JPS58122768A - Semiconductor device - Google Patents

Abstract

PURPOSE:To reduce the impurity diffusion length and thus contrive the improvement of the linear characteristic of poly Si resistance, by selectively oxidizing a part of the side to diffuse the impurity of a poly Si layer into a thin layer. CONSTITUTION:After patterning the poly Si layer 21, an SiO2 layer 22 is formed, then an Si3N4 mask 23 is applied resulting in a selective oxidation, and thus the poly Si 21 is slightly left at the lower end of the layer 21. Next, after superposing a CVDSiO2 layer 26, an impurity 27 is diffused. Thereat, since the diffusion route is formed narrow on its halfway, the density decreases at the region wherein the route is enlarged, and accordingly the diffusion length xj can be reduced. As a result, the linear characteristic of poly Si resistance is remarkably improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a semiconductor device in which the diffusion length of an impurity is made as short as possible when diffusing impurities in a 4-Si resistor to avoid the 1141 characteristic of a 4-Si resistor.

Technical Background of the Invention At present, wafer silicon is widely used in semiconductor devices, such as by introducing impurities and changing the impurity concentration to use it as a wiring material or a high-resistance portion. In this case, if polysilicon is to be used as a high-resistance portion and a low-resistance portion at the same time, there is a method described below: First, process the polysilicon layer 11, turn it with a tin, and then
Zero-order -CVD # to form a thin 8102 layer 11 on the surface
Ibari silicon 1 covered with lO, layer 11 to make it high resistance
cvngto formed on layer 1, outside o gto of layer 13
,only? Removed by PEP (photo etchant S). As a result, the impurity 1
4. For example, pt-introduction. Here, the lateral diffusion length t of the impurity 140 into the silicon layer 11
If it is XJ, then L-2x5 remains as the high resistance part. ζThe equation that approximates the current that flows when a voltage V is applied across the polysilicon resistor created in this way is as follows. f is a constant that depends on rear height, k is Meltzmann constant, T is absolute 11, N
represents the Dalene number of polysilicon of unit length P. As is clear from the above equation (1), the VI voltage is linear in a region where the voltage V is small, and when the voltage V becomes very hot, the electric current 151X increases exponentially with respect to the voltage VK. Therefore, it is preferable to use the VI curve in the 01111 region for more stable characteristics, that is, it is better to make L-2xjri as large as possible. By the way, L cannot be made larger due to restrictions associated with microbialization, so is it currently treated as an impurity? When diffusing XJ, if XJ is set to 0 length until the impurity concentration reaches 10"fi-", the result is 6J-S, but efforts are being made to reduce this.

BACKGROUND TECHNOLOGY As a major means of reducing the above-mentioned diffusion -1kxJ, attempts have been made to lower the diffusion temperature change and introduce impurities with a small diffusion coefficient, A friend who can't get a head.

Purpose of the Invention The present invention has been made in view of the above point Kli, and therefore, when forming high-resistance portions and low-resistance portions, the resistance υ formed by the polysilicon layer is reduced by reducing the diffusion length of the impurity. It is an object of the present invention to provide a semiconductor device having improved performance.

Overview of li #4 By selectively oxidizing a part of the side silicon layer for diffusing impurities in the polysilicon layer and thinning a part of the silicon layer, the diffusion length of the cine fine particles is reduced. , the formed /IJ polysilicon resistor type characteristics have been improved.

*m example of invention Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

First, as shown in FIG. 2, the 5101 layer 21 is formed by data-turning the silicon layer 21 and then oxidizing it.

After that, 5IN4JJ deposit seal and 81NiljJ
The silicon 21' is selectively oxidized through the holes 24.degree.

Then, after the 1iiN layer 11 is doubled, a cross-sectional view similar to that shown in the second figure is obtained. In the above selective oxidation, I
In order to oxidize all the way to the bottom of the phosphor layer 21, the oxidation tube should be interrupted with only a small amount of silicon remaining.
Next, as shown in FIG. 0) on the 1110° layer 1j, C■1110. Form layer 2C. And the same figure (2)
As shown in Figure 2, impurity ZVO diffusion such as KP is performed, but since the impurity diffusion path is narrowed in the middle, the impurity 2r
When the meeting spreads, the KFi route expands again and impurity controversy f
may decrease, making tXJ smaller.

In the structure shown in the same figure (b), when x = o, 6 voices - 1y work 2 l111Ia i m 0.06 l1111, and when side cropping is done in the same 10 cess, the diffusion layer XJ t
It can be made smaller by 2.

Effects of the Invention As detailed above, according to the present invention, a part of the I-Si layer for diffusing impurities in the I-Si layer is selectively oxidized to thin the I-Si layer. This makes it possible to reduce the diffusion length and improve the ivA type characteristics of the formed polysilicon resistor.

[Brief explanation of the drawing]

Figure 111 is a cross-sectional view showing a conventional polysilicon resistor.
FIGS. (4) to (I) are diagrams showing the manufacturing process of the semiconductor device according to the present invention. 21...I silicon l-122...810271
1. J!・81N II, j [CVD5i0
2nd layer, j7-... impurity. 1 person for application, 1 speaker, Takehiko Kakee 6
AA 0
0

Claims (1)

[Claims] 1. A semiconductor device in which a portion of the I-Si layer on the side where impurities is diffused is selectively oxidized to thin a portion of the I-Si layer in the I-Si resistor.