WO1998008246A1

WO1998008246A1 - Semiconductor component with foreign atoms introduced by ion implantation and process for producing the same

Info

Publication number: WO1998008246A1
Application number: PCT/EP1997/003977
Authority: WO
Inventors: Wolfgang Wondrak; Vera Lauer; Gerhard Pensl; Thomas Dalibor; Wolfgang Skorupa; Hans Wirth
Original assignee: Daimler-Benz Aktiengesellschaft
Priority date: 1996-08-17
Filing date: 1997-07-23
Publication date: 1998-02-26
Also published as: DE19633183A1

Abstract

A semiconductor component is disclosed with foreign atoms introduced by implantation and electrically activated by a regeneration process. Immediately after the regeneration process, the component has a mean surface roughness of less than 15 nm. For that purpose, silicium is added to the component during the regeneration process.

Description

Semiconductor component with introduced by ion implantation

Foreign atoms and process for its production

description

The invention relates to a semiconductor component with foreign atoms introduced by ion implantation and a method for its production.

US Pat. No. 5,322,802 discloses electrically activating foreign atoms in semiconductor components, in particular SiC components, by curing the radiation damage in the semiconductor caused by ion implantation of the foreign atoms in a thermal annealing process at high temperature.

Furthermore, it is known in the literature that high temperatures of well above 1500 ° C. are necessary for the electrical activation of the foreign atoms. On the one hand, the resistance of the component should be low, i.e. A sufficient number of foreign atoms in the semiconductor must be activated. Secondly, microscopic examinations show that the regions of the semiconductor near the surface which are disturbed by the implantation of the foreign atoms only recrystallize significantly above this temperature and thus again show a sufficient crystalline order.

Particularly silicon-containing components, such as SiC components, are usually heated during the healing process in containers which are made of or coated with SiC, in order to avoid silicon loss from the component surface due to an increased Si vapor pressure in the vicinity of the component. After the annealing process at high temperature, with improved electrical properties, despite this measure, however, a significant deterioration in the surface morphology of the component is observed. This is e.g. B. in the publication by JR Flemish, K. Xie, H. Du, SP Withrow, Journal of the Electrochemical Society, vol. 142, No. 9 September 1995, pp. L144-L146. However, to produce highly integrated components, surfaces that are as smooth as possible are necessary. In order to achieve this purpose, complex and time-consuming polishing processes are necessary after the healing process.

The invention has for its object to provide a silicon carbide component and a method for its production, in which the healing process at temperatures above 1500 ° C is made possible, the surface roughness of the component increases by no more than 15 nm compared to the initial value and the electrical activation is improved.

The object is achieved by the features of claim 1 and claim 9, respectively. Further and advantageous refinements can be found in the subclaims and the description.

According to the invention, a component is subjected to a healing process in which the component is heated in a container, with a silicon-containing material other than SiC, particularly preferably silicon, being added to the component during the healing process. Immediately after the healing process, the component surface has a mean roughness value without further measures, which does not differ significantly from the initial value before the healing process.

An advantageous embodiment consists of dividing the healing process into at least two phases, the surface of the component first being conditioned and then the regions of the component close to the surface being electrically activated. In a first step, the regions of the semiconductor close to the surface are preferably conditioned at a temperature Ti and in a second step the implanted foreign atoms in the semiconductor are electrically activated at a temperature T ₂ such that the mean roughness of the component surface after activation is less than 15 nm.

In the first step of the healing process, the areas of the component near the surface are conditioned and stabilized against the further process steps. The use of high temperatures in a subsequent process step is therefore optimal electrical activation of foreign atoms possible, the temperatures being comparable to the temperatures usually used in annealing processes. A two-stage process with two successive temperature steps with increasing temperature level is favorable. However, the transition from conditioning to activation can expediently also take place by means of one or more temperature ramps in the process or else by means of temperature profiles which combine temperature plateaus and temperature ramps.

It is particularly favorable to initiate the conditioning already during the ion implantation if this takes place at an elevated temperature.

Immediately after the healing process, the component according to the invention, without further measures, has a low average surface roughness and a large number of electrically activated foreign atoms. It is particularly advantageous that the surface morphology after the annealing process is practically unchanged despite the effect of high temperatures compared to the initial state. Measures such as complex polishing processes, which are time-consuming and cost-intensive in an industrial manufacturing process, are omitted.

It has proven to be advantageous that such smooth surfaces are particularly suitable for being connected using a solder and adhesive-free bonding process, in which the connection is brought about by the action of quantum electrodynamic effects between the atoms of the two surfaces to be connected.

The method according to the invention is suitable for all semiconductors with appropriately modified material layers and material additions. It is preferably used for those which tend to lose material at elevated temperatures, for example by sublimation of a component of a semiconductor material. Preferably, at least that elementary material is introduced into the container, which is a volatile component of the semiconductor component in the course of the annealing process. In the following, the features, insofar as they are essential for the invention, are explained in detail and described in more detail with reference to figures. Show it

1 is a schematic representation of a component after the implantation of foreign atoms,

2 shows a schematic representation of a component after the healing process according to the prior art,

3 shows a schematic representation of a component treated according to the invention,

Fig. 4 temperature profiles for conditioning and activation of a component according to the invention.

The examples below essentially describe results obtained on SiC components; however, the invention is not limited to this class of material.

A semiconductor wafer, in particular made of SiC, with a highly polished surface serves as the starting material. The wafer is doped with foreign atoms, preferably aluminum, phosphorus, boron and / or nitrogen, by means of ion implantation. Fig. 1 shows schematically the section through such a semiconductor with implanted Al foreign atoms. The dose is preferably up to 10 ¹⁵ cm ^"2. The surface has a very low roughness (according to DIN 4768) with a mean roughness value R _{a of} typically 1 to 10 nm. In ion implantation, in particular with heavier foreign atoms, higher energies and / or higher doses, the area close to the surface of the semiconductor is severely disturbed up to the amorphization of the crystalline structure. The surface morphology essentially does not change with the ion implantation, the surface roughness roughly corresponds to the state before the implantation.

The radiation damage in the semiconductor caused by the ion implantation is healed by bringing the wafer to a higher temperature and holding it there for a predetermined time, preferably several minutes, particularly preferably at least 10 minutes. It is expedient to heat the wafer in an inert atmosphere, in particular in noble gas or nitrogen. It is very particularly advantageous to choose the atmosphere so that no undesired doping and / or oxidation from the residual gas atmosphere and / or Desired loss of a volatile component from the semiconductor occurs. A favorable embodiment is to carry out the healing process in a vacuum

Particularly with silicon-containing materials such as SiC, there is a risk that silicon loss occurs in the area near the surface of the wafer above about 1300 ° C. due to sublimation of Si. For the electrical activation of implanted foreign atoms, however, significantly higher temperatures must be able to act on the semiconductor, preferably in the range above 1200 ° C., particularly preferably above 1600 ° C., up to the possible melting temperature or sublimation temperature of the material. To suppress the Si loss, the wafer is used Usually encapsulated, for example in a container, in order to increase the Si vapor pressure and thereby to minimize any loss of silicon from the semiconductor. The container is made of SiC or another suitable inert material

Despite these measures, when the temperature rises to, for example, 1600-1800 ° C., a deteriorated surface morphology is subsequently observed. This can be seen in FIG. 2. The surface has a roughness of typically 100 nm to a few micrometers In order to be able to continue using a semiconductor process with many successive component levels, complex polishing processes are necessary, which in turn damage the areas close to the surface and can impair the surface properties

According to the invention, a silicon-containing material other than silicon carbide is additionally added to the component during the annealing process, preferably at the beginning. Metallic silicon is particularly preferably added, although this melts at atmospheric pressure and temperatures above 1410 ° C. and usually has to be feared that the component surface will be contaminated It is only necessary to ensure that the melt does not reach the component surface, preferably by placing a piece of silicon in the container next to the semiconductor component

Immediately after the healing process at the usual high temperatures of 1600 ° to 1800 ° C, the surface has a mean roughness value which corresponds essentially to the value of the healing process. A coloration of the SiC crystal is evident, which is lighter than after a process without additional addition of a silicon-containing material, which indicates an optimal crystalline order of the semiconductor An advantageous embodiment of the method according to the invention then consists in carrying out a conditioning process step in which the surface of the semiconductor is ordered, at least in regions, before the high-temperature step, which is absolutely necessary for activating the foreign atoms

Expediently, the first step at a temperature T |, preferably above T, = 700 ^o C-900 ^o C, particularly preferably above by T. = 1200 ° C is carried out. At this temperature, the mobility of the atoms and ions in the semiconductor is large enough so that crystalline ordering processes can begin in the areas near the surface and / or the bonding relationships between the atoms in the disrupted structure are stabilized.The temperature is, among other things, of the half-liter material and the strength of the Radiation damage dependent

With SiC, for example, it can be observed that the semiconductor material, which is clear and transparent before the implantation, has a discoloration after the implantation. If the implantation is carried out near room temperature, a dark, brownish discoloration can be observed, for example Semiconductors optically improved, ie the discoloration decreases. After an implantation temperature of preferably 900 ° C., the discoloration is considerably less than after an implantation at, for example, 500 ° C., which may indicate crystalline ordering processes already starting during the implantation. If the radiation damage in the semiconductor lattice is largely healed by exposure to a higher temperature, the semiconductor stall becomes clear and transparent again

If the semiconductor is left at or near the temperature T) for a time t, then the radiation damage to the areas of the semiconductor near the surface may already have healed in part and / or the areas near the surface may at least be in a less disordered state. The ordered enthalpy of atoms in the semiconductor, for example SiC the bond enthalpy between silicon and carbon, is greater than in the disordered state, in which a large number of unsaturated electron pair bonds are present on one or more of the semiconductor constituents silicon-containing semiconductor compounds strongly suppresses the possible sublimation of silicon in the temperature range between T) and the high temperature T ₂ The first step in the annealing process which stabilizes the regions of the semiconductor near the surface is referred to as the conditioning step.

The conditioning step in the process according to the invention leads to the result that after the subsequent, second step in the healing process at a temperature T ₂ , preferably a temperature greater than T, there is practically no deterioration in the surface morphology with respect to the morphology immediately after the ion implantation. The surface morphology after the second step of the method according to the invention can be seen in FIG. 3 on the basis of a schematic sectional view through a component treated according to the invention. The surface roughness is considerably lower than in FIG. 2. The average roughness R _a is less than 15 nm, in particular less than 10 nm, although the temperature T ₂ for activating the foreign atoms is comparable to or equal to the usual activation temperatures of 1600-1800 ° C. Following the activation step, the number of electrically activated, implanted foreign atoms in the semiconductor is high and at least as large as the usually achievable degree of activation.

The degree of activation that can be achieved depends specifically on the type of foreign atoms implanted, the degree of radiation damage during the ion implantation and the implantation conditions. It can be observed in SiC that atoms such as aluminum or especially nitrogen with e.g. 50% has a higher degree of activation than, for example, boron, in which 20% already corresponds to a very high degree of activation. A high degree of activation of the foreign atoms is usually favorable. The degree of activation is usually determined using Hall measurements. In the case of implanted nitrogen, a degree of activation of almost 100% is observed from an activation temperature of 1600 ° C. Aluminum is approx. 25% from a temperature of 1550 ° C, approx. 30% from a temperature of 1600 ° C, approx. 75% from a temperature of 1700 ° C and almost 100% from a temperature of 1800 ° C implanted atoms activated.

A preferred embodiment of the healing process is that the temperature rises during the healing process, in particular stepwise, and is kept constant at at least two temperatures T and T ₂ for a respectively predetermined period of time t i and t ₂ . The times and temperatures for different semiconductors and foreign atoms must be coordinated. A further preferred embodiment then exists between the first step at the temperature T | and to insert an intermediate step in the second step at the temperature T ₂ , in which the surface condition of the semiconductor is checked, preferably optically.

The temperature Tj in the conditioning step according to the invention is preferably lower than the temperature T ₂ in the activation step of the healing process, preferably greater than or equal to 800 ° C., particularly preferably less than or equal to 1500 ° C. Favorable if T _{2 is} at least 1200 ° C.

In a further preferred embodiment, the temperature Ti and the time period ti of the first step are determined and varied until the mean roughness value of the semiconductor surface falls below the desired value at a temperature T after the second step

It is expedient to heat the semiconductor as a whole in an inert atmosphere with or without encapsulation of the semiconductor. However, it can be particularly advantageous if the heating takes place from the surface and not from the semiconductor body, for example by local action of electromagnetic radiation in the form of continuous radiation or in the form of radiation pulses on the regions of the semiconductor near the surface

A further preferred embodiment of the healing process is that the temperature rises continuously in the form of a temperature ramp R during the healing process. A slow temperature ramp R means that the temperature is preferably changed at a rate between 5 ° C./min and 30 ° C./min A rapid temperature ramp means that the temperature is changed at a rate between 30 ° C / min and above 100 ° C / min. The upper limit is essentially dependent on the choice of heater

4 shows several favorable temperature profiles as a function of time for the method according to the invention. A preferred method is to leave the implanted semiconductor at the temperature Ti for a time ti and at the temperature T ₂ for a time ti. The semiconductor is heated up quickly or slowly. The gradient of the temperature ramp R can be constant, preferably slow. A particularly preferred embodiment The slope of the ramp R> near the conditioning temperature Ti is steeper than the ramp R near the activation temperature T ₂ . Between the two temperatures T | and T ₂ the temperature can also be briefly reduced before it is raised to T.

It is also possible to combine temperature plateaus and temperature ramps in the healing process. A temperature close to T | is preferred set quickly, and then with a slow, steady temperature ramp T | started. The transition to T ₂ then takes place quickly again, T ₂ then either preferably being kept constant or being approached with a ramp.

The method according to the invention is particularly advantageous and favorable for shortening the process time if the conditioning of the regions of the component near the surface is at least partially carried out during the ion implantation. For this purpose, the ion implantation is carried out at elevated temperature, preferably above 700 ° C., particularly preferably above 900 ° C.

It is very particularly advantageous to combine the additional addition of a silicon-containing material with the healing process, which contains the conditioning phase and a separate activation phase.

A semiconductor component according to the invention made of SiC with foreign atoms introduced by ion implantation, preferably for example aluminum, with a typical dose close to the amorphization limit at room temperature of 10 cm ", which, when conditioning the areas near the surface, takes about t | = 15 min at T | about 1200 ° C and then cured for about 15 minutes at T ₂ = 1700 ° C. for a period of t ₂ , immediately after the curing process has a mean roughness value R _a of less than 15 nm. Furthermore, immediately after the curing process, at least or more than 10%, preferably more than 50%, electrically activated, implanted foreign atoms are present It is expedient not to exceed the amorphization threshold of the semiconductor during the implantation, since the radiation damage in the semiconductor cannot be completely healed after the annealing at temperatures above 1000 ° C, the semiconductor in a container, which is formed from or coated with SiC in order to increase the Si vapor pressure in the atmosphere surrounding the semiconductor. A component which has such an improved surface is particularly suitable for being connected to other surfaces using a solder and adhesive-free connection method, in which the permanent connection is brought about by the action of quantum electrodynamic effects between the atoms of the two surfaces to be connected is coming. It is thus possible to bond different semiconductor materials or, for example, high-performance cooling bodies or heat spreaders, for example made of diamond, onto the component according to the invention.

Claims

claims

1. A method for producing a silicon carbide semiconductor component, in which foreign atoms are introduced into its regions near the surface by ion implantation, which are subsequently electrically activated in a healing process in which the semiconductor component is placed in a container together with a body which increases vapor pressure characterized in that pure silicon is additionally introduced into the container adjacent to the semiconductor component in the course of the healing process.

2. The method according to claim 1, characterized in that the semiconductor component is heated to a temperature T ₂ between 1200 ° C and the melting temperature of the semiconductor component.

3. The method according to claim 1 or 2, characterized in that in the annealing process in a first step, at least the near-surface areas of the semiconductor component are conditioned and in a subsequent second

Step the foreign atoms are electrically activated, the semiconductor component being heated to a temperature Ti in the first step for a period ti, the temperature T | is lower than in the second step, so that after the second step a mean roughness R _{a of} the semiconductor component surface of less than 15 nm is achieved.

4. The method according to claim 3, characterized in that between the first and the second step, a test step of the surface quality of the semiconductor component is carried out.

5. The method according to claim 3 or 4, characterized in that the temperature is continuously increased during the healing process.

6. The method according to claim 4 or 5, characterized in that the temperature increases gradually and at at least two temperatures T | and T _{2 is} kept constant for a predetermined period of time t] and t ₂ .

7. The method according to claim 6, characterized in that the first step is carried out at a temperature Ti between 500 ° C and 1500 ° C and / or the second step at a temperature T ₂ between 1200 ° C and the melting temperature or sublimation temperature of the semiconductor component.

8. The method according to claim 3, characterized in that the first step is already carried out during the ion implantation.

9. A semiconductor device comprising introduced by ion implantation in areas near the surface of foreign atoms which are electrically activated by a thermal annealing process, characterized in that the component has immediately after the annealing process a mean roughness R _a of less than 15 nm.

10. The semiconductor component according to claim 9, characterized in that the component has at least 10% electrically activated implanted foreign atoms immediately after the healing process.

1 1. Semiconductor component according to claim 9 or 10, characterized in that the component comprises silicon.

12. Semiconductor component according to claim 9, 10 or 11, characterized in that the component has at least one carbon-silicon compound.