CN114308872A - Cleaning and recycling process for waste small-size silicon wafers covered with male molds - Google Patents

Abstract

The invention discloses a cleaning and recycling process for waste small-size silicon wafers covered with male molds, and the cleaning method has no difference from the use of new silicon wafers for silicon wafers with simple chip structures, narrow SU-8 structures and less male mold coverage. The invention cleans high channel and complex structure which can not be cleaned repeatedly by mechanical damage. In the previous step, after acetone soaking and acetone ultrasonic cleaning, acetone can dissolve SU-8 components and infiltrate the SU-8 components between the SU-8 glue and the silicon wafer, the adhesion strength of the SU-8 glue and the silicon wafer is reduced, the glue is easy to fall into the silicon wafer under the action of an external acting force, and the removing operation should be performed after acetone ultrasonic cleaning. If the operation is not carried out, SU-8 is still attached to the silicon wafer possibly through subsequent operation, and the cleaning effect of the subsequent process can be greatly improved by removing the SU-8. This operation can improve the silicon wafer recovery rate.

Description

Cleaning and recycling process for waste small-size silicon wafers covered with male molds

Technical Field

The invention belongs to the field of chip processing, and relates to a cleaning and recycling process of a silicon wafer after photoetching, in particular to a cleaning and recycling process of a waste small-size silicon wafer covered with a male die.

Background

When a chip is processed and manufactured, a silicon wafer carrying SU-8 is often required to be subjected to photoetching to etch a chip structure, which is fine processing, and the silicon wafer with the chip structure is called a male die. After the chip is used, the male die of the chip is useless, and the silicon chip can be cleaned and recycled after being recovered. The price of a domestic 7.5 cm-diameter common round silicon wafer is 50-80 yuan, the price of an imported silicon wafer is higher, and in order to save resources, the silicon wafer which is not used any more and is carved with the anode film can be recycled. Some male molds have simple structures, silicon wafers without large-area SU-8 coating are easy to recycle, and the use difference of the recycled silicon wafers and new silicon wafers is not large. The silicon wafer recovery and cleaning work belongs to batch operation, and about 5 silicon wafers can be recovered at one time. The cost of the reagent used for recycling is lower than that of the silicon chip.

Disclosure of Invention

The purpose of the invention is as follows: in order to solve the defects of the prior art, the invention provides a cleaning and recycling process for waste small-size silicon wafers covered with male molds.

The technical scheme is as follows: a cleaning and recycling process for waste small-size silicon wafers covered with male molds comprises the following steps:

step one, recovering a silicon wafer: manufacturing a PDMS chip, immersing a silicon wafer in solid PDMS, carefully peeling the silicon wafer from the PDMS, and selecting a first silicon wafer which is relatively easy to recycle from the PDMS chip for recycling when the number of the obtained silicon wafers is large;

step two, silicon wafer cleaning: carrying out high-power ultrasound for half an hour in acetone on a silicon wafer with a male die, and trying to remove an SU-8 positive film on the surface of the silicon wafer; during operation, 5 silicon wafers are vertically placed in a 500mL high-temperature-resistant glass beaker, and the middle of the glass wafer is separated by a clean short glass rod; the usage amount of acetone is only needed to submerge the silicon wafer, the silicon wafer is sealed by a plastic film during ultrasonic treatment, if the effect of one-time ultrasonic treatment is not good, ultrasonic cleaning can be carried out for many times, the acetone added during the first ultrasonic treatment can be recycled acetone, the acetone is replaced by new acetone after the ultrasonic treatment, and the ultrasonic treatment is continued;

if the SU-8 positive film is thick and difficult to remove ultrasonically, the SU-8 positive film can be removed by using a tool, a glass slide is used for shoveling the surface of the silicon wafer for several times like a snow scraper, the solidified SU-8 is fragile and is easy to break under the action of the strong external force, and then acetone ultrasonic cleaning is carried out; when in operation, the silicon chip is placed on a flat table top without any protrusion, and the silicon chip is easy to break when force is applied to one point; after the surface of the silicon wafer is basically removed and acetone is ultrasonically cleaned again, cleaning with hydrogen peroxide and concentrated sulfuric acid can be carried out;

step three, cleaning with hydrogen peroxide and concentrated sulfuric acid: piranha prepared from hydrogen peroxide and concentrated sulfuric acid is a strong oxidant for cleaning organic matters on the surface of a glass silicon wafer, and the hydrogen peroxide is prepared from the following components in percentage by volume: concentrated sulfuric acid is 1:3, the concentration of the concentrated sulfuric acid is 98 percent, and the concentration of hydrogen peroxide is 30 percent; completely volatilizing the residual acetone after the previous step of cleaning, wherein Piranha is generally prepared on site, personal protection is needed before operation, hydrogen peroxide and concentrated sulfuric acid are added in sequence, the hydrogen peroxide is added firstly, one part of hydrogen peroxide is poured, and then 3 parts of concentrated sulfuric acid are poured until the silicon wafer is submerged; when concentrated sulfuric acid is added, the concentrated sulfuric acid is slowly poured along the wall of the beaker, and when the concentrated sulfuric acid meets hydrogen peroxide, a large amount of bubbles and heat can be generated, and then acid mist can be generated, so that the operation is carried out in a fume hood, and organic matters are not placed in the fume hood; after pouring, the mixture is covered by a large glass culture dish, so that the volatilization of acid mist is reduced; the Piranha after heating has better cleaning effect, the Piranha is heated to boiling and is also carried out in a fume hood, an organic matter reagent which is combustible and explosive, in particular, is cleaned in the fume hood, an electric heating flat plate is placed in a ventilation position, a cooled Piranha beaker is placed on the heat flat plate and is covered by a large glass culture dish so as to reduce the volatilization of acid mist, the Piranha is electrically heated to boiling, the Piranha can achieve better cleaning effect after boiling for thirty minutes, a person needs to watch during heating, and the Piranha is cooled to room temperature to carry out the next operation;

step four, transferring the mixture into an ultrasonic machine, and ultrasonically cleaning for half an hour at the maximum power;

step five, after the ultrasonic treatment is finished, taking out the beaker, pouring out the acid liquor, cleaning for 7 times by using ultrapure water, pouring the ultrapure water to submerge the silicon wafer, performing ultrasonic cleaning for half an hour, pouring out the ultrapure water, and adding water for ultrasonic treatment once;

after the ultrasound is finished, drying water in an ultra-clean room by using a nitrogen gun, heating the water on a hot plate at 150 ℃ for 1 hour, cooling the water, packing the water in a box, and storing the water in a clean and dry environment;

seventhly, if the silicon segments of the male die are divided into two halves, the male die can be continuously used as long as the structure of the chip is not influenced; the two halves of silicon wafers can be aligned and simultaneously bonded on a whole piece of glass to form a whole, and the method comprises the following specific operations: finding a piece of glass with the size of a silicon chip, cleaning and drying the glass, hanging a layer of PDMS film on the surface of the glass by a spin coater after cooling, aligning two clean silicon chips, placing the two clean silicon chips on the PDMS film, placing the two clean silicon chips in a 60 ℃ oven for baking for one hour, wherein the two hardened silicon chips become a whole and can be used continuously, but the two silicon chips are not on the same plane, and independent chips can only be manufactured on the complete half surface and cannot span cracks.

As an optimization: in the first step, the chips with thin lines, small occupied area of the patterns, no coverage of large area SU-8 and low chip channels are better recycled.

As an optimization: in the second step, the power ultrasound is 250W, the beaker is a high-temperature resistant glass beaker, plastic or non-high-temperature resistant glass beaker is not used, the dissolving volume is 500ml, and the dissolving volume is better, and is not suitable to be larger or smaller.

Has the advantages that: the specific advantages of the invention are as follows:

1. the silicon wafer with simple chip structure, narrow SU-8 structure and less male die coverage is not different from a new silicon wafer after the cleaning method of the invention is used.

2. The invention cleans high channel and complex structure which can not be cleaned repeatedly by mechanical damage. In the previous step, after acetone soaking and acetone ultrasonic cleaning, acetone can dissolve SU-8 components and infiltrate the SU-8 components between the SU-8 glue and the silicon wafer, the adhesion strength of the SU-8 glue and the silicon wafer is reduced, the glue is easy to fall into the silicon wafer under the action of an external acting force, and the removing operation should be performed after acetone ultrasonic cleaning. If the operation is not carried out, SU-8 is still attached to the silicon wafer possibly through subsequent operation, and the cleaning effect of the subsequent process can be greatly improved by removing the SU-8. This operation can improve the silicon wafer recovery rate.

And 3, the Piranha solution has different use modes to influence the cleaning effect, the number of silicon wafers can be properly reduced for improving the cleaning effect, and the cleaning effect can be improved by heating the Piranha solution. The Piranha solution is prepared fresh and has better cleaning effect, and then is heated and cleaned, and then is subjected to ultrasonic cleaning, so that the cleaning capability of the Piranha solution is exerted to the maximum extent.

4. The broken silicon wafer is still valuable on the premise of not influencing the use, the silicon wafer is adhered together and reinforced to play a role continuously, the chip structure cannot span a crack, and the use is limited.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below so that those skilled in the art can better understand the advantages and features of the present invention, and thus the scope of the present invention will be more clearly defined. The embodiments described herein are only a few embodiments of the present invention, rather than all embodiments, and all other embodiments that can be derived by one of ordinary skill in the art without inventive faculty based on the embodiments described herein are intended to fall within the scope of the present invention.

Examples

A cleaning and recycling process for waste small-size silicon wafers covered with male molds comprises the following steps:

step one, recovering a silicon wafer: different chips have different processing and manufacturing processes, if the chips are PDMS chips and the silicon chips are immersed in solid PDMS, the PDMS is carefully stripped from the silicon chips, and the conventional silicon chips are fragile and damaged due to slight deformation. The obtained silicon wafers are more in number, can be selected from the silicon wafers to be recycled firstly, and generally have thinner pattern lines, smaller occupied area of the pattern, no large-area SU-8 covering, lower chip channels and better recycling. In the chip processing, the male die structure of SU-8 spin coating after the silicon chip is cleaned by plasma is difficult to clean.

Step two, silicon wafer cleaning: after the silicon wafer with the male die is taken, performing high-power ultrasound in acetone for half an hour (250W) to try to remove the SU-8 male film on the surface of the silicon wafer. During operation, 5 silicon wafers are vertically placed in a 500mL high-temperature-resistant glass beaker, the middle of the glass beaker is separated by a clean short glass rod, and the cleaning effect is influenced because more silicon wafers are not recommended to be placed. It is firstly emphasized here that the subsequent process requires that the beaker used must be a high temperature resistant glass beaker, not a plastic or non-high temperature resistant glass beaker, with a dissolution volume of 500ml being preferred and not readily larger or smaller. The usage amount of acetone is only needed to submerge the silicon chip, and the silicon chip is sealed by a plastic film during ultrasonic treatment, so that volatilization is reduced. If the one-time ultrasonic effect is not good, the ultrasonic cleaning can be carried out for a plurality of times. The acetone added during the first ultrasonic treatment can be recycled acetone, and is changed into new acetone after the ultrasonic treatment, so that the ultrasonic treatment is continued, the reagent is saved, and the cleaning efficiency can be improved.

If the SU-8 positive film is thick and difficult to remove ultrasonically, the SU-8 positive film can be removed by using a tool, a glass slide is used for shoveling the surface of the silicon wafer for several times like a snow scraper, the solidified SU-8 is fragile and is easy to break under the action of the strong external force, and then acetone ultrasonic cleaning is carried out. When in operation, the silicon chip is placed on a flat table top without any protrusion, and the silicon chip is easy to break when force is applied to one point. The glass slide shovel is also used for preventing the applied external force from being a point-shaped acting force, and if the glass slide shovel is used for shoveling by a sharp tool, the silicon wafer is fragile. The friction between the hard object and the silicon wafer can damage the silicon wafer, and the redundant friction should be avoided as much as possible. After the surface of the silicon wafer is basically removed and the acetone is ultrasonically cleaned again, cleaning with hydrogen peroxide and concentrated sulfuric acid can be carried out.

And step three, preparing Piranha which is a strong oxidant for cleaning organic matters on the surface of the glass silicon wafer by using hydrogen peroxide and concentrated sulfuric acid, wherein the volume ratio of the used components is 1:3 (hydrogen peroxide to concentrated sulfuric acid), the concentration of the concentrated sulfuric acid is 98%, and the concentration of the hydrogen peroxide is 30% (more than 50% can cause explosion). The acetone remained after the cleaning in the last step is completely volatilized completely, and the acetone is certainly volatilized completely because the acetone is a flammable and explosive organic matter and can cause an accident when being violently responded by concentrated sulfuric acid, and the acetone can be continuously performed only when being volatilized completely. Piranha is generally prepared at present, personal protection (acid-proof and corrosion-proof protective clothing, protective apron, nitrile gloves, rubber acid-proof and corrosion-proof gloves with sleeves, strong acid and alkali-proof mask hoods and mouth masks) is required to be done before operation, and hydrogen peroxide and concentrated sulfuric acid are added in sequence, namely hydrogen peroxide is added first, one part of hydrogen peroxide is poured, and then 3 parts of concentrated sulfuric acid are poured until a silicon wafer is submerged. When concentrated sulfuric acid is added, the concentrated sulfuric acid is slowly poured along the wall of the beaker, and when the concentrated sulfuric acid meets hydrogen peroxide, a large amount of bubbles and heat can be generated, and then acid mist can be generated, so that the operation is carried out in a fume hood, and organic matters are not placed in the fume hood. After pouring, the mixture is covered by a large glass culture dish, so that the volatilization of acid mist is reduced. The strong oxidizing property, strong acidity and high heat can destroy the structure of organic SU-8 and other organic impurity structures, which is also the main reason that the beaker for cleaning must use a high-temperature resistant beaker. Piranha is generally prepared fresh and has a good effect, the cleaning effect of the Piranha after heating is better, the Piranha is heated to boiling and is also carried out in a fume hood, a combustible and explosive organic reagent is cleaned in the fume hood, an electric heating flat plate is placed in a ventilation place, a cooled Piranha beaker is placed on the electric heating flat plate and is covered by a large glass culture dish to reduce the volatilization of acid mist, and the Piranha is electrically heated to boiling and can realize a good cleaning effect after boiling for thirty minutes. The heating process must be attended, and the next operation is carried out after the temperature is cooled to room temperature.

And step four, transferring the mixture into an ultrasonic machine, and ultrasonically cleaning for half an hour at the maximum power.

And step five, after the ultrasonic treatment is finished, taking out the beaker, pouring out the acid liquor, cleaning for 7 times by using ultrapure water, pouring the ultrapure water to submerge the silicon wafer, performing ultrasonic cleaning for half an hour, pouring out the ultrapure water, and adding water for ultrasonic treatment once.

And step six, after the ultrasonic treatment is finished, drying water in an ultra-clean room by using a nitrogen gun, heating the water on a hot plate for 1 hour at 150 ℃, cooling the water, packing the cooled water into boxes, and storing the boxes in a clean and dry environment.

And seventhly, the silicon wafer is broken into two halves, the common silicon wafer is very fragile like thin glass, the common silicon wafer is very carefully operated and generally cannot be damaged by a large force, and the silicon wafer is broken into two halves from the middle after being slightly denatured. If the male silicon segment is divided into two halves, the male silicon segment can be used continuously as long as the structure of the chip is not influenced. Therefore, the silicon chip still has use value and can be continuously used. The two halves of silicon wafers can be aligned and simultaneously bonded on a whole piece of glass to form a whole, and the operation is as follows: finding a piece of glass with the size of a silicon chip, cleaning and drying the glass, hanging a layer of PDMS film on the surface of the glass by a spin coater after cooling, aligning two clean silicon chips, placing the two clean silicon chips on the PDMS film, placing the two clean silicon chips in a 60-degree oven for baking for one hour, wherein the two hardened silicon chips become a whole and can be continuously used, but the two silicon chips are not on the same plane, and independent chips can only be manufactured on the complete half surface and cannot span cracks.

The invention is suitable for small-scale recovery of small silicon wafers, and the silicon wafers can be arranged in a 500-plus-600 mL beaker, and the diameter of the silicon wafers is not more than 7.5 cm.

The silicon wafer with simple chip structure, narrow SU-8 structure and less male die coverage is not different from a new silicon wafer after the cleaning method of the invention is used.

The invention cleans high channel and complex structure which can not be cleaned repeatedly by mechanical damage. In the previous step, after acetone soaking and acetone ultrasonic cleaning, acetone can dissolve SU-8 components and infiltrate the SU-8 components between the SU-8 glue and the silicon wafer, the adhesion strength of the SU-8 glue and the silicon wafer is reduced, the glue is easy to fall into the silicon wafer under the action of an external acting force, and the removing operation should be performed after acetone ultrasonic cleaning. If the operation is not carried out, SU-8 is still attached to the silicon wafer possibly through subsequent operation, and the cleaning effect of the subsequent process can be greatly improved by removing the SU-8. This operation can improve the silicon wafer recovery rate.

The different use modes of the Piranha solution can influence the cleaning effect, the number of silicon wafers can be properly reduced for improving the cleaning effect, and the cleaning effect can be improved by heating the Piranha solution. The Piranha solution is prepared fresh and has better cleaning effect, and then is heated and cleaned, and then is subjected to ultrasonic cleaning, so that the cleaning capability of the Piranha solution is exerted to the maximum extent.

The broken silicon wafer is still valuable on the premise of not influencing the use, the silicon wafer is adhered together and reinforced to play a role continuously, the chip structure cannot span a crack, and the use is limited.

Claims (3)

1. A technology for cleaning and recovering waste small-size silicon wafers covered with male molds is characterized by comprising the following steps: the method comprises the following steps:

step one, recovering a silicon wafer: manufacturing a PDMS chip, immersing a silicon wafer in solid PDMS, carefully peeling the silicon wafer from the PDMS, and selecting a first silicon wafer which is relatively easy to recycle from the PDMS chip for recycling when the number of the obtained silicon wafers is large;

step two, silicon wafer cleaning: carrying out high-power ultrasound for half an hour in acetone on a silicon wafer with a male die, and trying to remove an SU-8 positive film on the surface of the silicon wafer; during operation, 5 silicon wafers are vertically placed in a 500mL high-temperature-resistant glass beaker, and the middle of the glass wafer is separated by a clean short glass rod; the usage amount of acetone is only needed to submerge the silicon wafer, the silicon wafer is sealed by a plastic film during ultrasonic treatment, if the effect of one-time ultrasonic treatment is not good, ultrasonic cleaning can be carried out for many times, the acetone added during the first ultrasonic treatment can be recycled acetone, the acetone is replaced by new acetone after the ultrasonic treatment, and the ultrasonic treatment is continued;

if the SU-8 positive film is thick and difficult to remove ultrasonically, the SU-8 positive film can be removed by using a tool, a glass slide is used for shoveling the surface of the silicon wafer for several times like a snow scraper, the solidified SU-8 is fragile and is easy to break under the action of the strong external force, and then acetone ultrasonic cleaning is carried out; when in operation, the silicon chip is placed on a flat table top without any protrusion, and the silicon chip is easy to break when force is applied to one point; after the surface of the silicon wafer is basically removed and acetone is ultrasonically cleaned again, cleaning with hydrogen peroxide and concentrated sulfuric acid can be carried out;

step three, cleaning with hydrogen peroxide and concentrated sulfuric acid: piranha prepared from hydrogen peroxide and concentrated sulfuric acid is a strong oxidant for cleaning organic matters on the surface of a glass silicon wafer, and the hydrogen peroxide is prepared from the following components in percentage by volume: concentrated sulfuric acid is 1:3, the concentration of the concentrated sulfuric acid is 98 percent, and the concentration of hydrogen peroxide is 30 percent; completely volatilizing the residual acetone after the previous step of cleaning, wherein Piranha is generally prepared on site, personal protection is needed before operation, hydrogen peroxide and concentrated sulfuric acid are added in sequence, the hydrogen peroxide is added firstly, one part of hydrogen peroxide is poured, and then 3 parts of concentrated sulfuric acid are poured until the silicon wafer is submerged; when concentrated sulfuric acid is added, the concentrated sulfuric acid is slowly poured along the wall of the beaker, and when the concentrated sulfuric acid meets hydrogen peroxide, a large amount of bubbles and heat can be generated, and then acid mist can be generated, so that the operation is carried out in a fume hood, and organic matters are not placed in the fume hood; after pouring, the mixture is covered by a large glass culture dish, so that the volatilization of acid mist is reduced; the Piranha after heating has better cleaning effect, the Piranha is heated to boiling and is also carried out in a fume hood, an organic matter reagent which is combustible and explosive, in particular, is cleaned in the fume hood, an electric heating flat plate is placed in a ventilation position, a cooled Piranha beaker is placed on the heat flat plate and is covered by a large glass culture dish so as to reduce the volatilization of acid mist, the Piranha is electrically heated to boiling, the Piranha can achieve better cleaning effect after boiling for thirty minutes, a person needs to watch during heating, and the Piranha is cooled to room temperature to carry out the next operation;

step four, transferring the mixture into an ultrasonic machine, and ultrasonically cleaning for half an hour at the maximum power;

step five, after the ultrasonic treatment is finished, taking out the beaker, pouring out the acid liquor, cleaning for 7 times by using ultrapure water, pouring the ultrapure water to submerge the silicon wafer, performing ultrasonic cleaning for half an hour, pouring out the ultrapure water, and adding water for ultrasonic treatment once;

after the ultrasound is finished, drying water in an ultra-clean room by using a nitrogen gun, heating the water on a hot plate at 150 ℃ for 1 hour, cooling the water, packing the water in a box, and storing the water in a clean and dry environment;

seventhly, if the silicon segments of the male die are divided into two halves, the male die can be continuously used as long as the structure of the chip is not influenced; the two halves of silicon wafers can be aligned and simultaneously bonded on a whole piece of glass to form a whole, and the method comprises the following specific operations: finding a piece of glass with the size of a silicon chip, cleaning and drying the glass, hanging a layer of PDMS film on the surface of the glass by a spin coater after cooling, aligning two clean silicon chips, placing the two clean silicon chips on the PDMS film, placing the two clean silicon chips in a 60 ℃ oven for baking for one hour, wherein the two hardened silicon chips become a whole and can be used continuously, but the two silicon chips are not on the same plane, and independent chips can only be manufactured on the complete half surface and cannot span cracks.

2. The process for cleaning and recovering waste small-size silicon wafers covered with a male die as claimed in claim 1, wherein: in the first step, the chips with thin lines, small occupied area of the patterns, no coverage of large area SU-8 and low chip channels are better recycled.

3. The process for cleaning and recovering waste small-size silicon wafers covered with a male die as claimed in claim 1, wherein: in the second step, the power ultrasound is 250W, the beaker is a high-temperature resistant glass beaker, plastic or non-high-temperature resistant glass beaker is not used, the dissolving volume is 500ml, and the dissolving volume is better, and is not suitable to be larger or smaller.