JPS62248222A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To form a plural number of impurity regions, in which respective impurities are different with each other in their implanted amounts, by one-time ion implantation, by covering a plural number of the impurity regions with a mask layer and decreasing the thickness of the mask layer in conformity with the impurity concentration. CONSTITUTION:A given patterning photo resist 17 is attached to a nitriding Si film 13 on an element formation region Y, to perform allover etching. Thickness of the nitriding Si film 13 serving as a mask layer is properly controlled, in this process, in conformity with the respective regions. Then, the photo resist 17 is removed, to leave only a nitriding Si film in a given thickness on the upper surface of the Y region. Impurities definite in ion concentration are concurrently implanted under constant implanting conditions from element-formation regions X and Y surfaces. Resultantly, the region Y becomes larger in an implanting amount of impurities than the region X, because it is covered with the SiO2 films 12 and 13, finally enabling two transistors different in their threshold values to be formed on a single substrate.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing a semiconductor device, and more particularly, a method for manufacturing a semiconductor device having a plurality of depletion type MO5FETs with different threshold voltages on a single semiconductor substrate. Regarding.

(Prior Art) As a conventional method for manufacturing this type of semiconductor device, for example, the method shown in FIGS. 2A to 2F is known.

First, a silicon dioxide film 2 is deposited on a semiconductor substrate 1,
Furthermore, a silicon nitride film 3 is deposited thereon (FIG. A
).

Next, an opening is formed in the silicon nitride film 3 by predetermined patterning (FIG. 3B).

Then, a field oxide film 4 is formed by a thermal oxidation method (C in the same figure).

Furthermore, the silicon nitride film 3 is removed from the silicon dioxide film 2 by, for example, etching (FIG. 3D).

Next, the element formation region X on one side is masked with a photoresist 5, and with the surface of the element formation region Y on the other side exposed, a low concentration impurity is introduced into the surface of the semiconductor substrate 10 by ion implantation (the same figure). E).

After that, the element formation region Y on the other side is masked with a photoresist 6, and with the surface of the element formation region X on the -blade side exposed, high concentration impurities are introduced into the surface of the semiconductor substrate 1 by ion implantation. (Figure F).

In this way, a semiconductor device having depletion type MOSFETs having different threshold values can be formed on a single semiconductor substrate.

(Problems to be Solved by the Invention) In such a conventional semiconductor device manufacturing method, the same impurity must be implanted in a separate process at Mitaka, and photoresist coating and peeling are required for each process. Is required. In addition, in the Mitaka process of ion implantation of low concentration impurities and ion implantation of high concentration impurities, it is necessary to make the implantation conditions different for each, which is extremely troublesome in terms of control work. During low-concentration implantation, the control current for the number of implanted ions is on the order of [μA], resulting in lack of control stability, and since the number of implanted ions is small, it is greatly influenced by the surface condition of the wafer substrate, resulting in variations in the concentration distribution.

(Means for Solving the Problems) Therefore, the present invention provides a step of covering the plurality of impurity regions with a mask layer and a step of covering the plurality of impurity regions with a mask layer in manufacturing a semiconductor device having a plurality of impurity regions each having a different impurity concentration. The method includes a step of reducing the thickness of a mask layer in a region in accordance with the impurity concentration, and a step of simultaneously implanting impurities into each impurity region under constant implantation conditions.

(Operation) A plurality of impurity regions are covered with a mask layer, and the thickness of this mask layer is decreased according to the concentration of the impurity, so the thickness of the mask layer for each impurity region is adjusted according to the concentration of the impurity. The thickness will be increased. Therefore, a plurality of impurity regions each having a different amount of impurity implanted are formed by one ion implantation.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIGS. 1A to 1E are partial cross-sectional views of a semiconductor device showing each process according to an embodiment of the present invention.

First, a silicon dioxide film 12 is deposited on a semiconductor substrate 11, and a silicon nitride film 13 is further formed thereon to a predetermined thickness, for example, to a thickness of about 3000 (FIG. 1A).
.

Next, a plurality of frontage portions 1 are formed by predetermined patterning in correspondence to a plurality of element forming regions of the silicon nitride film 13.
3A (Figure 1B).

Next, a field oxide film 15 of a predetermined thickness is simultaneously formed on the opening portion 13A using a thermal oxidation method, and this oxide film 15
The element formation areas X and Y are defined by the public corporation. In this case, the silicon dioxide film 1 in these element formation regions X and Y
A silicon nitride film 13 remains on 2 (FIG. 1C)
).

Next, a predetermined patterning photoresist 17 is deposited on the silicon nitride film 13 on the element forming region Y, and then the entire surface is etched.

As a result, the silicon nitride film 13 on the element formation region X is removed, and the surface of the silicon dioxide film 120 is exposed in the region X, while the silicon nitride film 13 of a predetermined thickness still remains in the element formation region Y ( Figure 1 D). That is, in this step, the silicon nitride film 13 serving as a mask layer is
The thickness of the area is controlled as appropriate for each area.

Next, this photoresist 17 is removed, leaving only the silicon nitride film 13 of a predetermined thickness on the upper surface of the region Y.

Here, impurities with a predetermined ion concentration are simultaneously implanted from the surfaces of these element forming regions X and Y using an ion implantation method under certain conditions.

Introduce it to Y. The implantation conditions include, for example, the implantation energy, implantation amount, etc., which are set so as to obtain a desired impurity concentration in the region X. As a result, since the upper surface of the element formation region Y is covered with the silicon dioxide film 12 and the silicon nitride film 13 (mask layer), the amount of ions reaching the substrate 11 is smaller than that in the element formation region X. . That is, in these element formation regions X and Y, the amount of impurity implanted in region X is smaller than in region Y, resulting in a lower concentration.

Thereafter, through predetermined processes such as forming source and drain regions, two transistors with different threshold values can be formed on a single semiconductor substrate 11 (Fig. 1E). In the above embodiment, the thickness of the silicon nitride film 13 serving as a mask layer is made different for the two impurity regions X and Y, and impurity regions having different implantation amounts are formed in each of the two impurity regions X and Y. However, the present invention is not limited thereto, and can also be applied, for example, to a case where three impurity regions having different concentrations (implanted amounts) are formed on a single semiconductor substrate. In this case, it is sufficient to vary the thickness of the mask layer in each region, and this can be achieved by one ion implantation as described above.

(Effects) As described above, according to the present invention, the number of manufacturing steps can be reduced in the method of manufacturing a semiconductor device. As a result, the work can be made extremely easy, for example by requiring only one mask. In addition, by implanting impurities at a fixed concentration all at once, impurity regions with different concentrations can be easily formed on a single semiconductor substrate, and the performance of product devices can also be stabilized. This effect is achieved.

[Brief explanation of drawings]

1A to 1E are partial sectional views of the device in each step showing an embodiment of the method for manufacturing a semiconductor device according to the present invention, and FIG.
Figures A to F are partial cross-sectional views of a semiconductor device at each step showing a conventional manufacturing method. 11...Semiconductor substrate

Claims (1)

[Claims] In a method for manufacturing a semiconductor device having a plurality of impurity regions each having a different impurity concentration, there is a step of covering the plurality of impurity regions with a mask layer, and adjusting the thickness of each mask layer of these impurity regions according to the impurity concentration. 1. A method of manufacturing a semiconductor device, comprising: a step of reducing the impurity by reducing the impurity, and a step of simultaneously implanting impurities into each impurity region under constant implantation conditions.