JP3062975B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor manufacturing technique and, more particularly, to a method for selecting a semiconductor substrate when manufacturing a semiconductor device, for example, for use in manufacturing a GaAs MESFET (gallium arsenide metal semiconductor field effect transistor). To a suitable technology.

[0002]

2. Description of the Related Art The characteristics of a semiconductor device such as a MESFET depend on the characteristics of a semiconductor substrate to be used. Therefore, in order to manufacture GaAs MESFETs having stable characteristics with good yield, it is important to select a GaAs wafer to be used. Conventionally, as a method of selecting a wafer to be used for manufacturing a GaAs MESFET (hereinafter simply referred to as an FET), an active layer and a Schottky electrode are formed on the surface of the wafer,
A method of measuring the pinch-off voltage of the ET and using a wafer falling within a predetermined range has been considered. But,
In this method, various steps such as ion implantation, activation annealing, photolithography, electrode material deposition, and patterning must be performed before the pinch-off voltage can be measured. Control is necessary. On the other hand, the characteristics such as the pinch-off voltage of the GaAs MESFET largely depend on the resistivity of the wafer. Therefore, a simple wafer selection method has been considered in which a carbon concentration closely related to the resistivity of a wafer is measured and a carbon concentration within a predetermined range is used.

[0003]

However, in the above-mentioned method of measuring the carbon concentration of a wafer and selecting a wafer to be used, the measurement accuracy can be reduced to ± 0. 0 by using a practical method of measuring the carbon concentration. Since it is as large as 3 × 10 ¹⁵ cm ⁻³ , the variation in the carbon concentration of the selected wafer is relatively large, and a significant improvement in yield cannot be expected. on the other hand,
In the selection method of measuring the pinch-off voltage and using a voltage falling within a predetermined range, various steps are required until a measurement result is obtained, so that a variation of about 10 mV cannot be avoided. There is a problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a GaAs wafer suitable for manufacturing a GaAs MESFET having stable characteristics with a high yield by a simple method. The purpose is to provide selectable technologies.

[0005]

The present inventors have noticed that the measurement accuracy of the sheet resistance of the active layer of the wafer is higher than the measurement accuracy of the carbon concentration, and ion-implanted the surface to form the active layer. The sheet resistance of the formed GaAs wafer was measured, and the carbon concentration of the GaAs wafer was measured by a highly accurate measuring method, and the measured values were compared. As a result, they found that there is a proportional relationship between the sheet resistance of the GaAs wafer and the carbon concentration, as shown in FIG. Further, if the ion implantation conditions are the same, there is a certain relationship between the pinch-off voltage Vp of the GaAs MESFET and the carbon concentration of the GaAs wafer as shown in FIG. However, FIG.
Has a threshold voltage V instead of the pinch-off voltage Vp.
Using th (= 0.7-Vp), the relationship is shown on the vertical axis and the carbon concentration on the horizontal axis. The ion implantation conditions of the FET shown in FIG. 1, the implantation energy is 70 keV, implantation dose is 1.5 × 10 ¹² cm- ^2.

The present invention has been made based on the above-described findings, and is based on the finding that the sheet resistance and carbon concentration of a semiconductor substrate (wafer) on which an active layer is formed under the same ion implantation conditions prior to the manufacture of a semiconductor device. The relationship and the relationship between the pinch-off voltage of an FET (field effect transistor) formed on a semiconductor substrate having an active layer and the carbon concentration of the semiconductor substrate are determined, and a predetermined sheet resistance determined from these relationships is determined. It is proposed to use a semiconductor substrate having a value as a substrate for manufacturing a field effect transistor. In the above case, preferably, a plurality of ion implantation conditions are set, and the relationship between the pinch-off voltage of the FET and the carbon concentration of the semiconductor substrate is checked for each of the ion implantation conditions.

[0007]

According to the above means, the carbon concentration corresponding to the target pinch-off voltage is obtained from the relationship between the previously obtained pinch-off voltage and the carbon concentration of the wafer, and the sheet resistance and the carbon concentration obtained in advance are obtained. By determining the sheet resistance corresponding to the above carbon concentration from the relationship with the above, and using a semiconductor substrate having such a sheet resistance as a substrate for manufacturing FETs, it is possible to manufacture FETs having predetermined characteristics with high yield. it can. In addition, when the target pinch-off voltage or the ion implantation conditions of the active layer are not determined, the pinch-off voltage of the FET obtained by once preparing a semiconductor substrate having various sheet resistance values and manufacturing the FET is determined. By measuring and identifying the semiconductor substrate used for the FET having the desired pinch-off voltage, a semiconductor substrate having the same sheet resistance value as the substrate is used as a substrate for manufacturing the FET, so that the FET having predetermined characteristics is obtained. Can be manufactured with good yield.

[0008]

The EXAMPLES Liquid Encapsulated Czochralski method, foster ten GaAs single crystal having different carbon concentrations, each lots A, B, C, and ...... J cut into wafers, any from among them The wafers were taken out one by one and MESFETs were formed on those wafers under the same process conditions. The active layer was formed by implanting Si + as an ion species at an energy of 70 keV so as to have an implantation amount of 1.5 × 10 ¹² cm ⁻² and performing a heat treatment at a temperature of 830 ° C. for 10 minutes. The gate electrode material is Ti (20n) from the substrate side.
m) / Pt (100 nm) / Au (300 nm)
The gate length was 1 μm, the gate width was 5 μm, and the distance between the source and the drain was 4 μm. The ohmic electrodes of the source and drain are Au-Ge (100 nm) / N from the substrate side.
i (20 nm) / Au (700 nm).

Next, the MESFET fabricated under the above conditions
Was measured for the threshold voltage Vth. FIG. 3 shows the measurement results. In the figure, the squares indicate the threshold voltage Vth of the FET measured for each wafer (rod) and the average value is plotted. In FIG. 3, the standard deviation value σ is shown as a range of the variation of the threshold voltage. From the figure, the GaAs substrate was randomly selected and the MES
It can be seen that when an FET is formed, the threshold voltage Vth is dispersed from an average value of 0.52 V to 0.73 V. Therefore, the target threshold voltage is set to 0.62
Assuming 5 ± 0.025V, the yield of the FET in this case is about 31.6%. FIG. 4 shows the threshold voltage Vth (=
0.7-Vp) and the carbon concentration of the used GaAs substrate.

Next, a case where the method of the present invention is applied will be described. First, when the target pinch-off voltage Vp or threshold voltage Vth of the GaAs MESFET is determined, the carbon concentration of the wafer to be used is determined using FIG. For example, if the target threshold voltage Vth is 0.62
If it is 5 ± 0.025V, it is understood from FIG. 4 that the carbon concentration of the wafer to be used is 1.8 × 10 ¹⁵ cm ⁻³ and 2.71 ×
It can be seen that it must be 10 ¹⁵ cm ⁻³ or less.

Next, FIG. 2 shows that the carbon concentration is 1.8 × 10
The sheet resistance of the wafer in the range of ¹⁵ cm ⁻³ to 2.71 × 10 ¹⁵ cm ⁻³ is determined. In this case, the sheet resistance of the usable wafer is 2108Ω / □ to 2158Ω /
It turns out that it is □. GaAs single crystal 10 present the B <br/> Tsu preparative A, B, C, among ...... J, the sheet resistance is 210
When a sample having a resistance of 8Ω / □ to 2158Ω / □ was searched for, it was found that four of C, F, H and I corresponded. Therefore, when a MESFET is manufactured using a wafer cut from these rods, the FES having a desired threshold voltage Vth (0.625 ± 0.025 V) is obtained.
The ET yield was 58 . It turns out that it becomes 8%. Thus, by applying the method of the present invention, the yield of FET is reduced from 31.6% to 58 . It turns out that it improves to 8%.

[0012]

As described above, the present invention relates to the relationship between the sheet resistance and the carbon concentration of a semiconductor substrate (wafer) having an active layer formed under the same ion implantation conditions prior to the manufacture of a semiconductor device, and the active layer. The relationship between the pinch-off voltage of the FET formed on the semiconductor substrate having the above and the carbon concentration of the semiconductor substrate is examined, and the semiconductor substrate having a predetermined sheet resistance value determined from these relationships is used as the substrate for manufacturing the FET. Therefore, the carbon concentration corresponding to the target pinch-off voltage is obtained from the relationship between the previously obtained pinch-off voltage and the carbon concentration of the wafer, and the relationship between the previously obtained sheet resistance and the carbon concentration is obtained. To determine a sheet resistance corresponding to the above carbon concentration, and to use a semiconductor substrate having such a sheet resistance value as a substrate for FET production. Ri, there is an effect that can be produced with high yield FET having a predetermined property.

[Brief description of the drawings]

FIG. 1 is a correlation diagram showing a relationship between a sheet resistance and a carbon concentration of a GaAs wafer.

FIG. 2 is a correlation diagram showing a relationship between a pinch-off voltage Vp of a GaAs MESFET and a carbon concentration of a GaAs wafer.

FIG. 3 is a diagram showing a measurement result of a threshold voltage Vth of a MESFET created under the conditions of the example.

FIG. 4 is a correlation diagram showing a relationship between a measured value of a threshold voltage Vth of a MESFET prepared under the conditions of the example and a measured value of a carbon concentration of a substrate.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/337-21/338 H01L 21/02 H01L 29/775-29/778 H01L 29/80-29 / 812

Claims (3)

(57) [Claims] 1. A semiconductor device having an active layer formed under the same ion implantation conditions prior to the manufacture of a semiconductor device, the relationship between the sheet resistance and the carbon concentration, and a field effect transistor formed on the semiconductor substrate having the active layer. The relationship between the pinch-off voltage or the threshold voltage of the semiconductor substrate and the carbon concentration of the semiconductor substrate is examined , and the target pinch-off voltage or the threshold voltage is first determined.
And determine the desired pinch-off voltage or threshold
If the pinch-off voltage is higher than the carbon concentration corresponding to
Or the sheet resistance corresponding to the carbon concentration is determined from the relationship between the threshold voltage and the carbon concentration.
Determined from the relationship between the resistance and the carbon concentration, a method of manufacturing a semiconductor device, which comprises using a semiconductor substrate having the predetermined sheet resistance value as a field effect transistor fabrication substrate. 2. The semiconductor substrate is a GaAs substrate.
The method of manufacturing a semiconductor device according to claim 1, wherein:
Law. 3. The semiconductor device according to claim 1, wherein the semiconductor device is a GaAsMESFE.
3. The method according to claim 1, wherein
Manufacturing method of the semiconductor device described above.