JPS63239939A - Method and apparatus for introducing impurity into semiconductor substrate - Google Patents

Abstract

PURPOSE:To make it possible to introduce impurities into an inner wall part such as a groove and the like, which are formed in a semiconductor substrate, uniformly with good controllability as in a flat part, by exposing the semiconductor substrate in a pressure reduced compound gas atmosphere including impurities, and heating the substrate. CONSTITUTION:Compound gas including impurities, which are to be introduced into a semiconductor substrate 8, is introduced into a container 2, the inside of which is exhausted. The pressure of the gas in the container 2 is reduced lower than an atmospheric pressure. The temperature of the semiconductor substrate 8, which is provided in the container 2, is made higher than the temperature of the inner wall of the container 2. For example, the silicon substrate 8 is mounted on a sample stage 13 in the impurity introduced chamber 2. Arsine is introduced through a gas introducing system 18. The substrate 8 is heated with infrared-ray lamps 14. A temperature of 1,000 deg.C is kept for one minute. The arsine is decomposed on the surface and in the vicinity of the surface of the substrate. Arsenic is introduced into the surface of the substrate. Then the arsine is evacuated, and argon is introduced. Thereafter the substrate 8 is heated again with the infrared-ray lamps 14. The temperature of 1,000 deg.C is kept for 30 minutes, and the arsenic, which is introduced in the surface of the substrate, is diffused. Thus an N-type conductor layer is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method and apparatus for introducing impurities into a semiconductor substrate.

(Prior art) In recent years, semiconductor integrated circuits such as dynamic RAM (dRAM) have become highly integrated due to miniaturization of component elements.
Particularly in a dRAM using memory cells with a one-transistor/one-capacitor configuration, reducing the number of memory cells is important. A problem when reducing memory cells is that it is important to reduce the amount of charge stored in cell capacitors in order to ensure an SZN ratio with sufficient read margin and to ensure soft error resistance. The conventional method of maintaining the amount of stored charge by thinning the capacitor insulating film is currently difficult to apply because the insulating film approaches its thinning limit in terms of electric field strength and reliability.

Instead, a structure (trench capacitor cell) in which a trench is dug in the surface of the silicon substrate in the capacitor region and the sidewalls of the trench are used to increase the effective capacitor area is seen as a promising method for maintaining the amount of stored charge. has been done.

Various structures have been considered for trench capacitor cells, but the structure in which a highly concentrated impurity diffusion layer is formed inside the trench prevents the depletion layer from extending toward the substrate, reducing the amount of accumulated charge in the capacitor. Therefore, it is also possible to operate at 1/2 Vcc, and the load on the capacitor insulating film is also reduced. In this case, it is important to have a method for doping impurities uniformly and with good control on the vertical side surfaces inside the narrow and deep trench.

Conventionally, in integrated circuit processes, ion implantation has been widely used to form diffusion layers due to its characteristic good controllability. However, when applying the ion implantation method to a trench structure, since the direction of implantation of impurity ions is constant, a portion is formed that shadows the implanted ions on the vertical side surfaces of the trench, resulting in a region where no impurity is implanted. Possible means of eliminating shadowed regions include changing the implantation tilt angle and rotating the silicon substrate. However, none of these methods can be applied to narrower and deeper grooves that are expected to result from future high integration.

As a method of forming an impurity diffusion layer of a trench capacitor in place of the ion implantation method, a method using in-phase diffusion can be considered. This is a method in which a polycrystalline silicon film or a silicon oxide film doped with impurities is formed inside the trench as a diffusion source, and then the impurities are introduced into the surface of the silicon substrate by thermal diffusion. In this case, the problem is how to form the diffusion source, and it is necessary to uniformly form a homogeneous film with an appropriate impurity concentration on the inner wall of the trench. However, the narrower the groove opening and the deeper the groove, the more difficult it becomes to form a uniform diffusion source.

For example, in the case of forming by chemical vapor deposition (CVD), the closer to the bottom of the groove the coverage becomes worse and the film becomes thinner. This thinning causes an insufficient amount of impurity diffusion, and the concentration of the impurity diffusion layer becomes uneven between the top and bottom of the U. In addition, with the method of applying and drying a solution containing impurities and using it as a diffusion source, there is a risk that the air bubbles inside the groove may not be completely removed.
It is thought that it becomes more difficult to introduce a solution into the grooves, which number more than 100 squares per chip, without leaking, as the opening width of the grooves becomes narrower and the depth thereof becomes deeper. Furthermore, in any case, in the solid-phase diffusion method, it is necessary to remove the diffusion source after diffusion, which inevitably results in a complicated process.

In other words, with existing impurity introduction methods, it is possible to controllably introduce impurities not only into capacitor cells of dynamic random access memory but also into the inner walls of deep trenches with narrow openings formed on the silicon surface. It is difficult to do so.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned points, and its purpose is to provide the inner wall portion of a groove etc. formed in a semiconductor substrate with a flat portion similar to a flat portion. It is an object of the present invention to provide a method and apparatus for introducing impurities into a semiconductor substrate, which makes it possible to introduce impurities uniformly and with good controllability.

[Structure of the invention]

(Means for Solving the Problems) The present invention is a method for introducing impurities into a semiconductor substrate by exposing the semiconductor substrate to a reduced pressure atmosphere of a compound gas containing impurities and heating the semiconductor substrate. The purpose is to decompose the compound at or near the surface of the substrate and diffuse the impurities into the semiconductor substrate. The present invention also provides an apparatus for introducing impurities for the above method, which includes means for introducing and exhausting a compound gas containing impurities into a container, means for reducing the pressure in the container to below atmospheric pressure, and a device disposed in the container. The semiconductor substrate is heated to a higher temperature than the inner wall of the container.
and holding means.

(Function) According to the present invention, it is possible to introduce impurities uniformly and with good controllability into, for example, a groove with a narrow and deep opening in a semiconductor substrate, similarly to the flat portion.

In other words, by using a compound gas containing impurities in a reduced pressure state as an impurity diffusion source, the mean free path of the compound molecules containing impurities is lengthened.
For example, it is possible to reliably infiltrate compound molecules containing impurities as a diffusion source into the inside of a narrow and deep groove of an opening on a semiconductor substrate, and the impurity can be uniformly distributed deep into the groove in the same way as in a flat area. can be introduced. Furthermore, by increasing the amount of impurity-containing compounds contained in the atmosphere, the amount of impurities introduced into the semiconductor substrate is determined by the solid solubility limit and diffusion coefficient of the impurity in the substrate at the temperature at which the semiconductor substrate is heated. Therefore, it is possible to introduce impurities with good controllability. Further, unlike the case where an in-phase diffusion source is used, since the diffusion source is in a gas phase, a process for removing the diffusion source is not necessarily required, and there is an advantage that the impurity introduction process is not complicated.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a schematic diagram showing an embodiment of an impurity introduction device according to the present invention.

This device includes a sample introduction chamber 1 into which a sample is introduced.

An impurity introduction chamber 2 for diffusing and introducing impurities into a sample and a sample transfer chamber 3 for taking out a sample are arranged in sequence via a first gate valve 4 and a second gate valve 5, respectively. The sample transport device 11 and the second sample transport device [12] sequentially transport impurities into a semiconductor substrate 8, which is a sample, such as a silicon substrate.

Further, the impurity introduction chamber 2 is connected to a turbo molecular pump 9 via a third gate valve 6 and to a rotary pump 10 via a fourth gate valve 7, and is evacuated. is possible. Although not shown, the sample introduction chamber 1 and the sample transfer chamber 3 can also be evacuated.

Furthermore, a first gas introduction system 1 is provided in the impurity introduction chamber 2.
8 and a second gas introduction system 19 are connected via a first valve 16 and a second valve 17, respectively, and introduce a gas containing an impurity compound and an inert gas into the apparatus. can do.

Further, in the impurity introduction chamber 2, there is provided a sample support device 15 that can vertically move a sample having a sample stage 13 made of quartz.
The sample support device 15 further includes an infrared lamp 14, which can heat the sample 8 to a desired temperature.

Next, as an embodiment of the method of the present invention, a method of introducing arsenic into the surface of a silicon substrate having a deep groove with a narrow opening using the above-mentioned apparatus will be described.

First, the silicon substrate of the sample is transferred to the transfer device 1 in the sample introduction chamber 1.
1, the introduction chamber 1 is sealed.

By evacuating, the pressure in the introduction chamber is reduced to 10-4~
Reduce the pressure to about 10-'Pa.

The impurity introduction chamber 2 is normally equipped with a turbo molecular pump 9 toSP.
After opening the first gate valve 4, the sample is transferred to the sample stage 13 on the sample support device 15 in the impurity introduction chamber 2 using the transfer device 11. And the first
After closing the gate valve 4 and the third gate valve 6 to seal the impurity introduction chamber 2, the first valve 16 is opened and arsine (a hydrogen compound of arsenic) is introduced from the first gas introduction system 18. AgH,) is introduced. After arsine is introduced at a pressure of about 10 -1 to 10 Pa, the first valve 16 is closed and arsine gas is sealed into the impurity introduction chamber 2 .

In this state, the sample silicon substrate (corresponding to the semiconductor substrate 8) 8 was heated with the infrared lamp 14, and
By holding at 0° C. for 1 minute, arsine is decomposed on and near the substrate surface, and a desired amount of arsenic is introduced onto the substrate surface.

Thereafter, the fourth gate valve 7 is opened, and the arsine in the impurity introduction chamber 2 is exhausted by the rotary pump 10. Thereafter, the second valve 17 is opened and argon is introduced at a pressure of about 10-1 to 10 Pa, and then the silicon substrate 8 of the sample is heated again by the infrared lamp 14.
By keeping the temperature at ooo°C for 30 minutes, the arsenic introduced into the substrate surface is diffused, and an n-type groove itN with a desired diffusion depth is formed.
form. Thereafter, by closing the gate valve 7 and evacuating the impurity introduction chamber 2, the steps 10-4 to 10-
Reduce the pressure to about 'Pa.

Next, open the second gate valve 5.

Using the transport device 12, the silicon substrate 8 on the sample stage 13 is
is transferred to the transport device 12 and transported to the sample transport chamber 3 where the pressure is reduced to about 10-4 to 10-'Pa. Thereafter, the gate valve 5 is closed to return the sample transfer chamber 3 to atmospheric pressure, and then the sample silicon substrate 8 is taken out from the apparatus.

By going through the above steps, the process of diffusing arsenic onto the silicon substrate surface is completed, but since arsine, which is a vapor phase impurity diffusion source, is used, the openings formed on the silicon substrate, which is the sample, are It becomes possible to uniformly form arsenic even inside the narrow and deep groove shape.

In the above example, in an impurity compound atmosphere.

Although the substrate heating process is performed, the impurity compound gas may be introduced in a state where the substrate is heated in advance and the substrate temperature is raised.

A thin film containing impurities may be formed on the surface and the impurities may be diffused from this thin film.

Furthermore, in the above embodiments, the high temperature heating step for diffusing impurities introduced into the substrate surface is performed in the same device, but this high temperature heating step may be performed in a separate device.

Furthermore, in the above example, arsine was used as the impurity compound, but if the impurity element to be diffused is phosphorus, arsenic, antimony, boron, or gallium, it may be a hydride, chloride, or fluoride of the element. It's okay.

Furthermore, in the above example, an infrared lamp was used as a method of heating the silicon substrate, but various other methods can be used as long as they irradiate light with energy that can be absorbed by the semiconductor substrate. be.

Furthermore, in the above-mentioned embodiments, the decomposition of compounds containing impurities was carried out by thermal reaction, but it may also be carried out by irradiation with light having sufficient energy for decomposition, or by electron, cyclotron, resonance or magnetron. Using.

A method may be used in which the impurity compound is decomposed and turned into plasma, and then deposited on the surface of the semiconductor substrate or introduced into the substrate.

Using the method according to the above embodiment, FIG. 2(a), (
Figure 2(C) shows the C-V (capacitance-voltage) characteristics of a MOS capacitor when a diffusion layer is formed inside the trench and on the main surface of a silicon substrate, as shown in the plane and cross section in Figure 2(C). In FIG. 2(C), the C-■ characteristics of the capacitors formed by the conventional example and the above embodiment are compared. In the conventional example, as shown in cross-sections in FIGS. 2(d) and 2(e), there is a region in the groove portion of the semiconductor substrate into which impurities are not introduced, so that the substrate becomes depleted in that region and the capacitance decreases. But 1
In this embodiment, the impurities are uniformly diffused as shown in the cross section of FIG. 2(d), so that the capacitance can be maintained.

In this embodiment, the case of a MOS capacitor was explained, but
By applying the invention to the process of introducing impurities into other semiconductor substrates with shapes such as narrow and deep grooves on the surface, a uniform and well-controlled impurity diffusion layer can be created not only on the flat parts but also inside the grooves. can also be formed.

〔Effect of the invention〕

According to the present invention, the surface of a silicon substrate having concave grooves is suitable for high integration. It is possible to form an impurity layer that is uniform and provides a predetermined conductivity type with good controllability. Therefore, for example, as the aspect ratio of grooves formed on the surface increases with the miniaturization of element regions, it becomes possible to diffuse impurities into the inside of the fine deep grooves, thereby increasing the degree of integration of elements. and is effective for speeding up.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an embodiment of an impurity introduction device according to the present invention, and FIG. 2 shows the effect of the embodiment of the present invention by M
FIG. 3 is a diagram showing the results of evaluation in comparison with a conventional example based on C-■ characteristics of an OS capacitor. 1... Sample introduction chamber, 2... Impurity introduction chamber,
3... Sample carry-out chamber, 4... First gate valve, 5... Second gate valve, 6... Third gate valve, 7... Fourth gate valve, 8. ...Silicon substrate, 9...Turbo molecular pump, 10...Rotary pump, 11.12...
Sample transport device, 13... Quartz sample stand, 14...
- Infrared lamp, 15... sample support device, 16.
17...Valve. 18...First gas introduction system, 19...Second gas introduction system. 101...P-type silicon substrate, 102...gate insulating film, 103...polysilicon gate electrode, 104...n
type impurity diffusion layer. 105...A deep groove with a narrow opening. Agent Patent Attorney Nori Chika Ken Yudo Kikuo Takehana Diagram 2! Figure 2

Claims (13)

[Claims] (1) Introducing a compound gas containing impurities to be introduced into a semiconductor substrate into a container, evacuating the inside of the container to reduce the gas pressure in the container to below atmospheric pressure, and installing the compound gas in the container. A method for introducing impurities into a semiconductor substrate, the method comprising heating the heated semiconductor substrate to a higher temperature than the inner wall of the container. (2) In the method for introducing impurities into a semiconductor substrate according to claim 1, after heating the semiconductor substrate in the container exposed to a reduced pressure atmosphere of a compound gas containing impurities, the impurities are introduced into the semiconductor substrate. 1. A method of introducing impurities into a semiconductor substrate, comprising decomposing a compound contained therein at or near the surface of the semiconductor substrate and diffusing the impurity into the semiconductor substrate. (3) In the method for introducing impurities into a semiconductor substrate according to claim 1, after heating the semiconductor substrate in a container exposed to a reduced pressure atmosphere of a compound gas containing impurities,
The method is characterized in that the impurity compound is decomposed on the surface of the semiconductor substrate or in the vicinity thereof, the impurity is deposited on the surface of the semiconductor substrate, and then the semiconductor substrate is heat-treated to diffuse the impurity into the semiconductor substrate. A method of introducing impurities into a semiconductor substrate. (4) In the method for introducing impurities into a semiconductor substrate according to claim 1, a deposition gas of a compound containing an impurity is introduced into a container, and the inside of the container exposed to the reduced pressure gas atmosphere is The semiconductor substrate is heated to cause a decomposition reaction of impurity compounds and deposition gas at or near the surface of the semiconductor substrate to deposit a thin film containing impurities on the surface, and the semiconductor substrate is subjected to semiconductor heat treatment to remove the impurities. A method of introducing an impurity into a semiconductor substrate, characterized in that the impurity is diffused into the semiconductor substrate through the thin film containing the above. (5) In the method for introducing impurities into a semiconductor substrate according to claim 1, after heating the semiconductor substrate in the container under reduced pressure, a compound gas containing impurities is introduced into the container, and the impurity is removed. A method for removing impurities into a semiconductor substrate, characterized in that a compound is decomposed on the surface of the semiconductor substrate or in its vicinity, a desired amount of impurities is diffused into the semiconductor substrate, and immediately thereafter, the impurity gas is exhausted again. How to introduce it. (6) In the method for introducing impurities into a semiconductor substrate according to claim 1, after heating the semiconductor substrate in a container under reduced pressure, a gas containing an impurity compound is introduced into the container. After the compound is decomposed on or near the semiconductor surface and deposited on the surface of the semiconductor substrate, the gas of the impurity compound is exhausted, and then the semiconductor substrate is heat-treated to diffuse the impurity into the semiconductor substrate. A method for introducing impurities into a semiconductor substrate, characterized by: (7) In the method for introducing impurities into a semiconductor substrate according to claim 1, after heating the semiconductor substrate in a container under reduced pressure, a deposition gas containing an impurity compound is introduced into the container. , the impurity compound and the deposition gas are decomposed and reacted on or near the semiconductor surface to deposit a thin film containing the impurity on the surface, the impurity compound and the deposition gas are exhausted, and then the semiconductor 1. A method of introducing impurities into a semiconductor substrate, comprising heating the substrate and diffusing impurities into the semiconductor substrate through a thin film containing impurities. (8) A method for introducing impurities into a semiconductor substrate according to any one of claims 2 to 7, wherein the semiconductor substrate is silicon. (9) Impurities in the semiconductor substrate according to claims 2 to 7, characterized in that a groove or hole with an opening having a minimum width of 2 μm or less is formed on the surface of the semiconductor substrate. How to introduce it. (10) As the impurity compound, a hydride of an element such as phosphorus, arsenic, antimony, boron, or gallium;
A method for introducing an impurity into a semiconductor substrate according to claims 2 to 7, wherein the impurity is a chloride or a fluoride. (11) A method for introducing impurities into a semiconductor substrate according to any one of claims 2 to 7, characterized in that the semiconductor substrate is heated by irradiation with light having energy that can be absorbed by the semiconductor substrate. (12) Decomposition of the impurity compound by thermal reaction, photoreaction,
Alternatively, the method for introducing impurities into a semiconductor substrate according to claims 2 to 7, characterized in that the method is carried out by a plasma reaction using ECR or a magnetron. (13) a container, a means for introducing a compound gas containing impurities into the container, a means for evacuating the inside of the container, a means for reducing the gas pressure in the container to below atmospheric pressure; An apparatus for introducing impurities into a semiconductor substrate, comprising: heating means for heating and maintaining the semiconductor substrate to be installed at a higher temperature than the inner wall of the container.