JPH04144132A - Substrate drying method - Google Patents

Abstract

PURPOSE:To dry substrates stably and with high reproducibility by a method wherein the descending speed of a washing bath is so controlled as to be slow enough to have washing solution adhering to the surfaces of treated substrates which are successively exposed from the washing solution absorbed by the surface tension of the washing solution in the washing bath. CONSTITUTION:A washing bath 7 which is floating on support liquid 5 is made to descend and the surface of overflowing washing solution gradually with a certain slow steed. By making the surface of the washing solution 14 descend with the certain slow speed, washing solution drops and washing solution films adhering to the surfaces of treated semiconductor substrates 9 which are successively exposed from the washing solution 14 are attracted by the surface tension of the washing solution 14 in the washing bath 7 and the completely dried treated semiconductor substrates 9 which are free from the washing solution drops and the washing solution films are successively exposed into a vapor phase above the washing solution 14. Moreover, as the washing solution 14 is made to overflow, almost no particles are contained in it and almost no particles adhere to the surfaces of the treated semiconductor substrates 9.

Description

[Detailed Description of the Invention] [Summary] Regarding a substrate drying method, especially a substrate drying method used for drying a semiconductor substrate after wet processing such as pre-processing and post-processing in a semiconductor process, when the diameter of the substrate is increased, It is possible to dry substrates free from stains and particles using simple equipment without using complicated and large lifting equipment.
With the aim of providing a method for drying a substrate that can be performed stably and with good reproducibility, the substrate to be processed is immersed almost vertically into a cleaning tank overflowing with cleaning liquid, and the cleaning is performed while the substrate is fixed in a fixed position. A method for drying the substrate to be processed by lowering the liquid level of the overflowing cleaning liquid by lowering the tank, and exposing the substrate to be processed from the cleaning liquid to the gas phase sequentially, the method comprising: The cleaning tank has a configuration in which the descending speed of the cleaning tank is controlled at such a rate that either the cleaning liquid adheres to the surface of the substrate to be processed that is successively exposed from the cleaning liquid or is absorbed by the surface tension of the cleaning liquid in the cleaning tank.

[Industrial application field]

The present invention relates to a substrate drying method, and particularly to a substrate drying method used for drying a semiconductor substrate after wet processing such as pre-processing and post-processing in a semiconductor process.

In the pre-processing and post-processing of each step in the semiconductor process, wet processing such as cleaning is performed, followed by drying, but as semiconductor devices become more highly integrated and semiconductor substrates in particular become larger in diameter, As a result, conventional drying methods are unable to prevent stains and particles from adhering to the surface of the semiconductor substrate, and this becomes particularly noticeable for semiconductor substrates that are water repellent.

And [stains] and [particles] on the semiconductor substrate surface.
Since the adhesion of these substances reduces the manufacturing yield and reliability of semiconductor devices, a method for drying a substrate that does not cause the adhesion of the above-mentioned stains and particles is desired.

[Conventional technology]

Conventionally, heater drying and spin drying have been the mainstream methods for drying semiconductor substrates used in the manufacturing process of semiconductor devices.

In heater drying, for example, about 30 semiconductor substrates are lined up in a quartz basket and heated and dried in a gas phase. However, since the entire surface of the substrate is not dried instantly, it is difficult to improve the water repellency of the substrate surface. [Stains] are likely to occur due to evaporation residues of water droplets that have partially accumulated in the form of islands on the exposed surface of the semiconductor (silicon) that the substrate has, and this phenomenon becomes particularly noticeable as the diameter of the substrate increases.

In addition, in spin drying, fluororesin PFA (Per Fl
For example, about 30 semiconductor substrates are lined up in a wafer carrier made of wafer carriers such as u-oro Alcoxy, and dehydrated and dried by centrifugation. The device becomes larger to withstand the volume, and the substrate is more likely to be damaged due to vibration.

Therefore, recently, a method has been developed to lift the semiconductor substrate mounted in the basket from the cleaning liquid at such a low speed that the water droplets or water film adhering to the semiconductor substrate surface are completely absorbed by the surface tension of the cleaning liquid in the cleaning tank. has provided a pull-drying method that prevents the occurrence of stains, and relatively good results have been obtained in terms of drying quality. The total weight of the bow is heavy (approximately 3 to 4 kg), which increases the size of the mechanism, and at the same time, it becomes difficult to change or adjust the bow raising speed, resulting in a problem in that the stability and reproducibility of the operation are impaired.

Under these circumstances, the inventors first fixed a carrier carrying a semiconductor substrate in a cleaning solution filled in a tank, and by discharging the cleaning solution from the bottom of the tank, surface tension caused the carrier to be exposed in the gas phase. We devised a liquid draining drying method in which the level of the cleaning liquid is gradually lowered at a low speed that gradually sucks up the water belly on the surface of the substrate to be discharged.This method not only simplifies and downsizes the equipment, but also stabilizes the quality of cleaning. Although this method improves the accuracy and reproducibility, a problem arises in that particles floating in the cleaning solution adhere to the surface of the semiconductor substrate.

[Problem to be solved by the invention]

Therefore, even when the diameter of the substrate is increased, the present invention can stably and reproducibly dry the substrate without adhering to stains or particles using a simple device without using a complicated and large lifting device. The purpose of the present invention is to provide a method for drying a substrate that can be performed efficiently.

[Means to solve the problem]

The above problem is solved by immersing the substrate to be processed almost vertically into a cleaning tank overflowing the cleaning liquid, fixing it in a fixed position, and lowering the cleaning tank to lower the level of the overflowing cleaning liquid. A method for drying the substrate to be processed by lowering the substrate to sequentially expose the substrate from the cleaning liquid to a gas phase, the method of drying the substrate to be processed by sequentially exposing the substrate from the cleaning liquid to the gas phase, the method of drying the substrate to be processed by lowering the cleaning tank, The substrate drying method according to the present invention controls the speed at which the cleaning liquid adhering to the surface of the substrate to be processed is absorbed by the surface tension of the cleaning liquid in the cleaning tank, or the cleaning tank is used as a means for lowering the cleaning tank. This book uses a method in which the support liquid is suspended on a support liquid filled in a support liquid tank having a liquid draining means at the bottom, and the height of the support liquid level is sequentially lowered by draining the support liquid from the liquid draining means. The problem is solved by the substrate drying method according to the invention.

[For production]

That is, in the method of the present invention, after the substrate to be dried is immersed almost vertically into a cleaning solution that has overflowed and the particles in the solution are being sufficiently removed and fixed at a certain position, The cleaning tank is gradually lowered while the cleaning solution continues to overflow, and the droplets and liquid film of the cleaning solution adhering to the substrate, which are gradually exposed from the surface of the cleaning solution, are removed from the gas phase in the cleaning tank. The substrate is dried by suction and removal using the surface tension of the cleaning solution.

According to this method, droplets and liquid films of the cleaning liquid adhering to the surface of the substrate to be processed are completely removed, similar to the conventional draining and drying method, so that there are no [stains] on the surface of the dried substrate to be processed. The formation of particles is prevented, and because the cleaning solution is constantly overflowing, particles floating inside and on the surface of the cleaning solution are almost completely removed, so there are no particles on the dried surface of the substrate to be processed. It also prevents adhesion.

In addition, as a means to lower the level of the overflowing cleaning solution, the cleaning tank is floated on the support solution using a float, and the support solution is sequentially drawn out at a predetermined flow rate to lower the level of the support solution at a predetermined speed. By using a method of lowering the temperature by 200 ms, the equipment is simpler than the conventional pull-drying method, which obtains the same cleaning effect as the present invention by gradually lifting the substrate to be processed from the cleaning solution while the cleaning solution is overflowing. Furthermore, in the method of the present invention, the horizontal cross-sectional area of each part of the support liquid tank is formed to a desired different value, or the horizontal cross-sectional area of each part of the support liquid tank is made uniform and the support liquid is By controlling the liquid discharge rate according to a predetermined speed profile, it becomes possible to stably and reproducibly control the profile of the rate of decrease in the cleaning liquid level, which changes depending on the location of the substrate to be processed.

〔Example〕 The present invention will be specifically explained below with reference to illustrated embodiments.

FIGS. 1(a) to (C) are process cross-sectional views of one embodiment of the method of the present invention, and FIG. 2 is a schematic cross-sectional view of another example of the apparatus used in the present invention.

Identical objects are indicated by the same reference numerals throughout the figures.

Refer to FIG. 1(a). For example, as shown in this figure, the method of the present invention has a supporting liquid outlet 2 which is open at the top and equipped with a flow meter 3 and a flow control valve 4 at the closed bottom. A support liquid tank 1 is formed in which the horizontal cross-sectional area of each part is equal, and a support liquid 5 such as pure water filled in this support liquid tank 1 is floated via a float 6 fixed to the bottom surface. is closed, the top surface is open, and the cleaning tank 7 can be inserted into the support liquid tank 1, and the cleaning liquid inlet pipe 8, such as pure water, inserted into the cleaning tank 7 and opened near the bottom thereof, is in a floating state. A carrier hanger 11 holds and fixes a wafer carrier 10 on which, for example, about 30 semiconductor substrates 9 to be processed are vertically set at a predetermined height position in a cleaning tank 7, and a drain port 1 for receiving overflowing cleaning liquid.
The drying process is carried out using a substrate drying apparatus having an outer tank 13 having an outer tank 2 and an outer tank 13. The float 6 is formed to have a buoyancy that can float the cleaning tank 7 above the support liquid 5 when the cleaning tank 7 is filled with the cleaning liquid 14 and overflows. This buoyancy may be supplemented with a balance weight or the like.

When drying the semiconductor substrate 9 to be processed, a cleaning liquid 14 made of, for example, pure water is flowed in from the cleaning liquid inflow pipe 8, and the cleaning liquid 14 floats on the support liquid 5 in an overflow state. After holding and fixing the wafer carrier 10 on which the semiconductor to be processed 9 is set at a predetermined position in the cleaning tank 7 via a carrier hanger 11, the support liquid 5 is heated to a surface of 100 nm via a flow meter 3 and a flow control valve 4. The support liquid 5 is discharged at a constant flow rate that descends at a constant low speed of about ~15wn/rain, and the cleaning tank 7 floating on the support liquid 5 is lowered accordingly to remove the overflowing cleaning liquid. The liquid level of No. 14 is slowly lowered at a constant low speed similar to the above.

(See FIG. 1 et al.) This figure shows a state in which about half of the surface of the semiconductor substrate 9 to be processed is exposed in the gas phase (for example, nitrogen atmosphere).
By lowering the liquid level of the cleaning liquid 14 at a constant low speed as described above, the cleaning liquid adhering to the surface of the semiconductor substrate 9 to be processed is gradually exposed from the liquid level of the cleaning liquid 14 into the gas phase. The droplets and liquid film are absorbed by the cleaning liquid 14 in the cleaning tank 7 due to surface tension, and in the gas phase above the cleaning liquid 14, there is a completely dry semiconductor substrate 9 to be processed without any droplets or liquid film attached of the cleaning liquid. They will be revealed one after another. Moreover, since the cleaning liquid 14 has overflowed, there are almost no particles contained therein, and almost no particles that adhere to the surface of the semiconductor substrate 9 to be processed exposed in the gas phase are also eliminated.

In addition, the descending speed of about 10 to 15 on/win is as follows:
/ It is a low speed that works.

Refer to FIG. 1(C) This figure shows that the semiconductor substrate 9 to be processed is set by draining the support liquid 5 to the bottom of the support liquid tank 1 and lowering the cleaning tank 7 completely into the support liquid tank 1. A state in which the wafer carrier 10 is completely exposed to the gas phase and drying is completed is shown.

In the above embodiment, the rate of descent of the cleaning liquid level was set to a constant low speed, but the limit value of the rate of descent of the cleaning liquid level at which the surface tension of the cleaning liquid contributes to the drying effect is determined by the relationship between the substrate to be processed and the cleaning liquid level. It has the property of increasing as the contact area becomes smaller. Therefore, in the above embodiment, the discharge flow rate of the supporting liquid is adjusted so that the descending speed of the cleaning liquid level is the highest in the range where the surface tension functions, depending on the position where the contact area with the surface of the cleaning liquid on the substrate to be processed differs. By controlling the flow rate according to a predetermined flow rate profile, the drying rate can be accelerated more than in the above embodiments.

Refer to Figure 2 This figure shows an example of a substrate drying apparatus used to optimize the rate of descent of the cleaning liquid 14 depending on the position where the surface of the substrate to be processed has different contact areas with the cleaning liquid. In this apparatus, the horizontal cross-sectional area of the support liquid tank 21 is changed in accordance with the position of the surface of the semiconductor substrate 9 to be processed, and the side wall surface of the support liquid tank 21 is shaped like a spherical side wall surface 22. is formed. The other parts are the same as the apparatus shown in FIG.

Using such a device, when the support liquid 5 is discharged from the support liquid tank 21 at a constant flow rate, it is faster in areas where the cross-sectional area of the support liquid tank 21 is small, and slower in areas where the cross-sectional area is large (the liquid level of the support liquid 5 is lowered). Therefore, the curved shape of the side wall surface 22 of the support liquid tank 21,
By fixing the discharge flow rate of the support liquid 5 to an appropriate value, it is possible to stably and reproducibly obtain a cleaning liquid level descending speed optimized according to the position of the surface of the semiconductor substrate 9 to be processed, thereby improving the cleaning quality. The cleaning speed can be increased at the same time.

In the substrate drying apparatus shown in the embodiment, the cleaning liquid inflow pipe 8 may be fixed to the cleaning tank 7 or may be formed integrally with the cleaning tank 7.

Furthermore, the substrate drying method of the present invention can of course be applied to drying masks, ceramic substrates, etc. in addition to semiconductor substrates.

〔Effect of the invention〕

As explained above, according to the substrate cleaning method of the present invention,
Even when the diameter of the substrate becomes larger, we can dry high-quality substrates that are free from stains and particles using a simple device.
It can be performed stably and with good reproducibility.

Therefore, when the present invention is applied to the manufacture of semiconductor devices, it greatly contributes to improving the manufacturing yield and reliability thereof.

[Brief Description of the Drawings] Figures 1 (a) to (C) are process sectional views of one embodiment of the method of the present invention, and Figure 2 is a schematic sectional view of another example of the apparatus used in the present invention. . In the figure, 1 is a support liquid tank, 2 is a support liquid outlet, 3 is a flow meter, 4 is a flow rate control valve, 5 is a support liquid, 6 is a float, 7 is a cleaning tank, 8 is a cleaning liquid inlet pipe, and 9 is a cleaning liquid inlet pipe. A semiconductor substrate to be processed, 10 is a wafer carrier, 11 is a carrier hanger 12 is a drain port, 13 is an outer tank, 14 is a cleaning liquid, 21 is a support liquid tank, and 22 is a spherical side wall surface.

Claims (1)

[Claims] 1. A substrate to be processed is immersed and fixed almost vertically into a cleaning tank in which cleaning liquid overflows, and with the substrate fixed in a fixed position,
In this method, the liquid level of the overflowing cleaning liquid is lowered by lowering the cleaning tank, and the substrates to be processed are sequentially exposed from the cleaning liquid to the gas phase, thereby drying the substrates to be processed. The lowering speed of the cleaning tank is controlled to a speed at which the cleaning liquid that adheres to the surface of the substrate to be processed, which is successively exposed from the cleaning liquid, is absorbed by the surface tension of the cleaning liquid in the cleaning tank. Substrate drying method. 2. The means for lowering the cleaning tank is such that the cleaning tank is suspended on a support liquid filled in a support liquid tank having a liquid draining means at the bottom, and the supporting liquid is discharged from the liquid draining means. 2. The method of drying a substrate according to claim 1, further comprising sequentially lowering the level of the support liquid in the support liquid tank. 3. The rate of descent of the cleaning liquid level is changed depending on the position of the substrate to be processed by keeping the discharge speed of the support liquid constant and changing the horizontal cross-sectional area of the support liquid tank. A method for drying a substrate according to claims 1 and 2. 4. Make the horizontal cross-sectional area of the support liquid tank uniform in each part,
Claims 1 and 2, characterized in that the rate of descent of the cleaning liquid level is changed in accordance with the position of the substrate to be processed by changing the rate of discharge of the support liquid from the liquid draining means.
The substrate drying method described.