KR20090086873A - Method for forming photomask to suppress haze - Google Patents

Abstract

A method for forming a photo mask is provided to prevent the haze in a following exposure process by suppressing the ions on the photo mask after a cleaning process. A mask pattern is formed on a substrate(100). A foreign material generated in a mask pattern forming process is removed from the substrate and the mask pattern. A cleaning solution is sprayed on the substrate through a nozzle. The cleaning solution is made of the mixture of the hydrogen peroxide and the sulfuric acid. A surface layer(101) of the substrate and the mask pattern is etched to remove the remaining ions(330). A diluted ammonium nitrate solution(403) is sprayed on the substrate and the mask pattern. The diluted ammonium nitrate solution has the conductivity of 0.5 ms to 1.0 ms. The dilute ammonium nitrate solution has the conductivity of 0.5 mS to 1.0 mS.

Description

Method for forming photomask to suppress haze}

TECHNICAL FIELD The present invention relates to lithography technology, and more particularly, to a method of forming a photo mask that suppresses haze.

Lithographic processes are being performed to integrate semiconductor devices on wafers. The lithography process is performed by designing a layout of a circuit pattern to be formed on a wafer and fabricating a photomask that implements a mask pattern on a transparent quartz substrate that follows the layout of the designed circuit pattern. . An exposure process using the manufactured photomask is performed to pattern transfer the mask pattern to a photoresist layer on the wafer.

In this exposure process, an exposure light source having a shorter wavelength band is used to transfer a pattern having a smaller line width. As exposure light sources of shorter wavelength bands are introduced, growth of foreign matter or haze on the photomask surface is more frequently caused by relatively high exposure energy of light sources of shorter wavelength bands. Growth phenomena such as haze are caused by the presence of residual sulfuric acid, pellicles from the mask fabrication process, and emissions from the out-gassing of the storage box material during storage, and the environment of the process fab itself. It is generated by atmospheric substances due to urea. The reaction combination of these materials may be growth foreign bodies such as ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) or ammonium nitrate ((NH ₄ ) ₂ NO ₃ ).

Sulfide ions (SO ₄ ^2- ) and ammonium ions (NH ₄ ⁺ ), which induce the formation of such a growth foreign material, are etch residues induced during plasma etching after plasma etching a mask substrate on a quartz substrate. It is estimated to be generated from the cleaning liquid or chemical liquid used in the cleaning process to remove the by-products and remain on the photomask surface. These residual ions are activated and activated by an exposure light source applied during the exposure process, thereby growing into growth foreign materials such as ammonium sulfate ((NH ₄ ) ₂ SO ₄ ).

The growth foreign material or haze generated as described above lowers the transmittance of the surrounding transparent quartz substrate portion, leading to a pattern defect in which the pattern portion is formed in the portion where the actual pattern does not exist. If such a pattern defect is caused on the wafer, a bridge defect may occur where circuit patterns are undesirably connected. In order to prevent pattern defects caused by these foreign materials, many efforts have been made to suppress the generation of haze or other foreign materials in the photomask.

Since the main factor of the haze or growth foreign material is evaluated as the residue of the cleaning liquid or chemical liquid used in the cleaning process, efforts have been made to remove the cleaning residue from the photomask as much as possible. Decomposition of residual ions by, for example, introduction of a hot rinse with hot deionized water (DIW) after a cleaning process using a sulfuric acid and hydrogen peroxide mixture (SPM) or by heat-treatment. The development of a cleaning process using ozone water in combination with these methods has been proposed.

On the other hand, in order to suppress sulfide ions which are evaluated as a major cause of haze, attempts have been made to exclude the use of sulfuric acid for providing sulfide ions. However, the cleaning process using ozone water and ultraviolet (UV) irradiation, which has been proposed in place of SPM, which is considered to have excellent organic matter removal ability, is evaluated to have a limited cleaning ability compared to SPM, and thus, various contaminations that may occur during the mask manufacturing process. And it can be evaluated that it has a limit in removing the foreign matter completely. Therefore, efforts are still underway to develop new chemicals that can surpass the foreign matter removal ability of SPM.

Accordingly, efforts to lower the residual amount of sulfide ions have been made more effectively while applying SPM cleaning. For example, a heat treatment for a photomask is introduced to attempt to decompose and remove residual ions through heat treatment. Nevertheless, it is estimated that there is a limit in decomposing and removing residual sulfide ions by this heat treatment.

As a result, undesirably lowering the yield of the semiconductor device and lowering the productivity are caused by the occurrence of haze on the photomask. Therefore, in order to improve the manufacturing yield of semiconductor elements and to improve productivity, development of a method capable of suppressing the occurrence of haze in a photomask is required.

The present invention is to provide a method of forming a photomask that can suppress the generation of haze.

One aspect of the invention, forming a mask pattern on a substrate; A cleaning step of removing foreign substances caused when the mask pattern is formed; And etching the substrate and the mask pattern using a dilute ammonium nitrate (NH ₄ OH) aqueous solution to remove residual ions that penetrate into the surface during the cleaning and to remove haze. A method of forming a mask is presented.

The washing step may be performed to remove the foreign matter using a mixture of sulfuric acid and hydrogen peroxide (SPM). The washing step may involve hot rinse using deionized water (DIW) at a temperature higher than room temperature after washing with the mixture of sulfuric acid and hydrogen peroxide (SPM).

The dilute ammonium nitrate (NH ₄ OH) aqueous solution may be introduced by diluting ammonium nitrate in deionized water to have a conductivity of 0.5 mS to 1.0 mS.

The surface etching may be performed such that the etching amount is maintained at 10 kPa or less.

The surface etching may be performed such that when the mask pattern includes the phase shift layer, the change in transmittance of the phase shift layer is maintained within 0.2%, and the change in phase difference between the phase shift layer and the substrate is maintained within 1.0 °. Can be.

Mounting the cleaned substrate on a spin chuck; And spraying through the nozzle while applying ultrasonic waves to the diluted ammonium nitrate (NH ₄ OH) aqueous solution on the substrate while rotating the spin chuck. In this case, the nozzle swings on the substrate 8 to 10 times within a 19 ° angle range at a rotational speed of 5 kW per second, and the spin chuck may be rotated at 270 rpm to 330 rpm. In addition, the ultrasonic wave may be applied at the same time 1MHz frequency and 3MHz frequency. The surface etching may involve removing residual ammonia by a rinse process using high temperature deionized water at 77 ° C. to 83 ° C.

Embodiments of the present invention can provide a photomask formation method that can suppress the generation of haze.

In an embodiment of the present invention, after forming a mask pattern including a phase inversion layer on a transparent quartz substrate, a cleaning process is performed to remove foreign substances such as organic contaminants involved in the patterning process. Subsequently, using a cleaning apparatus that rotates the photomask substrate, a dilute ammonium nitrate (NH ₄ OH) aqueous solution is sprayed onto the photomask substrate to introduce surface etching for removing some thickness etching of the surface of the photomask. By surface etching, residual ions, such as sulfide ions, that penetrate or remain in the photomask surface and inside the surface in the cleaning step are removed with the removal of the surface layer. Accordingly, it is possible to suppress the cleaning residual ions such as sulfide ions from remaining on the photomask. Therefore, it is possible to effectively suppress the growth and growth of foreign matter or haze generated by the reaction of residual ions in the exposure process using a subsequent photomask.

1 to 3 are schematic views illustrating a method of forming a photomask for suppressing haze according to an embodiment of the present invention. 4 and 5 are diagrams schematically illustrating a process of performing photomask surface etching according to an embodiment of the present invention.

Referring to FIG. 1, in the photomask forming method according to an embodiment of the present invention, a phase inversion layer such as molybdenum silicon nitride (MoSiN) is formed on a transparent quartz substrate 100 as a mask layer. . Subsequently, a mask pattern is formed by patterning a mask layer by performing electron beam exposure and selective etching. In this patterning process, foreign particles (particles 310) including contaminants such as etching by-products or organic substances may be caused on the mask pattern 200 and the substrate 100.

In order to remove the foreign material 310 from the surface of the substrate 100 and the mask pattern 200, a cleaning process using the cleaning liquid 401 is performed. In this case, the cleaning solution 401 may use a mixture (SPM) of sulfuric acid (H ₂ SO ₄ ) and hydrogen peroxide (H ₂ O ₂ ). The cleaning liquid 401 may be sprayed onto the substrate 100 through a nozzle, and cleaning may be performed by the rotation of the substrate 100. In addition, when spraying the cleaning liquid 401, ultrasonic waves may be applied to the cleaning liquid 401. Ultrasonic waves are simultaneously applied to the cleaning liquid 401 at a frequency of 1 MHz and 3 MHz, and the cleaning liquid 401 to which the ultrasonic waves are applied is directly injected through the nozzle. These SPM cleanings show excellent removal of organic contaminants, but may involve the retention of sulfide ions (SO ₄ ^{2 −} ) that can cause haze generation during subsequent exposures. In order to suppress the residual of sulfide ions, after the SPM cleaning, rinse the substrate 100 by spraying hot deionized water (DIW) at a temperature higher than room temperature, for example, approximately 80 ° C. to 3 ° C. variation range. The process can be performed.

Referring to FIG. 2, residual ions (330 of FIG. 2) may penetrate into and remain on the surface layer 101 on the surface of the substrate 100 or the cleaned and rinsed mask pattern (200 of FIG. 1). In order to remove these residual ions more reliably, embodiments of the present invention introduce a fine surface etching process.

A diluted ammonium nitrate (NH ₄ OH) aqueous solution 403 is sprayed onto the surfaces of the substrate 100 and the mask pattern 200 to partially etch the surfaces of the substrate 100 and the cleaned mask pattern 200. To remove it. Accordingly, a new surface of the surface etched substrate 100 and the surface etched mask pattern 201 is revealed, and the surface layer 101 to which the residual ions 330 are adsorbed or penetrated and fixed is etched away.

At this time, the thickness (D) of the surface layer 101 to be etched is adjusted not to exceed 10Å. Accordingly, as shown in FIG. 3, a substrate 100 and a mask pattern 200 having a clean surface from which residual ions are removed are formed.

Referring to FIGS. 2 and 4, the dilute ammonium nitrate solution 403 used for surface etching is introduced by diluting ammonium nitrate (NH ₄ OH) in DI water to have a conductivity of 0.5 mS to 1.0 mS. At this time, it is very important to maintain the conductivity of the diluted aqueous ammonium nitrate solution 403 within the range of 0.5 mS to 1.0 mS. If the conductivity of the dilute ammonium nitrate aqueous solution 403 is considerably low, the surface etching rate may be lowered, which may require a lot of processing time, and it may be difficult to maintain the etching amount for the mask patterns 201 uniformly for each region. In contrast, if the conductivity of the dilute ammonium nitrate aqueous solution 403 is considerably high, it may cause a loss of phase shift value of the attenuated phase shift mask in which the mask pattern 201 is formed as a phase inversion layer. Can be.

In addition, in the embodiment of the present invention, the surface etching is performed such that the amount of surface etching is substantially maintained within a thickness of 10 kPa. This is because the penetration depth of the residual ions after the SPM cleaning does not exceed approximately 10 mV, and when the etching amount exceeds 10 mV, a disadvantage arises in that the line width (CD) change of the mask pattern 200 becomes large. In order to finely adjust the surface etching amount as described above, in the embodiment of the present invention, as shown in FIG. 4, the SPM cleaned substrate 100 is mounted on a spin chuck 510 and a spin chuck ( Rotating 510 is applied to the diluted ammonium nitrate aqueous solution 403 on the substrate 100 through a nozzle 530. In this case, a guide 511 may be installed on the spin chuck 510 to suppress the detachment of the substrate 100 during rotation.

Ultrasonic waves by the ultrasonic vibrator 531 are applied to the dilute ammonium nitrate aqueous solution 403 immediately before being injected through the nozzle 530. The diluted ammonium nitrate aqueous solution 403 is sprayed onto the substrate 100 while ultrasonic waves are applied. Ultrasonic waves are simultaneously applied to the dilute ammonium nitrate aqueous solution 403 at a frequency of 1 MHz and a frequency of 3 MHz. The surface etching speed of the substrate 100 and the mask pattern 201 can be enhanced by the resonance of the two frequencies by using the 1 MHz and 3 MHz frequencies simultaneously, and the surface cleaning action can also be promoted. In the case of the removal of impurity particles, even when these two vibration frequencies are used separately, the cleaning promoting effect can be obtained by vibration and cavitation effect of OH radical, but quartz (fused SiO) of the substrate 100 can be obtained. ₂ ) and in order to obtain relatively fast etching of the MoSiN of the mask pattern 201, it is quite effective to induce resonance of both vibration frequencies.

On the other hand, the nozzle 530 is swinged at a predetermined angle range around the swing axis 535. Referring to FIG. 5, the nozzle 530 is set to swing on the spin chuck 510 on which the substrate 100 is mounted 8 to 10 times within an angle range of 19 ° at a rotational speed of 5 ° per second. do. At this time, the spin chuck 510 is set to rotate in the range of 10% rotational speed at 300 rpm rotational speed. When the rotation speed of the spin chuck 510 is slow, there is a risk of pattern collapse of the mask pattern (201 of FIG. 4) by the ultrasonic vibration force, so that the rotation speed of 300 rpm ± 10%, for example, 270 rpm to The 330 rpm range is preferably maintained.

The number of rotational movements of the nozzle 530 may be 8 to 10 times to preserve the metrology characteristics of the mask pattern 201 and to remove residual sulfide ions through surface etching. When less than five repetitions, it is estimated that sulfide ions are likely to remain due to incomplete surface etching. In addition, when more than 10 times, the critical dimension (CD), the phase shift amount (transition shift) or the change in transmittance of the MoSiN layer may be out of the allowable range. Based on the attenuated PSM for exposure using an ArF light source, 8 to 10 repetitions were experimentally evaluated to satisfy a CD change of 10 Hz or less, a phase difference within 1.0 °, and a MoSiN layer transmittance change within 0.2%. do.

6 and 7 illustrate measurement line width wafer maps for explaining the change in line width (CD) associated with photomask surface etching according to an embodiment of the present invention. FIG. 6 illustrates distribution of line widths (CD) of the mask patterns 201 measured when the swing repetition of the nozzle (530 of FIG. 5) is set to three times during surface etching according to an exemplary embodiment of the present invention. FIG. 7 shows the distribution of the line width CD of the mask patterns 201 measured before performing surface etching to obtain the line width distribution of FIG. 6. 6 and 7, the average line width (CD) is measured at 230.8 nm in FIG. 6, and the line width variation within the tolerance range is shown in comparison with the average line width 230.6 measured in FIG. At this time, the line width uniformity of the MoSiN layer used as the mask pattern 201 is calculated to be within 3 nm of 3 sigma.

Meanwhile, after performing the surface etching according to the embodiment of the present invention, the process of rinsing the surfaces of the substrate (100 of FIG. 3) and the mask pattern 201 using deionized water may be further performed. At this time, for effective removal of residual ammonia, rinsing with high temperature deionized water of 80 (± 3) ° C, for example, high temperature deionized water of 77 ° C to 83 ° C, is performed for about 5 minutes. As a result, residual ammonia is removed on the substrate 100. Thereafter, spin dry is performed to implement the photomask.

As described above, in the embodiment of the present invention, residual sulfuric acid is effectively removed by etching sulfide ions or sulfuric acid residues, which are representative of haze or growth foreign substances, which may occur on the surface of the photomask during photolithography, and etching the surface layer itself to which residual sulfuric acid is fixed. Can be removed. Accordingly, it is possible to suppress the occurrence of haze contamination in advance during wafer exposure, and this result can lead to an increase in yield and productivity improvement of the wafer product.

1 to 3 are schematic views illustrating a method of forming a photomask for suppressing haze according to an embodiment of the present invention.

4 and 5 are diagrams schematically illustrating a process of performing photomask surface etching according to an embodiment of the present invention.

6 and 7 illustrate measurement line width wafer maps for explaining the change in line width (CD) associated with photomask surface etching according to an embodiment of the present invention.

Claims (11)

Forming a mask pattern on the substrate; A cleaning step of removing foreign substances caused when the mask pattern is formed; And Surface etching the substrate and the mask pattern using a dilute ammonium nitrate (NH ₄ OH) aqueous solution to remove the residual ions that penetrate the surface during the cleaning to remove the haze (haze) comprising a Forming method. The method of claim 1, The cleaning step is a method of forming a photomask to suppress the haze (haze) is performed to remove the foreign matter by using a mixture (SPM) of sulfuric acid and hydrogen peroxide. The method of claim 2, The washing step is a method of forming a photomask for suppressing haze accompanying hot rinse using DI water having a temperature higher than the normal temperature after washing with the mixture of sulfuric acid and hydrogen peroxide (SPM). . The method of claim 1, The dilute ammonium nitrate (NH ₄ OH) aqueous solution has a conductivity of 0.5 mS to 1.0 mS photomask formation method of inhibiting the haze (amze) is introduced by diluting ammonium nitrate in deionized water. The method of claim 1, The surface etching is a method of forming a photomask to suppress the haze (etch) is performed so that the etching amount is maintained below 10Å. The method of claim 1, The surface etching is a method of forming a photomask to suppress the haze (haze) is performed so that the change in the line width (CD) of the mask pattern is maintained below 10Å. The method of claim 1, The surface etching is performed such that when the mask pattern includes the phase shift layer, the change in transmittance of the phase shift layer is maintained within 0.2%, and the change in phase difference between the phase shift layer and the substrate is maintained within 1.0 °. A photomask formation method which suppresses haze. The method of claim 1, The surface etching is Mounting the cleaned substrate on a spin chuck; And Rotating the spin chuck and applying ultrasonic waves to the dilute ammonium nitrate (NH ₄ OH) aqueous solution on the substrate and spraying through a nozzle to suppress haze. The method of claim 8, The nozzle swings on the substrate eight to ten times within a 19 ° angle range at a rotational speed of 5 Hz per second, The spin chuck is a photomask forming method for suppressing haze (rotation) at a rotational speed of 270 rpm to 330 rpm. The method of claim 8, The ultrasonic wave is a photomask forming method for suppressing haze applied to 1MHz frequency and 3MHz frequency at the same time. The method of claim 1, The surface etching is a method of forming a photomask to suppress haze accompanying the step of removing residual ammonia by a rinse process using a high temperature deionized water of 77 ℃ to 83 ℃.

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