JPS6325496B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for manufacturing a semiconductor device that includes a step of irradiating a semiconductor substrate with laser light, such as laser annealing.

Generally, when manufacturing semiconductor devices, it is essential to form a transparent insulating film, such as a silicon dioxide film, on a silicon semiconductor substrate, etc., and in the presence of such an insulating film, various processing and
For example, it is necessary to perform pattern formation by etching, region formation by implanting impurity ions, laser annealing, etc.

Incidentally, in recent years, so-called laser annealing technology, in which a semiconductor substrate is subjected to heat treatment by irradiating laser light, has been making remarkable progress. Laser annealing is very convenient because it is possible to raise the temperature of only the desired location in a short time, so annealing can be performed without adversely affecting other element areas of the semiconductor device due to heat. be.

Now, when manufacturing semiconductor devices, lasers and
Specific examples of application fields of annealing technology include:
Examples include repairing crystal damage that occurs when impurity ions are implanted to form a region and ion activation. The laser annealing at this time is performed on the semiconductor substrate surface exposed within the window in the field insulating film formed on the semiconductor substrate, that is, the impurity region, but in that case, the edge of the insulating film is Phenomena often occur that cause swelling and unevenness, which hinders subsequent processes.

This type of unevenness is called ripple, and is currently becoming a problem. Even if the energy density of the laser beam is controlled to be optimal for annealing silicon, for example, the edges of silicon dioxide occurs in The reason for this is still unclear, but it is thought that the edge of the insulating film changes continuously and becomes thinner as it approaches the window, that is, the exposed surface of the semiconductor substrate.
One example of this is that interference effects due to laser light are becoming more likely to occur.

The present invention can be applied to, for example, a window for forming an impurity region.
The present invention provides a method for manufacturing a semiconductor device that can prevent the edge of the insulating film from waving even when annealing is performed by irradiating a laser beam onto a portion where the surface of a semiconductor substrate and an insulating film are in contact. Yes, this will be explained in detail below.

The present inventors had estimated that the above-mentioned waving phenomenon was caused by interference of laser light at the edge of the insulating film. After repeated research to invent a technology that can be easily implemented,
It has been found that good results can be obtained by irradiating a semiconductor substrate to be laser annealed with laser light through the required liquid.

The liquid used at this time must be selected so that it has a refractive index similar to that of the insulating film, does not contaminate the semiconductor substrate, and does not adversely affect subsequent steps.
Note that since the refractive index is not matched, the effect is slightly inferior, but ordinary water can be used as the liquid, and in this case, post-processing becomes extremely simple.

As a method for interposing a liquid between the laser light source and the semiconductor substrate, the semiconductor substrate may be immersed in the liquid, or depending on the type of liquid, the liquid may be applied to the semiconductor substrate. In any case, if you do this, the semiconductor substrate will be equivalent to having an insulating film with a uniform thickness on its surface, so interference of laser light will be less likely to occur, and the waving phenomenon of the insulating film will be reduced. Prevented.

Specific example: A silicon semiconductor substrate with a silicon dioxide film (refractive index: ~1.45) is formed with a window to selectively expose the surface of the substrate, and then glycerin (refractive index: 1.46) is formed.
2 to 3 [mm] onto a silicon semiconductor substrate.
A certain amount of glycerin layer is present. Next, a ruby laser (wavelength: 6943 [Å]) is used to increase the energy density.
Even when annealing is performed by irradiating at 1.5 to 1.6 [J/cm ² ], no waving phenomenon is observed at the edge portions of the silicon dioxide film. Incidentally, if laser light is irradiated without going through glycerin, the energy density will be 0.6~
When the pressure is about 0.8 [J/cm ² ], a waving phenomenon appears. In the case of the present invention, the glycerin layer may absorb some laser light, but even taking this into consideration, it is judged that the effect of making the silicon dioxide film substantially thicker and more uniform is significant. Furthermore, since the semiconductor substrate is immersed in the liquid and is in a liquid-cooled state, it is possible to reduce the influence of the heat of annealing on the portions that are not irradiated with the laser. Note that since glycerin has viscosity, it can also be applied onto a semiconductor substrate. However, in this case, it is unavoidable that there will be a slight decrease in effectiveness.

Although glycerin was used as the liquid in the above-described specific example, other materials such as carbon tetrachloride (CCl ₄ , refractive index: 1.46) may also be used. Note that the refractive index of water is 1.33, which was also quite effective. Also, as a laser light source, in addition to ruby,
Lasers such as YAG and argon can be used.

When carrying out the present invention, if there is a concern about laser beam energy loss in the liquid, it is effective to insert a glass plate in the middle of the liquid, and
In order to improve the intra-beam uniformity of the laser light, one method is to interpose a diffuser made of, for example, a ground glass-like sapphire plate in the liquid.

As can be seen from the above explanation, according to the present invention, when laser annealing is performed, a liquid layer is interposed on the semiconductor substrate and the laser beam is irradiated, so that the semiconductor substrate is uniformly coated with laser light. Since the annealing is performed in a state equivalent to the presence of the insulating film, no interference of laser light occurs, and therefore it is possible to prevent the appearance of waving at the edge portions of the insulating film.

Claims (1)

[Scope of Claims] 1. A semiconductor substrate having an insulating film on which a window is selectively formed is immersed in a liquid having a refractive index substantially equal to that of the insulating film, and the liquid fills the window and flows over the insulating film. A method for manufacturing a semiconductor device, comprising the steps of: uniformly covering the semiconductor substrate; and then annealing the semiconductor substrate by irradiating the liquid with a laser beam.