JP2517012B2 - How to diffuse impurities - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for diffusing impurities in a solid.

2. Description of the Related Art A conventional method for diffusing impurities introduced into silicon by high temperature heat treatment will be described with reference to FIG. In the silicon LSI manufacturing process, as shown in FIG. 4, an opening 8 is formed at a desired portion using a normal photoresist, and impurity ions 9 are introduced by an ion implantation method. In the case of diffusing the impurities, the photoresist 6 is usually removed as shown in b, and then the entire silicon substrate is heated to diffuse the impurities at a temperature of several hundreds to several hundreds of degrees Celsius to form the diffusion layer 16 like C. obtain.

Problems to be solved by the invention In today's LSI manufacturing process, it is necessary to perform ion implantation ten times or more, and those profiles must be carefully calculated and grasped after multiple heat treatments. There is.
Further, since the entire substrate is heated, impurities in unnecessary parts are diffused.

Means for Solving Problems The present invention diffuses impurities into a solid by exposing the solid containing the impurity to plasma generated by discharge using electron cyclotron resonance conditions (ECR) and radio frequency (RF). Is the way.

Action In the vicinity of the surface of a solid exposed to plasma, ionization occurs due to the collision of electrons in the plasma. The ionized electrons collide with other electrons to cause secondary ionization, and a large number of electron-hole pairs are generated. When this electron-hole pair is recombined, the energy of the electron system is transferred to the lattice system. As a result, the lattice movement mode becomes dominant among the excited lattice vibrations, so that the constituent atoms of the solid substrate and the impurities move, resulting in the diffusion of the impurities. That is, the diffusion of lattices, vacancies, and impurities occurs in the range of several tens nm to hundreds of tens nm of the surface, which is affected by plasma excitation. This phenomenon is not so-called thermal diffusion that occurs when the temperature of the entire substrate rises like in electric furnaces, lamp furnaces, and DC glow discharges, so only the impurities in the sites that are selectively opened using a mask material are targeted for diffusion. You can do it.

Embodiment An embodiment of the present invention will be described with reference to FIGS. This example concerns impurities in a silicon substrate. As shown in FIG. 1a, using the CVD oxide film 4 and the photoresist 6 as a mask on the silicon substrate 2,
A desired opening portion 8 is provided. Impurities are introduced by, for example, ion implantation to form the impurity layer 10. In the same manner as described above, the photoresist 6 or the like is used as a mask to open only a desired portion of the impurity layer 10 thus introduced, and the exposed portion is exposed to plasma.

The plasma typically used the following method. In Fig. 2, 6 sccm of He gas was made to flow through the chamber 12, and the vacuum degree was 5 × 10 ^-4 t.
kept at orr. This gas is discharged using electron cyclotron resonance conditions (ECR) and radio frequency (RF). The silicon substrate 2 is placed on the cathode 14 in this plasma. First
Although FIG. C shows the silicon substrate after plasma irradiation, the impurity layer in the opening is diffused to become the diffusion layer 16.

Fig. 3 shows BF ⁺ ₂ ▼ ions of boron (B) after being exposed to the plasma for 10 minutes at a dose of 1 × 10 ¹⁵ ions / cm ² at a dose of 10 KeV with an ion implanter. It is a profile. It can be seen that boron diffuses toward the surface side and the back of the substrate with respect to the peak (projection range ~ 8 nm) immediately after ion implantation. In this way, using photoresists as mask materials with different depth profiles,
It can be formed selectively at low temperatures.

In addition, the diffusion state can be changed by changing, for example, the degree of vacuum during operation, the flow rate of the plasma carrier gas, the power applied to discharge, the time of exposure to plasma, the type of discharge, etc., among the plasma generation conditions described above. You can control. Further, since the use of photoresist is a great advantage, it is desirable to cool the silicon substrate to 100 ° C. or lower for protection thereof.

Also, in the above example, the diffusion of impurities introduced into silicon, so to speak, necessary for semiconductor device manufacturing was described, but unnecessary impurities such as oxygen in CZ type Si are also called outward from the inside toward the free surface. Diffusion is caused by the plasma and the concentration near the surface can be lowered.

Effects of the Invention As described above, according to the present invention, by using plasma irradiation for impurity diffusion in the vicinity of the surface of a solid, the temperature from room temperature to 100 ° C
It can be diffused to some extent while using the photoresist. In other words, since the temperature of the entire substrate does not rise, it is possible to diffuse impurities only in the selectively opened parts, which makes it possible to finely control the impurity profile in the LSI manufacturing process, which will become more and more complicated in the future, and to improve the performance of high-performance semiconductor Contribute to manufacturing.

[Brief description of drawings]

FIG. 1 is a process diagram for explaining an embodiment method of the present invention, FIG. 2 is a schematic configuration diagram of an apparatus for performing plasma irradiation, FIG. 3 is a characteristic diagram showing a state of diffusion by plasma irradiation, and FIG. The drawings are process drawings for explaining a conventional method. 2 ... Silicon substrate, 4 ... CVD oxide film, 6 ...
Photoresist, 8 ... Aperture, 9 ... Ion, 10 ...
Impurity layer, 12 ... Chamber, 14 ... Cathode, 16 ... Diffusion layer.

Claims (1)

(57) [Claims] 1. A step of introducing an impurity into a masked semiconductor substrate by ion implantation, a step of selectively forming a photoresist on the impurity-doped semiconductor substrate, and electron cyclotron resonance. Exposing the plasma generated by discharging under the condition and high frequency to the semiconductor substrate on which the photoresist is formed to diffuse the impurity without causing thermal diffusion.