JP5090968B2 - Method for manufacturing silicon carbide semiconductor device - Google Patents

Description

  The present invention relates to a method for manufacturing a silicon carbide semiconductor device.

  In order to fabricate a silicon carbide semiconductor device, it is necessary to control the conductivity type and carrier concentration for a specific region on the surface of the silicon carbide substrate or the surface of the silicon carbide substrate in which an epitaxial layer serving as an active region of a semiconductor element is formed on the surface layer. There is. As a method for forming an impurity doped layer in a specific region on the surface of the silicon carbide substrate, an ion implantation method is generally used. After forming the impurity doped layer, annealing is performed to activate the implanted ion species. At this time, when a silicon carbide substrate having an off angle is used, there is a problem that surface roughness called step bunching occurs on the surface of the silicon carbide substrate due to annealing.

  As a countermeasure against such a problem, in order to prevent bunching due to annealing, a method of depositing carbon on the surface of the silicon carbide substrate by sputtering (see, for example, Patent Document 1) or a substrate by heating the silicon carbide substrate in a reduced pressure atmosphere. There is a method in which a carbon layer is formed on the surface and annealing is performed after carbon formation (see, for example, Patent Document 2).

JP 2005-353771 A International Publication No. 2005-076327 Pamphlet

  In Patent Document 1, the carbon layer formed by sputtering has poor adhesion to the surface of the silicon carbide substrate, and local film peeling may occur, and bunching occurs when annealing is performed at the location where film peeling has occurred. To do. As a result of the occurrence of bunching, there is a problem that device characteristics deteriorate due to a decrease in breakdown voltage due to the concentration of an electric field in the bunching portion or a decrease in channel mobility due to carrier scattering.

  Further, in Patent Document 2, when a silicon carbide substrate is heated under a reduced pressure atmosphere, silicon (hereinafter referred to as Si) is sublimated from silicon carbide (hereinafter referred to as SiC) to form a carbon layer. At this time, since the sublimation amount of Si changes in the depth direction, a transition region in which the composition ratio of Si and C is shifted is formed between the silicon carbide substrate and the carbon layer. When the film thickness of the transition region is thick, the outermost surface of the silicon carbide substrate after the carbon layer is removed becomes the transition region. When the transition region becomes a MOS interface or a Schottky barrier interface, there is a problem that device characteristics are deteriorated.

  The present invention has been made to solve these problems. The adhesion between the silicon carbide substrate and the carbon layer is good, and the composition ratio deviation between Si and C on the surface of the silicon carbide substrate after the removal of the carbon layer is reduced. It aims at providing the manufacturing method of the silicon carbide semiconductor device which suppresses.

  In order to solve the above problems, a method for manufacturing a silicon carbide semiconductor device according to the present invention includes: (a) a step of implanting second conductivity type impurity ions into a first conductivity type underlayer made of silicon carbide; b) After step (a), a step of forming a carbon layer on the underlayer by heating in a reduced pressure atmosphere; and (c) forming a carbon deposition layer on the carbon layer formed in step (b). And (d) after step (c), annealing to activate impurity ions, and (e) after step (d), removing the carbon layer and the carbon deposition layer. It is characterized by that.

  According to the present invention, (a) a step of implanting impurity ions of the second conductivity type into the first conductivity type ground layer made of silicon carbide, and (b) after step (a), by heating in a reduced-pressure atmosphere. Adhesion between the silicon carbide substrate and the carbon layer because the method includes a step of forming a carbon layer on the underlayer and a step of forming a carbon deposition layer on the carbon layer formed in step (c). It is possible to suppress the deviation of the composition ratio between Si and C on the surface of the silicon carbide substrate after the carbon layer is removed.

  Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1>
In the first embodiment, after impurity ions are implanted, a carbon layer is formed by annealing in a reduced pressure atmosphere, and then a carbon deposition layer is formed on the formed carbon layer, and then annealing for activating the impurity ions is performed. It is characterized by that.

  FIG. 1 is a cross-sectional structure diagram of a silicon carbide semiconductor device according to Embodiment 1 of the present invention. In the first embodiment, a cross-sectional structure of an n-channel silicon carbide MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is illustrated as an example. As shown in FIG. 1, an n-channel silicon carbide MOSFET according to Embodiment 1 includes an n-type substrate 1 made of n-type silicon carbide, an n-type drift layer 2 formed on the n-type substrate 1, and a p-type base. The region 3 includes an n-type source region 4, an n-type drift layer 2, a p-type base region 3, a gate insulating film 7 formed on the n-type source region 4, a gate electrode 8, and a source electrode 9.

  2 to 12 are cross-sectional views illustrating a method for manufacturing an n-channel silicon carbide MOSFET that is the silicon carbide semiconductor device according to the first embodiment of the present invention. Hereinafter, the manufacturing method of the n-channel silicon carbide MOSFET according to the first embodiment will be described in order.

  As shown in FIG. 2, n made of n-type (first conductivity type) silicon carbide on an n-type substrate 1 having an inclination (preferably 8 °) in the <11-20> direction from the plane orientation (0001). The type drift layer 2 is formed by an epitaxial growth method. In this way, the base layer is constituted by the n-type substrate 1 and the n-type drift layer 2.

  In FIG. 3, after the n-type drift layer 2 is formed, a mask is formed with a resist or the like at portions separated by a predetermined interval of the n-type drift layer 2, and impurity ions are implanted to form a pair of p-type (first (2 conductivity type) base region 3 is formed. Examples of p-type impurities forming the p-type base region 3 include boron (B) and aluminum (Al).

  In FIG. 4, a mask is formed with resist or the like for the p-type base region 3 formed in FIG. 3, and a pair of n-type source regions 4 are formed by implanting impurity ions. Examples of the n-type impurity forming the n-type source region 4 include phosphorus (P) and nitrogen (N).

  As shown in FIG. 5, after forming the n-type source region 4, the carbon layer 5 is formed by heating in a reduced pressure atmosphere in a heating furnace and sublimating Si from SiC. After the carbon layer 5 is formed, a carbon deposition layer 6 is formed as shown in FIG. Next, as shown in FIG. 7, the wafer implanted in FIG. 6 is heat-treated using a heat treatment apparatus, thereby electrically activating ions implanted into the p-type base region 3 and the n-type source region 4. Let After the heat treatment, as shown in FIG. 8, the carbon layer 5 and the carbon deposit layer 6 are removed. The processing shown in FIGS. 5 to 8 is a feature of the present invention, and will be described in detail later.

After removing the carbon layer 5 and the carbon deposition layer 6, as shown in FIG. 9, silicon dioxide (SiO ₂ ) is formed as a gate insulating film 7 by a deposition method. For the formation of SiO ₂ , SiH ₄ and O ₂ are used and grown at a growth temperature of about 500 ° C. to 700 ° C. and a thickness of about 50 to 100 nm. In this case, since the transition region due to the difference in composition ratio between Si and C can be made smaller than the carbon layer formed only by sublimating Si, deterioration of element characteristics can be prevented.

As a gas used when forming the gate insulating film 7 by a deposition method, a gas containing silicon includes disilane (Si ₂ H ₆ ), dichlorosilane (SiH ₂ Cl ₂ ), and a gas containing oxygen includes Nitric oxide (NO), dinitrogen monoxide (N ₂ O), and the like can be given. Moreover, the formation method of the gate insulating film 7 may be a thermal oxidation method, or a combination of a thermal oxidation method and a deposition method.

  Even when the thermal oxidation method is used, depending on the film thickness of the thermally oxidized film, a transition region in which the composition ratio of Si and C deviates may remain. In such a case, the deterioration of device characteristics should be prevented. Can do. Also, the same effect as described above can be obtained by combining the thermal oxidation method and the deposition method. In the first embodiment, a method using silicon dioxide has been described as a method for forming the gate insulating film 7. However, the same effect can be obtained even if silicon nitride, silicon oxynitride, or the like is used.

  Next, as shown in FIG. 10, a gate electrode 8 is formed on the gate insulating film 7. Aluminum (Al) is used for the gate electrode 8, and the gate electrode 8 as shown in FIG. 10 is formed through film formation and patterning. The gate electrode 8 is formed by patterning so that the pair of p-type base region 3 and n-type source region 4 are located at both ends and the drift layer 2 is located at the center. Therefore, the removed portion of the carbon layer 5 and the carbon deposit layer 6 is used as a channel portion.

After the formation of the gate electrode 8, as shown in FIG. 11, the remaining part of the gate insulating film 7 on the source region 4 is removed by lithography and etching techniques. After the remaining portion of the gate insulating film 7 is removed, as shown in FIG. 12, Al as the source electrode 9 is formed and patterned on the portion where the source region 4 is exposed. Thereafter, Al as the drain electrode 10 is formed on the back surface of the n-type substrate 1 to become a main part of the element structure shown in FIG.

  In the first embodiment, Al is used for the gate electrode 8, the source electrode 9, and the drain electrode 10, but gold (Au), platinum (Pt), nickel (Ni), titanium (Ti), or the like may be used. Good.

  Next, the processing from FIG. 5 to FIG. 8 which is a feature of the present invention will be described in detail.

  FIGS. 13 to 15 show an example of the relationship between temperature and time in the reaction furnace for a series of steps from formation to removal of the carbon layer 5 and carbon deposition layer 6 as shown in FIGS. FIG.

  First, the flow of the entire process will be described. The wafer on which the p-type base region 3 and the n-type source region 4 are formed is introduced into a reaction furnace at room temperature, and a rare gas such as argon (Ar) or helium (He) is sublimated in a reduced-pressure atmosphere to carbonize the carbon. The temperature in the reactor is raised to a temperature at which layer 5 can be formed.

  After the temperature rise, Si is sublimated and held for a predetermined time until the carbon layer 5 is formed. After the formation of the carbon layer 5, the temperature is increased until the carbon deposition layer 6 is formed, and after the temperature increase, a raw material gas for forming the carbon deposition layer 6 is introduced into the reaction furnace and maintained for a predetermined time. The carbon deposition layer 6 is formed by (Chemical Vapor deposition) method. Note that a thermal CVD method may be used to form the carbon deposition layer 6.

  After the carbon deposition layer 6 is formed, the temperature is raised to an annealing temperature for activating the implanted impurity ions, and the n-type and p-type impurity ions implanted are electrically stored by holding for a predetermined time after the temperature rise. To activate.

  After the impurity ions are activated by annealing, the temperature is lowered until the carbon layer 5 and the carbon deposition layer 6 are removed, and after the temperature is lowered to the removal temperature, oxygen is introduced into the reaction furnace and heat treatment is performed. By this treatment, carbon layer 5 and carbon deposit layer 6 are removed, and the silicon carbide substrate surface is exposed.

  The carbon layer 5 formed in the first embodiment is desirably a film thickness of 10 nm or less in order to suppress the deviation of the composition ratio between Si and C on the surface of the silicon carbide substrate. Even if it is thick, an effect can be obtained with respect to improvement in adhesion. Further, the formation temperature of the carbon layer 5 is preferably about 1150 ° C. to 1200 ° C. in consideration of the controllability of the layer thickness depending on the formation time, but the same effect can be obtained even if the carbon layer 5 is formed outside this temperature range. It is done.

  For the formation of the carbon deposition layer 6, a dense layer is formed by CVD using acetylene as a source gas. The formation temperature is desirably about 1100 ° C. to 1300 ° C., but the formation temperature may be less than 1100 ° C. The pressure is desirably 50 Torr or less, more preferably 10 Torr or less. As a growth gas by the CVD method, ethyl alcohol, methyl alcohol, or the like may be used in addition to a hydrocarbon gas such as propane.

  Although the carbon deposition layer 6 can be formed even with the temperature profile as shown in FIG. 13, it is necessary to lower the temperature from the formation temperature of the carbon layer 5 to the formation temperature of the carbon deposition layer 6, or the CVD accompanying the temperature decrease. The stability of the formation temperature deteriorates due to overshoot and undershoot when the carbon deposition layer 6 is formed by the method. Therefore, the carbon layer 5 and the carbon deposition layer 6 are formed at the same temperature as shown in FIG. 14, or the carbon layer 5 is formed in the process of raising the temperature in the reactor to the carbon deposition layer 6 as shown in FIG. It is more desirable to let

  Oxygen is introduced into the reaction furnace when the carbon layer 5 and the carbon layer 6 are removed. At the same time as the removal of the carbon layer 5 and the carbon deposition layer 6, the surface of the silicon carbide substrate is oxidized and fluorinated after being removed from the reaction furnace. By removing the oxide film with hydrogen acid, it is possible to obtain a silicon carbide substrate surface with less deviation of the composition ratio between Si and C.

  The temperature in the reaction furnace at the time of introducing oxygen is preferably about 1100 ° C. However, if an oxide film is formed, the same effect as described above can be obtained, and the temperature may be other than 1100 ° C. At this time, if oxygen is introduced into the reaction furnace at the temperature, there is a possibility of damaging the carbon material that becomes a jig. Therefore, a jig made of silicon carbide or a carbon material coated with silicon carbide is used instead. It is desirable. The thickness of the oxide film is preferably about 10 nm. Even in the case of 10 nm or more, the same effect can be obtained. However, since it is necessary to lengthen the oxidation time, there is a decrease in throughput, and damage to the jig used in the reaction furnace is also increased. On the other hand, when the thickness of the oxide film is 10 nm or less, the effect is reduced because the layer in the transition region where the composition ratio of Si and C is shifted cannot be sufficiently removed. The series of processing steps described above need not be performed in one reactor, and the same effect can be obtained even when separate reactors are used.

  In the first embodiment, the CVD method is used as a method for forming the carbon deposition layer 6. However, after the carbon layer 5 is formed, it is removed from the reaction furnace and deposited using sputtering or the like. Even with this method, the same effect can be obtained. However, when the above two methods are used, diffusion of impurities into the silicon carbide substrate and contamination in the reaction furnace cause problems, and therefore, the CVD method in the same reaction furnace is preferable.

  From the above, by forming the carbon deposition layer 6 after forming the carbon layer 5 by heating in a reduced-pressure atmosphere, the adhesion between the carbon deposition layer 6 and the silicon carbide substrate is improved, and the carbon deposition layer 6 Film peeling can be suppressed. Moreover, since the film thickness of the carbon layer 5 can be made thinner than before, the deviation of the composition ratio between Si and C on the silicon carbide surface after the removal of the carbon layer 5 and the carbon deposition layer 6 is suppressed. be able to. From these things, it is effective in suppressing the deterioration of the element characteristic of a silicon carbide semiconductor device.

<Embodiment 2>
The second embodiment is characterized in that the processing steps from formation to removal of the carbon layer 5 and the carbon deposition layer 6 described in the first embodiment are used for silicon carbide SBD (Schottky Barrier Diodes).

  16 to 18 are cross-sectional views showing a method for manufacturing the silicon carbide semiconductor device according to the second embodiment of the present invention. As shown in FIG. 16, an n-type epitaxial layer 20 is epitaxially grown on an n-type substrate 1 having an inclination (8 ° is desirable) from the plane orientation (0001) to the <11-20> direction, and the surface is sacrificial oxidized. . Next, a photoresist patterning mask having a desired pattern is formed on the surface of the n-type epitaxial layer 20 in order to produce the termination structure 11 for increasing the breakdown voltage. After the mask is formed, impurity ions are implanted to form an ion implanted layer in the region where the termination structure 11 is formed in the n-type epitaxial layer 20. Thereafter, the mask and the sacrificial oxide film are removed.

  After removing the mask and the sacrificial oxide film, the carbon layer 5 and the carbon deposition layer 6 are formed. Since the formation conditions of the carbon layer 5 and the carbon deposition layer 6 are the same as those of the first embodiment, the description thereof is omitted here.

  After the formation of the carbon layer 5 and the carbon deposition layer 6, as shown in FIG. 17, annealing is performed to activate ions implanted in the formation region of the termination structure 11, thereby forming the p-type termination structure 11.

  After the termination structure 11 is formed, the carbon layer 5 and the carbon deposition layer 6 are removed, Ni as the ohmic electrode 12 is formed on the back surface of the n-type substrate 1 as shown in FIG. Further, Ti is formed as a Schottky electrode 13 on the surface.

  The ohmic electrode 12 may be Au or the like. The Schottky electrode 13 may be a metal that forms a Schottky barrier, such as Pt, molybdenum (Mo), Ni, tungsten (W), iridium (Ir), rhenium (Re), and ruthenium (Ru). The effect is obtained.

  In Embodiments 1 and 2 of the present invention, silicon carbide MOSFET and silicon carbide SBD have been described as examples of the silicon carbide semiconductor device. However, the semiconductor device needs to activate impurity ions implanted in another silicon carbide semiconductor device. Even if it exists, the same effect will be acquired if the method described in this embodiment is applied.

  From the above, by using the removed portion of carbon layer 5 and carbon deposit layer 6 as a Schottky contact interface, a good silicon carbide SBD can be obtained without deteriorating the electrical characteristics of the diode.

1 is a cross-sectional structure diagram of a silicon carbide semiconductor device according to a first embodiment of the present invention. It is sectional drawing which shows the manufacturing method of the silicon carbide semiconductor device by Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the silicon carbide semiconductor device by Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the silicon carbide semiconductor device by Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the silicon carbide semiconductor device by Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the silicon carbide semiconductor device by Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the silicon carbide semiconductor device by Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the silicon carbide semiconductor device by Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the silicon carbide semiconductor device by Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the silicon carbide semiconductor device by Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the silicon carbide semiconductor device by Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the silicon carbide semiconductor device by Embodiment 1 of this invention. It is a figure which shows an example of the relationship between the temperature in reaction furnace and time from formation of a carbon layer by Embodiment 1 of this invention to removal. It is a figure which shows an example of the relationship between the temperature in reaction furnace and time from formation of a carbon layer by Embodiment 1 of this invention to removal. It is a figure which shows an example of the relationship between the temperature in reaction furnace and time from formation of a carbon layer by Embodiment 1 of this invention to removal. It is sectional drawing which shows the manufacturing method of the silicon carbide semiconductor device by Embodiment 2 of this invention. It is sectional drawing which shows the manufacturing method of the silicon carbide semiconductor device by Embodiment 2 of this invention. It is sectional drawing which shows the manufacturing method of the silicon carbide semiconductor device by Embodiment 2 of this invention.

Explanation of symbols

  1 n-type substrate, 2 n-type drift layer, 3 p-type base region, 4 n-type source region, 5 carbon layer, 6 carbon deposition layer, 7 gate insulating film, 8 gate electrode, 9 source electrode, 10 drain electrode, 11 Termination structure, 12 ohmic electrode, 13 Schottky electrode.

Claims (7)

(A) implanting impurity ions into the underlying layer made of silicon carbide;
(B) after the step (a), a step of forming a carbon layer on the underlayer by heating in a reduced pressure atmosphere;
(C) forming a carbon deposition layer on the carbon layer formed in the step (b);
(D) after the step (c), annealing to activate the impurity ions;
(E) after the step (d), removing the carbon layer and the carbon deposition layer;
A method for manufacturing a silicon carbide semiconductor device comprising:   2. The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein in the step (b), the film thickness of the carbon layer is 10 nm or less.   The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein in the step (c), the carbon deposition layer is formed by a thermal CVD method.   The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the processes from step (b) to (e) are performed in the same reactor.   2. The method according to claim 1, wherein in the step (e), oxygen is introduced when removing the carbon layer and the carbon deposition layer to oxidize the surface of the base layer to a thickness of about 10 nm. A method for manufacturing a silicon carbide semiconductor device.   2. The silicon carbide semiconductor device according to claim 1, further comprising a step of forming a semiconductor device using the surface after removal of the carbon layer and the carbon deposition layer as a channel portion after the step (e). 3. Manufacturing method.   2. The silicon carbide according to claim 1, further comprising a step of forming a semiconductor device after the step (e) using the surface after removal of the carbon layer and the carbon deposition layer as a Schottky contact interface. A method for manufacturing a semiconductor device.

Images