JPH0750273A - Short time annealing equipment - Google Patents

Abstract

PURPOSE:To provide a short time annealing equipment wherein the uniformity and the controllability of wafer temperature can be obtained while the wafer is maintained in a necessary gas pressure atmosphere. CONSTITUTION:In an equipment wherein an almost disk-shaped semiconductor substrate 1 is put on a retainer 2 which is heated in a short time by a heating means 6, short time anneal of the semiconductor substrate 1 is performed mainly by the heat conduction from the retainer 2, a ring-shaped cover 3 which covers the outer periphery of the semiconductor substrate 1 and has a hole whose diameter is 55-80% of the diameter of the semiconductor substrate 1 in the central part is put on the retainer 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a short-time annealing apparatus for improving the characteristics of semiconductor substrates such as Si and GaAs.

[0002]

2. Description of the Related Art A short-time annealing method is capable of obtaining a high concentration activation of carriers and a steep concentration profile of a semiconductor substrate of Si or GaAs (hereinafter referred to as a wafer), and thus has no thermal influence on the wafer. Since it is scarce, it is widely used in the development stage.

However, in the short-time annealing method, the wafer holder (hereinafter referred to as a susceptor), the heating furnace main body, and the atmosphere gas are not in thermal equilibrium, so that the temperature uniformity of the wafer is obtained. Is difficult and accurate temperature control is also difficult. For this reason, there is a serious problem in practical use that crystal defects such as slip lines are likely to occur due to temperature non-uniformity in the wafer when annealing a large diameter wafer with poor reproducibility.

S. J. Pearton et al. Reported that in the short-time annealing of GaAs wafers, the indirect heat conduction from the carbon-graphite susceptor was used, and the temperature uniformity was improved by following the lid to prevent the occurrence of slip lines ( J. Appl. Phy
s. Vol 66 (1989) pp 663).
Further, according to the report, a slip line occurs when there is a temperature difference of 6 ° C. to 7 ° C. or more between the central part of the wafer being annealed and the outer peripheral part.

[0005]

However, it is difficult to obtain sufficient temperature uniformity even by the above method.
Also, compounds containing constituent elements with high vapor pressure, such as GaA
When the wafer of s is annealed, As easily evaporates.
It is essential to control the As partial pressure in the atmosphere in order to suppress the dissociation of As.

For example, if the Si which is an n-type dopant is 5 ×
GaAs wafers implanted at 10 ¹³ cm ^-2 at 900 ° C 12
Fig. 3 shows the relationship between the sheet carrier concentration in the case of annealing for a short time of 0 second and the partial pressure of AsH ₃ as the atmosphere during annealing.
Is obtained as. From this result, AsH ₃ partial pressure is 3T
It is shown that below orr, the carrier concentration decreases due to the dissociation of As in the wafer. Therefore, in this case, a susceptor in which the lid completely covers the wafer is not preferable.

An object of the present invention is to provide a short-time annealing apparatus capable of obtaining uniformity and controllability of wafer temperature while keeping the wafer in a necessary gas pressure atmosphere.

[0008]

The short-time annealing apparatus of the present invention has a substantially disk-shaped wafer 1 as shown in FIGS. 1 and 2, for example.
Is placed on the susceptor 2, the susceptor 2 is heated for a short time by the heating means 6, and the wafer 1 is annealed in a short time mainly by heat transfer from the susceptor 2. This is a short-time annealing apparatus in which a ring-shaped cover 3 having a hole having a diameter of 55% to 80% of the diameter of the wafer 1 is placed on the susceptor 2.

[0009]

The wafer 1 on the susceptor 2 is heated by the heat transfer from the susceptor 2 which is heated first.
A temperature distribution (the temperature is higher toward the lower surface) occurs in the thickness direction of the wafer 1, and the wafer 1 warps upward due to thermal expansion. As a result, since the peripheral portion of the wafer 1 is separated from the susceptor 2, heat transfer is reduced, and the temperature of the outer peripheral portion of the wafer 2 becomes lower than that of the central portion. In order to prevent the temperature distribution generated in this manner, it is particularly effective to use the ring-shaped cover 3 that covers only the outer peripheral portion of the wafer 1. The use of the cover that covers the central portion of the wafer 1 also raises the temperature of the central portion and rather impairs the effect of temperature uniformity. According to the experiments conducted by the present inventor, 55% to 80% of the wafer diameter
It is effective to uniformize the temperature to cover only the outer peripheral portion of the wafer 1 with the ring-shaped cover 3 having a hole with a diameter in the range of%.

Further, the use of the ring-shaped cover 3 having such a large opening hole causes almost no obstacle in maintaining the required atmospheric gas pressure. Further, since the surface temperature of the central portion of the wafer during annealing can be monitored by the radiation thermometer through the hole in the cover, the temperature controllability during annealing is improved.

[0011]

Embodiments of the short-time annealing apparatus of the present invention will be described below with reference to the drawings. FIG. 1 is a conceptual diagram showing the configuration of a short-time annealing apparatus according to an embodiment of the present invention. Further, FIG. 2 is an enlarged view of the main part thereof.

In FIG. 1, 1 is a wafer to be annealed,
Reference numeral 2 denotes a circular susceptor on which the wafer 1 is placed. A portion on which the wafer 1 is mounted has a thickness d and a stepped portion 2a and a ring-shaped cover 3 for stably placing the wafer 1 are provided on the outer peripheral portion thereof. A dam having a step portion 2b for stably placing the wafer 1 away from the upper surface of the wafer 1 is provided.

Here, the height of the step portion 2a may be such that the warped wafer during annealing does not come into contact with it. The susceptor 2 is horizontally supported in a transparent fused quartz tube 4 via a transparent fused quartz plate 5.

The inside of the fused quartz tube 4 is filled with N 2 as an atmosphere.
A mixed gas of ₂ , H _2, and AsH ₃ is flown. A plurality of heating light bulbs 6, for example, halogen light bulbs (for example, reference, physics dictionary, Baifukan, published in 1984) are provided below the fused silica tube 4. Reference numerals 7, 8, 9, and 10 denote heat shield plates made of a metal plate plated with gold.

In the short-time annealing device configured as described above, by turning on the halogen bulb 6,
Radiant light from the halogen bulb 6 is absorbed by the susceptor 2 through the fused quartz tube 4 and the fused quartz plate 5, and the susceptor 2 rapidly rises in temperature. Then, the wafer 1 is heated by heat transfer from the susceptor 2. Here, the temperature of the susceptor 2 is measured by the thermocouple 12, and the upper surface temperature of the central portion of the wafer 1 is a hole 7 which is opened in communication with the heat shield plates 7 and 8.
It is monitored by a radiation thermometer 13 through a, 8a and the fused silica tube 4.

The short-time annealing of the wafers in Examples and Comparative Examples described later was performed under the following conditions except for the inner diameter of the cover.

Wafer: A GaAs substrate on which Si is ion-implanted at 5 × 10 ¹³ / cm ^-2 , diameter: 76 mm, thickness: 0.6 m
m.

The susceptor is made of carbon graphite and has an outer diameter of 100 mm, and the thickness of the portion on which the wafer is placed (d) 2
mm.

Cover: A material made of carbon graphite having an outer diameter of 86 mm and a thickness of 0.5 mm, and a hole having a predetermined diameter in the examples and comparative examples is formed in the center of the disk.

Atmosphere: A mixed gas of N ₂ , H ₂ and AsH _{3 and} a partial pressure of AsH ₃ was set to 5 Torr.

Heating: heating with a halogen bulb, heating rate at 50 ° C./sec, holding at a preset temperature of the susceptor of 900 ° C. for 120 sec, followed by natural cooling.

As an evaluation means for the annealing result,
The following method was used. A) Observation of defects such as slip lines by X-ray topography b) Observation of defect density by etch pits (KOH solution is used as etching liquid) c) Sheet carrier concentration measurement by hole measurement (Van
der Pauw method); 5 mm × 5 mm was cut out from the central portion and the peripheral portion of the annealed wafer and measured.

Example 1 As a cover, a ring-shaped cover in which a hole of 80% of the diameter of the wafer was formed in the center of a carbon graphite disk was used, and annealing was performed for a short time under the above conditions. As a result, the occurrence of slip lines was not recognized on the X-ray topography. No increase in etch pits was observed as compared with the wafer before annealing. The carrier concentration by hole measurement was 3.06 × 10 ¹³ cm ^-2 in the central part of the wafer and 2.95 × 10 ¹³ cm ^-2 in the outer peripheral part of the wafer, and there was almost no difference between the central part and the outer peripheral part of the wafer. .

Example 2 As a cover, a ring-shaped cover having a hole of 55% of the diameter of the wafer formed in the center of a carbon-graphite disk was used and annealed in the same manner as in Example 1 for a short time. The result was the same as that of Example 1, and no slip line was observed.

Comparative Example 1 Short-time annealing was performed in the same manner as in Example 1 except that nothing was used as a cover. As a result, the annealed wafer was found by the X-ray topography to show the occurrence of slip lines with a significant density. Also, the etch pit density was increased compared to the wafer before annealing.

The carrier concentration by hole measurement is 3.05 × 10 ¹³ cm ^{-2 in} the central portion of the wafer and 2.6 × 10 ¹³ cm ^-2 in the outer peripheral portion of the wafer. The carrier concentration in the outer peripheral portion of the wafer is higher than that in the central portion. Is quite small. From these results, it is shown that the heating temperature in the outer peripheral portion of the wafer is much lower than that in the central portion of the wafer in the short-time annealing without the cover.

Comparative Example 2 The same short-time annealing as in Example 1 was performed using a ring-shaped cover having a hole of 85% of the wafer diameter formed in the center of a carbon graphite disk as a cover.

Comparative Example 3 As a cover, a ring-shaped cover having a hole of 50% of the diameter of the wafer in the center of a carbon / graphite disk was used, and short-time annealing similar to that in Example 1 was performed.

Comparative Example 4 As a cover, a ring-shaped cover having a hole of 30% of the diameter of the wafer formed in the center of a carbon / graphite disk was used and the short-time annealing similar to that in Example 1 was performed.

Comparative Example 5 A short-time annealing similar to that in Example 1 was performed using a carbon-graphite disk having no holes as a cover.

In each of Comparative Examples 1 to 5, the occurrence of slip lines and the increase of etch pits were recognized. The density of occurrence of slip lines was determined from the photographs of the X-ray topography, and was in the following order for Comparative Examples 1 to 5. Comparative Example 5> Comparative Example 1> Comparative Example 4> Comparative Example 3≈Comparative Example 2 The density of etch pits was also in the above order.

In Comparative Example 5, the surface of the annealed wafer was clouded and rough, and it is considered that As was dissociated. It should be noted that the occurrence of the slip line was most remarkable in Comparative Example 5 using the cover having no hole. J. It does not match the report of Pearon et al., But the reason is unknown.

[0033]

According to the present invention, the wafer temperature can be made uniform while maintaining the wafer in a necessary gas pressure atmosphere, and as a result, short-time annealing can be performed while preventing the occurrence of defects such as slip lines. Further, since the temperature of the surface of the central portion of the wafer can be monitored by the radiation thermometer, the temperature controllability in annealing is improved.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a configuration of a short-time annealing apparatus according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of the present invention.

FIG. 3 is a diagram showing a measurement result of a short-time annealing atmosphere (AsH ₃ partial pressure) and a sheet carrier concentration of a GaAs wafer into which Si ions are implanted.

[Explanation of symbols]

 1 Wafer 2 Susceptor 3 Ring Cover 4 Fused Quartz Tube 6 Halogen Light Bulb 12 Thermocouple 13 Radiation Thermometer

Claims (1)

[Claims] 1. An apparatus for placing a substantially disk-shaped semiconductor substrate on a holder, heating the holder for a short time by a heating means, and for annealing the semiconductor substrate for a short time mainly by heat transfer from the holder. A short-time annealing apparatus, characterized in that a ring-shaped cover having a hole having a diameter of 55% to 80% of the diameter of the semiconductor substrate in the central portion, which covers the outer peripheral portion of the semiconductor substrate, is placed on a holder.