JPH0822947A - Pattern forming method and semiconductor device manufacturing method - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to a pattern forming method for forming a pattern of a photosensitive film by patterning a photosensitive film formed on a substrate having a step using a photolithography technique. Even if the film thickness of the resist film before exposure is different on the plane and the lower plane, a pattern having a uniform line width is obtained. A pattern forming method in which a photosensitive film 4 is formed on a substrate 3 having a step, and the photosensitive film 4 is exposed and developed to form patterns 4a and 4b of the photosensitive film. A substrate having a stepped photosensitive film 4 having a thickness such that Eth for the photosensitive film 4 (minimum exposure amount capable of dissolving the photosensitive film 4 with a developing solution) and Eth for the photosensitive film 4 on the step upper surface are equal. 3 and expose the photosensitive film 4 with an exposure amount Eth × k (k represents a positive real number of 1 or more).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a pattern and a method for manufacturing a semiconductor device, and more specifically, a photosensitive film formed on a substrate having a step is patterned by a photolithography technique to form a photosensitive film. The present invention relates to a pattern forming method for forming a film pattern and a semiconductor device manufacturing method using the pattern forming method.

[0002]

2. Description of the Related Art Conventionally, when a resist pattern as an etching resistant mask is formed on a patterning object by using a photolithography technique, before forming a resist film (photosensitive film) on the actual patterning object. The optimum film thickness is selected by forming resist films of various film thicknesses on a flat substrate for investigation, exposing and developing the resist films.

That is, a resist pattern is formed by changing the resist film thickness and the exposure amount on a flat substrate, and the correlation data between Eth and the resist film thickness is acquired to select the resist film thickness at which Eth is maximized. To do. The term "Eth" refers to the minimum exposure amount capable of dissolving a resist film having a predetermined film thickness with a developing solution. In general, it is said that the optimum film thickness of the resist film to be used is a film thickness at which Eth is maximized in the correlation characteristic between the resist film thickness and Eth. On the other hand, the exposure amount with which a predetermined line width is obtained is usually determined to be k times Eth. Where k
Is called the Eth coefficient.

FIG. 4 is a characteristic diagram showing the correlation of Eth with respect to the resist film thickness. For example, a film thickness a that maximizes Eth is selected as the optimum film thickness of the resist film, and the exposure amount at that time is 80 mj. Then, if a predetermined line width is obtained when k = 2, the optimum exposure amount is 80 × 2 = 160 m.
j. After that, a resist film is formed on an actual substrate by a spin coating method under the coating conditions that the above film thickness is formed, and the line width is made uniform by exposing the resist film at the optimum exposure amount determined above and developing it. Pattern will be obtained.

[0005]

However, there are many cases where unevenness such as a wiring layer exists on the actual semiconductor substrate on which the resist pattern is formed. Therefore, when a resist film is formed on such a semiconductor substrate by a coating method,
It becomes thicker in the concave portion and thinner in the convex portion. For example, it is assumed that the film thickness of the thin portion becomes a (Eth = 80 mj) shown in FIG. 4, and the film thickness of the thick portion becomes b (Eth = 60 mj) in the same figure.

From the above example, the optimum exposure amount is set to the thin film thickness a.
When 160 mj is taken as a reference, the Eth coefficient becomes 160/60 = 2.67 at the thick film thickness b, and the exposure amount becomes excessive. Therefore, in the case of the positive resist, the line width of the resist pattern can be obtained almost as designed at the thin film thickness a, but the line width of the resist pattern becomes thin at the thick film thickness b.

On the other hand, if the optimum exposure amount is determined with reference to the thick film thickness b, the exposure amount is insufficient at the thin film thickness a, and the line width of the resist pattern to be formed becomes large. is there. The present invention was created in view of the problems of the related art, and when a pattern of a photosensitive film is formed on a substrate having a step by using the photolithography technique through the same process, the upper part of the step is formed. Provided are a pattern forming method and a semiconductor device manufacturing method using the pattern forming method, in which a pattern having a uniform line width can be obtained even if the resist film before exposure has different film thicknesses on a plane and a lower plane. The purpose is.

[0008]

The first object of the present invention is to form a photosensitive film on a substrate having steps, expose the photosensitive film, and develop the photosensitive film to form a pattern of the photosensitive film. In the pattern forming method, Eth (minimum exposure amount capable of dissolving the photosensitive film with a developing solution) for the photosensitive film on the step lower plane is equal to Eth for the photosensitive film on the step upper plane. The photosensitive film having a film thickness is formed on a substrate having the step, and the photosensitive film is exposed with an exposure amount Eth × k (k represents a positive real number of 1 or more). Second, a photosensitive film is formed on a substrate having steps,
In the pattern forming method of exposing the photosensitive film and developing the photosensitive film to form a pattern of the photosensitive film, the photosensitive film formed on a flat substrate has a thickness (E Substrate having a step difference in the two film thicknesses between the two film thicknesses at which the Eth is equal based on the correlation, which is obtained by obtaining a correlation of a minimum exposure amount capable of dissolving the film with a developing solution. It is necessary to determine Eth so as to be equal to the dimension of the above step, form a photosensitive film on the substrate having the step, and perform exposure with exposure amount Eth × k (k represents a positive real number of 1 or more). A third aspect of the present invention is achieved by a pattern forming method characterized by the above, thirdly, the constant k is 2, and achieved by the pattern forming method according to the first or second aspect of the present invention. The film is a resist film or photosensitive polyimide First, characterized by being a membrane
A fifth aspect of the present invention is achieved by the pattern forming method according to the second or third invention, and fifthly, the photosensitive film is formed by a spin coating method. Sixthly, an etching resistant pattern of a photosensitive film is formed on an object to be patterned by using the pattern forming method according to the first, second, third, fourth or fifth invention. It is achieved by a method of manufacturing a semiconductor device, which comprises forming and etching and removing the patterned object using the etching resistant pattern as a mask.

[0009]

In the pattern forming method of the present invention, the first
In addition, a step of a photosensitive film having a thickness such that Eth (minimum exposure amount capable of dissolving the photosensitive film with a developer) on the lower plane of the step and Eth for the photosensitive film on the upper plane of the step are equal to each other. Formed on a substrate having an exposure dose of Eth × k (k
Indicates a positive real number of 1 or more).

In this case, a photosensitive film is formed on an actual substrate having a step, the correlation between the pattern line width and the film thickness of the photosensitive film is investigated, and the above relationship is established. The spin coating conditions of the photosensitive material are determined, and the photosensitive film is formed on the actual substrate under the conditions. According to the investigation, as shown in FIG. 4, Eth changes periodically with respect to the film thickness.
There are two film thicknesses such that Therefore, it is possible to form the photosensitive films having different thicknesses on the upper and lower planes of the step on the substrate having the step by the same coating step.

For example, the film thickness of the photosensitive film and the line width of the pattern obtained when the photosensitive film having various thicknesses is formed on a substrate having a step difference of 150 nm and the exposure amount is kept constant at 130 mj. The correlation is shown in FIG. The film thickness of the photosensitive film indicates the film thickness on a flat substrate formed under the same coating conditions as the actual coating conditions formed on the substrate. From FIG. 3, it can be considered that the area where the line width of the pattern on the upper plane of the step and the line width of the pattern on the lower plane are equal is where the exposure amount is equal. Therefore, the step 15
If a photosensitive film is formed on an actual substrate having a thickness of 0 nm under the same coating conditions as described above, excess or deficiency of the exposure dose does not occur on the upper and lower flat surfaces of the step. Therefore, the line widths of the patterns formed on the upper plane and the lower plane of the step become equal.

Secondly, regarding the photosensitive film formed on the flat substrate for the investigation, Eth with respect to the film thickness of the photosensitive film
A substrate having a difference in the two film thicknesses between the two film thicknesses at which Eth is equal based on the correlation obtained (the minimum exposure amount that can dissolve the photosensitive film with the developing solution). An Eth that is equal to the size of the upper step is determined, and the exposure amount Eth is applied to the photosensitive film formed on the substrate having the step.
Exposure is performed with × k (k is a real number).

The above corresponds to the special case of the first invention,
It is applied when the step difference directly causes a difference in film thickness of the photosensitive film. In this case, it is shown that a pattern with a uniform line width can be formed more easily than in the first invention. As such a case, for example, there is a case where the area of the convex portion is sparsely present as compared with the area of the concave portion and the area of the upper plane of the convex portion is small. In this case, a photosensitive film having a film thickness almost equal to that of the photosensitive film formed on the flat substrate is formed on the plane of the concave portion, and a film thickness on the plane of the concave portion is formed on the plane of the convex portion. A photosensitive film having a film thickness obtained by subtracting the height of the step is formed.

On the contrary, when the concave regions are sparser than the convex regions and the area of the bottom plane of the concave is small, the convex plane is formed on a flat substrate. A photosensitive film having a film thickness substantially equal to that of the photosensitive film is formed, and a photosensitive film having a film thickness on the plane of the concave portion plus the height of the step is formed on the plane of the concave portion. It In such a case, based on the correlation, Eth is determined such that the difference between the two film thicknesses at which Eth is equal becomes equal to the dimension of the step on the substrate having the step. Eth is equal in both the thin photosensitive film formed on the upper plane of the step and the thick photosensitive film formed on the lower plane of the step.
Therefore, since the exposure amount Eth × k with which the predetermined line width is obtained can be made equal, the line widths of the formed patterns are uniform.

Furthermore, by using the above-mentioned pattern forming method in the method for manufacturing a semiconductor device of the present invention, in particular, a line width is formed on a substrate in which a selective oxide film, a wiring layer and the like are present during the manufacturing, and unevenness exists. A uniform resist pattern or the like can be formed. As a result, it is possible to improve the patterning accuracy of the object to be patterned under the resist pattern and to increase the density of the semiconductor device.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. (1) Description of First Embodiment A method of acquiring correlation data used in the method of forming a resist pattern according to the first embodiment of the present invention will be described. The correlation data shows the correlation between the line width of the resist pattern and the film thickness of the resist film formed on the flat substrate.

Regarding the method of preparing the survey sample, FIG. 1 (a)
2 to FIG. 2A will be described. FIG.
2A to 2C are cross-sectional views of the substrate to be coated. First, as shown in FIG. 1B, a positive type resist having a predetermined film thickness is formed on the polysilicon film 3 having a step difference of 150 nm as shown in FIG. A film (photosensitive film) 4 is formed. For the experiment,
Various samples were prepared in which the film thickness of the resist film 4 was changed in the range of 1150 to 1280Å. At the same time, to investigate the film thickness,
A sample having a resist film formed on a flat silicon substrate was also prepared.

In order to form resist films of various thicknesses, it is necessary to change the viscosity that determines the thickness of the resist film, the coating time, etc., but in the embodiment, the semiconductor substrate 1 during resist coating is changed. The number of rotations was changed. According to the experiment, the film thickness can be controlled within the range of ± 5 nm by changing the rotation speed, and the controllability of the resist film thickness is extremely good.

Next, as shown in FIG. 1C, the line width 0.
Using the mask 5 having a mask pattern of 55 μm formed, the resist film 4 formed on the polysilicon film 3 as described above is exposed to ultraviolet rays at an exposure dose of 130 mj / cm ²
To expose. Next, as shown in FIG. 2A, the resist film in the exposed region is melted by immersing it in a developing solution to form resist patterns 4a and 4b.

Thereafter, the line width dimensions of the resist patterns 4a and 4b formed on the upper and lower portions of the step were measured, respectively. The above process was repeated for samples with various film thicknesses, and correlation data was obtained. The result is shown in FIG. In FIG. 3, the vertical axis represents the line width (μm) of the resist pattern on the linear scale, and the horizontal axis represents the film thickness (nm) of the resist film on the linear scale.

According to the result shown in FIG. 3, the film thickness of the resist film 4 is about 1160 nm (f point), 1225 nm (g point) and 1255 n.
Resist pattern 4 above and below the step at m (point h)
The line widths of a and 4b became equal. At this time, when the resist film thicknesses were about 1160 nm and 1225 nm, the resist pattern line width was about 0.55 μm, and line widths almost as designed were obtained.
It is shown that the upper and lower surfaces of the step have the same exposure amount and the absolute exposure amount is appropriate.

Further, when the resist film has a thickness of about 1255 nm, the line width is equal to about 0.63 μm, but the line width is wider than the designed value. This indicates that the exposure amount is equal on the upper surface and the lower surface of the step, but the absolute exposure amount is insufficient. Film formation under such conditions is not preferable in terms of pattern accuracy. The resist film thickness at which the line width of the resist pattern becomes equal is Eth in FIG.
It is considered to represent two film thicknesses where the (minimum exposure amount capable of dissolving the resist film with the developing solution) is equal. FIG.
Is a characteristic diagram showing the correlation of Eth with respect to the resist film thickness. Since Eth changes periodically with respect to the resist film thickness, two film thicknesses where Eth is equal always exist.

In the above embodiment, the exposure amount is 130 m.
j, the case of a step of 150 nm was investigated, but by similar experiments, it is possible to select the resist film thickness such that the resist pattern line width becomes equal for various steps. Next, a pattern forming method according to a first embodiment of the present invention and a semiconductor device manufacturing method using the same will be described with reference to FIGS. 1 (a) to 1 (c), FIGS. 2 (a), (b), and FIG. It will be explained with reference to FIG.

FIG. 1A shows the semiconductor substrate before applying the resist film. In the figure, 1 is a semiconductor substrate, 2 is a LOC
An oxide film 3 having a step of 150 nm, which is selectively formed on the semiconductor substrate 1 by the OS method (selective oxidation method), is a polysilicon film (patterned body) formed on the semiconductor substrate 1 and the oxide film 2. . The above constitutes a substrate having steps.

First, as shown in FIG. 1B, a positive type resist film (photosensitive film) 4 is formed on the polysilicon film 3 on such a substrate by a spin coating method. At this time, the coating conditions such as the number of coating rotations are determined in advance so that the film thickness of the resist film is about 1225Å on a flat substrate, and the resist film 4 is formed on the actual semiconductor substrate 1 under the same conditions. This film thickness corresponds to point g in FIG. That is, the film thickness is such that Eth is equal on the upper plane and the lower plane of the step.

Next, as shown in FIG. 1C, the line width 0.
Using the mask 5 having a mask pattern of 55 μm formed, the resist film 4 formed on the polysilicon film 3 as described above is exposed to ultraviolet rays at an exposure dose of 130 mj / cm ²
To expose. At this time, the thickness of the resist film 4 is such that Eth is equal, so that the resist film 4 is exposed without excess or deficiency of the exposure amount on both the upper plane and the lower plane of the step.

Next, as shown in FIG. 2A, the resist film 4 in the exposed area is melted by immersing it in a developing solution. As a result, resist patterns 4a and 4b having a designed width dimension of about 0.55 μm are formed. After that, as shown in FIG. 2B, the underlying polysilicon film 3 is etched and removed by RIE (reactive ion etching) using a chlorine-based reaction gas with the resist patterns 4a and 4b as a mask. , The patterning of the polysilicon film is completed. At this time, the resist patterns 4a, 4
The width of b is the designed width of about 0.55 μm on both the upper and lower planes of the step, and since the line widths are uniform, the line width is almost equal to the designed value and It is possible to obtain the patterns 3a and 3b having a uniform width. Thereby, the patterning accuracy can be improved and the density of the semiconductor device can be increased. (2) Second Embodiment The first embodiment described above can be applied to the case where resist patterns 4a and 4b are formed on a substrate 1 having a general step, and a concave portion is mainly formed on the substrate having the step. This is effective in the case where the convex portions and the convex portions are appropriately present, but in the following cases, it is possible to more easily select the resist film thickness and form a pattern having a uniform line width.

In other words, this is the case where the step difference directly causes the difference in film thickness of the resist film. In such a case, the area of the convex portion may be sparsely present as compared with the area of the concave portion, and the area of the upper plane of the convex portion may be smaller. In this case, a resist film having a film thickness substantially equal to the film thickness of the resist film formed on the flat substrate is formed on the plane of the concave portion, and a step difference from the film thickness on the concave plane is formed on the plane of the convex portion. A resist film having a thickness less than the height is formed.

On the contrary, the second embodiment can be applied to the case where the concave region is sparsely present as compared with the convex region and the area of the bottom plane of the concave is small. In this case, a resist film having a film thickness almost equal to that of the resist film formed on the flat substrate is formed on the plane of the convex portion, and a film thickness on the plane of the convex portion is formed on the plane of the concave portion. A resist film having a film thickness including the step height is formed.

In the above-mentioned case, as shown in FIG. 4, for the resist film formed on the flat substrate, Eth (minimum exposure amount capable of dissolving the resist film with the developing solution) with respect to the film thickness of the resist film. Get the correlation. In FIG. 4, the vertical axis represents Eth and the horizontal axis represents the film thickness of the resist film. As shown in FIG. 4, Eth changes periodically with respect to the film thickness of the resist film, so that there exist two film thicknesses where Eth is equal.

Then, based on the obtained correlation, E
Eth is determined so that the difference between the two film thicknesses where th is equal becomes equal to the step difference on the substrate having the step difference. For example, the difference e between the two film thicknesses d and e at the intersection of the auxiliary line L (straight line parallel to the horizontal axis) and the correlation curve C written in FIG.
Choose Eth such that −d is equal to the step. next,
Under the same conditions as the spin coating conditions for forming a resist film on a flat substrate, a positive type resist is applied on a polysilicon film (body to be patterned) on a semiconductor substrate having a step to form a resist film.

Next, after exposing the formed resist film with an exposure amount Eth × k (for example, k = 2),
Develop to form a resist pattern. According to the above
Eth is equal in both the thin resist film formed on the upper plane of the step and the thick resist film formed on the lower plane of the step. Therefore, since the exposure amount Eth × k for obtaining a predetermined line width can be made equal, the line widths of the resist patterns formed above and below the step are uniform.

Thereafter, the underlying polysilicon film or the like is dry-etched to form gate wirings and the like having a uniform width above and below the step. As described above, also in the second embodiment, it is possible to form a resist pattern having a uniform line width on a substrate having irregularities such as a selective oxide film and a wiring layer during manufacturing.

As a result, it is possible to improve the patterning accuracy of the object to be patterned under the resist pattern and to increase the density of the semiconductor device. Although ultraviolet rays are used as the exposure light in the above embodiment, excimer laser or other exposure light can be used. Although a positive resist is used, a negative resist can be used.

[0035]

As described above, according to the pattern forming method of the present invention, since the photosensitive film having the film thickness such that Eth is equal is formed on the substrate having the step, the upper flat surface of the step is formed. Also, even if the film thickness of the photosensitive film is different on the lower plane, neither excess nor deficiency of the exposure amount for each photosensitive film occurs. Therefore, the line widths of the patterns formed on the upper plane and the lower plane of the step become equal.

Further, with respect to the photosensitive film formed on the flat substrate, the correlation of Eth with respect to the film thickness of the photosensitive film is obtained, and based on this correlation, between the two film thicknesses where Eth is equal, After determining Eth such that the difference between the two film thicknesses is equal to the step size on the stepped substrate, a photosensitive film is formed on the stepped substrate and the exposure amount Eth × k (k is a real number) Exposure).

As a result, Eth becomes equal for both the thin photosensitive film formed on the upper plane of the step and the thick photosensitive film formed on the lower plane of the step.
Therefore, since the exposure amount Eth × k with which the predetermined line width is obtained can be made equal, the line widths of the formed patterns are uniform. Furthermore, by using the above-described pattern forming method in the method for manufacturing a semiconductor device of the present invention, by patterning the underlying object to be patterned using this pattern as a mask, the patterning accuracy is improved and the density of the semiconductor device is increased. Can be planned.

[Brief description of drawings]

FIG. 1 is a sectional view (1) showing a method for forming a resist pattern according to a first embodiment of the present invention.

FIG. 2 is a sectional view (No. 2) showing the method of forming a resist pattern according to the first embodiment of the present invention.

FIG. 3 is a characteristic diagram showing the correlation between the resist pattern line width and the resist film thickness applied to the resist pattern forming method according to the first embodiment of the present invention.

FIG. 4 is a characteristic diagram showing a correlation of Eth with respect to a resist film thickness applied to a resist pattern forming method according to a second embodiment of the present invention.

[Explanation of symbols]

 1 semiconductor substrate (substrate), 2 oxide film, 3 polysilicon film (patterned object), 3a, 3b pattern, 4 resist film (photosensitive film), 4a, 4b resist pattern, 5 mask.

Claims (6)

[Claims] 1. A pattern forming method comprising forming a photosensitive film on a substrate having a step, exposing the photosensitive film, and developing the photosensitive film to form a pattern of the photosensitive film. The photosensitive film having a film thickness such that Eth (minimum exposure amount capable of dissolving the photosensitive film with a developing solution) with respect to the photosensitive film and Eth with respect to the photosensitive film on the upper surface of the step are equal to each other have the step. A pattern forming method comprising: forming on a substrate and exposing the photosensitive film with an exposure amount Eth × k (k represents a positive real number of 1 or more). 2. A pattern forming method comprising forming a photosensitive film on a substrate having a step, exposing the photosensitive film, and developing the photosensitive film to form a pattern of the photosensitive film, which is formed on a flat substrate. For the photosensitive film, a correlation of Eth (minimum exposure amount capable of dissolving the photosensitive film with a developing solution) with respect to the film thickness of the photosensitive film is obtained, and based on the correlation, the two Eth values are equal to each other. Et is determined such that the difference between the two film thicknesses is equal to the dimension of the step on the stepped substrate, a photosensitive film is formed on the stepped substrate, and the exposure amount E
A pattern forming method, wherein exposure is performed by th × k (k represents a positive real number of 1 or more). 3. The pattern forming method according to claim 1, wherein the constant k is 2. 4. The method according to claim 1, wherein the photosensitive film is a resist film or a photosensitive polyimide film.
Alternatively, the pattern forming method according to claim 3. 5. The pattern forming method according to claim 1, wherein the photosensitive film is formed by a spin coating method. 6. An etching resistant pattern of a photosensitive film is formed on an object to be patterned using the pattern forming method according to claim 1, claim 2, claim 3, claim 4 or claim 5, A method for manufacturing a semiconductor device, which comprises etching and removing the object to be patterned using the etching resistant pattern as a mask.