Method of stripping a photoresist from a semiconductor substrate using dimethylacetamide or a combination of monoethanolamine and dimethylsulfoxide

In the fabrication of semiconductor devices, a method of forming a fine pattern on a semiconductor substrate includes the steps of exposing and developing a photoresist deposited on a film of a semiconductor substrate in order to remove selected portions of the photoresist, etching portions of the film left exposed when the selected portions of the photoresist are removed, and subsequently removing any of the photoresist remaining on the semiconductor substrate with dimethylacetamide, or a combination of monoethanolamine and dimethylsulfoxide. Such stripping solutions are capable of removing photoresists in the Deep-UV group as well as the conventionally used photoresists in the I-line group.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a method of manufacturing semiconductor
 devices. More particularly, the present invention relates to a process of
 stripping photoresist from a semiconductor wafer using a solution of
 dimethylacetamide or a solution of monoethanolamine and dimethylsulfoxide.
 2. Description of the Related Art
 In general, the fabricating of semiconductor devices involves the use of
 photolithography for forming a pattern on a semiconductor wafer.
 In photolithography, a photoresist deposited on the semiconductor wafer is
 selectively removed in a series of processing steps, such as an exposure
 step, a development step, etc. A pattern designed according to the desired
 characteristics of the semiconductor device is formed on the semiconductor
 wafer using the photoresist as a mask.
 Photoresists can be classified into two groups: positive photoresists and
 negative photoresists. Whether a photoresist is considered to be of a
 positive type or of a negative type depends on the region thereof which is
 removed after selected portions of the photoresist are irradiated during
 the exposure process.
 That is, the positive type of photoresist is one in which the exposed
 regions of the photoresist are removed from the semiconductor substrate.
 The negative type of photoresist is one in which the non-exposed regions
 of the photoresist are removed from the semiconductor substrate.
 On the other hand, photoresists can also be classified according to the
 wavelength at which the photoresist responds with respect to its exposure
 and development. Photoresists classified in this way include those of the
 I-line group, the G-line group, and the Deep-UV group.
 When an Hg-Arc lamp is used as the general light source in the
 semiconductor device manufacturing process, photoresists are classified in
 the I-line group, G-line and Deep-UV according to the wavelength of light
 from the spectrum of the Hg-Arc lamp. More specifically, a photoresist in
 the I-line group responds to light having a wavelength of 365 nm. A
 photoresist in the G-line group responds to light having a wavelength of
 436 nm, and a photoresist in the Deep-UV group responds to light having a
 wavelength of 248 nm.
 In a conventional semiconductor device fabrication process, a positive
 photoresist in the I-line group is normally used. That is, the regions of
 a photoresist exposed to light having a wavelength of 365 nm are
 selectively removed from the semiconductor substrate.
 However, photolithography using a positive photoresist in the I-line group
 has its limits. In particular, such a process can only form a pattern as
 small as 0.3 .mu.m. Such a process, therefore, is not suitable for
 manufacturing the highly miniaturized semiconductor devices which are now
 in demand.
 Accordingly, recent semiconductor device fabrication processes employ
 photoresists in the Deep-UV group. These photoresists can be used to form
 patterns smaller than even 0.2 .mu.m.
 However, photoresists in the Deep-UV are inferior to those in the I-line
 group in terms of their resistance to light and heat. This is because the
 constituents of the photoresists in the I-line group and the photoresists
 in the Deep-UV group, such as the polymer component, the light-reactant,
 and the solvent, are different from each other.
 In fact, photoresists in the Deep-UV group are not widely used in
 semiconductor device fabrication because no chemical has yet been
 developed which can completely remove a Deep-UV group photoresist
 remaining on a semiconductor substrate after the photolithography has been
 completed.
 SUMMARY OF THE INVENTION
 An object of the present invention, therefore, is to provide a
 semiconductor device fabrication method including a process in which a
 Deep-UV group photoresist can be completely removed from the semiconductor
 substrate.
 Another object of the present invention is to provide a semiconductor
 device fabrication method including a process which is so flexible that it
 can be used to completely remove either a Deep-UV group photoresist or an
 I-group photoresist from a semiconductor substrate.
 To achieve these and other objects and advantages, the present invention is
 characterized in that it uses only dimethylacetamide to strip any
 remaining photoresist from the semiconductor substrate after the exposure
 and development steps of the photolithography process are carried out.
 The present inventors have found that dimethylacetamide can remove either a
 positive photoresist in the Deep-UV group or a positive photoresist in the
 I-line group. The photoresist is typically formed on a film, such as an
 insulating film, a metallic film, or a multilayered-film comprising an
 insulating layer and a metallic layer.
 Preferably, the stripping process is carried out for less than 300 sec.
 while the dimethylacetamide is maintained at about 10.degree. C. to
 40.degree. C. In addition, the stripping process is preferably carried out
 by spraying the dimethylacetamide onto the photoresist.
 The method further comprises a step of baking the photoresist before the
 photoresist is exposed. The baking step is preferably carried out at a
 temperature below 200.degree. C. for less than 300 seconds.
 To also achieve the above-described and other objects and advantages,
 another embodiment of the present invention is characterized in that it
 uses a mixture of monoethanolamine and dimethylsulfoxide to strip any
 remaining photoresist from the semiconductor substrate after the exposure
 and development steps of the photolithography process are carried out.
 The mixture is preferably 20 to 80 weight % monoethanolamine with the
 remainder being the dimethylsulfoxide.
 The present inventors have found out that such a mixture of
 monoethanolamine and dimethylsulfoxide can remove either a positive or
 negative photoresist in the Deep-UV group, as well as either a positive or
 negative photoresist in the I-line group.
 The monoethanolamine and dimethylacetamide are maintained at a temperature
 of about 10.degree. C. to 40.degree. C. while they are sprayed on the
 semiconductor substrate. Preferably, the monoethanolamine and the
 dimethylsulfoxide are sprayed separately onto the photoresist where they
 mix.
 In addition to the baking step mentioned above, the process also includes a
 step of rinsing the semiconductor substrate once the photoresist has been
 removed therefrom by the monoethanolamine and the dimethylsulfoxide.
 The rinsing is preferably carried out for less than 120 sec. at a
 temperature of about 10.degree. C. to 40.degree. C. The rinsing may be
 carried out using deionized water or acetone.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The preferred embodiments of the present invention will now be described in
 detail with reference to the accompanying drawings. Before this proceeds,
 however, it is to be noted that throughout this disclosure the term
 "semiconductor substrate" is used. Such a term is to be understood as
 referring to both the substrate per se and a substrate on which a film(s)
 has been formed.
 First Embodiment
 FIG. 1 shows the sequence of steps in a first embodiment of a method of
 forming a pattern on a semiconductor substrate according to the present
 invention.
 More specifically, the method includes the steps of depositing photoresist
 on a semiconductor substrate, baking the photoresist, exposing the
 photoresist to light having a certain wavelength, removing selected
 portions of the photoresist, etching a portion of the product, e.g. a
 film, left exposed by the removal of the selected portions of the
 photoresist, and completely removing any photoresist remaining on the
 semiconductor substrate.
 The photoresist can be a positive photoresist in the I-line group, wherein
 a predetermined portion thereof is removed by light having a wavelength of
 365 nm, or a positive type of photoresist in the Deep-UV group, wherein a
 predetermined portion thereof is removed by light having a wavelength of
 248 nm.
 In either case, dimethylacetamide is used for completely removing the
 photoresist from the substrate.
 EXAMPLE 1
 In this example, a positive photoresist in the Deep-UV group (product name:
 UV III, manufacturer: SHIPLY ) is used.
 First, the photoresist is deposited over a film disposed on a semiconductor
 substrate. The film can be an insulating film, a metallic film, or
 multi-layered film including both an insulating layer and a metallic
 layer. The photoresist is deposited on the film by a spray type of
 spin-coater 10 shown in FIG. 2. In this device, a semiconductor substrate
 W is rotated while the photoresist is sprayed thereon through a nozzle 12.
 Then, the solvent component of the photoresist deposited on the
 semiconductor substrate is removed, and the photoresist is baked in order
 to stabilize the photoresist. The photoresist is baked at a temperature
 below 200.degree. C. and for less than 300 sec. In this example, the
 photoresist is baked at a temperature of 100.degree. C. for 120 sec.
 Next, selected portions of the photoresist are exposed to light having a
 wavelength of 248 nm. The photoresist can be exposed using a step-by-step
 technique or a scanning technique.
 Then, the photoresist is developed to remove the portion of the photoresist
 exposed to the light. Subsequently, the underlying film now exposed by the
 selective removal of the photoresist is etched.
 Next, a stripping process is carried out. The stripping process completely
 removes any photoresist remaining on the semiconductor substrate after the
 developing step. According to the first embodiment of the present
 invention, the stripping process is carried out by subjecting the
 remaining photoresist to dimethylacetamide at a temperature of 10 to
 40.degree. C. and for less than 300 sec. In the first example, the
 stripping process is carried out at a temperature of 25.degree. C. for 180
 sec.
 In addition, the stripping process is executed by the spray type of
 spin-coater 10 shown in FIG. 2. That is, the dimethylacetamide is sprayed
 onto the remaining photoresist from the nozzle 12 of the spin-coater 10.
 EXAMPLE 2
 In the second example, a positive photoresist in the I-line group (product
 name: THMR i3100) is used. Accordingly, the photoresist is irradiated with
 light having a wavelength of 365 nm during the exposure step. After the
 photolithography process is completed in the manner described above in
 connection with the first example, the remaining photoresist is completely
 removed with dimethylacetamide.
 In the first embodiment of the present invention, dimethylacetamide is used
 for removing the photoresist remaining on the substrate after the
 photolithography is completed. Because dimethylacetamide will remove
 photoresists in both the I-line group and the Deep-UV group, the
 semiconductor device fabrication line can manufacture various devices
 using the photoresist best suited for making the pattern of the device.
 That is, the photoresist can be selected according to the type of pattern
 to be produced.
 In addition, because the stripping step is executed by the spin-coater 10,
 the method of the present invention eliminates the standby-time required
 in the conventional method in which H.sub.2 SO.sub.4 is used to strip the
 photoresist. Accordingly, the present invention is more efficient than the
 conventional process.
 Still further, dimethylacetamide affects the underlying layer, i.e. the
 insulating, metallic or multi-layered film, less than sulfuric acid.
 Second Embodiment
 FIG. 3 shows the sequence of steps in a second embodiment of a method of
 forming a pattern on a semiconductor substrate according to the present
 invention.
 More specifically, the method includes the steps of depositing photoresist
 on a semiconductor substrate, baking the photoresist, exposing the
 photoresist to light having a certain wavelength, removing selected
 portions of the photoresist, etching a portion of the product, e.g. a
 film, left exposed by the removal of the selected portions of the
 photoresist, completely removing any photoresist remaining on the
 semiconductor substrate, and rinsing the semiconductor substrate.
 In this embodiment, the photoresist can be a positive photoresist in the
 I-line group, wherein a predetermined portion thereof is selectively
 removed by light having a wavelength of 365 nm, a positive photoresist in
 the Deep-UV group, wherein a predetermined portion thereof is selectively
 removed by light having a wavelength of 248 nm, or a negative photoresist
 in the Deep-UV group.
 In any case, a mixture of monoethanolamine and dimethylsulfoxide is used
 for completely removing the photoresist from the substrate. The mixture is
 20 to 80 weight percent monoethanolamine with the remainder being the
 dimethylsulfoxide. Preferably, the solution is 60 weight percent
 monoethanolamine and 40 weight percent dimethylsulfoxide.
 First Example
 In the first example of the second embodiment, a positive photoresist in
 the Deep-UV group (product name: UV III) is used.
 First, the photoresist is deposited over a film disposed on a semiconductor
 substrate. The film can be an insulating film, a metallic film, or
 multi-layered film including both an insulating layer and a metallic
 layer. The photoresist is deposited on the film by a spray type of
 spin-coater 10 shown in FIG. 4. In this device, a semiconductor substrate
 W is rotated while the photoresist is sprayed thereon through one of the
 nozzles 12.
 Then, the solvent component of the photoresist deposited on the
 semiconductor substrate is removed, and the photoresist is baked in order
 to stabilize the photoresist. The photoresist is baked at a temperature of
 up to 200.degree. C. and for less than 300 sec. In this example, the
 photoresist is baked at a temperature of 100.degree. C. for 120 sec.
 Next, selected portions of the photoresist are exposed to light having a
 wavelength of 248 nm. The photoresist can be exposed using a step-by-step
 technique or a scanning technique.
 Then, the photoresist is developed to remove the portion of the photoresist
 exposed to the light. Subsequently, the underlying film now exposed by the
 selective removal of the photoresist is etched.
 Next, a stripping process is carried out. The stripping process completely
 removes any photoresist remaining on the semiconductor substrate after the
 development step. According to the second embodiment of the present
 invention, the stripping process is carried out by subjecting the
 remaining photoresist to a solution of monoethanolamine and
 dimethylsulfoxide at a temperature of about 10.degree. C. to 40.degree. C.
 In this example, the solution is maintained at a temperature of 25.degree.
 C. and the stripping process is carried out for 180 sec. The solution is
 actually formed by the spin-coater 10 shown in FIG. 4. In this device, the
 monoethanolamine and the dimethylsulfoxide are sprayed onto the
 photoresist through nozzles 12, respectively.
 Next, the semiconductor substrate is rinsed. The rinsing process removes
 any of the stripping solution remaining on the semiconductor substrate and
 is developed based on the viscosity of the stripping solution. In
 addition, the rinsing process of the present invention is carried out for
 120 sec. at a temperature of 10 to 40.degree. C. In this example, the
 semiconductor substrate is rinsed for 60 sec. at a temperature of
 25.degree. C.
 In particular, the semiconductor substrate is rinsed with deionized water
 or acetone. However, ethylpyruvate, tetrahydrofurane,
 propyleneglycolmonoethylacetate, T-butyrolacetone, N-methyl-2-pyrollidone,
 N-butylacetate, or a mixture of these chemicals can be used as the rinse
 instead of deionized water or acetone.
 The rinsing process is also performed by the spin-coater 10 shown in FIG.
 4. That is, the chemical(s) used in the rinsing process are sprayed onto
 the semiconductor substrate through the nozzle(s) 12.
 Example 2
 In this example, a negative photoresist in the Deep-UV group (product name:
 TDUR-N908) is used. Accordingly, the portion thereof that is exposed to
 light is allowed to remain on the semiconductor substrate.
 All other steps are essentially the same as those described above with
 respect to the first example.
 Third Example
 In this example, a positive photoresist in the I-line group (product name:
 THMR i3100, manufacturer: TOK) is used. Accordingly, in the development
 step, the photoresist is exposed to light having a wavelength of 365.
 Again, all other steps are essentially the same as those described above
 with respect to the first example.
 In the second embodiment of the present invention, a mixture of
 monoethanolamine and dimethylsulfoxide is used for removing the
 photoresist remaining on the substrate after the photolithography is
 completed. Because a mixture of monoethanolamine and dimethylsulfoxide
 will remove positive and negative photoresists in both the I-line group
 and the Deep-UV group, the semiconductor device fabrication line can
 manufacture various devices using the photoresist best suited for making
 the pattern of the device. That is, the photoresist can be selected
 according to the type of pattern to be produced.
 In addition, because the stripping step is executed by the spin-coater
 10,the method of the present invention does not require the standby-time
 required in the conventional method in which H.sub.2 SO.sub.4 is used to
 strip the photoresist. Accordingly, the present invention is more
 efficient than the conventional process.
 Still further, a mixture of monoethanolamine and dimethylsulfoxide affects
 the underlying film less than conventional sulfuric acid.
 The production yield (%) of semiconductor devices produced according to the
 first and the second embodiments of the present invention are shown in the
 graph of FIG. 5.
 As is quite clear from this graph, using dimethylacetamide, or a mixture of
 monoethanolamine and dimethylsulfoxide to remove photoresist after
 photolithography provides better results than using sulfuric acid to do
 the same.
 The present invention, as described above, allows various types of
 photoresists to be used during the semiconductor device manufacturing
 process. Because these photoresists include those in the Deep-UV group,
 fine patterns having a size of less than 0.2 .mu.m can be produced.
 Accordingly, the present invention can be used to meet the current demand
 for miniature semiconductor devices.
 Finally, if the spin-coater 10 employs a suitable number of nozzles, e.g.
 three nozzles, the photoresist, stripping solution, and rinsing solution
 can be respectively sprayed onto the substrate without the need for
 stand-by time. Accordingly, the present invention is very efficient in
 terms of saving time.
 The stripping solutions of the present invention may be used for both
 normal photoresist removal processes and for abnormal (or "rework")
 photoresist removal processes. A normal process refers to removing
 photoresist remaining after a normal etching process. An abnormal or
 rework process refers to removing photoresist after a photoresist failure,
 exposure failure, or photoresist pattern alignment failure occurring in a
 photolithography process before the etching process. The stripping
 solutions of the present invention are especially effective in the rework
 process.
 Although the present invention has been described in detail above, various
 changes, substitutions and alterations thereto will become apparent to
 those of ordinary skill in the art. All such changes, substitutions and
 alterations are seen to be within the true spirit and scope of the
 invention as defined by the appended claims.