KR19990071133A - Manufacturing Method of SRAM Cell - Google Patents

Abstract

The present invention relates to a method for fabricating an SRAM cell suitable for reducing cell size and improving cell stability through a symmetrical structure, wherein an active region and a field region are defined in the semiconductor substrate to form a field oxide film in the field region. Forming a first trench at a predetermined depth in a semiconductor substrate adjacent to the field oxide layer, forming a first gate line of a drive transistor on the first trench and a semiconductor substrate adjacent thereto; Forming a second gate line of an access transistor on a semiconductor substrate adjacent to the gate line, forming a first interlayer insulating film on a surface of the second gate line, and forming a semiconductor on both sides of the first and second gate lines Forming a source and drain impurity region in the substrate surface, and between the second gate line Forming a second trench at a predetermined depth in the conductor substrate to isolate the active region, and forming a second interlayer insulating film on the semiconductor substrate in front of the semiconductor substrate, and forming a via hole to expose a predetermined portion of the source and drain impurity regions and the first gate line. Forming a third gate line of the thin film transistor connecting the source and drain impurity regions and the first gate line through the via hole; and forming a thin film on the semiconductor substrate perpendicular to the third gate line. And forming a channel region of the transistor.

Description

Manufacturing Method of SRAM Cell

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to semiconductor memory devices, and more particularly, to a method of manufacturing an SRAM cell suitable for reducing cell size and improving cell stability through a symmetrical structure.

Generally, an SRAM cell consists of four transistors (eg, two access transistors and two drive transistors) and two polysilicon load resistors, or six transistors.

In particular, 4M or higher integrated cells are generally configured in the form of CMOS, which consists of four NMOS transistors and two PMOS transistors.

In addition, low density products use an asymmetric cell, which is advantageous in terms of area.As a result of the high integration, the area of the cell is reduced and the asymmetry has a great influence on the operation. Using the line width makes the area somewhat larger.

Therefore, it is now a matter of concern to reduce the area while maintaining the symmetry.

Hereinafter, an SRAM cell of the related art will be described with reference to the accompanying drawings.

1 is a circuit diagram illustrating a typical SRAM cell.

As shown in FIG. 1, a first PMOS load connected in common with first and second access transistors TA1 and TA2 connected by a word line W / L and a source terminal of the first access transistor TA1. A transistor TL1 and a first drive transistor TD1, a second PMOS load transistor TL2 and a second drive transistor TD2 connected in common with a source terminal of the second access transistor TA2, and the The gate of the first PMOS load transistor TL1 and the gate of the first drive transistor TD1 are common to the second PMOS load transistor TL2, the second drive transistor TD2, and the second access transistor TA2. And a gate of the second PMOS load transistor TL2 and a gate of the second drive transistor TD2 are connected to the first PMOS load transistor TL1 and the first drive transistor. (TD1) and a first access transistor (TA1) is a terminal connected in common, being connected to the drain terminal of said first access transistor (TA1) at the bit ( ) Is contacted, and the bit line B / L is contacted to the drain terminal of the second access transistor TA2.

However, in the SRAM cell of the prior art as described above, there is a problem that the cell is unstable due to the large size of the active region and the asymmetry of the access transistor.

Disclosure of Invention The present invention has been made to solve the above problems, and an object thereof is to provide a method of manufacturing an SRAM cell which minimizes an active region to reduce cell size and improve cell stability through a symmetrical structure.

1 is a circuit diagram of a typical SRAM cell

2A to 2G are plan views illustrating a method of manufacturing an SRAM cell according to the present invention.

3A to 3G are cross-sectional views of an SRAM cell taken along line IV-IV ′ of FIGS. 2A to 2G.

Explanation of symbols for main parts of the drawings

21: semiconductor substrate 22: P-well

23: field oxide film 24: first gate oxide film

25: first gate line 26: second gate oxide film

27: second gate line 28: first interlayer insulating film

29 source and drain impurity region 30 trench

31: second interlayer insulating film 32: via hole

33: third gate line 34: third gate oxide film

35: channel region of thin film transistor

According to an aspect of the present invention, there is provided a method of manufacturing an SRAM cell in which a field oxide film is formed in a field region by defining an active region and a field region in a semiconductor substrate, and a semiconductor substrate adjacent to the field oxide layer. Forming a first trench with a predetermined depth, forming a first gate line of a drive transistor on the first trench and a semiconductor substrate adjacent thereto, and forming an access transistor on a semiconductor substrate adjacent to the first gate line. Forming a second gate line, forming a first interlayer insulating film on a surface of the second gate line, and forming source and drain impurity regions in a semiconductor substrate surface on both sides of the first and second gate lines; And forming a second trench at a predetermined depth in the semiconductor substrate between the second gate line. Separating the reverse region, forming a second interlayer insulating film over the semiconductor substrate, and forming a via hole to expose a portion of the source and drain impurity regions and the first gate line, and forming a source and drain through the via hole. And forming a third gate line of the thin film transistor connecting the impurity region and the first gate line, and forming a channel region of the thin film transistor on the semiconductor substrate perpendicular to the third gate line. It is characterized by.

Hereinafter, a method for manufacturing an SRAM cell according to the present invention will be described in detail with reference to the accompanying drawings.

2A to 2G are layout views illustrating a method of manufacturing an SRAM cell according to the present invention, and FIGS. 3A to 3G are cross-sectional views taken along line IV-IV ′ of FIGS. 2A to 2G.

As shown in FIGS. 2A and 3A, P-type impurity ions are selectively implanted into the entire surface of the n-type semiconductor substrate 21 to form a P-well 22 in the surface of the semiconductor substrate 21.

Subsequently, an active region and a field region are defined in the semiconductor substrate 21 to form a field oxide film 23 in the field region.

2B and 3B, trenches are formed in the semiconductor substrate 21 adjacent to the field oxide layer 23 to a predetermined depth, and a first trench is formed on the surface of the semiconductor substrate 21 on which the trenches are formed. A gate oxide film 24 is formed.

Subsequently, a first conductive layer is deposited on the entire surface of the semiconductor substrate 21 including the trench, and selectively patterned to remain only on the semiconductor substrate 21 adjacent to the trench and the first gate line 25 of the drive transistor. To form.

As shown in FIGS. 2C to 3C, a second gate oxide layer 26 and a second conductive layer are deposited on the entire surface of the semiconductor substrate 21, and the second conductive layer and the second gate oxide layer 26 are deposited. And selectively removed to form a second gate line 27 of the access transistor.

The second gate line 27 is formed to be adjacent to the first gate line 25.

Subsequently, a first interlayer insulating film 28 is formed on the surface of the second gate line 27 as a cap insulating film and an insulating film sidewall.

As shown in FIGS. 2D and 3D, a high concentration of n-type impurity ions are implanted into the entire surface of the semiconductor substrate 21 to form a surface of the semiconductor substrate 21 on both sides of the first and second gate lines 25 and 27. Source and drain impurity regions 29 are formed.

Next, a photomasking process of the semiconductor substrate 21 is performed to form trenches 30 in the semiconductor substrate 21 deeper than the source and drain impurity regions 29 to separate active regions.

2E and 3E, a second interlayer insulating film 31 is formed on the entire surface of the semiconductor substrate 21 including the trench 30, and the second interlayer insulating film is formed by photolithography and etching processes. 31 is selectively removed to form the via holes 32 to expose a portion of the surface of the semiconductor substrate 21.

Here, the via hole 32 is for connection between the gate line of the drive transistor and the source and drain impurity regions 29 of the other drive transistor.

As shown in FIGS. 2F and 3F, a third conductive layer is deposited on the entire surface of the semiconductor substrate 21 including the via holes 32 and then subjected to a photolithography process to perform source and drain through the via holes 32. A third gate line 33 of the thin film transistor connected between the impurity region 29 and the first gate line 25 is formed.

The third gate line 33 is formed in one direction at regular intervals.

Subsequently, a third gate oxide layer 34 is formed on the surface of the third gate line 33.

2G and 3G, in order to form the channel region of the thin film transistor, a fourth conductive layer is deposited on the entire surface of the semiconductor substrate 21 and then selectively removed by a photolithography process to remove the channel region of the thin film transistor. (35) is formed.

The channel region 35 is formed to extend across the third gate line 33 in a direction perpendicular to the third gate line 33, and the third gate line 33 is offset. Form.

As described above, the method of manufacturing the SRAM cell according to the present invention has the following effects.

First, the cell size can be reduced by separating the active region to minimize the width of the active region.

Second, the gap between the thin film transistors can be secured to the maximum, thereby improving the reliability of the device.

Third, cell stability can be achieved by using two access transistors.

Claims (2)

Defining an active region and a field region in the semiconductor substrate to form a field oxide film in the field region; Forming a first trench in a semiconductor substrate adjacent to the field oxide layer to a predetermined depth; Forming a first gate line of a drive transistor on the first trench and a semiconductor substrate adjacent thereto; Forming a second gate line of an access transistor on a semiconductor substrate adjacent to the first gate line; Forming a first interlayer insulating film on a surface of the second gate line; Forming source and drain impurity regions in a surface of the semiconductor substrate on both sides of the first and second gate lines; Forming a second trench at a predetermined depth in the semiconductor substrate between the second gate lines to separate the active region; Forming a via hole on the semiconductor substrate to expose a portion of the source and drain impurity regions and the first gate line after forming a second interlayer insulating layer on the semiconductor substrate; Forming a third gate line of a thin film transistor connecting a source and drain impurity region and a first gate line through the via hole; And And forming a channel region of the thin film transistor on the semiconductor substrate orthogonal to the third gate line. The method of claim 1, And forming the second trench deeper than the source and drain impurity regions.