JP2572291B2 - Method of manufacturing semi-insulating InP single crystal substrate - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semi-insulating InP single crystal used for an electronic device, in particular, an OEIC, a HEMT, an ion-implanted FET, and a method for producing the same.

[Prior Art] In order to make a compound semiconductor material semi-insulating, a method of adding Fe, Co, Cr or the like as a deep acceptor to a material containing Si or S as an n-type impurity is industrially used. ing. This semi-insulating property is due to a mechanism of compensating a shallow donor with a deep acceptor. Therefore, if the amount of the element that becomes a deep acceptor is not larger than the amount of the donor contained in the crystal material,
It is said that it cannot be made semi-insulating.

However, when semi-insulating properties are obtained by doping with Fe, Co, Cr, or the like, it is desirable that these amounts be as small as possible. Because Fe, Co, Cr, etc. act as deep acceptors, they lower the activation rate in ion-implanted electronic devices (FETs, etc.) or operate at high frequencies (OEICs, HEMTs, etc.) In these cases, these elements diffuse into the epitaxial film and act as traps to hinder high frequency and high speed.

Further, these elements are liable to segregate, and the concentration of Fe or the like is different between the upper and lower portions of the crystal, so that the activation rate is not uniform and the yield is low.

Conventionally, Fe-doped InP has been mainly used as semi-insulating InP used for electronic devices.

However, when the Fe content is less than 0.2 ppmw, the resistivity becomes lower than 10 ⁶ Ω · cm, and the semi-insulating property is reduced. In order to make this a semi-insulating crystal, the doping amount of Fe had to be more than a certain amount (0.2 ppmw).

In general, it has been considered that the resistivity decreases when the content concentration of Fe, Cr, or the like in a compound semiconductor decreases, because impurities serving as donors are present as residual impurities in the crystal to that level. However, the present inventors believe that the mechanism of semi-insulating InP single crystal involves not only compensation by a donor and a deep acceptor, but also an electrically active point defect. By controlling the concentration of point defects by heat-treating the crystal, it has been found that the compound semiconductor can be made semi-insulating even at a much lower impurity concentration of the deep acceptor than in the prior art.

Accordingly, the present inventors have previously developed a compound semiconductor manufacturing technique in which the total concentration of any one or more of Fe, Co, and Cr is 0.2 ppmw or less and the resistivity is 10 ⁷ Ωcm or more. It was proposed (Japanese Patent Application No. 63-220632).

That is, a compound semiconductor material containing 0.2 ppmw or less of Fe, Co or Cr is vacuum-sealed in a quartz ampoule, and a constituent element of the compound semiconductor material or a separate compound semiconductor material containing the constituent element is contained in the quartz ampule. The quartz ampoule is placed at a pressure higher than the dissociation pressure of the compound semiconductor material made of the thin plate in the quartz ampule.
Heating at 400-640 ° C.

On the other hand, D. Hofmann et al., "Appl. Phys. A 48, P315-319 (198
9)), the non-doped InP single crystal wafer having a carrier concentration of 3.5 × 10 ¹⁵ cm ⁻³ was subjected to a phosphorous pressure of 5 bar (about 5 kg / cm ² ).
It is reported that an InP wafer having a resistivity of 2 × 10 ⁷ Ω · cm was obtained by performing a heat treatment at a concentration of 900 ° C. for 80 hours. This is considered to be due to the fact that electrically active point defects are involved as in the above-mentioned invention.

[Problems to be Solved by the Invention] However, according to our subsequent studies, in the above-mentioned prior invention, the non-doped, that is, the concentration of one or more impurities of Fe, Co or Cr is 0.05 ppmw or less. It was found that the heat treatment of the single crystal did not make it semi-insulating.

According to the method of D. Hofmann, the carrier concentration is 3.5
When a non-doped InP single crystal of × 10 ¹⁵ cm ^-3 was heat-treated, the resistivity was 10 ⁶ Ωcm or more, but the mobility was 4500 cm ² / Vs or more, but 3000 cm ² / V・ It drops to s or less. Also, when the carrier concentration of the InP single crystal was high, the resistivity was 10 ¹ to 10 ⁵ Ω · cm, and it was not easy to achieve a resistivity of 10 ⁷ Ω · cm or more.

[Means for Solving the Problems] The present inventors have comprehensively examined these results, and have found that a semi-insulating InP single crystal having sufficient mobility unless the phosphorus vapor pressure with respect to the heat treatment temperature exceeds a certain limit value. Came to the conclusion that it could not be obtained.

The present invention has been made based on the above findings, and is manufactured from a raw material polycrystalline InP having a carrier concentration of 3 × 10 ¹⁵ cm ⁻³ or less, without intentionally adding impurities, and presenting Fe present as a residual impurity. It is proposed to heat-treat an InP single-crystal thin plate having a total concentration of at least one of Co, Cr and at least 0.05 ppmw in a phosphorus vapor pressure atmosphere exceeding 6 kg / cm ² .

[Examples] (First Example) Fe, Co, and Cr pulled up from liquid polycrystalline InP having a carrier concentration of 1 × 10 ¹⁵ cm ^{−3 by} the liquid sealing Czochralski method are all lower than the analysis lower limit (0.05 ppmw). A 0.5 mm thick as-cut non-doped InP wafer (thin plate) and red phosphorus are set in a quartz ampoule, the inside of the quartz ampule is evacuated to 1 × 10 ^-6 Torr, and then the quartz ampoule is evacuated by an oxyhydrogen burner. The opening was sealed. At this time, the amount of red phosphorus is determined as follows: the phosphorus vapor pressure in the quartz ampoule is 15 kg / cm ² (absolute pressure) at the heat treatment temperature.
It was adjusted to be. Next, this quartz ampule was placed in a horizontal heating furnace, heated and maintained at a heat treatment temperature of 900 ° C. for 20 hours, and then cooled.

The horizontal heating furnace is a closed type that can be pressurized to a pressure of 100 kg / cm ² (gauge pressure). At the time of heating and cooling, argon gas with a pressure corresponding to the phosphorus vapor pressure for that temperature is used in the heating furnace. To prevent the destruction of the quartz ampule while maintaining the balance between the pressure inside and outside the quartz ampule.

(Example 2) The amount of red phosphorus was adjusted so that the phosphorus vapor pressure in the quartz ampoule was 7.5 kg / cm ² (absolute pressure) at the heat treatment temperature (900 ° C). Other conditions were the same as in the first example.

For the wafer obtained in each of the above examples, the surface of the wafer was removed by 50 μm lapping in order to examine the electrical characteristics, and then the resistivity and mobility were measured by the Van der Pauw method.
Measured at 300K.

 Table 1 shows the results.

The above table shows the results of Hofmann, namely, heat treatment temperature of 900 ° C,
As a comparative example, the resistivity and mobility of a non-doped InP single crystal subjected to a heat treatment at a phosphorus vapor pressure of 5 kg / cm ² (absolute pressure) for 80 hours are shown.

FIG. 1 shows the measured values in the above table as a graph.

According to the figure, by using a non-doped InP single crystal and increasing the phosphorus vapor pressure during heat treatment to a value exceeding 6 kg / cm ² (absolute pressure), the resistivity is 1 × 10 ⁶ or more and the mobility is 3000 cm ^2.
It can be seen that a semi-insulating InP single crystal exceeding / V · s can be obtained.

Furthermore, the high mobility semi-insulating In obtained in the above example
In order to confirm that the resistivity does not decrease when a device is created using P single crystal, a 1500 Å SiNx film was
After performing cap annealing at 0 ° C. for 15 minutes, the resistivity was measured. The results are shown in FIGS. 2 and 3. In the figure, the closed circles indicate the values before cap annealing,
The marks indicate the values after cap annealing. FIG. 2 shows that the resistivity hardly decreases before and after annealing regardless of the phosphorus pressure. In addition, although the mobility is slightly lowered as shown in FIG. 3, it is 3200 cm ² / V · s or more, and it can be seen that the mobility is sufficiently within a practical range.

(Third Embodiment) A 0.5 mm thick as-cut InP wafer cut out from an InP single crystal pulled up by a liquid-sealed Czochralski method from a raw material polycrystalline InP having a carrier concentration of 5 × 10 ¹⁴ cm ⁻³ was first used. The heat treatment was carried out under the same conditions as in the above example. That is, the above In
Place the P wafer in a quartz ampoule with red phosphorus,
After evacuating each quartz ampule to 1 × 10 ^-6 Torr,
The quartz ampule was sealed with a burner. At this time, the amount of red phosphorus depends on the phosphorus vapor pressure in the quartz ampoule at the heat treatment temperature.
The pressure was adjusted to be 0 kg / cm ² , 7.5 kg / cm ² , and 15.0 kg / cm ² (absolute pressure). Next, these quartz ampoules were placed in a horizontal heating furnace, heated and held at a heat treatment temperature of 900 ° C. for 20 hours, and then cooled.

After removing the surface of the above wafer by 50 μm lapping, the resistivity and the mobility were set to 300K by Van der Pauw method.
Was measured.

 The result is shown in FIG.

In the same figure, the mark ● represents the resistivity of the InP wafer to which the present embodiment was applied, and the mark △ represents the non-doped material pulled up from the raw material polycrystalline InP having a carrier concentration of 5 × 10 ¹⁵ cm ^{-3 by} the liquid sealing Czochralski method. This shows the resistivity when the InP single crystal was heat-treated under the same conditions as above.

As can be seen from FIG. 4, in the case of an InP wafer using a raw material polycrystal having a carrier concentration of 5 × 10 ¹⁵ cm ⁻³ , even if a phosphorus pressure of 7.5 kg / cm ² (absolute value) or more is applied and heat treatment is performed, the resistance cannot be increased. On the other hand, In using a raw material polycrystal having a carrier concentration of 5 × 10 ¹⁴ cm ⁻³
It can be seen that the resistivity of the P wafer can be increased by applying a phosphorus pressure exceeding 6 kg / cm ² (absolute pressure) and performing heat treatment. In addition, the mobilities were all 4000 cm ² / V · s or more.

FIGS. 5 and 6 show that the non-doped I.P.
The resistivity and the mobility when the same heat treatment is performed by applying a phosphorus pressure of 7.5 kg / cm ² (absolute pressure) using an nP single crystal are shown.

From FIGS. 5 and 6, it can be seen that the resistivity does not exceed 10 ⁶ Ωcm and the mobility does not exceed 300 cm ² / V · s unless the carrier concentration of the raw material polycrystalline InP is 3 × 10 ¹⁵ cm ⁻³ or less. In FIG. 6, the reason why the mobility is high when the carrier concentration is 5 × 10 ¹⁵ cm ⁻³ or more is that the material does not become semi-insulating.

Note that, in each of the above embodiments, the case where the heat treatment temperature of the InP single crystal was set to 900 ° C. was described. However, without intentionally adding impurities, there is a residual impurity.
The sum of the concentrations of at least one of Fe, Co and Cr is
By using a non-doped InP single crystal thin plate of 0.05 ppmw or less, even under other temperature conditions, by heat treatment under a phosphorus vapor pressure, the resistivity at 300 K is 10 ⁶ Ωcm or more, and the mobility is 3000 cm ²
A semi-insulating InP single crystal exceeding / V · s can be obtained.

[Effects of the Invention] As described above, in the InP single crystal of the present invention, the concentration of at least one of Fe, Co, and Cr present as residual impurities without intentionally adding impurities. Is high, and has high mobility, despite being less than 0.05 ppmw, so that it is particularly suitable as a semi-insulating compound semiconductor substrate for electronic devices.

In addition, an InP single crystal in which the total concentration of at least one of Fe, Co, and Cr present as residual impurities is 0.05 ppmw or less without intentionally adding impurities is OEIC or H
When used as an EMT substrate, since the Fe concentration is low, there is no diffusion of Fe in the epitaxial film, and high frequency and high speed can be achieved. In addition, for ion-implanted FETs, the activation rate of implanted ions is high due to the low Fe concentration, and the segregation of the Fe concentration above and below the crystal is negligible, and the activation rate is uniform, thus improving the yield. .

Further, according to the method for producing an InP single crystal of the present invention, a non-doped InP single crystal thin plate is vacuum-enclosed in a quartz ampoule and heat-treated under predetermined conditions to obtain a high resistivity and high mobility. This has the effect that a semi-insulating InP single crystal having a high density can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the phosphorus vapor pressure and the mobility of a non-doped InP single crystal wafer during heat treatment, and FIG. 2 is a graph showing the change in resistivity when the above-mentioned heat-treated InP single crystal wafer is cap-annealed. FIG. 3 is a graph showing a change in mobility when the InP single crystal wafer after the above heat treatment is subjected to cap annealing, and FIG. 4 is a graph showing a change in mobility of an InP single crystal wafer produced from raw material polycrystalline InP having different carrier concentrations. FIG. 5 is a graph showing a relationship between phosphorus vapor pressure and resistivity, and FIG. 5 is a graph showing carrier concentration of raw material polycrystalline InP and InP after heat treatment.
FIG. 6 is a graph showing the relationship between the resistivity of a single-crystal wafer and FIG.
4 is a graph showing a relationship with the mobility of a single crystal wafer.

Claims (1)

(57) [Claims] 1. One of Fe, Co or Cr, which is produced from a raw material polycrystalline InP having a carrier concentration of 3 × 10 ¹⁵ cm ^-3 or less and which is present as a residual impurity without intentionally adding impurities. The total of the above concentrations is 0.05 ppmw or less
A method for producing a semi-insulating InP single crystal substrate, comprising heat-treating an InP single crystal thin plate in a phosphorus vapor pressure atmosphere exceeding 6 kg / cm ² .