JPS58123723A - Impurity doping method onto semiconductor crystal - Google Patents

Abstract

PURPOSE:To dope impurity at positioning of high accuracy being less than + or -1mum, by a method wherein a mask material before becoming a compound is expanded in volume by a given ratio when it becomes a compound at a prescribed condition. CONSTITUTION:A first mask 4 is formed on a surface of a semiconductor crystal 1 and first impurity doping is performed, thereby a first impurity doping layer 2 is formed. A metal film 3 is formed on whole surface by means of vacuum evaporation. The mask 4 is removed and a second mask 3' is obtained. Second impurity doping is performed using the mask 3'. Al mask 3'' is obtained by expansion and required impurity doping of third time is performed using the Al mask 3'', thereby n<+> region 2'' is selectively formed. Finally, injection element is annealed and activated, thereby the impurity doping is completed.

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. To dope impurities only in predetermined areas.

There are ion implantation methods and diffusion methods. For example, in ion implantation, it is most common to apply photoresist to a wafer, then provide a photoresist window in a predetermined area, and then implant ions through the window.

For diffusion, 5ins, 51mN4, etc. are normally 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 at precisely predetermined positions, but in conventional methods, how accurately it is possible to open windows at the positions of predetermined areas depends on the pattern of the photomask. It is determined by the positioning accuracy during exposure transfer to the 7-photoresist, and with conventional exposure equipment, the limit is ±1 μm, and it has been difficult to obtain higher accuracy. In recent years, there has been an increasingly strong demand for improved high-frequency characteristics and higher integration of semiconductor devices, but in order to meet these demands, it is necessary to reduce the size of the devices. 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 impurity doping with highly accurate positioning of 1 μm or less.

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

In FIG. 1, l is a semiconductor crystal, for example a semi-insulating Ga
It is an As crystal substrate. First, a first mask 4 is formed on the surface of the semiconductor crystal, and a first impurity doping is performed to form a first impurity doped layer 2. For example, a shallow n-type region is formed by ion implantation of Se. The mask 4 was formed by patterning a 1.5 .mu.m thick photoresist using normal gluing lithography.

Next, as shown in Figure 2, a metal film of 3, for example 0.8μ, is applied to the entire surface.
An m-thick At layer is formed by vacuum evaporation. Thereafter, the first mask 4 is removed using, for example, acetone to obtain a second mask 3' as shown in FIG. A second impurity doping is performed using this mask 3'. For example, an n-type region 2' deeper than the first impurity layer 2 is formed by ion implantation of Se.
form. Next, the At mask 3' is expanded by anodic oxidation or the like to form a kt mask pattern 3'' (fourth
figure). When the surface is insulated by oxidation or nitridation as in the case of anodic oxidation, the insulating film generally expands outward by half the thickness of the formed insulating film.

Here, the At mask 3' is anodized with 0.25 gn 4
The disk 3' was expanded by 02 Spm on each side.

Thereafter, using the expanded At mask 3'' as a mask, desired third impurity doping is performed, for example, by ion implantation of S9 to selectively form the n0 layer region 2'' (FIG. 4).

Finally, the implanted elements are activated by annealing to complete the impurity doping. Here, it is also possible to further protect the semiconductor crystal surface against anodic oxidation by forming an insulating thin film on the surface of the semiconductor crystal and the At mask 8' after the first impurity doping.

At this time, the anodic oxidation of the mask 8' progresses only on the side surfaces, yielding an At mask 8'' that expands in the lateral direction.The purpose of the present invention is achieved if the mask expands in the lateral direction, and both embodiments can be obtained. The effect will be the same.

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 2" This is an example of obtaining a structure in which a 2' deep n-type region is interposed between the n0 region.Here, the distance between 2 and 2" is At
The pattern size difference between the mask 3' and the expanded At mask 3' is determined by the amount of pattern expansion due to surface oxidation, but Az can be expanded with high precision by, for example, anodic oxidation, plasma anodization, etc. Therefore, the amount is ±
It can be controlled to within 1 μm, and therefore the spacing between 2 and 2″ 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 At in No. 8, other metals that can be anodized with high precision such as Ti, Mo, and Ta, or semiconductor materials such as Si can also be used. Broadly speaking, any material that can form not only oxides but also other compounds such as nitrides and carbides on the surface may be used. At this time, the first mask material is not limited to photoresist as long as it can be selectively removed with respect to the third material. Further, the impurity to be doped is not limited to Se, and any n-type or p-type impurity can be used. Moreover, the crystal is not limited to GaAs, but also Si, Ge,
Any material such as InP can be used.

As described above, according to the present invention, in order to take advantage of the fact that the volume of a mask material at a stage before it becomes a compound, such as At metal, expands at a predetermined rate when it is made into a compound under predetermined conditions, If doping is performed based on this mask, it becomes possible to perform doping with extremely high precision spacing differences. In addition, since two doping masks are used with the same pattern reversed, doping layers that are in contact with each other are formed, and the positional relationship is extremely precise and at least one of depth, concentration, and conductivity is matched. Eight different types of impurity doping are realized.

[Brief explanation of the drawing]

1 to 4m are cross-sectional views showing the steps of the manufacturing method of the present invention. DESCRIPTION OF SYMBOLS 1... Semiconductor crystal substrate, 2... First impurity doped region, 3, 3'... Mask material For example, A/.

Claims (1)

[Claims] (1) In a method of selectively doping impurities into a semiconductor crystal, a first mask material is formed on the surface of the semiconductor crystal, and the first impurity doping is performed using this material as MarsF. It is made of metal, etc. that has been reversed. A semiconductor characterized in that a second mask is formed and a second impurity doping is performed, and then the second mask material is changed into a compound to expand it by a predetermined amount, and then an eighth impurity doping is performed. Method of doping impurities into crystals.