JPH03295236A - Substrate cleaning method and device - Google Patents

Abstract

PURPOSE:To eliminate a reduction in the solubility of a solvent and to contrive an effective cleaning by a method wherein high-pressure liquefied gas is injected to a substrate in a cleaning container in a liquefied state to clean the substrate. CONSTITUTION:Propane gas fed from a propane bomb 11 is filtered by a filter 8. The filtered gas is liquefied by a liquefying device 1 and the liquefied gas is sent by a high-pressure pump 2 to boost, is adjusted its temperature by a temperature adjusting device 3 and is turned into liquefied gas, which has a prescribed pressure and satisfies temperature conditions. This liquefied gas is sprayed on a substrate 20 in a cleaning container 5 via a nozzle 4 and the substrate surface is cleaned. According to the need, a third substance in a solvent tank 10 is added to the liquefied gas by a solvent pump 9, the gas is mixed with the solvent, the mixture is sprayed to removed attachments on the substrate surface, then, the pump 9 is stopped and the liquefied gas only is sprayed to remove the solvent and to clean the substrate surface.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention uses liquefied gas to remove contaminants from the substrate surface, such as fine particles and deposits on the surface of a semiconductor wafer, and powder flux remaining on a mounted printed board. The present invention relates to a method and apparatus for cleaning a substrate.

[Conventional technology]

Removing contaminants from the surface of semiconductor wafers is a serious problem in the semiconductor manufacturing process or in the quality of finished products. For example, the semiconductor ueno\ is a Si single crystal plate with 5iOz, Si
A protective film, such as N or Ru.

The same is true in fields such as magnetic and optical disks; taking magnetic disks as an example, cleaning oil and other organic matter adhering to the surface of the ^1, ^1-Mg alloy is essential for subsequent thin film formation. .

On the other hand, for example, ICs manufactured under strict quality control,
Semiconductor chips such as LSIs are mounted on printed circuit boards with circuit turns by soldering, but soldering leaves behind solder flux residue or solder balls, which affects the reliability of parts and printed boards. It is necessary to remove and clean these in order to give The following will mainly explain the printed board.

The solder is mainly 5N60% by weight, Pb40% by weight, and 20% by weight.
A paste-like spreadable mixture is used, which is a uniform mixture of 0 to 250 mesh powder, flux, binder, and the like. The flux is mainly rosin type, and the chlorine content is 0, 1 to 0 as specified by JIS.
5% by weight is used. Conventionally, when mounting a printed board, solder paste is applied to the printed board using a screen printing method, and semiconductor components such as ICs and LSIs are mounted and soldered onto the printed board. For soldering, the soldering method, which heats the printed board and the entire mounted components, is widely used. However, after reflow soldering, the aforementioned solder flux residue and solder balls remain. For this reason, organic solvents such as fluorocarbons and trichlorethylene are mainly used to remove and clean rosin-based fluxes.

The cleaning methods include (1) immersion cleaning in which the substrate is immersed in the solvent, (2) ultrasonic cleaning in which ultrasonic vibrations are added to the solvent, (3) spray cleaning in which the solvent is sprayed onto the substrate with high pressure spray, (4) There is steam cleaning, which involves cleaning with solvent vapor.

Here, the cleaning fluorocarbon is mainly fluorocarbon 113. Freon 113 has stability, low boiling point, insolubility in resin,
It has excellent properties such as not corroding metals, high electrical insulation, and low toxicity, and is an essential material for high-tech industries such as semiconductors and precision machinery. However, when released into the atmosphere, it can cause the depletion of the atmospheric ozone layer. Given this, certain CFCs have been decided to be reduced or completely abolished under the International Environmental Plan.

On the other hand, trichlorethylene is highly toxic and is subject to regulation, and its ability to dissolve solvents is large, so it has a large impact on resin parts. Under these circumstances, various technologies have been announced as development technologies, but none of them are superior to Freon cleaning, and there is an urgent need to develop effective alternative technologies.

[Problem to be solved by the invention]

The cleaning fluorocarbons mainly used in the above-mentioned conventional technology, particularly certain fluorocarbons (such as fluorocarbons 11, 12, 113, etc.), are being completely phased out and are no longer usable. Furthermore, trichlorethylene and carbon tetrachloride, which have excellent detergency, are also subject to regulations, and there is an urgent need to develop alternative technologies.

SUMMARY OF THE INVENTION In view of the above background, an object of the present invention is to provide a new method and apparatus for cleaning a substrate as an alternative to fluorocarbon cleaning.

[Failure to solve the problem]

In order to achieve the above object, the present invention provides a method for cleaning a substrate, in which liquefied gas at a higher pressure than the container pressure is injected in a liquefied state due to a pressure difference onto a substrate in a cleaning container at an arbitrary pressure and temperature. In order to achieve the above-mentioned other objects, the present invention provides a substrate cleaning method characterized by: (a) used for cleaning; (b) Means for housing or holding the substrate and movable it, and means for controlling the pressure and temperature conditions to maintain the gas in a liquefied state. (e) means for injecting the liquefied gas at a higher pressure from the cleaning container toward the substrate with a pressure difference; and (d) storing the injected liquefied gas and changing the pressure or temperature. (e) means for cleaning the separated gas and means for supplying the purified gas to the liquefaction means. It is.

In the present invention, the liquefied gas that can be used is preferably a hydrocarbon-based gas or carbon dioxide gas, and these liquefied gases include substances that are mutually dissolvable between contaminants on the substrate and the liquefied gas. For example, an organic solvent and an acid or alkali may be added.

The present invention cleans organic substances and fine particles such as oils and fats adhering to the surfaces of semiconductor wafers, disks, etc., and contaminants on the substrate surfaces such as solder flux residue on printed circuit boards.
For removal, liquefied gas is used in place of conventionally used organic solvents such as chlorofluorocarbons and trichlorethylene. Specific measures will be described below.

providing an opening/closing section for taking in and out the substrate, accommodating a stage that supports the substrate, and setting the pressure and temperature conditions in a cleaning container that has a mechanism for sliding or rotating the stage to maintain the gas in a liquefied state; For example, propane gas supplied from a cylinder is liquefied in a liquefier, and the gas is pumped and pressurized using a high-pressure pump, and the liquefied gas at an arbitrary pressure and temperature condition higher than that in the cleaning container is passed through the nozzle with a pressure difference. Spray onto the substrate surface inside the cleaning container. The substrate is moved by arbitrarily moving the support stage so that the cleaning surface of the substrate is efficiently cleaned by the jetting.

As a result, deposits on the surface of the substrate can be effectively removed and cleaned using the dissolving power of the liquefied gas and the mechanical force of the jet. In addition, in the case of liquefied carbon dioxide, the third
The cleaning effect can be improved by adding a substance such as hydrocarbon-based organic solvents such as toluene, hexane, kerosene, etc. to increase the dissolving power and spraying.

The liquefied gas from which deposits on the substrate surface have been removed passes through a pressure-holding valve and is introduced into a separation tank. Here, reduce the pressure to the desired pressure,
When the liquefied gas is changed to the gas phase, dissolved substances dissolved in the liquefied gas are precipitated in the gas, fall by gravity, and are separated at the bottom of the separation tank. The separated precipitate is appropriately extracted from the bottom of the separation tank using internal pressure.

In one gas, precipitates or fine particles are scattered and entrained as mist or dust, so they are filtered through a filter and recycled as clean gas. Also, in the gas
For example, chlorine contained in solder flux may be entrained as chlorine ions. In this case, an activated carbon or calcilum packed tower that adsorbs or reacts with chlorine is installed in front of the filter, and the chlorine is removed by passing through it.

In this manner, when the substrate cleaning is completed, the supply and injection of liquefied gas are stopped, the pressure inside the cleaning container is reduced, and the substrate is taken out.

Particularly in the case of cleaning solder flux from printed circuit boards, hydrocarbon gases such as liquefied gases such as propane, methane, and ethane are effective as the solvent gas.

[Effect]

Figure 6 shows a density-pressure diagram of propane.

The use of liquefied gas as an extraction solvent requires a pressure-resistant cleaning vessel. For example, if the operating temperature of liquefied propane gas is 47°C, the pressure must be maintained at 15 atmospheres or more.

Here, a rosin-based solder paste was applied to a printed board and heated to prepare a test piece in which solder flux (approximately 40 cm) remained, and a dissolution/cleaning test was conducted. The results are shown in FIG.

The flux residue is rosin and remains in the form of a pale yellow resin film. The removal rate was calculated from the weight change. In addition to liquefied carbon dioxide as the extraction solvent, results are also shown for trichlorethylene and ethanol as organic solvents.

The components other than the liquefied gas were immersed in each solvent in a beaker, and the solvents were slowly stirred with a starter. The amount of ethanol added to the liquefied gas was 0.5% by weight, but it was not injected onto the substrate surface. Flux residue can be removed in a short time with trichlorethylene, which has a large KB value, and liquefied propane can be removed almost equally. Ethanol has a KB value equivalent to that of Freon 113, and has a removal rate of 93%. Liquefied carbon dioxide alone is 50%
On the other hand, ethanol-added liquefied carbon dioxide has the same removal rate as ethanol.

Here, when the treated samples of ethanol and ethanol-added liquefied carbon dioxide are vibrated in their respective solvents,
The remaining residue could be easily removed. Similar results were obtained even when ultrasonic waves were added.

That is, the present invention was made based on the above-mentioned knowledge, focusing on the fact that even if the flux residue is dissolved, a small amount of deposit remains, but it can be easily removed by the mechanical force of the injection of liquefied gas. be.

Furthermore, in the case of carbon dioxide gas, the solubility of a third substance such as ethanol in the resin parts is extremely small because the proportion of the solvent is as small as 0.5% by weight of the liquefied carbon dioxide gas in the example. The amount of waste solvent generated can be reduced. Further, it is possible to remove the substrate in a dry state by stopping the addition of the solvent, injecting only liquefied carbon dioxide gas to wash away the solvent adhering to the substrate surface after removing the residue, and then reducing the pressure. That is, a drying step is not necessary.

〔Example〕

The present invention will be described below with reference to the drawings, but the present invention is not limited thereto.

Embodiment 1 FIG. 1 is a process diagram showing a process for removing solder flux residue and cleaning a printed board according to an embodiment of the present invention.

The apparatus is composed of a liquefier 1, a high pressure pump 2, a temperature regulator 3, a nozzle 4, a cleaning container 5 that accommodates a substrate 2o, a pressure holding valve 6a, a separation tank 7, and a filter 8. In operation, propane gas supplied from the propane cylinder 11 is filtered through the filter 8. The filtered gas is liquefied
The gas is liquefied by the high-pressure pump 2 to increase the pressure, and the temperature is adjusted by the temperature regulator 3 to obtain a liquefied gas under predetermined pressure and temperature conditions.

This liquefied gas is injected onto the substrate 20 in the cleaning container 5 through the nozzle 4 to clean the substrate surface. If necessary, the third substance in the solvent tank 10 is added to the liquefied gas from the solvent pump 9, the liquefied gas and the solvent are mixed and sprayed to remove deposits on the substrate surface, and then the solvent pump 9 is stopped. The solvent is then removed and cleaned by injecting only liquefied gas.

The pressure inside the cleaning container 5 is maintained by a pressure-holding valve 6a, and the injected liquefied gas flows through the pressure-holding valve 6a, is depressurized, and introduced into the separation tank 7. Here, when the pressure is reduced by the pressure holding valve 6a, the gas is expanded and cooled. Therefore, it is heated by the heater 13 so that it becomes a gas phase. The deposits removed from the substrates separated in the separation tank 7 settle to the bottom of the separation tank, and are extracted using internal pressure as appropriate.

Since fine particles of the removed deposits may be scattered and entrained in one of the gases, they are removed by a demister in the separation tank, and then filtered and cleaned by the filter 8.
It is recycled as the feed gas.

Next, the operation during cleaning will be explained with reference to the longitudinal section of the cleaning container 5 in FIG. 2, and the bird's-eye view of the substrate stage in FIGS. The lid 51 of the container is opened, the substrate 2° is attached to the stage 53 in FIG. However, in this state, since the inside of the container is at atmospheric pressure, the liquefied gas becomes a gas under reduced pressure. Here, the release valve 57 is opened slightly to replace the air in the container with gas within an arbitrary period of time, and then the release valve is closed.

Liquefied gas at a predetermined pressure and temperature is injected into the container, and is injected onto the substrate to clean it. If necessary, the stage 53 is moved multiple times by the rack 54,
Clean the entire substrate surface.

Note that cleaning can be effectively achieved by spraying from the spray nozzle at an angle, such as when the gap between the printed board and the component is small.

According to this embodiment, the substrate can be cleaned and taken out in a dry state, so a drying step is not necessary. It is also possible to install a plurality of cleaning containers and perform continuous processing by switching valves.

FIG. 5 shows a cross-sectional view of a cleaning container that is an example of using a magnetic disk. Each symbol is the same as in FIG.

〔Effect of the invention〕

The present invention is a technology that can effectively clean the surface of a substrate in place of the conventional fluorocarbons and special organic solvents whose use has been regulated and abolished, and has the following effects.

1) Since liquefied gas is used as the solvent, it can be recycled and used, and the amount of emissions is small.

2) Since the amount of the third substance added to the liquefied gas is small, its processing is easy.

3) Since the gas is purified and recycled, a new solvent is always used when cleaning the substrate, so there is no decrease in solubility, and
Can be cleaned effectively.

4) When cleaning the substrate, it is a wet method using liquefied gas, but since it is gasified, the substrate can be taken out in a dry state.

Therefore, a drying step is not necessary.

[Brief explanation of drawings]

FIG. 1 is a processing process diagram showing an embodiment of the present invention, FIG. 2 is a longitudinal sectional view of a cleaning container, and FIG. 3 is a sectional view taken along line A-A in FIG. 2.
Fig. 4 is a bird's-eye view of the substrate stage, Fig. 5 is a cross-sectional view of a magnetic disk cleaning container in another embodiment, Fig. 6 is a propane density-pressure diagram, and Fig. 7 is the cleaning and dissolution test results. This is a graph showing. 1. Liquefier, 2. High pressure pump, 3. Temperature regulator, 4. Nozzle, 5. Washing container, 6a, 6b.
・Pressure valve, 7・ ・Separation tank 1, 8...filter 9
・Solvent pump, 10...Solvent tank, 11 ・
Gas cylinder, 20... Board figure 1

Claims (8)

[Claims] 1. A method for cleaning a substrate, characterized in that the substrate is cleaned by injecting liquefied gas at a higher pressure than the container pressure onto the substrate in a liquefied state due to a pressure difference onto the substrate in a cleaning container at an arbitrary pressure and temperature. cleaning method. 2. 2. The method of cleaning a substrate according to claim 1, wherein the substrate is a printed circuit board, a semiconductor wafer, a magnetic disk, or an optical disk. 3. 2. The substrate cleaning method according to claim 1, wherein the liquefied gas is a hydrocarbon gas or carbon dioxide gas. 4. 2. The method of cleaning a substrate according to claim 1, wherein the liquefied gas contains a third substance that is mutually soluble in contaminants on the substrate and the liquefied gas. 5. 5. The method of cleaning a substrate according to claim 4, wherein the third substance is an organic solvent, an acid, or an alkali. 6. In an apparatus for cleaning a substrate, (a) a means for liquefying the gas used for cleaning into liquefied gas under arbitrary pressure and temperature conditions; (b) a means for accommodating or holding the substrate and moving the gas; (c) means for injecting the liquefied gas at a higher pressure from the cleaning container toward the substrate with a pressure difference; (d) the A means for storing the injected liquefied gas and gasifying and separating it by changing the pressure or temperature; (e) a means for cleaning the separated gas and supplying the purified gas to the liquefaction means of (a) above; A substrate cleaning device comprising: means. 7. 7. The substrate cleaning apparatus according to claim 6, wherein the gas used for said cleaning is a hydrocarbon gas or a carbon dioxide gas. 8. 7. The substrate cleaning apparatus according to claim 6, wherein the liquefied gas contains a third substance that is mutually soluble in contaminants on the substrate and the liquefied gas.