it takes a few minutes to restore the IPA temperature. Is substantially 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.
[0013]
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 thus collected is also in the IPA tank. This is a cause of temperature drop. That is, even if the heating temperature of the heater 8 is increased to increase the density of the IPA vapor, the amount of IPA cooled by the cooling water pipe 7 and recovered in the IPA tank 9 through the liquid receiver 14 also increases. The IPA vapor density temporarily increases and decreases without sufficiently reflecting the temperature rise of the heater 8.
[0014]
Therefore, an object of the present invention is to efficiently apply water droplets having a diameter of micron to sub-micron or less on a wafer in a drying process after cleaning (in particular, pre-furnace cleaning prior to furnace processing for forming an oxide film and a nitride film). The purpose is to remove the watermark on the wafer with good and reproducibility.
[0015]
[Means for Solving the Problems]
According to the present invention,
(1) an IPA tank containing liquid isopropyl alcohol (IPA);
(2) Side walls provided around the IPA tank,
(3) a cooling pipe provided at a predetermined interval above the IPA tank and in the vicinity of the side wall;
(4) Heating means provided at least in the lower part of the IPA tank,
(5) IPA supply means including preheating means for supplying preheated liquid IPA to liquid IPA in the IPA tank,
(6) a transfer means for taking a silicon wafer into and out of a space defined by the IPA liquid level in the IPA tank, the side wall and the cooling pipe; and (7) a mixture of IPA and moisture on the silicon wafer. Discharging means for collecting and discharging out of the space;
An IPA vapor drying apparatus for silicon wafers is provided.
[0016]
In the above IPA vapor dryer,
1. The preheating means comprises an in-line heater and a heating tank (particularly, a quartz tank containing IPA and a heater disposed at least in the lower part thereof);
2. The drainage means includes a drain receiver and a drain extending out of the space from the drain receiver;
3. Immediately below the cooling pipe, a liquid receiver and an IPA recovery pipe extending from the liquid receiver toward the preheating means are provided;
4). The IPA supply means further includes a supply port provided close to or in contact with the liquid IPA in the IPA tank;
Is preferred.
[0017]
According to the invention,
(1) The level of the liquid IPA contained in the isopropyl alcohol (IPA) tank, (2) a side wall provided around the IPA tank, and (3) a predetermined interval upward from the IPA tank And a step of heating the liquid IPA to fill the IPA vapor in a space defined by a cooling pipe provided near the side wall,
Holding the silicon wafer in the space filled with IPA vapor and mixing the moisture on the silicon wafer surface with IPA;
Discharging the mixture of moisture and IPA out of the space and replacing the moisture on the silicon wafer with IPA;
Moving the silicon wafer whose moisture has been replaced by IPA out of the space and evaporating IPA from the silicon wafer; discharging the mixture of moisture and IPA out of the space; and from the silicon wafer outside the space Supplying IPA to the IPA tank to replenish the loss of IPA in the IPA tank due to evaporation of the IPA;
In a method for drying a silicon wafer containing
The method for drying a silicon wafer is characterized in that the IPA supplying step supplies preheated liquid IPA to the IPA tank.
[0018]
In the above drying method,
1. Collecting the IPA liquefied by the cooling pipe, reheating, and supplying the IPA tank as the preheated liquid IPA;
2. The temperature of the preheated liquid IPA is 50 to 82.4 ° C .;
Is preferred.
[0019]
In the present invention, it is a novel feature that the IPA tank in the apparatus is replenished with the preheated liquid IPA. That is, the replenishment liquid IPA is preheated by the preheating unit, and the temperature difference between the replenished IPA and the IPA bath can be reduced to prevent the temperature drop of the IPA bath due to the IPA replenishment. . 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, since it is possible to always perform the drying process in a constant IPA vapor atmosphere, it is possible to efficiently remove moisture on the wafer in a limited processing time. Further, there is no need to wait for the temperature recovery of the IPA bath, and the drying efficiency is improved.
[0020]
See the examples below. In Example 1, the wafer was dried using the IPA vapor drying apparatus of the present invention shown in FIG. 2 configured such that only the preheated liquid IPA (75 ° C.) was supplied to the IPA tank. This is an example. According to this example, the temperature of the IPA bath hardly changes during the drying time of the wafer (see FIG. 6), and stable vapor supply is possible. Therefore, the watermark generation rate after drying is 3 It becomes clear that the number of wafers / wafer is very low. In contrast, Comparative Example 1 uses a conventional IPA vapor drying apparatus shown in FIG. 1 that is configured so that only liquid IPA (20 ° C.) that is not preheated is supplied to the IPA tank. This is an example of drying. According to this example, it is clear that the temperature of the IPA bath is remarkably lowered by the replenishment of IPA during the wafer drying time (see FIG. 7), and the supply of IPA vapor is not stable. Therefore, in Comparative Example 1, the watermark generation rate after drying is as high as 20 / 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 is the longest. Because there are cases.
[0021]
Thus, according to the present invention, the generation of watermarks can be significantly reduced by supplying heated IPA from the preheating unit.
In the present invention, in order to supply the preheated liquid IPA, an IPA supply port extending from the IPA supply means is provided close to or in contact with the liquid IPA in the IPA tank. Is preferred.
[0022]
When the IPA supply port is provided away from the liquid IPA, the IPA bath liquid level undulates due to the falling IPA when the IPA is supplied, which tends to make the IPA vapor supply 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.
[0023]
The IPA supply port is preferably provided in the liquid IPA in order to maintain the IPA liquid level stably. In this case, a pipe extending from a preheating means for supplying IPA from the top of the IPA bath may be introduced into the liquid IPA, or a supply port may be provided on the bottom wall or side wall of the IPA bath.
[0024]
When the pipe extending from the preheating means is introduced into the liquid IPA, it is more preferable to provide the supply port so as to be positioned near the bottom wall in order to stabilize the liquid level. In particular, if the supplied IPA is made to flow along the heater on the bottom wall, not only the disturbance of the liquid level but also the temperature drop of the liquid level can be sufficiently prevented.
[0025]
When providing a supply port on the bottom wall or side wall of the IPA bath, a valve may be provided on the supply line between the supply port or the supply port and the preheating unit in order to prevent backflow of IPA when not supplied. preferable.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 2 is a schematic view showing an example of the IPA vapor drying apparatus 200 of the present invention provided with an IPA preheating unit. Unlike the conventional IPA vapor drying apparatus shown in FIG. 1, a preheating unit 17 is installed outside the apparatus 200 and between the IPA tank 9 and the replenishment IPA supply line 6. By providing such a preheating unit, it is possible to replenish the preheated IPA (liquid) to the IPA tank 9 in the apparatus. 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.
[0027]
In the preheating part 17, a heating tank (FIG. 3) and an in-line heater (FIG. 4) can be used as a heating means of IPA. In order to supply heated IPA every time the wafer is dried (each batch), it is preferable to use the form of a heating tank. Moreover, in order to supply heated IPA continuously, it is preferable to use the form of an in-line heater.
[0028]
The temperature of the IPA can be heated from 50 ° C. to 82.4 ° C. by the preheating unit 17, but it is optimal to set the temperature to 70 ° C. to 80 ° C. This minimizes the temperature drop at the time of replenishment, ensures the safety of the IPA supply line, and when preheating the IPA in an open system, IPA loss due to evaporation can be reduced and consumption can be minimized. It is.
[0029]
In the present invention, as shown in FIG. 2, the IPA returned to the liquid by 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. By comprising in this way, it becomes possible to prevent the temperature fall of the IPA tank by IPA returned to the liquid with the cooling water pipe 7 falling in an IPA tank.
[0030]
Quartz or electrolytically polished stainless steel can be used for the steam drying tank 16 filled with IPA steam.
The cooling water pipe 7 is usually made of quartz, and city water or pure water is usually used as a cooling medium.
[0031]
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 to the upper part of the intermediate standby position 3.
[0032]
The waste liquid receiver 13 is usually made of SUS (stainless steel) or quartz.
For IPA vapor drying of the wafer, it usually takes 8 to 10 minutes, more preferably 6 to 8 minutes. According to the present invention, since uniform IPA vapor can be supplied, for example, in the conventional apparatus, the drying time (for example, the time for leaving the wafer in the lower standby position in FIG. 1) is shortened to 8 minutes or less. Even if it is difficult to do so, it can be shortened to 6 minutes or less, particularly to about 4 minutes, by using the apparatus of the present invention.
[0033]
【Example】
The present invention will be further explained by the following examples, but the present invention is not limited to these examples.
[0034]
[Example 1]
The wafer after the RCA cleaning process was dried using the IPA vapor drying apparatus of FIG. 2 equipped with the heating tank shown in FIG. 3 as the preheating unit. 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.
[0035]
The temperature of IPA supplied from the preheating unit is 75 ° C., and one supply is 200 mL / min. For 30 seconds.
Fifty 6-inch silicon wafers were arranged on a carrier with the wafer surface vertical, and were conveyed by the elevator 12 at a time and dried. The silicon wafer was left for 4 minutes in the lower standby position, and the wafer was brought into contact with IPA vapor. Thereafter, the elevator 12 was raised and the wafer was left at the intermediate standby position for 4 minutes to evaporate the IPA on the wafer.
[0036]
As a result, the number of watermarks on the wafer was 3 / wafer (see FIG. 5B). The temperature change of the IPA tank during the drying time is shown in FIG. In FIG. 6, the time when the wafer starts to be loaded into the apparatus is defined as 0 minute, the waiting time at the lower standby position: 4 minutes, the waiting time at the intermediate standby position: 4 minutes, and the vertical movement time in the apparatus: 30 seconds. Then, after a total of 8 minutes and 30 seconds, the wafer was unloaded from the apparatus.
[0037]
[Comparative Example 1]
The wafer after the RCA cleaning process was dried using the conventional IPA vapor drying apparatus of FIG. 1 having no preheating unit.
[0038]
The temperature of IPA supplied from the IPA supply line for replenishment is 20 ° C., and one supply is 200 mL / min. For 30 seconds.
The number and size of silicon wafers to be dried were the same as in Example 1. Further, the drying time at the lower standby position and the standing time at the intermediate standby position were the same as in Example 1.
[0039]
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 FIG. 7, the time when the wafer starts to be loaded into the apparatus is defined as 0 minute, the waiting time at the lower standby position: 4 minutes, the waiting time at the intermediate standby position: 4 minutes, and the vertical movement time in the apparatus: 30 seconds. Then, after a total of 8 minutes and 30 seconds, the wafer was unloaded from the apparatus.
[0040]
【Effect of the invention】
According to the present invention, the replenishment IPA is preheated by the preheating unit, and the temperature difference between the replenished IPA and the temperature of the IPA bath is reduced, so that the IPA is replenished during the drying process. Even if it is done, it becomes possible to suppress the generation amount and concentration of the IPA vapor. Therefore, it is possible to perform the drying process with the IPA bath always in a constant state, so that water on the wafer is sufficiently removed and a water mark is hardly generated. Also, since it is not necessary to wait for the temperature recovery of the IPA bath at the time of IPA replenishment, the efficiency of the wafer drying process is improved.
[0041]
According to the present invention, the apparatus and method of the present invention can be easily incorporated even in a large-scale production line because it is based on a relatively easy apparatus improvement in which the preheating unit is attached to a part of the IPA supply line. Moreover, the effect is enormous and extremely practical.
[Brief description of the drawings]
FIG. 1 is a schematic view of a conventional IPA vapor drying apparatus.
FIG. 2 is a schematic view showing an example of an IPA vapor drying apparatus of the present invention equipped with an IPA preheating unit.
FIG. 3 is a diagram showing an example of a heating tank that can be used as a heating means for IPA in the preheating section 17 of FIG. 2;
4 is a diagram showing an example of an in-line heater that can be used as a heating means for IPA in the preheating unit 17 of FIG.
FIG. 5 is a diagram showing a watermark generation site on a wafer. (A) shows the wafer after drying by the conventional IPA vapor drying apparatus of FIG. 1, and (b) shows the wafer after drying by the IPA vapor drying apparatus of the present invention of FIG. In the figure, the part enclosed by an ellipse is a watermark generation part.
6 is a graph showing the 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. FIG.

Claims (9)

(1) an IPA tank containing liquid isopropyl alcohol (IPA);
(2) Side walls provided around the IPA tank,
(3) a cooling pipe provided at a predetermined interval above the IPA tank and in the vicinity of the side wall;
(4) Heating means provided at least in the lower part of the IPA tank,
(5) IPA supply means including preheating means for supplying preheated liquid IPA to liquid IPA in the IPA tank,
(6) Conveying means for taking the silicon wafer in and out of the space defined by the liquid level of the IPA in the IPA tank, the side wall and the cooling pipe ,
(7) discharge means for discharging into the space outside the mixture was collected with IPA and water on a silicon wafer, and
(8) An IPA vapor drying apparatus for a silicon wafer, which includes a liquid receiver and an IPA recovery pipe extending from the liquid receiver toward the preheating means, provided immediately below the cooling pipe .   The IPA vapor drying apparatus according to claim 1, wherein the preheating means is an in-line heater.   The IPA vapor drying apparatus according to claim 1, wherein the preheating means is a heating tank.   The IPA vapor drying apparatus according to claim 3, wherein the heating tank includes a quartz tank containing IPA and a heater disposed at least under the quartz tank.   The IPA vapor drying apparatus according to claim 1, wherein the discharging means includes a drain receiver and a drain extending from the drain receiver to the outside of the space.   The IPA vapor drying apparatus according to claim 1, wherein the IPA supply means further includes a supply port provided close to or in contact with the liquid IPA in the IPA tank. (1) The level of the liquid IPA contained in the isopropyl alcohol (IPA) tank, (2) a side wall provided around the IPA tank, and (3) a predetermined interval upward from the IPA tank And a step of heating the liquid IPA to fill the IPA vapor in a space defined by a cooling pipe provided near the side wall,
Holding the silicon wafer in the space filled with IPA vapor and mixing the moisture on the silicon wafer surface with IPA;
Discharging the mixture of moisture and IPA out of the space and replacing the moisture on the silicon wafer with IPA;
Moving the silicon wafer whose moisture has been replaced by IPA out of the space and evaporating IPA from the silicon wafer ;
The step of supplying IPA to the IPA tank in order to replenish the reduction of IPA in the IPA tank due to the discharge of the mixture of moisture and IPA out of the space and the evaporation of IPA from the silicon wafer outside the space. Supplying the preheated liquid IPA to the IPA tank, and
A method for drying a silicon wafer , comprising: recovering IPA liquefied by the cooling pipe, reheating, and supplying the IPA to the IPA tank as the preheated liquid IPA . The method for drying a silicon wafer according to claim 7 , wherein the temperature of the preheated liquid IPA is 50 to 82.4 ° C. 8. The silicon according to claim 7, wherein the step of supplying IPA to the IPA tank includes supplying IPA to the IPA tank through a supply port provided close to or in contact with the liquid IPA in the IPA tank. Wafer drying method.

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