DE1544321A1 - Board diffusion - Google Patents

Description

"Bordiffusion" takes place in the production of iialleiterbauelemente as is well known, often a boron diffusion application. For example, this is the base zone of diffused n-p-n silicon planar transistors today almost exclusively through Bordiffusion produced.

A number of methods and methods are known to obtain a Carry out board diffusion in practice. A comprehensive compilation of the various Diffusion methods for boron diffusion in silicon can be found e.g. in the book "Silicon Semiconductor Technology" by 1i. R. Runyan, published by Mc Qraw-Hill in 1965 Book Company (page 14'7 / 148). Several of the methods listed there are suitable for production purposes. The BC13 and BBr3 methods are particularly popular. The fluids BC13 and BBr3 serve as a source for the boron diffusion. A carrier gas enriched in BC13 or BBr3 (mostly N2 and some OZ) flows in the process in a so-called open diffusion system ("open tube system") via the silicon wafers arranged on a quartz layer. There are reactions between the doped carrier gas and the high temperature (approx. T = 11oooC) Silicon semiconductor surface.

Typical reactions in the case of the BC13 are: 1. 2 BC13 + 3 '02 + 3 112 ----- @ 2 ß203 + 6 HC1 2.2B203 + 3Si - --- e 3Si02 + 2B2 3. 4 licl + si ----- @ si c14 + 2 H2 4. S i + 0 2 ---- @ S i 0 2 Si02 + B2 form a "boron glass" from which the boron diffuses into the silicon. As a result of the reaction mentioned, the carrier gas is depleted of doping atoms as it flows over the silicon disks lying one behind the other in the diffusion furnace. In addition, the quartz tube and the quartz manufactured silicon wafer recording saturated in accordance with local temperatures with boron so as to serve as the boron source. the depletion of the carrier gas and the saturation of the quartz tube and the disc recording should in addition to a un- nügenden mixing of the doping gas with the Trä- gergas for the existing irregularities by the boron diffusion in the semiconductor body called impurity concentration hervorge- be responsible. Large variations in the impurity concentration of boron diffusion are found mainly at low Bordotierungen on each wafer and from wafer to wafer. also, through the use of GE closed Bordiffusionssystemen (closed box method) achieved no better results.

The invention is therefore based on the object of specifying a boron diffusion in which these disadvantages do not occur. To achieve the object set, the invention proposes the use of boron nitrogen as a diffusion source for diffusing boron into a semiconductor body.

Boron nitrogen (BN), whose melting point is 3000 ° C , is resistant up to 16600C. In particular, it can be pressed into shapes, for example in a plate shape or in a cylinder shape. In plate form the BN doping source can process take over the function of a disc recording during the diffusion time. The same applies to a certain modification for a hollow cylinder shape, with the disks to be diffused having to be arranged in the interior of the cylinder .

In the case of the boron diffusion shown in FIG. 1, a plate 1 made of boron nitrogen serves as a diffusion source. The silicon wafers 2 to be diffused are placed on the boron nitrogen plate 1. The boron nitrogen plate 1 is located on a quartz holder 3 during diffusion. Boron diffuses into the silicon wafers 2 by heating the system to the intended diffusion temperature.

In the diffusion of Figure 2 2. After the slices not to be diffused discs 2 on the diffusion source, the diffusion countries special source of boron nitride (1) befin- det inversely to the silicon to be diffused are figure 3, the Borstickstoffplatte 1 also be separated 'by small spacers 4 of the diffuses to exploding silicon wafers. 2

Of course there is also the possibility of powdered boron nitride and to use this example schiffchen in a quartz accommodate. In this case, the silicon wafers 2 are placed, for example, on the boron -nitrogen powder that has been spread out.

Since boron nitrogen has an unusually small thermal expansion and its mechanical strength is also very high, boron nitrogen has an extraordinarily high resistance to sudden changes in temperature .

The diffusion process can take place in an inert atmosphere or in an oxidized atmosphere. Suitable inert gases such as nitrogen and rare gases are possible.

If the diffusion process takes place in an inert atmosphere, the diffusion is controlled by the temperature and time by the vapor pressure of the nitrogen at the diffusion temperature. In the case of oydierenden atmospheric oxidation of the boron occurs according to the equation 4-BN + 4 02 ---- @ - 2 B203 + 2 N0_ + N2 a. The compound 8203 evaporates and reacts with the silicon according to the equation 2 B203 + 3 Si ---- b 2 SiO2 + 2 B2 As a result of the uniformity of the diffusion source with regard to the boron concentration and the geometric position in relation to the semiconductor wafers, a very uniform diffusion is achieved with a uniform temperature distribution. Since boron nitrogen has a high thermal conductivity, possible small temperature fluctuations in the diffusion space balance each other out relatively quickly. It is also important that boron nitrogen does not react with silicon. Likewise, at the diffusion temperatures in question, there is no reaction between boron nitrogen and aluminum, iron, copper and zinc; Chlorine gas has little effect.

Claims (1)

Patent claims 1) Use of boron nitrogen as a diffusion source for diffusing boron into a semiconductor body. 2) Method according to claim 1, characterized in that the semiconductor body to be diffused is placed on boron nitrogen material or, conversely, boron nitrogen is placed on the semiconductor body to be diffused . 3) Method according to claim 1 or 2, characterized by the use of boron nitrogen in powder form or in the form of a solid body. 4) Method according to one of the preceding claims, characterized in that the diffusion takes place in an inert or oxidizing atmosphere.