JPS6262045B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microfabrication method that is effective when applied to, for example, the manufacture of semiconductor devices.

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. Particularly 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 also being actively developed. However, even in the case of these manufacturing facilities with excellent performance, at present, ultraviolet exposure methods have not been adopted due to the complexity of handling, troublesome restrictions on the workpiece, and in addition, they are too expensive. We have not yet reached the stage of change.

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 steps or unevenness on its surface, and the side surfaces of the steps or unevenness are substantially perpendicular to the surface, the unevenness or steps can be removed by conventional ultraviolet exposure methods. It has been extremely difficult to process only the top side of the side surface of the part because the finer the shape of the workpiece, the more difficult it becomes to align the selective exposure mask with respect to the workpiece.

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 described above. The object of the present invention is to provide a microfabrication method that can be stably performed.

A specific object of the present invention is to provide a workpiece having an uneven surface or a stepped portion, and a side surface of the uneven or stepped portion being substantially perpendicular to the surface. It is an object of the present invention to provide a microfabrication method that can easily process at least only the top side of the structure without using the above-mentioned expensive equipment.

The contents 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', SiO ₂ is applied to the entire surface of silicon substrates 1 and 1', each having an uneven surface and a stepped portion, and the side surfaces of the uneven and stepped portion are substantially perpendicular to the surface. The state in which films 2 and 2' have been formed is shown. The unevenness and step portions of the silicon substrates 1 and 1' are previously formed by a conventional selective etching technique. In addition, in the same figure a, W ₁ represents the width of the convex part, and in the same figure a and a′, D ₁ and
D ₁ ′ represents the depth of the recess and step, respectively. Same figure b
and b', the wafers in the states of a and a' are suctioned and fixed on the horizontal rotary plate of a spinner with the surface with unevenness and steps facing up, and an organic film is applied to the surface with the commercially available product name KMR752 (Eastman Koda Co., Ltd.). (manufactured by Tsuku)
The negative type photoresist films 3 and 3' shown in FIG. 1 are coated using a spinner and immediately heated and cured on a hot plate.

In the figure, numerals 4 and 4' indicate openings that were automatically generated at that time. Figures c and c' show the photos after the SiO ₂ films 2 and 2' exposed through the openings 4 and 4' formed in Figures b and b' are selectively removed by a normal etching method. Resist films 3 and 3'
has been completely removed. d and d' in the same figure are the substrates in the state shown in b and b' in the same figure, which were treated in the same manner as in c and c' in the same figure, but using an etching solution for selective removal of the SiO ₂ films 2 and 2'. The immersion time was approximately twice that of cases c and c', indicating an overetched state. e and e' in the same figure are c and c' in the same figure.
In order to confirm whether holes were selectively formed in SiO ₂ films 2 and 2', the substrates in states c and c' were immersed in a normal etching solution for silicon to remove the openings by etching. Indicates the condition. Figures e and e' show the situation when the holes are well formed, and steps with an angle close to a right angle are formed. In the experiments that form the basis of the present invention, the depth of the initial irregularities and steps was
D ₁ and D ₁ ′ and the width W ₁ of the convex portion are appropriately selected, and the correlation between the viscosity of the photoresists 3 and 3 ′, the rotation speed during coating (rotation time is constant), and the heating temperature after coating is determined. Openings 4 as seen in Figures 1b and b'
and 4' were investigated. An example of the results is shown in FIG. Figure 2 shows D ₁ and D ₁ ′
3.0 μm, and the conditions for forming the partial openings 4 and 4' were determined by the relationship between the viscosity of the photoresist, that is, KMR752, and the rotational speed during coating when the heating temperature was 100°C and 150°C. It shows.
For example, in the case of KMR752 of 30 centistokes, if the heating temperature after application is set to 100℃, the rotation speed will be
It must be applied at a speed of 3000 rpm or more,
If you choose 150℃, it must be at least 2500 rpm. In the above experiment, no dependence on the width W ₁ of the convex portion was observed. As described above, in this experiment, by processing under the conditions shown in FIG. 2, it is possible to process at least only the top side of the vertical side surfaces of the stepped portion or the uneven portion. According to other data from this experiment, similar results were obtained when polyimide resin films such as commercially available product name PIQ (manufactured by Hitachi Chemical Co., Ltd.) and commercially available product name Trenice (manufactured by Toray Industries) were used as organic films. Therefore, it is presumed that similar results can be obtained with other organic films.

In addition, in the steps shown in Fig. 1b and b', rotation is applied using a spinner in order to coat the photoresist films 3 and 3' so that only the top side of the side surfaces of the unevenness and stepped portions are opened. However, it is not necessary to add such rotation. It is also possible to use other methods such as a spray method that does not involve rotation.

As described above, if the above experimental example is followed, there is no need for a selective exposure mask and alignment of the mask with respect to the workpiece, which is necessary when using the conventional ultraviolet exposure method. Micro-machining that can inexpensively and easily process at least the top side of the side surfaces of the unevenness or stepped portion of a workpiece having a side surface of the unevenness or stepped portion substantially perpendicular to the surface. method is obtained.

Hereinafter, as an example of the present invention based on the above-mentioned basic experiment, a static induction transistor having an N-channel notch structure will be described.
Transistor: 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.

Figure 3a shows N ⁺ which becomes the N ⁺ drain ohmic layer.
After growing the N ^- drain layer 22 on the silicon substrate 21 using normal vapor growth technology, forming SiO ₂ films 23 and 23' on the surface, SiO ₂ is formed in stripes using normal photoetching technology. A state in which the film 23 has been selectively removed is shown. Figure b shows a state in which the N ^- drain layer 22 is selectively etched using an ordinary chemical etching solution to form a groove 24 in the state shown in figure a. Figure c shows a state in which boron is diffused into the substrate in the state shown in figure b, and a P ⁺ layer 25 is formed by diffusing boron using the usual diffusion technique. This diffusion process results in SiO ₂
A membrane 26 is also formed. Figure d shows that after the diffusion of layer c has been completed, the entire substrate is immersed in an etching solution for SiO ₂ film to remove only the edge 27 of the SiO ₂ film in Figure 3c, and then the above-mentioned experiment, which is the basis of the present invention, is carried out. Based on the conditions in the example, negative type photoresist 28, commercially available product name KMR752, whose viscosity was adjusted to 30 centistokes, was applied for 20 seconds at a rotation speed of 2500 revolutions per minute, and immediately heated at 150°C for 15 minutes to harden it. show. Here, the manner in which the openings 29 are formed is as in the above-mentioned experimental example. In the same figure e is d
After removing the SiO ₂ film 26 exposed in the opening 29 by a normal method, a part of the P ⁺ layer 25 is selectively removed using a normal chemical etching solution, and the remaining P ⁺ layer is removed. 25 constitutes the gate of SIT. In the same figure f, after the step e is completed, the entire board is coated with hydrofluoric acid.
After removing the SiO ₂ film, a new SiO ₂ film 30 was formed on the entire surface, and a commercially available photoresist 32 with the trade name KMR752 whose viscosity was adjusted to 45 centistokes was applied at a speed of 3000 revolutions per minute, and then heated at 80°C. Preheat for 20 minutes at , 2.0 seconds full exposure, develop, rinse and 150
Shown after final heating at ℃ for 15 minutes. Here, an opening 31 is formed. In the same figure, after selectively removing and cleaning a part of the SiO ₂ film 30 exposed by the opening 31 at f, the N ⁺ source ohmic layer 33 is removed according to the usual diffusion technique. This shows the state in which it has been formed. 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 experimental example will be described with reference to FIGS. 3 c' to g'. Figure 3 c' shows the SiO ₂ film 23 applied to the substrate in the state shown in Figure 3 b using hydrofluoric acid.
After removing the SiO ₂ film 34, a new SiO 2 film 34 is shown. d' in the figure is exactly the same as in the case of the above-mentioned figure d, and is based on the conditions of the experimental example that forms the basis of the present invention.
This shows a state in which a negative type photoresist 35 of KMR752 is formed, and an opening 36 is formed. In the same figure, e' is exposed by the opening 36.
A state in which a portion of the SiO ₂ film 34 has been selectively removed using an ordinary etching solution for SiO ₂ films is shown. however,
Here, the immersion time in the etching solution is 2 times longer than usual.
The SiO ₂ film 34 on the vertical side surfaces is mostly removed because it has been extended to about double the length and caused overetching. Figure f' shows a state in which a P ⁺ diffusion layer 37 is formed immediately after the step e' by the usual method.
A SiO ₂ film 38 is formed by this diffusion process. In the same figure, g′ is after the process of f′ is completed, and from the above d to g
In exactly the same way as in the previous steps, the P ⁺ gate 37 and the N ⁺ source ohmic layer 33 are formed by the process including the process based on the experimental example that is the basis of the present invention, and the basic structure of the SIT is completed. shows.

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 required when using conventional ultraviolet exposure methods, and the surface has unevenness and steps. For a workpiece having a side surface of the unevenness or stepped portion substantially perpendicular to the surface, at least the top side of the side surface of the unevenness or stepped portion can be processed inexpensively and easily. A processing method is obtained.

[Brief explanation of the drawing]

FIGS. 1 and 2 are diagrams prepared to explain the contents of the experiment that formed the basis of the present invention. FIG. 3 is a diagram prepared to explain a case where the present invention is applied to the manufacturing process of a cut structure SIT as an embodiment of the present invention. 1,1'...Silicon substrate, 2,2'...SiO ₂ film,
3, 3'... Photoresist film, 4, 4'... Opening portion.

Claims (1)

[Claims] 1. A method for micromachining a workpiece having an uneven surface or a step, the side surface of the unevenness or step being substantially perpendicular to the surface, the method comprising: , a step of applying an organic film and heating and curing it so that at least the top side of the side surface of the unevenness or stepped portion is opened; and using the heated and hardened organic film as a mask, the surface of the workpiece is A microfabrication method characterized in that at least the top side of the side surface of the unevenness or stepped portion is etched.