JP2005236106A - Method for forming photoresist pattern - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems that many liquid-drop spots (watermarks) are formed on the whole surface of a semiconductor substrate up to the end of drying after rinsing in the case of forming a photoresist pattern by using a photoresist having a high hydrophobic property in order to form a fine pattern, and defects may be generated on a ground pattern which is formed by using the photoresist pattern as a mask. <P>SOLUTION: In a drying process after the development and rinsing of the photoresist, initial overshooting (first drying process) for rotating the semiconductor substrate at a rotational frequency of 250-500rpm is performed. The semiconductor substrate is once stopped, and then rotated at a high speed to be dried (second drying process). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for forming a photoresist pattern, and more particularly, in a photolithographic process of a semiconductor manufacturing process, a method for forming a photoresist pattern in which an exposed photoresist film is sequentially developed, rinsed and dried after being applied to a semiconductor substrate. About.

  In the photolithographic process of semiconductor manufacturing equipment, a photoresist film is applied and formed on a semiconductor substrate, the circuit pattern is selectively developed after exposure, developed with a developing solution, rinsed (rinsed) with a rinsing solution, and then dried to form a photoresist pattern. Then, using this as a mask, processing such as etching of the semiconductor substrate and the insulating film or conductive film formed thereon is performed. In recent years, with the miniaturization of circuit patterns, defects at the time of forming a photoresist pattern, which has not been manifested as a problem in the past, greatly affect yield stability.

  FIG. 6 is a schematic configuration of a paddle type photoresist pattern forming apparatus described in Patent Document 1. The photoresist pattern forming apparatus 1 is connected to a semiconductor substrate 2 to be developed, a photoresist film 3 that has been applied to the semiconductor substrate 2 and exposed to light, a rotating shaft 4 disposed at a predetermined position in the apparatus, and a rotating shaft 4. A spin chuck 5 for holding the semiconductor substrate 2, a developer 6 spilled on the semiconductor substrate 2, a developer supply nozzle 7, a rinse liquid supply nozzle 8, and a development cup 9. The semiconductor substrate 2 that has been coated and exposed to the photoresist film 3 is fixed on the spin chuck 5, and the developer is dropped onto the photoresist film 3 from the developer supply nozzle 7 guided on the center of the semiconductor substrate 2. After that, the spin chuck 5 is rotated at a low speed (10 to 100 rpm) for a short time, and the developer 6 is spread over the entire surface of the photoresist film 3 and is deposited by the surface tension. Next, the rotation of the spin chuck 5 is stopped, and the photoresist film 3 is developed by holding it for a predetermined time, and then rinsed and dried.

  FIG. 7 shows a change in the number of rotations after the rinsing step of the semiconductor substrate 2 held on the spin chuck 5 when the photoresist pattern disclosed in Patent Document 1 is formed. Here, the time when the rinsing liquid from the rinsing liquid supply nozzle 8 is dropped is shown by a solid line, and the time when the rinsing liquid is not dropped is shown by a dotted line. After developing for a predetermined time, the developer in which the photoresist is dissolved is replaced with the rinse liquid by rotating the spin chuck 5 while dripping a rinse liquid such as pure water from the rinse liquid supply nozzle 8 disposed above the spin chuck 5. The semiconductor substrate 2 is rinsed (cleaned). Then, after the predetermined time has elapsed, dripping of the rinsing liquid from the rinsing liquid supply nozzle 8 is stopped, the spin chuck 5 is rotated at a high speed (about 4000 rpm) as shown by the dotted line in FIG. 6, and the semiconductor substrate 2 is dried. The Patent Document 1 discloses that the rinsing process is performed in two stages as shown in FIG. 5 for the purpose of effectively preventing adhesion of particles during formation of a resist pattern. That is, for the first few seconds, the spin chuck is rotated at a low speed of about 200 to 300 rpm so that the photoresist dissolved in the developer does not come into contact with the inner wall of the developing cup installed around the spin chuck. The first rinsing step of replacing most of the developing solution with a rinsing solution while preventing the photoresist remaining in the developing solution from rebounding from adhering to the semiconductor substrate as particles, and subsequently for a predetermined time of about 1000 to 2000 rpm There is a second rinsing step in which the spin chuck is rotated at a medium speed to completely replace the developing solution in which the photoresist is dissolved with a rinsing solution.

Further, Patent Document 2 discloses that the cleaning solution has a rapid force for the purpose of removing fine particles presumed to be undissolved resist remaining between the resist patterns after formation of the resist pattern and impurities in the developer or cleaning solution. It is described that it is effective to provide a time (access time) of at least 1 second until reaching the main rotation speed of the substrate so as not to act.
JP 2002-75834 A Japanese Patent Laid-Open No. 10-189412

  However, when forming a photoresist pattern for processing a fine pattern by the methods disclosed in Patent Documents 1 and 2, droplet marks (watermarks) are formed on the surface of the semiconductor substrate after the rinsing and until the drying is completed. Many defects were formed over the entire surface of the substrate, and defects occurred in the underlying pattern formed using this photoresist pattern as a mask. In particular, it occurred frequently when forming a fine pattern with a pitch of 0.6 μm or less. This is presumed to be due to the following reason.

  Chemically amplified resists are often used as photoresists for the formation of fine patterns in recent years. However, because of their high hydrophobicity, the rinsing liquid easily forms droplets on the resist surface, and the droplets on the surface after drying. It is easy to form a mark (watermark). This chemically amplified resist includes a base resin having a protecting group that can be removed by an acid, a photoacid generator that generates an acid when irradiated with light, a solvent that uniformly dissolves the base resin and the photoacid generator, etc. Is included. Analysis of the droplet traces (watermarks) revealed that a low molecular weight substance presumed to originate from the components contained in the chemically amplified resist was deposited. It was difficult to remove this low molecular weight substance by plasma treatment or the like. For this reason, a fine resist pattern gap or a droplet mark (watermark) formed across adjacent resist patterns leads to a pattern defect in the base.

  An object of the present invention is to provide a method of forming a photoresist pattern with a high yield by reducing the formation of droplet marks (watermarks) when forming a fine photoresist pattern.

  The method for forming a photoresist pattern of the present invention includes a step of developing a photoresist film exposed on a semiconductor substrate after application with a developer, a step of rinsing the semiconductor substrate, and a step of drying the semiconductor substrate. A method of forming a photoresist pattern, wherein the rinsing step is a step of rinsing the semiconductor substrate while supplying a rinsing liquid to the semiconductor substrate, and the drying step performed after the rinsing step is within the range of 250-500 rpm. It has a 1st drying process which rotates a board | substrate, and a 2nd drying process which rotates the said semiconductor substrate by the rotation speed larger than the said 1st drying process, It is characterized by the above-mentioned. Further, the second rotational speed is 1000 rpm or more. Here, it is preferable to perform the first drying step for 30 seconds or more. Further, the rotation of the semiconductor substrate is temporarily stopped between the first drying step and the second drying step, and the rotation stop time is preferably not less than 1 second and not more than 1 minute. Here, the rinsing liquid is supplied from a rinsing liquid supply nozzle that is detachably disposed on the semiconductor substrate, and this rinsing liquid supply nozzle moves to the outside of the semiconductor substrate while the rinsing liquid remains on the semiconductor substrate. It is preferable to make it. The photoresist pattern is a fine pattern with a pitch of 0.6 μm or less.

  As a result of diligent research to reduce the number of droplet marks (watermarks) generated in the conventional photoresist pattern forming process, the present inventor performed rinsing liquid shaking (first drying process) at a low speed. I found it effective. Further, it has been found that it is more effective to temporarily stop the rotation between the rinsing liquid low-speed rotary swing-off step (first drying step) and the subsequent high-speed rotary drying step (second drying step). The main cause of the formation of droplet marks (watermarks) on the photoresist surface is that the hydrophobicity of the photoresist is extremely high. When a highly hydrophobic photoresist is used, the rinse liquid is shaken off as before. When drying is performed at a high speed, a large number of fine droplets are generated, which tends to form droplet marks (watermarks) on the substrate surface as mist, whereas the rinse liquid is shaken off at a low speed of about 250-500 revolutions. In the case of performing the above, it is considered that the rinsing liquid does not become a fine liquid droplet but is shaken off around the substrate in a certain large liquid mass, so that it is difficult to form a liquid drop mark (watermark). By performing the drying process of the present invention, it is possible to reduce droplet marks (watermarks) without overheating to completely remove the rinsing liquid on the substrate surface, and as a result, improve the yield in a short processing process. Can do.

  Next, embodiments of the semiconductor device of the present invention will be described with reference to the drawings. In the present invention, for example, the conventional paddle type photoresist pattern forming apparatus shown in FIG. 6 can be applied as it is. In the following embodiments, an acetal-based chemically amplified resist film is formed on a surface of an 8-inch wafer as a semiconductor substrate by spin coating under the condition that the thickness is approximately 600 nm, and then pre-baked at 95 ° C. for 90 seconds and at a pitch of 300 nm. The arrayed 150 nm square via pattern was baked at 105 ° C. for 90 seconds after exposure, and then developed using tetramethylammonium oxide (TMAH) 2.38% alkaline developer under a paddle time of 60 seconds. Used as a sample substrate. Although a wafer on which no semiconductor element is formed is used here as a sample substrate, it goes without saying that the semiconductor substrate in the present invention includes a semiconductor substrate on which a semiconductor element is formed.

(First embodiment)
FIG. 1 shows a change in the number of rotations after the rinsing step of the sample substrate 2 held on the spin chuck 5 when the photoresist pattern is formed in the first embodiment. The time when the rinse liquid from the rinse liquid supply nozzle 8 is dripped is shown by a solid line as in FIG. 7, and the time when it is not dripped is shown by a dotted line. In this embodiment, the rinsing process was performed in the first process at 2000 rpm for 5 seconds after the development, and subsequently in the second process at 100 rpm for 15 seconds. At the end of the second step, the supply of the rinsing liquid was stopped and the rinsing liquid supply nozzle 8 was immediately moved out of the semiconductor substrate 2. At the end of this rinsing step, the surface of the semiconductor substrate is sufficiently wet with the rinsing liquid.

  Then, the drying process for removing the rinse liquid which remains on a semiconductor substrate was implemented. First, as a first drying step, the spin chuck 5 was rotated at a low speed for 40 seconds at 400 rpm. When the rotation is stopped at the end of the low-speed rotation, a small amount of liquid droplets remain in the peripheral portion of the semiconductor substrate, but there is no liquid droplet in the central portion of the semiconductor substrate. It was confirmed that the rinse liquid was removed from the semiconductor substrate. This is probably because the photoresist is highly hydrophobic. In order to remove rinse droplets that could not be removed in the first drying step as the second drying step in this embodiment continuously from the first drying step, it is 1000 rpm or more, and in the example of FIG. The semiconductor substrate was dried at high speed for 15 seconds.

  When the number of droplet marks (watermarks) on the semiconductor substrate processed by the above series of steps was counted with a defect inspection apparatus (KLA-2138) manufactured by KLA-Tencor, it was about 930. On the other hand, when processing is performed in the same process except that the first drying process in the first embodiment is omitted and the rinsing liquid is suddenly removed at high speed (4000 rpm), droplet traces (watermarks) ) The number was about 2900. The addition of the first drying step at low speed rotation has the effect of reducing the number of droplet marks (watermarks) to 1/3 or less. It should be noted that the droplet remaining at the end of the low-speed rotation is mainly left in a small amount in the peripheral portion of the wafer, or by increasing the access time until shifting to the high-speed rotation described in Patent Document 2, There was no particular tendency to reduce the number of watermarks.

(Second Embodiment)
FIG. 2 shows a change in the number of rotations after the rinsing step when the semiconductor substrate 2 held on the spin chuck 5 is rotated during the formation of the photoresist pattern in the second embodiment. The difference from the first embodiment shown in FIG. 1 is that the spin chuck 5 is temporarily stopped between the first drying process and the second drying process, and is stopped for 5 seconds in the example of FIG. It is. That is, the spin chuck 5 was rotated at a low speed of 400 rotations for 40 seconds, the spin chuck 5 was stopped for 5 seconds, and then the semiconductor substrate was dried by high speed rotation at 4000 rpm.

  When the number of droplet marks (watermarks) on the semiconductor substrate processed by the above series of steps is counted in the same manner as in the first embodiment, it is about 40, and the number of droplet marks (watermarks) is more prominent. Was able to be reduced. The reason for this is not clear, but in the first embodiment, the semiconductor substrate is continuously rotated at a high speed after being rotated at a low speed. Although droplet marks (watermarks) are generated, the remaining droplets are once held by providing a rotation period between the low-speed rotation and the high-speed rotation, so that it is difficult to mist at high-speed rotation. It is estimated that

(Third embodiment)
FIG. 3 shows a change in the number of rotations after the rinsing step when rotating the semiconductor substrate 2 held on the spin chuck 5 when forming the photoresist pattern in the third embodiment. The main difference from the second embodiment shown in FIG. 2 is that the rinsing liquid supply nozzle 8 is moved to the outside of the semiconductor substrate 2 while the rinsing liquid remains sufficiently on the semiconductor substrate. This is that the number of rotations of the spin chuck 5 when the nozzle is moved is further reduced. In the example of FIG. 3, the spin chuck 5 is completely stopped, but it can also be rotated at a low speed where the rinse liquid remains on the substrate. By doing so, it is possible to reduce the influence of the rinsing liquid remaining in the rinsing liquid supply nozzle 8 dripping on the semiconductor substrate due to an impact when the rinsing liquid supply nozzle 8 moves, and droplet marks (watermarks) The effect of making the occurrence of the occurrence more difficult can be expected. It is preferable to carry out the first drying step after the rinsing liquid supply nozzle 8 has moved out of the semiconductor substrate.

  The inventor examined the influence of the number of rotations of the spin chuck 5 for initial rinsing of the rinse liquid on the number of droplet marks (watermarks) generated on the semiconductor substrate after drying the semiconductor substrate. In the process of the second embodiment described above, the initial rinse of the rinsing liquid, that is, only the number of rotations in the first drying step was changed, and the number of droplet marks (watermarks) at each number of rotations was counted. . The results are shown in FIG. In FIG. 4, the vertical axis represents the number of droplet marks (watermarks) on the surface of the semiconductor substrate, and the horizontal axis represents the number of rotations for rinsing off the rinse liquid.

  In the region where the number of rotations is small, the rinse liquid cannot be sufficiently shaken from the surface of the semiconductor substrate, so the number of droplet marks (watermarks) is large, but as the number of rotations increases, the number of droplet marks (watermarks) decreases. Although there are some variations depending on the species, the number of droplet marks (watermarks) became minimal at 250-500 rpm, and the number of droplet marks (watermarks) increased as the number of rotations increased to about 1000-2000 rpm. As a result of the study by the present inventor, the increase in the number of droplet marks (watermarks) accompanying the increase in the number of rotations at 600 to 1000 rpm was particularly remarkable. As the number of rotations further increased, the number of droplet marks (watermarks) tended to decrease again, but gradually, but the number tended to saturate, and the number of droplet marks (250-500 rpm) Watermark) was never less than the number. In Patent Documents 1 and 2, since the substrate rotation after stopping the rinsing liquid supply is performed at 600 rpm or more, the number of droplet marks (watermarks) is larger than that of the present invention.

  Further, in order to examine the influence of the time of the first drying step, in the process in the second embodiment described above, the first drying step is set to 250 rpm and only the rotation time is changed, and the droplets at each rotation time are changed. The number of marks (watermarks) was counted. The results are shown in FIG. In FIG. 5, the vertical axis indicates the number of droplet marks (watermarks) on the surface of the semiconductor substrate, and the horizontal axis indicates the substrate rotation time in the first drying step with the substrate rotation speed set at 250 rpm.

  When the substrate rotation time was less than 20 seconds, the number of defects was extremely high at 10,000 or more, but decreased to 1000 or less at 30 seconds or more. In particular, a small result of 100 or less was obtained in 40-50 seconds. From this, it was found that the first drying step is preferably 30 seconds or longer, particularly 40-50 seconds.

  From the above results, it became clear that setting 250-500 rpm at the initial stage of rinsing liquid shaking off is extremely effective in reducing the number of droplet marks (watermarks). It was also found that once the rotation was stopped between the low-speed shaking process and the high-speed drying process, the number of droplet marks (watermarks) was further reduced. In the above-described embodiment, the case where the rotation stop period is set to 5 seconds or 10 seconds is shown as an example. However, as long as the inventors have studied, it is confirmed that there is an effect if there is a stop period of about 1 second. Yes. Further, even if the stop period is further extended, the same effect can be obtained. However, if the stop period is lengthened, the productivity is lowered accordingly, so that it is preferable to keep it within 1 minute, preferably within 30 seconds. The first drying step is preferably 30 seconds or longer.

  In the above embodiment, the case where the chemically amplified resist is applied as a photoresist has been described as an example. However, the present invention is not limited to the case where the chemically amplified resist is applied. Droplet marks (watermarks) are also generated when a photoresist other than a chemically amplified resist is used, and it is essentially preferable that there are few droplet marks (watermarks). In the above embodiment, an example in which the low-speed rinsing liquid swing-off step and the high-speed drying step are each performed at a constant rotational speed has been shown, but the rotational speed is gradually increased in each step without departing from the gist of the present invention. The number of rotations can be changed as appropriate, such as by decreasing or increasing the number. In the embodiment of the present invention, an example in which a series of processes of development, rinsing, and drying is performed using the paddle type semiconductor manufacturing apparatus shown in FIG. 5 is shown. Needless to say, the present invention is not limited to the paddle type semiconductor manufacturing apparatus shown in FIG.

It is a figure which shows the rotation speed change of the semiconductor substrate after the rinse process at the time of the photoresist pattern formation concerning the 1st Embodiment of this invention. It is a figure which shows the rotation speed change of the semiconductor substrate after the rinse process at the time of the photoresist pattern formation concerning the 2nd Embodiment of this invention. It is a figure which shows the rotation speed change of the semiconductor substrate after the rinse process at the time of the photoresist pattern formation concerning the 3rd Embodiment of this invention. It is a figure which shows the correlation with the rotation speed of the semiconductor substrate in the rinse liquid shaking off process (1st drying process) in this invention, and the number of droplet traces (watermark) on the surface of a semiconductor substrate. It is a figure which shows the correlation with the rotation time of the semiconductor substrate in the rinse liquid shaking off process (1st drying process) in this invention, and the number of droplet traces (watermark) on the semiconductor substrate surface. It is a schematic sectional drawing of the photoresist pattern formation apparatus which can be used for this invention and the conventional photoresist pattern formation. It is a figure which shows the rotation speed change of the semiconductor substrate after the rinse process at the time of the photoresist pattern formation concerning conventional embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoresist pattern formation apparatus 2 Semiconductor substrate 3 Photoresist film 4 Rotating shaft 5 Spin chuck 6 Developer 7 Developer supply nozzle 8 Rinse solution supply nozzle 9 Developer cup

Claims (7)

A method for forming a photoresist pattern, comprising: developing a photoresist film exposed on a semiconductor substrate after application with a developer; rinsing the semiconductor substrate; and drying the semiconductor substrate.
The rinsing step is a step of rinsing the semiconductor substrate while supplying a rinsing liquid to the semiconductor substrate,
The drying step performed after the rinsing step includes a first drying step for rotating the semiconductor substrate within a range of 250 to 500 rpm, and a second rotation for rotating the semiconductor substrate at a higher rotational speed than the first drying step. And a drying step. A method for forming a photoresist pattern, comprising: a drying step. The method for forming a photoresist pattern according to claim 1, wherein the second rotational speed is 1000 rpm or more. The method for forming a photoresist pattern according to claim 1, wherein the first drying step is performed for 30 seconds or more. 4. The method for forming a photoresist pattern according to claim 1, wherein the rotation of the semiconductor substrate is temporarily stopped between the first drying step and the second drying step. The method for forming a photoresist pattern according to claim 4, wherein the rotation stop time of the semiconductor substrate is 1 second or more and 1 minute or less. The rinsing liquid is supplied from a rinsing liquid supply nozzle that is detachably disposed above the semiconductor substrate, and the rinsing liquid supply nozzle is disposed above and outside the semiconductor substrate during a period in which the rinsing liquid remains on the semiconductor substrate. 6. The method for forming a photoresist pattern according to claim 1, wherein the photoresist pattern is moved. 7. The method for forming a photoresist pattern according to claim 1, wherein the photoresist pattern is a fine pattern having a pitch of 0.6 [mu] m or less.

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