JP2901005B2 - Pattern formation method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pattern forming method useful for manufacturing a semiconductor device and the like, and is particularly suitable for a lithography technique combining an electron beam drawing method and a multilayer resist method. The present invention relates to a pattern forming method.

(Prior Art) With the increasing integration of semiconductor devices, a technology capable of forming a finer resist pattern is required. A multilayer resist method in which a lower resist is patterned with an upper layer pattern obtained by electron beam drawing using a multilayer resist having a resist having a property sensitive to electron beams (hereinafter abbreviated as electron beam resist). The lithography technique combined with the electron beam lithography has been attracting attention as an effective pattern forming method that can satisfy the above-mentioned requirements. However, when electron beam lithography is performed on the multilayer structure, the lower resist is charged by incident electrons when the thickness of the lower resist is large,
As a result, the deflection accuracy of the electron beam is reduced due to the effect of the electric field, and the drawing position is shifted from a desired position. As a result, a pattern shift occurs. In addition, regardless of the thickness of the lower resist, the workpiece and the substrate below the lower resist are also charged by the incident electrons, so that the pattern is displaced. Therefore, various methods have conventionally been taken to solve these problems.

First, as a method of preventing charging of a compound or the like existing under a multilayer resist structure, a conductive pin is brought into contact with the compound when the compound has a low resistance. FIGS. 10 (A) and (B) are cross-sectional views schematically showing the situation. FIG. 10 (A) is an explanatory view in the case where a two-layer resist is used, and FIG. () Is an explanatory diagram in the case where a three-layer resist is used. In both figures
11 is a silicon substrate, 13 is a low-resistance compound, 15 is a lower resist, 17 is an upper resist made of electron beam resist,
Reference numeral 19 denotes a grounding conduction pin. In FIG. 10 (B), reference numeral 15a denotes an intermediate layer in the three-layer resist.

However, this method using conductive pins cannot provide an effective effect when the workpiece is a high-resistance one or an insulator. Therefore, in order to improve this, as shown in FIG. 11, it is conceivable to remove a part of the high-resistance or insulating compound 21 and bring the conduction pin 19 into contact with the silicon substrate 11; If a part of the substrate is removed with a chemical solution, the process becomes complicated, and if it is performed with a laser or electric discharge, there is a fear of generation of dust and poor grounding due to surface roughness of an exposed portion of the substrate, which is not practical.

Further, the method using conductive pins has little effect on preventing the lower layer resist from being charged.

Therefore, for example, the following methods (1) to (4) have been proposed as countermeasures.

<Method> The method was to increase the conductivity of the upper resist surface. Specific examples include the following.

The surface of the resist layer for the electron beam is formed by cooling the workpiece after the application of the resist for the electron beam to room temperature after cooling, or by applying an organic solvent on the resist layer for the electron beam and vaporizing the organic solvent. A method of increasing the conductivity by forming a water layer on the surface (Japanese Patent Application Laid-Open No. Sho 60-74521).

A method in which the surface of the electron beam resist layer is modified with an inert gas plasma or an inert gas ion beam to increase conductivity (Japanese Patent Application Laid-Open No. 60-53023).

<Method> The method used a conductive layer as an intermediate layer of a three-layer resist. As a specific example, for example, JP-A-57-10
There was one disclosed in Japanese Patent No. 6034. FIGS. 12 (A) to 12 (E) are main part process drawings. According to this method, a photoresist layer 33, a conductive layer 35 formed of a metal layer having a thickness of about 1000 °, and an electron beam resist layer 37 are laminated in this order on a compound (in this example, a silicon substrate) 31. (FIG. 12 (A)). Next, this electron beam resist layer 37 is used.
Is irradiated with an electron beam 39 (FIG. 12 (B)), followed by development to form an electron beam resist pattern 37a (FIG. 12 (C)). Next, the conductive layer 35 is etched using the electron beam resist pattern 37a as a mask to form the electron beam resist pattern 37a.
Transcribed to 5. Thus, a pattern 35a of the conductive layer 35 is formed (FIG. 12D). Next, the photoresist layer 33 is exposed and developed using the conductive layer pattern 35a as a mask to obtain a photoresist pattern 33a.

According to this method, the charge generated in the region of the electron beam resist 37 irradiated with the electron beam can escape through the conductive layer 35, so that it is possible to prevent a decrease in electron beam deflection accuracy.

<Method> The method used a conductive organic material.
Specific examples include the following.

... One layer in a multilayer resist is composed of a conductive polymer film. For example, JP-A-63-181428, JP-A-63-181428
No. 204724, 2nd Preliminary Proceedings of Spring 1987
p.552 30p-H-5 and others.

A method of irradiating ions to the lower resist to modify the surface of the lower resist to increase conductivity and form a resist for electron beams thereon (SPIE Vol.923 (1988), p.281).

<Method> The method is a method in which a conductive thin film of, for example, aluminum or the like is further formed on an electron beam resist, and electron beam drawing is performed through the thin film. As a specific example, see, for example, the literature (Spring Proceedings of the Spring of 1988, 2nd volume, p.551 30
-P-H-4).

(Problems to be Solved by the Invention) However, the above-described method is considered to have poor reproducibility of the degree of increase in the conductivity of the electron beam resist, and thus prevents the charging of the multilayer resist and the charging of the workpiece. Cannot be performed sufficiently, and therefore, the effect of preventing the deterioration of the deflection accuracy of the electron beam becomes insufficient. Further, there is a problem that the exposure characteristics of the electron beam resist are changed because the electron beam resist is modified.

Further, in the above-described method, as is apparent from the experimental results described later (experimental results described with reference to FIGS. 5 to 9), the conductive layer itself is charged because the thickness of the conductive layer is large. Therefore, there is a problem that the accuracy of electron beam deflection is reduced. Here, it is conceivable to contact the conductive pin with the conductive layer in order to release the electric charge of the conductive layer, but it is difficult to make the conductive pin contact the conductive layer with good reproducibility and good satisfactorily. Poor practicality. Furthermore, since the thickness of the conductive layer is large, there is a problem that etching of this layer is not easy.

In the above-mentioned method, since the organic conductive material itself is still in the development stage, for example, the resistivity is still as high as about 10 ⁶ to 10 ^8, so that it is possible to sufficiently shield the electric field generated by the charging of the layer below this layer. There was no problem.

In the above-described method, the electric field due to the charging of the multilayer resist and the electric field due to the charging of the workpiece can be both sufficiently shielded. However, since the electron beam is irradiated through the aluminum thin film, the electron beam is scattered and the resolution is reduced. There was a problem. Further, there is a problem that the aluminum thin film needs to be peeled off after electron beam drawing and before development, which complicates the process.

Table 1 below is a table showing the presence or absence of the antistatic effect of each of the resist and the workpiece by the above-described methods 1 to 3. In Table 1, (shielding) indicates that the influence of charging can be prevented by shielding.

Thus, none of the conventional methods is technically satisfactory.

The present invention has been made in view of such a point,
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a method capable of forming a desired pattern by preventing a decrease in electron beam deflection accuracy due to charging with good reproducibility.

(Means for Solving the Problems) In order to achieve this object, according to the pattern forming method of the present invention, a step of forming a first resist layer on a workpiece, and a step of forming a first resist layer on the first resist layer Film thickness exceeds 30 mm
Forming a conductive film of less than 100 °, more preferably more than 30 ° and 50 ° or less, forming an electron beam resist layer on the conductive film, and irradiating the electron beam resist layer with an electron beam. Forming a pattern of an electron beam resist; and etching and removing the conductive film and the first resist layer using the pattern of the electron beam resist as a mask.

In the practice of the present invention, the conductive thin film described above,
W (tungsten), Ti (titanium), Cr (chromium) and
It is composed of a kind of material selected from Ta (tantalum),
Further, it is preferable that the film thickness be in the range of more than 30 ° and less than 100 °, more preferably in the range of more than 30 ° and 50 ° or less.

Here, considering the object of the present invention, it is most preferable that the conductive thin film according to the present invention is provided in contact with the electron beam resist. This is because all the electric fields generated when the lower resist, the workpiece, the substrate, and the like below the electron beam resist are charged can be shielded. However, if an intermediate layer is used between the electron beam resist and the lower layer resist to compensate for the poor plasma etching resistance of the electron beam resist, the load on the electron beam resist during patterning of the intermediate layer is reduced. Considering
It can be said that it is better that there is no excess between the electron beam resist and the intermediate layer. Therefore, in such a case, the conductive thin film according to the present invention is preferably formed below and in contact with the intermediate layer. Even if it does in this way, the effect of this invention will not change substantially. However, even in the case of using the intermediate layer, when the electron beam resist has a resistance with respect to the etching of the intermediate layer and the conductive thin film, the conductive thin film according to the present invention, as the object of the present invention, It is preferable to form it in contact with the electron beam resist.

(Operation) According to the pattern forming method of the present invention, the conductive thin film has an appropriate thickness, so that the conductive thin film itself does not become charged.
This shows a unique effect that an electric field generated when the resist and the workpiece below the resist are charged can be positively shielded. Further, since the unnecessary portion of the conductive thin film can be removed together with the patterning of the lower resist performed after the patterning of the electron beam resist, the process is simple.

(Example) Hereinafter, an example of the pattern forming method of the present invention will be described with reference to the drawings. It should be noted that the drawings used in the description are merely schematic descriptions to the extent that the present invention can be understood. Therefore, it is to be understood that the dimensions, shapes and arrangement relationships of the respective components, and the dimensional ratios between the respective components are also schematic, and that the present invention is not limited to only these illustrated examples.

First Embodiment First, the present invention relates to a method in which a workpiece is a silicon thermal oxide film, and an electron beam resist is formed on the workpiece as an upper layer.
An example in which the present invention is applied to a case where a mask pattern for processing a workpiece is formed by a layer resist method will be described. Fig. 1 (A)
FIGS. 7A to 7C are views for explanation, and are process diagrams showing the main parts of the pattern forming method of the first embodiment. Both figures are shown with cross-sectional views.

First, a thermal oxide film 43 having a thickness of 7,000 ° is formed on the surface of a silicon substrate 41 to obtain a workpiece. Then, this thermal oxide film
In this example, a novolak-based photoresist HRP-204 (a resist manufactured by Fuji Hunt Co.) is used as the lower resist 45 on the 43.
Coat to a thickness of 1.8 μm. Next, the resist-coated silicon substrate is heated at 250 ° C. for 10
Heat-treat for minutes.

Next, the conductive thin film according to the present invention, which is formed between the electron beam resist and the lower layer resist, and which is under the conductive thin film, can be shielded from an electric field caused by charging, and is irradiated with the electron beam. In some cases, the conductive thin film has a thickness of 50 mm without being charged and can be removed in the etching process of the lower resist when transferring the pattern after patterning the electron beam resist to the lower resist. The film 47 is formed on the lower resist 45 by a sputtering method in this example.

Next, an electron beam resist is formed on the tungsten film 47.
In this example, silicon-based electron beam resist PACS 49
(An electron beam resist manufactured by Oki Electric Industry Co., Ltd.) is applied to a film thickness of 0.25 μm in this example. Next, the PACS-coated substrate is heat-treated at 80 ° C. for 1 minute using a hot plate.

By the process as it is, the sample is in a state shown in FIG.

Next, the sample was not grounded at all, and the acceleration voltage was set to 20 KV and the exposure amount was set to 6 μV with respect to the electron beam resist 49.
An electron beam exposure treatment is performed under the conditions of c / cm ² . In this example, a 3 μm line and space pattern was drawn as an experiment. Next, development is performed for 45 seconds by a spray developing method using methyl isobutyl ketone, and spray rinsing is further performed for 60 seconds using isopropyl alcohol. As a result, an electron beam resist pattern 49a is obtained (FIG. 1 (B)).

Next, by using the electron beam resist pattern 49a as a mask, unnecessary portions of the tungsten thin film 47 and the lower resist 45 are removed by O ₂ RIE (Reactive Ion Etching) to pattern the thermal oxide film 43. (FIG. 1 (C)). At the time of this O ₂ RIE, patterning of the lower resist 45 could be performed without any trouble even if the tungsten film 47 was present. Further, the increase in the etching time required for etching the tungsten film 47 is limited by the pattern 49 of the electron beam resist.
a did not deteriorate.

FIG. 2A is a schematic diagram of an optical microscope photograph of the mask pattern of the first embodiment manufactured by the above-described procedure. FIG. 2 (B) is a schematic diagram of an optical microscope photograph of a mask pattern of a comparative example manufactured in exactly the same manner as the first example except that the tungsten thin film 47 is not used. Here, in both figures, reference numeral 43a denotes a portion of the workpiece exposed from the mask pattern 51.

As is clear from FIG. 2A, in the case of the embodiment, a desired line and space pattern was obtained. On the other hand, in the case of the comparative example, as shown in FIG. 2 (B), a disconnection portion 53 of the pattern occurred, and a desired pattern could not be obtained.

The reason why the desired mask pattern was not obtained in the method of the comparative example was that the silicon substrate 41, the workpiece 43, and the lower resist 45 were charged during electron beam exposure, and the electric field generated by this lowered the electron beam deflection accuracy. This is because the electron beam is irradiated to a position different from a desired position.

On the other hand, in the method of the embodiment, the silicon substrate 41, the workpiece 43 and the lower resist 45 are charged in the same manner as in the comparative example at the time of electron beam exposure, but the electric field generated by this charging is shielded by the tungsten thin film 47 and It does not reach the line resist side. Further, if the thickness of the tungsten thin film 47 is an appropriate thickness including the thickness of the embodiment, the electrification of the tungsten thin film 47 itself can be prevented. Therefore, in the method of the embodiment, since the deflection accuracy of the electron beam does not decrease, no pattern shift occurs.

The effect of changing the thickness of the conductive thin film 47 according to the present invention on the antistatic effect, that is, the effect on the electron beam deflection accuracy will be described in detail in the section of the third embodiment.

Second Embodiment Next, the present invention is applied to a case where a workpiece is a silicon thermal oxide film as in the first embodiment, but a mask pattern for processing the workpiece is formed by a three-layer resist method. An example will be described. FIGS. 3 (A) to 3 (D) are views provided for explanation thereof and are process diagrams showing the main parts of the pattern forming method of the second embodiment. In each of the figures, a cross-sectional view is shown, and the same components as those shown in FIG. 1 are denoted by the same reference numerals.

First, a thermal oxide film 43 having a thickness of 7,000 ° is formed on the surface of a silicon substrate 41 to obtain a workpiece. Then, this thermal oxide film
In this example, a novolak type positive photoresist ONPR-800 (Tokyo Ohka Kogyo Co., Ltd.)
Is applied to a thickness of 1.8 μm. Then
Resist coated silicon substrate using hot plate
Heat-treat at a temperature of 250 ° C for 10 minutes.

Next, a titanium film having a thickness of 50 ° in this example is formed on the lower resist 45 as a conductive thin film 47 according to the present invention, and a sputtering method is formed on the lower resist 45 in this example.
As a matter of course, a tungsten film may be used instead of the titanium film as in the first embodiment.

Next, on this conductive thin film 47, as the intermediate layer 61, amorphous silicon having a thickness of 1000 ° in this example is formed by sputtering. Next, on this intermediate layer 61, as a resist 49 for an electron beam, in this example, EBR-9 (resist for an electron beam manufactured by Toray Industries, Inc.) is formed to a thickness of 0.5 μm. Next, the substrate coated with EBR-9 was heated at 200 ° C. using a hot plate.
At a temperature of 1 minute.

By the process as it is, the sample is in a state shown in FIG. 3 (A).

Next, the sample was not grounded at all, and the acceleration voltage was set to 20 KV and the exposure amount was set to 8 μm with respect to the electron beam resist 49.
An electron beam exposure treatment is performed under the conditions of c / cm ² . The drawing pattern is a line and space pattern of 3 μm as in the first embodiment. Then, immersion development is performed for 3 minutes using a developing solution of methyl isobutyl ketone: isopropyl alcohol = 4: 1 (volume ratio), and spray rinsing is further performed for 60 seconds using isopropyl alcohol. As a result, an electron beam resist pattern 49a is obtained (FIG. 3 (B)).

Next, using this electron beam resist pattern 49a as a mask, RIE (Reactive Ion Etching)
Unnecessary portions of the intermediate layer 61 are removed to form an intermediate layer pattern 61a (FIG. 3C).

Next, using the intermediate layer pattern 61a as a mask, unnecessary portions of the conductive thin film and the lower resist 45 are removed by an O ₂ -RIE method to obtain a mask pattern 51 for patterning the thermal oxide film 43 (third pattern). (D). In this O ₂ -RIE, patterning of the lower resist 45 could be performed without any trouble even if the titanium film 47 was present.

When the mask pattern formed by the method of the second embodiment was observed with a microscope in the same manner as in the first embodiment, it was found that a desired mask pattern similar to that of the first embodiment was formed. Therefore, the effect of the present invention can be sufficiently obtained even when the intermediate layer is used and the conductive thin film according to the present invention is formed in contact with the lower resist side of the intermediate layer.

In the above-described second embodiment, a conductive thin film is provided below the intermediate layer in order to reduce the load of the electron beam resist when etching the intermediate layer. However, if the electron beam resist can withstand the conditions for etching both the conductive thin film and the intermediate layer, the conductive thin film may be provided between the electron beam resist and the intermediate layer as shown in FIG. It is preferable from the original purpose.

Third Embodiment Next, a description will be given of an experimental result obtained by examining a change in antistatic effect, that is, a change in pattern accuracy due to a change in electron beam deflection accuracy when the thickness of the conductive thin film 47 according to the present invention is changed. The sample used in this experiment was a thermal oxide film having a thickness of 0.7 μm and a HPR-2 film having a thickness of 1.8 μm on a silicon substrate.
04 Resist, tungsten film with various thickness, film thickness
A 0.4 μm EBR-9 electron beam resist was provided in this order. Here, the thickness of the tungsten film is 1000 mm,
Samples were prepared at 520 °, 400 °, 50 °, and 30 °. The electron beam exposure conditions for each sample, the development conditions for the EBR-9 electron beam resist, and the etching conditions for the lower layer resist are the same as those described in the first and second embodiments. Although the electron beam drawing pattern is the same for each sample, a different pattern from that of the first and second embodiments is used.

FIGS. 5 to 9 are diagrams for explaining the experimental results of the third embodiment.
It is a schematic mimic view of the microscope picture of the same part of the mask pattern on each sample set to {, 400, 50, 30}. It should be understood that the photographing magnification of each sample is partially different.

As is clear by comparing the respective replicated figures, when the thickness of the conductive thin film 47 is about 500 to 1000 mm, which is generally used as an intermediate layer in the conventional multilayer resist process, Even if a conductive thin film is provided below the resist for electron beams, the antistatic effect cannot be obtained, and the pattern shift occurs.
It was found that 71 was remarkably generated (FIG. 5, FIG. 6).
FIG. 7, FIG. 7). However, when the thickness of the conductive thin film 47 was 50 °, no pattern shift occurred at all (see the eighth embodiment).
Figure). Also, when the thickness of the conductive thin film 47 becomes extremely thin,
In this example, it has been found that when the angle is less than 30 °, the electric field is not sufficiently shielded, and the pattern shift 71 appears again (FIG. 9).

According to a detailed experiment conducted by the inventor separately,
The preferred film thickness that can shield the electric field without charging the conductive thin film itself is more than 30 mm when the conductive thin film is made of tungsten, titanium, chromium, tantalum, etc.
It was found to be within the range of less than 0 °.

The reason why the conductive thin film is made of tungsten, titanium, chromium, tantalum, or the like is that these metals have excellent thermal stability, and are used in various semiconductor devices and have excellent reliability. This is because there is a track record. However, it is clear that the constituent material of the conductive thin film is not limited to these metals, and other materials may be used as long as they have the same resistivity as these metals and satisfy requirements such as thermal stability.

The above is the description of the embodiment of the present invention. It should be noted that each of the above-described embodiments is merely an example, and the present invention relates to a workpiece, a photoresist, an electron beam resist,
Obviously, the present invention can be applied to cases other than the intermediate layer material.

(Effects of the Invention) As is clear from the above description, according to the pattern forming method of the present invention, an electron beam is formed in a state where a conductive thin film having a predetermined thickness is formed between an electron beam resist and a lower resist. Perform drawing. The conductive thin film having such a thickness does not charge itself, but can positively shield an electric field generated when the resist and the workpiece under the conductive thin film are charged. . Therefore, since it has a completely different effect from the case where the electric charge is released through the conductive thin film as in the method disclosed in JP-A-57-106034, for example, the substrate, the workpiece, and the resist layer are not grounded at all. In addition, it is possible to prevent a decrease in electron beam deflection accuracy due to charging of the substrate and charging of the resist. The same effect can be obtained regardless of whether the workpiece has a low resistance or an insulating property. Therefore, according to the present invention, a desired resist pattern can be obtained irrespective of the quality of contact between the conductive pin and the workpiece.

In addition, since the conductive thin film according to the present invention can be processed together with the processing of the lower layer resist, according to the present invention, except that the step of forming the conductive thin film increases, the conventional multilayer resist process can be used as it is. The effect is obtained.

In addition, since there is no treatment for modifying the electron beam resist, no change in the characteristics of the electron beam resist can occur, and since there is no need to provide a thin film on the electron beam resist, the scattering of the electron beam is reduced. This does not occur, and a desired pattern can be obtained with good reproducibility.

[Brief description of the drawings]

1 (A) to 1 (C) are process diagrams for explaining the first embodiment, and FIG. 2 (A) is a photomicrograph of a mask pattern obtained by the method of the first embodiment. 2 (B) is a mimic photo of a photomicrograph of a mask pattern obtained by the method of the comparative example, FIGS. 3 (A) to 3 (D) are process diagrams for explaining the second embodiment, and FIG. FIGS. 5 to 9 are diagrams for explaining another example of the second embodiment, and FIG. 5 to FIG. 9 are diagrams for explaining the third embodiment. FIGS. 10 (A) and (B), FIGS. 11 (A) and 11 (B), and FIGS. 12 (A) to 12 (E) show conventional pattern forming methods. FIGS. FIG. 41: Silicon substrate, 43: Workpiece 45: Lower resist, 47: Conductive thin film 49: Electron beam resist 49a: Electron beam resist pattern 51: To pattern the workpiece The mask pattern 43a is exposed from the mask pattern of the workpiece 53. The broken portion of the pattern 61 is an intermediate layer, 61a is an intermediate layer pattern 71 is a pattern shift.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/027

Claims (2)

(57) [Claims] A step of forming a first resist layer on a workpiece; a step of forming a conductive film having a thickness of more than 30 ° and less than 100 ° on the first resist layer; Forming an electron beam resist layer on the film; irradiating the electron beam resist layer with an electron beam to form an electron beam resist pattern; and using the electron beam resist pattern as a mask. Etching the conductive film and the first resist layer. A step of forming a first resist layer on the workpiece; a step of forming a conductive film having a thickness of more than 30 ° and not more than 50 ° on the first resist layer; Forming an electron beam resist layer on the film; irradiating the electron beam resist layer with an electron beam to form an electron beam resist pattern; and using the electron beam resist pattern as a mask. Etching the conductive film and the first resist layer.