METHODS AND APPARATUS FOR CLEANING SUBSTRATES

FIELD OF THE INVENTION

The present invention generally relates to method and apparatus for cleaning substrate. More particularly, relates to detaching bubbles from the surface of the substrate to avoid bubbles damaging implosion during the cleaning process, so as to remove fine particles more efficiently in patterned structures on the substrate.

BACKGROUND

Semiconductor devices are manufactured or fabricated on semiconductor substrates using a number of different processing steps to create transistor and interconnection elements. Recently, the transistors are built from two dimensions to three dimensions such as finFET transistors and 3D NAND memory. To electrically connect transistor terminals associated with the semiconductor substrate, conductive (e.g., metal) trenches, vias, and the like are formed in dielectric materials as part of the semiconductor device. The trenches and vias couple electrical signals and power between transistors, internal circuit of the semiconductor devices, and circuits external to the semiconductor device.

In forming the finFET transistors and interconnection elements on the semiconductor substrate may undergo, for example, masking, etching, and deposition processes to form the desired electronic circuitry of the semiconductor devices. In particular, multiple masking and plasma etching step can be performed to form a pattern of finFET, 3D NAND flash cell and or recessed areas in a dielectric layer on a semiconductor substrate that serve as fin for the transistor and or trenches and vias for the interconnection elements. In order to removal particles and contaminations in fin structure and or trench and via post etching or photo resist ashing, a wet cleaning step is necessary. Especially, when device manufacture node migrating to 14 or 16 nm and beyond, the side wall loss in fin and or trench and via is crucial for maintaining the critical dimension. In order to reduce or eliminate the side wall loss, it is important to use moderate, dilute chemicals, or sometime de-ionized water only. However, the dilute chemical or de-ionized water usually is not efficient to remove the particles in the fin structure, 3D NAND hole and or trench and via. Therefore the mechanical force such as ultra or mega sonic is needed in order to remove those particles efficiently. Ultra sonic or mega sonic wave will generate bubble cavitation which applies mechanical force to substrate structure, the violent cavitation such as transit cavitation or micro jet will damage those patterned structures. To maintain a stable or controlled cavitation is key parameters to control the mechanical force within the damage limit and at the same time efficiently to remove the particles.

FIG. 1AandFIG. 1Bdepict a transit cavitation damaging patterned structures1030on a substrate1010during cleaning process. The transit cavitation may be generated by an acoustic energy applied for cleaning the substrate1010. As shown inFIG. 1AandFIG. 1B, the micro jet caused by bubble1050implosion occurs above the top of the patterned structures1030and is very violent (can reaches a few thousands atmospheric pressures and a few thousands ° C.), which can damage the fine patterned structures1030on the substrate1010, especially when the feature size t shrinks to 70 nm and smaller.

The bubble cavitation damaging patterned structures on the substrate caused by the micro jet generated by bubble implosion has been conquered by controlling the bubble cavitation during the cleaning process. A stable or controlled cavitation on the entire substrate can be achieved to avoid the patterned structures being damaged, which has been disclosed in patent application no. PCT/CN2015/079342, filed on May 20, 2015.

In some case, even though the power intensity of an ultra or mega sonic applied for cleaning the substrate is reduced to a very low level (almost no particle removal efficiency), the damage of patterned structures on the substrate still occurs. The number of the damage is only a few (under 100). However, normally the number of the bubbles in the cleaning process under the ultra or mega sonic assisting process is tens of thousands. The number of the patterned structures damage on the substrate and the number of bubbles are not match. The mechanism of this phenomenon is unknown.

SUMMARY

According to one aspect of the present invention is to disclose a substrate cleaning method comprising the steps of: placing a substrate on a substrate holder; delivering cleaning liquid onto the surface of the substrate; implementing a pre-treatment process to detach bubbles from the surface of the substrate; and implementing an ultra or mega sonic cleaning process for cleaning the substrate.

According to another aspect of the present invention is to disclose a substrate cleaning apparatus comprising a substrate holder configured to hold the substrate; at least one inlet configured to deliver cleaning liquid onto the surface of the substrate; an ultra or mega sonic device configured to deliver acoustic energy to the cleaning liquid; one or more controllers configured to: control the ultra or mega sonic device with a first power to implement a pre-treatment process to detach bubbles from the surface of the substrate; and control the ultra or mega sonic device with a second power higher than the first power to implement an ultra or mega sonic cleaning process for cleaning the substrate.

According to another aspect of the present invention is to disclose a substrate cleaning apparatus comprising a substrate holder configured to hold the substrate; one or more inlets configured to deliver cleaning liquid onto the surface of the substrate for cleaning the substrate and deliver liquid chemical solution onto the surface of the substrate for implementing a pre-treatment process to detach bubbles from the surface of the substrate; an ultra or mega sonic device configured to deliver acoustic energy to the cleaning liquid for cleaning the substrate.

DETAILED DESCRIPTION

Referring toFIG. 2A, during the ultra or mega sonic assisting substrate cleaning process, there is a phenomenon that even though the power intensity of an ultra or mega sonic applied for cleaning the substrate2010is reduced to a very low level (almost no particle removal efficiency), the damage of patterned structures2030on the substrate2010still occurs. What is more, it is often the case that single wall of the patterned structure2030is damaged.FIG. 2Aillustrates the damage with two examples. One example is that single wall of the patterned structure2030is peeled toward a side. Another example is that a part of single wall of the patterned structure2030is removed. AlthoughFIG. 2Aillustrates two examples, it should be recognized that other similar damages may happen. What causes these damages?

Referring toFIG. 2BtoFIG. 2D, in the substrate cleaning process, small bubbles2050,2052tend to attach on solid surface such as the surface of substrate2010or side walls of patterned structures2030, as shown inFIG. 2BandFIG. 2C. When the bubbles2050,2052are attached on the surface of substrate2010or side walls of patterned structures2030, such as the bubble2052attaching on the bottom corner of the patterned structure2030and the bubble2050attaching on single side wall of the patterned structure2030, once these bubbles2050,2052implode, the patterned structures2030are peeled toward the direction in accord with the direction of bubble implosion force acting on the single side wall from the sub-layer on the substrate2010or a part of single side wall of the patterned structure2030is removed, as shown inFIG. 2A. Although the implosion is not as intense as the micro jet, however, due to the bubbles2050,2052attaching on the surface of the substrate2010and the side walls of the patterned structures2030, the energy generated by small bubbles implosion can also damage the patterned structures2030.

Moreover, during a wet process, the small bubbles may coalesce into bigger bubbles. Due to the tendency of bubble attachment on the solid surface, the coalescence on the solid surface such as the surfaces of the patterned structures and the substrate increases the risk of the bubbles implosion happening on the patterned structures, in particular, the critical geometrical portion.

FIG. 3AtoFIG. 3Hdepict the mechanism that the implosion of bubbles attached on a substrate damages patterned structures on the substrate during an ultra or mega sonic assist wet cleaning process according to the present invention.FIG. 3Aillustrates cleaning liquid3070is delivered onto the surface of a substrate3010having patterned structures3030and at least one bubble3050is attached on the bottom corner of the patterned structure3030. In a positive ultra or mega sonic working process shown inFIG. 3B, F1is the ultra or mega sonic pressing force working on the bubble3050, F2is the counter force working on the bubble3050generated by the side wall of the patterned structure3030while the bubble3050pressing on the side wall of the patterned structure3030, and F3is the counter force working on the bubble3050generated by the substrate3010while the bubble3050pressing on the substrate3010. In a negative ultra or mega sonic working process shown inFIG. 3CandFIG. 3D, the bubble3050is expanding due to the ultra or mega sonic negative force pulling the bubble3050. In the process of the bubble volume expanding, F1′ is the force of the bubble3050pushing the cleaning liquid3070, F2′ is the force of the bubble3050pushing the substrate3010, and F3′ is the force of the bubble3050pushing the side wall of the patterned structure3030. After the positive ultra or mega sonic and the negative ultra or mega sonic are alternately applied for a number of cycles, the gas temperature inside of bubbles increases higher and higher, the bubble volume grows bigger and bigger, and the bubble implosion3051occurs finally, which generates the implosion force F1″ acting on the cleaning liquid3070, F2″ acting on the substrate3010, F3″ acting on the side wall of the patterned structure3030, as shown inFIG. 3G. The implosion force causes the side wall of the patterned structure3030being damaged as shown inFIG. 3H.

For avoiding the patterned structures on the substrate being damaged caused by bubble implosion during the ultra or mega sonic assist wet cleaning process, it is preferable to detaching the bubbles from the surfaces of the patterned structures and the substrate before the acoustic energy is applied to the cleaning liquid for cleaning the substrate.

Hereinafter a plurality of methods is disclosed to detach bubbles from the surfaces of the pattern structures and the substrate.

FIG. 4AandFIG. 4Bshow an embodiment of a substrate pre-treatment for detaching bubbles from the surfaces of patterned structures on a substrate according to the present invention. While cleaning liquid4070is delivered onto the surface of a substrate4010having patterned structures4030, at least one bubble4050is attached at the bottom corner of the pattern structure4030as show inFIG. 4A. Therefore, a bubble detaching pre-treatment process is needed before an ultra or mega sonic cleaning process. In the bubble detaching pre-treatment process, a method such as increasing patterned structures4030surface wettability from the directions of D1and D2which are respectively along with the solid surface of the patterned structure4030and the solid surface of the substrate4010or using a minimal mechanical force to interfere from the directions of D1and D2is needed to cause the interfaces between the surface of the pattern structure4030as well as the surface of the substrate4010and the bubble4050shrinking gradually, so as to achieve the bubble detached from the pattern structure4030and the substrate4010at last, as shown inFIG. 4B.

One embodiment of the bubble detaching pre-treatment process according to the present invention is to modify the substrate4010surface from hydrophobic to hydrophilic by supplying liquid chemical solution on the substrate4010surface, such as supplying liquid chemical solution forming a hydrophilic coating layer on the substrate4010surface, or supplying liquid chemical solution like Ozone solution or SCl solution (NH4OH, H2O2, H2O mixture) oxidizing the hydrophobic surface material like Silicon or Ploy Silicon layer to hydrophilic Silicon oxide layer.

One embodiment of the bubble detaching pre-treatment process according to the present invention is to supply the liquid chemical solution containing surfactant, additives or chelating agent on the substrate4010surface. The liquid chemical solution containing surfactant, additives or chelating agent is capable of increasing the wettability of the liquid chemical solution on the substrate4010surface, so as to detach the bubbles attaching on the surfaces of the patterned structures4030and the substrate4010. The chemical such as carboxyl-containing ethylendiamine tetraacetic acid (EDTA), tetracarboxyl compound-ethylenediamine tetrapropionic (EDTP) acid/salt, etc. is used as a surfactant doped in the liquid chemical solution to increase the wettability of the liquid chemical solution.

Besides, a low power ultra or mega sonic is capable of being combined with the embodiments described above to improve the efficiency of the bubble detaching. The low power ultra or mega sonic generates a minimal mechanical force to contribute to a stable bubble cavitation, so as to generate the mechanical force to detach the bubble4050from the surfaces of the patterned structures4030and the substrate4010. The low power ultra or mega sonic is capable of running on a continuous mode (non-pulse mode), and the power density may be, for example, 1 mw/cm2-15 mw/cm2. The time duration of applying the low power ultra or mega sonic with continuous mode to the cleaning liquid for detaching the bubbles from the surfaces of the patterned structure4030and the substrate4010may be, for example, 10 s-60 s. More detailed description of applying the ultra or mega sonic with continuous mode to the cleaning liquid is disclosed in patent application no. PCT/CN2008/073471, filed on Dec. 12, 2008, all of which are incorporated herein by reference. The low power ultra or mega sonic is capable of running on a pulse mode, and the power density may be, for example, 15 mw/cm2-200 mw/cm2. The time duration of applying the low power ultra or mega sonic with pulse mode to the cleaning liquid for detaching the bubbles from the surfaces of the patterned structure4030and the substrate4010may be, for example, 10 s-120 s. More detailed description of applying the ultra or mega sonic with pulse mode to the cleaning liquid is disclosed in patent application no. PCT/CN2015/079342, filed on May 20, 2015, all of which are incorporated herein by reference.

Referring toFIG. 5AtoFIG. 5C, one embodiment of the bubble detaching pre-treatment process according to the present invention is to remove impurities such as metal impurities, organic contaminations and polymer residues attached on the substrate surface.

Bubbles5050are easy to attach around the impurities5090such as metal impurities, organic contaminations and polymer residues attached on the substrate5010surface, so that the bubbles5050attaching on the surfaces of the patterned structures5030and the substrate5010have a risk to implode and damage the patterned structures5030on the substrate5010during the subsequent ultra or mega sonic cleaning process. A pre-treatment method with supplying a liquid chemical solution on the substrate5010surface contributes to remove the impurities5090such as metal impurities and polymer residues on the substrate5010surface before the ultra or mega sonic cleaning process, such as using ozone solution to oxide the surficial polymer residues, and using the high temperature (90 to 150° C.) SPM solution (H2SO4, H2O2 mixture) to carbonize the surficial polymer residues. In another embodiment, the chemical like EDTA is also used for the surface metal ion chelating, so as to remove the metal impurities.

In some case, when the impurities5090such as organic contaminations or polymer residues accumulate at the corner of the patterned structure5030, the bubble5050is easy to attach on the impurities5090due to the poor wettability of the chemical solution onto the surface of the impurities5090. It may lead to the damaging implosion on the patterned structure5030surface. Two methods are disclosed to remove the impurities5090and detach the accumulated bubbles5050. In one embodiment, a chemical solution is used to remove the impurities5090in the pre-treatment step, such as using Ozone or SCl solution to remove the organic contamination as shown inFIG. 5A. The size of the impurities5090is shrinking as the chemical solution reacting with the impurities5090, as shown inFIG. 5B. Since the impurities5090are removed from the surfaces of the patterned structure5030and the substrate5010, the wettability of the chemical solution increases to cause the bubble5050leaves from the patterned structure5030surface, as shown inFIG. 5C.

Referring toFIG. 6AtoFIG. 6C, in another embodiment according to the present invention, a low power ultra or mega sonic process is used to improve the efficiency of removal the impurities6090in the pre-treatment step, such as using Ozone or SCl solution to remove the organic contaminations as shown inFIG. 6A. Due to applying the low power ultra or mega sonic, the size of bubble6050is expanding and shrinking alternatively, so as to expose the impurities6090to the chemical solution, further reacting with the chemical solution. This process accelerates the reaction efficiency of chemical solution and the impurities6090. Since the impurities6090are removed from the patterned structure6030surface, the wettability of the chemical solution increases to cause the bubble6050leaves from the patterned structure6030surface, as shown inFIG. 6C. The low power ultra or mega sonic is capable of running on a continuous mode (non-pulse mode), and the power density may be, for example, 1 mw/cm2-15 mw/cm2. The low power ultra or mega sonic is capable of running on a pulse mode, and the power density may be, for example, 15 mw/cm2-200 mw/cm2.

FIG. 7AandFIG. 7Bshow an embodiment of bubbles being detached from the surface of patterned structures on a substrate. If a particle7090is trapped at the corner of the patterned structure7030on the substrate7010, the bubbles7052,7054,7056are easier to accumulate around the surface of the particle7090due to the particle's irregularly geographic shape. The bubbles7052,7054,7056which are attaching on the surface of the patterned structure7030and the surface of the particle7090have a risk to implode and damage the patterned structure7030. Therefore, a particle removal and bubble detaching pre-treatment process is needed before an ultra or mega sonic cleaning process.

As shown inFIG. 7AandFIG. 7Baccording to the present invention, in the pre-treatment process, the particle7090is removed so as to further detach the bubbles7052,7054,7056from the surface of the patterned structure7030and the surface of the substrate7010. A low power ultra or mega sonic can be applied to the cleaning liquid7070to remove the particle7090and detach the bubbles7052,7054,7056from the surface of the patterned structure7030and the surface of the substrate7010before the subsequent ultra or mega sonic cleaning process. The low power ultra or mega sonic generates bubble cavitation on the bubbles7052,7054,7056. The cavitation of the bubbles7052,7054,7056generates mechanical forces f1, f2, f3and the combined force F to push the particle7090outwardly, as shown inFIG. 7A. The particle7090is lifted up finally, and the cavitation force of the bubbles7052,7054,7056also generates acoustic agitation for the bubbles7052,7054,7056being detached from the surface of the patterned structure7030and the surface of the substrate7010. The low power ultra or mega sonic is capable of running on a continuous mode (non-pulse mode), and the power density may be, for example, 1 mw/cm2-15 mw/cm2. The low power ultra or mega sonic is capable of running on a pulse mode, and the power density may be, for example, 15 mw/cm2-200 mw/cm2.

FIG. 8AandFIG. 8Bshow another embodiment of bubbles being detached from the surface of patterned structures on a substrate according to the present invention. In the pre-treatment process, the particle8090is removed so as to further detach the bubbles8052,8054,8056from the surface of the patterned structure8030and the surface of the substrate8010by supplying a liquid chemical solution8070on the substrate8010surface to react or dissolve the particle8090. The example of the chemical solution is Ozone solution or SCl solution, oxidizing the polymer particles. In this process, a low power ultra or mega sonic process can also be applied to assist the chemical reaction or dissolution before the subsequent ultra or mega sonic cleaning process. The low power ultra or mega sonic generates bubble cavitation on the bubbles8052,8054,8056that surrounding the particle8090trapped at the corner of the patterned structure8030. The cavitation of bubbles8052,8054,8056generates the mechanical force f1, f2, f3and the combined force F to push the particle8090outwardly. The liquid chemical solution reaction or dissolution on the particle8090combining with the mechanical force of the low power ultra or mega sonic contributes the particle8090being lifted up finally, and the bubbles8052,8054,8056cavitation force also generate the acoustic agitation for the bubbles8052,8054,8056detaching from the surface of the patterned structure8030and the surface of the substrate8010.

The present invention discloses a substrate cleaning method, comprising the steps of:

placing a substrate on a substrate holder;

delivering cleaning liquid onto the surface of the substrate;

implementing a pre-treatment process to detach bubbles from the surface of the substrate; and

implementing an ultra or mega sonic cleaning process for cleaning the substrate.

The time duration of implementing the pre-treatment process is 5 sec. or more than 5 sec.

FIG. 9shows an embodiment of a substrate cleaning method according to the present invention. In the embodiment, an ultra or mega sonic which runs on a pulse mode is applied to implement a pre-treatment process to detach bubbles from the surface of the substrate. The ultra or mega sonic has a first power. The power density may be, for example, 15 mw/cm2-200 mw/cm2. The time duration of applying the low power ultra or mega sonic with pulse mode for detaching bubbles may be, for example, 10 s-120 s. After the bubbles are detached from the surface of the substrate, subsequently, an ultra or mega sonic which runs on a pulse mode is applied to implement an ultra or mega sonic cleaning process for cleaning the substrate. The ultra or mega sonic has a second power higher than the first power. The power density may be, for example, 0.2 w/cm2-2 w/cm2. The time duration of applying the high power ultra or mega sonic with pulse mode for cleaning the substrate may be, for example, within 600 s.

FIG. 10shows another embodiment of a substrate cleaning method according to the present invention. In the embodiment, an ultra or mega sonic which runs on a continuous mode (non-pulse mode) is applied to implement a pre-treatment process to detach bubbles from the surface of the substrate. The ultra or mega sonic has a first power. The power density may be, for example, 1 mw/cm2-15 mw/cm2. The time duration of applying the low power ultra or mega sonic with continuous mode for detaching bubbles may be, for example, 10 s-60 s. After the bubbles are detached from the surface of the substrate, subsequently, an ultra or mega sonic which runs on a pulse mode is applied to implement an ultra or mega sonic cleaning process for cleaning the substrate. The ultra or mega sonic has a second power higher than the first power. The power density may be, for example, 0.2 w/cm2-2 w/cm2. The time duration of applying the high power ultra or mega sonic with pulse mode for cleaning the substrate may be, for example, within 600 s.

FIG. 11shows another embodiment of a substrate cleaning method according to the present invention. In the embodiment, an ultra or mega sonic which runs on a pulse mode is applied to implement a pre-treatment process to detach bubbles from the surface of the substrate. The ultra or mega sonic has a first power. The power density may be, for example, 15 mw/cm2-200 mw/cm2. The time duration of applying the low power ultra or mega sonic with pulse mode for detaching bubbles may be, for example, 10 s-120 s. After the bubbles are detached from the surface of the substrate, subsequently, an ultra or mega sonic which runs on a continuous mode (non-pulse mode) is applied to implement an ultra or mega sonic cleaning process for cleaning the substrate. The ultra or mega sonic has a second power higher than the first power. The power density may be, for example, 15 mw/cm2-500 mw/cm2. The time duration t2of applying the high power ultra or mega sonic with continuous mode for cleaning the substrate may be, for example, 10 sec.-60 sec. At the t2duration, the bubble implosion or transit cavitation may happen, however since it happens above the structure, therefore the impact force generated by micro jet may not damage the patterned structure on the substrate.

FIG. 12shows another embodiment of a substrate cleaning method according to the present invention. In the embodiment, an ultra or mega sonic which runs on a continuous mode (non-pulse mode) is applied to implement a pre-treatment process to detach bubbles from the surface of the substrate. The ultra or mega sonic has a first power. The power density may be, for example, 1 mw/cm2-15 mw/cm2. The time duration of applying the low power ultra or mega sonic with continuous mode for detaching bubbles may be, for example, 5 sec.-60 sec. After the bubbles are detached from the surface of the substrate, subsequently, an ultra or mega sonic which runs on a continuous mode (non-pulse mode) is applied to implement an ultra or mega sonic cleaning process for cleaning the substrate. The ultra or mega sonic has a second power higher than the first power. The power density may be, for example, 15 mw/cm2-500 mw/cm2. The time duration of applying the high power ultra or mega sonic with continuous mode for cleaning the substrate may be, for example, 10 sec.-120 sec.

It should be recognized that the pre-treatment methods for detaching bubbles disclosed inFIG. 4AtoFIG. 8Bcan be applied in or combined with the methods disclosed inFIG. 9toFIG. 12.

Referring toFIG. 13AandFIG. 13B, a substrate cleaning apparatus according to an embodiment of the present invention is illustrated.FIG. 13Ais a cross-sectional view of the substrate cleaning apparatus that includes a substrate holder1314holding a substrate1310, a rotation driving module1316driving the substrate holder1314, and a nozzle1312delivering cleaning liquid and liquid chemical solution1370to the surface of the substrate1310. The substrate cleaning apparatus also includes an ultra or mega sonic device1303situated above the substrate1310. The ultra or mega sonic device1303further includes a piezoelectric transducer1304acoustically coupled to a resonator1308in contact with the cleaning liquid. The piezoelectric transducer1304is electrically excited to vibrate and resonator1308transmits low or high sound energy into the cleaning liquid or the liquid chemical solution. Bubble cavitation generated by the low sound energy causes bubbles being detached from the surface of the substrate1310. Bubble cavitation generated by the high sound energy causes foreign particles, i.e., contaminants, on the surface of the substrate1310to vibrate and break loose therefrom.

Referring again toFIG. 13A, the substrate cleaning apparatus also include an arm1307coupled to the ultra or mega sonic device1303for moving the ultra or mega sonic device1303in a vertical direction Z, thereby changing the liquid film thickness d. A vertical driving module1306drives vertical movement of the arm1307. Both the vertical driving module1306and the rotation driving module1316are controlled by a controller1388.

Referring toFIG. 13Bwhich is a top view of substrate cleaning apparatus illustrated inFIG. 13A, the ultra or mega sonic device1303covers only a small area of the substrate1310, which has to rotate to receive uniform sonic energy across the entire substrate1310. Although only one such ultra or mega sonic device1303is illustrated inFIGS. 13A and 13B, in other embodiments, two or more sonic devices may be employed simultaneously or intermittently. Similarly, two or more nozzles1312may be employed to deliver respectively cleaning liquid and liquid chemical solution to the surface of the substrate1310.

In some aspects of the present disclosure, rotation of the substrate holder and application of acoustic energy may be controlled by one or more controllers, for example software programmable control of the equipment. The one or more controllers may comprise one or more timers to control the timing of rotation and/or energy application.

Although the present invention has been described with respect to certain embodiments, examples, and applications, it will be apparent to those skilled in the art that various modifications and changes may be made without departing from the invention.