JPS6128229B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a semiconductor substrate made of silicon on a region corresponding to a source region and a drain region from the main surface side of the semiconductor substrate made of silicon, and a channel region between them. Gate insulating layer made of oxide material: After forming the gate electrode etc. on this gate insulating layer, conductive layers connected to the source region, drain region and gate electrode are separated using an inert gas. This invention relates to improvements in the manufacturing method of MOS transistors formed by sputtering processing.

In the manufacturing method of such a MOS transistor, the conductive layer connected to the source region, drain region, and gate electrode is formed by sputtering treatment, so that the conductive layer has a desired roughness. It is more reliable and easier to form a conductive layer as a material, and to form the conductive layer without being affected by the unevenness of the surface on which it is to be obtained, compared to the case where it is formed by a vapor deposition process. It has the following characteristics.

Incidentally, in the sputtering process in the conventional method for manufacturing MOS transistors, argon gas is normally used as an inert gas during the process. However, when a conductive layer is formed by such a sputtering process, charges are unstablely generated at or near the interface between the silicon substrate and the gate insulating layer during the sputtering process. Therefore, the obtained MOS
There was a risk that the transistor would be manufactured with the threshold voltage, which determines one of its characteristics, having a large deviation from the intended value.

For this reason, in the conventional manufacturing method of MOS transistors in which a conductive layer is formed by sputtering using argon gas as an inert gas, hydrogen gas is After the atmosphere is formed, heat treatment is performed in a hydrogen gas atmosphere to eliminate charges generated at or near the interface between the silicon semiconductor substrate and the gate insulating layer during the sputtering process.

However, when heat treatment is performed in a hydrogen gas atmosphere in this way, the resulting MOS transistor has a threshold voltage with a deviation value from the intended value, compared to when heat treatment is not performed in a hydrogen gas atmosphere. However, the small deviation value cannot be obtained as small enough to be ignored, and it takes a relatively long time in a hydrogen gas atmosphere to obtain the small deviation value. It required time for heat treatment.

By the way, as shown in Figure 1A, 1×
A semiconductor substrate 1 made of P-type silicon having an impurity concentration of 10 ¹⁵ atoms/cm ³ is used.
N-type source region 2 and drain region 3 from the main surface side, and a channel region 4 between them;
A gate insulating layer 5 made of an oxide of the same material as the semiconductor substrate 1 in the region 1 corresponding to the channel region 4 on the main surface of the semiconductor substrate 1, that is, silicon oxide; A gate electrode 6 made of a crystalline semiconductor, that is, polycrystalline silicon; a source region 2 on the semiconductor substrate 1 and the gate electrode 6;
In order to partially expose the drain region 3 and gate electrode 6 to the outside, a field insulating layer 10 made of an oxide of the same material as the semiconductor substrate 1 in which windows 7, 8 and 9 are formed, that is, silicon oxide, is formed. (Such source region 2, drain region 3 and channel region 4; gate insulating layer 5; gate electrode 6;
(The order in which the field insulating layer 10 and the like are formed does not matter) After that, as shown in FIG. The conductive layers 12, 13 and 16 connected and extending over the field insulation layer 10 are formed by a sputtering process using argon gas (by a non-selective sputtering process). A series of conductive films are formed on the exposed surface of the semiconductor substrate 1, and then the conductive films are selectively etched. The target MOS transistor M after heat treatment
When manufacturing MOS transistor M
The threshold voltage (volts) of (when a voltage of zero volts is applied to the semiconductor substrate 1) is as shown in Fig. 2 with respect to the time (minutes) of heat treatment at approximately 400°C in a hydrogen gas atmosphere. Values within the range of values on curves 21 and 22 centered around the intended value on curve 20 were obtained.

For this reason, the present inventors and others
Obtained in the manufacturing method of MOS transistors
As a result of conducting various experiments in order to obtain a MOS transistor with a threshold voltage that is sufficiently smaller than the desired value so that the deviation value can be ignored,
When the sputtering process is performed using a mixed gas of argon gas and hydrogen gas containing 5 to 50 mol% hydrogen gas in argon gas as the inert gas used for the sputtering process, the mixed gas constitutes The hydrogen gas generated reaches the semiconductor substrate made of silicon, thereby suppressing the unstable generation of electric charges at or near the interface between the semiconductor substrate made of silicon and the gate insulating layer. For this reason, MOS transistors that can be obtained after the sputtering process without the need for heat treatment in a hydrogen gas atmosphere as described above,
It has been confirmed that the deviation value of this threshold voltage from the intended value can be obtained as a value sufficiently small to be ignored.

The reason why the lower limit of the amount of hydrogen gas constituting the mixed gas is 5 mol% is that below this lower limit, the resulting MOS transistor will not have the desired threshold voltage. This is based on the fact that it has been confirmed that the effect is significantly reduced when the deviation value from the value is small enough to be ignored. Also, the reason why the upper limit for the amount of hydrogen gas is 50 mol% is that even if the amount of hydrogen gas is 50 mol% or more, the resulting MOS
A transistor is obtained whose threshold voltage has a negligible deviation from its intended value. However, the time required to form the conductive layer formed by sputtering to the desired thickness exceeds the upper limit of 50 mol%. This is based on the fact that it has been confirmed that the length will be significantly longer.

Based on the above, the present inventors and others have proposed that the source region and drain region from the main surface side of a semiconductor substrate made of silicon, and the channel region between them; A gate insulating layer made of an oxide of the same material as the semiconductor substrate made of silicon; after forming a gate electrode on this gate insulating layer, conductive layers are connected to the source region, drain region, and gate electrode, respectively. In the manufacturing method of a MOS transistor, which is formed by a sputtering process using an inert gas, the sputtering process is
We have proposed a new method for manufacturing MOS transistors that uses a mixed gas of argon gas and hydrogen gas, in which 5 to 50 mol% of hydrogen gas is contained in argon gas, as an inert gas. It is ivy.

According to the manufacturing method of the present invention, as is clear from the above, the resulting MOS transistor can have a threshold voltage of It is manufactured so that the deviation value from the expected value is small enough to be ignored, and the subsequent heat treatment in a hydrogen gas atmosphere can be omitted by performing sputtering treatment, or the heat treatment can be performed. However, it has great features such as the fact that it takes only an extremely short amount of time.

This means that the source region, drain region, channel region, gate insulating layer, gate electrode, field insulating layer, etc. are formed in the same manner as described above in FIG. The source region, drain region and As an embodiment of the present invention, the purpose is to form a conductive layer connected to each gate electrode, and then perform heat treatment at about 400°C in a hydrogen gas atmosphere.
When manufacturing MOS transistors, the obtained
The threshold voltage of a MOS transistor (when a voltage of zero volts is applied to a semiconductor substrate made of silicon) changes as shown by curve 20 in Figure 2 with respect to the time of heat treatment at approximately 400°C in a hydrogen gas atmosphere. It will be clear from the fact that values were obtained within the range of values on curves 31 and 32 centered on the corresponding desired value on curve 30 of FIG.

[Brief explanation of the drawing]

FIGS. 1A and 1B are cross-sectional views showing an example of a method for manufacturing a MOS transistor according to the present invention. FIG. 2 is a curve diagram showing the relationship between the threshold voltage and the heat treatment time of a MOS transistor manufactured by a conventional MOS transistor manufacturing method. FIG. 3 is a curve diagram showing the relationship between the threshold voltage and the heat treatment time of a MOS transistor manufactured by the MOS transistor manufacturing method according to the present invention. 1... Semiconductor substrate, 2... Source region, 3
......Drain region, 4......Channel region,
5......Gate insulating layer, 6......Gate electrode, 1
0...Field insulating layer, 12, 13, 16...
...Conductive layer.

Claims (1)

[Claims] 1. A source region from the main surface side of a semiconductor substrate made of silicon, and a channel region therebetween: the semiconductor on a region corresponding to the channel region on the main surface of the semiconductor substrate. After forming the gate electrode of the gate insulating layer made of oxide of the same material as the substrate, the conductive layer connected to the source region, drain region, and gate electrode, respectively, is sputtered using an insoluble gas. In the method for manufacturing a MOS transistor, the sputtering process is performed using a mixed gas of argon gas and hydrogen gas containing 5 to 50 mol% hydrogen gas in argon gas as an inert gas. A manufacturing method for MOS transistors characterized by