JP2002246330A - Ion implantation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ion implantation method at a low cost, with which the degradation of the base surface of a resist coating film is prevented. SOLUTION: In this ion implantation method, a protective film is formed on a part other than a region to be doped on a substrate to be processed, the substrate is irradiated with ionized dopant atoms and the dopant atoms are doped to the surface layer part of the substrate without the protective film. The protective film is turned into a two-layer structure of a heat resistant film and a photoresist film, the heat resistant film 3 is formed between the substrate 2 and the photoresist film 4, and the heat resistant film is removed from the substrate together with the photoresist film, after ion implantation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an ion implantation method used in a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art Conventionally, in a process of manufacturing an electronic device using a semiconductor, mainly Si, a predetermined portion of a crystal of Si is doped with a predetermined amount of impurities. Conventionally, as a doping method, a diffusion method or an ion implantation method has been used. However, when a doping profile as shallow as about 1 μm is formed, the ion implantation method is used.

FIG. 2 shows the principle of a conventional ion implantation method. A protective mask (photoresist film) having an opening only on the part to be doped on the substrate 2 to be doped.
4 is formed. On this substrate 2, atoms to be doped (hereinafter referred to as dopants) are ionized, and several tens ke
Irradiation is performed by accelerating to a kinetic energy of about V. This allows the dopant to be implanted into the Si crystal through the opening. In order to change the density of the dopant implanted in the crystal, the dose of the implanted dopant may be controlled. The implantation depth of the dopant in the crystal can be controlled by changing the acceleration energy of the dopant.

[0004]

However, in the conventional ion implantation method, thermal deterioration of the protective mask 4 has been a problem. Conventionally, a photoresist film has been used for the protective mask 4 because the opening can be easily processed. The protective film has a function of preventing the implanted dopant from reaching the Si crystal. Therefore, heat is generated on the surface of the protective film during ion irradiation. When the ion irradiation amount is increased, the protective film is overheated, causing burn-in. As a result, the resist film is carbonized, sticks, and the surface of the Si is modified, and then, when the film is laminated thereon, the adhesion becomes poor,
This was a cause of yield deterioration. Therefore, after the ion implantation, a method of exposing to an oxygen plasma atmosphere to remove the sticking carbide, further oxidizing the surface of the Si crystal, and etching the surface with hydrofluoric acid has been adopted.

The method of exposing to such oxygen plasma is as follows.
There were problems such as high cost due to the dedicated device, time and labor costs. Such a problem is caused by the use of a resist as a protective film. To avoid this problem, a method using an SiO ₂ film or a Si ₃ N ₄ film has been proposed. In this case, a plasma CVD apparatus is required, which increases cost. Problem had arisen.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a low-cost ion implantation method capable of preventing deterioration of a base surface due to contact with a deteriorated resist coating film. With the goal.

[0007]

According to the ion implantation method of the present invention, a protective film is formed on a portion other than a region to be doped on a substrate to be processed, and the substrate is irradiated with ionized doping atoms. In an ion implantation method in which doping atoms are doped into a surface layer portion of a substrate without a protective film, the protective film has a two-layer structure of a heat-resistant film and a photoresist film, and the heat-resistant film is formed of a substrate and a photoresist film. The method is characterized in that the heat-resistant film is removed from the substrate together with the photoresist film after ion implantation.

It is desirable to use a glass film as the heat resistant film. In this case, it is preferable to use a spin coating glass film as the glass film.

As a method of forming a glass film, a solution in which alkoxylan (molecule obtained by combining oxygen, carbon and hydrogen in Si) is dissolved in an organic solvent is applied or spin-coated on a substrate to be processed, and then the substrate is cooled to room temperature. It is preferable that the organic solvent in the coating solution is volatilized by leaving the coating solution at high temperature or heating to a high temperature.

Further, it is preferable that an aqueous solution containing hydrofluoric acid is brought into contact with the substrate after the ion implantation, and a portion of the glass film is dissolved, so that the photoresist film thereon floats up and is removed from the substrate. .

(Effect) As shown in FIG. 1E, by inserting a glass film between the photoresist film and the substrate surface, even if the resist film is carbonized after ion implantation, the carbonized resist remains Since it is not in contact with the substrate surface, the substrate surface does not deteriorate. The resist film is carbonized, for example, at about 300 ° C., but the glass film does not deteriorate to about 1000 ° C. Due to this difference in durability temperature, even if the resist film is burned and carbonized at the time of ion implantation, the glass itself hardly deteriorates. If the glass is not deteriorated, the surface of the substrate is not deteriorated, thereby avoiding the problem of yield deterioration.

Conventionally, there has been a problem of sticking of the carbonized resist. However, in the present invention, since a glass film is inserted, the glass film is exposed to an aqueous solution containing hydrofluoric acid after ion implantation, and the glass film portion of the protective film is removed. By dissolving and lifting the resist film on the protective film, the protective film can be removed without leaving sticking. The sticking itself is caused by the reaction between the substrate and the carbonized resist.By inserting glass, the carbonized resist sticks to the glass film. Is done.

In the present invention, since an expensive apparatus is not used for coating in forming a glass film, an increase in cost due to a dedicated apparatus can be avoided as compared with the conventional method of forming a protective film using only a resist film. Further, in the step of removing sticking, the oxygen plasma treatment becomes unnecessary, and the cost can be reduced accordingly. In the above protective film, a glass film and a resist film
If only the glass film is used instead of the amount, the following problems occur. When a glass film is formed on a substrate to be processed, many cracks (cracks) occur in the glass film due to a difference in thermal expansion between the glass film and the substrate to be processed. Since the glass film is hard and brittle, cracks easily occur. If ion implantation is performed in a state where a crack has occurred, the implanted ion cannot be blocked at the crack, and the function as a protective film cannot be performed. On the other hand, by attaching a resist film to the glass film, the resist film itself has flexibility, does not crack, and functions completely as a protective film by ion implantation. Further, the advantage of avoiding sticking as described above can be enjoyed.

[0014]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In the present embodiment, a case where the ion implantation method of the present invention is used for manufacturing a semiconductor device will be described.

As shown in FIG. 1A, the silicon substrate 2 in the initial state has a thickness of 600 μm.

As shown in FIG. 1B, a solution in which alkoxylan (molecule obtained by combining oxygen, carbon, and hydrogen with Si) is dissolved in an organic solvent is applied to one surface of the silicon substrate 2, and the glass film 3 is formed. Form. It is desirable to use a spin coating method for applying the solution, but another coating method such as brush coating may be used.

After the application of the solution, the substrate 2 is left at room temperature for about 1 hour or heated to a high temperature of 100 ° C. or more to volatilize the solvent contained in the coating film and form a glass film 3 having an average thickness of 0.1 μm. And

A photoresist solution is applied onto the glass film 3 by a spin coating method and heated to a predetermined temperature to form a photoresist film having an average thickness of 2 μm. Next, the resist film 4 is pattern-etched by photolithography to form a resist film 4 having an opening 5a in which only the region to be ion-implanted is opened as shown in FIG.

The substrate 2 having the resist film 4 is immersed in an aqueous solution containing hydrofluoric acid for a short time to dissolve and remove the glass film 3 in the resist opening 5a. Thereby, as shown in FIG. 1D, an opening 5b from which the base of the silicon substrate 2 is exposed is obtained. The substrate 2 is washed and dried.

Thereafter, the silicon substrate 2 is loaded into an ion implantation device (for example, an electron beam excitation type ion implantation device), and n-type ions are implanted into the ion implantation region 5c under predetermined conditions. When high-energy ions are implanted, ions are also implanted into the photoresist film 4 around the ion-implanted region 5c, and a considerable part of the kinetic energy is converted into heat energy and becomes high temperature. Is carbonized. The carbonized photoresist film 4
Although it adheres firmly to the glass film 3 by burning, it does not stick to the silicon substrate 2 because the glass film 3 is inserted. Therefore, thermal deterioration of the silicon substrate 2 is effectively prevented.

Thereafter, the glass film 3 is completely removed by immersing the substrate in a hydrofluoric acid solution, so that the photoresist film 4 is simultaneously peeled off. Thereby, silicon substrate 2 having high concentration region 5c of the n-type dopant is obtained. The silicon substrate 2 thus obtained is suitable for the manufacture of high-quality semiconductor devices because the carbonized resist film does not stick to the surface except for the region 5c and is not deteriorated.

Next, examples of the present invention and comparative examples will be described. (Example) A silicon substrate 2 having a diameter of 4 inches was used as a substrate to be processed. The silicon substrate 2 has a thickness of 650 μm.

The formation of the protective film was performed as follows.

As a solution for forming a glass film, a 5.9% OCD agent solution manufactured by Tokyo Ohka Co., Ltd. prepared by dissolving alkoxylan in a butyl acetate solution was used. The same solution is supplied on the Si substrate 2 in a predetermined amount, and the substrate 2 is supplied at 2000 rpm.
m for about 30 seconds, and as shown in FIG.
A glass film 3 having an average thickness of 0.1 μm was formed on one surface of the i-substrate 2. Further, the substrate 2 was left in an atmosphere of about 85 ° C. for about 1 hour to volatilize the organic solvent contained in the glass film 3.

Thereafter, a positive resist agent manufactured by Tokyo Ohka Co., Ltd. was spin-coated on the substrate 2 to form a photoresist film 4 having an average film thickness of 2 μm. Then, the resist film 4 in the region to be ion-implanted was partially removed by photolithography pattern etching to form an opening 5a shown in FIG. 1C. The substrate 2 is immersed in a 1% aqueous solution of hydrofluoric acid for only a few seconds to dissolve and remove the glass film 3 exposed at the opening 5a, and to expose the substrate of the silicon substrate 2 shown in FIG. The portion 5b was formed.

Five substrates of the above embodiment were tested. Phosphorus (P) ions were accelerated to a kinetic energy of 50 keV, and each substrate was irradiated. The irradiation dose is 5
× 10 ¹⁵ / cm ² . As a result, the entire resist film on the surface was carbonized. However, this substrate was treated with 1% hydrofluoric acid.
By dipping in the solution for several minutes or more, the glass film 3 under the resist film was melted, so that the carbonized resist film was easily separated from the substrate. The surface characteristics of the silicon substrate after removing the resist were evaluated by microscopic observation. As a result of examining the five silicon substrates, there was no remaining residue or sticking of the resist.

(Comparative Example) As a comparative example, a case where ions are implanted into a substrate 5 without a glass film, that is, a region 5c of the substrate 2 directly coated with the resist film 4 shown in FIG. 2 will be described. Ten or more substrates of this comparative example were tested. Ion implantation was performed under the same conditions as in the above embodiment. As a result, the resist film was carbonized in all of the substrates, and the carbonized resist film could not be dissolved and removed by the chemical solution treatment, and was removed by oxygen plasma treatment. Further, discoloration was observed on the surface of the Si substrate after the removal, and alteration due to contact with the carbonized resist was also confirmed. In a part where the deterioration occurs, the metal film is peeled off when the metal film is laminated in a later step, which causes a decrease in the yield at the time of finishing the processing as an electronic device.

[0028]

According to the present invention, it is possible to avoid the problem of sticking and deterioration of the substrate surface due to burning of a resist as a protective film during ion implantation. As a result, when an electronic device is subsequently formed, problems such as deterioration of metal adhesion can be solved, and ultimately yield can be improved. In addition, oxygen plasma treatment was conventionally required to remove sticking due to burning of resist, but this can be omitted in the present invention, and the cost can be reduced.

[Brief description of the drawings]

FIGS. 1A to 1E are process diagrams showing an ion implantation method according to an embodiment of the present invention.

FIG. 2 is a principle diagram for explaining a conventional ion implantation method.

[Explanation of symbols]

 Reference numeral 2 denotes a silicon substrate; 3 denotes a heat-resistant film (glass film); 4 denotes a protective mask (photoresist film); 5a and 5b denotes an opening;

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroshi Sokita 3-1-1, Nishiawaji, Higashiyodogawa-ku, Osaka-shi, Osaka F term (reference) 4K029 AA06 BB03 BD01 CA10 HA05 5F058 AD05 AD08 AG03 AG06 BD01 BD07 BH11 BH15

Claims (4)

[Claims] A protective film is formed on a portion of a substrate other than a region to be doped on a substrate to be processed, and the substrate is irradiated with ionized doping atoms, so that doping atoms are applied to a surface layer portion of the substrate without the protective film. In the ion implantation method for doping, the protective film has a two-layer structure of a heat-resistant film and a photoresist film, and the heat-resistant film is formed between a substrate and a photoresist film. An ion implantation method characterized by removing the photoresist film from the substrate together with the photoresist film. 2. The method according to claim 1, wherein a glass film is used as the heat-resistant film. 3. A method of forming a glass film, comprising: applying or spin-coating a solution of alkoxylan (molecule obtained by combining oxygen, carbon, and hydrogen on Si) in an organic solvent onto a substrate to be processed; The method according to claim 2, wherein the substrate is left at room temperature or heated to a high temperature to volatilize the organic solvent in the coating solution. 4. The method according to claim 1, wherein an aqueous solution containing hydrofluoric acid is brought into contact with the substrate after the ion implantation, and a portion of the glass film is dissolved, so that the photoresist film thereon floats up and is removed from the substrate. The method according to claim 2, wherein