DE2000093C2 - Field effect transistor - Google Patents

Description

The invention relates to a field effect transistor according to the features in the preamble of claim 1.

A field effect transistor of this type is known from AT-PS 2 63 084. The well-known MOS field effect transistor consists of a semiconductor body of the first conductivity type, in which from one surface side in a certain distance from each other two zones of the second conductivity type as source and drain are let in. The space between the two source and drain forming diffused Zone is covered with an insulating layer on which the flat metal gate electrode is arranged. The pn junctions formed by the source and drain zones extend under the gate electrode load-bearing insulating layer.

The area of the semiconductor body of the first conductivity type in the area of the channel must have a certain degree Have minimum doping in order to achieve a desired electrical characteristic. This minimum funding however, it can produce a relatively high output capacitance.

On the other hand - as in AT-PS 2 63 084 - the doping of the semiconductor body of the first conduction type is claimed in the reverse direction Drain junction kept extremely low so is the output capacitance caused by this junction low, since the charge carrier-free space charge zone extends very far into the semiconductor body can expand. The doping of the rest of the semiconductor body will, however, meet the requirements in the channel region adapted and therefore chosen higher, so that the field effect transistor has the desired properties maintains.

The invention is based on the object of specifying a field effect transistor which, in addition to a low Output capacitance has a very low feedback capacitance Field effect transistor with the features specified in the preamble of claim 1 accordingly ί the features in the characterizing part of claim 1 solved.

The invention is to be explained in more detail below on the basis of two exemplary embodiments.
A semiconductor body 1 is shown in section in FIG. 1

ίο shown, for example from einkristaHinem Silicon is made of. In this semiconductor body were of one with an oxide masking layer 4, for example made of silicon dioxide, covered semiconductor surface side two zones 2 'and 3 of the n + -conductivity type in one diffused from each other at a certain distance. During the diffusion of the two zones 2 and 3, it is known Way the oxide layer is used as a diffusion mask. Zone 3 forms the source zone, while zone 2 represents the drain zone. Both zones are provided with an electrode 5 and 6, respectively. Between the two Zones 2 and 3 are located on the semiconductor surface, the insulating layer 4 covering the channel region 8 which the gate electrode 7 is arranged. The semiconductor base body has the opposite conductivity type

2 ^r > of zones 2 and 3 and is therefore p-conductive in the case of the above-mentioned conductivity type of zones 2 and 3. Below the drain zone 2, the semiconductor body is p-conductive, that is to say it is very weakly doped and therefore has a very high resistance. Limiting this weak

.'ο doped area 9 is indicated by a dashed line. The remaining part 10 of the semiconductor body is more heavily doped and thus has a lower resistance than the area 9. The doping ratios of the semiconductor base body described are produced, for example, by ^{starting from a p-conductive semiconductor body with a doping of approx. 5 · 10 17} atoms per cm ' , and that in a part of this semiconductor body impurities are diffused, which form donors in the semiconductor body. This contra-

4n doping should, however, only be carried out to the extent that, although the conductivity type does not yet change, there is a considerable increase in the specific resistance. In this way, a high-resistance semiconductor region 9 is obtained which, for example, has a net doping of approximately 10 ¹⁵ atoms per cm ³ . In the exemplary embodiment shown in FIG. 1, the high-resistance semiconductor region 9 comprises the entire cross section of the semiconductor body in the part which is below the drain zone 2

so lies or adjoins the drain zone. It is also possible to start from a correspondingly low-doped base body 10, which in the Ka.ialgebiet the required higher doping is obtained through a customary diffusion process, which corresponds to zone 9

> 5 correspondingly high-resistance substrate material remains. Of further can z. B. the method of selective epitaxy can be used for this by z. B. alone the channel region is provided with a layer of the desired higher doping.

The control electrode 7 ends at a certain distance in front of the barrier layer forming the drain zone. As a result, even at relatively low values of the voltage Us, the space charge zone emanating from the drain zone will collide with the channel generated by inversion fe5, so that the charge carriers transported in the channel in the space charge zone are transported to the drain electrode 5 by the existing electrical field. By shortening the

The control electrode in the vicinity of the drain zone was: according to the invention, the reaction capacity was reduced.

The semiconductor arrangement in FIG. 2 differs only slightly from that in FIG. 1 shown example. In the case of the FIG. 2 , only part of the cross section of the semiconductor body 1 is less doped below and in the immediate vicinity of the drain zone. This region, which is preferably produced by counter-doping, is produced using the known planar diffusion technique.

The F i g. 1 and 2 are supplemented by the voltage sources with which the semiconductor arrangement can be driven. If an> positive potential with respect to the source electrode 6 is applied to the gate electrode 7, an η-conducting channel 8 forms under the oxide layer. This channel starts from the source zone 3 and tapers towards the drain zone 2 when a voltage of the polarity shown is applied between the source and drain zones. The voltage Uds. which drives the drain current / _D through the channel, a voltage drop is caused in the channel region, which leads to the uneven cross-section of the channel region 8 in the operating case. In the

ίο the mode of operation shown is the barrier layer between the drain zone 2 and the semiconductor base body region 9 claimed in the reverse direction. Since the However, area 9 is very weakly doped, is the junction capacitance and thus the output capacitance

ι ϊ the semiconductor arrangement very low.

1 sheet of drawings

Claims (2)

Patent claims: 1. Field effect transistor with a semiconductor body of the first conductivity type and two in the semiconductor body brought in. Source and drain forming zones of the second conductivity type, between which, separated from the channel area of the field effect transistor by an insulating layer, an areal Gate electrode is arranged, the semiconductor body under the drain zone with the in operation in The barrier layer claimed in the reverse direction is less doped than in the other areas of the Semiconductor body or wherein the channel region is more heavily doped than the rest of the semiconductor body of the first conductivity type, characterized in that the gate electrode (7) at a distance ends in front of the barrier layer surrounding the drain zone (2) and the distance is chosen so that at relative low values of the drain-source voltage, the space charge zone emanating from the drain barrier layer abuts the channel created by inversion. 2. Field effect transistor according to claim 1, characterized in that the semiconductor body consisting of monocrystalline silicon under the drain zone (2) has a doping of approx. 10 ^lä atoms per cm ³ , while the semiconductor body has a doping of approx. 10 ¹⁷ atoms per cm ³ .