JPH0365891B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) This invention relates to a method for protecting a semiconductor substrate during a fabrication process.

(Prior Art) Compound semiconductors such as GaAs are attracting attention as materials for high-speed integrated circuits that utilize high electron mobility or opto-electronic devices that utilize light emitting properties.

Currently, most of the processes such as crystal growth, etching, and ion implantation for manufacturing the above-mentioned devices are performed using independent equipment. However, compound semiconductors have problems that silicon does not have when processing substrates, such as the substrate surface being easily oxidized and an oxide film forming on the surface even when exposed to the atmosphere, resulting in deterioration of device characteristics. For example, when performing processes such as epitaxial crystal growth, ion implantation, and dry etching, a natural oxide film with a thickness of several tens of angstroms has already been formed on the surface of a compound semiconductor substrate, so the surface must first be cleaned with acid treatment. must be carried out. Furthermore, since the semiconductor substrate is exposed to the atmosphere even after crystal growth, ion implantation, etching, etc., oxidation of the substrate surface is inevitable. In particular, in dry etching using a reactive gas, the surface of the substrate after etching is contaminated by the etching gas, making it impossible to obtain a highly clean surface. Therefore, when manufacturing devices by attaching electrodes after dry etching, a method is used in which the substrate surface is cleaned by heat treatment, but since this heat treatment is performed in equipment installed in the atmosphere, Therefore, oxidation of the substrate surface is inevitable.

Furthermore, when crystal growth is performed by molecular beam epitaxial method after dry etching, the substrate is baked at high temperature in a vacuum preparatory chamber to clean the surface, but it is difficult to remove the oxide film formed by exposure to the atmosphere. Not enough. For this reason, recently, various processes such as cleaning, ion implantation, and epitaxial growth are performed by connecting the respective devices airtightly.
A method has been proposed in which the process is performed continuously without exposing the semiconductor substrate to the atmosphere.

(Problems to be Solved by the Invention) However, even in a high vacuum of 10 ^-9 Torr, the etched substrate surface is clean and therefore tends to adsorb residual gas. Therefore, when a semiconductor substrate is moved between the above-mentioned connected devices, the processed surface of the substrate is contaminated and oxidized even under a certain degree of vacuum.

The above is a problem that mainly occurs when multiple processes are performed on compound semiconductors such as GaAs using different equipment, but it also occurs in the case of single-element semiconductors such as Si.
The surface of the substrate after dry etching is susceptible to contamination, as is the case with compound semiconductors.

This invention was made in view of the above, and
It is an object of the present invention to provide a method for protecting a semiconductor substrate, which prevents contamination and oxidation of the processed surface when the processed semiconductor is transported to the next process.

(Means for solving the problem) In order to solve the above-mentioned problem, in the present invention, as shown in the process diagram of FIG. 2, in the substrate processing apparatus A, after cleaning the semiconductor substrate, a predetermined Perform processing. Immediately on the surface of the processed semiconductor substrate, neutral chlorine radicals generated by discharge plasma are adsorbed at a temperature of 250°C or less to form a protective film, and then the substrate is airtightly connected to substrate processing equipment B. It is transported to the substrate processing apparatus B via the transport pipe C. In the substrate processing apparatus B, the next step of processing is performed after removing the protective film on the processing surface of the substrate by heat treatment or the like. In this way, a protective film made of neutral chlorine radicals is formed on the processed surface of the semiconductor substrate, and the surface of the semiconductor substrate is temporarily prevented from being contaminated or oxidized while being transported to the processing equipment for the next step. Therefore, the semiconductor substrate to which the present invention is applied is effective not only for compound semiconductors but also for single element semiconductors.

When adsorbing chlorine neutral radicals, the semiconductor substrate surface is held at a temperature below 250°C or around room temperature in order to efficiently adsorb chlorine neutral radicals on the substrate surface and form an effective protective film. 250℃
If this is the case, there is a risk that the surface of the substrate will be etched by the neutral chlorine radicals.

Although FIG. 2 shows a process diagram of the present invention, the present invention will be explained in detail by illustrating specific constituent devices of each step in FIG. 1. In Figure 1, A is a substrate processing device, B is a substrate processing device for the next process, and C is a transport pipe that airtightly connects both substrate processing devices, and the vacuum inside the pipe is approximately 10 ^-9 Torr. I'm keeping it. In the illustrated embodiment, the substrate processing apparatus A consists of a plasma chamber 1 and a sample processing chamber 2, and an opening formed at the interface between the two chambers has a large number of through holes, and a predetermined interval is maintained between the two chambers. An electrode 7 composed of two mesh electrode plates 7a and 7b arranged in parallel is provided. There is a support stand 6 below the electrode 7 in the sample processing chamber 2, on which a semiconductor substrate 3 to be processed is placed.

The next process substrate processing apparatus is a vacuum evaporation apparatus in this embodiment, and an evaporation source 9 is provided in the lower part of the evaporation chamber 8. Gas molecules 10 released from the evaporation source 9 by an appropriate heating means are applied to the semiconductor sample 3. is deposited on top.

The above substrate processing apparatuses A and B are airtightly connected by a transport pipe C, and the transport pipe is provided with a valve 11 as necessary, and a vacuum pump (not shown) is connected to the transport pipe, and the semiconductor substrate The structure is designed to maintain a vacuum level of approximately 10 ^-9 Torr inside the container during transportation.

(Operation) The semiconductor substrate 3 to be processed is placed on the support stand 6 in the sample processing chamber 2 of the substrate processing apparatus A. The surface of this semiconductor substrate 3 is cleaned in advance if necessary.

Etching gas such as Cl is supplied to the plasma chamber 1 from the gas introduction pipe 12, and discharge is caused by a microwave electric field to form plasma. By applying a positive potential to the electrode 7a and the plasma chamber, it acts as an ion extraction electrode, and the ions 4 in the plasma are guided to the sample processing chamber 2 while being accelerated, and the semiconductor substrate 3 is etched as shown in FIG. 3a. will be held.
The neutral chlorine radicals 5 in the plasma chamber 1 also diffuse into the sample processing chamber 2 through a number of holes provided in the electrode 7, come into contact with the semiconductor substrate 3, and are etched together with the ions.

After a predetermined amount of etching has been performed on the semiconductor substrate 3, the ions are prevented from entering the surface of the substrate by appropriate means, and the temperature of the semiconductor substrate 3 is kept below 250°C, so that the semiconductor substrate 3 is etched as shown in FIG. Board 3
The chlorine neutral radicals 5 begin to be adsorbed on the surface, and a chlorine neutral radical deposit layer 5' is formed. In this invention, this chlorine neutral radical deposited layer is used as a protective film against contamination, oxidation, etc. of the processing surface of a semiconductor substrate.

There are various methods to prevent ions in the discharge plasma from entering the substrate surface and to bring only chlorine neutral radicals into contact with the substrate. An appropriate rotation means (not shown) is provided to rotate the supporting base 6, and when the etching by ions 4 is completed and the step of forming a protective film by chlorine neutral radicals 5 begins, the supporting base 6 is rotated. Rotate 180 degrees so that the back surface of the support base 6 faces the electrode 7. As a result, since the ions 4 extracted from the electrode 7 into the sample processing chamber 2 have directionality, they collide with the back surface of the support base 6 and are prevented from entering the surface of the substrate 3. However, since the chlorine neutral radicals 5 have been diffused into the processing chamber, they come into contact with the semiconductor substrate 3 on the support stand 6 and are adsorbed, forming a protective film on its surface as shown in FIG. 3b.

In FIG. 4b, a shutter 13 is interposed between the electrode 7 and the semiconductor substrate 3, and the ions 4 traveling straight toward the semiconductor substrate are collided with the shutter 13 by utilizing the directionality of the ions. prevent entry into. On the other hand, the chlorine neutral radicals diffuse within the processing chamber 2 in the same manner as described above, come into contact with the semiconductor substrate, and form a protective film.

The above two examples have shown the method of physically preventing ions from entering the semiconductor substrate, but next we will explain the method of electrically preventing ions from entering the semiconductor substrate using Figure 4c. Of the electrodes 7 provided, a ground potential is applied to the electrode plate 7a, and a bias voltage such that the current value of the ion current monitor 14 becomes zero is applied to the electrode plate 7b. As a result, the ions in the plasma chamber 1 are repelled by the electrode plate 7b kept at a positive potential after passing through the holes in the electrode plate 7a, and are prevented from entering the sample processing chamber 2. On the other hand, since the neutral chlorine radicals have no electric charge, they are not reflected by the electrode 7, but are sequentially diffused into the processing chamber 2 through the many holes of the electrode, and are adsorbed and deposited on the surface of the semiconductor substrate. In FIG. 4d, a bias voltage is applied between the substrate 3 and the ground potential so that the surface of the semiconductor substrate 3 is kept at a positive potential and the current value of the ion current monitor 14 becomes zero. Therefore, since the substrate 3 is kept at a positive potential, the ions 4 extracted into the sample processing chamber 2 are
It is repelled and cannot enter the substrate 3. On the other hand, since neutral chlorine radicals have no charge as described above, they are adsorbed and deposited regardless of the positive or negative potential of the substrate. In Fig. 4e, in the sample processing chamber 2,
A pair of electrodes 15a and 15b are provided next to the electrode 7, and a voltage is applied to the electrode 7a and the plasma chamber wall so as to have a positive potential.
A voltage is applied so that one of a and 15b has a negative potential. For this reason, the electrode 7 acts as an ion extraction electrode, and ions are guided into the processing chamber 2 by accelerating the many holes in the electrode 7, but of the pair of electrodes 9a and 9b, the electrode held at a negative potential is The chlorine neutral radicals 5 are deflected to the side, are prevented from entering the substrate surface, and only the chlorine neutral radicals 5 are deposited on the semiconductor substrate surface.

After preventing ions from entering the semiconductor surface as described above and forming a protective film of a predetermined thickness on the surface of the semiconductor substrate 3 using neutral chlorine radicals, the substrate 3 is transferred to a transport pipe using a known appropriate method. C, and then transferred to the next process substrate processing apparatus B. At this time, the degree of vacuum within the transport pipe C is maintained at approximately 10 ^-9 Torr. Exposure of this protective film to the atmosphere is undesirable because acids will be formed by the moisture in the atmosphere, but under the above-mentioned vacuum conditions, radicals with a thickness of several 100 to 1000 Å are deposited, making it a useful protective film. Become.

After the semiconductor substrate 3 is installed at a predetermined position in the substrate processing apparatus B, the protective film is removed. This protective film can be easily removed by heating or irradiation with a charged beam. That is, as shown in FIG. 5a, a heating means 16 such as a heater or an infrared lamp is built into the support 6 of the substrate 3, and the substrate 3 is heated to 250° C. or higher, thereby depositing on the surface of the substrate 3. The protective film is evaporated and removed. Also, as shown in Figure 5b,
By disposing the heating means 16 on the upper surface of the substrate 3 and heating the substrate, the protective film can be easily removed as in the embodiment shown in FIG. 5a. Furthermore, as shown in FIG. 5c, the deposited neutral radicals 5 can be removed by scanning the surface of the substrate 3 with an electron beam or a slow ion beam 17. The type of protective film removal means to be used depends on the substrate processing apparatus B.
The protective film should be determined taking into account the structure of the semiconductor substrate, etc., but the protective film can be easily removed using any of the removal methods.In particular, the method shown in Figure 5c removes the protective film necessary for processing the semiconductor substrate. The protective film can be selectively removed only in regions.

As described above, after the protective film on the semiconductor substrate 3 is removed, subsequent processes such as crystal growth, ion implantation, metal vapor deposition, and etching are performed without cleaning.

(Example) A process of forming a gate portion of a recessed structure of a field effect transistor using GaAs as a semiconductor substrate will be described as an example of the present invention.

The basic configuration of the apparatus used is roughly the same as that shown in FIG.
A GaAs substrate 3 covered with a SiO ₂ mask was installed.

Cl ₂ gas was supplied as an etching gas from the gas introduction tube 12 to the plasma chamber 1 to generate plasma, and the etching was carried out for 5 minutes under the conditions of a gas pressure of 8 × 10 ^-4 Torr, an applied voltage of 500 V to the ion extraction electrode, and a substrate temperature of room temperature. Dry etching was performed.

After 5 minutes, as shown in FIG.
was rotated 180 degrees, and the back surface of the support was placed to face the electrode 7 to stop the ions from entering the GaAs substrate and adsorb and deposit Cl radicals. Flip to 10
After a few minutes, a protective film with a thickness of about 500 Å was formed on the substrate surface.

Next, the substrate 3 was moved into the vapor deposition chamber 8 of the substrate processing apparatus B through the transport pipe C maintained at a vacuum level of 5×10 ⁻⁹ Torr.

In the deposition chamber 15, a heating device is installed above the support stand, and the substrate 3 is heated at 300°C for 30 minutes to remove the protective film, and then the thickness is deposited on the substrate surface by vacuum evaporation.
A 1 μm Al film was formed and taken out from the deposition chamber, and the Al film formed on the Si mask of the substrate was removed by lift-off.

As a result of forming the gate electrode by etching the gate portion to form a recessed structure and protecting it from contamination, oxidation, etc. as described above, various characteristics of the Schottky junction of the gate electrode were improved.

(Effects of the Invention) As described above, according to the present invention, in a method for processing a semiconductor substrate by transporting the semiconductor substrate between the devices using a plurality of devices that are airtightly connected, when the semiconductor substrate is transported between the devices, By adsorbing and depositing chlorine neutral radicals in discharge plasma on the semiconductor surface and using it as a protective film, even slight contamination and oxidation during transportation can be completely prevented, improving the characteristics of the formed device.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of an apparatus for carrying out this invention, Fig. 2 is a process diagram showing the steps of this invention, and Fig. 3 is a schematic diagram of an apparatus for carrying out this invention.
Figure a is an explanatory diagram showing the etching process on the substrate surface;
Figure 3b is an explanatory diagram when a protective film is formed on the substrate surface, and Figure 4 is a method according to the present invention for preventing ions in plasma from entering the substrate surface and adsorbing only neutral radicals to the substrate surface. For example, the fourth
Figure a shows the method of inverting the substrate together with the support, the fourth
Fig. 4b shows a method using a shutter, Fig. 4c shows a method of providing an electrode held at a positive potential between the plasma chamber and the sample processing chamber, Fig. 4d shows a method of holding the semiconductor substrate at a positive potential, Fig. 4 5e is an explanatory diagram of a method using a deflection electrode, FIG. 5 is an example of a method for removing a protective film formed on a substrate surface, FIG. FIG. 5b is an explanatory view showing a method of arranging a heating means on the top of the substrate, and FIG. 5c is an explanatory view showing a method of removing by irradiating a beam. 1...Plasma chamber, 2...Sample processing room, 3...
Semiconductor substrate, 4... Ion, 5... Neutral radical, 5'... Protective film, 6... Support base, 7... Electrode,
8... Vapor deposition chamber, A, B... Substrate processing equipment, C...
transport pipe.

Claims (1)

[Claims] 1. A method for protecting a semiconductor substrate during a processing process, characterized by forming a protective film by adsorbing neutral chlorine radicals generated by discharge plasma onto the surface of a semiconductor substrate maintained at 250°C or lower.