JPS5950625B2 - Lifetime control method for silicon single crystal rods - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present application is to uniformly and accurately control the lifetime of a silicon crystal rod to a low value.

In recent years, switching elements with short turn-off times, high-voltage power transistors, rectifying elements, etc., have become necessary to save power, but these elements are usually manufactured using silicon monomers made by melting in a crucible zone. A crystal wafer is used, and gold or platinum is diffused into the wafer during device fabrication to reduce the lifetime, thereby imparting short turn-off time characteristics.

When diffusing gold, during the subsequent diffusion of phosphorus or boron, the injected gold is likely to be absorbed by the phosphorus glass or boron glass, which is the so-called gettering effect, and for this reason, accurate The drawback is that it is difficult to obtain a turn-off time.

For this reason, there has recently been a trend toward the diffusion of platinum to replace gold.

This is because platinum is not affected by the gettering effect of phosphorus glass or boron glass, so it has the effect of obtaining an accurate turn-off time, and it has also been found that reverse leakage current, which is unfavorable as a device characteristic, can be reduced. This is because.

An example of controlling the lifetime by diffusing platinum into a silicon crystal is disclosed in Japanese Patent Application Laid-Open No. 47-36860 (title of invention: "Method for diffusing platinum").

According to the report, a platinum-containing compound in a solution state is dispersed on the surface of a silicon wafer during device fabrication, and the platinum is diffused into the interior of the wafer crystal by heating. It has been shown that it can also be implemented.

However, when platinum is implanted into a silicon crystal by diffusion, the concentration of the implanted platinum depends not only on the amount of platinum added but also on the temperature, time, etc. during the diffusion, and even in thin wafers, the concentration of platinum implanted from the diffusion surface It tends to vary in the thickness direction.

Moreover, it is counterproductive because it takes a long time to uniformly diffuse platinum into the center of a crystal rod that is many inches in diameter.

The present application was invented to solve these drawbacks, and whereas the conventional means of lifetime control was "diffusion," this application utilizes the "segregation property" of platinum relative to silicon. It's meaningful.

One advantage is that when using diffusion, the amount of platinum added must be controlled very strictly, but when using segregation, other impurities (boron 101. Since the segregation coefficient of platinum to silicon is very small at 1o-5-1o" compared to that of aluminum 10""1. arsenic 1O-1), after crucible zone melting, the added platinum Most of it is removed from the crystal rod.

Therefore, even if there is some error in the amount of platinum added relative to the target concentration, the originally intended platinum concentration can be obtained, and the lifetime can be easily controlled.

In addition, unlike the case of diffusion, it is hardly affected by the processing temperature and processing time, so there are fewer determining factors for the concentration of Shinkin Banks, and the accuracy of the desired lifetime value is further improved, and the variation is reduced and uniform. become.

The second advantage is based on the sensitivity of lifetime to crystal integrity.

Normally, if a crystal has many dislocations, the lifetime value will be low, and if there are few dislocations, the lifetime value will be high.

For example, a dislocation-free crystal of several + Ωcm has a lifetime of 500 to 1,000μ, sec, and it has been difficult to achieve a low value, but according to the present application, a dislocation-free crystal with a lifetime of 100μ, sec or less is difficult to achieve. can easily be given a low lifetime value.

The third advantage is that when performing credit diffusion during device fabrication, the process is performed for each wafer or several wafers, but in this application, the wafer is processed in the conventional refining operation. By using the wafers manufactured in this application, it is possible to provide the required lifetime, sometimes several different levels of lifetime, to hundreds of rods at once. It can be omitted from the process.

A conventional diffusion method and an embodiment of the present application will be shown below.

Example... (1) Dissolve 5 g of H2PtCl6.6H20 in 50 cc of pure water, apply this evenly to the entire surface of a silicon single crystal rod with a diameter of 60 mm, except for the cross sections at both ends, and place it on a bench. Leave it for 10 hours to dry.

Next, this crystal rod is placed in a diffusion furnace and heated in an argon atmosphere for 24 hours to diffuse platinum into the crystal rod.

When the diffusion tendency of platinum was investigated for five ingots with a length of 100 mm cut from this diffusion rod, the range in which platinum diffusion was observed in each ingot was limited to within 25 mm inward from the outer peripheral surface.

This result shows that it is difficult to inject platinum into a large diameter crystal rod within a short time by diffusion.

Example (2) 1 g cr) H2PtCl6.6H20 is dissolved in 59 cc of pure water, and this is dripped onto the surface of a silicon crystal raw material rod with a diameter of 50 mm.

Using a pipette, add 1 drop at 1 cm intervals in the axial direction so that at least 1 drop is in the width of each zone along the entire length of the raw material rod.
Instill 0 μcc each.

The target lifetime value is 40μ near the seed crystal.

sec, 30μ at the part 400mm away from the seed crystal,
sec.

The drip rod was left to dry in a bench for 10 hours, then melted in a crucible zone at a pass speed of 4.5 mm/min in an argon atmosphere, and after an hour and a half, the rod had a diameter of 63 mm and a length of 400 mm.
A dislocation-free single-crystal rod with a diameter of mm was produced.

The lifetime of this single crystal rod is 40μ, sec near the seed crystal, and 30μ at a distance of 400mm from the seed crystal, as intended.

Sec, a single crystal rod with a uniform lifetime distribution was obtained.

Normally, the axial lifetime value of a dislocation-free crystal rod has a maximum value/minimum value ratio of about 2 to 3 times, but in the above example, it has been improved to 1.3 times.

Also, regarding the variation in lifetime in the diameter direction,
Both the rod surface and the center near the seed crystal are 40μ, se
c, even at a part 400 mm away from the seed crystal, both are 30
μ, sec, and the intended lifetime could be obtained.

The average concentration of platinum throughout the dislocation-free single crystal rod was about 10 atoms/silicon CC.

Example (3) Dissolve H2PtCl6 66H2O1 in 590 cc of pure water, drip it onto a raw material rod with the same diameter as in Example (2) in the same manner and conditions, dry it, and melt it to a diameter of 65 mm. A dislocation-free single-crystal silicon rod was made.

The average lifetime in the diameter direction of the cross section perpendicular to the axis of the crystal rod is 90μ, sec near the seed crystal, and 70μ at a distance of 300mm.

It was sec.

By changing the platinum concentration of the infusion solution in this way, the lifetime of the single crystal rod can be easily changed.

Example (4) The following experiment was conducted using the remaining aqueous solution from the above example.

Do not drip into a silicon raw material rod with a diameter of 50 mm and a length of 600 mm within 200 mm from one end, and between 200 mm and 600 mm, 10μ at 1 cm intervals.
Instilled cc at a time.

Thereafter, a single crystal having a diameter of 60 mm and a length of 420 mm was produced by drying and melting in a crucible zone under the same conditions as in Example (2).

The lifetimes of this single crystal rod are 600 μ, sec, 50 μ, sec, 43 at positions near the seed crystal, 100 mm, 200 mm, and 300 mm from the seed crystal, respectively.
μ, sec.

As this example shows, it is also possible to vary the lifetime value to more than one level within a single single crystal bar.

Example (5) Dissolve 1 g of H2PtCl6.9H20 in 370 cc of pure water, and drip 10 cc of this solution at intervals of about 1 cm in the length direction of a silicon raw material rod with a diameter of 52 mm.

The drip rod was melted in a crucible-free zone at a pass speed of 4.5 mm/min to produce a dislocated single crystal with a diameter of 63 mm.

The lifetime at both ends and center of the single crystal rod is 30~
It was 45 μ·sec.

As for the lifetime of a crystal with dislocations, the ratio of maximum value to minimum value generally varies by about 2 to 3 times.

However, according to the present application, variations can be reduced even in the case of dislocations.

H2PtCl6・6H20°H2P used in the above example
All of the tCl6·9H20 compounds are water-soluble.

It is easiest to drip an aqueous solution of such a water-soluble compound, and the amount added is also easy to control.

Others, such as PtCl4.5H20+PtCl4, are highly soluble in water.

Compounds such as Pt(OH)2 and PtBr2 are not water-soluble, but are well soluble in acids such as HCI and HBr.

Further, Pt(OH)2, as well as H2Pt(OH)6, etc., is soluble in alkali.

PtBr4, H2Pt(CN)4, Pt(SO
4) The compound 2 ・4H20 dissolves in alcohol and ether.

Platinum can be added to these compounds by simply dripping them into a raw material rod as a solution, but when using an acid or alkaline solution, it is best to use an acid or alkali containing an element with a large segregation coefficient relative to silicon. Since the element remains in the crystal and naturally affects the crystallinity and other properties of the crystal, such as resistivity, care must be taken when using it.

This also applies to the case where a platinum compound itself containing an element with a large segregation coefficient is used.

In addition, when using a solution of a platinum compound dissolved in alcohol or ether, carbon in the organic solvent is added to the crystal and remains, so it is wise to avoid this when making crystals with a low carbon concentration.

It is also possible to add platinum alone.

All you have to do is lightly rub the platinum rod and the silicon raw material rod together, but the amount added will vary somewhat compared to when a solution is dripped.

However, this method may also be convenient depending on how much lifetime is required.

Example (6) 1 mmg of platinum is added to the raw material rod by lightly rubbing platinum with a diameter of 5 mm and weight of 28.3 g in the longitudinal direction of the surface of a silicon raw material rod with a diameter of 50 mm and a length of 500 mm. .

Then, the raw material rod was subjected to crucible zone melting in an argon atmosphere at a pass speed of 4 mm/min.

The produced crystal rod has no dislocations, has a diameter of 60 mm, and has a lifetime of 20 μ, s measured at both ends and three points in the center of the crystal rod.
It was below ec.

In addition, as a method of adding platinum, it is also possible to vapor-deposit a platinum compound or a simple substance.

For example, a silicon raw material rod is installed so that it can move in the axial direction in a container with a reduced pressure system, and an aqueous solution of H2PtCl6/6H20 is poured into a tantalum evaporating dish with both ends connected to a power source, and this is poured onto the bottom of the raw material rod. Deploy.

H2PtCl6.6H20 is heated to its evaporation temperature of 115° C. or above and evaporated toward the side of the raw material rod, while the raw material rod is moved in the axial direction to deposit a thin film on its surface.

Thereafter, the vapor deposition rod is melted in a crucible zone.

However, according to the inventor's experiments, no particular advantage was found compared to the drip method.

Rather, the drip method is preferable in that a special container is required for vapor deposition.

Although some embodiments of the present application have been described above, other embodiments, such as implanting platinum ions into a raw material rod and melting them, are also possible without departing from the spirit of the invention shown herein.

Claims (1)

[Claims] 1. A control rod for the lifetime of a silicon single crystal rod, characterized in that the lifetime is controlled to a low value by adding platinum to the silicon crystal rod and melting it in a crucible zone. 2. Process according to claim 1, characterized in that the addition of platinum is carried out using a soluble platinum compound. 3. The method according to claim 1, wherein the addition of platinum is carried out using pure platinum.