JPS5885526A - Doping method of impurities to semiconductor crystal - Google Patents

Abstract

PURPOSE:To make doping of impurities possible with accurate positioning of less than + or -1mum accuracy, by a method wherein doping is performed on the basis of a mask before and after expansion, utilizing the fact that the volume of the mask is expanded at the fixed ratio when the mask is made of compound under the fixed conditions. CONSTITUTION:An Al layer 3 is formed on the crystal surface by evaporation, and a resist pattern 4 is further formed on the layer 3. The Al layer is then processed by the method such as etching, and the resist 4 is removed to form an Al layer 3'. After that, the first desired doping of impurities is selectively performed to form n type region 8, which is deeper than the conductive type region 2, within the semiconductor crystal by the implantation of ion such as Se. Then, the Al mask 3' is expanded to form an Al mask pattern 3'' by the method such as anode oxidation, and the Al mask 3' is anode oxidized by 0.25mum so as to expand toward both sides by 0.25mum, respectively. The second desired doping of impurities is now performed utilizing the Al mask 3'' as a mask, and n<+> layers 7 are selectively formed by implanting ion such as Se.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in impurity doping techniques in semiconductor device manufacturing.

In the manufacture of diodes, transistors, and integrated circuits, the most basic and important technique is to selectively dope a predetermined region of a semiconductor crystal with a predetermined impurity by diffusion or ion implantation. There are ion implantation methods and diffusion methods for doping only a predetermined region with impurities. For example, in ion implantation, it is most common to apply a photoresist to a wafer, then provide a photoresist window in a predetermined area, and perform ion implantation through this window.

For diffusion, 5i02, Si3N, or the like is usually used as a mask material, and the diffusion through the windows of this mask material is utilized.

In any case, the doping mask must have windows formed in precisely the predetermined positions, but in conventional methods, how accurately it is possible to open the windows in the predetermined areas depends on the photomask window. It is determined by the positioning accuracy during exposure transfer to the first resist, and with conventional exposure equipment, the limit is 118 m, and it was difficult to obtain higher accuracy. In recent years, there has been an increasingly strong demand for improved high-frequency characteristics and increased integration of semiconductor devices, but in order to meet these demands, it is necessary to reduce the size of the devices, and therefore, it is necessary to reduce the size of the devices by doping impurities. There is an increasing demand for highly accurate positioning in smaller areas.

The present invention was made in view of this situation, and ±
The purpose is to perform Y-ping of impurities with highly accurate positioning of 1 μm or less.

The present invention will be explained in detail below using figures.

In Fig. 1, ■ is a semiconductor crystal, such as semi-insulating Ga.
The As crystal substrate 2 is a region of one conductivity type formed in advance on one principal surface of the crystal substrate 1, for example, an n-type GaAs epitaxial layer. First, eight A1 layers are formed on the crystal surface by vapor deposition.

A resist pattern 4 is formed on top of it by normal photolithography, and the A1 layer is processed by etching or other methods.
By removing the resist, the AJ mask 3' in FIG.
form. After this, a desired first impurity doping is selectively performed. For example, an n-type region 8 deeper than one conductivity type region 2 is formed in the semiconductor crystal by ion implantation of Se (FIG. 2). Next, the A mask 3' is expanded by an anodic oxidation method or the like to form an Ai mask pattern 3'' (Fig. 3).When the surface is insulated by oxidation or nitridation as in the anodic oxidation method, generally It expands outward by half the thickness of the formed insulating film.Here, the Ai mask 3
' was anodized to a thickness of 0.25 μm, and the mask 3' was expanded by 0.25 μm on each side. After this, AI mask 3″
Using this as a mask, a desired second impurity doping is performed, for example, by ion implantation of Se to selectively form the n-soil layer region 7 (FIG. 3). In another embodiment, as shown in FIG. 2, the first impurity doping is performed while leaving the resist pattern 4, and then the A nomask 3' is anodized in the same manner as in the previous embodiment, as shown in FIG. As shown in FIG. 1, an Ai mask 8'' is obtained which expands only in the lateral direction.The purpose of the present invention is achieved if the mask expands in the lateral direction, and the effect obtained in the second embodiment is the same. After the second impurity doping, the semiconductor crystal and the A no mask 8'
It is also possible to protect the semiconductor crystal surface from anodic oxidation by forming an insulating thin film on the surface of the semiconductor crystal.

In this example, the second ion implantation was performed deeper than the first ion implantation, that is, with high energy and at a lower dose than the first, and the n-type region 2 and the n-type region 7 were implanted. This is an example of obtaining a structure in which eight deep n-type regions are interposed between ten regions. Here, the interval between 7 and 8 is determined by the pattern size difference between the A mask 3' and the expanded M mask 3'', that is, the amount of pattern expansion due to surface oxidation. Since precision expansion is possible, the amount can be controlled within ±1 μm, and therefore the interval between 7 and 8 can be controlled with high precision.

Obviously, the present invention can be modified and applied in various ways other than the above examples. For example, for A in No. 8, other metals that can be anodized with high precision such as Ti, Mo, and Ta, or semiconductor materials such as Si may be used. Broadly speaking, any material may be used as long as it is not only an oxide but also other compounds such as nitrides and carbides.

Further, the impurity to be doped is not limited to Se, and any n-type or p-type impurity can be used. Further, the crystal is not limited to GaAs, and any crystal such as 5i1Ge and InP can be used.

As described above, according to the present invention, the volume expands at a predetermined rate by forming a compound under predetermined conditions in a mask material at a stage before it becomes a compound, such as metal A. In addition, if doping is performed based on the masks before and after expansion, it becomes possible to perform doping with extremely high precision spacing differences.

[Brief explanation of the drawing]

Figures 1 to 4. FIG. 2 is a cross-sectional view showing steps of the manufacturing method of the present invention. 1...Semiconductor crystal substrate 2...-Conductivity type region 3.3'...Mask material For example, A, i! ! 4...
...Mask material, for example, photoresist resist pattern 7...First impurity doped region 8 -Second impurity doped region 3'...Expanded mask material -〇-

Claims (1)

[Claims] (1) In a method of selectively doping impurities into a semiconductor crystal, a mask material made of metal or the like is formed on the surface of the semiconductor crystal, and this is used as a mask to perform the first impurity doping. 1. A method of doping impurities into a semiconductor crystal, which comprises expanding the semiconductor crystal by a predetermined amount by changing it into a compound, and then performing a second impurity doping.