Process for removal of post- baked photoresist layer

’ The invention relates to a device for the stripping of photoresist from semiconductor wafer and/or hybrid substrates. The invention further relates to a process for effecting such stripping.

The stripping is effected by means of a scanning technique, the energy source being light source, such as a suitable laser or other high-energy sources. The energy applied is such as to completely remove the photoresist, yet not adversely affect the base or electronic characteristics.

BACKGROUND OF THE INVENTION :

The invention relates to the semiconductor devices processing and hybrid circuits. This product has attained in recent years a very important role in electronics and especially in computer technology and the value of such products is of the order of billions of US-$ per year. One of the repeat steps during semiconductor wafer and hybrid processing is the application of a photo resist coating, which has to be removed at the end of each such step. The order of size of such wafers is about 1 to 8. The essentially complete removal of the photoresist in each production step constitutes a serious problem and is presently effected mainly by two alternative processes: one being based on a wet chemical process, the other being based on the use of plasma. The drawbacks of existing processes is in that they do not warrant complete removal of the photoresists unless quite extreme conditions are resorted to; on the other hand application of such drastic process conditions may qause damage to the wafer-substrate and/or to the components on the wafer.

During the production of such wafers, there ar^e applied photoresist coatings of the order of from 3 to about 15 coatings during the production process.

The present invention is intended to overcome the drawbacks of the existing processes based on chemical solutions and also on the use of reactive gases in a plasma generator in an oxidizing environment, where residual photoresist contamination frequently remains on some parts of the area of the wafer, and where damage occurs sometimes during plasma use, both of which result in a high rate of rejection and which increase production costs per device.

SUMMARY OF THE INVENTION :

The invention relates to a process for the essentially complete removal of photoresist during the production of semiconductor devices and hybrid circuits .

The process of the invention comprises sweeping the surface of the wafer by a high-energy beam, the energy of the beam per unit area of the wafer being above the threshold energy required for such complete removal, yet below the threshold of the energy which is apt to damage the semiconductor substrate or the components on the surface of the wafer.

The resulting ablation of the photoresist is essentially complete, and the duration of treatment for such removal is short.

The high-energy beam used may be a light beam. There can alsq be used beams of other types pf electromagnetic radiation of suitable energy per unit area.

The high-energy beam can be applied in the form of short pulses, there can also be used a continuous radiation source.

Good results were attained using a narrow elongated beam, of a length at least that of the dimension of the wafer, or swept over the entire wafer in a plurality of steps, where the wafer is sub^ jected to a sweeping scan by such beam, the duration of exposure per unit area being adequate to completely remove the photoresist, without any undesired side-effects.

Experiments were carried out with a variety wavelengths of light sources of the 150 nm to 11,000 nm range. Advantageously, pulsed lasers can be used as energy source, with pulses of the nanosecond range of duration. The laser beam can be applied either in an inert, or in a chemically reactive atmosphere. When such brief pulses are used, the light energy is absorbed by the photoresist which is thus removed־, yet as the thermal conductivity is not a good one, energy transfer to the underlying strata is limited and no adverse side effects are encountered.

The thickness of the photoresist coating is generally of the order of from about 1 to 10 microns, and usually in the 2 micron range. The energy applied depends on the thickness of the photoresist, its nature, and also on the wave-length of the applied energy beam, and its absorption by the photoresist.

The required energy is generally of the order of 10 mJ to about 2 2

1000 mJ per cm , and preferably between 50 mJ and 300 mJ per cm , in the 150 nm to 11,000 nm range.

With other energy beams, a similar energy per unit area has to be applied, one of the considerations being the absorption of the energy by the photoresist.

The process of the invention is effected in a dry manner. The wafer is located in the free atmosphere or in a suitable container, in which the atmosphere can be a controlled one.

When an inert atmosphere is desired, there can be used an environment of an inert gas or gas-mixture; there can also be used nitrogen. Thus, suitable gases are helium, argon, nitrogen or the like.

The process can be effected in a reactive atmosphere, such as that of oxygen, carbon tetrachloride vapor, nitrogen-trifluoride,etc.

It is possible to apply energy to the wafer which is treated, by external CW or by another light-source, thus decreasing the energy to be applied by the sweep of the energy beam. The energy beam can be used to sweep over the surface of the wafer, or the wafer can be moved respective the beam, so as to expose the surface of the wafer to an adequate energy per unit area for photoresist removal.

As for example, when a laser of the Excimer type is used, of a pulse duration of about 10 nanosecond, at a pulse frequency of 100 Hz, a wafer of 3x3 is scanned by a light beam of 193 nm of a width of 0.5 mm at a linear sweep-rate of 7 mm/sec. so that each square centimeter of the wafer surface is swept by, and exposed to an energy of 100 mJ/cm .

The invention further relates to devices for photo-resist removal by exposure of the surface of the wafer to a high-energy beam.

It is advantageous to concentrate the beam by suitable means to a narrow rectangle, the length of which is such as to warrant a sweep of the entire length or width of the waiter which is being swept by the energy beam.

When a light beam is used, conventional optical elements can be used to concentrate the light-beam to such narrow rectangle. As stated, there may be used a pulsed beam or a continuous one. The width of the energy beam will be generally of the order of from 0.2 mm to about 10 mm. the preferred range being from 0.3 mm to about 1 mm, the length of the beam being of the order of 10 to 200 mm, the swep being with the direction of sweep perpendicular to the long dimension of the beam. The entire area of a wafer can be swept within from 5 to 100 seconds, resulting in complete photoresist removal .

The invention is illustrated with reference to the enclosed drawings, which are of a schematical nature, not according to scale, and in which:

Fig. 1 - is an illustration of the basic concept of a device for carrying out the process of the invention;

Fig. 2 - illustrates a device for carrying out such process; Fig. 3 - illustrates photoresist removal in a reactive environment. Fig. 4 - is a:diagram illustrating the critical parameters of the process of the invention.

The principle of the device is illustrated with reference to Fig.l where a light-source 11 directs a beam of light 12 which is concentrated by optical lens 13 and mirror 14 and lens 15 to an elongated narrow beam at 16, i.e. the surface of the wafer 17, Part of the wafer 17 is shown with photoresist (18), while the other part, 19, has already been swept by the beam 16, and the photoresist removed. The beam can be swept over the surface of the wafer, or the wafer can be moved as indicated by arrow 20, respective to the stationary light beam. The two motions ♦ can be combined.

A device is illustrated in Fig.2, where the device comprises a housing 21, wherein there is provided a light-source 11, directing a light beam viaoptical element 13 and mirror 14 and lens 15, onto the surface of a wafer 17. Other wafe-s are stored before photoresist removal in cassette 21, while wafers after photoresist removal are stacked at the right in stack 22. The unit comprises means 23 for adjusting the process parameters.

The process of the invention can be effected in a reactive environment. The principle of such process is illustrated with reference to Fig.3, where light coming from a source is illustrated by arrow 31, and where optica.l element 32 is used to focus the light to an elongated rectangular beam 33, after passing through shutter 34, said beam being directed at wafer 35.

The process is being effected in a reactive environment, where the light beam is used to dissociate reactive species in gaseous (vapor) form, which resulting reactive species interact with the photoresist, the products of decomposition being removed from the chamber. The wafer can be moved respective the beam or viceversa.

The critical parameters of the process are illustrated with reference to Fig.4, which is a diagram showing energy density versus effect on the wafer/wafer components. As shown, there exist quite distinct areas, passing from left to right; photo-resist removal starts at energy threshold 41, the energy density up to 42 being without adverse effects on the wafer. The optimum range of energy density per unit area for clean photoresist removal is between and 44, the slope of line 45 being indicative of the removal rate of the photoresist.

At an energy density of at least that indicated by 46, damage to the wafer substrate and/or electronic co00“״nents starts, and 3s the eneray per unit area further increases the damage rate indicated by line 47 increases. The energy indicated on the X-axis can be that per light-beam Dulse, it can also indicate the energy applied per unit area of the wafer as this is exposed to the energy-beam.

Example 1 :

To a silicon wafer of 50 mm diameter, there was applied a photoresist layer of 1.8 micrometer thickness. After processing, this had to be removed. The removal was effected by means of a light beam of 193 nm wavelength, the light source being a pulsed Excimer laser which was operated at a pulse rate of 100 pulses per second, with a pulse duration of about 10 nanosecond.

The light beam was concentrated to a length of 75 mm by 0.5 mm, and the wafer was swept by this rectangular light beam.

__ I

The sweeping was effected at a rate of 4 mm/second.

Thus, each square centimeter of the area of the wafer was exposed to an energy of 100 mJ, which resulted in the complete removal of the photoresist without adverse effects on the wafer or the electronic components .

Example 2 :

A photoresist removal was effected in ή reactive atmosphere. The process chamber was charged with oxygen vapors,and there was used a light beam of 193 mm, of 20 mm by 8 mm which was directed at the 73 mm by 1 mm wafer. The energy beam resulted in the formation of reactive species which interacted with the photoresist, facilitating the removal of same. With a beam of 150 mJ /cm2, exposure of each square centimeter of the wafer to an energy of 110 mJ resulted in complete photoresist removal.

'ז

PROCESS FOR REMOVAL POST-BAKED PHOTORESIST LAYER

שיטה להסרה של שכבת פוטו־רזיסט אחר אפייתה

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FIELD OF THE INVENTION :

The invention relates to a device for the stripping of photoresist from semiconductor wafer and/or hybrid substrates. The invention further relates to a process for effecting such stripping.

The stripping is effected by means of a scanning technique, the energy source being light source, such as a suitable laser or other high-energy sources. The energy applied is such as to completely remove the photoresist, yet not adversely affect the base or electronic characteristics.

BACKGROUND OF THE INVENTION :

The invention relates to the semiconductor devices processing and hybrid circuits. This product has attained in recent years a very important role in electronics and especially in computer technology and the value of such products is of the order of billions of US-$ per year. One of the repeat steps during semiconductor wafer and hybrid processing is the application of a photo resist coating, which has to be removed at the end of each such step. The order of size of such wafers is about 1 to 8. The essentially complete removal of the photoresist in each production step constitutes a serious problem and is presently effected mainly by two alternative processes: one being based on a wet chemical process, the other being based on the use of plasma. The drawbacks of existing processes is in that they do not warrant complete removal of the photoresists unless quite extreme conditions are resorted to; on the other hand application of such drastic process conditions may cause damage to the wafer-substrate and/or to the components on the wafer.

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During the production of such wafers, there are applied photoresist coatings of the. order of from 3 to about 15 coatings during the production process.

The present invention is intended to overcome the drawbacks of the existing processes based on chemical solutions and also on the use of reactive gases in a plasma generator in an oxidizing environment, where residual photoresist contamination frequently remains on some parts of the area of the wafer, and where damage occurs sometimes during plasma use, both of which result in a high rate of rejection and which increase production costs per device.

SUMMARY OF THE INVENTION :

The invention relates to a process for the essentially complete removal of photoresist during the production of semiconductor devices and hybrid circuits .

The process of the invention comprises sweeping the surface of the wafer by a high-energy beam, the energy of the beam per unit area of the wafer being above the threshold energy required for such complete removal, yet below the threshold of the energy which is apt to damage the semiconductor substrate or the components on the surface of the wafer.

The resulting ablation of the photoresist is essentially complete, and the duration of treatment for such removal is short.

The high-energy beam used may be a light beam. There can alsp be used beams of other types of electromagnetic radiation of suitable energy per pnit are?.

The high-energy beam can be applied in the form of short pulses, there can also be used a continuous fc(dia(tion source.

Good results were attained using a narrow elongated beam, of a length atleast that of the dimension of the wafer, or swept over the entire wafer in a plurality of steps, where the wafer is subjected to a sweeping scan by such beam, the duration of exposure per unit area being adequate to completely remove the photoresist, without any undesired side-effects.

Experiments were carried out with a variety 'wavelengths of light sources of the 150 nm to 11,000 nm range. Advantageously, pulsed lasers can be used as energy source, with pulses of the nanosecond range of duration. The laser beam can be applied either in an inert, or in a chemically reactive atmosphere. When such brief pulses are used, the light energy is absorbed by the photoresist which is thus removed-^-yet as the thermal conductivity is not a good one, energy transfer to the underlying strata is limited and no adverse side effects are encountered.

The thickness of the photoresist coating is generally of the order of from about 1 to 10 microns, and usually in the 2 micron range. The energy applied depends on the thickness of the photoresist, its nature, and also on the wave-length of the applied energy beam, and its absorption by the photoresist.

The required energy is generally of the order of 10 mJ to about 2 2

1000 mJ per cm , and preferably between 50 mJ and 300 mJ per cm , in the 150 nm to 11,000 nm range.

With other energy beams, a similar energy per unit area has to be applied, one of the considerations being the absorption of the energy by the photoresist. -

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The process of the invention is effected in a dry manner. The wafer is located in the free atmosphere or in a suitable container, in which the atmosphere can be a controlled one.

When an inert atmosphere is desired, there can be used an environment of an inert gas or gas-mixture; there can also be used nitrogen. Thus, suitable gases are helium, argon, nitrogen or the like. &amp;#1523;

The process can be effected in a reactive atmosphere, such as that of oxygen, carbon tetrachloride vapor, nitrogen-trifluoride,etc. It is possible to apply energy to the wafer which is treated, by external CW or by another light-source, thus decreasing the energy to be applied by the sweep of the energy beam. The energy beam can be used to sweep over the surface of the wafer, or the wafer can be moved respective the beam, so as to expose the surface of the wafer to an adequate energy per unit area for photoresist removal.

As for example, when a laser of the Excimer type is used, of a pulse duration of about 10 nanosecond, at a pulse frequency of 100 Hz, a wafer of 3x3 is scanned by a light beam of 193 nm of a width of 0.5 mm at a linear sweep-rate of 7 mm/sec. so that each square centimeter of the wafer surface is swept by, and exposed to an energy of 100 mJ/cm .

The invention further relates to devices for photo-resist removal by exposure of the surface of the wafer to a high-energy beam. It is advantageous to concentrate the beam by suitable means to a narrow rectangle, the length of which is such as to warrant a sweep of the entire length or width of the waiter which is being swept by the energy beam.

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When a light beam is used, conventional optical elements can be used to concentrate the light-beam to such narrow rectangle. As stated, there may be used a pulsed beam or a continuous one. The width of the energy beam will be generally of the order of from 0.2 mm to about 10 mm. the preferred range being from 0.3 mm to about ! mm, the length of the beam being of the order of. 10 to 200 mm, the swep being with the direction of sweep perpendicular to the long dimension of the beam. The entire area of a wafer can be swept within from 5 to 100 seconds, resulting in complete photoresist removal .

The invention is illustrated with reference to the enclosed drawings, which are of a schematical nature, not according to scale, and in which:

Fig. 1 - is an illustration of the basic concept of a device for carrying out the process of the invention;

Fig. 2 - illustrates a device for carrying out such process; Fig. 3 &amp;#1470; illustrates photoresist removal in a reactive environment. Fig. 4 - is a:diagram illustrating the critical parameters of the process of the invention.

The principle of the device is illustrated with reference to Fig.l where a light-source 11 directs a beam of light 12 which is concentrated by optical lens 13 and mirror 14 and lens 15 to an elongated narrow beam at 16, i.e. the surface of the wafer 17, Part of the wafer 17 is shown with photoresist (18)» while the other part, 19, has already been swept by the beam 16, and the photoresist removed. The beam can be swept over the surface of T the wafer, or the wafer can be moved as indicated by arrqw 20/ respective to the stationary light beam. The two motions can be combined.

A device is illustrated in Fig.2, where the device comprises a housing 21, wherein there is provided a light-source 11, directing a light beam viaoptical element 13 and mirror 14 and lens 15, onto the surface of a wafer 17. Other wafe&amp;#1524;s are stored before photoresist removal in cassette 21, while wafers after photoresist removal are stacked at the right in stack 22. The unit comprises means 23 for adjusting the process parameters.

The process of the invention can be effected in a reactive environment. The principle of such process is illustrated with reference to Fig.3, where light coming from a source is illustrated by arrow 31, and where optica.1 element 32 is used to focus the light to an elongated rectangular beam 33, after passing through shutter 34, said beam being directed at wafer 35.

The process is being effected in a reactive environment, where the light beam is used to dissociate reactive species in gaseous (vapor) form, which resulting reactive species interact with the photoresist, the products of decomposition being removed from the chamber. The wafer can be moved respective the beam or viceversa.

The critical parameters of the process are illustrated with reference to Fig.4, which is a diagram showing energy density versus effect on the wafer/wafer components. As shown, there exist quite distinct areas, passing from left to right; photo-resist removal starts at energy threshold 41, the energy density up to 42 being without adverse effects on the wafer. The optimum range of energy density per unit area for clean photoresist removal is between and 44, the slope of line 45 being indicative of the removal rate of the photoresist.

At an energy density of at least that indicated by 46, damage to the wafer substrate and/or electronic co’-oonents starts, and as the enerqy per unit area further increases the damage rate indicated by line 47 increases. The energy indicated on the X-axis can be that per light-beam pulse, it can also indicate the enerqy applied per unit area of the wafer as this is exposed to the enerqy-beam.

Exampl e l_:

To a silicon wafer of 50 mm diameter, there was applied a photoresist layer of 1.8 micrometer thickness. After processing, this had to be removed. The removal was effected by means of a light beam of 193 nm wavelength, the light source being a pulsed Excimer laser which was operated at a pulse rate of 100 pulses per second, with a pulse duration of about 10 nanosecond.

The light beam was concentrated to a length of 75 mm by 0.5 mm, and the wafer was swept by this rectangular light beam.

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The sweeping was effected at a rate of 4 mm/second.

Thus, each square centimeter of the area of the wafer was exposed to an energy of 100 mJ, which resulted in the complete removal of the photoresist without adverse effects on the wafer or the electronic components .

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Example 2 :

A photoresist removal was effected in a reactive atmosphere. The process chamber was charged with oxygen vapors,and there was used a light beam of 193 mm, of 20 mm by 8 mm which was directed at the 73 mm by 1 mm wafer. The energy beam resulted in the formation of reactive species which interacted with the photoresist, facilitating the removal of same. With a beam of 150 mJ /cm2, exposure of each square centimeter of the wafer to an energy of 110 mJ resulted in complete photoresist removal.