JPS63119229A - Diffusing method of boron - Google Patents

Abstract

PURPOSE:To control the rate of oxidation at the time of a drive diffusion, to balance the lowering of silicon surface concentration by the segregation effect of boron and the activation of boron by heat and to equalize surface impurity concentration in a substrate surface and in a substrate by adding oxygen into N2 gas. CONSTITUTION:In a boron diffusion method in which boron is deposited on silicon substrates 2, and heated in an atmosphere containing no boron, and a drive diffusion is conducted and boron is redistributed, the drive diffusion is accelerated in an atmosphere in which O2 is added into an inert gas such as N2 by 0.1% or 20%. Since concentration distribution on a substrate surface after the diffusion is subject to an increasingly larger effect at an increasingly earlier step of a drive diffusion process, a sufficient effect is displayed even when only a substrate insertion process is performed in said mixed atmosphere. The addition ratio of O2 is determined by impurity concentration on the substrate surface after the drive diffusion required and the whole sequence.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a boron diffusion method in a semiconductor manufacturing equipment process.

[Prior Art] Generally, when boron is diffused in a semiconductor device, it is performed in three steps: first, pre-deposition of boron on a substrate, then drive pre-treatment, and drive diffusion.

That is, first, a relatively thin high-concentration boron layer is deposited on the surface of the silicon substrate by pre-deposition and diffused into a shallow layer. Next, the supersaturated boron glass layer adhering to the substrate surface is removed by pretreatment with a chemical solution, and then the boron is heated by drive diffusion to redistribute the boron introduced into the substrate.

This drive diffusion step is carried out in a diffusion furnace in an N2 (nitrogen) atmosphere, an 02 (oxygen) atmosphere, or a water vapor atmosphere.

Further, the supersaturated boron glass layer formed on the silicon surface during pre-deposition has various distributions depending on the placement of the silicon substrate in the diffusion furnace during pre-deposition. For example, as shown in FIG. 1, when a silicon substrate 2 is stood upright in a direction perpendicular to the gas flow in a horizontal diffusion furnace in which a furnace tube 1 is arranged horizontally, supersaturated boron glass on the silicon surface The distribution of the layers is shown in FIG. 2(a). In the figure, a pin-shaped supersaturated boron glass layer is formed on the surface of a silicon substrate 2, with a high concentration at the periphery and gradually decreasing toward the center.

It is difficult to completely remove this boron glass layer in the drive pre-treatment, and if the drive diffusion in the post-process is performed in an N2 atmosphere, the surface impurity concentration will be reduced as shown in Figure 2(b). The S degree distribution is similar to a).

[Problem to be Solved by the Invention 1] As described above, in the conventional diffusion method, the distribution of the supersaturated boron glass layer formed on the surface of the silicon substrate after pre-deposition is uneven, and the drive This will significantly deteriorate the uniformity of the silicon surface impurity concentration after diffusion.

This is a major cause of a decline in the yield rate of semiconductor devices as silicon substrates become larger in diameter.

Means for Solving Problem E] This invention was made in view of the conventional problems such as soft soil, and provides a boron diffusion method that makes the substrate surface concentration uniform. .

In the boron diffusion method of this invention, the drive diffusion step is performed using N2
The test is carried out in an atmosphere in which 0.1% to 20% oxygen is added to an inert gas such as gas.

(Embodiments of the invention This invention will be explained in detail below.

Generally, the drive diffusion process is performed in the following steps.

(a) Inserting the i-plate into the diffusion furnace → (b) Preheating or raising the temperature → (C> drive diffusion → (d) Afterheating or lowering the temperature → (e) Taking out the substrate from the furnace.

In each of the above steps (a) to (e), N
Diffusion proceeds in an atmosphere in which 0.1% to 20% of 02 is added to an inert gas such as No.2.

Furthermore, in each of the above steps, when the drive diffusion step (C) is performed in a steam atmosphere, only the substrate insertion step (a) and the preheating or temperature raising step (b) are performed in the 02 mixed atmosphere.

Further, depending on the required impurity concentration on the surface of the silicon substrate, only the substrate insertion step (a) may be performed in the above mixed atmosphere.

The concentration distribution on the substrate surface after diffusion is greatly affected at the early stages of each of the drive diffusion steps (a) to (e) above, so even if only the substrate insertion step (a) is performed in the above mixed atmosphere, sufficient effects can be obtained. There is.

Further, the addition rate of 02 is determined by the required drive substrate surface impurity concentration after diffusion and the overall sequence.

In this diffusion method, the thermal diffusion of boron in the 02 atmosphere is different from the case of phosphorus or arsenic, and due to the segregation effect that boron in the silicon substrate is incorporated into the silicon oxide film, impurities on the silicon surface after diffusion S degree decreases.

Furthermore, supersaturated boron increases the oxidation rate of silicon, so when the concentration of supersaturated boron around the edge of the substrate is high as described above, if drive diffusion is performed in 02, the diffusion rate will be higher than in N2. As shown in FIG. 2(C), the surface impurity concentration at the edge of the substrate decreases.

FIG. 3 shows the relationship between the impurity concentration on the substrate surface after drive diffusion and the sheet resistance ρ of the diffusion layer at 021 degrees in N2 gas according to the diffusion method of the present invention. The sheet resistance ρ of this diffusion layer is inversely proportional to the impurity 11 degrees on the substrate surface.

In addition, the conditions are pre-dead position>975”05 minutes,
Drive diffusion at 1000°C for 18 minutes.

FIG. 4 shows the relationship between the film thickness of silicon on the surface of the substrate after drive diffusion for 0211 degrees under the same conditions as above.

From FIGS. 3 and 4, when 0211 degrees is 20% or more, both the surface impurity concentration and the glass layer thickness change little with respect to 0211 degrees, and the effect of reducing nonuniformity is weak, 0.1%.
By controlling the silicon oxidation rate to 20%, it becomes possible to balance the reduction in the silicon substrate surface concentration due to the boron segregation effect and the activation of boron due to heat.

This allows the surface impurity concentration within the substrate to be made uniform.

In the above example, the two-step diffusion method of pre-prepared position and drive diffusion was explained as a boron diffusion method, but we applied it to one-step diffusion in which both of these steps are performed consecutively in the same furnace. The process may be carried out in a mixed atmosphere between the two.

The same applies even when the process is divided into multiple stages.

[Effects of the Invention] As described above, according to the present invention, by adding oxygen to N2 gas, the oxidation rate during drive diffusion is controlled, and the silicon surface concentration is reduced due to the boron segregation effect.
Since a balance can be achieved with the activation of boron by heat, the surface impurity concentration within the surface of the substrate and within the substrate can be made uniform.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a general horizontal diffusion furnace, Figure 2 (a) is a diagram showing the supersaturated boron glass distribution on the substrate surface by the conventional diffusion method, and Figure 2 (b) is a diagram showing the distribution of supersaturated boron glass on the substrate surface by the conventional diffusion method. Figure 2(C) is a diagram showing the substrate surface impurity concentration distribution after drive diffusion. Figure 2(C) is a diagram showing the substrate surface impurity concentration distribution after drive diffusion according to the present invention. Figure 3 is a diagram showing the substrate surface concentration and 02 concentration according to the present invention. FIG. 4 is a diagram showing the relationship between the sheet resistance value and the relationship between the silicon oxide film thickness and the temperature between 02 and 1 degrees according to the present invention.

Claims (1)

[Claims] In a boron diffusion method in which boron is deposited on a silicon substrate and then heated in a boron-free atmosphere to perform drive diffusion and redistribute the boron, part or all of the drive diffusion process is performed using an inert gas. A boron diffusion method characterized in that it is carried out in an atmosphere containing 0.1% to 20% oxygen.