JPS586305B2 - Microfabrication method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Is the present invention effective when applied to, for example, the manufacture of semiconductor devices? Regarding a certain microfabrication method.

It is well known that in recent years, especially in the semiconductor industry, all objects have been aimed at miniaturization, and many microfabrication methods have been proposed and implemented for this purpose.

In particular, recently, excellent manufacturing equipment such as electron beam exposure equipment and X-ray exposure equipment has been developed and put into practical use, and along with this, photoresist materials are being actively developed.

However, even in the case of these manufacturing facilities with excellent performance, at present, they are difficult to handle, have troublesome restrictions on the workpieces, and are too expensive.
At present, we have not reached the stage where it will replace the ultraviolet exposure method.

However, in the conventional ultraviolet exposure method, it is necessary to align a selective exposure mask to a workpiece whose entire surface is coated with a photoresist film before exposing it to ultraviolet light.

Therefore, in the case of a workpiece that has angular irregularities on its surface,
Processing only the top side of the side surface of the unevenness or only the top surface of the convex part of the unevenness using the conventional ultraviolet exposure method is
The finer the shape of the workpiece, the more difficult it becomes to align the selective exposure mask with respect to the workpiece.
It was extremely difficult.

For example, when forming openings in a photoresist film so that only the top surfaces of the convex portions of the unevenness are formed, it becomes almost impossible if the width of the top surface is 5 μm or less.

The general purpose of the present invention is to easily perform processing that is difficult to achieve using conventional ultraviolet exposure methods, without using the expensive equipment mentioned above. Moreover, it is an object of the present invention to provide a microfabrication method that can be stably performed.

A specific object of the present invention is to provide a microfabrication method that can easily process only the convex portions of a workpiece having angular irregularities on its surface without using the above-mentioned expensive equipment. It is about providing.

The content of the experiment that formed the basis of the present invention will be described in detail below with reference to the drawings.

FIGS. 1 and 2 show the content of experiments that form the basis of the present invention.

1a and a' are silicon substrates 11 and 11' having angular irregularities and steps on their surfaces, respectively.
The state in which films 12 and 12' have been formed is shown.

Further, the width of the convex portion is W3, and the depth of the concave portion and the depth of the stepped portion are D3 and D'3, respectively.

Figures b and b' in the same figure show the state in which negative type photoresists 13 and 13', commercially available product name KMR752, whose viscosity is appropriately adjusted, are coated on the entire surface of the substrate in the state of a and a' in the figure, and C and C in the figure ' is photoresist 13 and 13'
The substrate is preheated (pre-baked) at a temperature of 80°C for 20 minutes, then the entire surface of the substrate is exposed to ultraviolet light for 2.0 seconds or more, further developed, rinsed, and finally heated (post-baked) at a temperature of 100°C for 20 minutes. ) is performed.

Comparison of C and C' in the figure shows that when the width of the convex portion becomes narrower, the photoresist on the surface of the convex portion is peeled off by development or rinsing.

Figure d shows the Si exposed by the opening in Figure C.
The photoresist 13 is removed after selectively removing the 02 film 12 by etching, and d' in the same figure is different from C' in the same figure because the resist 13' is not opened.
The SiO2 film 12 was subjected to the same treatment as
' is not drilled.

This experimental example, which is the basis of the present invention, utilizes the phenomenon that when the width of the convex portion becomes narrow, the photoresist on the top surface of the convex portion is peeled off by development or rinsing, and the top surface of the convex portion becomes open.

In this experimental example, when the depth D3 of the convexity is fixed at 4.0 μm, we investigated the conditions under which the above phenomenon occurs in the correlation between the width W3 of the convexity and the coating conditions of the photoresist, that is, the viscosity and the rotation speed during coating. did.

The results are shown in FIG.

The photoresist used is commercially available product name KMR752.
Two types of viscosity were selected: 30 centistokes and 45 centistokes.

The results shown in Fig. 2 show that, for example, when the width W3 of the convex portion is 7.0 μm, when KMR752 of 30 centistokes is used, the speed is 2000 revolutions per minute or more, and when the width W3 of the convex part is 45 centistokes, the speed is 3000 revolutions per minute. If you apply at a speed higher than rotation, pre-bake (preheat) at 80℃ for 20 minutes as described above.
Full-body exposure for 2.0 seconds or more, development, rinsing, 2 at 100℃
Through a series of processes called post-baking (final heating) for 0 minutes, holes can be formed only on the top surface of the square-shaped convex portion.

In this experimental example, it has been confirmed that similar results can be obtained even when the photoresist used is replaced with another negative type photoresist.

As described above, according to this embodiment, there is no need for a selective exposure mask and alignment of the mask with respect to the workpiece, which were necessary when using the conventional ultraviolet exposure method. It is possible to obtain a microfabrication method that can inexpensively and easily process only the top surface of the convex portion of the unevenness of a workpiece having the above-mentioned irregularities.

Hereinafter, as an example of the present invention based on the above-mentioned basic experiment,
Static induction transistor with N-channel notch structure
An application to the manufacturing process of a vertical junction field effect transistor exhibiting triode characteristics (hereinafter referred to as SIT) will be described with reference to FIG.

FIG. 3a shows a state in which an N drain layer 22 is grown on an N+ silicon substrate 21, which will become an N drain ohmic layer, by a normal vapor phase growth technique, and a SiO2 film 23 is formed on the surface.
After forming 23', the SiO2 film 23 is selectively removed in stripes by ordinary photo-etching technology.

Figure b shows a state in which the N-drain layer 22 is selectively etched using a normal chemical etching solution to form a groove 24 in the state shown in figure a.

Figure C shows the substrate in the state shown in figure b, which is processed using the usual diffusion technique.
A state in which a P+ layer 25 is formed by diffusing boron is shown.

The SiO2 film 26 is also formed by this diffusion process.

Figure d shows a negative type photo in which the viscosity was adjusted to 30 centistokes after the diffusion of C was completed and the entire substrate was immersed in an etching solution for Si02 film to remove only the eaves 27 of the SiO2 film in Figure C. Resist 28, commercially available product name KMR752, is rotated at a rotational speed of 2500 revolutions per minute.
It shows a state in which it was applied for 0 seconds and immediately heated at 150° C. for 15 minutes to cure it.

An opening 29 is formed here.

Figure e shows a state in which after the 8102 film 26 exposed in the opening 29 in d is removed by a normal method, a part of the P layer 25 is selectively removed using a normal chemical etching solution, and the remaining part is removed. The P+ layer 25 constitutes the gate of the SIT.

In the figure f, after the step e is completed, the SiO2 film on the entire substrate is removed with hydrofluoric acid, and then a new SiO2 film 30 is formed on the entire surface.
Furthermore, the viscosity was set to 4 based on the conditions of the experimental examples that form the basis of the present invention.
Commercial product name KMR 7 adjusted to 5 centistokes
5. After coating the photoresist 32 at a speed of 3000 revolutions per minute for 20 seconds, preheating at 80°C for 20 minutes,
The state is shown after 0 second full exposure, development, rinsing and final heating at 100° C. for 15 minutes.

Here, the manner in which the openings 31 are formed is as in the above-mentioned experimental example.

The figure g shows the S exposed by the opening 31 at f.
A part of the iO2 film 30 is selectively removed and cleaned using a conventional method, and then an N 2 source ohmic layer 33 is formed according to a conventional diffusion technique.

As described above, according to the present invention, the notch structure SIT can be created extremely easily by performing the microfabrication process using a method that eliminates the need for a conventional selective exposure mask and alignment of the mask with respect to the workpiece. It will be done.

Next, another embodiment will be described with reference to FIGS. 3C' to 3G'.

FIG. 3e' shows that after removing the SiO2 film 23 using hydrofluoric acid from the substrate in the state shown in FIG.
A state in which a film 34 is formed is shown.

Figure d' shows a state in which a negative type photoresist 35 with the commercially available product name KMR752 is formed as an organic film in exactly the same way as in the case of Figure d described above, and openings 36 are formed. .

In the same figure, e' shows the SiO2 film 3 exposed through the opening 36.
4 is selectively removed using a common etching solution for SiO2 films.

However, here the immersion time in the etching solution is 2 times longer than usual.
The SiO2 film 34 on the vertical side surfaces is mostly removed because it is extended to about double the length and over-etched.

Figure f' shows a state in which a P+ diffusion layer 37 is formed immediately after the step e' by a normal method.

A SiO2 film 38 is formed by this diffusion process.

In the same figure, g' shows that after the step f' is completed, the N+ gate 37 and the N+ source ohmic layer are formed by the process including the process based on the experimental example that is the basis of the present invention, in exactly the same way as the process from d to g described above. 33 is formed and the basic structure of SIT is completed.

As explained above, according to the present invention, there is no need for a selective exposure mask and alignment of the mask with respect to the workpiece, which were necessary when using the conventional ultraviolet exposure method.
A microfabrication method can be obtained that can inexpensively and easily process only the top surface of the convex portion of a workpiece having angular irregularities on its surface.

Although the spinner method was used in the above example to apply the photoresist film, it is not necessarily necessary to apply rotation, and other methods such as a spray method that do not apply rotation may also be used.

[Brief explanation of drawings]

Figures 1 and 2 show the contents of the experiment that formed the basis of the present invention.
It is a diagram prepared for explanation. FIG. 3 is a diagram prepared to explain a case where the present invention is applied to a manufacturing process of a cut structure SIT as an embodiment of the present invention. 11, 11'...Silicon substrate, 12, 12'
...SiO2 film, 13,13'...photoresist film.

Claims (1)

[Claims] 1. A negative type photoresist film is applied to the entire surface of a workpiece having angular irregularities on the surface, and the photoresist film is sequentially subjected to pre-baking, full-surface exposure, dust imaging, and rinsing. a step of forming an opening in the film through which only the top surface of the rectangular convex portion of the workpiece is exposed; a step of subjecting the photoresist film in which the opening has been formed to a post bake; etching the surface of the workpiece using the photoresist film that has been subjected to etching as a mask.