JPS6223452B2 - - Google Patents

Description

Detailed Description of the Invention The present invention uses an organic photosensitive film as a shielding mask for ion implantation, and when implanting impurity ions into a semiconductor substrate, the gas released as the organic photosensitive film progresses and the implanted ions are combined. The present invention relates to an ion implantation method that can eliminate errors in detecting the amount of ion implantation caused by neutral particles generated by collisions of particles.

Organic photosensitive films are easy to form on semiconductor substrates and can also be selectively punched, and are widely used as shielding masks for selectively introducing impurity ions into semiconductor substrates. However, although it has the above advantages, when used as a shielding mask for high-concentration ion implantation, ion implantation progresses hardening and reduces the degree of vacuum in the vacuum chamber where a large amount of gas is generated.
Neutral particles are generated due to the collision between the generated gas and the implanted ions, resulting in inconveniences such as a decrease in the control accuracy of the ion implantation amount. By the way, regarding the amount of such neutral particles generated, a report was published on February 14 and 15, 1971, sponsored by the RIKEN Semiconductor Laboratory, the Japan Society of Applied Physics, and the 132nd Charge Beam Committee of the Japan Society for the Promotion of Science. This was already discussed in the 9th Symposium on ``Ion Implantation and Submicron Processing,'' held on both days, on pages 51 to 54, ``Atmosphere Effects During Ion Implantation.'' In other words, gases such as hydrogen (H), neon (Ne), and argon (Ar) are introduced into a vacuum chamber, and the amount of neutral particles generated is estimated from the degree of vacuum and the rate of decrease in ion beam current, as shown in Figure 1. It is shown that the value is as shown in .

Figure 1 shows the beam current reduction rate (Beam
This is a diagram showing the pressure (Pressure) on the horizontal axis, and when the introduced gas is Ar gas, the reduction rate of the beam current when the degree of vacuum is 15 × 10 ^-5 Torr is about 10%, i.e. , the generation rate of neutral particles is a large value of approximately 10%. Therefore,
In order to control the ion implantation amount with accuracy of several percent or less, the degree of vacuum must be maintained at a high degree of vacuum of 10 ^-6 Torr or less. Although this value varies somewhat depending on the structure of the ion implantation device, qualitatively the same can be said.

For example, a photoresist film commercially available under the trade name OMR83 is coated on a silicon substrate to a thickness of 1 μm as a shielding mask, exposed and developed, and then post-baked at a temperature of 150°C for 30 minutes. Phosphorous ions (P ⁺ ) are added to a silicon substrate on which an ion implantation mask is formed.
In order to inject at 100KeV with an injection amount of 1×10 ¹⁵ cm ^-2 , if the injection rate is 1×10 ¹² cm ^-2・sec ^-1 , the degree of vacuum in the vacuum chamber will be 3×10 ^-5 Torr. The time required for injection was approximately 1000 seconds. Furthermore, when a silicon substrate with the same implantation mask as above is prepared and the injection rate is set to 2×10 ¹¹ cm ^-2 sec ^-1 , the degree of vacuum in the vacuum chamber is 5×10 ^-6 Torr or less. The time required for injection was approximately 5000 seconds.

As is clear from this example, when the injection rate is increased (1 × 10 ¹² cm ^-2 sec ^-1 ), the time required for injection becomes shorter, but the degree of vacuum decreases, and neutral particles are generated. This results in the inconvenience that the ratio becomes significantly higher. On the other hand, when the injection rate is lowered (2
×10 ¹¹ cm ⁻² ·sec ⁻¹ ), the generation rate of neutral particles is significantly lowered, but the time required for implantation becomes longer, leading to higher ion implantation costs.

The present invention provides an ion implantation method that can eliminate inconveniences caused by the phenomenon in which the organic photosensitive film is cured by implanted ions when the organic photosensitive film is used as a shielding mask. The method of the present invention is characterized by curing the organic photoresist film in advance with an ion beam that does not affect conductivity even if it is injected into the semiconductor substrate, thereby creating an organic photoresist film with extremely low gas release. The purpose of this method is to implant impurity ions at a high injection rate and maintain a high degree of vacuum during this process.

Below, the case of forming the p-type source region and p-type drain region of a p-channel MOS transistor in a complementary MOS semiconductor integrated circuit (C-MOS IC) by making full use of the ion implantation method of the present invention is shown in FIGS. This will be explained in detail with reference to d.

As shown in FIG. 2a, a p
After selectively forming a type well 2 and forming a gate consisting of a gate oxide film 3 and a polycrystalline silicon layer 4 and a field oxide film 5 on a predetermined portion of the surface of the n-type silicon substrate 1, a photoresist is formed. (Product name: OMR83) to a thickness of 1 μm,
By performing exposure and development processing, a photoresist film (shielding mask) 8 having ion implantation windows 6 and 7 is formed. The photoresist film 8 thus formed was then heated at 150°C.
Bake for about 30 minutes at a temperature of .

Next, the silicon substrate is placed in the target chamber of the ion implanter in order to perform ion implantation for forming source and drain regions into the n-type silicon substrate portions exposed in the ion implantation windows 6 and 7.
Evacuate. By the way, in the method of the present invention, ion implantation is performed to harden the photoresist film 8 prior to implantation of p-type impurity ions such as boron ions (B ⁺ ) for forming source and drain regions. This ion implantation process is performed only to harden the photoresist film, and the ions implanted in this process must not be involved in determining conductivity. For such ion implantation, in the present invention, boron trifluoride (BF ₃ ), for example, is used as an ion source gas, and fluorine ions (F ⁺ ) are accelerated at an energy of 50 KeV and an implantation rate of 2×10 ¹² cm ^-2 .
Inject at sec ^-1 for about 200 seconds (injection volume 4 x 10 ¹⁴ cm ^-2 ).

FIG. 2b is a diagram showing the step of implanting the fluorine ions (F ⁺ ), and the photoresist film 8 is hardened by the implantation of the fluorine ions (F ⁺ ). 9 is an ion implantation layer formed by this process.

After the photoresist layer 8 is cured in this manner, boron ions (B ⁺ ) are implanted to form ion implantation layers 10 and 11, as shown in FIG. 2c. At this time, the injection conditions were as follows: acceleration energy 50KeV, injection rate 1×10 ¹² cm ^-2 sec ^-1
The time required to perform injection with an injection volume of 1×10 ¹⁵ cm ⁻² was approximately 1000 seconds. Note that in this ion implantation, the degree of vacuum during implantation can be maintained at 5×10 ^-6 Torr or less, and the generation of neutral particle beams can be suppressed to a few percent or less, resulting in accurate ion implantation.

In the method of the present invention, ion implantation is performed twice, the first time being fluorine ions (F ⁺ ) and the second time being boron ions (B ⁺ ), so this switching is necessary. Switching between fluorine ions (F ⁺ ) and boron ions (B ⁺ ) uses boron trifluoride (BF ₃ ) as the ion source gas for the first ion implantation.
This can be easily done by changing the mass spectrometry magnet current of the ion implanter.

By the way, in the method of the present invention, the time required for two ion implantations is 1200 seconds, but this time is longer than the usual method, that is, the method of implanting only boron ions (B ⁺ ), when the implantation rate is reduced to 2. ×10 ¹¹ cm ^-2・
This is approximately 1/4 of the required time of approximately 5000 seconds when sec ^-1 , which is a significant reduction in processing time.

The photoresist film 8 on the n-type silicon substrate, on which the boron ion (B ⁺ ) implanted layers 10 and 11 have been formed through the above steps, is then removed by an oxygen plasma method or the like to remove the second layer. The state shown in Figure 2 is obtained, and finally, by performing annealing to activate the implanted boron ions ( ^B Region 12 and drain region 13 are formed.

According to the method of the present invention exemplified above, fluorine ions (F ⁺ ) are implanted into the source region 12 and drain region 13 at approximately 2×10 ¹⁴ cm ⁻² , but the fluorine ions (F ⁺ ) are implanted into the silicon substrate. Since defects caused by fluorine ion (F ⁺ ) implantation are removed by annealing, their influence on the characteristics of the completed semiconductor device is negligible.

As is clear from what has been explained above,
According to the ion implantation method of the present invention, when an organic photosensitive film is used as a shielding mask for ion implantation, there are disadvantages such as a decrease in the degree of vacuum caused by the gas released from the film or the generation of neutral particles. is eliminated, and effects such as improved control accuracy of ion implantation amount and shortened ion implantation time are achieved.

In the example explained above, fluorine ions (F ⁺ ) were shown as ions for curing the photoresist film, but silicon ions (Si ⁺ ), chlorine ions (Cl ⁺ ), and oxygen ions ( It is possible to use ions such as O ⁺ ) or nitrogen ions (N ⁺ ) that are inert to the substrate and do not affect the properties in minute amounts.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the atmosphere effect during ion implantation, and FIGS. 2 a to 2 e show the p-type source region and p-type
It is a figure which shows the process of forming a type|mold drain region. 1...n-type silicon substrate, 2...p-type well,
3... Gate oxide film, 4... Polycrystalline silicon layer, 5
... Field oxide film, 6, 7 ... Window for ion implantation, 8 ... Photoresist film, 9 ... Ion implantation layer for curing photoresist film, 10, 11 ...
Boron ion implantation layer, 12... p-type source region, 13... p-type drain region.

Claims (1)

[Claims] 1. When forming an organic photoresist film that serves as an ion implantation shielding mask on a semiconductor substrate and ion-implanting impurities of a predetermined conductivity type into the semiconductor substrate that is not covered by the organic photoresist film, prior to the ion implantation, Impurity ions that are not involved in determining the conductivity type of the semiconductor substrate are implanted into the organic photoresist film to cure the organic photoresist film and convert it into an organic film that releases less gas. An ion implantation method comprising ion-implanting the impurity of the predetermined conductivity type into the interior.