HK1050957B - Removal of photoresist and residue from substrate using supercritical carbon dioxide process - Google Patents

Description

Removal of photoresist and residue from a substrate using supercritical carbon dioxide process

RELATED APPLICATIONS

This application is a continuation-in-part application of co-pending U.S. application No.09/389,788, filed on 3.9.1999, which is a continuation-in-part application of co-pending U.S. application No.09/085,391, filed on 27.5.1998, which claims priority to U.S. provisional application No.601047,739, filed on 27.5.1997, all of which are incorporated herein by reference.

This application also claims priority from U.S. provisional patent application No.60/163,116, filed on.11/2/1999, U.S. provisional patent application No.60/163,120, filed on.11/2/1999, and U.S. provisional patent application No.60/199,661, filed on.4/25/2000, all of which are incorporated herein by reference.

Technical Field

The present invention relates to the field of removing photoresist and residue from a substrate. More particularly, the present invention relates to the field of removing photoresist and residue from a substrate using supercritical carbon dioxide.

Background

Semiconductor manufacturing uses photoresist in ion implantation, etching, and other processing steps. In the ion implantation step, the photoresist masks a region of the semiconductor substrate where the dopant is not implanted. In the etching step, the photoresist masks regions of the semiconductor substrate that are not etched. Examples of other processing steps include the use of photoresist as an overlying protective coating for the wafer being processed or for MEMS (micro-electro-mechanical systems) devices.

After the ion implantation step, the photoresist appears as a hard shell covering a colloidal core. The hard crust causes difficulty in photoresist removal.

After the etching step, the remaining photoresist exhibits a hardened property, which causes difficulty in photoresist removal. After the etching step, the photoresist residue mixed with the etching residue covers the sidewalls of the etching feature (feature). Depending on the type of etching step and the material being etched, there are complex removal problems with photoresist residue mixed with etch residue, since photoresist residue mixed with etch residue is typically strongly bonded to the sidewalls of the etched features.

Typically, in the prior art, the photoresist and photoresist residue are passed through a reactor at O₂Plasma ashing was performed in a plasma and then stripped in a stripper solution (stripper bath).

Fig. 1 shows an n-p-n FET (field effect transistor) structure 10 after ion implantation and before photoresist removal. The n-p-n structure 10 includes a source region 12, a gate region 14, and a drain region 16 having an isolation trench 18 that isolates the n-p-n structure 10 from adjacent electronic devices. The first photoresist 20 shields all regions except the source and drain regions 12 and 16. During ion implantation, a high energy ion source implants n-type dopants into source and drain regions 12 and 16. The high energy ion source also exposes the first photoresist 20 to n-type dopants, which creates a crust on the upper surface 22 of the first photoresist 20. In the prior art, the first photoresist 20 is removed by a prior art plasma ashing and stripping solution.

Fig. 2 shows a first via structure 30 of the prior art after RIE (reactive ion etch) etching and before photoresist and residue removal. The first via structure 30 includes a via 32 in the first SiO₂Layer 34 is etched to reach the first TiN layer 36. In the first via structure 30, the via 32 stops at the first TiN layer 36 because the first TiN layer 36 is the first SiO₂The RIE etch of layer 34 provides an etch stop. The RIE etch is complicated by the etching of the first TiN layer 36 because of the additional etch chemistry required for the first TiN layer 36; the TiN layer 36 is not etched for this particular etch. The first TiN layer 36 is located on a first Al layer 38, which is located on a first Ti layer 40. Comprising SiO with₂The first residue of the mixed photoresist residue 42 of etch residue 44 covers sidewalls 46 of via 32. The second photoresist 48 remains on the first SiO₂On the exposed surface 50 of layer 34. In the prior art, the second photoresist 48, photoresist residue 42 and SiO are removed using a prior art plasma ashing and stripping solution₂The etching residue 44.

Note that the particular layer materials and particular structures described with respect to the first via structure 30 and other thin film structures discussed herein are illustrative. Many other layer materials and other structures are often used in semiconductor fabrication.

FIG. 3 shows a second prior art via junction after RIE etching and before photoresist and residue removalAnd a mechanism 60. The second via structure 60 includes a second via 62 etched through the first SiO₂Layer 34 and first TiN layer 36 reach first Al layer 38. Device performance is improved by etching of the first TiN layer 36 because the contact resistance with the first Al layer 38 is lower than the contact resistance with the first TiN layer 36. The second via 60 also includes a first Ti layer 40. Comprising SiO with₂The first residue of the mixed photoresist residue 42 of etch residue 44 covers the second sidewall 64 of the second via 62. A second residue comprising the pre-photoresist residue 42 mixed with the TiN etch residue 66 covers the first residue. The second pre-etch 48 remains on the first SiO₂On the exposed surface 50 of layer 34. In the prior art, the second photoresist 48, the photoresist residue 42, SiO are removed using the prior art plasma ashing and stripping solution₂Etch residue 44 and TiN etch residue 66.

Note that the first type of residue (fig. 2 and 3) and the second type of residue (fig. 3) are the worst case. Depending on the particular etching method, either the first type of residue or the second type of residue may not be present.

Fig. 4 shows the metal line structure 70 after metal RIE etching and before residue removal. The metal line structure 70 includes a second TiN layer 72 on a second Al layer 74, the second Al layer 74 being on a second Ti layer 76. The second TiN layer 72, the second Al layer 74 and the second Ti layer 76 form a metal line. The second Ti layer 76 contacts the W via 78, and the W via 78 contacts the first Al layer 38. W via 78 is connected to the first SiO via through sidewall barrier 80₂The layers 34 are separated. The third residue, comprising halogen residue 82 mixed with metal etch residue 84, is located in the first SiO₂On the exposed surface 50 of layer 34. A third residue comprising halogen 82 and metal etch residue 84 is also on the exposed surface 86 of the second TiN layer 72. A fourth residue comprising a mixture of photoresist residue 42 and metal etch residue 84 covers side 88 of the metal line. The edge 90 of the fourth residue extends above the second exposed surface 86 of the second TiN layer 72. In the prior art, the photoresist 42, halogen residues 82 and metal etch residues 84 are removed using prior art plasma ashing and stripping solutions.

Fig. 5 shows a prior art dual damascene structure 100 after a dual damascene (damascone) RIE etch and before photoresist and photoresist residue removal. Dual damascene structure 100 includes dual damascene lines 102 formed over dual damascene vias 104. By a second SiO₂Layer 106 and first SiN layer 108 etch dual damascene via 102. By third SiO₂Layer 110 and second SiN layer 112 etch dual damascene via 104. The dual damascene via is etched to the underlying Cu layer 114.

In the post-photoresist and residue removal process, the exposed surfaces of the double corrugated lines and vias 102 and 104 are covered with a barrier layer, and then the double corrugated lines and vias 102 and 104 are filled with Cu.

Returning to FIG. 5, including SiO₂The fifth residue of mixed photoresist residue 42 of etch residue 44 covers line sidewalls 116 and via sidewalls 118. The sixth residue, which includes photoresist residue 42 mixed with SiN etch residue 120, covers the fifth residue. The seventh residue including the photoresist residue 42 mixed with the Cu etching residue 122 covers the sixth residue. Photoresist 48 remains on the second SiO₂On a second exposed surface of layer 106. In the prior art, the photoresist 48, the photoresist residue 42, and SiO are removed using the prior art plasma ashing and stripping solution₂Etch residue 44, SiN etch residue 120, and Cu etch residue 122.

Note that the fifth, sixth, and seventh residues are the worst case. Depending on the particular etching method, the fifth, sixth or seventh residue may not be present.

Recent advances in semiconductor technology have led to proposals to replace the second and third dielectric layers 106 and 110 of the dual damascene structure 100 with low dielectric constant materials. Replacing the second and third dielectric layers 106 and 110 with low dielectric constant materials increases the speed of the electronic device. Efforts to develop low dielectric constant materials have resulted in a first and second class of low dielectric constant materials. The first class of low dielectric constant materials is C-SiO₂Material in which C (carbon) reduces SiO₂The dielectric constant of (2). Second classThe dielectric material is a spin-on polymer, which is a highly crosslinked polymer specifically designed to provide a low dielectric constant. An example of a spin-on polymer is SILK from dow chemical. SILK is a registered trademark of Dow Chemical.

Via and line geometries are evolving towards smaller dimensions and larger depth to width ratios. As via and line geometries move to smaller dimensions and larger depth to width ratios, prior art plasma ashing and stripping solutions are becoming less effective at removing photoresist and photoresist residues. In addition, SiO is replaced by a low dielectric constant material₂The difficulty of continuous plasma ashing is improved. For C-SiO₂Material, O₂The plasma erodes C. For C-SiO₂Material, O₂The plasma may be H₂Plasma is substituted, but this reduces the overall effectiveness of plasma ashing. For spin-on polymers, especially Dow Chemical's SILK, plasma ashing is not a viable process for removing photoresist or photoresist residues, as plasma ashing erodes the spin-on polymer.

What is needed is a more efficient method of removing photoresist.

What is needed is a more efficient method of removing debris.

What is needed is a more efficient method of removing photoresist.

What is needed is a more efficient method of removing residue.

What is needed is a method of removing photoresist from a substrate in which the dimensions of the via and line geometries are small.

What is needed is a method of removing residue from a substrate in which the via and line geometries are small in size.

What is needed is a method of removing photoresist from a substrate in which the ratio of the depth to the width of the via and line geometry is large.

What is needed is a method of removing residue from a substrate in which the ratio of the depth to the width of the via and line geometry is large.

What is needed is a method of removing photoresist from a substrate, wherein the C-SiO₂Features are etched in the low dielectric constant material.

What is needed is a method of removing residue from a substrate, wherein the residue is on C-SiO₂Features are etched in the low dielectric constant material.

What is needed is a method of removing photoresist from a substrate in which features are etched on a spin-on polymer low dielectric constant material.

What is needed is a method of removing residue from a substrate in which a feature is etched on a spin-on polymer low dielectric constant material.

Summary of The Invention

The present invention is a method of removing photoresist and residue from a substrate. Typically, photoresist, or photoresist and residue, or residue, remains on the substrate after previous semiconductor processing steps, such as ion implantation or etching. The method begins by maintaining supercritical carbon dioxide, an amine, and a solvent in contact with a substrate such that the amine and the solvent at least partially dissolve the photoresist and residue.

Preferably, the amine is a secondary or tertiary amine. More preferably, the amine is a tertiary amine. More preferably, the amine is selected from the group consisting of 2- (methylamino) ethanol, PMDETA, triethanolamine, triethylamine, and mixtures thereof. Most preferably, the amine is selected from the group consisting of 2- (methylamino) ethanol, PMDETA, triethanolamine, and mixtures thereof. Preferably, the solvent is selected from the group consisting of DMSO, EC, NMP, acetylacetone, BLO, acetic acid, DMAC, PC, and mixtures thereof.

The photoresist and residue are then removed from the vicinity of the substrate. Preferably, the method continues with a rinsing step, wherein the substrate is rinsed with supercritical carbon dioxide and a rinsing agent. Preferably, the rinse agent is selected from the group consisting of water, alcohols, ketones, and mixtures thereof. More preferably, the rinse agent is a mixture of alcohol and water. Preferably, the alcohol is selected from isopropanol, ethanol and other low molecular weight alcohols. More preferably, the alcohol is ethanol.

In a first alternative embodiment, the amine and solvent are substituted with aqueous fluoride. In a second alternative embodiment, a solvent is added to the aqueous fluoride of the first alternative embodiment. In a third alternative embodiment, an amine is added to the aqueous fluoride and solvent of the second alternative embodiment.

According to another embodiment of the present invention, a method of processing a substrate includes the steps of: (a) maintaining supercritical carbon dioxide and aqueous fluoride in contact with a substrate having a silicon dioxide surface bearing a material selected from the group consisting of photoresist, photoresist residue, etch residue, and combinations thereof, such that the aqueous fluoride undercuts the silicon dioxide surface from the material, thereby causing the material to become an undercut material; (b) maintaining water and supercritical carbon dioxide in contact with the undercut material such that the undercut material separates from the silica surface, thereby causing the undercut material to become a separated material; and (c) removing the separated material from the vicinity of the substrate.

In yet another embodiment of the present invention, a method for removing a material selected from the group consisting of photoresist, photoresist residue, etch residue, and combinations thereof from a silicon dioxide surface, the method comprising the steps of: (a) maintaining supercritical carbon dioxide and aqueous fluoride in contact with the material and the silica surface such that the aqueous fluoride undercuts the silica surface from the material; (b) maintaining water and supercritical carbon dioxide in contact with the material such that the material separates from the silica surface; and (c) removing the material from the vicinity of the surface of the silicon dioxide.

Brief Description of Drawings

Figure 1 shows a prior art n-p-n structure after ion implantation and prior to photoresist removal.

Fig. 2 shows a first prior art via structure after RIE etching and before photoresist and residue removal.

Fig. 3 shows a second prior art via structure after RIE etching and before photoresist and residue removal.

Fig. 4 shows a prior art metal line structure after RIE etching and before residue removal.

Fig. 5 shows a prior art dual damascene structure after RIE etching and prior to photoresist and residue removal.

FIG. 6 is a flow chart showing the steps of a preferred method of the present invention.

Figure 7 shows a preferred processing system of the present invention.

FIG. 8 shows a preferred timeline of the present invention.

Detailed description of the preferred embodiments

The present invention is a method of removing photoresist and residue from a substrate using supercritical carbon dioxide. The residues include photoresist residues and etching residues. The substrate is typically a semiconductor wafer. In addition, the substrate is a non-wafer substrate such as a puck (puck). Photoresist is typically placed on the wafer to mask a portion of the wafer during a preceding semiconductor fabrication processing step. These previous processing steps include ion implantation and etching steps.

In the ion implantation step, the photoresist masks regions of the wafer that are not implanted with dopants, while implanting dopants into the wafer in unmasked regions. The ion implantation step forms a hardened shell on the photoresist, leaving a jelly-like core under the hardened shell.

In the etching step, the photoresist masks the wafer areas that are not etched while etching the unmasked areas. In the etching step, the photoresist and the wafer are etched, resulting in an etched part, while also producing photoresist residue and etching residue. The etching of the photoresist produces a photoresist residue. The etching of the etched features produces etch residues. The photoresist and etch residue typically cover the sidewalls of the etched features.

In some etching steps, the photoresist is not completely etched, so a portion of the photoresist remains on the wafer after the etching step. In these etching steps, the etching process hardens the remaining photoresist. In other etching steps, the photoresist is completely etched, so no photoresist remains on the wafer during such etching steps. In the latter case, only residues, which are photoresist residues and etching residues, remain on the wafer.

The present invention preferably relates to photoresist removal for geometries of 25 microns and less. In other words, the present invention preferably relates to removing I-line exposed photoresist and smaller wavelength exposed photoresist. These are UV, deep UV, and smaller geometry photoresists. In addition, the present invention relates to removing larger size photoresist.

It will be readily understood by those skilled in the art that although the present invention is described with respect to removing photoresist and residue, it may be equally applicable to removing photoresist and residue, or removing only photoresist, or removing only residue.

A preferred embodiment of the present invention is to remove photoresist and residue from a wafer using supercritical carbon dioxide, an amine and a solvent. Preferably, the amine is selected from secondary and tertiary amines. More preferably, the amine is a tertiary amine. More preferably, the amine is selected from the group consisting of 2- (methylamino) ethanol, PMDETA (pentamethyldiethylenetriamine), triethanolamine, triethylamine, and mixtures thereof. Most preferably, the amine is selected from the group consisting of 2- (methylamino) ethanol, PMDETA, triethanolamine, and mixtures thereof. Preferably, the solvent is selected from DMSO (dimethyl sulfoxide), EC (ethylene carbonate), NMP (N-methyl-2-pyrrolidone), acetylacetone, BLO (butyrolactone), acetic acid, DMAC (N, N' -dimethylacetamide), PC (propylene carbonate), and mixtures thereof. More preferably, the solvent is selected from the group consisting of DMSO, EC, NMP, acetyl acetone, BLO, glacial acetic acid, and mixtures thereof.

A preferred method of the present invention is illustrated in the block diagram of fig. 6. The preferred method 200 begins by placing a wafer having photoresist and residue on the wafer in a first process step 202 in a pressure chamber and sealing the pressure chamber. In a second process step 204, the pressure chamber is pressurized with carbon dioxide until the carbon dioxide becomes supercritical carbon dioxide (SCCO)₂). In a third step 206, the supercritical carbon dioxide carries the amine and solvent into the process chamber. In a fourth process step 208, the supercritical carbon dioxide, amine and solvent are maintained in contact with the wafer until the photoresist and residue are removed from the wafer. In a fourth process step 208, the amine and solvent at least partially dissolve the photoresist and residue. In a fifth process step 210, the pressure chamber is partially vented. In a sixth process step 212, the wafer is rinsed. In a seventh process step 214, the preferred method 200 ends with depressurizing the pressure chamber and removing the wafer.

A preferred supercritical processing system of the present invention is shown in fig. 7. The preferred supercritical processing system 220 includes a carbon dioxide supply vessel 222, a carbon dioxide pump 224, a pressure chamber 226, a chemical supply vessel 228, a circulation pump 230, and an exhaust gas collection vessel 234. The carbon dioxide supply vessel 222 is connected to the pressure chamber 226 by a carbon dioxide pump 224 and a carbon dioxide conduit 236. The carbon dioxide conduit 236 includes a carbon dioxide heater 238 located between the carbon dioxide pump 224 and the pressure chamber 226. The pressure chamber 226 includes a pressure chamber heater 240. The circulation pump 230 is located on a circulation conduit 242 that is connected to the pressure chamber 226 at a circulation inlet 244 and a circulation outlet 246. The chemical supply container 228 is connected to the circulation line 242 through a chemical supply line 248, and the chemical supply line 248 includes a first injection pump 249. The rinse supply container 250 is connected to the circulation line 242 by a rinse supply line 252, the rinse supply line 252 including a second injection pump 253. The exhaust collection vessel 234 is connected to the pressure chamber 226 by an exhaust conduit 254. Those skilled in the art will readily appreciate that the preferred supercritical processing system 220 includes valves, control electronics, filters, and equipment connections, as are typical in supercritical fluid processing systems.

It is easily understood by those skilled in the art that an additional chemical supply container may be connected to the first injection pump 249 or an additional chemical supply container and an additional chemical injection pump may be connected to the circulation pipe 242.

Referring to fig. 6 and 7, the preferred method 200 is performed beginning with a first process step 202 in which a wafer with photoresist or residue or both is placed in a wafer cavity 256 of a pressure chamber 226 and the pressure chamber 226 is then sealed. In a second process step 204, the pressure chamber 226 is pressurized with carbon dioxide from the carbon dioxide supply vessel 222 by the carbon dioxide pump 224. During the second step 204, the carbon dioxide is heated by carbon dioxide heater 238 while the pressure chamber is heated by pressure chamber heater 240 to ensure that the temperature of the carbon dioxide within pressure chamber 226 is above the critical temperature. The critical temperature of carbon dioxide is 31 ℃. Preferably, the temperature of the carbon dioxide within the pressure chamber 226 is between 45 ℃ and 75 ℃. Additionally, the temperature of the carbon dioxide within the pressure chamber 226 is maintained at from 31 ℃ to about 100 ℃.

Upon reaching the initial supercritical conditions, the first injection pump 249 pumps the amine and solvent from the chemical supply vessel 228 through the recycle line 242 into the pressure chamber 226 while the carbon dioxide pump further pressurizes the supercritical carbon dioxide in the third process step 206. Once the desired amount of amine and solvent has been fed into the pressure chamber 226 and the desired supercritical conditions are reached, the carbon dioxide pump 224 stops pressurizing the pressure chamber 226, the first injection pump 249 stops feeding the amine and solvent into the pressure chamber 226, and the circulation pump 230 begins circulating the supercritical carbon dioxide, amine, and solvent in the fourth step 208. The supercritical carbon dioxide maintains the amine and solvent in contact with the wafer by circulating the supercritical carbon dioxide, amine, and solvent. In addition, the fluid flow enhances removal of photoresist and residue on the wafer by circulating supercritical carbon dioxide, amine and solvent.

Preferably, in the fourth process step 208, the wafer is held stationary in the pressure chamber 226. Additionally, during the fourth process step 208, the wafer is rotated within the pressure chamber 226.

After the photoresist and residue have been removed from the wafer, the pressure chamber 226 is partially depressurized by venting portions of the supercritical carbon dioxide, amine, solvent, removed photoresist and removed residue into an exhaust collection vessel 234 to restore the conditions in the pressure chamber 226 to near the initial supercritical conditions in the fifth process step 210.

In a sixth process step 212, a second injection pump 253 pumps rinse agent from the rinse agent supply tank 250 through the circulation line into the pressure chamber 226 while the carbon dioxide pump 224 pressurizes the pressure chamber 226 to near the desired supercritical conditions, and the circulation pump 230 then circulates the supercritical carbon dioxide and rinse agent to rinse the wafer. Preferably, the rinse is selected from the group consisting of water, alcohol, acetone and mixtures thereof, more preferably, the rinse is a mixture of alcohol and water. Preferably, the alcohol is selected from isopropanol, ethanol and other low molecular weight alcohols. More preferably, the alcohol is selected from isopropanol and ethanol. Most preferably, the alcohol is ethanol.

Preferably, the wafer remains stationary in the pressure chamber 226 during the sixth process step 212. Additionally, during the sixth process step 212, the wafer is rotated within the pressure chamber 226.

In a seventh process step 214, the pressure chamber 226 is depressurized by venting the pressure chamber 226 into the waste gas collection container 234, and the wafer is finally removed from the pressure chamber 226.

A preferred timeline of the present invention is diagrammatically shown in fig. 8. The preferred timeline 260 represents the preferred method 200 as a function of time and also represents the pressure 262 as a function of time. Those skilled in the art will readily appreciate that the time axes in fig. 8 are merely illustrative and do not represent relative time periods on a scale. Of course, it is desirable that all time should be minimized in order to achieve an economically efficient process.

At an initial time t₀Previously, in a first process step 202, a wafer is placed within the pressure chamber 226 and the pressure chamber is sealed. From an initial time t₀Through a first time t₁To a second time t₂In a second step 204, the pressure chamber 226 is pressurized. At a first time t₁The pressure chamber reaches the critical pressure Pc. Critical pressure P of supercritical carbon dioxide_cIs 1,070 psi. Preferably, in the third process step 206, at a first time t₁And a second time t₂In between, the amine and solvent are injected into the pressure chamber 226. Preferably, the injection of amine and solvent is initiated at about 1100-. In addition, at a second time t₂Around or at a second time t₂Thereafter, the amine and solvent are injected into the pressure chamber. The pressure chamber is at a second time t₂To an operating pressure P_op. Preferably, the operating pressure P_opAbout 2,800 psi. Alternatively, the operating pressure P_op1,070psi to about 6,000 psi.

The preferred timeline 260 continues in the fourth step 208 with the supercritical carbon dioxide, amine, and solvent being maintained in contact with the wafer until the photoresist and residue are removed from the wafer, which is done at a second time t₂To a third time t₃In the meantime. In a fifth step 210, the pressure chamber 226 is at a third time t₃To a fourth time t₄And partially exhausting. Preferably, the pressure is controlled during the first venting from the operating pressure P_opLowered to 1,100-_opThis can be done by reducing to 1,100-1,200psi during the second exhaust. Additionally, pressurized refilling and a second venting are not performed as part of the fifth process step 210. Additionally, additional recharging and venting are performed as part of the fifth process step 210, wherein one or more of the vents may be a full vent.

The preferred timeline 260 continues at a sixth step 212 from a fourth time t₄After the fifth timet₅To a sixth time t₆The wafer is rinsed. The sixth process step 212 begins with a second pressurized refill during which the rinse is preferably from a fourth time t₄To a fifth time t₅Into the pressure chamber 226. In a seventh process step 214, the pressure chamber 226 has started from a sixth time t₆To a seventh time t₇And (5) exhausting. Preferably, this is accomplished by reducing the operating pressure to about 1,100-_opAnd finally reduced to atmospheric pressure in the final exhaust. Additionally, a third venting and a third pressurized refilling are not performed as part of the seventh process step 214. Additionally, additional venting and pressurized refilling are performed as part of the seventh process step 210.

The first alternative embodiment of the present invention adds aqueous fluoride to the preferred embodiment. In a first alternative embodiment, supercritical carbon dioxide, an amine, a solvent, and an aqueous fluoride remove photoresist and residue. Preferably, the aqueous fluoride is selected from fluoride bases and fluoride acids. More preferably, the aqueous fluoride is selected from aqueous ammonium fluoride (aqueous NH)₄F) And aqueous hydrofluoric acid (HF).

In the presence of silicon dioxide (SiO)₂) The first alternative embodiment is useful when the surface is to remove at least a portion of the photoresist or a portion of the residue. Aqueous fluoride by slightly etching SiO₂Surface undercutting of SiO from photoresists and residues₂A surface. Although aqueous fluoride from SiO of the wafer₂Surface removal of photoresist and residue is useful, but aqueous fluoride cannot be used when the wafer contains an exposed aluminum layer. This is because the aqueous fluoride rapidly etches the exposed aluminum layer.

A second alternative embodiment of the invention adds additional water to the first alternative embodiment. The additional water enhances the effect of the first embodiment because the photoresist is hydrophilic, while the SiO₂The surface is hydrophobic. Thus, additional water is used for photolithographyGlue and SiO₂And (5) separating the surfaces.

A third alternative embodiment of the invention uses supercritical carbon dioxide and aqueous fluoride to remove photoresist and residue. In a third alternative embodiment, no amine and no solvent are used.

A fourth alternative embodiment of the invention adds additional water to the supercritical carbon dioxide and aqueous fluoride.

Fifth alternative embodiment of the invention to the third alternative embodiment a solvent is added.

In a first alternative timeline, the fourth process step 208 is performed at an initial cleaning pressure and a final cleaning pressure. Preferably, the initial purge pressure is about 1,100-. At the initial pressure, a first solubility of certain chemicals is less than a second solubility at the final cleaning pressure. During the initial cleaning phase, which is performed at the initial cleaning pressure, the less soluble chemicals condense on the wafer. This provides a greater concentration of low solubility chemicals on the photoresist and residue, thus enhancing the separation of the photoresist and residue from the wafer. During the final cleaning phase, which is performed at the final cleaning pressure, the low solubility chemistry is no longer or less condensed on the wafer, thus reducing the concentration of the low solubility chemistry on the wafer when the fourth process step 208 is expected to be completed.

In a second alternative timeline of the present invention, a second flush is performed after the first flush is performed.

Detailed description of the preferred embodiments

The first to seventh specific embodiments of the present invention are discussed below. Each of the first through seventh embodiments is an overview of the specific chemistry and specific methodology used in a laboratory system, similar to the preferred supercritical processing system 220. The laboratory system is used to remove photoresist, or remove photoresist and residue, or remove residue from a test wafer. The laboratory system is characterized by a total internal volume of about 1.8 liters for the pressure chamber 226, the circulation pump 230 and the circulation conduit 242. The first through seventh embodiments, which are part of the concept validation feasibility study, are intended to illustrate the feasibility of the present invention for semiconductor fabrication. Before the present invention is introduced in semiconductor manufacturing, it is envisioned that further process modifications may be made.

First embodiment

In a first embodiment, the SiO formed in the previous via etching step₂And removing the photoresist and the residues in the through hole structure, wherein the etching step is finished when the aluminum etching endpoint is reached. The specific chemicals used were as follows: 2 ml of 2-methylaminoethanol (amine), 20 ml of DMSO (first component of solvent), and 20 ml of EC (second component of solvent). The pressure chamber was maintained at 50 ℃. The amine and solvent were cycled at 2,800psi for 5 minutes. Two partial vents and one full vent were used between the removal and rinse steps, where the pressure was reduced from 2,700psi to 1,100psi for the partial vent and from 2,700psi to atmospheric pressure for the full vent. The rinse agent for the rinse step was 56 ml of acetone. The rinse and supercritical carbon dioxide were circulated for 5 minutes. A partial degassing is carried out before a complete degassing after the rinsing step.

After removing the photoresist and residue in the first embodiment, a first SEM photograph was taken. The first SEM picture shows the removal of photoresist and residue in the first embodiment.

Second embodiment

In a second embodiment, residues, including photoresist residues and etch residues, are removed from the metal line structures formed in the previous metal line etching step, wherein the etching step ends when the oxide etch endpoint is reached. (test wafers according to the second embodiment are provided by Lucent Technologies). The specific chemicals used were as follows: 1.5 ml PMDETA (amine), 7.5 ml NMP (first component of solvent) and 6 ml acetylacetone (second component of solvent). The pressure chamber was maintained at 50 ℃. The amine and solvent were cycled at 2,800psi for 2 minutes. One partial vent and one full vent were used between the removal and rinse steps. The rinse agent for the rinsing step was 20 ml of a mixture of 80% ethanol and 20% water by volume. The rinse and supercritical carbon dioxide were cycled for 1 minute. Complete venting is performed after the rinsing step.

A second SEM photograph was taken before the residue was removed in the second embodiment. The second SEM picture showed residue on the sidewalls of the metal line, indicated a skirt where the residue protruded above the metal line, and indicated residue remaining on the top of the metal line. Third and fourth SEM photographs were taken after the residue was removed in the second embodiment. The third and fourth SEM pictures show that the residue was removed in the second embodiment.

Third embodiment

In a third embodiment, the photoresist is removed from the wafer after the medium dose ion implantation. The specific chemicals used were as follows: 0.15 ml of 24 vol% aqueous ammonium fluoride (aqueous fluoride), 20 ml of BLO (first component of solvent), 20 ml of DMSO (second component of solvent), 0.15 ml of glacial acetic acid (third component of solvent), and 1 ml of additional water. The pressure chamber was maintained at 70 ℃. The aqueous fluoride and solvent were circulated at 1,250psi for 2 minutes, and then the pressure chamber was pressurized to 2,800 psi. Two partial vents and one full vent were used between the removal and rinse steps, where the pressure was reduced to 1,100psi at 2,700psi for the partial vent and from 2,700psi to atmospheric pressure for the full vent. The rinse used in the rinse step was 20 ml of a mixture of 80% ethanol and 20% water. The rinse and supercritical carbon dioxide were cycled for 1 minute. A partial degassing is carried out before a complete degassing after the rinsing step.

Previous and subsequent XPS (x-ray photoelectron spectroscopy) experiments showed that the photoresist was removed in the third embodiment.

Fourth embodiment

In a fourth embodiment, the photoresist is removed from the wafer after the high dose ion implantation. The specific chemicals used were as follows: 0.22 ml of 24% by volume aqueous ammonium fluoride (aqueous fluoride), 20 ml of DMSO (first component of the solvent), 20 ml of EC (second component of the solvent) and 2 ml of additional water. The pressure chamber was maintained at 70 ℃. The aqueous fluoride and solvent were circulated at 2,800psi for 2 minutes. Two partial vents were employed between the removal and rinse steps, where the pressure was reduced from 2,700psi to 1,100psi for the partial vents, and from 2,700psi to atmospheric pressure in the full vents. The rinse used in the rinse step was 20 ml of a mixture of 80% ethanol and 20% water. The rinse and supercritical carbon dioxide were cycled for 1 minute. A partial degassing is carried out before a complete degassing after the rinsing step.

Previous and subsequent XPS experiments showed that the photoresist was removed in the fourth embodiment.

Fifth embodiment

In a fifth embodiment, the SiO formed from the previous via etching step₂The via structure removes the photoresist, wherein the etching step ends when the TiN etch endpoint is reached. The specific chemicals used were as follows: 0.15 ml of 24% by volume aqueous ammonium fluoride (aqueous fluoride) and 8 ml of additional water. The pressure chamber was maintained at 50 ℃. The aqueous fluoride and additional water were circulated at 1,500psi for 2 minutes. Two partial vents and one full vent were used between the removal step and the first rinse step, wherein the pressure was reduced from 1,500psi to 1,050psi for the partial vents and from 1,500 to atmospheric pressure in the full vents. The rinse agent in the first rinse step was 12 ml of water. In the first rinse step, the rinse agent and supercritical carbon dioxide are circulated at 1,500psi for 1 minute, followed by raising the pressure to 2,800 psi. Between the first rinsing step and the second rinsing stepTwo partial exhausts and one full exhaust, where the pressure is reduced from 2,800psi to 1,100psi for the partial exhausts and from 2,800psi to atmospheric pressure in the full exhausts. The second rinse was 20 ml of methanol. In the second rinsing step, the rinsing agent and supercritical carbon dioxide were circulated at 2,800psi for 1 minute. A partial purge is performed before a full purge after the second rinse step is performed.

Before removing the photoresist in the fifth embodiment, a fifth SEM photograph was taken. The fifth SEM photograph shows that in SiO₂Photoresist over the via structure and TiN etch endpoint at the via bottom. After the photoresist was removed in the fifth embodiment, a sixth SEM was taken. The sixth SEM photograph shows that the photoresist was removed in the fifth embodiment.

Sixth embodiment

In a sixth embodiment, the SiO formed in the previous via etching step is removed₂And removing the photoresist from the through hole structure. The specific chemicals used were as follows: 1.5 ml of 24% by volume aqueous ammonium fluoride (aqueous fluoride) and 8 ml of DMSO (solvent) and 4 ml of additional water. The pressure chamber was maintained at 50 ℃. The aqueous fluoride, solvent and additional water were cycled at 2,800psi for 2 minutes. A partial bleed and a full bleed are used between the removal step and the rinse step. The rinse was 20 ml of a mixture of 80% ethanol and 20% water. The rinse and supercritical carbon dioxide were circulated at 2,700psi for 1 minute. A partial degassing is carried out before a complete degassing after the rinsing step.

After the photoresist was removed in the sixth embodiment, a seventh SEM photograph was taken. The seventh SEM photograph shows that the photoresist was removed in the sixth embodiment.

Seventh embodiment

In a seventh embodiment, the C-SiO formed from the previous via etching step₂In the corrugated structureAnd removing the photoresist and the residues. The specific chemicals used were as follows: 0.15 ml of 24% by volume aqueous ammonium fluoride (aqueous fluoride), 20 ml of BLO (first component of solvent), 20 ml of DMSO (second component of solvent), 0.15 ml of glacial acetic acid (third component of solvent) and 1 ml of additional water. The pressure chamber was maintained at 70 ℃. The aqueous fluoride, solvent and additional water were cycled at 2,800psi for 2 minutes. Two partial evacuations and one full evacuations were used between the removal step and the rinse step. The rinse used in the rinse step was 20 ml of 50% ethanol and 50% water. The rinse and supercritical carbon dioxide were circulated at 2,700psi for 1 minute. A partial degassing is carried out before a complete degassing after the rinsing step.

After the photoresist and residue removal in the seventh embodiment, an eighth SEM photograph was taken. The eighth SEM photograph shows that in the seventh embodiment, the photoresist and the residue were removed.

It will be readily appreciated by those skilled in the art that other various modifications could be made to the preferred embodiment without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (34)

1. A method of processing a substrate, comprising the steps of:

a. maintaining supercritical carbon dioxide and aqueous fluoride in contact with a substrate having a silicon dioxide surface bearing a material selected from the group consisting of photoresist, photoresist residue, etch residue, and combinations thereof, such that the aqueous fluoride undercuts the silicon dioxide surface from the material, thereby causing the material to become an undercut material;

b. maintaining water and supercritical carbon dioxide in contact with the undercut material such that the undercut material separates from the silica surface, thereby causing the undercut material to become a separated material; and

c. the separated material is removed from the vicinity of the substrate.

2. The method of claim 1, wherein the aqueous fluoride is selected from the group consisting of aqueous ammonium fluoride, hydrofluoric acid, and mixtures thereof.

3. The method of claim 2, wherein the aqueous fluoride is aqueous ammonium fluoride.

4. The method of claim 1, wherein the step of removing the separated material from the vicinity of the substrate comprises flowing supercritical carbon dioxide over the substrate.

5. The method of claim 1, further comprising the step of at least partially dissolving the undercut material with a solvent.

6. The method of claim 5, wherein the solvent is selected from the group consisting of BLO, DMSO, acetic acid, EC, DMAC, NMP, and mixtures thereof.

7. The method of claim 6, wherein the solvent is selected from the group consisting of BLO, DMSO, acetic acid, EC, and mixtures thereof.

8. The method of claim 7, wherein the solvent is BLO.

9. The method of claim 1, further comprising the step of at least partially dissolving the material to be separated with a solvent.

10. The method of claim 9, wherein the solvent is selected from the group consisting of BLO, DMSO, acetic acid, EC, DMAC, NMP, and mixtures thereof.

11. The method of claim 10, wherein the solvent is selected from the group consisting of BLO, DMSO, acetic acid, EC, and mixtures thereof.

12. The method of claim 11, wherein the solvent is BLO.

13. The method of claim 1, further comprising the step of rinsing the substrate with supercritical carbon dioxide and a rinse agent.

14. The method of claim 13, wherein the rinse comprises water.

15. The method of claim 13, wherein the rinse agent comprises an alcohol.

16. The method of claim 15, wherein the alcohol comprises ethanol.

17. The method of claim 13, wherein the rinse agent comprises acetone.

18. The method of claim 1, wherein the substrate comprises a low dielectric constant material.

19. The method of claim 18, wherein the low dielectric constant material comprises a spin-on polymer.

20. The method of claim 18, wherein the low dielectric constant material comprises C-SiO₂A material.

21. A method for removing material selected from the group consisting of photoresist, photoresist residue, etch residue, and combinations thereof from a silicon dioxide surface, the method comprising the steps of:

a. maintaining supercritical carbon dioxide and aqueous fluoride in contact with the material and the silica surface such that the aqueous fluoride undercuts the silica surface from the material;

b. maintaining water and supercritical carbon dioxide in contact with the material such that the material separates from the silica surface; and

c. the material is removed from the vicinity of the silicon dioxide surface.

22. A method of processing a substrate, comprising the steps of:

a. maintaining supercritical carbon dioxide, an amine and a solvent in contact with a material on a surface of a substrate, the material selected from the group consisting of a photoresist, a photoresist residue, an etch residue and mixtures thereof, by circulating the supercritical carbon dioxide such that the amine and the solvent at least partially dissolve the material; and

b. removing the material from the vicinity of the substrate.

23. The method of claim 22, wherein the amine comprises a secondary amine.

24. The method of claim 22, wherein the amine comprises a tertiary amine.

25. The method of claim 24, wherein the tertiary amine is selected from the group consisting of 2-methylaminoethanol, PMDETA, triethanolamine, triethylamine, and mixtures thereof.

26. The method of claim 25, wherein the amine is selected from the group consisting of 2-methylaminoethanol, PMDETA, triethanolamine, and mixtures thereof.

27. The method of claim 22, wherein the solvent is selected from the group consisting of DMSO, EC, NMP, acetyl acetone, BLO, acetic acid, DMAC, PC, and mixtures thereof.

28. The method of claim 22, wherein the amine is selected from the group consisting of secondary amines, tertiary amines, diisopropylamines, triisopropylamines, diglycolamine, and mixtures thereof.

29. The method of claim 22, further comprising the step of rinsing the substrate with supercritical carbon dioxide and a rinse agent.

30. The method of claim 29, wherein the rinse comprises water.

31. The method of claim 29, wherein the rinse agent comprises an alcohol.

32. The method of claim 31, wherein the alcohol comprises ethanol.

33. The method of claim 29, wherein the rinse agent comprises acetone.

34. A method of processing a substrate, comprising the steps of:

a. maintaining supercritical carbon dioxide, a tertiary amine, and a solvent in contact with a material on the surface of the substrate selected from the group consisting of photoresist, photoresist residue, etch residue, and mixtures thereof by circulating supercritical carbon dioxide such that the material is at least partially dissolved; and

b. removing the material from the vicinity of the substrate.