JPH0533819B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to substrate cleaning, and in particular to improving the shape of a cleaning tank used in a substrate cleaning process in a semiconductor device manufacturing process to shorten the cleaning time. With the goal.

BACKGROUND ART With the automation of semiconductor device manufacturing equipment, automation of substrate cleaning equipment that immerses a semiconductor substrate in a carrier into a container filled with a chemical solution or water is also progressing.
Concerning the structure of containers (cleaning tanks) for filling chemical solutions and pure water, tanks with larger sizes and more creative shapes have been developed in order to add various functions.
However, in the batch cleaning method, as the size of the tank increases, the flow rate of the chemical solution or pure water on the most important substrate surface tends to decrease.

Problems to be Solved by the Invention For example, when a silicon substrate 5 with a diameter of 150 mm is inserted almost perpendicularly into a SEMI standard carrier 4 and washed with water as shown in FIG. 11, the dimensions of the top surface of the carrier 4 containing 25 substrates is approximately 180mm x 150mm (178mm x 143mm for Fluoroair A182-60 series)
It is. The porous member (perforated plate) 2 has holes 6 with a pitch of 10 mm in both the direction in which the substrates 5 are lined up and in the direction parallel to the substrate surface, and the density of holes 6 is uniform over almost the entire surface. This tank is connected at 20/min from the pure water supply pipe 3 at the bottom.
The substrate 5 is supplied with pure water and discharged from the top of the tank.
It is used for cleaning.

However, in such a tank, carrier 4
The flow of pure water is influenced by the shape of the substrate 5, so that the flow velocity of pure water is high near the center C of the substrate 5, and the flow velocity is low at the periphery P where the carrier and the substrate are in contact. An example of actual measurement of flow velocity is shown in FIG. FIG. 12 shows the results of measurement using a laser Doppler current meter at the center of the gap between the substrates arranged at a pitch of 4.76 mm on the line Z--Z' in FIG. Even if the actual flow velocity is kept constant, the actual flow velocity fluctuates in a short period of one second or less, so the actual flow velocity is the average of the flow velocity measured over several minutes.

As is clear from the figure, the speed is fast only at the center of the silicon substrate 5, and it is extremely slow at the periphery. Especially in the periphery, the flow velocity cannot be measured due to the influence of the carrier groove, but it is extremely small, about 1/10 of that in the center. In other words, ions and etching agent contaminants adhering to the substrate are removed in a relatively short period of time near the center, but it takes a long time to clean the periphery and the carrier due to the extremely slow flow rate. We calculated this using a simple model. In Figure 10A, it is assumed that the space between the two plates is divided into two parts α: (1 - α), and that pure water flows in one space at an average flow velocity v ₁ and in the other space at an average flow velocity v ₂ . . As shown in Figure 9B, the ion concentration at the inlet of pure water is C=O, and the concentration at the outlet is C _put1 , respectively.
C _put2 Let the average concentration between the substrates at time t = 0 be Co. If t is large enough, C _put1 /Co and C _put2 /
In a range where Co is quite small, C _put1 = Co _exp (-kv ₁ t) in the fast flow part and C _put2 = Co _exp (-kv ₂ t) in the slow flow part. Then, the average concentration C _put of the confluence of C _put1 and C _put2 is C _put = C _put1 v ₁ α + C _put2 v ₂ (1 − α) / v ₁ α + v ₂ (1 − α
) becomes. k is a constant.

Assume now that α=0.9, v ₁ =10, v ₂ =1 v ₁ =10, v ₂ =0.1, and k=0.1. The calculation results are as shown in Figure 9. At the beginning of cleaning, the high flow rate section is
In the latter stage, the cleaning characteristics of the low flow rate section directly affect the overall average concentration, and in order to shorten the time required to obtain a sufficient cleaning effect, it is necessary to eliminate the low flow rate section (increase the overall speed. It can be seen that it is necessary to reduce the area of the flow velocity region.

In other words, when cleaning substrate etching materials, etc., the ion concentration of pure water at the discharge outlet immediately decreases in areas where the flow rate is high, and the residual ion concentration on the substrate surface becomes sufficiently small, but the ion concentration decreases in areas where the flow rate is slow. This means that water will have to continue to flow unnecessarily in areas where the flow velocity is high until the flow rate is sufficiently reduced.

According to the conventional configuration, as shown in this example, pure water that enters between the substrates from the bottom of the substrate passes through a nearly linear trajectory, reaches the top of the substrate, and is discharged. It is. Therefore, the part near the central part C where the flow velocity is high is cleaned in a short time, and the pure water that passes through this part thereafter is discharged from the upper part of the tank, which contributes to the cleaning. On the other hand, the flow velocity is low in the peripheral area, so in this situation,
It takes a long time to completely remove impurity ions from the silicon substrate surface and carrier surface.
Since a large amount of expensive pure water is unnecessarily required, this causes an increase in the cost of products such as semiconductor devices. In other words, most of the supplied pure water is concentrated in the portion where the flow rate is high, and the remaining small portion where the flow rate is low is washed over a long period of time. Such a situation at the periphery is widely used as a method of breaking the flow. For example, this can be easily confirmed by an experiment in which a colored water-soluble liquid such as ink is injected through a thin tube such as a syringe needle.

Means for Solving the Problems The present invention holds a plurality of substrates to be cleaned, which are placed substantially parallel to each other, in a cleaning tank in a substantially vertical direction, and a hole is formed in the lower part with a width on which the substrates are to be placed. , forming a cleaning liquid water supply section with a perforated plate locally disposed between the substrates in a length range, and supplying the cleaning liquid from the water supply section to the substrate surface via the perforated plate to supply the cleaning liquid. generating a flow and discharging the cleaning liquid from the upper part of the cleaning tank, and creating a flow of the cleaning liquid flowing from one end of the substrate surface to the other end on the substrate surface and a circular flow on the substrate surface. This is to clean the substrate surface. The perforated plate has an open area in which a plurality of holes are formed and an unopened area in which a plurality of holes are formed in a width and length range on which the substrate is to be placed, and the open area and the unopened area Between each of the substrates in the area: The maximum distance in the length direction within which the substrate is placed is approximately 1/4 or more of the length of the substrate to be placed in any area between the substrates to be cleaned. .

In particular, when a circular substrate is used, it is desirable to supply the circular flow so that the size of the circular flow is larger than 1/4 of the outer diameter of the substrate.

Furthermore, it will be even more effective if the present invention is used for the purpose of removing chemical components (etching material) used in wet etching and unnecessary surface foreign matter generated during dry etching after etching a semiconductor substrate.

Effect As described above, if a vortex flow (circular flow) with a diameter preferably about 1/4 of the substrate diameter exists, ions on the substrate surface near the holes of the porous plate are removed in a short time, and then, The pure water that passes through this portion and contains almost no ions contributes to the removal of ions from the entire surface of the substrate (particularly from the edge surface) by the vortex action. this is,
Since the water is supplied from an area where the flow rate is high and the ion concentration has decreased in a short period of time, this corresponds to reusing water that would previously have been drained. In this way, by optimizing the structure of the tank so that the pure water can be reused within the tank, the efficiency of using pure water can be improved and the amount of pure water used can be reduced. Therefore, cost reduction and cleaning time can be reduced.

Embodiment As an embodiment of the present invention, a washing tank for a 6″φSi semiconductor substrate (wafer) will be explained.
1 is a schematic cross-sectional view showing the basic concept of the cleaning device of the embodiment, in which 1 is a cleaning tank, 2 is a perforated plate, 3 is a water supply pipe, 4 is a carrier, and 5 is a Si substrate. In this specification, the width of the substrate to be placed on the perforated plate is
The distance between the Si substrates placed at both ends of the plurality of Si substrates 5 held almost vertically and placed almost in parallel,
The length of the substrate to be placed on the porous plate is defined as the length of the diameter of the Si substrate. Here, the Si to be cleaned
The aperture distribution (plan view) of the holes 6 of the perforated plate 2 in an area of about 1/4 of the width and length range on which the substrate 5 is to be placed and its outer periphery is shown in Fig. 3, and in Fig. 1. X-X
Figure 2 shows the average flow velocity distribution on the line. The porous plate 2 has an open area and holes 6 in which a plurality of holes 6 are formed in the range of width and length on which the silicon substrate 5 is to be placed.
It has an unopened area in which no is formed.
The distribution of the holes 6 is 10 mm in the board radial direction and 4.76 mm in the board arrangement direction, which corresponds to the pitch where the boards are arranged almost parallel to each other, and is located near the center of the board in the radial direction within the distance between the boards. Open areas are provided and holes 6 are locally distributed. If a perforated plate with such a porosity distribution is used, the supplied pure water W will flow, for example, into a vortex 7, as outlined by the arrows in FIG.
This is a vortex flow with a diameter D that is approximately 1/4 or more of the substrate diameter, the flow velocity near the center of the substrate is very high, and a fast downward flow occurs around the periphery, and the water used for cleaning is discharged from the top of the tank. Ru.

In order to generate such a large eddy current, it is sufficient to locally arrange holes 6 in the perforated plate between the substrates to have the same diameter as the eddy current. In addition, in the first embodiment, if a large vortex having a diameter of about 1/4 is formed, a small amount of eddy current is formed in the unopened area of the perforated plate 2 where no holes are formed, as shown in FIG. It goes without saying that holes 6 may be formed.

A second embodiment will be described using FIGS. 4 to 6. FIG. 4 is a basic conceptual diagram of the cleaning device of the second embodiment, and FIG. 5 shows the flow velocity distribution on the Y-Y' line in the cleaning device shown in FIG. In this case, the perforation distribution (plan view) of the perforated plate 2 in the entire lengthwise central area of the width and length range on which the Si substrate 5 to be cleaned is to be placed and its outer periphery is shown. It is shown in FIG. The porous plate 2 is a silicon substrate 5
It has an open region in which a plurality of holes 6 are formed and an unopened region in which no holes 6 are formed in the range of width and length in which the device is to be placed. Opening hole distribution is 10mm pitch in the board radial direction and 4.76mm pitch in the board alignment direction.
An opening area is provided on one side from the center of the substrate in the radial direction, and local openings 6 are provided. When a perforated plate 2 with such a porosity distribution is used, a vortex flow having a diameter approximately equal to the substrate diameter is generated, as shown by the arrow in FIG. The flow velocity becomes faster in the downward direction.

When a vortex is generated in this way, the total flow rate in the tank becomes larger than when only a laminar flow is used, so there are no localized portions where the flow velocity is extremely low. Various other methods can be considered to generate the vortex, such as installing a pure water spout on the side of the tank.

When the present invention is implemented, firstly, the time required for cleaning is shortened. FIG. 7 shows the case where the first embodiment of the present invention is applied and the case where a conventional cleaning tank is used.
Shows resistivity recovery time. The experiment was carried out using a standard wafer carrier (Fluoroair A182MJ) with a diameter of 150 mm.
25 silicon substrates were inserted into the carrier, the carrier was immersed in 1N sulfuric acid, the liquid was drained in the air for about 30 seconds, and the carrier was placed in a washing tank. The amount of pure water supplied is
20/min. The horizontal axis shows the time from the time of filling the tank, and the vertical axis shows the relative resistivity of the water collected from the top of the tank. In the figure, curve I indicates the resistivity recovery characteristic of the conventional washing tank, and curve B indicates the resistivity recovery characteristic of the washing tank according to the first embodiment of the present invention. As is clear from the figure, the specific resistance recovers in about half the time compared to conventional methods, making it possible to shorten the cleaning time.

Second, if the washing time is short as described above, the amount of pure water used can be reduced. In the previous experiment, 20/
If the time is reduced by approximately 8 minutes compared to the min water supply amount, the reduction is 20 x 8 = 160/min. Pure water 1
Assuming that the price of t is 1000 yen, it becomes 1000 yen/t x 160/1000 = 160 yen. The reduction is 160/25 = 6.4 yen per ticket. This greatly contributes to the mass production of semiconductor devices.

Furthermore, in conventional cleaning tanks, for example, a silicon substrate is treated with a chemical solution using a removal agent such as hydrofluoric acid, which is commonly used, to remove an oxide film on the substrate surface, and then the chemical solution is removed from the substrate surface. When removing it, the flow rate of pure water is high near the center of the substrate, so the chemical component can be removed in about 2 to 3 minutes, whereas the flow rate is extremely slow in the area that is in contact with the carrier, so it takes about 15 minutes. . In this case, even if the oxide film on the surface of the substrate is removed using hydrofluoric acid, the central part of the substrate 5 is washed with pure water for at least 10 minutes after the fluorine ions are removed. An oxide film 20 is formed as shown in FIG. The thickness depends on the pure water temperature, and at around 23°C it is about 10 Å when measured with an ellipsometer. On the other hand, in the part of the substrate near the carrier, after the fluorine ions are removed,
Since it is exposed to pure water for only about 2 minutes, almost no oxidation occurs. When it is necessary to form a thermal oxide film of 30 to 40 Å with good uniformity on the substrate surface, such as the gate oxide film of an ultra-high-density MOSLSI, if the initial oxide film is uneven, This causes large variations in threshold voltage when formed.

By using the present invention, cleaning time can be shortened, unnecessary films 20 such as such oxide films are less likely to be formed, and uniform transistors and the like can be formed.

Further, for example, deep grooves 30, 31 on the surface of the substrate 5.
When a large number of grooves and holes are formed by selective etching, the chemical component that is the etching material inside the grooves and holes is removed mainly by a diffusion mechanism. As shown in FIG. 8B, when the flow rate of pure water on the surface is high, such as in the center of the substrate 5, the chemical component 40 that has diffused out from the holes and grooves quickly flows away. The difference in concentration of the chemical liquid component between the vicinity of the entrance of the groove 30 and the bottom becomes large, and diffusion is promoted. However, at the edge of the substrate 5 near the carrier, if the surface flow velocity is low as in conventional cleaning,
At the ends, the chemical components that have diffused and come out near the entrances of the holes and grooves 31 stagnate, and the rate of diffusion from the bottoms of the holes and grooves becomes extremely low. Therefore, in such a case, the difference in washing time between the central part of the substrate and the part near the carrier becomes even larger.

With the present invention, even when cleaning substrates with such deep grooves and holes, there is little time difference to completely remove chemical components from the center to the periphery, so this phenomenon is unlikely to occur and the chemical components can be removed uniformly. , and an unnecessary oxide film based on these factors is formed on the substrate 5.
It is also less likely to occur on the surface or in the grooves. Therefore, the present invention is also advantageous for cleaning substrates that have been subjected to such etching processing.

The reason why the present invention produces such an effect is that the pure water ejected from the holes of the perforated plate removes chemical components, etc. on the substrate surface near the holes, passes through the cleaned surface, and then, This is due to reaching the area where the chemical components still remain. Furthermore, whereas in the past, the average length of the process for pure water ejected from the hole until it was discharged from the top of the tank was at most the diameter of the substrate or the height of the tank, in the present invention, a large vortex is created. This is achieved by increasing the process length within the substrate plane.

This is also true even if there is no carrier and this does not restrict the flow of pure water.
As shown in the conventional example, it is more effective to make pure water into a vortex flow than into a laminar flow, and the present invention is also effective when there is no carrier.

In order to make the most of the eddy current effect, even if a small eddy current occurs, the effect is small, and it is desirable to have a large eddy current with a diameter of about 1/4 of the size of the substrate.

It goes without saying that the present invention is applicable to cleaning not only semiconductor substrates but also other substrates such as metals and insulators.

Effects of the Invention As described above, by using the present invention, it is possible to improve the cleaning speed and reduce the amount of pure water used, and it has an excellent industrial effect in improving the efficiency of cleaning work and improving the cleaning effect. It is something that can be demonstrated. In particular, the present invention makes it possible to uniformly clean the surface of a semiconductor substrate that has been subjected to an etching process, thereby greatly contributing to the uniform manufacture of high-density semiconductor integrated circuit devices.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional diagram showing a schematic cross-section of the cleaning device according to the first embodiment of the present invention and flow velocity vectors, and FIG. 2 is a diagram showing the actual measured value of the average flow velocity near the center between the substrates in the first embodiment of the present invention. 3 is a plan view of essential parts near the perforated plate of the first embodiment, FIG. 4 is a schematic cross-sectional view of the cleaning device of the second embodiment, and FIG. 5 is a diagram of the substrate in the second embodiment. Fig. 6 is a plan view of the main part near the perforated plate in the second embodiment, and Fig. 7 shows the conventional example and the first embodiment of the present invention.
Fig. 8 is a cross-sectional view of a semiconductor substrate during cleaning, and Fig. 9 is a diagram of resistivity recovery characteristics for comparing the chemical removal speed when applying the embodiment. A diagram showing the calculation results for estimating the concentration reduction characteristics of chemical liquids when one flow rate is high and the other is low. Figure 10 is an explanatory diagram of the assumptions for calculation to obtain Figure 9. Figure 11 is a conventional cleaning tank. Schematic cross-sectional diagram of the configuration,
FIG. 12 is a diagram showing actual measurement results of the average flow velocity in a conventional cleaning tank. 1...Cleaning tank outer wall, 2...Porous plate, 3...Pure water supply pipe, 4...Carrier, 5...Si substrate, 6...
Hole, 7... vortex.

Claims (1)

[Scope of Claims] 1. A cleaning tank for storing a cleaning liquid, a plurality of substrates to be cleaned held substantially perpendicularly inside the cleaning tank and mounted almost in parallel, and a flow velocity distribution of the cleaning liquid inside the cleaning tank. a perforated plate for controlling, and a water supply section for introducing the cleaning liquid into the cleaning tank from below the perforated plate; Between
In order to form a large vortex flow along the surface of the substrate inside, the perforated plate has an open area with a plurality of holes and no holes in the width and length range on which the substrate is to be placed. and an unopened area, and the maximum distance between the substrates in the open area and the unopened area in the length direction on which the substrate is placed is the same in any area between the substrates to be cleaned. A cleaning device characterized in that the length is about 1/4 or more of the length to be placed. 2. A substrate to be cleaned is placed on a carrier for holding the substrate, and is made of a semiconductor substrate from which a surface coating has been removed or a semiconductor substrate with grooves or holes formed by etching, and the coating is removed using a cleaning liquid. 2. The cleaning device according to claim 1, wherein the removal material or the etching material remaining in the groove or hole is removed by cleaning. 3. A water supply provided below a perforated plate that holds a plurality of substrates to be cleaned, which are placed substantially parallel inside a cleaning tank that stores cleaning liquid, almost vertically, and controls the flow velocity distribution of the cleaning liquid inside the cleaning tank. The cleaning solution is introduced into the cleaning tank through the opening section, and the perforated plate has an open area with a plurality of holes formed therein and an unopened area with no holes formed in the width and length range on which the substrate is to be placed. between the substrates in each of the open area and the unopened area. By making the length between the substrates approximately 1/4 or more of the length to be cleaned, the surfaces of the substrates are cleaned by a large vortex of the cleaning liquid in the cleaning tank that is formed along the surfaces of the substrates inside the cleaning tank. A cleaning method characterized by: 4. The cleaning method according to claim 3, wherein the substrate has a circular shape, and the size of the circular flow is larger than 1/4 of the outer diameter of the substrate. 5. The substrate to be cleaned is a semiconductor substrate from which a surface coating has been removed or a semiconductor substrate in which grooves or holes have been formed by etching, and the cleaning liquid is used to remove the coating removal material or the etching remaining in the grooves or holes. 4. The cleaning method according to claim 3, further comprising washing and removing the material.