JPS6092610A - Control method of quantity of boron diffused - Google Patents

Abstract

PURPOSE:To obtain a wafer, in which there are few crystal defects and in a diffusion region therein inequality is not generated, by using a poly-boron film (PBF) by changing over gases at a first step and a second step in an atmosphere in a diffusion furnace and controlling time at the first step. CONSTITUTION:A PBF5 is applied on a wafer 4 in which an SiO2 layer 2 is formed on an Si substrate 1. A quartz pipe 13 is put into a diffusion furnace 11, and N2 and O2 are forwarded, and the PBF layer 5 is burnt to form a boron glass layer 6. When a temperature is elevated to 900 deg.C, boron is diffused into the substrate 1 from the boron glass layer 6, and a boron diffusion region 7 is shaped. The generation of the inequality of projections at both ends of the bottom of the boron diffusion region 7 and an extent in the lateral direction is inhibited because said first process is executed for approximately 10min or 2hr and boron is supplied uniformly from the boron glass layer 6 in a short time. When a temperature is elevated to 1,100 deg.C and gases, etc. are changed over to O2 in a second process, diffustion from the boron glass layer 6 is stopped, and shifted to the extending diffusion only of the inside of the boron diffusion region 7.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for controlling the amount of boron diffused in a semiconductor wafer;
In particular, the present invention relates to a method of controlling the amount of boron diffusion when expanding fI& of boron using a polyboron film (PBF).

Conventionally, BN (boron nitride) has been used as a source for base diffusion of transistors. However, BN has a disadvantage in that crystal defects occur in the formed wafer due to its large heat capacity. Therefore, in order to eliminate this drawback, P and BF containing boron in an organic polymer were applied to the wafer using a spin-on method, and the wafer coated with this PBF was placed in a diffusion furnace, and nitrogen gas and a trace amount of oxygen were added to the wafer. A method of heating and diffusing in an atmosphere has been attempted.

However, with this method, it is not possible to control the amount of boron diffusion during diffusion, and in order to achieve a certain amount of diffusion, the wafer must be removed from the diffusion furnace when the sheet resistance value reaches a certain value. Ta.

Also, when applying PBF, unevenness in the wafer pattern causes uneven film thickness on the diffusion area, and if diffusion continues, protrusions will form on both ends of the bottom of the diffusion area and the construction will be uneven. There was a drawback. Therefore, there is a problem in that the amount of boron diffused by this PBF is difficult to use for element formation such as base diffusion.

The purpose of this invention is to use PBF to obtain a wafer with few crystal defects, without protrusions on both ends of the bottom surface of the diffusion region, and with no non-uniform lateral spread, and furthermore, the sheet resistance can be easily controlled. An object of the present invention is to provide a method for controlling the amount of boron diffusion.

In order to achieve the above object, the method of controlling the boron diffusion amount of the present invention is to change the atmosphere in the diffusion furnace to nitrogen gas and a trace amount of oxygen gas in the first step, and to change it to oxidizing gas in the second step. The diffusion of boron is controlled by switching and controlling the time of the first stage.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

As one embodiment of the present invention, a case will be described in which transistor pace diffusion is performed.

First, as shown in FIG. 1(a), 12 layers of silicon dioxide (SiO2) are formed on a silicon (Si) substrate 1, and a base opening 3 is formed in this silicon dioxide layer 2 on a pattern of a wafer 4. , as shown in Figure 1(b), P
Apply BF5.

This application is performed by a spin-on method.

FIG. 2 shows the state in which the wafer 4 is placed in the diffusion furnace.

In FIG. 2, the diffusion furnace 11 has a heating section 12 into which a quartz tube 13 is inserted. 4 are arranged and stored vertically. The quartz tube 13 is supplied with nitrogen gas N2, oxygen gas 02, and water vapor H2Q from the side, and the heating section 12 is configured to be temperature controllable. However, the diffusion furnace 11 itself shown here is already well known.

The wafer 4 placed in the diffusion furnace 11 is subjected to temperature control and gas control in accordance with the order shown in FIG.

The inside of the diffusion furnace 11 is initially maintained at 800°C. When the quartz tube 13 is put into the diffusion furnace 11 and nitrogen gas N2 and oxygen gas 02 are sent to the quartz tube 13, the wafer 4 is heated in the gas atmosphere. The PBF layer 5 burns and becomes a boron glass layer 6 as shown in FIG. 1(C).

In the first process prl, when the temperature is further heated from 800° C. to 900° C. in the above gas atmosphere, boron diffuses from the boron glass layer 6 into the silicon substrate 1, forming a boron diffusion region 7. . This first process prl is carried out for approximately 10 minutes to 2 hours, and during this time the boron concentration and therefore the sheet resistance Rs
is controlled. If this time is made longer, the boron concentration becomes higher and the sheet resistance Rs becomes smaller, and if the time is made shorter, the sheet resistance Rs becomes larger.

Further, while the time of this process prl is short, since boron is supplied uniformly from the boron glass N6, the bottom surface of the boron diffusion region 7 is also uniform, and non-uniform lateral spread does not occur.

Next, in the second process pr2, the temperature is raised to 1100° C., and the gas is switched from N2 + trace amount 02 to 02. This stops the diffusion from the boron glass layer 6,
Diffusion progresses only within the boron diffusion region 7. Sunawaji,
By switching the gas atmosphere from N2+02 to 02, the diffusion of boron expressed by an error function from the boron glass layer 6 is terminated, and the process shifts to stretching diffusion expressed by a Gaussian distribution.

Next, in the third process, the temperature remains at 1100°C, N20 is sent into the quartz tube 13, a boron-diffused SiO2 film is formed on the boron diffusion region 7, the concentration of the high concentration boron glass is reduced, and the I'm trying to eliminate the impact.

And in process pr4, the gas is changed to N2 +0 at the same temperature.
The SiO2 layer formed after reverting to No. 2 is annealed.

As the atmospheric gas in the embodiment, nitrogen gas N2 may be used in the first process, and oxygen gas 02+water vapor H20, only water vapor H20, or nitrogen gas N2+a large amount of oxygen gas 02 may be used in the second and subsequent processes.

As described above, according to the present invention, in the first step, boron is supplied and diffused from the boron glass layer as a gas atmosphere, nitrogen gas, and a trace amount of oxygen gas, and in the second step, the gas is switched to an oxidizing gas. Then, the boron supply from the boron glass layer is stopped, and the diffusion is limited to the boron diffusion region, and the time of the first stage is increased to three times, so the transition from the first stage to the second stage is By appropriately performing the switching, it is possible to prevent the occurrence of protrusions on both ends of the bottom surface of the diffusion region and the occurrence of non-uniformity in the thickness. Therefore, boron diffusion in PBF can be applied to element formation, for example, base diffusion, and it is possible to obtain an element wafer that effectively utilizes the characteristic of PBF that fewer crystal defects occur. Furthermore, since the diffusion of boron from the boron glass layer can be interrupted at any time, the sheet resistance can be easily controlled and its variation can be reduced.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a wafer at each stage in an embodiment of the present invention, Fig. 2 is a diagram showing a diffusion furnace used in carrying out the invention, and Fig. 3 is a diagram showing each step in an embodiment of the invention. It is a figure showing the state of temperature control and gas control in . 1: Silicon substrate, 4: Semiconductor wafer, 5: Polyboron film layer, 11: Diffusion furnace Patent applicant: ROHM Co., Ltd. Agent, Patent attorney: Shin Nakamura Shigeru Nakamura Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] (1) Coating a polyboron film on a semiconductor wafer,
A method for controlling the amount of boron diffusion when a coated semiconductor wafer is housed in a diffusion furnace and heated to perform boron diffusion, the method comprising: controlling the atmosphere in the diffusion furnace in a first step by adding nitrogen gas and a small amount of nitrogen gas; Oxygen gas, then switched to oxidizing gas in the second stage,
A method for controlling the amount of boron diffusion, characterized in that boron diffusion is controlled by controlling the time of the first step.