JPH0752723B2 - Impurity introduction method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for introducing impurities into a substrate.

2. Description of the Related Art One conventional method for forming a doping layer on a Si wafer is a solid diffusion method using a flat plate (solid diffusion source) containing doping impurities and compounds thereof. This method comprises a solid-state diffusion source having almost the same shape as the wafer, and
Put a Si wafer in a quartz tube and raise it to a high temperature of 800 ° C to 1000 ° C under atmospheric pressure in an inert gas atmosphere to move impurity atoms from the diffusion source to the surface of the wafer to remove impurities. Doping inside. [RE
Tressler et al., Solid State Technology (soli
d state technology) Japan version, p54-60, 12th (1984
Year). Problems to be Solved by the Invention In the conventional solid diffusion method, in order to thermally decompose the diffusion source, a high temperature of at least about 800 ° C. to 900 ° C. is required. When it is used for production, there is a problem that the impurities introduced in the previous step re-diffuse. The reason for this is, for example, As solid diffusion source (AlAs
Consider the case of O ₄ ). AlAsO ₄ causes a decomposition reaction as shown in the following formula (*).

2AlAsO ₄ (solid) Al ₂ O ₃ (solid) + As ₂ O ₃ (gas) + O ₂
(Gas) ...... (*) AlAsO ₄ undergoes thermal decomposition, the generated As ₂ O ₃ flies to the Si surface, and an oxide film containing arsenic is formed on the surface. Arsenic atom
As thermally diffuses from the oxide film on the substrate surface into Si to form a doping layer. Therefore, unless the temperature is higher than the thermal decomposition temperature of the solid diffusion source, As ₂ O ₃ vapor is not generated, so that doping cannot be performed. Therefore, when using the As solid diffusion source,
A temperature of 850 ° C or higher was required.

Means for Solving the ProblemsTherefore, in the present invention, for the purpose of performing doping at a lower temperature, a flat plate containing, for example, AlAsO ₄ , SiP ₂ O ₇ or BN is arranged substantially parallel to the Si substrate, and The method is characterized by including a configuration in which plasma is generated under reduced pressure in an active gas or a gas atmosphere containing a trace amount of oxygen.

Operation In the present invention, the above solid diffusion source is introduced into plasma to promote decomposition of the solid diffusion source at a lower temperature, a layer containing a dopant is formed on the substrate surface, and then heat treatment is performed at a low temperature. By this, it is possible to dope impurities from the surface. Further, since the present invention is performed in a reduced pressure atmosphere, the mean free path of molecules containing impurities is increased, and for example, a trench groove provided on the surface of a Si substrate. Molecules containing impurities easily enter the inside of the groove, and a uniform doping layer can be formed on the side wall of the groove in the depth direction of the groove.

Also, by setting a reduced pressure atmosphere, As and P on the Si substrate surface
Since the relative concentration of As can be lowered, the controllability of As and P concentrations is improved even in the relatively low concentration region of 10 ¹⁸ cm ³ .

EXAMPLE FIG. 1 shows a cross-sectional view of a doping apparatus having a substrate heat treatment mechanism in a low pressure plasma atmosphere as an example of the present invention. In a quartz tube 5, an As solid diffusion source 6 (for example, AS1000L manufactured by Carborundum Co.) having the same shape as the wafer containing AlAsO ₄ on the surface and a Si wafer 7 are provided on both sides of one solid diffusion source. The quartz boats 8 arranged one by one are inserted.
Argon (Ar) with a purity of 6N and 5000ppm as atmosphere gas
A mixed gas of argon / oxygen containing oxygen (O ₂ ) is used. The flow rate of argon is 600cc / min, the flow rate of the mixed gas of argon / oxygen is 100cc / min, and the oxygen content is about 70.
Set to 0 ppm.

The inside of the tube is set to a reduced pressure atmosphere 9 of 0.2 Torr by a mechanical pump, and the temperature inside the tube is set to 400 ° C. by an external heater 10. This is because the temperature rises due to the plasma, but this causes the temperature inside the substrate surface to become non-uniform due to heat conduction at the contact portion between the substrate and the boat, so an external heater
This is because the temperature is controlled by 10 to improve the 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 MHz and a DC bias voltage of several hundred volts were applied.

At this time, since the mean free path of the molecule is about 5 μm, the amount of impurity atoms reaching the trench groove having a depth of 5 μm or less is the same as that on the bottom surface regardless of the depth. The doping layer 3 can be formed uniformly. If plasma is not used, the amount of As ₂ O ₃ that is thermally decomposed from one As solid diffusion source 6 having a diameter of 6 inches is 900 ° C.
In an argon atmosphere containing 700 ppm of oxygen, it was found from the weight loss of the solid diffusion source that 4.5 × 10 ¹⁷ cells were generated by the heat treatment for 30 minutes. In the low-pressure plasma atmosphere 9, it is possible to generate more As, and this amount is larger than that of a trench structure using a 6-inch wafer.
When manufacturing 4M DRAM, 1 × 10 ¹⁸ / cm ^{3 on the} trench sidewall
The required amount of As is about 10 when doping As with a certain concentration.
^{Since there are 15} wafers / wafer, there is a difference of about 3 digits from the generated amount, and the adhesion coefficient of As to the substrate and As ₂ O ₃
It is a sufficient amount even if the amount exhausted as is considered.

Further, as the plasma generating mechanism, a high frequency coil wound around a quartz tube can be used. In this case, the uniformity of plasma in the tube is improved.

As described above, according to the present invention, As
Or P or the like can be doped. This includes not only thermal diffusion but also the effect of introducing impurities into the substrate by exposing the substrate such as Si to plasma. 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 the low-pressure plasma atmosphere of the present invention, the mean free path of the impurity species is lengthened, and the sidewall of the trench groove can be uniformly doped. In addition, the precise control of the doping amount into the trench groove with the opening of 0.5 μm and 3 μm depth has become possible on the order of 10 ¹⁸ cm ⁻³ . In addition, by suppressing the entrainment of oxygen in a low temperature and reduced pressure atmosphere, formation of an oxide film on the substrate surface was prevented, and doping with good controllability, uniformity, and reproducibility was made possible.

[Brief description of drawings]

The figure is a block diagram showing an example of the configuration of a doping apparatus using the method of the present invention. 5 ... Quartz tube, 6 ... As solid diffusion source, 7 ... Si wafer, 8 ... Quartz boat, 9 ... Reduced pressure atmosphere, 10 ...
External heater, 12, 13 ... Plasma generating electrode.

Claims (2)

[Claims] 1. An impurity for generating a low-pressure plasma in an inert gas or in a gas atmosphere containing a small amount of oxygen in the inert gas, with a flat plate containing a compound of a doping impurity and a plurality of semiconductor substrates facing each other substantially in parallel. Introduction method. 2. AlAs as a compound of doping impurities
The method of introducing impurities according to claim 1, which contains O ₄ , SiP ₂ O ₇ , or BN.