JPH01196816A - Introduction of impurity - Google Patents

Abstract

PURPOSE:To enable the execution of doping at a room temperature, by a method wherein a flat plate containing a compound of a doping impurity and a semiconductor substrate are disposed in parallel substantially and a reduced-pressure plasma is generated in a gas atmosphere of an inactive gas. CONSTITUTION:A flat plate 6 containing AlAsO4, SiP2O7 or BN or the like is disposed substantially parallel to an Si substrate 7. A tube 5 is filled up with an inactive gas or a gas atmosphere containing this gas and a minute quantity of oxygen. The atmosphere inside the tube 5 is set to be a reducedpressure atmosphere 9 by a mechanical pump. A temperature inside the tube 5 is set at 400 deg.C by an outside heater 10. A high-frequency power and a DC bias voltage are impressed on plasma electrodes 12 and 13. Since a mean free path of a molecule is about 5mum, the quantity of an impurity atom arriving at the bottom surface of a trench groove having a depth of 5mum or below is equal to that on the surface thereof, and consequently a doping layer 3 is formed in the groove uniformly. By this method, the execution of doping at a room temperature is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of introducing impurities into a substrate by heat treatment.

2. Description of the Related Art One conventional method for forming a doped layer on Si wafer is the solid phase diffusion method.

This method uses a solid diffusion source with the same shape as Waeno, and
81 By placing the wafer in a quartz tube and heating it to a high temperature of 80°C to 100°C under normal pressure in an inert gas atmosphere, impurity atoms are transferred from the diffusion source to the wafer surface, and the impurities are converted to Si. It is meant to diffuse inside. (R, K, Tressler, etc.0.Solid state technology (S01 Engineering dstate tec
hnology) Japanese Edition, p54-60.12 (1984)] Problems to be Solved by the Invention Conventional methods require high temperatures of at least SOO°C to 900°C, so submicron structural control is required. When used to create miniaturized devices, there is a problem in that impurities introduced in the previous process re-diffuse. The reason for this is
For example, consider the case of a MuS solid diffusion source (Mu$As04). AlAsO4 undergoes a decomposition reaction as shown in the following formula (2).

2U! AS04 (solid): Mu'J203 (sol
id) Ten people s203 (gas) +02 (gas)
---(g) AlAsO4 undergoes thermal decomposition, and the generated As2O3 flies to the surface of 81 and decomposes into arsenic atoms and oxygen atoms, and S diffuses into Si to form a doped layer. Therefore, doping cannot be performed unless the temperature is higher than the thermal decomposition temperature. Therefore, in the case of Mu5203, a temperature of 860°C or higher was required.

Means for Solving the Problems Therefore, in the present invention, for example,
iP20. Alternatively, a method including a step of arranging a flat plate containing BN or the like almost parallel to the 81 substrate and performing heat treatment at a low temperature while generating plasma under reduced pressure in an inert gas or a gas atmosphere containing a trace amount of oxygen. adopt.

Function: In the present invention, since the decomposition of the above-mentioned diffusion source is promoted by plasma, doping can be performed even at almost room temperature.

Furthermore, the present invention is carried out under a reduced pressure atmosphere.

The mean free path of the impurity-containing molecules becomes large, and for example, the impurity-containing molecules easily penetrate into the trenches provided on the surface of the 81 substrate, forming a uniform doping layer on the sidewalls of the trenches as well.

By creating a decompressed atmosphere, the relative concentrations of As and P can be lowered, so that the controllability of the concentrations of As and P can be improved even in a relatively low concentration region of 1018-level.

Embodiment The figure shows a sectional view of a substrate heat treatment apparatus in a reduced pressure plasma atmosphere as an embodiment of the present invention. In the quartz tube 6, a MU S solid diffusion source 6 having the same shape as the wafer containing MU 1KSO4 on the surface (for example, MU S 1OO made by Carborundum) is placed.
oL) and Slx-''7f, one quartz boat 8 is inserted on each side of one solid diffusion source.

An argon/oxygen mixture containing fulvic 7 (Ar) with a purity of 6N and 50001)9m oxygen (02) is used as the atmospheric gas. The flow rate of argon is set to 1 eoo CC/min, and the flow rate of argon/oxygen mixed gas is set to 100 cc/min, so that the oxygen content is approximately 700 ppm.

The inside of the tube is 0.2 Torr by a mechanical pump.
The reduced pressure atmosphere 9 is set to 9, and the temperature inside the tube is set to 40Q°C using an external heater 1o.

This is because although the temperature increases due to plasma, this makes the temperature non-uniform, so the temperature is controlled by the external heater 1o to improve uniformity.

In this state, high frequency power and DC bias voltage are applied to the plasma electrodes 12 and 13 inside the quartz tube.

In this case, a high frequency of 13.56 Ml-1 and a DC bias voltage of several hundred volts were applied.

At this time, the mean free path of molecules is about 5 μm, so for trenches with a depth of 6 μm or less.

The amount of impurity atoms that reach the bottom surface is the same as that on the surface, and the doped layer 3 can be uniformly formed on the trench sidewall 2 regardless of the depth. In addition, when plasma is not used.

The amount of pyrolyzed 5203 released from the 6-inch diameter 6-inch solid diffusion source 6 was as follows:
4.5 x 10” generated reduced pressure plasma atmosphere 9
In this case, it is possible to generate more S than that amount, and the required amount of S to be doped on the sidewall of a trench corresponding to 4M DRAM in a 6-inch wafer is about 10.
Since it is 15 pieces/wafer, there is a difference of about 3 orders of magnitude between the generation amount and the adhesion coefficient of As to the substrate.
Even considering the amount exhausted as s0, this is a sufficient amount.

Furthermore, a device in which a high-frequency coil is completely wound around a quartz tube can also be used. In this case, the uniformity of the plasma inside the tube is improved and there is no need for external heating.

Effects of the Invention As described above, by using the present invention, it is possible to dope S, P, etc. even at room temperature. This is not done by thermal diffusion, but by exposing the substrate such as 81 to plasma.
Impurities are diffused into the substrate. Therefore, redistribution of impurities in the impurity introduction region formed in the previous step due to thermal diffusion can be extremely reduced.

Moreover, by using the impurity doping method in a reduced pressure plasma atmosphere of the present invention, the mean free path of the impurity work becomes longer, making it possible to uniformly dope the side walls of the trench. Furthermore, it has become possible to precisely control the amount of doping into a trench with an opening of 0.5 μm and a depth of 3 μm on the order of 10 cm 2 . In addition, by suppressing the entrainment of oxygen at low temperatures and in a reduced pressure atmosphere, it is possible to prevent the formation of an oxide film on the substrate surface, making it possible to perform doping with good controllability, uniformity, and reproducibility.

[Brief explanation of the drawing]

The figure is a configuration diagram showing an example of the configuration of a doping apparatus using the method of the present invention. 5...Quartz tube, 6...S solid diffusion source, 7...S1 wafer, 8...
Quartz boat, 9... reduced pressure atmosphere, 1Q...
...External heater, 12.13...Plasma generation electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person5-
Me quartz nayu ~bu 6---As solid = 9. Source '7---SL Way 7\ 1O---One part Heater/2,13---Brassma female electrode

Claims (2)

[Claims] (1) An impurity introduction method in which a flat plate containing a doping impurity compound and a semiconductor substrate are arranged almost parallel to each other, and low-pressure plasma is generated in an atmosphere of an inert gas or a gas containing a trace amount of oxygen. (2) As a doping impurity compound, AlASO_
4. The impurity introduction method according to claim 1, which contains SiP_2O_7 or BN.