JP2511461B2 - Method for manufacturing semiconductor substrate - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor substrate such as a so-called SOI (Silicon on Insulator) substrate formed by forming a good-quality semiconductor single crystal thin film on an insulator.

[Problems to be Solved by Conventional Techniques and Inventions] Conventionally, as one of means for obtaining an SOI substrate, there is a SIMOX method, that is, a method of forming a buried insulating layer by a large amount of implantation of oxygen ions. The SIMOX method has the advantages of excellent mass productivity and excellent uniformity of the obtained SOI substrate. However, the crystallinity of the surface silicon layer (SOI layer) and the electrical characteristics of the interface between it and the insulating layer (interface The characteristic that leakage current does not flow along is desirable) is not always good. The reason is as follows.

In the SIMOX method, since it is necessary to form a buried insulating layer at a sufficient depth, a beam 1 of normal oxygen ions is accelerated and implanted at a high energy of 800 keV or more as shown in FIG.
At this time, the upper single crystal silicon layer is significantly damaged by the rush ions. The degree of damage is relatively mild near the surface, but it is particularly remarkable at a depth at which rush ions are stopped or at a depth at which channeling is blocked. Therefore, many electrically active crystal defects are generated near the boundary between the buried insulating layer 2 and the surface silicon layer 3.
Although some of these damages or defects can be recovered by the subsequent heat treatment, the crystallinity and electrical characteristics near this boundary are inferior to those of existing silicon substrates and the electrical characteristics of the silicon-oxide film interface. For example, it was extremely inferior. This is because it requires a high temperature of more than 1000 degrees Celsius in order to thermally promote atomic rearrangement for repairing damage by a simple heat treatment, whereas under such a high temperature, ion irradiation causes an amorphous state. This is due to the fact that crystal nuclei are actively generated inside the converted silicon layer, and as a result, random crystal grains grow.

Therefore, the conventional SIMOX SOI substrate has high integration,
It has been insufficient as a substrate for forming an integrated circuit that requires high reliability.

In view of the above problems, the present invention is directed to a surface silicon layer (SOI
It is an object of the present invention to provide a method for manufacturing a semiconductor substrate such as an SOI substrate in which a layer) has excellent crystallinity and an interface between the layer and the insulating layer has good electric characteristics.

[Means and Actions for Solving Problems]

A method of manufacturing a semiconductor substrate according to the present invention is a method of manufacturing a semiconductor substrate, which comprises implanting oxygen ions into a single crystal silicon substrate to form a buried silicon oxide layer, and then heat treating the buried silicon oxide layer. It is characterized in that an electric field is applied from the outside between the surface silicon layers to induce movement in the electric field of the embedded silicon oxide layer to change the embedded depth of the embedded silicon oxide layer.

That is, the method of manufacturing a semiconductor substrate according to the present invention includes a process of migrating a silicon oxide layer in silicon, a process of amorphization of crystalline silicon accompanying it, and a process of solid phase epitaxial growth behind a moving oxide film. It is roughly divided into three points. First, the mechanism of movement of the silicon oxide layer in silicon will be described. As is conventionally known, at high temperatures, the silicon oxide film has ionic conductivity with oxygen ions as charge carriers. That is, the electric field applied to the silicon oxide film induces the movement of oxygen ions. The movement of oxygen ions in silicon is nothing but the movement of the region having the composition of SiO ₂ . That is, at high temperature, the embedded silicon oxide film a in silicon can be moved by applying an electric field, as shown in FIG.

Utilizing this fact, in the method of manufacturing a semiconductor substrate according to the present invention, first, in the heat treatment step following the formation of the buried oxide film 4 as shown in FIG. 2A, the process shown in FIG. As described above, by moving the buried oxide film 4 toward the substrate surface, it is possible to form an interface between the surface silicon layer 5 and the buried oxide film 4 in a shallow region which is less damaged by ion irradiation.

Here, the region of SiO ₂ composition in silicon does not have the crystal structure of silicon but has the glass structure of SiO ₂ . Therefore, the oxide film 4 is moved by the application of the electric field and new SiO ₂ is added.
The composition region loses the crystallinity of silicon regardless of whether it is a single crystal or a polycrystal. That is, there is another advantage that the silicon oxide in the newly oxidized region can be made amorphous by moving the buried oxide film 4 toward the surface.

On the other hand, when the buried oxide film 4 moves due to the application of an electric field, amorphized silicon appears at the interface behind the moving direction. However, if the system is at a sufficiently high temperature, atomic rearrangement occurs immediately due to thermal motion, and the amorphous silicon that appears recrystallizes using the adjacent single crystal silicon layer as a seed. That is, as shown in FIG. 1, at the rear interface of the moving oxide film a, a solid phase epitaxial growth region b of silicon is created and becomes crystalline.

Further, by utilizing this fact, in the method for manufacturing a semiconductor substrate according to the present invention, as shown in FIG. Is applied to increase the burying depth of the buried oxide film 4 and sequentially recrystallize the silicon layer appearing behind (the substrate surface side) with respect to the moving direction.

As described above, in the method of the present invention, the silicon layer to be recrystallized is forcibly once made amorphous beforehand, and is always adjacent to the good quality single crystal silicon layer. This means that it is difficult for random crystal grains to grow due to the sudden generation of crystal nuclei. Therefore,
The crystallinity of the surface silicon layer (SOI layer) 5 after the heat treatment and the electrical characteristics of the interface between it and the buried oxide film 4 are excellent.

〔Example〕

 Next, examples will be described.

Example 1 On an n-type single crystal silicon substrate at a substrate temperature of 800 degrees, 800
KeV, 150 mA oxygen ion beam was injected to form a buried insulating layer. Embedding depth 5000 Å, thickness 60 in about 60 minutes
A 00Å buried oxide film was formed. Next, at a temperature of 1200 ° C. in an argon atmosphere, a voltage of 100 V was applied from the platinum electrode or Si electrode provided in contact with the upper and lower sides of the substrate to move the buried oxide film upward. At this time, the polarity of the applied voltage was set to be positive on the SOI layer side with respect to the substrate. The thickness of the SOI layer was reduced to about 3000Å during the voltage application process for about 2 hours, and the interface state density of the SOI layer / buried oxide film interface was 10 15 to 10 13 per normal square cm.
It has decreased to the power of two. After that, epitaxial growth of a silicon single crystal was performed on the surface of the SOI layer to recover the reduced thickness of the SOI layer.

Example 2 According to the procedure of Example 1, the buried oxide film was formed, and then the external voltage having the above-mentioned polarity was applied, and then the polarity of the applied voltage was reversed to move the buried oxide film downward. Similarly, the SOI layer was restored to its original thickness by the voltage application treatment for 2 hours. Further, the interface state density at the SOI layer / buried oxide film interface was further reduced to the 10th to 11th power per square cm.

〔The invention's effect〕

As described above, the method of manufacturing a semiconductor substrate according to the present invention has a very important advantage that the crystallinity of the SOI layer of the semiconductor substrate and the electrical characteristics of the interface between the SOI layer and the silicon oxide layer are excellent.

[Brief description of drawings]

FIG. 1 is a diagram showing a mechanism of movement of a silicon oxide film in a silicon substrate, and FIGS. 2 (A), (B) and (C) are diagrams showing respective steps of a method for manufacturing a semiconductor substrate according to the present invention. FIG. 3 is a diagram showing how a single crystal silicon substrate is damaged by a large amount of oxygen ion irradiation. 1 ... Ion beam, 4 ... Buried oxide film, 5 ... Surface silicon layer.

Claims (1)

(57) [Claims] 1. A method for manufacturing a semiconductor substrate, which comprises implanting oxygen ions into a single crystal silicon substrate to form a buried silicon oxide layer, and then heat treating the buried silicon oxide layer. A method for manufacturing a semiconductor substrate, characterized in that a more electric field is applied to induce movement in the electric field of the embedded silicon oxide layer to change the embedded depth of the embedded silicon oxide layer.