JPH0645270A - Method for heat-treating semiconductor substrate - Google Patents

Abstract

PURPOSE:To reduce a lattice defect of the part where ions are implanted by suitably heat treating after ion implantion. CONSTITUTION:After ions of As, P, B, BF2, etc., are implanted in a semiconductor substrate, a first heat treatment is conducted at 600 to 800 deg.C, and then a second heat treatment is executed at 800 less than 1000 deg.C. It is desirable to execute the second treatment for 500sec or longer. The first treatment is conducted by lamping, and the second treatment can be executed for 500sec or longer. Further, the first and second treatments may be conducted in a lamp- annealing furnace.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heat treating a semiconductor substrate, and more particularly to a semiconductor device such as an integrated circuit, particularly a lattice of a semiconductor device such as As, P, B and BF ₂ where ions are implanted. The present invention relates to a heat treatment method for reducing defects.

[0002]

2. Description of the Related Art Ion implantation of impurities is widely used as a method of forming an element on a semiconductor substrate of an LSI because it is easy to control the shape of the implantation layer.
However, in order to implant ions to a required depth, it is necessary to apply energy according to the implanted ion species, substrate crystal plane, ion implantation direction, and substrate surface condition. The implantation depth and dose depend on the type of device, but 10-500 keV
Of high implantation energy, which inevitably results in lattice defects in the substrate. In particular, in the portion where a high concentration of ions is implanted, such as the source and drain portions, the implantation layer no longer has a crystal structure, and the arrangement of individual Si atoms is irregular and amorphous. A layer containing lattice defects does not exhibit the required semiconductor characteristics even if it has such an amorphous or crystalline structure, and therefore heat treatment is performed after the ion implantation to recover the crystallinity. These techniques are disclosed in JP-A-6
It is disclosed in JP-A-3-181418, JP-A-2-56927 and JP-A-3-278525.
Further, a technique of heating a silicon substrate to 900 ° C. or higher at the time of ion implantation is also disclosed in JP-A-61-22623.

[0003]

Techniques for eliminating the lattice defects formed by ion implantation by heat treatment are widely known, and certain effects have been obtained. However, with the miniaturization of LSIs, a higher degree of crystal perfection is required, whereas according to the heat treatment that has been conventionally performed, lattice defects still remain in the silicon substrate, which may deteriorate semiconductor characteristics. It was revealed by the investigation of the present inventors that this is done. On the other hand, it is obvious that the higher the heat treatment temperature is, the more effective it is to eliminate the lattice defects. However, with the miniaturization of the device, the ion implantation region should be made shallower, and the shape of the implantation layer and the impurity concentration should be precise to prevent hot carriers. Therefore, high temperature heat treatment is disadvantageous because it causes diffusion of impurities. For this reason, the appearance of heat treatment for eliminating lattice defects at a relatively low temperature has been awaited. The present invention solves the above-mentioned problems, and an object of the present invention is to provide a heat treatment method for a semiconductor substrate, which appropriately performs heat treatment after ion implantation and significantly reduces lattice defects in the ion implanted portion.

[0004]

A feature of the present invention is to reduce the lattice defects formed by ion implantation by performing heat treatment at a relatively low temperature after heat treatment at a low temperature. As a result of extensively investigating the state of residual lattice defects by changing the heat treatment conditions after ion implantation, the density of residual lattice defects decreases as the heat treatment temperature increases, but it is difficult to completely eliminate them, and it is difficult to completely eliminate them. It has been found that the existence of the lattice defects can be controlled at a deep position that does not affect the electrical characteristics by the heat treatment method of the present invention. Therefore, the present invention has adopted the following method. That is, after implanting ions into the semiconductor substrate, the first heat treatment is performed at a temperature higher than 600 ° C. and lower than 800 ° C.
A method for heat treating a semiconductor substrate is characterized in that the second heat treatment is performed at a temperature of less than ° C. It is preferable to perform the second heat treatment for more than 500 seconds. Alternatively, the first heat treatment may be performed by ramping and the second heat treatment may be performed for more than 500 seconds. It is preferable to perform the first and second heat treatments in a lamp annealing furnace.

[0005]

The reason for limiting the numerical values of the claims of the present invention will be described. First heat treatment temperature: If the temperature is 600 ° C. or lower, crystallization of the region amorphized by ion implantation does not occur sufficiently,
On the other hand, when the temperature exceeds 800 ° C., the crystallization process in which residual lattice defects remain near the pole surface as described above is taken, and the lattice defect-free pole surface layer, which is the object of the present invention, cannot be obtained. Therefore, if the heat treatment temperature exceeds 600 ℃ and 800 ℃
Below. Second heat treatment temperature: In the heat treatment at 800 ° C. or less, the crystal integrity is not sufficient, fine lattice defects remain, and the electrical activation rate of the dopant is not sufficient, so that the required electrical characteristics cannot be obtained. That is, at 1000 ° C. or higher, the diffusion of the dopant becomes remarkable and the spatial distribution of the dopant as intended cannot be obtained. Second heat treatment time: When the second heat treatment time is short, depending on the ion implantation conditions, the lattice defects do not completely disappear and remain, which may affect the electrical characteristics of the device. If the heat treatment is performed for 500 seconds or longer, lattice defects that affect the electrical characteristics do not remain regardless of the ion implantation conditions. Therefore, the heat treatment for 500 seconds or longer is desirable.

[0006]

EXAMPLE An SiO ₂ film having a thickness of 11 nm was formed on the surface of a P-type (100) Si substrate by a thermal oxidation method. A on the substrate surface
5 × 10 ¹⁵ atom of s ion with energy of 70 keV
Injection was performed at a density of s / cm ² . After forming a SiON film for surface protection during the preparation of a thin film sample for electron microscope observation, heat treatment at 650 ° C. for 300 seconds and 980 ° C. for 300 seconds, which is the method of the present invention, and heat treatment at 1000 ° C. for 30 minutes as a comparative example. Was applied. A cross-sectional thin film sample for a transmission electron microscope was prepared and the state of residual lattice defects was observed. When the heat treatment of the present invention is applied, lattice defects remain only at a depth of 100 nm from the surface indicated by A, but in the comparative example (conventional heat treatment method), B indicates 1
Only 40n from the surface indicated by C in addition to the 00nm depth position
It can be seen that lattice defects remain at the m depth position, which is inconvenient for the LSI manufacturing process. Table 1 shows residual depths of lattice defects under other heat treatment conditions. This embodiment is A
This is an example of s ion implantation, but the same effect can be obtained by selecting the above-mentioned heat treatment conditions even in the case of implanting other elemental ions such as B, P, BF _{2 and the} like for imparting required transistor characteristics, and molecular ion implantation. Is clear. Further, in each of the examples, the substrate was inserted into the heat treatment furnace maintained at a predetermined temperature, but the situation does not change even if the substrate is rapidly heated in the lamp annealing furnace. In this example, an 11 nm-thick oxide film was formed before ion implantation, but the presence or absence of a thin film does not significantly affect the recovery behavior by ion implantation or heat treatment.

[0007]

[Table 1]

[0008]

According to the present invention, the influence of residual lattice defects after ion implantation can be significantly reduced in the LSI manufacturing process, and therefore, the LSI productivity is improved.

[Brief description of drawings]

FIG. 1 is a cross-section transmission electron microscope photograph after As ion implantation on a Si substrate surface.

FIG. 2 shows the method of the present invention at 650 ° C. after As ion implantation:
It is a cross-section transmission electron microscope photograph which shows the state of the residual lattice defect after heat-processing for 300 seconds and 980 degreeC: 300 seconds.

FIG. 3 is a comparative example at 1000 ° C. after As ion implantation:
It is a cross-section transmission electron microscope photograph which shows the state of the residual lattice defect after heat processing for 30 minutes.

Claims (4)

[Claims] 1. 600 after implanting ions into a semiconductor substrate
A method for heat treating a semiconductor substrate, which comprises performing a first heat treatment at a temperature higher than 800 ° C. and lower than 800 ° C., and then performing a second heat treatment at a temperature higher than 800 ° C. and lower than 1000 ° C. 2. The method for heat treating a semiconductor substrate according to claim 1, wherein the second heat treatment is performed for more than 500 seconds. 3. The method for heat treating a semiconductor substrate according to claim 1, wherein the first heat treatment is performed by ramping, and the second heat treatment is performed for more than 500 seconds. 4. The heat treatment method for a semiconductor substrate according to claim 1, wherein the first and second heat treatments are performed in a lamp annealing furnace.