JPH02144973A - Manufacture of thermal diffusion layer and manufacture of variable-capacity diode using the manufacturing method - Google Patents

Abstract

PURPOSE:To easily control a concentration distribution by a method wherein ions of an impurity element of a large thermal diffusion coefficient are implanted into a semiconductor substrate, an annealing process for rapid heating in a short time is then applied to the semiconductor substrate and a thermal diffusion layer is formed by a thermal diffusion treatment at a comparatively low temperature for many hours. CONSTITUTION:A semiconductor base body where an N<-> type epitaxial layer 3 has been formed on an N<+> type semiconductor substrate 4 is pretreated; after that, an N<+> impurity element is implanted from the main surface of the semiconductor base body via a prescribed mask by an ion implantation method. In succession, the ion-implanted semiconductor substrate is rapidly heated by using a heating source in a clean atmosphere or under a reduced pressure for a short time; an annealing process is executed. A next thermal diffusion process is executed at a temperature which is lower than a heating temperature at the annealing process and by thermal diffusion for comparatively many hours. An N<+> type diffusion layer 2 is formed. After that, a P<+> conductivity-type diffusion layer 1 is formed by a thermal diffusion process of a P-type impurity; a P-N junction J0 is formed at a prescribed depth. IN succession, a silicon dioxide film in a prescribed part is removed; an electrode 5 is formed. Thereby, it is possible to easily manufacture the diffusion layer whose diffusion length is shallow.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing a thermal diffusion layer of a semiconductor device in which a shallow diffusion layer is formed by a thermal diffusion process, and a variable capacitor formed by this manufacturing method. The present invention relates to a method for manufacturing a diode element. In particular, the present invention relates to control of the impurity concentration distribution of impurity elements having a large diffusion coefficient, and relates to a method of manufacturing a variable capacitance diode element that can obtain a sufficient change in capacitance with a relatively low voltage source.

[Background of conventional technology]

As is well known, the impurity concentration distribution of the thermal diffusion layer in the manufacture of semiconductor devices is determined by the function f (T, V) of the temperature T ('C) during thermal diffusion and the thermal diffusion time t (minutes). Ru. The diffusion length of the thermal diffusion layer is determined by: D is the diffusion coefficient of the impurity element determined by temperature.

In addition, compared to the case where the temperature during thermal diffusion is relatively high and the thermal diffusion process time is short (1 to 10 minutes), the temperature during thermal diffusion is relatively low and the time is long (more than 30 minutes). It is known that the accuracy of the impurity concentration distribution is better in a thermal diffusion layer in which this is performed.

As described above, in manufacturing semiconductor devices, it is easier to control the impurity concentration distribution by performing thermal diffusion at a relatively low temperature for a long time. This is due to the thermal conductivity of the semiconductor substrate inserted into the heat diffusion furnace during short-term heat diffusion, or the temperature distribution between the center and the surrounding area of the heat diffusion furnace may vary. Although variations tend to occur, these factors can be ignored by performing thermal diffusion for a long time.

In the manufacturing method of variable capacitance diode elements, in order to control the impurity concentration distribution, after setting the amount and depth of impurity implantation according to the conditions of the ion implantation method, such as the dose amount and the implantation energy of the impurity element, After the annealing process, the diffusion length is controlled by a combination of the temperature T ("C) during thermal diffusion and the diffusion time t (minutes). Usually,
In the manufacturing process of a variable capacitance diode element, impurities are implanted into a semiconductor substrate by ion implantation, an annealing process is performed, and then a first thermal diffusion process is performed. Usually, in the first thermal diffusion step, the thermal diffusion temperature is around 1000° C. and the thermal diffusion time is 10 minutes or more, although it depends on the type of impurity element.

Subsequently, a second thermal diffusion process is performed to form PN at a predetermined depth.
Form a junction.

FIG. 3 is a sectional view of a variable capacitance diode element for boat fishing. An N-type epitaxial layer 3 with a low impurity concentration is formed on an N° type semiconductor substrate 4 with a high impurity concentration, a high concentration N゛゛ diffusion region 2 is formed on a part of the surface of the epitaxial layer 3, and further epitaxial A diode structure is known in which a P' diffusion region 1, which is shallower than the N' diffusion region 2 and has a wider area in the lateral direction, is formed on the surface of the layer 3 so as to overlap the N' diffusion region 2 at the center thereof. It is being 5
is an insulating film.

Thermal theory: When manufacturing a variable capacitance diode element consisting of a semiconductor layer of a conductivity type opposite to that of the embodiment shown in FIG. 3, a P' type scattering layer and boron may be used, but boron has a large diffusion coefficient It has the property of being diffused deeply in a short time.

Now, the method for manufacturing the variable capacitance diode element will be explained based on FIG. 2. An impurity element of N conductivity type is implanted into the epitaxial layer 3 by ion implantation. The concentration distribution becomes a Gaussian distribution as shown by the dotted curve (A). Subsequently, an annealing process is performed in an electric furnace, and the material is diffused as shown by the dotted curve (b). Next, by performing thermal diffusion so that the impurity concentration distribution has a predetermined diffusion length, the profile of the N conductivity type impurity element is
It approaches a Gaussian distribution like the dotted curve (C).

Thereafter, by forming a P″ conductivity type diffusion layer 1, a P″ conductivity type diffusion layer 1 is formed.
A NN junction furnace is formed to form an N type diffusion layer 2 with a predetermined diffusion length, and a variable capacitance diode element is manufactured.

[Problem to be solved by the invention]

When trying to form a PN junction J0 at a relatively shallow depth from the main surface of the semiconductor substrate as shown in FIG. 2 using the conventional manufacturing method of a variable capacitance diode element, it is difficult to form the PN junction J0 in the annealing process performed after ion implantation. , is diffused into a deep position (b) beyond the shallow region where the PN junction is to be formed.

Furthermore, the thermal diffusion process for forming the PN junction moves the boundary region to a deeper position. In this way, since the boundary region of the diffusion layer is formed deep from the desired PN junction J0,
There is a drawback that it is difficult to form a variable capacitance diode element that can obtain sufficient junction capacitance with a voltage as low as about 1.

Generally, in a variable capacitance diode element that generates junction capacitance when an applied voltage is about 1 to 8 .mu.m, the diffusion length of the element is relatively deep, so that the diffusion time can be set for a long time. However, in a variable capacitance diode element used at a low applied voltage of about 0.2 to 1V, a thermal diffusion layer with a steep impurity distribution must be formed in a shallow part of the semiconductor substrate. The process must be thermally diffused in a short time. With the conventional thermal diffusion method, which involves annealing in an electric furnace and heat treatment for a long time to control the heat and diffusion layer to have a uniform impurity concentration distribution, it is not possible to manufacture a variable capacitance diode element with the above characteristics. It was difficult.

Furthermore, when forming a variable capacitance diode element of a conductivity type opposite to that shown in FIG. 3, boron is usually used to form a P'' type scattering layer on the N° type diffusion region 2 shown in FIG. Boron is M
Since the amount is light, it has a large diffusion coefficient and has the property of being diffused deeply in a short time. In the case of an impurity element with a large thermal diffusion coefficient, the dispersion of the impurity concentration distribution tends to be large, which poses a problem when trying to form a diffusion layer with a shallow diffusion length in a long thermal diffusion process. .

The present invention has been made to solve the above-mentioned problems, and its main purpose is to create a thermal diffusion layer that can form a diffusion layer with a relatively shallow diffusion length using an impurity element with a large thermal diffusion coefficient. The present invention provides a manufacturing method and provides a variable capacitance diode element using the manufacturing method.

Another object of the present invention is to provide a manufacturing method that can control the diffusion length of a variable capacitance diode element that can provide sufficient junction capacitance even at a voltage as low as IV.

Still another object is to provide a method for manufacturing a variable capacitance diode element in which the concentration distribution of a thermal diffusion layer can be easily controlled when an impurity element having a large diffusion coefficient is used as an impurity element of P conductivity type.

[Means to solve problems]

The present invention has been made to solve the above problems, and includes an annealing process in which an impurity element having a large thermal diffusion coefficient is ion-implanted into a semiconductor substrate and then rapidly heated in a short period of time, so-called RT P ( rapid thermal p
rocess) on the semiconductor substrate to activate the semiconductor layer in which crystal defects have occurred due to ion implantation, and then thermal diffusion treatment is performed at a relatively low temperature for a long time to form a thermal diffusion layer. For a variable capacitance diode element having a shallow diffusion layer, this manufacturing method is used to form a thermal diffusion layer with a shallow diffusion length, and then performs a thermal diffusion treatment of the opposite conductivity type to manufacture the variable capacitance diode element. .

[Effect]

In a method for manufacturing a thermal diffusion layer using an impurity element with a relatively large diffusion coefficient, before entering the first thermal diffusion step, a semiconductor substrate into which an impurity element of a first conductivity type has been ion-implanted is rapidly heated in a short period of time. Through the annealing process (RTP), the ion-implanted impurity elements are activated without being diffused. In the next thermal diffusion step, the diffusion temperature is set at a relatively low temperature and the diffusion time is set at a relatively long time to form a diffusion layer with a predetermined diffusion length. In forming a variable capacitance diode element, a diffusion layer with a shallow diffusion length is formed in the first thermal diffusion process, and a PN layer is formed in the shallow part in the second thermal diffusion process.
By forming a junction, it is possible to easily manufacture a variable capacitance diode element that can obtain a sufficient variable capacitance with a voltage source as low as 1 .mu. or less.

〔Example〕

A method for manufacturing a thermal diffusion layer according to the present invention and a method for manufacturing a variable capacitance diode element using the thermal diffusion process will be described with reference to FIGS. 1 and 3.

In the first manufacturing process, after pre-treating the semiconductor substrate in which N-type epitaxial N3 is formed on the N°-type semiconductor substrate 4, an N-type impurity element is added to the main surface of the semiconductor substrate through a predetermined mask. Inject using ion injection technique. As a result of this ion implantation process, the profile of the implanted N-type impurity element has a Gaussian distribution as shown in FIG. 1(a).

Next, the ion-implanted semiconductor substrate is heated in a clean atmosphere or under reduced pressure using a rapid short-time heating source such as a tungsten halogen lamp that emits infrared rays to activate the ion-implanted N-type impurity elements. The annealing process (RTP) is started. This is an annealing process commonly called lamp annealing. This annealing process activates the impurity element implanted into the semiconductor substrate, and the diffusion profile at this time is as shown in Figure 1(a).
The Gaussian distribution generated immediately after the injection of ion is activated while maintaining almost the same profile.

After performing the annealing process, the next thermal diffusion process begins. Since activation has already been completed, the diffusion temperature at this time is lower than the heating temperature in the annealing step of the N-type scattering layer 2, and the layer is formed by thermal diffusion for a relatively long time. The N-type scattered layer has a profile as shown in FIG. 1(b). After that, P-type impurities are removed through a thermal diffusion process.
A P type diffusion layer 1 is formed to form a PN junction J0 at a predetermined depth.

Subsequently, a predetermined portion of the silicon dioxide film deposited on the main surface of the semiconductor substrate is removed to form an electrode, thereby manufacturing a variable capacitance diode element.

In the lamp annealing process, the heating temperature is set to 900°C or higher and lower than 1200°C using a mixed gas such as a clean inert gas or active gas, or under reduced pressure, and the heating time is 3 seconds to 60°C. The impurity element implanted by the ion implantation method is activated within a range of seconds. The heat source for the lamp annealing process is a tungsten lamp or xenon lamp that emits infrared rays that are easily absorbed by the semiconductor substrate.

Alternatively, an arc lamp or the like may be used.

Next, to explain the variable capacitance diode element of the opposite conductivity type, boron is used in the first thermal diffusion step to form a P conductivity type diffusion layer. Since boron has a relatively large thermal diffusion coefficient, it is difficult to form a diffusion layer with a shallow diffusion length.
It is relatively difficult.

Therefore, after boron is implanted into the semiconductor body by an ion implantation process, a lamp annealing process is performed. The heating temperature at that time was set to 1000°C ± 100°C, and the infrared radiation time was set to 15 ± 5 seconds to activate the impurity elements.
Immediately, the diffusion length is controlled by the next thermal diffusion process using a thermal diffusion furnace. At this time, since the ion-implanted impurity element has already been activated, the thermal diffusion temperature is set to about 900°C, which is lower than the heating temperature in the lamp annealing process, and the thermal diffusion time is set to be relatively long. Thereby, the impurity concentration distribution can be controlled with high precision to form a P' type thermal diffusion layer.

Furthermore, when phosphorus is used, the diffusion length can be easily controlled by setting the heating temperature in the lamp annealing process to around 1100°C and the radiation time to 15±5 seconds for activation. . The heat diffusion temperature at this time can be set to a temperature lower than the temperature of the lamp annealing step, as described above.

〔effect〕

According to the present invention, even if an element such as boron, which has a large thermal diffusion coefficient, is used as an impurity element, the manufacturing method is such that after ion implantation, a lamp annealing process by RTP is performed, and the thermal diffusion process is immediately started. By forming the diffusion layer, it is possible to easily manufacture a diffusion layer with a shallow diffusion length. Therefore, since it is easy to form a shallow PN junction, it is possible to easily manufacture a variable capacitance diode element that can obtain a sufficient junction capacitance with a voltage of about 1.

Further, according to the method for manufacturing a variable capacitance diode element of the present invention, it is possible to rapidly heat and activate the impurity element implanted by the ion implantation method in a short period of time. Since the diffusion layer can be formed by thermal diffusion at a relatively low temperature and for a relatively long time, the diffusion layer has a desired diffusion length and the concentration distribution in the depth direction can be easily controlled. Therefore, it is an extremely effective device that can easily manufacture a variable capacitance diode element that can obtain a sufficient junction capacitance with a predetermined applied voltage.

[Brief explanation of the drawing]

FIG. 1 is a profile diagram showing the impurity concentration distribution for explaining the manufacturing method of the variable capacitance diode element according to the present invention, and FIG. 2 is for explaining the conventional method for manufacturing the variable capacitance diode element. FIG. 3 is a cross-sectional view of a typical variable capacitance diode element.

Claims (5)

[Claims] (1) In a manufacturing method in which an impurity element is implanted into a semiconductor substrate by ion implantation and a diffusion layer is formed by thermal diffusion, an impurity element with a relatively large diffusion coefficient is implanted into the semiconductor substrate, and then rapidly in a short period of time. A method for producing a thermal diffusion layer, comprising performing an annealing step (RTP) in which the diffusion layer is heated to a temperature of 100 nm, and then thermally diffusing an impurity element at a lower temperature than the annealing step to control the diffusion layer to a predetermined diffusion length. (2) The impurity element is boron, and the heating temperature in the annealing step (RTP) is in the range of 1000±100°C, and the heating time is in the range of 15±5 seconds. A method for manufacturing a heat diffusion layer according to claim 1. (3) An ion implantation step in which an impurity element of the first conductivity type is implanted into the semiconductor substrate, and an annealing step (RTP) in which the semiconductor substrate is irradiated with infrared rays in a clean atmosphere to rapidly heat the semiconductor substrate in a short period of time. Following the annealing step, a first thermal diffusion step of controlling the diffusion layer of the first conductivity type to a predetermined diffusion length at a temperature lower than the heating temperature in the annealing step, and adding an impurity element of the second conductivity type. A method for manufacturing a variable capacitance diode element, comprising: a second thermal diffusion step of diffusing to form a PN junction. (4) the impurity element of the first conductivity type is boron,
The heating temperature of the annealing process (RTP) is 1000±
4. The method for manufacturing a variable capacitance diode element according to claim 3, wherein the heating temperature is in the range of 100° C. and the heating time is in the range of 15±5 seconds. (5) The impurity element of the first conductivity type is phosphorus, and the heating temperature in the annealing step (RTP) is 1100±10
4. The method for manufacturing a variable capacitance diode element according to claim 3, wherein the heating temperature is in the range of 0° C. and the heating time is in the range of 15±5 seconds.