JPS5936418B2 - Impurity diffusion method for silicon substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for diffusing impurities into a silicon substrate,
In particular, an improved impurity diffusion method is provided that provides diffusion into silicon substrates with fewer defects.

Conventionally, deep diffusion into a silicon substrate is performed using B, O, etc., for example, for the formation of a single electrode deposit in the formation of a silicon rectifier, the formation of a collector region in a triple diffusion transistor, and the emitter diffusion of a power device.

, P2O, and other impurity oxides belonging to Groups 1 and V are dissolved in an organic solvent such as ethyl alcohol, methylcellosolve, etc., and this is applied by a method such as a soot coating, which is the so-called Painton diffusion. However, according to the above diffusion method, when forming highly concentrated layers such as the emitter layer and collector electrode, lattice distortion occurs due to the difference in the tetrahedral radius of the impurity element and the silicon atom. A large number of line defects are observed. These defects not only adversely affect the electrical characteristics of semiconductor devices such as noise, but also cause emitter dips and
Lateral diffusion occurred, resulting in extremely poor controllability. In response to the above, boron silicate glass (hereinafter abbreviated as BSG) diffusion, phosphorus-arsenic diffusion, etc. have been proposed, and low-frequency noise can be reduced for shallow diffusion in planar transistors, bibolar ICs, etc. results were seen.

However, in the case of phosphorus-arsenic used for N+ diffusion, the diffusion coefficient of arsenic is one order of magnitude smaller than that of phosphorus, so diffusion is delayed, especially in deep diffusion, for example, emitter diffusion where Xj>15μ (Xj is the layer thickness). A sufficient concentration cannot be obtained for the strain canceling mechanism to work. On the other hand, defect-free diffusion by BSG diffusion also occurs in the shaded area in the figure, that is, when Ns (surface concentration) is 4×1020
/1 or less and the total boron amount Q is 2×1016/Cf
Only the range below lt is defect-free. Ns≦4×1020/(-JmoVi in the above range can be corrected by BSG, but Q≦2×10'6/Cil becomes unsatisfactory as soon as Xj becomes large (deep diffusion). For example, Ns= When Xj is 4×1020/d, defects occur at around 1μ.The present invention improves the drawbacks of the conventional diffusion methods described above, and provides a method for easily achieving deep defect-free diffusion. It is something.

The method for diffusing impurities into a silicon substrate according to the present invention is characterized in that when a group I or V element as an impurity is simultaneously diffused into a silicon substrate, the group element is added from its oxide.

Further, in the above method, the group element is added in the form of an oxide, and at the same time, this oxide is added in the form of a solution dissolved in an acid solution with a pH of 1 or less or an alkaline solution with a pH of 3 or more. Furthermore, in order to diffuse the Group I or V element into the silicon substrate with fewer crystal defects, the addition ratio is determined by paying attention to the segregation phenomenon between the above element and the group element glass and silicon. Further, the method is characterized in that a solution of an oxide of a group I or group V element is dissolved in a water-soluble organic solvent, and the solution is coated on a silicon substrate in layers or as a mixed solution. Furthermore, the organic solvent is alcohol and/or methylcellosolve. Next, the progress of development of the present invention and further examples will be described.

In the embodiment, it was devised to simultaneously diffuse the impurity element Ge in order to compensate for the compression caused by atoms having a smaller tetrahedral radius than Si, such as boron (B) and phosphorus. Ge is a group element and has the advantage of having little electrical effect on device characteristics. Gecl4 cannot be used as a diffusion impurity source in the form of a single element, and Gecl4
Then, CVD (Chem
icalvapOrdepOsitiOn) is difficult and may rust the CVD equipment.
Furthermore, since GeH4 is difficult to produce and obtain, diffusion of Ge has hardly been put into practical use. In the present invention, P2O5 and B2O3 are used as donor impurities and acceptor impurities, and GeO2 is used as a strain canceling impurity.

At present, there is no solvent that can dissolve both of the above at the same time, so a method was adopted in which each was dissolved in a solvent that dissolved each, and then the mutual solutions were mixed. B2 as an example
When O3 is used, it is dissolved using methyl cellosolve or ethanol, and GeO2 is dissolved using concentrated HCl or concentrated alkali, and then the two are mixed and spin (
We have discovered a method of applying the coating using a spin-on method, a spray method, etc., and then diffusing it. Next, one embodiment of the present invention will be described.

A solution (IC) is prepared as follows.

(Prepared solutions (sub) to (C) are common to each example below) Example (1) 3" solution (C) to 677
A mixed solution consisting of 11 was prepared, and the diameter was 43”φ and the thickness was 35
Spin on an N-type wafer with a resistivity of 0μ and a resistivity of 30 to 50Ω.
Turn on, and perform diffusion for 30 hours in an oxygen atmosphere (02 flow rate 21/Mm) in a diffusion furnace at 1285°C.
1019/DC7) Ns was obtained.

Example (2) A mixed solution consisting of 3 solutions (Q3) and 6 solutions (C) was prepared, and Ns=
6.5×1019/Cld. We obtained xj=27μ.

Example (3) A mixed solution consisting of 3mi of solution (3mi x 9mi of solution (C)) was prepared, and the diameter was 43171Lφ and the thickness was 350μ.
, coated on an N-type wafer with a specific resistance value of 30 to 50 Ω, and
In a diffusion furnace at 85°C, oxygen 20cc/min and nitrogen 2
90TRi in a mixture atmosphere of 1/WLm! Perform the diffusion of t and get Ns=1.3×102/(V7f.Xj=15
．． 5μ was obtained.

When examining the dislocation densities of the wafers obtained in Examples (1) to (3) above, the order is (1)>(2)>(3), especially (
In the case of 3), the number of defects was 1000 pieces/d or less, and it appeared that there were almost no defects. Next, the radius of the tetrahedron in B(7)Si is 0
．． 88λ, while Ge is 1.22λ and S
The former is small and the latter is large compared to 1.17λ of i.

Theoretically, when mixed at a ratio of Ge:B = 5.3:1, CompressiOn(5ExpansiOn) should be balanced and have no distortion, but in reality GeO2(
The defect-free diffusion conditions differ depending on the diffusion atmosphere and the diffusion temperature (both of which affect the oxidation rate) due to the problem of the segregation coefficient between Si (or in SiO2) and Si. In the examples, the addition ratio was set to GeO2:1/2B203=3, taking into consideration the segregation phenomenon.
:Defects decreased under the condition of 1. In the same manner as described above, defect-free diffusion can also be achieved for deep donor diffusion. That is, defect-free formation can be achieved by dissolving P2O and GeO2 in ethyl alcohol and organic alkali, respectively, and spin-on coating and diffusion using a mixed solution thereof. In order to prevent the vaporization of P2O5, the vaporization point (591℃) and melting point (569℃)
After melting by heating at an intermediate temperature of about 580°C (100°C), the temperature is raised to the diffusion temperature. As mentioned in the above example, defect-free diffusion can be achieved by selecting the size of the tetrahedral radius, but even from the 3:1 GeO2:KiB2O3 example, it is possible to increase the solid solution. It can also be seen that the number of defects is reduced.

In addition, if the liquids are mixed to form a precipitate, they may be applied separately and dried.

When applying the above separately, apply GeO2 first, and
Hcl,N(CH3)40H dissolving eO2
It is necessary to apply B2O3 after decomposing and evaporating the liquid so that it will not be affected by the subsequent liquid.

[Brief explanation of the drawing]

The figure is for explaining diffusion in BSG diffusion.

Claims (1)

[Claims] 1. Group III or group V elements as impurities are added to the silicon substrate.
A method for diffusing impurities into a silicon substrate, characterized in that a group IV element is added from its oxide when being diffused simultaneously with a group element. 2. The method according to claim 1, characterized in that the group IV element is added in the form of its oxide, and at the same time, this oxide is added in the form of a solution dissolved in an acid solution with a pH of 1 or less or an alkaline solution with a pH of 13 or more. Impurity diffusion method for silicon substrate. 3. A patent characterized in that, in order to diffuse group III or V group elements into a silicon substrate with fewer crystal defects, the addition ratio is determined in advance with consideration to segregation development between the above elements and group IV elements between glass and silicon. A method for diffusing impurities into a silicon substrate according to claim 1. 4. Silicon according to claim 1, characterized in that a group III or V group element or an oxide thereof is dissolved in a water-soluble organic solvent to form a solution, and the solution is coated over a substrate or a mixed solution is applied. Method for diffusing impurities into the substrate. 5. The method for diffusing impurities into a silicon substrate according to claim 4, wherein the water-soluble organic solvent used to dissolve the oxide of a group III or group V element is alcohol and/or methylcellosolve.